Post by: Jeff Wheeler on April 06, 2010, 03:59:32 AM
Another good choice would be for him to just buy two 2268H drivers and roll his own cabinets. The guy can build anything. I was thinking of just measuring the vent dimensions of my 728s and having him build two half-sized versions of it, instead of copying the smaller port area of the 718s. This would save him quite a bit of money since the drivers are available from JBL for about $450 vs ~$800 for a 718S.
Post by: Paul O'Brien on April 06, 2010, 11:21:23 AM
http://www.parts-express.com/wizards/searchResults.cfm?srchE xt=CAT&srchCat=583
Post by: Tim Weaver on April 06, 2010, 12:13:28 PM
B&C or Eminence will also tell you exactly what kind of enclosure to build too.
The TBX100 is a hoss.
Post by: Art Welter on April 06, 2010, 01:14:59 PM
| Tim Weaver wrote on Tue, 06 April 2010 10:13 |
+1 B&C or Eminence will also tell you exactly what kind of enclosure to build too. The TBX100 is a hoss. |
Copying a known good bass reflex cabinet is simple, so the alignment process has already been worked out for the OP.
The 4018LF has an Xmax of 7.9 mm.
The B&C 18TBX100 has an Xmax of 10 mm.
The 2268 has an X max of 23 mm.
There is no replacement for displacement.
That said, in a club where people may listen with their eyes, having twice as many speakers costing half as much would look louder
.Art Welter
Post by: Jeff Wheeler on April 06, 2010, 01:32:34 PM
Post by: Tim Weaver on April 06, 2010, 03:40:32 PM
And my recommendation for the B&C is due to output AND sound quality. A properly built dual 18 with 2 TBX100's is a better sub than an SRX728. It may not be louder, but it is more accurate. I'd pick the B&C sub over the 728 any day of the week. Besides, it's no slouch when it comes to output either!
Post by: Art Welter on April 06, 2010, 07:57:20 PM
| Tim Weaver wrote on Tue, 06 April 2010 13:40 |
Building from a plan provided by a manufacturer is actually less work than measuring what you have and then halving the volume. And my recommendation for the B&C is due to output AND sound quality. A properly built dual 18 with 2 TBX100's is a better sub than an SRX728. It may not be louder, but it is more accurate. I'd pick the B&C sub over the 728 any day of the week. Besides, it's no slouch when it comes to output either! |
Tim,
How do you define "accurate"?
Have you measured the distortion in both speaker types at various drive levels?
Post by: Gus Housen on April 06, 2010, 09:29:47 PM
Post by: Adam Schaible on April 06, 2010, 10:01:30 PM
Do you know if that is +/- 23mm, or +/- 11.5mm for the JBL driver? Either way, that's a lot.... but if the box is tuned correctly for what you're trying to do, I don't really see 8mm of xmax as an issue.
Jeff,
I'd have him build some boxes for the 4018lf. You can get them for about 225 each.. if you need a source PM me. That and $150 of other supplies would be a bare-bones dual 18 sub. Probably be able to build 2 for the price of 1 srx 728 and I'd guess the dual 4018lf cab would perform pretty close, dare I say better than the srx 728.
The two cabs would probably have about the same resale as a single 728, and depending on his woodworking abilities, he may or may not be able to build a cab that works. He can save money if his time is considered free. he could probably sell the cabs for $400/each down the road without too much issue .. so his net cost of ownership would be just $400. That, to me, is a pretty cheap option.
Post by: Charlie Tappa on April 06, 2010, 10:12:04 PM
Charlie Tappa
President
Pro Sound Service Inc
Braintree, Ma. 02184 USA
Exclusive B&C USA Parts Distributor
ATM Flyware Stocking Distributor
Loudspeaker Repair and Parts Specialists
www.prosoundparts.com
info@prosoundservice.com
781-849-1285
Post by: Matt Errend on April 06, 2010, 10:46:34 PM
| Adam Schaible wrote on Tue, 06 April 2010 21:01 |
Hi Art, Do you know if that is +/- 23mm, or +/- 11.5mm for the JBL driver? Either way, that's a lot.... but if the box is tuned correctly for what you're trying to do, I don't really see 8mm of xmax as an issue. |
That has to be the P-P spec, otherwise the surround would be much much beefier.
I would assume that the "real" xmax is 11.5mm, in relation to the other drivers listed.
Post by: Tim Weaver on April 07, 2010, 01:38:43 AM
| Art Welter wrote on Tue, 06 April 2010 18:57 | ||
Tim, How do you define "accurate"? Have you measured the distortion in both speaker types at various drive levels? |
By ear alone. Mostly by comparing different subs while in use.
Older SR4719's were pretty decent subs for the day. They would be used in the same fashion that we are seeing SRX728's today. Mid-level club rigs up to regional summer festival stages using a bunch of them under some higher priced arrays. 4719's had a bit of muddiness to them when you got down low. Say under 60 hz. They would really have a loss of cone control (for lack of a better word) when you pushed them with pedal tones. Low key riffs, and 5 string bass would not be reproduced faithfully.
The SRX728 is an improvement on an order of magnitude compared to the 4719, but still exhibits some of these traits. These cabs have a ton of output though so they get paired up with some higher end array cabinets in order to fill riders. I've seen them under hangs of vertecs a bunch of times.
Compare though an SRX728 to the Vertec sub 4880 and no one would argue with you that the vertec sub sounds better, hits harder, and goes lower with more authority. Even the Dual 15 4882 will run circles around the 728, and it gives up a good deal of displacement to the dual 18. Bass lines are quite faithfully reproduced with these cabs.
The tbx100 from B&C is more in line with a high end arena rig subwoofer than it is the club level SRX type box. If you build a proper box for it, it will give you everything you would expect from an A level subwoofer.
That's what I mean by "more accurate". It gives me more of what I want and less of what I don't....
Post by: Mike Caldwell on April 07, 2010, 08:08:40 AM
Post by: Jeff Wheeler on April 07, 2010, 09:12:39 AM
| Tim Weaver wrote on Tue, 06 April 2010 14:40 |
Building from a plan provided by a manufacturer is actually less work than measuring what you have and then halving the volume. |
Well, the 728 is two separate chambers, one for each woofer, so it is actually easy to copy half of it. I did take a few minutes to input the 18TBX100 into WinISD and other than some WinISD funkyness that I can probably get past with more time spent on it, its prediction is quite good for the application with a box tuned to 35Hz. I may go this route.
Actually, I was surprised at how good the prediction looked. I might build a single 18 for myself and see how it sounds.
Post by: Tom Reid on April 07, 2010, 10:17:23 AM
| Paul O'Brien wrote on Tue, 06 April 2010 10:21 |
Nobody in their right mind would buy those JBL drivers for a DIY cab when you can buy high quality drivers with similar capability from B&C and others for 1/2 the price or better. If he wants to roll his own have him pick up some B&C TBX100's or Emenince Definimax 4018LF for about $300ea from Parts express and load them in an appropriately sized box. There are other even less expensive drivers he could use too but but output and power handling begins to drop off with the lesser drivers, but then it depends what the needs are, PV Lowriders will come pretty close to these for about $200 a driver. http://www.parts-express.com/wizards/searchResults.cfm?srchE xt=CAT&srchCat=583 |
If power compression and heat are issues, the 2268h will rule over the 1/2 priced baskets. Differential drive woofers will take a magnitude of heat above the competition.
Post by: Tom Reid on April 07, 2010, 10:26:17 AM
| Tim Weaver wrote on Wed, 07 April 2010 00:38 | ||||
By ear alone. Mostly by comparing different subs while in use. Older SR4719's were pretty decent subs for the day. They would be used in the same fashion that we are seeing SRX728's today. Mid-level club rigs up to regional summer festival stages using a bunch of them under some higher priced arrays. 4719's had a bit of muddiness to them when you got down low. Say under 60 hz. They would really have a loss of cone control (for lack of a better word) when you pushed them with pedal tones. Low key riffs, and 5 string bass would not be reproduced faithfully. The SRX728 is an improvement on an order of magnitude compared to the 4719, but still exhibits some of these traits. These cabs have a ton of output though so they get paired up with some higher end array cabinets in order to fill riders. I've seen them under hangs of vertecs a bunch of times. Compare though an SRX728 to the Vertec sub 4880 and no one would argue with you that the vertec sub sounds better, hits harder, and goes lower with more authority. Even the Dual 15 4882 will run circles around the 728, and it gives up a good deal of displacement to the dual 18. Bass lines are quite faithfully reproduced with these cabs. The tbx100 from B&C is more in line with a high end arena rig subwoofer than it is the club level SRX type box. If you build a proper box for it, it will give you everything you would expect from an A level subwoofer. That's what I mean by "more accurate". It gives me more of what I want and less of what I don't.... |
VT8880 uses are redesigned 2268h (aptly named 2269h) that was designed to extend low frequency response. Otherwise the drivers are mechanically identical. The same applies to the 15" version of the VT sub.
There's nothing wrong with B&C drivers. I'm a fan, and have replaced some beloved JBL drivers with B&C product.
However, the JBL will produce more output with less distortion and handle more heat.
Post by: Jeff Wheeler on April 07, 2010, 10:46:34 AM
Post by: Phil Lewandowski on April 07, 2010, 02:22:31 PM
| Tom Reid wrote on Wed, 07 April 2010 10:17 | ||
If power compression and heat are issues, the 2268h will rule over the 1/2 priced baskets. Differential drive woofers will take a magnitude of heat above the competition. |
To back up what Tom is saying I would very much agree that the 2268's do a great job with heat, and I have always been impressed with how they handle higher "heating" power for several hours.
