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Old 16th November 2009, 10:14 PM   #1
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Default PA vs Car Audio

Ok, I looked though the threads and could not find an answer to my question.

I know this is probably a really stupid n00b question, but I cant seem to find any straight answers on the net about it.

What is the difference between car audio subs and PA subs? The only thing I know is that the car audio subs seem to have a much larger excursion then their PA counterparts.

I used to do tons of car audio installs back in the day but now I'm looking at putting some PA cabs together and really would like to know what advantages the PA style subs have over the much cheaper car audio versions.

Also, if anyone could point me at some decent PA subs. I don't need 10 million watt monsters but I'm looking at something like 500 watts RMS 15"s or 18"s

Thanks in advance for any help!
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Old 16th November 2009, 11:06 PM   #2
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just compare the specs - if you can find specs for car subs...
PA drivers are usually much more efficient, require a much larger cabinet, and have a higher Fs (i.e don't go as low) compared to car subs.
They're also usually rated in RMS watts as opposed to ** watts...
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Old 17th November 2009, 02:49 AM   #3
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For spec'ing PA stuff one usually starts with real numbers for a MaxSPL goal. Bass is always the hardest for PAs (hip-hop, reggae, etc) and are usually spec'd about 10 dB hotter than the 1kHz range of your tops. MaxSPL is your peak with average (C-weighted) about 12dB lower to give yourself headroom on the console.

I like 107dB(SPL) average for a live rock band in the "hot zone" where the dancing is just off the stage. Let's say the hot zone is 5 meters from your subs located under the stage. You're doing a center-only horizontal stack under the stage, right?

goal+distance+headroom is your answer: 107dB + 20*log(5) + 12dB = 134 dB(SPL) @ 1 meter = MaxSPL

Most of the energy down there is not around 30Hz, it's around 80Hz for a kick drum. You really don't need to go below 40Hz for live sound. Efficiency is the key factor, not frequency response as you can adjust that externally. There is no such thing as an efficiency knob on any outboard gear. Folded horn subs are about the best way to go, IMO.

Look over www.billfitzmaurice.com and consider building a pair of T48s to run V-coupled.

Some car subs work pretty well in folded horns, but you'd need to do some design homework to find which ones and for what cabinet it's to go in.
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Last edited by davygrvy; 17th November 2009 at 03:15 AM.
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Old 17th November 2009, 03:06 AM   #4
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Hey thanks for the quick responses!

Im going to do some more research on folded horns. But in the mean time Im still a little confused as to why a PA sub would be better. From what I gather its because car audio subs are designed to play very low while PA subs are designed to play a bit higher/punchier?
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Old 17th November 2009, 03:09 AM   #5
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Quote:
Originally Posted by davygrvy View Post
For spec'ing PA stuff one usually starts with real numbers for a MaxSPL goal. Bass is always the hardest for PAs (hip-hop, reggae, etc) and are usually spec'd about 10 dB hotter than the 1kHz range of your tops. MaxSPL is your peak with average (C-weighted) about 12dB lower to give yourself headroom on the console.

I like 107dB(SPL) average for a live rock band in the "hot zone" where the dancing is just off the stage. Let's say the hot zone is 5 meters from your subs located under the stage. You're doing a center-only horizontal stack under the stage, right?

goal+distance+headroom is your answer: 107dB + 20*log(5) + 12dB = 134 dB(SPL) @ 1 meter = MaxSPL

Most of the energy down there is not around 30Hz, it's around 80Hz for a kick drum. You really don't need to go below 40Hz for live sound. Efficiency is the key factor, not frequency response as you can adjust that externally. There is no such thing as an efficiency knob on any outboard gear. Folded horn subs are about the best way to go, IMO.

Look over www.billfitzmaurice.com and consider building a pair of T48s to run V-coupled.
Actually its for a techno/house DJ setup. But im sure the same formula would still apply correct?
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Old 17th November 2009, 06:19 AM   #6
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PA subs aren't designed to not play low - they're designed for efficiency, ie, getting the most out of your watts. If you look at car audio subs, they generally have low efficiency, compared to PA stuff, the efficiency of which is usually in the mid to high 90s. The fact that they don't play low is something every manufacturer has to balance against how loud it goes.

For the bass, use something fairly cheap, as you'll be kicking yourself if something expensive was to give off the magic smoke.

