160 dB at 16Hz

[CECAA850]

http://www.realmofexcursion.com/videos/Various/mythbusters.1.wmv

These guys crack me up.

[Jay481985]

It lasted only a few seconds until the sunroof popped open exposing the subwoofer to no pressure while it excursioned and hence it overexcursioned and broke itself. BTW to people not seeing this, it was not an electromagnet speaker but one driven by the diesel motor of the car.

[CECAA850]

I'll bet if they had a way to keep the stroke a little more linear, it would have lasted a little longer.

[brennyE]

hehehehe imagine sitting in the car!

[Jay481985]

Technically it could not over excurt due to the fact it was on a crankshaft limiting max excursion, unlike electromagnets that can because there is no physical contact with the vc and motor or well there should be no physical contact.

If you noticed carefully if you watched the time when they show the sunroof open and the cone the cone tends to distort when the air is released. Think of the air in the car as a backpressure holding the cone in a way that the cone moves linear. Once the air was released and there was no backpressure the cone and the cone wildly distorted and moved in a non linear way ripping the surrounds. that was why prior to the shooting they showed that green truck have doors that had to be bolted in place due to the immense pressure. Think of the car now as a reversed sealed box. Once the pressure is released its like a ported system where the cone can overexcursion if not careful.

[wuzzzer]

I watched that episode on TV the other night. I think my insides would turn to jello with 16Hz at 160dB!

[darkside]

That's just sick, but sooo cool! [H] 160dB at 16hz, I'm jealous []

[brennyE]

deisel powered subs......this might start a new trend......lol [^o)]

[Jay481985]

hopefully not..... What they did was make a crankshaft with the cone directly the engine. It is only made for one thing, noise. Not sound quality. And it is the ultimate "one" tone maker as it will make really just one particular band unless you alter the disel engine. And then you would need to defeat the diesel noise. But an electromagnet is much cleaner in sq and better controlled (it can adjust and heck servos adjust to minimize distortion. Think of this woofer as a pipeorgan. You would need a whole bunch of them to make make a full spectrum (think how large churches are.

[darkside]

think how large churches are.

Actually, i know of some rather small churches []

[Coytee]

I saw the video. Isn't there a wrong premise going on or am I missing something?

they connected the driver to a crankshaft. As they reved the engine or perhaps, changed gears, they were not making the driver louder (bigger amplitude), they were playing it at a higher frequency.

Seems to me since the driver was connected to a crankshaft, its stroke (amplitude/loudness?) is fixed to the stroke of the crank. As the crank spins faster, the amplitude stays the same but the frequency will go up.

So, is that right? Did they say that too? (I never heard them make those comments if they did)

[Jay481985]

If I remember correctly, they were not going for a set hertz they were achieving but they were trying to go pure all out spl. Hence the amplitude did stay the same but the crank goes up increasing the frequency which in turn goes louder. Since the lower the hertz the more air it needs it gives up spl for depth, as the crank spun faster it has more total cone area to increase spl over depth. Well that is my thinking, tell me I am wrong now guys.

[DrWho]

I was thinking the same thing Coytee until I remembered that it takes less excursion for a fixed diameter driver to produce a specified SPL at a higher frequency. For example, it takes 60mm P-P excursion for a 15" driver to produce 96dB at 10Hz. At 20Hz, it only requires 14mm of P-P excursion. 60mm P-P at 20Hz would result in 108dB. So that's what, 12dB for every octave? (the natural roll off of a sealed enclosure).

So theoretically, they could have achieved 172dB at 32Hz, or 184dB at 64Hz - yikes! []

(simply by turning the crank faster).

[Jay481985]

I was thinking the same thing Coytee until I remembered that it takes less excursion for a fixed diameter driver to produce a specified SPL at a higher frequency. For example, it takes 60mm P-P excursion for a 15" driver to produce 96dB at 10Hz. At 20Hz, it only requires 14mm of P-P excursion. 60mm P-P at 20Hz would result in 108dB. So that's what, 12dB for every octave? (the natural roll off of a sealed enclosure).

wait this is anechoic free air?

So theoretically, they could have achieved 172dB at 32Hz, or 184dB at 64Hz - yikes! []

(simply by turning the crank faster).

are we still using the 15 inch diameter or the 48 inch diameter they used?

[DrWho]

The first paragraph is all about any 15" driver in half-space (playing in the middle of a field).

The second paragraph is talking about their crazy contraption in the car (a normal driver doesn't have a "crank").

[Jay481985]

oh, and is the 15 inch in free air or in an enclosure?

[DrWho]

It doesn't matter (as long as the rear wave is somehow seperated from the front wave). I guess that implies "infinite baffle" but it doesn't matter. The only time the "enclosure" comes into play is when trying to figure out how much power is needed to achieve the displacement.

[Jay481985]

So we are talking baffle loaded and not free air.

[Chris Robinson]

As many of you know, Tom Danley was involved in designing sonic boom generators for the US gov't.

Here is a post he put on the AVS Forum last Fall. I have a hard time imagining 165 db at 4.5 Hz. Talk about guts turning to Jello.

________________________________________________

I had designed a couple sonic boom simulators in the past so I can answer your question.

A typical sonic boom is what they call an N wave, it starts with a VERY rapid rise to some peak value, then it has a nearly straight line decay past zero to some peak negative value, with a rapid return to Zero (with some ringing).

The lowest frequency component is related to the speed and length of the plane, a longer plane makes a lower Fundamental at the same speed as a shorter one.

A sonic boom has a distinct sound, a very definite KAAA BOOOM, you hear the fast rise and fall as two events. Airplanes actually make a great deal of noise going fast but I would doubt if they were supersonic as the sound would break windows for a long way and given a lot of foot ball fans a critical bathroom related cloths problem at a minimum.

Aboard aircraft carriers there is a ritual where one flys by the ship at mach, it is so intense that few actually choose to be on deck, although I know I would have to try it.
On our web site is a clean photo of a jet doing a carrier flyby at mach. What you cant see is the pressure wave, which is in front of the white condensation that a low pressure produces.

Danleysoundlabs.com

In the systems I built, the intention was testing ground level sound from aircraft.
The sealed system (a sealed bunker thing) used 27 of the ConraBass style motor systems (no passive radiators) and could produce 165 dB down to 4.5 Hz which is enough to break windows and doors etc (the intention of the project was to classify building stuff I think).

The other system, much harder was to expose the exterior of a house to the sonic boom from the NASA space plane. It would be much higher in the air BUT produced a much lower frequency signature. Add that to the fact it is 2 meters away from the house wall and outdoors, made it a project from hell. That system could produce 132 dB on the house wall, from 5KHz down to 3 Hz. The lower range (30 Hz to 3Hz) was handled by large low pressure flow modulators and required its own 50KW 3 phase service to run.

Anyway, thats what I can tell you about it.

Dont get any ideas about a home unit.

Best,

Tom Danley

Danley Sound Labs

[damonrpayne]

Reminds me of an episode of the X-Files where a 2 mile long antenna caused all sorts of wackiness in people.