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using CHT 18" drivers for LLT type subs. Bad idea?

post #1 of 23
Thread Starter 
I'd like to convert my CHT CS18.2 (dual 18") to two vented subs.

This would be the first time I model/build a subwoofer. I'd like to hear your opinion about the the idea in general and, most importantly, if this kind of project should even be considered by a noob like me.

The drivers are Eminence OEM used in all current Chase Home Theater subs, both sealed and vented.

Their vented one, VS18.1, did well in recent data-bass benchmarks, so it is known that the driver can deliver in a 7-8cu.ft box tuned to 19Hz or so.

I have room for bigger subs behind the screen. they can realistically be up-to 17 cu.ft volume (30x20x50). I am curious if going LLT maybe a better option in my case.

UPDATE: the models below are based on overstated Sd numbers. For models based on more realistic assumptions see http://www.avsforum.com/t/1445228/using-cht-18-drivers-for-llt-type-subs-bad-idea#post_22702909


Here is how 7 cu.ft. @ 19Hz vs 17cu.ft. @ 14Hz tune boxes model with 300W signal. both have HPF just below tuning frequency.



the same boxes and power, no HPF on the LLT version




The specs for the drivers are not listed but they were measured by user LilGator.

Re: 6.963 Ohms
Fs: 21.53 Hz
Qts: 0.324
Qes: 0.355
Qms: 3.707
Le: 3.461 mH
Mms: 369.4 g
Vas: 19.78 Cu Ft
SPL: 93.86 1W/1m
BL: 31.31 N/A
Cms: 0.15 mm/N
Sd: 0.1642 m^2 more likely 0.1140 m^2

from the CHT site:
Xmax: 0.75in (edited. originally had it at 1.5 for peak to peak,did not realize i had to divide it by two)
Pe:800W


what do you guys think?
Edited by zheka - 12/14/12 at 5:13pm
post #2 of 23
I'd think you might get more for your money by selling the CHT sub, and buying drivers, since the complete sub would be worth more than just the drivers (speculating, not sure what the going price might be with CHT's future still up in the air - but regardless, the subs work well).
post #3 of 23
Thread Starter 
Quote:
Originally Posted by Brad Horstkotte View Post

I'd think you might get more for your money by selling the CHT sub, and buying drivers, since the complete sub would be worth more than just the drivers (speculating, not sure what the going price might be with CHT's future still up in the air - but regardless, the subs work well).

you are right. i should be able to buy a pair of well known drivers and somebody would get a great deal on a very solid sub. great advise, thank you.

still, is large vented enclosure a good candidate for first DIY project? or should i stick to sealed?
post #4 of 23
The upcoming Stereo Integrity HT18's coming out work as drop-in replacements if you dare to build my LLT's. (check sig)
post #5 of 23
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

The upcoming Stereo Integrity HT18's coming out work as drop-in replacements if you dare to build my LLT's. (check sig)

wow
post #6 of 23
Thread Starter 
the highest i can go is 19cu.ft each (40x50x20)
post #7 of 23
zheka,

the chase subs works fine in ported. the only thing is to keep an eye on excursion because with the larger and lower tuned subs, you get more excursion above the tuning frequency for a given power level.

the lilgator specs seem about right except for the driver diameter which seems way off. while the chase driver may be different, almost all nominal 18" subs have a much lower effective diameter and in turn much lower sd than lilgator specs.

the dd spec is typically taken to be from approximately the inner 1/3 of the surround side to side, not from the edge of the frame side to side. typical values for an 18" are in the neighborhood of 15"-15.5" providing approximately 1200 cm^2 of radiating area for sd. lilgator has measured about 1600cm^2, which is more like a 21" driver.

edit: also the xmax spec is too high. that is probably a peak to peak number vs. a one way number, so divide that by two.

you will be fine in up to 17 cubic feet tuned to 14hz with up to 1000 watts (maybe even a little more).
Edited by LTD02 - 12/14/12 at 3:24am
post #8 of 23
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

zheka,
the chase subs works fine in ported. the only thing is to keep an eye on excursion because with the larger and lower tuned subs, you get more excursion above the tuning frequency for a given power level.
the lilgator specs seem about right except for the driver diameter which seems way off. while the chase driver may be different, almost all nominal 18" subs have a much lower effective diameter and in turn much lower sd than lilgator specs.
the dd spec is typically taken to be from approximately the inner 1/3 of the surround side to side, not from the edge of the frame side to side. typical values for an 18" are in the neighborhood of 15"-15.5" providing approximately 1200 cm^2 of radiating area for sd. lilgator has measured about 1600cm^2, which is more like a 21" driver.
edit: also the xmax spec is too high. that is probably a peak to peak number vs. a one way number, so divide that by two.
you will be fine in up to 17 cubic feet tuned to 14hz with up to 1000 watts (maybe even a little more).

Thank you very much.
I measured the driver per your instructions, Dd is slightly short of 15". This changes Sd to 1140 cu.cm and sensitivity to around 90dB.

it looks like with this specs there is little benefit from going extra large.

to compare, 17 cu.ft vs 8 cu.ft, both tuned to 14Hz with HPF at 12Hz (600W signal)

17 vs 8

excursion at 1000W

excursion at 1000W

in my room (basement, concrete floor and 3 walls, moderate to strong cabin gain), 8cu.ft may be a better choice.
post #9 of 23
Quote:
Originally Posted by zheka View Post


from the CHT site:
Xmax: 0.75in (edited. originally had it at 1.5 for peak to peak,did not realize i had to divide it by two)
Pe:800W

.75" xmax is 1.5" peak to peak. I've got these drivers and when I had them out of the boxes I ran a few sweep tests and can say that they are definitely not limited to .75" two-way xmax.