Take Care,
Phil
Post by: David Morison on April 07, 2010, 06:01:36 PM
| Jeff Wheeler wrote on Wed, 07 April 2010 15:46 |
I am real partial to the 2268 drivers because I already own them, but I am going to take Charlie's suggestion and spend some time with WinISD to see if the B&C drivers come out significantly ahead. I only did the 18TBX100 real quickly so far, to see if it would be hard to make it -3dB at 35Hz, and I have an Xmax problem, but I will be able to spend more time on it this weekend and see if it is solvable. |
Hi Jeff,
Here's a quick comparison of the TBX, 2268 and Definimax, all in 360 litre 218 configurations tuned to 36Hz and all fed with 2kW. It looks like the JBL wants a bigger box if it's going to reach as low as the others. (frequency range shown is 25Hz to ~ 325Hz, the axis got cropped off when I edited it to fit the forum)
About the Xmax, I notice from comparing WinISD with Eminence's recommended designs that WinISD seems to overestimate the actual excursion, by as much as 25% in some cases, so that may not be as much of an issue as you think. If you have the time, try modelling some of their recommendations to see for yourself.
Here's what WinISD thinks the 3 drivers from the above comparison will do for excursion, again on 2kW for each 218.
Regards,
David.
Edit - added excursion graph.
Post by: Art Welter on April 07, 2010, 06:21:54 PM
| Matt Errend wrote on Tue, 06 April 2010 20:46 | ||
That has to be the P-P spec, otherwise the surround would be much much beefier. I would assume that the "real" xmax is 11.5mm, in relation to the other drivers listed. |
That would be a wrong assumption, and if you look at JBL’s double voice coil differential drive magnet structure you can see they came up with a rather different (and patented) approach to making a woofer than the traditional method.
You can also see how the other JBL woofers have Xmax similar to other traditional drivers.
Xmax was traditionally defined by the overhang method. Overhang is the length of coil in mm that extends past either side of the top plate and is determined by the formula:
Xmax = gap height – [voice coil length/2]
The Audio Engineering Society (AES2-1984) defines Xmax as:
“The voice-coil peak displacement at which the “linearity” of the motor deviates by 10%. Linearity may be measured by percent distortion of the input current or by percent deviation of displacement versus input current. Manufacturer shal state method used. The measurement shall be made in free air at Fs.”
Wolfgang Klippel has a much more specific idea of what Xmax should be, but that is another kettle of fish...
In the 2008 JBL Theile Small parameters and definitions PDF that I quoted the Xmax figures from, their definition for Xmax is:
Peak linear displacement of driver diaphragm (0 to peak).
So the figures are one way.
The 2268 (23 mm Xmax) should be capable of 46 mm “linear displacement” peak to peak, about 1.75 inch of movement.
Art Welter
Post by: Art Welter on April 07, 2010, 06:37:52 PM
The 4018LF has an Xmax of 7.9 mm.
The B&C 18TBX100 has an Xmax of 10 mm.
According to your sim, they both have exceeded Xmax with 2kW.
The 2268 is no where near its rated Xmax of 23 mm, could you check what its output level would be when you reach that excursion ?
Art Welter
Post by: Art Welter on April 07, 2010, 06:45:32 PM
| Tom Reid wrote on Wed, 07 April 2010 08:26 | ||||||
VT8880 uses are redesigned 2268h (aptly named 2269h) that was designed to extend low frequency response. Otherwise the drivers are mechanically identical. The same applies to the 15" version of the VT sub. There's nothing wrong with B&C drivers. I'm a fan, and have replaced some beloved JBL drivers with B&C product. However, the JBL will produce more output with less distortion and handle more heat. |
Appears you and Tim Weaver disagree about the JBL distortion
.Interesting, the VT4880 uses the 2258H (19mm Xmax), VT4880A uses the 2269H (also 19mm Xmax) both rated at less Xmax than the 2268 (23 mm Xmax) used in the SRX 728.
The Eminence speakers I have tested meet their X max specifications.
I have not tested any JBL cones to see if their X max figures are correct, but I have no reason to doubt them.
Have you ever looked at the excursion of the speakers in your SRX 728 at “full tilt boogie”?
A white dot on the cone makes it easy to measure the excursion.
Art Welter
Post by: Adam Schaible on April 07, 2010, 07:41:11 PM
Post by: Phillip_Graham on April 07, 2010, 07:59:39 PM
| Art Welter wrote on Wed, 07 April 2010 18:37 |
David, The 4018LF has an Xmax of 7.9 mm. The B&C 18TBX100 has an Xmax of 10 mm. According to your sim, they both have exceeded Xmax with 2kW. Art Welter |
I'm going to pipe up in Art's defense here, as I think he is correct in supporting the driver in question.
It should also be mentioned that the change in voice temperature is not likely being factored into these simulations, which are based on small-signal T/S parameters.
Raise the voice coil temperature by 150C, thereby changing Re appreciably, and the needed tuning for good performance will have changed dramatically. Qe has effectively increased, and driver excursion will also increase.
The WinISD simulations presented are not going to give a realistic portrayal of the driver performance at high input voltages. It will also result in the production of a subwoofer box that will not be properly tuned when driven the way most professional loudspeakers are driven.
The JBL differential drive speakers have quite good thermal performance compared to more conventional designs, if you look at the thermal time constants that JBL publishes for their conventional drivers compared to differential drivers. Even if the driver Xmax was the same as the other drivers mentioned above, the JBL likely still has a thermal performance advantage.
Post by: Art Welter on April 07, 2010, 08:14:06 PM
| Adam Schaible wrote on Wed, 07 April 2010 17:41 |
I know that much/any power in the 30hz area makes them sound like total shit (srx 728) .. but this is sine wave's - like 20 volts. That probably says just as much about the box as the driver, just my experience. I didn't have the grill off to measure, but it didn't look like 1.75" peak to peak and they definitely distort severely at that level. |
20 volts into 4 ohms is around 100 watts.
Was your observation outdoors?
What was the nature of the “total shit”?
Was it frequency dependent?
Box rattle, cone flap, harmonic distortion?
Both cones sound the same?
Post by: Adam Schaible on April 07, 2010, 08:21:16 PM
| Art Welter wrote on Wed, 07 April 2010 19:14 | ||
20 volts into 4 ohms is around 100 watts. Was your observation outdoors? What was the nature of the “total shit”? Was it frequency dependent? Box rattle, cone flap, harmonic distortion? Both cones sound the same? |
Was your observation outdoors?
Yup
What was the nature of the “total shit”?
Lots of cone flap
Was it frequency dependent?
Yup, 30hz..ish
Box rattle, cone flap, harmonic distortion?
flap
Both cones sound the same?
yeah
I don't expect it to respond well at 30hz, just saying the extreme xmax didn't seem to help distortion below box tuning.
Post by: Art Welter on April 07, 2010, 09:08:02 PM
| Adam Schaible wrote on Wed, 07 April 2010 18:21 |
I don't expect it to respond well at 30hz, just saying the extreme xmax didn't seem to help distortion below box tuning. |
Below box tuning excursion goes up radically, and ports make flapping noises.
What was the Fb ?
Did you notice distortion above the FB?
Post by: Adam Schaible on April 07, 2010, 09:34:51 PM
Post by: Silas Pradetto on April 07, 2010, 09:51:51 PM
| Adam Schaible wrote on Wed, 07 April 2010 21:34 |
...XMax doesn't really help above fb ... |
I guess all those manufacturers got it wrong then....we should all still be using http://www.jblpro.com/pub/obsolete/2220hj.pdf since they're so amazing at producing thumping bass
Post by: Adam Schaible on April 07, 2010, 09:53:24 PM
+/- 8mm is fine.
23mm doesn't seem necessary.
Post by: Silas Pradetto on April 07, 2010, 09:57:43 PM
| Adam Schaible wrote on Wed, 07 April 2010 21:53 |
You really like to take things out of context. +/- 8mm is fine. 23mm doesn't seem necessary. |
To go low and loud you need Xmax. Period.
Most any sub I've ever used has run out of excursion before power capacity, with the exception of using dubstep as program material. The 2268H loaded subs go lower than just about any other front loaded sub on the market and they sound very good doing it. That extra Xmax is quite useful.
Post by: David Morison on April 08, 2010, 07:29:48 AM
| Art Welter wrote on Wed, 07 April 2010 23:37 |
David, The 4018LF has an Xmax of 7.9 mm. The B&C 18TBX100 has an Xmax of 10 mm. According to your sim, they both have exceeded Xmax with 2kW. <snip image> The 2268 is no where near its rated Xmax of 23 mm, could you check what its output level would be when you reach that excursion ? Art Welter |
Hi Art,
Will do once I'm back at home with WinISD rather than here at the day gig. I'd suspect that it would take so much power to get to 23mm that you'd be well over the thermal handling of the drivers, so it may be a moot point. I will also have a look how the temp rise Phillip G mentions pans out.
I agree the others do model over Xmax, though as stated I'm not 100% sure the actual excursion is as bad as modelled.
Not trying to knock the JBL, I'm sure it is a better driver, but just wanted to help show some potential benefits of the other drivers - i.e. getting down to the target 35Hz range in a smaller box, albeit with some trade-offs.
Regards,
David.
Post by: David Morison on April 08, 2010, 07:39:40 AM
Thanks for joining in.
I actually agree on all points, and will have a play with the temp rise later today. I wasn't really trying to knock the JBL, as I'm sure that it is a better driver all round. I just wanted to show some of the potential benefits of the cheaper drivers, such as getting to the target 35Hz range in a relatively smaller box (albeit with some trade-offs). Given the implied budget constraints, I thought it was interesting to have a look at both sides of the coin.
