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streetbeats 11 December 2011

Hi Guys, I'm new to these forums and trying to think outside the box and any suggestions would be appreciated. I own a car audio shop in Sydney Australia and compete in DB Drag Racing SPL competition. I know this is not the correct forum but your knowledge of sound pressure behavior is maybe at a higher level or different than in the car audio industry.

A quick run down. The name of the game is to achieve the highest possible SPL level within a closed vehicle cabin in a 30 second period. There are many classes but to keep it short my class allows for 2 12 inch woofers and only 1 battery. Also, the enclosure must remain within the cargo area and not be above the window line.

In saying all this, my car has achieved 153.4DB consistently to date using a 9kw rms amplifier. (clamped doing 6800wrms due to the battery restriction)
I have sealed every opening/vent/breather in the cars body to the atmosphere. Applied sound/resonance deadening to the rear 1/2 of the car body (score drops in front 1/2) The box is 2 14 inch tubes with the 12's facing forward and ports facing rearward. 1.2cuft enclosures, ports are 6 inch dia and 9.5 inches long, using flared ends. car resonates at 62hz and this is what it has been tuned to. (Honda CRX series 2)

We measure SPL on the lower front passenger windscreen with a device known as a termlab. (Can be googled) Very accurate and can measure in excess of 180DB. Unaffected by temp/altitude/mic hangover etc.

Any suggestions from a fresh resource such as yourselves would be much appreciated on how to increase my SPL, and happy to share my SPL knowledge as well. I am 0.6 DB off the aust record for the class and about 3db off the world record. Worse comes to worse I will throw another 9kw amp which should be good for over 1db but a fresh set of brains may make my setup more efficient.

Thanks, Andrew

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streetbeats Mon, 12/12/2011 - 14:39

Hi Niclaus, We have to achieve our score between 20-80hz. In this particular car I use a test tone of 62hz. It is loud and I have sat in it (makes you feel pretty dizzy afterwards). The system is that highly tuned for that particular frequency that it sounds rubbish on music though and can hurt the equipment. We only "burp" our cars for around 3 seconds, after that the battery is depleted. Sounds ridiculous but we enjoy the science of it and the competition, that's why we do it.

RemyRAD Tue, 12/13/2011 - 14:12

I think what you need are custom made 12 inch drivers. These drivers will have no voice coils, no magnets. The speaker cones will have to be made out of some kind of titanium with a flexible rubberized surround capable of a couple of inches of travel. An electric motor with some type of active DC control will physically pump the speaker cones. Why utilize coils of wire with magnets when you can rely upon horsepower instead? And this is not an original idea. There have actually been speakers made like this in a similar fashion minus the titanium cones. But titanium is very light, impervious to high temperatures, extremely rigid for maximum transfer of motion and power. Still capable I believe with a battery. After all, your battery has to crank your engine with a tiny motor and this tiny motor cranks a gigantic multi-hundred pound metallic behemoth. So take your cue from engine design.

Duhhh...Dat Zounds Lojikold...
Mx. Remy Ann David

streetbeats Tue, 12/13/2011 - 16:26

Thanks Remyrad,

Awesome suggestion, yes we have thought about servo driven speakers but alas our rules of comp stipulate we can only use commercially available electro-magnetic loudspeakers. The kind of help i was looking for on here is more to do with cabin acoustics, resonance, cancellation etc. I would love to build a vehicle with servo driven speakers one day for display purposes but am yet to find an affordable pair.

Thanks, Andrew.

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