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DIY => DIY Audio => Topic started by: Zane on December 11, 2008, 12:46:28 PM

Title: 12 or 15" Subwoofers
Post by: Zane on December 11, 2008, 12:46:28 PM
Hallo All,

I am busy planing a DIY sub for my setup at home, I have a O-Audio 300W RMS @ 4ohm sub amp to be used.

What s-woofers would you sugest I use for nice deep and strong bass?

Thx  :)
Title: Re: 12 or 15" Subwoofers
Post by: Hennie on December 11, 2008, 01:51:57 PM
Three or four smaller subs (10" or 8") distributed in the room would work better than a single big sub. Even two subs is an improvement over one. Personally I have never been happy with a single sub. The concept of multiple subs is not about increasing output, it is about combating room resonances and smoothing response. See the following thread:

http://www.avforums.co.za/index.php/topic,2292.msg30503.html#msg30503

Expect 20dB or more ripple in bass response with a single sub. Moving the sub around does not change things much.
Title: Re: 12 or 15" Subwoofers
Post by: Zane on December 11, 2008, 02:29:03 PM
Thanks Hennie,

What do you think of 2 x 10" SEAS Prestige woofers?

Fs: 20hz
Qms: 2.15
VAS:171
Qts: 0.33
Linear coil travel: 14mm
Max coil travel: 35mm
Sensitivity: 88db
125W RMS 8ohm
Title: Re: 12 or 15" Subwoofers
Post by: GearSlave on December 11, 2008, 04:33:45 PM
Zane,

I think Hennie was referring to two separate subs, as in, not in the same enclosure. I'm assuming that could be a problem as you have just one amp?

I quite like the 12" JBL's that I got, although they definately on the budget end of the scale. I only use the subs for HT and was not too concerned about getting a "musical" sub.
Title: Re: 12 or 15" Subwoofers
Post by: Hennie on December 11, 2008, 05:14:52 PM
What do you think of 2 x 10" SEAS Prestige woofers?

At first look, not too bad, except that the enclosures may be big. But they seem to be woofers, not specialized sub drivers. If you give me the type numbers, I can have a closer look. Why are you interested in them? Are they available locally?

Your amp seems 4 ohms capable, so it makes sense to use two 8 ohms drivers in two separate enclosures, mount the amp on one enclosure and physically separate the two enclosures. Gert is right, if u plan to use that one amp, 4 subs are a bit ambitious. But two separate enclosures will always give you better placement / response optimization options.

The JBL drivers Gert used are really cool in the sense that they are quite cost effective, widely available locally and are said to offer great performance (I have not used them myself). I think there is a thread where Gert wrote up his effort. Or just ask him whatever you need to know, like cabinet size etc.


Title: Re: 12 or 15" Subwoofers
Post by: Zane on December 12, 2008, 07:42:11 AM
Getting two subs definately is someting I'll be looking at, I think in a sence it will also help with the stereo effect. I thought about installing the amp in a separate enclosure (it's own) and then feeding the subs via proper speaker wire from there.

These SEAS drivers are locally available yes, but they are EXPENSIVE, selling at about R2600 each. So if they are not great, I would rather look for something else.

I have also pondered on the idea of getting a single 12" or 15" JBL Gti (R4000). Both have a nice sensitivities (92db if I recall correctly) but I am not sure if my 300W is enough power for it, as it runs at 700W/800W RMS. What I am also concerned about these are that they are dual 6ohms so you can either run them at 12 or 3ohms.
Title: Re: 12 or 15" Subwoofers
Post by: iondb on December 12, 2008, 07:57:58 AM
Maybe you could also look at some car audio subs like JL, DD and RE.  They have some nice musical orientated subs that won't cost as much.  Just a thought....

I also read in one of our local mags about the Earthquake mini-me 8" subwoofers (active subs).  Not d.i.y, but maybe worth having a listen.  Haven't heard them myself.  Also, just a thought....
Title: Re: 12 or 15" Subwoofers
Post by: chipwelder on December 12, 2008, 08:55:54 AM
It will only help with the stereo effect if it gets stereo signal and stereo amp, just checking...
I suspect only if you go above 80 Hz... although usually one uses 100Hz as a guide, but the sub will play higher frequencies, you may have a filter that minimizes this...
Title: Re: 12 or 15" Subwoofers
Post by: Timber_MG on December 12, 2008, 09:07:54 AM
A friend of mine is looking for something to compliment an active monitor in a small room and I am thinking of trying out a quad of those JBL subs (at R500 each, why not?). Probably sealed with some EQ. They have a good Vd (volume displacement) / R and might make for a good write up eventually.