Regards,
David.
Post by: Jeff Wheeler on April 08, 2010, 07:58:38 AM
Post by: Adam Schaible on April 08, 2010, 08:23:34 AM
That said, anyone have experience with the B&C 21SW152? Doesn't Yorkville use this in one of their subs?
Post by: Tom Reid on April 08, 2010, 09:59:55 AM
| David Morison wrote on Thu, 08 April 2010 06:29 |
Not trying to knock the JBL, I'm sure it is a better driver, but just wanted to help show some potential benefits of the other drivers - i.e. getting down to the target 35Hz range in a smaller box, albeit with some trade-offs. Regards, David. |
David,
I picked this reply, but my response can fit anywhere.
In my opinion multiple boxes are the only way to achieve the below 35hz range. A single or tandem woofer box is going to flail at VLF of noticeable level.
JBL makes a good product. So does B&C. What tool do you want for the job? Comparing based on price doesn't take into account that the JBL is made of a different technology.
When a company redesigns the brake to allow for more excursion, doubles the coils in a way that wicks heat away from the core, and balances flux as to reduce 2nd and 3rd order harmonics to all time lows (2268h +2% 50hz-100hz @114dbspl) it should win the pencil pushers over.
But how does it sound? Well, there's the rub. No two people agree on the same sound. If we did, the world would be a boring place, and we wouldn't have as many good loudspeaker companies.
All JBL differential drive speakers are magnetic shielded. Each coil is opposing resulting in no external magnetic field. So go ahead an put your plasma display on top of your 728s (if you want to shake it to death).
Post by: Paul O'Brien on April 08, 2010, 10:53:57 AM
Post by: Tom Reid on April 08, 2010, 11:33:12 AM
| Paul O'Brien wrote on Thu, 08 April 2010 09:53 |
All this discussion about which driver is superior is sorta missing the point here though. The customer in question won't spend big money and by the sounds of it both he and visiting bands are more impressed with quantity than unseen quality, so wouldn't it make more sense to give him a pair of double 18's with slightly less cutting edge but still very good drivers for about the same cost? If the main source music is typical rock band stuff then uber low response isn't needed anyway so the B&C or Definimax drivers would be more than sufficent. |
That's one or two valid data points for selecting a tool for a job.
Post by: Jamin Lynch on April 08, 2010, 11:37:54 AM
.Art Welter[/quote]
That's funny as hell, but so true.
Post by: David Morison on April 08, 2010, 02:18:24 PM
| Art Welter wrote on Wed, 07 April 2010 23:37 |
David, The 2268 is no where near its rated Xmax of 23 mm, could you check what its output level would be when you reach that excursion ? Art Welter |
Here you go, orange is cold as before, red is with 150K increase in voice coil temp as suggested by Phillip G. Power required to reach 23mm is 8600W cold and 4300w hot, for the pair in the same box as before.
Regards,
David
Post by: Josh Ricci on April 08, 2010, 02:20:46 PM
| Adam Schaible wrote on Thu, 08 April 2010 07:23 |
That said, anyone have experience with the B&C 21SW152? Doesn't Yorkville use this in one of their subs? |
Just purchased a pair for a DIY project. Haven't had a chance to load them and power them up yet, but I don't believe they are going to disappoint.
Post by: David Morison on April 08, 2010, 02:24:55 PM
| Jeff Wheeler wrote on Thu, 08 April 2010 12:58 |
I am satisfied with the cabinet dimensions of the SRX subwoofers. I suspect the box could shrink and change vent dimensions, and the low-end be beefed up with EQ, to still produce useful output if you really wanted a smaller cabinet. I am not convinced there is any compelling reason to use a different driver. This will be a huge upgrade from the current subs anyway. |
Fair enough. In that case you would be able to get the 2268s to reach a little deeper - the 360l per pair I picked worked for getting the other 2 drivers down to 35ish Hz, but is probably a bit smaller than the 728.
All the best,
David.
Post by: Josh Ricci on April 08, 2010, 02:27:53 PM
| Paul O'Brien wrote on Thu, 08 April 2010 09:53 |
All this discussion about which driver is superior is sorta missing the point here though. The customer in question won't spend big money and by the sounds of it both he and visiting bands are more impressed with quantity than unseen quality, so wouldn't it make more sense to give him a pair of double 18's with slightly less cutting edge but still very good drivers for about the same cost? If the main source music is typical rock band stuff then uber low response isn't needed anyway so the B&C or Definimax drivers would be more than sufficent. |
This...I agree with.
A set of 4 good quality B&C's or Eminence's will offer better bang for the buck than only 2 2268H's even if it is a better driver technically. In a 2 on 1 situation it's almost always the 1 that loses.
I seem to recall that Beyma's big 21" 21SW1600ND is going for $399ea a few places. That could be an option.
Post by: Adam Schaible on April 08, 2010, 02:30:43 PM
Post by: Jeff Wheeler on April 08, 2010, 03:46:13 PM
While it is correct that bar-bands and patrons "hear with their eyes" and Art's remark is not lost on me, I do not think I want the owner to spend more money on that "look factor" when he can get what he needs in a single 18, which is actually what he has now (though they are cheap Pyle Pro subs.) He has a whole lot of "sounds like shit factor" to worry about before he spends time and money making it look impressive.
It does need to go to 35Hz because for example, in April the venue calendar includes:
* 3 nights with one band each
* 2 nights with "dance music" / DJ
* 13 nights with karaoke
I think their entertainment strategy is totally wrong for a 200-capacity venue but that's a larger issue and one that he does not listen to anyone about. But in any case, he put the house PA in to save money on the DJ/karaoke bullshit, which occupies way more dates on the calendar, so if it cannot do that effectively there is no point in upgrading.
Post by: Tom Reid on April 08, 2010, 03:51:44 PM
Post by: Adam Schaible on April 08, 2010, 04:19:01 PM
| Jeff Wheeler wrote on Thu, 08 April 2010 14:46 |
The price of comparable drivers is about the same honestly. Two cheaper drivers, like the 4018LF, also cost about the same as one 2268H. A pair of them might look more efficient than one 2268H on paper / in WinISD, but once you heat them up that is no longer true. While it is correct that bar-bands and patrons "hear with their eyes" and Art's remark is not lost on me, I do not think I want the owner to spend more money on that "look factor" when he can get what he needs in a single 18, which is actually what he has now (though they are cheap Pyle Pro subs.) He has a whole lot of "sounds like shit factor" to worry about before he spends time and money making it look impressive. It does need to go to 35Hz because for example, in April the venue calendar includes: * 3 nights with one band each * 2 nights with "dance music" / DJ * 13 nights with karaoke I think their entertainment strategy is totally wrong for a 200-capacity venue but that's a larger issue and one that he does not listen to anyone about. But in any case, he put the house PA in to save money on the DJ/karaoke bullshit, which occupies way more dates on the calendar, so if it cannot do that effectively there is no point in upgrading. |
I wouldn't be so quick to discount the 4018lf. 1:1 they might not fare as well as the 2268 but 2:1 .. I think you're mistaken if you believe a single 2268 will be more efficient or handle more heat. True, a 2268 has two voice coils, but so do 2 4018's. I have my doubts that differiental drive is 200% more efficient at dissipating heat than a standard VC.
Look at some charts Silas has made with his dual 4015lf sub in comparison to commonly available production subs if you have the time.
Post by: Jeff Wheeler on April 08, 2010, 04:34:09 PM
I am fairly confident that two SRX718S-alike boxes will provide more than adequate output to send the door man/designated volume cop rushing to yell at any idiot DJs if the bass anywhere near enough to damage 2268H drivers. Also there is only one 20A circuit for the whole PA so a breaker would trip before the voice coils got smoked. And I put the snake fan-tail in a location that causes most people to setup their FoH equidistant from the two subs, and the stage is basically a big bass trap below about 125Hz, so DJs sitting in either position should not need to fight with the PA to hear what they want to hear.
One thing I do not like about the way I have the existing equipment deployed is the SF25 horns are way brighter on-axis than at FoH if they are pointed the right direction to cover the room. That combined with insufficient height causes the HF to be painfully loud, so I often find myself fiddling with the PA's LPF knob and giving up on the high-end. But this is as much a product of the shitty speakers as anything else, and it will not get fixed until the owner realizes it is a problem in the first place.
If he would have spent the $8k I suggested he would not have these issues, but instead he spent $3k, so he gets what he paid for and will continue to waste money replacing crappy gear he shouldn't have bought.
I think we are getting a new snake next week, 16x8, to replace a 16x4 with 4 dead channels he had sitting in storage (owner used to be a DJ, which is part of the problem, he thinks he knows things sometimes.) I suggested a 24x8 because, for example, later this month we may have to do karaoke/band/karaoke/band due to a scheduling error on his part with a charity event that already spent money advertising "karaoke contest $100 prize" on a night when he booked band also. So he will probably spend $400 on a new EWI snake and within weeks of it getting here, we will have a night where I run out of channels and have to put up a second snake, or re-patch things several times unnecessarily, or do my karaoke crap from behind the PA, because he wants to save $100 and not buy the 24 channel snake. Go figure. Also, instead of paying $100 to convert 4 of the fan-tail returns to TRS connectors, he is going to buy $30 worth of XLR to TRS adapters. And buy them again 5 times a year as bands steal or lose them. And deal with the headache of calling me for help when bands show up and there are no adapters, because they are idiot bands that just expect TRS ends to plug right into the TRS jacks on their mixer, with no adapters, patch panels, or outboard.
Sorry for the rant, just to give you an idea of how this situation is, "buy once, cry once" is a concept he refuses to learn.