JP
post #10 of 23
You maximum excursion (xmech) could be as much as double the xmax. .75" one-way xmax is nothing to scoff at, 1.5" one-way xmax would be rather exceptional.
Quote:
Originally Posted by zora View Post

.75" xmax is 1.5" peak to peak. I've got these drivers and when I had them out of the boxes I ran a few sweep tests and can say that they are definitely not limited to .75" two-way xmax.
JP
post #11 of 23
Quote:
Originally Posted by imagic View Post

You maximum excursion (xmech) could be as much as double the xmax. .75" one-way xmax is nothing to scoff at, 1.5" one-way xmax would be rather exceptional.

I didn't say that it was 1.5" one-way xmax. If the driver's one-way xmax is .75" then the two-way (peak to peak in different terminology) would have to be 1.5" (2 x .75"). I was simply clarifying the comments that suggested these drivers can't have a 1.5" two-way xmax.

JP
post #12 of 23
Quote:
Originally Posted by zora View Post

I didn't say that it was 1.5" one-way xmax. If the driver's one-way xmax is .75" then the two-way (peak to peak in different terminology) would have to be 1.5" (2 x .75"). I was simply clarifying the comments that suggested these drivers can't have a 1.5" two-way xmax.
JP
If it's Eminence I doubt it has more than 15mm xmax, and a lot less than that if it's a pro model. It should be obvious which Eminence motor it's using by looking at it.
post #13 of 23
Thread Starter 
Here is what Josh Ricci had to say about excursion capabilities of the driver
Quote:
The xmax of the driver is listed as about 19mm one way with a recommended power rating of about 800 watts. In use the driver would produce this much stroke but the xmech seems to be at almost the same point as the useful excursion and the surround and/or suspension seemed to be the most limiting factor

http://www.data-bass.com/data?page=system&id=83
post #14 of 23
Thread Starter 
here is what Mike P of HTS came up with



Green is 800 watts and a 15 hz HPF. Yellow is 700 watts and a 13 hz HPF.
post #15 of 23
Quote:
Originally Posted by Bill Fitzmaurice View Post

If it's Eminence I doubt it has more than 15mm xmax, and a lot less than that if it's a pro model. It should be obvious which Eminence motor it's using by looking at it.

It isn't a pro model. I don't believe that anyone is stating that it is a "super" driver but it is one of the best I've seen from Eminence. It is simply a solid, high value driver.

JP
post #16 of 23
I think what Bill means is that Eminence can not build a woofer with over 15mm X-max. And I believe that was only until recently they could go that high. The woofer may go over that, but it wasn't designed to.
Edited by Erich H - 12/14/12 at 11:14pm
post #17 of 23
Thread Starter 
excursion chart to go with the SPL one from http://www.avsforum.com/t/1445228/using-cht-18-drivers-for-llt-type-subs-bad-idea#post_22705143



Green is 800 watts and a 15 hz HPF. Yellow is 700 watts and a 13 hz HPF.

well within the xmax limits.
post #18 of 23
.[/quote]
Quote:
Originally Posted by Erich H View Post

I think what Bill means is that Eminence can not build a woofer with over 15mm X-max.
Not that they can't, just that by and large they don't. I'm not personally aware of any. The LAB 15 is one beefy driver, and it's only 11.8mm.
Quote:
Green is 800 watts and a 15 hz HPF. Yellow is 700 watts and a 13 hz HPF...well within the xmax limits.
If they're accurate. I didn't see on Data Bass testing above 35 volts; it would take at least 50 volts to reveal non-linearity and THD that might indicate xmax had been reached.
post #19 of 23
the craig sub is ported and tuned to around 19hz.

ricci tested it cea max burst 116db at 2m at 31.5hz.

31.5hz is roughly where the cone motion will be peaking in such a setup.

backing out the cone motion gives roughly 25-26mm required for that spl.
post #20 of 23
I would just build something equivalent to the vs18.1. And give it 500 w or so. The driver hits xmech near 20mm. The suspension is simply done around that point. It does not take a lot of power to get there and tuning lower in a bigger cab will reduce power handling more at the upper excursion maximum.

Also Lilgators sd spec above is not right it should be about 1200 cm give or take. It is an 8 ohm driver too despite some people saying it is 4 ohm nominal.
Edited by Ricci - 12/15/12 at 7:25am
post #21 of 23
Thread Starter 
The models by Mike P. are based on Sd of 1140sq.cm (Dd 15). the wdr file is attached.

I decided against using the CHT drivers. Brad is right, it makes no sense to break perfectly working subwoofer for the drivers that objectively cannot compete with the current budget 18" favorites.

So for me it is Dayton vs SI now.

CHT with reasonable DD.txt 1k .txt file
Edited by zheka - 12/15/12 at 8:35am
post #22 of 23
Thread Starter 
I understand Xmax value of the Dayton HO 18" is understated.
What number should I use for modeling? Is 20mm reasonable?
post #23 of 23
yeah...that's reasonable.
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