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[Bill Burford]

haaaaaa ha haa.. listen with their eyes.
oh man.  a lot of people do that whether they admit it or not.

[Bill Burford]

they must have been blown.
20 volts.

you put 20 volts on a sub and say it sounds like shit.

what subs do you like?

[Adam Schaible]

Bill, 30hz is below box tuning by 10ish hz.  My point is that below box tuning, excursion will rise so fast that a few mm of xmax is insignificant.

I do like the 728, but a 30hz sine wave will make a lot of cone flap.

[Bill Burford]

I don't even build speakers.
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?

[Art Welter]

Elliot Thompson wrote on Mon, 12 April 2010 07:22

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,

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

[Elliot Thompson]

Art Welter wrote on Mon, 12 April 2010 17:49

Elliot Thompson wrote on Mon, 12 April 2010 07:22 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, 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,

[Bill Burford]

So where do you think the cone is at peak power?  maybe during a rock kick?

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.

[Jeff Wheeler]

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.

[Bill Burford]

I have no argument on the hip-hop versus rock.

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.

[Evan Kirkendall]

BIll,
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