Post by: Jeff Wheeler on April 08, 2010, 04:43:42 PM
| Adam Schaible wrote on Thu, 08 April 2010 15:19 |
I wouldn't be so quick to discount the 4018lf. 1:1 they might not fare as well as the 2268 but 2:1 .. I think you're mistaken if you believe a single 2268 will be more efficient or handle more heat. True, a 2268 has two voice coils, but so do 2 4018's. I have my doubts that differiental drive is 200% more efficient at dissipating heat than a standard VC. Look at some charts Silas has made with his dual 4015lf sub in comparison to commonly available production subs if you have the time. |
The 2268H is -3dB from power compression at RMS power, while most cheap sub drivers are roughly -6dB, including a lot of Eminence products. Also the 4018LF runs out of Xmax much more easily than a 2268H, and that is a legitimate consideration for DJ-duty subs, much more so than subs that are used for kick drum and a little bit of bass guitar.
Seriously, there is no comparing cheap Eminence shit to serious sub drivers. Eminence makes plenty of good things, but the stuff you can buy off Parts-Express, you get what you pay for. A $200 driver is a $200 driver, and a $400 driver is, not surprisingly, about twice as useful.
Oh, and Silas's double 15 is not for this kind of use either. I do not doubt his ingenuity and I am sure he makes plenty of money with those subs, but there is a huge difference between a kick drum sub and a good DJ-duty sub, and Silas' double 15s lie somewhere in-between.
Post by: Art Welter on April 08, 2010, 11:03:14 PM
| Jeff Wheeler wrote on Thu, 08 April 2010 14:43 | ||
The 2268H is -3dB from power compression at RMS power, while most cheap sub drivers are roughly -6dB, including a lot of Eminence products. Also the 4018LF runs out of Xmax much more easily than a 2268H, and that is a legitimate consideration for DJ-duty subs, much more so than subs that are used for kick drum and a little bit of bass guitar. Seriously, there is no comparing cheap Eminence shit to serious sub drivers. Eminence makes plenty of good things, but the stuff you can buy off Parts-Express, you get what you pay for. A $200 driver is a $200 driver, and a $400 driver is, not surprisingly, about twice as useful. Oh, and Silas's double 15 is not for this kind of use either. I do not doubt his ingenuity and I am sure he makes plenty of money with those subs, but there is a huge difference between a kick drum sub and a good DJ-duty sub, and Silas' double 15s lie somewhere in-between. |
Jeff,
One important detail, Silas' double 15s 4015LF are in a too small box, in a larger box the 4015LF goes low, and the 4018LF goes lower yet, but requires a larger box.
All the 18 inch speakers we discussed have very similar efficiency.
The 2268H, by virtue of design and almost double the X max, could put out approximately what two of the less expensive drivers can, and take up about half the space, though from the sim, to get the best LF performance it could use a slightly larger box than the other drivers.
That said, doubling bass drivers gives 3 dB more efficiency, so the 2268H would require double the power to equal two of the other drivers.
In simple terms, 2000 watts to one 2268H, would be equaled with 500 watts each into a pair of 4018LF, or B&C 18TBX100.
I would not want to bet that the 2268H, even with it’s heat wicking design, would exhibit less thermal compression at 2000 watts than the other speakers would at 500.
In a portable system, size and weight matter, both for transport and storage.
In an install, extra size may be an advantage for stacking and perceived loudness.
Doubling cones saves a lot of amplifier and wall power, and puts less heat into the room.
Art Welter
Post by: Silas Pradetto on April 09, 2010, 03:40:51 PM
Post by: Jeff Wheeler on April 09, 2010, 05:29:39 PM
| Art Welter wrote on Thu, 08 April 2010 22:03 |
In simple terms, 2000 watts to one 2268H, would be equaled with 500 watts each into a pair of 4018LF, or B&C 18TBX100. I would not want to bet that the 2268H, even with it’s heat wicking design, would exhibit less thermal compression at 2000 watts than the other speakers would at 500. |
I think the 2268H would indeed be superior except that the two Eminence in a box approximately twice as large would be less likely to be driven beyond Xmax and stop giving useful output for more power. The opinions shared with me on the 18TBX100 and other B&C drivers are good, however those have similar cost to the JBL.
If amplifier power was an issue I would reconsider, but honestly, the cost difference between the 4018LF and the 2268H is not as much as I expected, and my ability to spare components for him, and rent him more essentially identical boxes in case some band demands it, are also advantages.
| Silas Pradetto wrote on Fri, 09 April 2010 14:40 |
I have personally destroyed a pair of 2268H woofers (in SRX718 boxes) powered on 1 channel of an IT8000 with no limiters set, but no clipping; this was with dance music for a 3-hour event. They failed about 10 minutes from the end. So even with 2000 watts peak per driver, they can still die like any other woofer. |
I said to the doctor, I said, "Doctor, my subs smoke when I over-drive them!" The Doctor said, well, don't do that!
I am curious if the failure mode was heat or Xmech.
Post by: Jeff Wheeler on April 10, 2010, 05:15:45 PM
| Adam Schaible wrote on Thu, 08 April 2010 15:19 |
I wouldn't be so quick to discount the 4018lf. 1:1 they might not fare as well as the 2268 but 2:1 .. I think you're mistaken |
I finally got around to trying this in WinISD today. Obviously my post is all relevant "on paper" only, as I have not built and listened to these potential subwoofer options.
The 4018LF reaches Xmax at 50% power somewhere between 40Hz and 50Hz in every box/vent configuration I tried that is -3dB at 30Hz or even 35Hz. It gets really close to Xmech at 100% RMS power and obviously has no room to peak. Crappy driver or else the first dozen boxes I tried in WinISD were just totally wrong.
The 2268H, on the other hand, will take 2700w before reaching Xmax in a box that is similar to half of a 728S, with a rectangular vent spanning the bottom. So it has plenty of room to peak before it should sound distorted.
The B&C 18SW115, which costs a little bit more, seems like it will work in a much smaller cabinet. It reaches Xmax around 1700w, its RMS power rating, at about 40Hz in a box that gets it to -4dB at 30Hz; but WinISD predicts very high port air velocity, 90m/s at 40Hz with RMS power. I think this would cause noise. There is a trade-off between port air velocity and how much output the driver will produce before it reaches Xmax.
I think the 18SW115 would be really great if I needed a smaller box, but I am not convinced this is a compelling reason to buy a more costly driver and risk port noise within the desired bandpass. If I did not need it to play so low it would be easy to solve these problems, too.
So the SRX718S-alike looks like the way to go. I am going to have my bar-owner friend build two and if they turn out well, I will have him make several more for me, as I apparently also need more subs these days.
Post by: Paul O'Brien on April 10, 2010, 06:18:09 PM
Post by: Art Welter on April 10, 2010, 07:55:06 PM
| Jeff Wheeler wrote on Sat, 10 April 2010 15:15 | ||
I finally got around to trying this in WinISD today. Obviously my post is all relevant "on paper" only, as I have not built and listened to these potential subwoofer options. The 4018LF reaches Xmax at 50% power somewhere between 40Hz and 50Hz in every box/vent configuration I tried that is -3dB at 30Hz or even 35Hz. It gets really close to Xmech at 100% RMS power and obviously has no room to peak. Crappy driver or else the first dozen boxes I tried in WinISD were just totally wrong. |
Jeff,
Sounds like you are designing too low Fb for the 4018LF with high power.
The SRX 728s is not flat to 30, as JBL’s “Frequency Response” shows.
It appears to be about 8 dB down at 30 Hz compared to 100 Hz.
The dual 4018LF, even with a Fb of 40 Hz is about 10 dB down at 30 Hz, not much different. Looks like the LF corner of the SRX 728s is a couple Hz lower.
A half version of the 728 would have 6 dB less output, at 3200 watts it would put out 130 dB compared to the dual 4018LF putting out about 132 dB with 1600 watts.
I still am partial to the Lab 12 (about $150 per) , as it goes lower than the above speakers in a cabinet half the size, the green trace is a Lab 2x12” in a 7.76 (gross) cubic foot box.
In an outdoor side by side gig, I found four of these boxes with only 900 watts per box put out 2 dB more at 40 Hz than eight Meyers 650P dual 18 cabinets.
Art Welter
Post by: Jeff Wheeler on April 10, 2010, 08:29:52 PM
| Art Welter wrote on Sat, 10 April 2010 18:55 |
Sounds like you are designing too low Fb for the 4018LF with high power. |
Yes, I can figure out how to make the speaker go low, or get loud, but not both. I suspect a small 6th order bandpass box would work better but at the expense of requiring more corrective EQ and a more complex box.
| Quote: |
The SRX 728s is not flat to 30, as JBL’s “Frequency Response” shows. |
True, my simulated box is still a little wrong, as I do not know the driver displacement. Also I've thought about making it a bit larger and tuning the box a little lower since the driver is capable of doing it.
I am not sure how to determine if such a modification would make a different box incompatible with an OEM box. Should I be looking at the difference in output phase shift?
| Quote: |
A half version of the 728 would have 6 dB less output, at 3200 watts it would put out 130 dB compared to the dual 4018LF putting out about 132 dB with 1600 watts. |
If they both had a similar power compression curve, but I think it is safe to say they do not.
| Quote: |
I still am partial to the Lab 12 (about $150 per) , as it goes lower than the above speakers in a cabinet half the size, the green trace is a Lab 2x12” in a 7.76 (gross) cubic foot box. |
I remembered your posts on this subject and it didn't take me long to come up with something that looked feasible. I don't know if I can coax the prediction into looking so much better than the 718S that it's worth making a change from something that is essentially a "de-badged box," but compatible with the real OEM ones that I own, to a true DIY; but I will give it more thought.