Chris
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Old 17th November 2009, 08:15 AM   #7
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Quote:
Originally Posted by jason51873 View Post
Actually its for a techno/house DJ setup. But im sure the same formula would still apply correct?
The numbers will be different. I'd say 103 average for discotheque level and a bit less headroom, maybe 10 over and maybe the people will be a bit closer.

103dB(SPL) hotzone target + 20*log(3 meters) + 10dB headroom = 122.5dB(SPL) @ 1 meter

That's easily doable. A single T48 with 225W of drive should do that @ 50 Hz if I'm reading this chart correct for the single cab.

target 122.5dB(SPL) - 99dB(SPL)@50Hz = 23.5dB
antilog(23.5/10) = 223.87W of power gain

I'm guessing that was measured in 1/2 space (open field), so if you put that in a corner you'd need a whole lot less drive to get there.

Click the image to open in full size.

I'm not saying you should go with a T48. I'm showing you an example.

Ohh... I almost forgot. Consider using a "real" loudspeaker processor for the active crossover such as a DBX DriveRack PA-II or a Behringer DCX2496 as they allow for some nice advanced stuff like time alignment, limiting to protect your speakers, and especially the nice EQ.
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Last edited by davygrvy; 17th November 2009 at 08:26 AM.
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Old 17th November 2009, 09:32 AM   #8
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Quote:
Originally Posted by jason51873 View Post
Ok, I looked though the threads and could not find an answer to my question.

I know this is probably a really stupid n00b question, but I cant seem to find any straight answers on the net about it.

What is the difference between car audio subs and PA subs? The only thing I know is that the car audio subs seem to have a much larger excursion then their PA counterparts.

I used to do tons of car audio installs back in the day but now I'm looking at putting some PA cabs together and really would like to know what advantages the PA style subs have over the much cheaper car audio versions.

Also, if anyone could point me at some decent PA subs. I don't need 10 million watt monsters but I'm looking at something like 500 watts RMS 15"s or 18"s

Thanks in advance for any help!
The difference between car audio subs and home audio subs is that they're engineered with different goals in mind.

In car audio everyone wants a box that's small and can handle a lot of power. Due to Hoffman's Iron Law, to get a lot of SPL out of a small sub, you need an outrageous amount of power. Hi power leads to high excursion, and explains why companies like JL Audio offer $800 subwoofers with over 20mm of xmax.

In pro sound the primary goal is sheer output. And again, due to Hoffman's Iron Law, you can trade box size for efficiency. Because prosound woofers are generally designed for enclosures that are an order of magnitude larger than a car audio driver, the drivers themselves have a set of parameters which is "tuned" to large enclosures.

At this point, you might ask yourself, why not use a car audio woofer with high xmax in a prosound application? The answer is that there's no benefit. Due to lower efficiency, you'd end up requiring two or even four enclosures to match the output of a single prosound cabinet.

Or you might ask, why don't prosound woofers have xmax that's as high as car audio woofers? The answer to that one is that they don't need it; they're typically designed for enclosures where the low end is augmented by a port or a horn.

So at low frequencies the cone isn't moving at all. And below that is a steep high pass filter.

Does that make sense?

Also, like all rules, this one is bent all the time. I use prosound drivers in my car audio projects. (I'm running BMS and B&C.) And there are prosound vendors who've used car audio woofers in prosound applications. (google matterhorn)

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Old 17th November 2009, 04:47 PM   #9
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Hey thanks alot for all the info guys. I am looking at building a Tuba36 - seems like one of those would be perfect for what I want to do!

Also the Eminence Delta 15LF that the build suggests seems like it would be perfect for the job.
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Old 17th November 2009, 05:25 PM   #10
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Quote:
Originally Posted by jason51873 View Post
Hey thanks alot for all the info guys. I am looking at building a Tuba36 - seems like one of those would be perfect for what I want to do!

Also the Eminence Delta 15LF that the build suggests seems like it would be perfect for the job.
Based on a lot of work by some others here, that cabinet will work great with some boundary reinforcement. It really likes corner loading. There are other SPL plots out on the web that show the actual groundplane performance of the T36. If you do not have corners or walls to load against, build two cabinets and couple the mouths or build a different enclosure (jbell's set of four tapped horns).
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