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[Silas Pradetto]

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.

[Jeff Wheeler]

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.

[Jeff Wheeler]

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.

[Paul O'Brien]

Sounds good.. but I have only once seen the 2268H available for sale and it was about $700+ a copy, if you can get them for anywhere near the price of the other drivers then obviously it's the better one to have.

[Art Welter]

Jeff Wheeler wrote on Sat, 10 April 2010 15:15

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.

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

[Jeff Wheeler]

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.

[David Morison]

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.

[Jeff Wheeler]

I can build the cabinet correctly since I have JBL ones to measure; I just don't have it quite right in WinISD, which is the reason for the differences Art pointed out between my figures and the JBL published specs.

[Art Welter]

Jeff Wheeler wrote on Sat, 10 April 2010 18:29

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.

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

[Elliot Thompson]

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,