Post by: David Morison on April 11, 2010, 10:35:47 AM
| Jeff Wheeler wrote on Sun, 11 April 2010 01:29 |
True, my simulated box is still a little wrong, as I do not know the driver displacement. Also I've thought about making it a bit larger and tuning the box a little lower since the driver is capable of doing it. |
Also, you'd want to decide if it were the response of the 728 or the 718 you were trying to match - the 728 is bigger than just 2x718, and goes lower (538l gross vs 454l and about -8dB at 30Hz relative to 100Hz rather than approx -11dB for the 718).
I'd use a ballpark figure of 5-6l for the displacement of the 2268 in the cab, I think 5 is the smallest I've seen for a neo 18" but they will vary depending on the bulk of any external heatsinks. Conventional 18"s are usually more like 7-8l.
Just a couple of random thoughts,
Regards,
David.
Post by: Jeff Wheeler on April 11, 2010, 11:00:49 AM
Post by: Art Welter on April 11, 2010, 02:33:35 PM
| Jeff Wheeler wrote on Sat, 10 April 2010 18:29 | ||||||||
Yes, I can figure out how to make the speaker go low, or get loud, but not both. I suspect a small 6th order bandpass box would work better but at the expense of requiring more corrective EQ and a more complex box.
True, my simulated box is still a little wrong, as I do not know the driver displacement. Also I've thought about making it a bit larger and tuning the box a little lower since the driver is capable of doing it. I am not sure how to determine if such a modification would make a different box incompatible with an OEM box. Should I be looking at the difference in output phase shift?
If they both had a similar power compression curve, but I think it is safe to say they do not.
I remembered your posts on this subject and it didn't take me long to come up with something that looked feasible. I don't know if I can coax the prediction into looking so much better than the 718S that it's worth making a change from something that is essentially a "de-badged box," but compatible with the real OEM ones that I own, to a true DIY; but I will give it more thought. |
A 6th order bandpass box will sound completely different and won’t play well with your present cabinets. It would not go any deeper, but would give more output in the middle of the bandpass.
Getting different types of ported cabinets phase to line up is not impossible.
If you are going to copy for compatibility, don’t change the box design from the JBL, or you will want different HP and EQ for the different alignments, complicating your set up.
That said, the SRX728S is an odd size, (no 90 inch truck integers) and at 19 cubic feet gross, a pretty big box even compared to the 14 cubic foot dual 4018LF Large Dance Club Sub. Designing a different box that fits your needs better, and selling the 728 cabinets may be an idea to consider if your box costs are really low and the builder competent.
As far as heat issues leading to power compression, without some actual test results I find it hard to believe the 2268H would safely dissipate more than four times the heat energy required to keep up with a pair of 4018LF.
As Silas pointed out, he managed to destroy a pair of 2268H with 2000 watts per cone, but you would need 3200 watts input to equal the SPL of 800 per cone using two 4018LF.
JBL specifies the 2268H “thermally-limited maximum electrical input power” is 1200 watts. With highly compressed sine wave like LF input typical in dance music, the dynamic range may be less than 3dB, so 2000 watts can release the magic smoke.
The 2268H linear displacement looks phenomenal, but with out dynamic material, heat death will still rule.
Art Welter
Post by: Elliot Thompson on April 12, 2010, 09:22:23 AM
| Jeff Wheeler wrote on Sun, 11 April 2010 01:29 |
True, my simulated box is still a little wrong, as I do not know the driver displacement. Also I've thought about making it a bit larger and tuning the box a little lower since the driver is capable of doing it. |
Jeff,
The JBL 2268H's xmech (not xmax) is 23 mm one-way peak or 46 peak to peak. You can estimate 11.5 mm +/- of available xmax.
Based on my records, it is the replacement for the JBL 2241, which offers 3 mm peak (or 6 mm peak to peak) in terms of x-mechanical damage over the JBL 2241 (20 mm peak or 40 peak to peak).
It offers a 3-inch dual voice coil and is rated 800 watts getting pink noise ranging from 30 - 300 Hertz. Skimming through the threads I am not sure where the wattage recommendation came about however, for DJ purposes you will lose this driver if you feed it over 1000 watts. The voice coil is small and the x-mechanical is no better than other 18-inch drivers offering voice coils ranging from 4 – 5 inches.
Also, if you are going to use WinISD, use the pro version.
Best Regards,
Post by: Bill Burford on April 12, 2010, 09:56:37 AM
oh man. a lot of people do that whether they admit it or not.
Post by: Bill Burford on April 12, 2010, 10:11:03 AM
20 volts.
you put 20 volts on a sub and say it sounds like shit.
what subs do you like?
Post by: Adam Schaible on April 12, 2010, 10:15:14 AM
I do like the 728, but a 30hz sine wave will make a lot of cone flap.
Post by: Bill Burford on April 12, 2010, 11:46:46 AM
I'm more of a consumer when it comes to these things. I like to read about Xmax and all this other stuff.
but when it comes down to it,
I just like to mix on a system that fits the room.
I thought of one solution for you.. if you have any crappy speakers already there.. just leave them there and plug a dummy cable into the back of them.. then just get one 718 for the room and place it closest to the center of the room. It sounded like it was a small room anyways. but if you want to save money, you could probably score a used one also. ( the used gear option had to rear its head into this ).. but dummy speakers look really loud to people who see sound.
I know nothing about the other drivers you guys were talking about. but it triggered some thoughts to consider.
Xmax maybe high for the 2268 driver and those graphs were really impressive and everything and I WISH I could make those measurements because there are a lot of questions I could answer. (for example, I'd love to see an impedence plot for SRX subs).
those graphs were made using sine waves right?
I was thinking about how amps are capable of delivering some nice impulse power sometimes-- short quick sounds probably wont overheat a 2268 and the excursion will probably be closest to Xmax on a kick. or from the "pluck" on the bass guitar. that Xmax comes in handy for creating punchy music-- some bands hear with their eyes..but they also like to feel the kick. My old sub was an MP418-- I know the kick wasn't really very punchy but a low bass not would get the room vibrating at some frequencies. I could be wrong, but I attribute that at least in part to Xmax. perhaps with more power, I could have made it hit harder.. it only had 500 watts on it.
As Art or someone had pointed out -- you certainly don't want to be at risk of exceeding Xmax. Whether I went with one or two subs, I'd probably get the JBL driver.
Now remember, this thinking is coming from a guy would probably never make a DIY 718. but just thinking about it, you could probably get your tuning and have a longer narrower subwoofer that fit better into the room. There could be some saved space involved. But on the other hand, with a SRX 718, you get that nice heavy grill on the front which can take kicks and bumps. That alone is somethign to consider in bar.
on the other hand, saving money is nice. but then you can make a low-ball offer on used gear and might get lucky. Just think, if you could score a factory sub, wouldn't that be sweet?
I made speaker stands once out of wood. the materials cost was over $200 all said and done. Plywood is expensive. The guy could be an excellent carpenter but its still a pain in the neck to make speaker cabinets.
I'd love to hear the drivers in a DIY though. I'm really curious to hear them actually. I'd like to know if JBL has come up with some "magic" measurements or how much of those dimensions are a tradeoff. It seems the shape of the 718 is to maximize the surface area on the ground.
That said, I know of a place that has them flown on the ceiling.
Need I say more on that?
Post by: Art Welter on April 12, 2010, 12:49:53 PM
| Elliot Thompson wrote on Mon, 12 April 2010 07:22 | ||
Jeff, The JBL 2268H's xmech (not xmax) is 23 mm one-way peak or 46 peak to peak. You can estimate 11.5 mm +/- of available xmax. Based on my records, it is the replacement for the JBL 2241, which offers 3 mm peak (or 6 mm peak to peak) in terms of x-mechanical damage over the JBL 2241 (20 mm peak or 40 peak to peak). It offers a 3-inch dual voice coil and is rated 800 watts getting pink noise ranging from 30 - 300 Hertz. Skimming through the threads I am not sure where the wattage recommendation came about however, for DJ purposes you will lose this driver if you feed it over 1000 watts. The voice coil is small and the x-mechanical is no better than other 18-inch drivers offering voice coils ranging from 4 – 5 inches. Also, if you are going to use WinISD, use the pro version. Best Regards, |
Elliot,
It would not be the first time I have seen JBL publish conflicting specifications, but the June 9, 2009 TS LF Parameters & Definitions lists the 2241 as 7.62 mm Xmax, 600 watts, and the 2268 as 23 mm Xmax, 1200 watts.
No Xmech figures are given.
I am curious as to whether the 2268 specs are correct, it would be interesting to see the results of an excursion test on an actual speaker.
Art Welter
Post by: Elliot Thompson on April 12, 2010, 11:46:55 PM
| Art Welter wrote on Mon, 12 April 2010 17:49 | ||||
Elliot, It would not be the first time I have seen JBL publish conflicting specifications, but the June 9, 2009 TS LF Parameters & Definitions lists the 2241 as 7.62 mm Xmax, 600 watts, and the 2268 as 23 mm Xmax, 1200 watts. No Xmech figures are given. I am curious as to whether the 2268 specs are correct, it would be interesting to see the results of an excursion test on an actual speaker. Art Welter |
Art,
It seems JBL purposely marketed the JBL 2268H with a high xmax however, never explained it is based on xmax damage.
In order for the JBL 2268H to offer a 23 mm xmax, the efficiency would be very low since all of the coil will be sitting outside the magnetic gap. Yet, it offers an no.% of 2.8
The numbers are based directly from the engineer’s specifications. I would imagine this is before marketing got their pretty little hands on it. There is no xmax rating on the engineer’s sheet. However it clearly states, “Xmax, damage 23 mm peak before the spider bottoms on gap sleeve.” It also states, “Special Notes: JBL 2241H Replacement in Neo Differential Drive line of transducers.”
