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jtriggs 27th January 2003 09:09 AM

Affordable subwoofer

I live in Sydney, Australia and recently purchased a 5 speaker surround package with Sony amp:

Overall I am pretty happy with the sound, except when I ran some THX tests I realised the bass response below 100Hz is pretty poor. I started looking at building my own subwoofer, but am a bit confused on which is the best way to go.

I would like to only spend about A$300 - A$400. It would be used mostly for movies, but also music. In general, I prefer better quality than loud volume. So now for the questions:

1) If I build a sub am I likely to get it right the first time if the calculations look OK on paper? Or am I better off getting something like the Sony SA-WM40?

2) Considering the fronts are 50W, surrounds 30W and centre 40W, what power subwoofer will I need?

3) Are there any good sites that can step me through the whole process, i.e. from choosing the drivers, designing and then building the box?

Any other suggestions on where to start would be much appreciated.



subwo1 27th January 2003 11:30 AM

Hello. You should build your own.

A sealed enclosure is the way to go. I believe it offers advantages which cannot be outweighed by other methods.

Make the enclosure small so that construction is easiest for a solid box. I suggest using two 8" high-excursion subwoofer drivers in a 1 to 2 cubic foot box. Don't be concerned about low end roll-off, there is plenty of cone excursion capability to permit the of use active equalization to give full response (down to 30Hz-40Hz).

Use speaker design software to optimize the box size for the drivers. Obtain drivers with a Qts figure no higher than 0.4. Much higher figures result in muddy response. Put lots of damping material in the box. You can obtain some bed pillows and remove the stuffing to use inside the box.

You should use an amplifier capable of putting out at least 200 watts of peak power for good results. You can obtain free software programs which can produce a full spectrum of sine waves to get your active equalization settings close to where you want them. You may like the idea of using an automobile amp/equalizer combination. The more equalization adjustments you have at differing frequencies in the subwoofer band the better the results.

Brian Foley 28th January 2003 10:02 PM

You might want to read the article linked below. It has a nice step-by-step description of how to build an inexpensive sealed sub. I don't know if Apex ships to Australia, or whether comparable parts are readily available there, but the description of the process ought to be valuable.

DIY Sub Article

Peter M 28th January 2003 11:23 PM

An 88 L sealed and stuffed enclosure and a 100-250 W amp should do you well without EQ.

Ilianh 29th January 2003 05:45 PM

Many people prefer to use vented designs in home theaters,

Get a program like Winisd and play around with different drivers you know, check the frequency response plot and phase plot and such.

Go around in stores, and hear how vented sounds and how sealed designs sound, sealed subwoofers are not as available as vented ones, but I've seen some.

Vented subwoofers can sound very good for movies.
No wonder most of the subwoofers made for home theaters are vented..

Brian Foley 29th January 2003 07:18 PM

The big benefit to a vented design is better response in the 20-30 Hz range. But they are bigger, harder to do well and less forgiving of mistakes. A sealed design will generally produce better results in the frequency range that it covers, and it's easier to get right. Given his priorities, experience, and budget, a sealed design seems like a better way to go.

I have a DIY sealed subwoofer, and the only thing I ever miss are the full force of explosions in action movies. In return, I get exceptional bass quality from 30-something Hz up to 80, and I spent only about $500 US to get it. I have a song on one of my CDs that I always use when auditioning speakers. It has some really low, crystal clear, lingering bass notes. That song sounds lousy on most speakers under $3500. It does sound good on B&W 803's, which cost $5000. And it sounds at least as good on my system, with my mid-fi Pioneer Elite receiver, $500 DIY subwoofer, and $1000/pr North Creek kit speakers. So I have no complaints about my sealed subwoofer, especially where music is concerned.

jtriggs 30th January 2003 11:16 AM

Thanks for all the info so far. I have been doing a lot of browsing and learning in the last couple of days. At this stage I have decided on a sealed box, 12" woofer and a 250W amp. I wil use internal bracing like the Adire 88.5L sealed cabinet. Time for a few more questions:

1) When stuffing the box, should the internal walls also be covered in some material? If so what is best?

2) When calculating box volume, do you need to take into account the volume used by the internal bracing and the speaker? What about the stuffing? Are there any rules of thumb such as 1kg stuffing increases box volume by ???L

3) Are there any other T/S parameters other than a Qts < 0.4 that I should be looking for? I believe I should also be looking for a low Fs and a high Xmax. Anything else?

4) I understand the Gain and SPL plots in WinISD, but what do the Phase plot and group delay graphs mean? Is it correct that the "tighter bass" people speak about is signified by a flatter and smaller group delay? What driver parameters or box size variables result in a lower and flatter group delay?

5) Do box dimensions make any difference or is it only the box volume? (I know not to use a cubic box)

6) What do I need to look for to know if the driver can be mounted facing down? (This appears to be the best mounting method)

7) An active EQ will obviously improve the frequency response, but what about the cleanness / tightness of the base? Will it introduce any side effects?

8) Does anyone know of a good place to get drivers in Sydney, Australia?

Thanks for all the help. I am already starting to dream about the rumbles!

SkinnyBoy 30th January 2003 11:40 AM

I'm happy with my 10inch el'cheapo Subwoofer with a 65watt amp... It seems to give better bass than the main speakers (with 12inch woofers) Its not all that clear, but what can you expect for $35?? The total cost including the box was about $60... I'm not complaining.. :) Perhaps you could look at the Jaycar isobaric subwoofer? Its a vented enclosure, but you can buy a kit so you don't need to design the box, just assemble it.. :) it uses a 50 litre box (I think) and only a 150watt amplifier for 2 12 inch woofers... Go to your local jaycar, and ask to hear it.. :) Costs about $700 Australian (I think) lol, very much thinking going on today.. lol :) Ohh, and that includes an amplifier.. lol

Peter M 30th January 2003 12:53 PM

1) Yes. Polyfill and fiberglass insulation work well.

2) Yes, no, and yes.

3) Yes; Pe, Sd, Vd, Vas, and efficiency numbers are all good to look at.

4) Yes;

Box volume has an effect on GD at different frequencies. I'm not familiar with the T/S parameters that directly affect GD - perhaps motor strength?

5) Only box volume. Feel free to make a cube - standing waves won't be an issue.


If 100gCmsMms/Xmas<5, you're set.

7) I've never used EQ, but Siegfried Linkwitz seems to use it with great success.


The website seems to be down, but I'd talk to John Woodhead to see if he can ship a Shiva or something to you.

Hope this helps,


Dave Bullet 31st January 2003 10:49 AM

I highly recommend the following - although they will blow your $500 budget....

I bought a Shiva from John Woodhead @ Acoustic concepts. Great service and delivery within 5 days (to NZ). Well packaged.

I also bought a plate amp from redgum audio. 300watts (It seems to push that xmax of the Shiva) - also well made. It goes flat to 0Hz (unlike some of the taiwanese amps I'm told which some start to rolloff from 35Hz or so down).

I built a dual purpose sealed / vented box - with a sealed Q of about 0.5. I need to damp the box though (sounds a bit muddy) and still needs breaking in.

I also braced the hell out of the box. Very rigid and heavy. I recommend anything bigger than 100L and you do the same. I also went with a 1.5" thick baffle.

I've only been allowed to test it in the garage - but it seems to create enough rattles in there!.

Looking forward to the finishing and putting inside.

Let us know what you decide.


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