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palesha 20th October 2002 12:28 PM

Small sub Cabinet
 
I wish to make one subwoofer for my car. I want to make it as small as possible. Hence i must select proper driver for it. I wish to use preferably ported enclosure. Kindly guide me what driver parameter i should check in thiele small parameters to make the box smallest possible? Any other suggestions welcome.
Mahendra Paleha

jag 20th October 2002 01:59 PM

Check out the shiva white paper and application notes at adire audio website. They have a specific application for small car subs, and also describe constraints & considerations.

BrianGT 21st October 2002 04:49 AM

Here are some links for you:

Adire product page for the 12" shiva:
http://www.adireaudio.com/diy/Drivers/Adire/shiva.htm

White paper:
http://www.adireaudio.com/Files/ShivaWhitePaper-V2.PDF

Applications:
http://www.adireaudio.com/tech_papers/shiva_apps.htm

If you want minimum size for this woofer, go for a sealed box. The smallest sealed box is 25.5L (350mm cubed) You can easily find out the space that you have available in your car and design a box to match this volume.

Good luck!

--
Brian

planet10 21st October 2002 05:37 AM

When the Adire (Avatar at the time) Shiva 1st came out, there was a lot of traffic on the basslist about them. The small box was a cubic foot in volume (the one Brian suggested) with a Linkwitz pole-shifter circuit to adjust the Q. It requires a lot of power but the Shiva is well-suited. In a car it would giv eyou the benefit of being able to dial in the Q you need to get maximum performance in your car.

In a car with its small volume & huge bass lift, a sealed box is preferrable to vented most of the time (but i'd say that even if it was your house).

dave

hifiZen 21st October 2002 06:17 AM

Yep, sealed will give you a smaller box with most drivers. You may want to consider a driver made for car audio, as they're built to withstand abuses which your average home theatre sub will not be exposed to (temp., humidity, vehicle accelerations etc.). My personal preference for car subs is JL Audio... they're a well engineered product, and you'll find tons of good technical info on enclosure design on their website... in contrast to most car audio products, which are 99.9% marketing, 0.1% engineering effort.

Also, if you're building your own sub, a sealed box is far less sensetive to the exact box dimensions than vented or other designs. You can also tune a sealed box (tweak it's Q) by adjusting the amount of stuffing (just cheap polyfill you can buy at hobby or crafts stores... it's polyester fibre used to fill pillows).

For reference, a JL 10W3 10" sub goes nicely into a 0.65 sq. ft. enclosure, and rolls off around 44 Hz. Qtc for this woofer/box combo is just less than 0.9, considered a little high, but this is for the unstuffed box, and can be brought down with stuffing. Also remember that inside an enclosed space such as a car, the actual Q will be a bit lower. A car's small interior volume will also provide something in the neighborhood of +6dB/octave boost at the lowest frequencies, so the gentle -6dB/octave roll-off of a sealed sub will best compliment the bass lift provided by the car's interior, giving you the flattest total response.

If you go vented, you can push the -3dB point down to a lower frequency, but then you roll off at -12dB/octave, and I think you'll find that the bass lift produced by the enclosed space of a car will not fully compensate for this. Also, with a vented enclosure, you'll want to have an electronic sub-sonic filter to keep you from destroying your woofer. At the very lowest frequencies, a vented enclosure no longer controls cone displacement, and the driver can very easily exceed it's maximum excursion... not a good situation.

OK, now the Theil/Small (T/S) parameter you want to look for to get a small enclosure will be Vas (equivalent compliance)... this should be as small as possible. There are other parameters which come into play, but this one will dominate the box volume. The other parameter I look for is fs (resonant frequency)... the lower this is, the deeper the bass you can get out of the sub. A large Xmax (linear excursion) will allow the driver to be pushed harder, giving you more acoustic output, or alternatively giving you a larger margin for abuse.

Beyond T/S params, there are other factors which will help you determine what sub you buy... price, obviously, robustness and design quality are all important. This is the major reason I usually choose JL over other brands. They have quality, robust and underrated designs which sound very good, and are also a good value. Even their low-end subs, the W0 series, are an excellent driver.

FrankDIY 21st October 2002 12:07 PM

I totally agree with Dave and hifiZen on the sealed box. I have built several car sub (vented, sealed and hybrid). The difference in sound or SPL is very minor but you get almost an half size box with the sealed one. All these boxes was for hatchback cars, I have no idea if this affirmation is different when putting the box in a sealed trunk.

BrianGT 21st October 2002 01:09 PM

I love my hatchback.. with one small 10" sub, I can achieve more then enough bass. I used to have a 12" sub (car was broken into last year and it was stolen) in an angled box that was pointed towards my curved rear window, and it would produce enough bass to give me headaches and set off nearby car alarms. I had to have the gain on my amplifier turned way down to keep the bass to bearable levels.

Also, it is great for moving wood and projects.

--
Brian

ashok 21st October 2002 01:42 PM

Car sub in India
 
Hi Palesha,
The web gives us wonderful suggestions from all the great guys on it. The only catch being that in India we cannot get the drivers as easily as they do. I believe that today we can import these for personal use but with the added cost of freight ( Indian being an expensive destination by courier) and customs duty.
You could of course use the local "Bolton" brand with no traceable specifications or the Peerless India drivers with hard to get specs. I do have a few drivers which do not match up to the 'specs' that I received. I could send you the specs of the 'real' drivers if you want.
You never mentioned if you have a hatch back or a bigger car. With the hatchback you could use a driver in a box. Otherwise you could use a driver ( typically a 6x9 inch) on the rear deck. For the rear deck you should get a driver with a Q of 0.7 or less in free air but preferably not less than 0.5. The resonant frequency should be as low as you can get - locally this may be about 40 Hz.
Most Bolton woofers have a high Q but this varies considerably depending on the batch !!
I know this is tough but if you want I can supply you with some real figures. Doing these things in India is a greater challenge than 'most' other parts of the world!As always, we need to thank the guys on this forum for their great support.
Cheers.

FrankDIY 21st October 2002 03:12 PM

Quote:

Originally posted by BrianGT
I love my hatchback.. with one small 10" sub, I can achieve more then enough bass. I used to have a 12" sub (car was broken into last year and it was stolen) in an angled box that was pointed towards my curved rear window, and it would produce enough bass to give me headaches and set off nearby car alarms. I had to have the gain on my amplifier turned way down to keep the bass to bearable levels.

Also, it is great for moving wood and projects.

--
Brian

This is really bad for ears


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