It seems the JBL 2241 offers the mathematical xmax. As we know, manufactures were more conservative on their specifications when the “2241” was classed JBL’s best decades ago. Today, that 7.62 mm measurement would be marketed as 9 mm taking distortion into account.
Best Regards,
Post by: Bill Burford on April 13, 2010, 11:20:25 AM
or during a 5th string bass slide.. at some frequency on the way down on one of those, it seems like you can see the subs hit some sort of maximum excursion (probably no where near xmax from what I've seen).. I'm just curious if the things are exceeding 9mm on the newer srx subs under normal operation.
My guess is probably not.
But you have to consider, a new sub with higher specs can probably get much closer on a regular basis to an older design's maximum specs without breaking a sweat.
Post by: Jeff Wheeler on April 13, 2010, 01:45:21 PM
| Bill Burford wrote on Tue, 13 April 2010 10:20 |
So where do you think the cone is at peak power? maybe during a rock kick? |
My subs get the most abuse playing "dance music" and backing tracks for a hip-hop/rap artist I started working with recently. Rock bands are easy on subwoofers compared to that.
Post by: Bill Burford on April 13, 2010, 02:15:26 PM
I'm just trying to figure out where peak excursion happens. I was guessing it occurs during a kick-drum (be it synth or real).
no doubt, the sub-frequencies in most hip-hop seem to be much harder on subs and sub-amps.
I wouldn't put it past all bands though.. certainly I've heard some bassists with sub-harmonic processing that have some really crucial bass.. and some really nicely tuned floor-toms though. They definitely get the subs booming really low.
Of course, it is easier to push subs with a synth or track which has no chance of feedback. but I can definitely get subs booming really hard with toms and bass---
However, I'm just wondering if peak excursion happens on any of that--- after all, the beat of any music happens with the kick which has to cut through the bass-line so its not buried.
I don't know if the peak excursion right during a kick is greater than that of a bass-line or a hip-hop track-- which ever.
those are impressive bass-- maybe even peak excursion-- but you'd think the peak would be with the kick so it could cut through the mix. even with bands that use a sampler with massive hip-hop-style bass tracks or bass-drops, the kick still cuts through (talking about low frequency).
even when cutting some of the lows on the kick to make it tighter, it seems to cut through in the subs.
its not shaking the walls like a bass-line, but then it might be, its just so short of a sound. I'm thinking the peak excursion might last for a couple of miliseconds or something where as - and I don't know if this is true, but the really impressive low low bass that sounds awesome might have lower excursions but they are sustained for a long time-- like several seconds.
Post by: Evan Kirkendall on April 13, 2010, 02:22:57 PM
Standard "Rock" stuff doesn't really push subs all that low. You'll hardly ever have anything below 40hz with a standard rock group. Yes, you get some excursion with the kick drum, and you can launch drivers if you're not careful there. But, the real kicker for subs comes with pre-recorded music. A lot of the hip-hop and dance tracks today have heavy synth lines that can easily extend below 20hz. Its this stuff that heats up subs and pushes them to their limits.
You'll see a good amount of movement with a kick drum, but you don't get the heating that comes with dance stuff. And at the end of the day, it's the heat that kills quicker then anything.
Evan
Post by: Bill Burford on April 13, 2010, 02:37:48 PM
people just love to argue with you even when you are asking a question.
I said BANDS THAT USE SAMPLERS AND SUB HARMONIC SYNTHS ON THEIR BASS
ps. max excursion probably occurs at MIN impedance
Post by: Bill Burford on April 13, 2010, 02:41:53 PM
and the kick always punched through the bass of whatever tracks they were playin
Post by: Adam Schaible on April 13, 2010, 02:42:59 PM
A whole lot of drum kits are triggered. More than you think!
Post by: Bill Burford on April 13, 2010, 03:03:35 PM
bass or kick. to clarify my question, synth or accoustic bass or synth or accoustic kick.
in a later post I mentioned some hip-hop/r&b.
In the cases I am thinking about, I assure you these drums are accoustic and not triggers.
if you would rather correct me I guess you don't know the answer.
I know the answer.
(sarcasm)
to find it, you can simply view recorded tracks and zoom in real close. Inspect the peaks of the synth wave-forms and compare them to the peaks of the kick waveforms. there, you have your answer. (more sarcasm)
seriously is there an answer? I know this depends on the mix. assuming a typical good mix. and assuming the mix is on a given box and tuning, the max excursion will still occur at some point in the mix relative to the smaller excursions at all other parts of the same mix.
Post by: TJ (Tom) Cornish on April 13, 2010, 03:06:26 PM
Post by: Bill Burford on April 13, 2010, 03:10:50 PM
the original post for cabinets for 2268 drivers mentioned that there were only some days with live music and other nights there were dj's..
this was really interesting to me..
so I asked where anyone thought in live music (mixed differently) than recorded music, did max-excursion occur?
I didn't state a bunch of facts.. I asked a question.
can anyone answer it? or is it slam fest for asking a question?
( NO STUPID IT COULD HAVE BEEN A TRIGGER )
??????? what? how does that connnect to my question?
its like people want to read into my thinking and find something wrong with it.. without attempting to even talk about the original question
yeah thanks.. do you see my point
there is more to my question as to why it is even a question.
everyone knows amps have more impulse power than continuous power. or do they? anyhow, considering a kick is more of an impulse than a sustained track or bass-line, in my mind, that meant that the kick had an even higher chance of creating max-excursion (as opposed to a bass line)
also, the instrumentation used to measure this for the fancy plots could be using data from the amp-- I don't do those plots so I don't know. but could it be possible that they calculate those plots based on signal used to drive the amplifier.. however, is this the same as the actual physical motion of the driver? or is it based on voltages?
or current drawn?
how much of that energy was converted to heat?
how much of the actual physical woofer motion mimicked the chart?
my question also has more purpose: the answer may help the original poster decide which drivers to use in his boxes.
what if the other woofers made more excursion for a sine wave but as someone said, the excursion exceeded their specs xmax?
well, then, wouldn't this mean that physical damage could occur during a live mix?
in JBL's case, they may have a cone which is physically made to take more physical abuse than any of the electrical abuse which is ever thrown at it.. in other words, perhaps the driver is designed to operate with a max voltage, max current which will never achieve xmax on purpose-- for longevity reasons.
Also, if you over design the cone physically, you might lose some of the efficiency but they may be more capable of withstanding extended exposure to sunlight (could be helpful for anyone else reading this thread if answered).
I actually dont know the answer.. I'm just thinking about it. I'd like to know. but I'm thinking in practical terms, if I knew the answer to where maximum excursion occured, I could use that information to decide if they actually had made the cone more durable than necessary. this could encourage me to buy more of them or not.. or it could help me decide how maybe a friends drivers were actually damaged or if someone asks me.. 'hey, do you think this setup is ok?' it may help me give them advice of what to watch out for.. say someone asks.. where do I put my limiter on this amp which is more powerful than the spec.. all kinds of reasons for asking this question.
Post by: Seth Hochberg on April 13, 2010, 03:15:42 PM
If you have driver x placed in a box tuned at 50hz and I have driver x in a box tuned to 30hz, even when fed the same signal from the same amplifiers to the same speaker, we will each receive dramatically different results for our particular setup's peak excursion.
Post by: Evan Kirkendall on April 13, 2010, 03:18:47 PM
| Bill Burford wrote on Tue, 13 April 2010 14:37 |
This is why I love this site!!!! people just love to argue with you even when you are asking a question. I said BANDS THAT USE SAMPLERS AND SUB HARMONIC SYNTHS ON THEIR BASS |
Bill,
There's no arguing going on here. Just stating facts. If you can't figure out that a kick drum is an impulse that creates a good amount of cone movement, then you probably should consider a new hobby.
Here's an easy excursion test: At your next sound check, have somebody hit the kick drum. Push the fader up until you hear the subs bottom out. Now do the same with the bass guitar. I bet you'll get a lot more volume out of it. However, that bass guitar is going to create a lot more heat then the impulse of the kick drum.
| Bill Burford wrote on Tue, 13 April 2010 14:37 |
ps. max excursion probably occurs at MIN impedance |
Actually, that's completely wrong. Maximum excursion occurs where the impedance is the highest. As the voice coil cuts through the magnetic field, the impedance rises.
Here's an example:
(Pulled from EV's website, the QRX218S)
You see that big impedance bump at 70hz? That's where the cone is hitting hard. It's a bit above the tuning of the cabinet, and within the operating range of the cab. If you were to run a sine sweep from 100-40hz, you'd see the most cone movement at 70hz.
Evan
Post by: Bill Burford on April 13, 2010, 03:38:43 PM
I would bet that the max excursion occurs at around 35Hz on that cab.
the reason why is it has the lowest impedence.. this causes the most current throught the coil which causes the greatest EMF against the magnets which will move it the farthest.
again, I could be wrong but I'd bet if you are going to invert that driver, putting a high-powered 35Hz signal into it is the best way to get the coil to hang up on the basket.
either way, you are telling me to get a new hobby. for me the hobby years were 7, 8 years ago.. well beyond hobby. that is like a personal attack dont you think?
where have I gotten personal in here? I am more than happy to take challenges and even admit if I'm wrong without ever attacking someone personally. bands don't like that too well.
I don't take it personally at all. I've already said I could be wrong about this.. but you've definitely got my attention on the impedence curve for a driver. I'd like to hear from a JBL engineer on this one. I will happily admit my error. I'm a mixer and don't really do this kind of study myself. I have no need to.. I operate well within the spec sheets.
