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Old 22nd December 2009, 04:36 PM   #1
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Default Car subwoofers for OB?

I went to a car audio place today, and noticed that the subwoofers have very stiff suspensions - I could push them 1/4 an inch, tops. Some of them refused to move much (1mm or less)

This got me thinking - a woofer with a stiff suspension should be good for OB, right? I mean, it wouldn't flap around like the really loose subwoofers would.

At the shop, I noticed some Sony Xplod either 8 or 10" for 30 - would it be worth a go?

This whole thing may be fundamentally flawed (efficiency perhaps), but it could still be worth a look........

Thanks for reading
Chris
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Old 22nd December 2009, 05:32 PM   #2
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The problem is, a lot of them are big-motored beasts that have very low Qtc's...
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Old 22nd December 2009, 06:26 PM   #3
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Yeah, the "loose" drivers with the "flappy" cones are specifically chosen as bass drivers for narrow (20 inches width or less) OB. Stiff suspension = low qts = no bass in OB.

The Sony 8 or 10 inch car drivers will work great on OB - as long as you use them as midranges. You won't get any bass out of them.
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Old 22nd December 2009, 06:50 PM   #4
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I'd have thought that the higher Qts = increased driver damping, so wouldn't a stiffer suspension help this?

The problem with OB is there's no (or very little) loading on the speaker, like a ported box below tuning. Therefore, I would have thought that a speaker that takes a lot of power to visibly vibrate it would be better than one that relied entirely on a box for mechanical damping. Take one of those out of the box, it will bottom out very quickly. It seems that those car subs don't really bother if they're in a box or not - the suspension stops the speaker being bottomed out......

These are designed as sub drivers, so they're not cut out for midrange use at all. Plastic cones, big voice coils.

This is the kinda thing, but no box....

http://3.bp.blogspot.com/_duYmx9IiyW...0/Dscf3126.jpg
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Old 22nd December 2009, 07:09 PM   #5
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Quote:
Originally Posted by chris661 View Post
I'd have thought that the higher Qts = increased driver damping, so wouldn't a stiffer suspension help this?
Wrong way round actually The higher the Qts the less control the amplifier has over the driver cone, this is one reason why high Qts drivers sound terrible in a bass reflex enclosure as this has less damping than a sealed box.

You may not be able to move the cone very much by pushing it, but as soon as you apply a sine wave to the thing, it's mass will get it moving quite well.

Actually i have found that so called car subwoofers (even with multiple stacked magnets) tend to have a rather high Qts & due to the rather stiff (no kidding) suspension tend to have a low Vas.

Here is a for instance I happen to own 4 of these beasts & they'll be going into sealed boxes simply because the Qts i measured (compared to the little slip of paper with the rather exagerated specs) just didn't add up. Ok maybe a bit of breaking in can alter things slightly but this is what i found:-

FS 35Hz
Qts 0.84
Vas 58L

Here is the thing in question Yes, the 15" one.. It really does have an xmax (one way) of 17.5mm (i bought a dead one cheap & removed the magnet to measure voice coil overhang) Cheap as for that kind of air movement.
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Old 22nd December 2009, 07:19 PM   #6
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Quote:
It seems that those car subs don't really bother if they're in a box or not - the suspension stops the speaker being bottomed out......
Believe me, you can hit backplate just fine with a lot of them
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Old 22nd December 2009, 08:47 PM   #7
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Originally Posted by chris661 View Post
The problem with OB is there's no (or very little) loading on the speaker
That's not necessarily a problem, lots of people consider it an advantage. It's inefficient but it sounds nice.
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Old 22nd December 2009, 08:58 PM   #8
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Stiff suspension, heavy cone, usually equals low Vas. Therefore, they don't need a large box, which is a design aim in car audio. And although they'll bottom out quick enough in OB use, you'll likely find that if you put them in an optimum sized sealed box, that they exactly reach xmax at their rated maximum power... in other words, they're designed to be "idiot proof".
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Old 23rd December 2009, 07:37 AM   #9
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I guess that's that idea pretty much down the drain.

I guess the heavy cone would be the reason for the inefficiency of most of them - all that motor power is used to shift something heavy...

Do we think it would still be worth a mess about - if, say, they came on offer for 20?

Edit - I think I get it now - you need the woofer to "flap" to some extent, otherwise you'd get no bass output, ie, the woofer isn't moving enough to create some noise, because of it's stiff suspension... But in a box, it will be fine because it won't notice a small(ish) box due to it's own mechanical damping, but the box will cancel the rearwaves, meaning you get bass output.
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Last edited by chris661; 23rd December 2009 at 07:46 AM.
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Old 23rd December 2009, 04:24 PM   #10
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Here's a page from my website that shows how to design OB bass (flat baffle only). You can actually estimate this stuff in your head. All you need is driver fs, qts and baffle width to get a pretty good idea. OB Design (amateur audio)

If you don't want to read that, just download XLBaffle or PCD for free and model your ideas.
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