Those Seas are woofers and will work great, but for the money I'd definitely look elsewhere. Not only does one gain efficiency with multiple woofers, but in the end even at elevated listening levels the individual woofers are still well within their limits. It is usually more cost-effective to use multiple woofers than to put all one's eggs into one basket, especially where music reproduction is involved. The sonic advantage of multiple subs has little to do with stereo and is all about the improved room interaction. The ear doesn't localize much below 300Hz, but rattles, distortion and noise induced by the subwoofer often make it sensible to cross below 100Hz.
Title: Re: 12 or 15" Subwoofers
Post by: Hennie on December 12, 2008, 10:01:12 AM
These SEAS drivers are locally available yes, but they are EXPENSIVE, selling at about R2600 each. So if they are not great, I would rather look for something else.

I think that's just too expensive for something that's not really a sub driver.

Quote
I have also pondered on the idea of getting a single 12" or 15" JBL Gti (R4000).

That's one hell of a sub driver, but it needs a big box. Personally, I would rather go for more smaller, cheaper subs than one "super sub" though.

Quote
Both have a nice sensitivities (92db if I recall correctly)

Car sub sensitivity figures are usually a little inflated. The figures are stated like that because you get a lot of cabin gain in a car.  The GTI's model out at about 89db IIRC.

Quote
...but I am not sure if my 300W is enough power for it, as it runs at 700W/800W RMS.

A simulation will provide the answers.

Quote
What I am also concerned about these are that they are dual 6ohms so you can either run them at 12 or 3ohms.

The only think one can do here is to look closer at both the amp and the sub driver's specs. Is the 6 ohms an impedance or a voice coil resistance figure? On the data I have of the Mark I 15GTi, the voice coil resistance is 3 ohms, which is typical for a driver with a 4 ohms impedance rating. In this case your amp should be OK with it. In any case, below 100 Hz the impedance is dominated by reactance, so the amp's ability to drive that reactive load is probably more important.
Title: Re: 12 or 15" Subwoofers
Post by: Shonver on December 12, 2008, 11:48:39 AM
Car sub sensitivity figures are usually a little inflated. The figures are stated like that because you get a lot of cabin gain in a car.  The GTI's model out at about 89db IIRC.

...and few car subs have sufficiently low extension for home use. So simulate first...
Title: Re: 12 or 15" Subwoofers
Post by: Hennie on December 12, 2008, 03:34:56 PM
The JBL subs generally have the adequate extension, but JBL has stopped providing T&S parameters. I have some T&S previously published, but not for all drivers, and not for the GTi Mark II subs.
Title: Re: 12 or 15" Subwoofers
Post by: Timber_MG on December 13, 2008, 12:18:34 PM
At first I though that that was shocking, but downloading the manual proves hennie's statement!

Any T/S params for that 12" GT4?

Edit: Their site has these parameters and a stated one way Xmax of 12mm....but barely enough for a simulation.

General   
Frequency Response   28Hz - 450Hz
Sensitivity   93dB
Impedance   4 Ohms
Voice-Coil Diameter   50mm
Cutout Diameter   283mm
Mounting Depth   161mm
Overall Diameter   311mm
Vas   100.45 liter
Qts   0.43
Fs   24.75Hz
Qes   0.46
Qms   6.46
Sealed Enclosure (vol)   28L
Vented Enclosure (vol)   64L
Title: Re: 12 or 15" Subwoofers
Post by: Hennie on December 13, 2008, 07:03:56 PM
No Sorry Timber, I don't have more than what's on their website. This is one driver I also had a look at, but I could not find more data.

What driver did Gert use? Maybe he measured it?
Title: Re: 12 or 15" Subwoofers
Post by: GearSlave on December 14, 2008, 08:41:55 AM
I think those are the ones I use. I got them for R500 a piece at Autostyle. I've not looked at the specs in a while, so I'll have to find it again. If I forget please send a friendly reminder ;)
Title: Re: 12 or 15" Subwoofers
Post by: BWS on December 14, 2008, 09:41:39 AM
I was once toying with the idea of one of THESE JBL W15 GTI mk2  ;D ;D




Well implimented they should pretty well blow anything but SERIOUS money out of the water