Post by: Bill Burford on April 13, 2010, 03:46:31 PM
Knowledge!!!!!!!!!
Post by: Bill Burford on April 13, 2010, 03:49:57 PM
great point.
xmax could change for the exact same mix in other words depending on the box.
earlier-- I hadn't thought of it like that.
that pretty much means my question is a bad one.
it might be a decent question if we were talking about a specific sub-- but i've had enough of the beat down for today.
Post by: Adam Schaible on April 13, 2010, 04:02:31 PM
Xmax is a specification of a speaker, and doesn't change.
Excursion will change based upon the mix -- but that should be obvious. As you mentioned, live sound instruments don't really produce sine waves. I really haven't seen any synths produce sine waves, but the crest factor is similar.
The reason you're getting the beat down is because you ask a question, someone answers it correctly (re: evan) and then you try and correct him when you have no clue what you're talking about.
Excursion is the lowest at the box tuning. For an 18" subwoofer in a cabinet tuned around 40hz, you'll see the cone barely move at all at 40hz, less than 1mm.
Kick drums, as has been stated, are impulses. Often times in a mix the kick is way louder than the bass (10db, maybe more). The bass kind of sits in the pocket but the kick gets out in front of it. In that case, it's likely that the kick is going to create more excursion than a bass guitar. This is subjective, as was stated, it depends on the sub, bass guitar note, kick tuning, relative levels, etc.
Also, as Evan said, as long as the kick isn't bottoming out the subs it's not likely to create issues because since it's an impulse it's not generating heat and heat is going to be the killer. Crank the bass up until the sub bottoms and you're more likely to have thermal issues. Trying to look at sine waves and determine how much excursion exists at xyz frequency and xyz input power doesn't tell the whole story.
Post by: Bill Burford on April 13, 2010, 04:20:26 PM
I still haven't said anything that is contradictory to anything anyone else has said. if you really read into what I said,
I mentioned where in a mix did max excursion occur.
you'd have to stretch to imply that I meant that the mix could be moved from box to box in order to change the meaning of my question.
In other words, you would have to be searching for something wrong with me to bring that up.. because when someone asks ME where in a live-mix does max excursion occur, I would assume that they were asking for a live mix that was using the same box for the entire mix.
now you did bring up a good point when you mentioned it depends on the box.. the max might actually occur at a different location for different boxes.. although, in my humble opinion, it would probably occur at nearly the same mix for just about any commercial box even if the performance of those boxes varied greatly.. maybe for the worst subwoofer vs the best subwoofer.
but for comparable subs, I'd say it occurs in roughly the same spot for the same mix.
Now if you are saying that you are the greatest subwoofer designer in the world and you can think of one box with the exact same driver where the kick creates the most excursion, but you have another box where the tuning causes a "trumpet" to cause max excursion.. well, excuse me for asking you a bad question. (completely joking about the trumpet by the way)
Post by: TJ (Tom) Cornish on April 13, 2010, 04:37:28 PM
| Bill Burford wrote on Tue, 13 April 2010 15:20 |
ha ha.. I have no idea what I'm talking about. I still haven't said anything that is contradictory to anything anyone else has said. |
Bill, the problem is that you contradict yourself.
For example:
Up a few posts you ask a question. People try to answer it. You say they're wrong and that you know the answer. Then later on you restate and agree that it was an unclear question. Then you say people were picking on you by putting strange conditions on the circumstances and that your question was perfectly valid in the first place.
On some posts you are talking about one thing, then you either post something else, or edit your original post to change your mind. Your posts often are confusing to read and hard to figure out what you are saying. People aren't attacking you personally - and I'm not now either. They are just trying to answer questions in a way where the truth gets out and bad info quashed. After this happens a few times, people get frustrated and it comes out in their language. Slow down in your posting and think a bit more carefully, you'll get better answers to better questions.
BTW, it is completely reasonable for someone to not answer a question in the way a person wants. If I ask "What's the best vehicle to get to Mars - a pontoon boat or a pickup truck?" The problem is not that someone tells you that actually a rocket is the best tool, but rather the asker doesn't understand as much about Mars as they think they do.
Post by: Bill Burford on April 13, 2010, 04:40:25 PM
now I did go back and edit something. I added
| Quote: |
(sarcasm) and (more sarcasm) |
but I didn't add anything to the question. the question asked already about recorded music/ synth bass or accoustic bass.
I asked a question and they said I was wrong. I never said they were wrong. not in this thread. I was responding to a guy who has personally attacked me before on here.
and sure enough, it came right back again.
telling me I should get
| Quote: |
another hobby |
you said:
| Quote: |
Up a few posts you ask a question. People try to answer it. |
let me stop you right there, they didn't try to answer it. they said I was wrong if anything. but certainly tried to find a problem with the question.
| Quote: |
You say they're wrong and that you know the answer. Then later on you restate and agree that it was an unclear question. Then you say people were picking on you by putting strange conditions |
no by getting personal and telling me I need a new hobby other than sound-- or other comments designed to discredit me personally in other threads by the same person..
continue...further, I never said they were wrong. in one spot maybe you could say that, I didn't really say they were wrong but I did say that min impedance is where I thought that max excursion would occur. and I tend to believe that is closer than the max impedance. but that was a separate issue not really related to my question.
| Quote: |
on the circumstances and that your question was perfectly valid in the first place. |
whoah whoah whoah.. strange conditions arent my problem. I could care less.
my only gripe was that people want to argue or find something wrong with the question rather than to have a discussion.
In that, it is not contradictory at ALL for me to concede that my question was actually not very clear (in an attempt to NOT fight about it)..
however, it WAS clear to me. and probably plenty of other people who are ignoring this because its pointless.
I can say the question is not clear and that it is clear.
without saying who it is clear to..
the question was always clear to me.
I can see how some people might not however. But then, I'm a reasonable guy. Some people might say it would take an unreasonable guy to say that I am contradicting myself by attempting to be diplomatic like that. But I'm not personally saying that you are unreasonable. I'm only saying that I can understand if someone else might.
Post by: Art Welter on April 13, 2010, 05:49:46 PM
| Elliot Thompson wrote on Mon, 12 April 2010 21:46 |
Art, It seems JBL purposely marketed the JBL 2268H with a high xmax however, never explained it is based on xmax damage. In order for the JBL 2268H to offer a 23 mm xmax, the efficiency would be very low since all of the coil will be sitting outside the magnetic gap. Yet, it offers an no.% of 2.8 The numbers are based directly from the engineer’s specifications. I would imagine this is before marketing got their pretty little hands on it. There is no xmax rating on the engineer’s sheet. However it clearly states, “Xmax, damage 23 mm peak before the spider bottoms on gap sleeve.” It also states, “Special Notes: JBL 2241H Replacement in Neo Differential Drive line of transducers.” It seems the JBL 2241 offers the mathematical xmax. As we know, manufactures were more conservative on their specifications when the “2241” was classed JBL’s best decades ago. Today, that 7.62 mm measurement would be marketed as 9 mm taking distortion into account. Best Regards, |
Elliott,
Your JBL engineering note quote does sound convincing that the 2268H does not have substantially more Xmax than other drivers, in which case the lesser power compression due to double the voice coil surface area (and lighter weight) would be the main advantage.
One correction to a previous post of mine, the 2268H is only 800 watts(PE), the "Ultra Long Excursion" 2269H is 1200 watts (PE).
I found no Xmech figures for JBL differential drive speakers other than on the VT4880A spec sheet, which states an 89 mm (3.5”) maximum peak to peak excursion, in other words a 44.5 Xmech (or Xlim, whichever flavor you prefer) for the 2269H, which is only rated 19 mm Xmax.
The 2269H has only a fraction of the efficiency of the 2268H or 2241H, what one would expect from extra long (and heavy) coils that extend well beyond the magnetic gap.
This would correspond to the engineering note you mentioned, I’m inclined to agree the 2268H is basically a differential drive dual coil version of the 2241H.
In which case a pair of decent Xmax drivers like the Eminence Lab 12, the 4018LF or the B&C18TBX100 will certainly walk over a single 2268H.
The Lab 12 has an Xmax of 13 mm, 659 cc Vd.
Vd is the amount of air that can be linearly displaced by the speaker, just like in car engines, the more displacement, the more ultimate power.
The 4018LF has an Xmax of 7.9 mm, 939 cc Vd.
The B&C 18TBX100 has an Xmax of 10 mm, 1188 cc Vd.
The 2268H most likely lies right between the two 18”, if it has the same ratio of Xmax to Xlim as the 2269H, it would have an Xmax of 9.82 mm, about 1167 cc Vd.
Before laying out the big cash for 2268H speakers, rather than the others, I’d be doing a quick and simple Xmax check to verify what is real, and what is a print mistake.
Art Welter
Post by: Jeff Wheeler on April 13, 2010, 06:04:59 PM
Post by: Art Welter on April 13, 2010, 06:11:40 PM
| Jeff Wheeler wrote on Tue, 13 April 2010 16:04 |
My experience emailing JBL for spec help has been mixed, but I will try that and see what they say. |
Contacting JBL would be interesting, but I was suggesting you check the excursion yourself, since you have the cabinet, amp, etc. needed to do the test.
