Pro Audio Subwoofers vs. Car Audio Subwoofers

[cvxsmitty58]

This is from pk sound's website.

Specs for the woofers in their cabinets.......

Two high performance 18” neodymium extended low frequency transducers provide a lightweight package while offering unequalled reliability. State of the art 5.3” voice coils, triple silicon spiders and large displacement suspension systems allow 70mm of excursion before damage with 28mm of linear Xmax.

http://www.pksound.ca/cx800/

[Matthew Stanley]

That's a nice looking unit and going by the dimensions that box is no bigger than what i intend to build in my van. if anything it might be smaller. i notice how they are designed to make the sound travel further forwards from the sub rather than behind. but I'm hoping this is mostly down to enclosure desig.

[SnowDrifter]

PA drivers tend to be in a loaded horn enclosure and don't need to have low frequency extension below 40-45 hz. So they tend to be designed for use in these enclosures - which also provide lots of cone control and extremely high efficiency, so there is less of a need for a high xmax.

[Matthew Stanley]

Yeah I've just checked the data sheet it says 10mm xmax and it sound like nothing compared to above mentioned 26mm. Oh and i intend to use for day to day use with everthing from happy hardcore to r&b to hiphop to dudstep btw.

[Matthew Stanley]

And claimed usable frequency response from 33hz to 300hz and not suitable for horn loading (but I've read somewhere that it is)

[phistula]

http://www.diyaudio.com/forums/subwoofers/155161-pa-vs-car-audio.html

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.

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.

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.



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.

__________________

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?