Post by: Mike Caldwell on April 13, 2010, 06:24:52 PM
Post by: Elliot Thompson on April 13, 2010, 07:00:48 PM
| Art Welter wrote on Tue, 13 April 2010 22:49 | ||
Elliott, Your JBL engineering note quote does sound convincing that the 2268H does not have substantially more Xmax than other drivers, in which case the lesser power compression due to double the voice coil surface area (and lighter weight) would be the main advantage. One correction to a previous post of mine, the 2268H is only 800 watts(PE), the "Ultra Long Excursion" 2269H is 1200 watts (PE). I found no Xmech figures for JBL differential drive speakers other than on the VT4880A spec sheet, which states an 89 mm (3.5”) maximum peak to peak excursion, in other words a 44.5 Xmech (or Xlim, whichever flavor you prefer) for the 2269H, which is only rated 19 mm Xmax. The 2269H has only a fraction of the efficiency of the 2268H or 2241H, what one would expect from extra long (and heavy) coils that extend well beyond the magnetic gap. This would correspond to the engineering note you mentioned, I’m inclined to agree the 2268H is basically a differential drive dual coil version of the 2241H. In which case a pair of decent Xmax drivers like the Eminence Lab 12, the 4018LF or the B&C18TBX100 will certainly walk over a single 2268H. The Lab 12 has an Xmax of 13 mm, 659 cc Vd. Vd is the amount of air that can be linearly displaced by the speaker, just like in car engines, the more displacement, the more ultimate power. The 4018LF has an Xmax of 7.9 mm, 939 cc Vd. The B&C 18TBX100 has an Xmax of 10 mm, 1188 cc Vd. The 2268H most likely lies right between the two 18”, if it has the same ratio of Xmax to Xlim as the 2269H, it would have an Xmax of 9.82 mm, about 1167 cc Vd. Before laying out the big cash for 2268H speakers, rather than the others, I’d be doing a quick and simple Xmax check to verify what is real, and what is a print mistake. Art Welter |
Exactly!
If we examine the B&C 18 TBX 100, it offers an xmax of +/-9 mm with an Xvar of +/-11 mm. “Xvar” may be B&C’s terminology of xmax with, if I remember correctly, 10% distortion for, it falls within the voice coil’s winding depth of 25 mm. Half of 25 is 12.5 which seems to be the true xmax. Although, B&C being very conservative, markets the xmax rating at +/- 9 mm to ensure very low distortion when driven within those parameters.
Of course this is pure speculation based on calculating a few TS Parameter figures. However, it may not be not too far from the truth.
Personally, I never focus heavily on xmax for manufacturers have their own methods on measuring xmax. I’ve learned that many years ago comparing an EV EVX 180 B to an RCF 18 LP 300. For me, it is a matter of examining various prospects using Eminence Designer and, choosing which driver suits my requirements.
Best Regards,
Post by: Evan Kirkendall on April 13, 2010, 07:02:28 PM
| Bill Burford wrote on Tue, 13 April 2010 16:40 | ||||
you said:
let me stop you right there, they didn't try to answer it. they said I was wrong if anything. but certainly tried to find a problem with the question.
no by getting personal and telling me I need a new hobby other than sound-- or other comments designed to discredit me personally in other threads by the same person.. continue...further, I never said they were wrong. in one spot maybe you could say that, I didn't really say they were wrong but I did say that min impedance is where I thought that max excursion would occur. and I tend to believe that is closer than the max impedance. but that was a separate issue not really related to my question. |
Bill,
Since your post is obviously directed toward me, I'd like to set some things straight. First of all, I never once argued with you, or personally attacked you. All of my posts in this thread have been pretty harmless. You have just chosen to take them personally for reasons I do not understand.
And, you've really taken my quote out of context. Here's the original quote:
| Evan Kirkendall wrote on Tue, 13 April 2010 15:18 |
Bill, There's no arguing going on here. Just stating facts. If you can't figure out that a kick drum is an impulse that creates a good amount of cone movement, then you probably should consider a new hobby. |
I didn't tell you to get a new hobby, I simply joked about it, as it is something anyone should be able to figure out. The
should make it pretty obvious that you can take it with a grain of salt. These forums are here for people to learn. It's the community's job to make sure that correct information is given to people, and that the incorrect information is corrected. If you're not willing to learn, and admit being wrong, then you really shouldn't post. I know when I'm wrong, and I'm fine with being corrected, because I'm learning. People have to sift through your posts to try and make sense of what you say as is, and it doesn't help when you just repeat yourself over and over.
I don't know what beef you have with me, but it's not helpful to this website, and it's rather childish to keep claiming to be the victim of some non-existant attacks.
Jeff,
I'm sorry this thread is drifting so far off topic. I'm done with this, and hopefully you've figured out what you need to do.
Evan
Post by: Jeff Wheeler on April 13, 2010, 07:24:33 PM
| Evan Kirkendall wrote on Tue, 13 April 2010 18:02 |
Jeff, I'm sorry this thread is drifting so far off topic. I'm done with this, and hopefully you've figured out what you need to do. |
Off-topic discussion is often educational. As long as no one asks what kick drum mic I am using, I will keep reading the thread.
| Art Welter wrote on Tue, 13 April 2010 17:11 | ||
Contacting JBL would be interesting, but I was suggesting you check the excursion yourself, since you have the cabinet, amp, etc. needed to do the test. |
I don't understand how I could measure Xmax if it is defined as when the driver begins producing more than 10% distortion vs useful output, except if I measured in a particular cabinet with an analyzer capable of measuring distortion vs program material or generated signal.
Incidentally I did briefly look at the 2269 drivers but it looks like they are over-engineered to take a lot of abuse at the expense of efficiency, which is not what I think I need.
Post by: Bill Burford on April 13, 2010, 07:26:38 PM
joke:
"Bill, if you can't [A], then you should probably not "?
ha ha.. i get it
I should probably not "post" any more?
since you've deemed me wrong or at least failing to admit I was wrong.. and/or deemed that I've failed to learn.
and I'm also childish.
-- this is coming from a guy who posts a picture of an air-conditioning unit mounted in the back window of a van.
I have no beef with you. I am willing to admit I'm wrong.. and I still tend to think that I there haven't been any significant revelations as far as the technical aspects of what I was talking about are concerned. I'm reading what these other guys are saying and I'm following it.. its pretty cool. Definitely learning something.
Are you learning anything?
Post by: Art Welter on April 13, 2010, 09:45:54 PM
| Jeff Wheeler wrote on Tue, 13 April 2010 17:24 | ||||||
Off-topic discussion is often educational. As long as no one asks what kick drum mic I am using, I will keep reading the thread.
I don't understand how I could measure Xmax if it is defined as when the driver begins producing more than 10% distortion vs useful output, except if I measured in a particular cabinet with an analyzer capable of measuring distortion vs program material or generated signal. Incidentally I did briefly look at the 2269 drivers but it looks like they are over-engineered to take a lot of abuse at the expense of efficiency, which is not what I think I need. |
Jeff,
Distortion testing does not require fancy equipment, though fancy equipment makes it faster.
You can make a real excursion chart , and see what power level is required to exceed Xmax by using the chart below to measure distortion.
You can also just do it “by ear”, if harmonics are quite noticable, you have exceeded Xmax.
It will require an RTA, and a sine wave source, which are available as free software. You will need a flat response test microphone able to handle high SPL with low distortion. You will also want to check your amplifier output to see that you do not exceed the power your speaker can safely handle.
You will need to remove the grill to see the cone excursion clearly. A dot of Whiteout or a silver sharpie makes cone movement easy to track because of persistance of vision, holding a ruler next to the dot will make it easy to measure. You will be seeing peak to peak motion, Xmax is measured as half of that.
Wear hearing protection, the test will get loud.
The test should be done outdoors so room rattles and standing waves do not effect the results, but if the microphone is placed quite close to the center of the cones and port, an indoor test will still give you a reasonable idea.
Below Fb, the box tuning, excursion and distortion will rise dramatically, so it is a good idea to find Fb by rocking the sine wave tone up and down in frequency, the excursion minima will be Fb.
Testing below Fb is interesting,but watch out that Xlim or Xmech is not exceeded, obvious bottoming out of the spider of voice coil, or suspension pushed to the point where the pleats are stretched flat.
You will find that Xmax can be exceeded with very little power below Fb. The excursion test will allow you to set a prudent HP, usually just a few Hz below Fb.
Now advance the level of the sine wave tone into cabinet, raise level until a harmonic is noted at 10% distortion of the fundamental tone, in other words, if 50 Hz measures 100dB SPL, and 100 Hz (the second harmonic) measures 80 dB SPL, you have reached Xmax.
Well, technically you need a little more math, adding up the contributions of all the harmonics, but usually the second harmonic is far enough above the third and fourth that their contribution is minimal above Fb. However, the odd order harmonics, being not musically related, are more objectionable.
This test will reveal much about the character of the sound of your speaker, and how it changes as level is increased. It may suprise you with how much LF distortion you accept as “not too much”.
Since JBL says the PE is 800 watts for the 2268H, to be safe, do not exceed 80 volts for more than a few seconds at a time. If you do approach that level, don’t apply it for much time, and back off if you start to smell anything funny.
If you want to get a feel for the different distortion levels,(they will go up as the level is increased) for a four ohm load, a 2 volt(1 watt), 6.3 v (10 w), 20 v (100 w), 63.3v (1000 w) and 80v (1600 w) .
For an 8 ohm load, those wattage levels are 2.83 v (1) , 9 v (10), 28.3 v (100), 63.3 v (500), 80v (800).
Probably best to use 60 Hz to set your voltage levels, unless you know your volt meter is accurate at all frequencies.
Sine waves really make it clear what a speaker is capable of, and show distortion quite easily.
Art Welter
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Post by: Dave Rickard on April 15, 2010, 01:04:10 PM
| Mike Caldwell wrote on Tue, 13 April 2010 16:24 |
During the course of this thread I could have cranked out pair of double 18's and been listening to them! |
Priceless.