I sold my motors book a long time ago and dont have any of the equations to calculate efficiency for regular DC, AC, and 3 phase motors. Does anybody know the theoretical maxes of each type?

would there be much to gain in the way of efficiency by using one of the above mentioned motors connected to a moving wall type piston provided the connecting rods were frictionless.

I seem to remember 3 phase motors have an efficiency of like 90%, but i slept a lot during that class and it might be completely off.

Would there be an easy way to relate an aforementioned motor setup to a BL product and an RE ?

thanks a lot

Measured at one meter, a speaker producing 92db with one watt of input has an efficiency of:

To solve for power radiated by driver at 1m,

92db = 10 log (x/I) where I is 10^-12w/m2
9.2 = log (x/I)
10^9.2 = x/I
10^-12(10^9.2) = x
---------------= 10^-2.8 w/m2

In percentage, 10^-2.8 is .158% of 1 watt.

Therefore, one eigth of one percent efficiency for a 92db 1w/1m speaker.

As for different motor structures on a speaker- You couldn't use a DC motor or a three phase motor simply because these aren't congruent with the nature of sound, if used with a conventional voice coil, which is a single alternating wave that resolves to a single displacement function of time.

However, several companies DO use a rotary motor attached to a moving diaphragm by connecting rods, a three phase (or three-armatured?) motor would work just fine for this application, as would a variable DC motor or a regular single-phase AC motor, however it is prohibited by the rules of DB drag and the latency and size involved restrict its usability in-car for any other purpose.

Good idea, though

ShadowStar

I am sorta grasping at straws here, but would it be feasable to "calculate" the BL product from a "normal" electric motor just by using the lorentz force law to use in the rest of the audio equations? Or would it take something much more complicated.

F/i = Bl

thanks

.5(D v w2 s2) = I

This is, one half times the change in energy with respect to time due to Bulk modulus variation of a compressible fluid in harmonic motion or:

.5(Density of liquid*waveSpeed*(w)^2*(Speed of element/(cos(kx-wt))^2

where k = 2Pi/wavelength and w= 2Pi*freq

This equation gives the average power in a wave.

When this equation is equal to one watt, taken in reference to the threshold of hearing (an experimentally arrived value), then the intensity level expressed in dB is equal to:

10*log(1 watt/Threshold(10^-12w))= 120dB

Therefore, 120dB of Sound INTENSITY (SL) is equal to one watt per square meter.

However, the average pressure variation can be directly related to the sound intensity as:

I= (dPressure)^2/V(soundspeed)x&(air dens.)

I= dP^2 * .00234 where dP is one half the change in pressure (or the amplitude of the pressure variation)

Therefore, log(I/Io)= log(P/Po)^2 or

20*log(P/Po)= intensity in dB

For longitudinal waves where bulk modulus is adiabatic (sound frequencies),

20*log(P/Po)=10*log(I/Io),

where Po = atmospheric pressure
where Io = 10^-12 watt/m^2

then one can directly relate pressure variation in terms of power, frequency independant.

All of this hinges on the experimental value of Io (10^-12) which is the threshold of hearing. I take it to be a pretty accurate value!

Dank- If you consider that 120db is 1w per square meter, then perhaps the concentration of energy at the microphone (which is certainly not a square meter) might relate some consistency? However, it is theoretically impossible to impart more than 120db of sound energy into the air using ONLY one watt, simply by definition. Measurement microphones are designed around the above mathematica.

The car/speaker/room/whatever can't theoretically create more than 120db at one meter for a radiated watt unless it concentrates more of that watt in a given area.. Like a tweeter, perhaps.. Directional.. Hmm.. remember the "tweets for SPL debacle" on Carsound? I think there was some interesting physics to debate on that one, but it turned into a mud-sling fit."

For 1 watt radiated in a linear fashion, you can do say a sqare centimeter, which would be 1w/.0001m^2, or 10,000w/m^2, which is a whopping 160db energy variation OR a pretty considerable pressure variation, percentage-wise.. In fact, as you minimize the area to be measured by, you start approaching the actual energy imparted to the moving coil by the magnetomotive force, don't you? I'd think that would be the maximum radiating efficiency for a given system, however, it doesn't segue into any loudspeaker efficiency considerations.. Or does it

However sound is a diffusing longitudinal wave and will always disperse to some degree. But, taking the area of the microphone into consideration and the concentration of energy at that point (IE gain) you can do more than that theoretical value, as you said, jellis.

I'd really like to see this discussed more. can anybody find problems with the concentration of energy per given area ?

BIG BOX + BIG AMPS = BIG NUMBERS

It would also only work as a low frequency sub and would need some sort of computer control for phase etc. and a compressor.

Could work very well, have many orifices to put gas into the chamber, have a minimum sized chamber, large vacumn piston to provide a decent restoring force.

Could only do low frewuencies well at first, but with computer control and modern materials it may be able to reach 80Hz. Output would largely depend on PSI of input gas, and Xmax, The compressor would also need to continuously support the vaccum for obvious reasons.

Other idea is why bother with a surround at all, you could just use a pistonic slider effect, allowing for as much Xmax as you can imagine, and with high PSI gas you could reach an almost limitless dB level so long as you ran it sealed.

Now where's RC, he'd probably go off an build one......

Oh, and last one to the patent office is a rotten egg!

You see, I may not post immensely complicated formulas, but when it comes to the crunch.
Damn, I want to build one now just to see.

Shock, Don? Anyone? Someone must see the potential here. You could play music on it as well Looooow bass

Let me know anyway.

too much Dank tonight .......

It would be easier to have two low pressure chambers than one vacumn chamber thinking about it, certainly easier to maintain.

Any sort of engine although efficient when running would be plagued by problems as you would need to start it up. It would inherently have a large moving mass and would never be able to play music. The pneumatic design would be able to play music.

Easiest way to test this would be to get a pneumatic drill and attach a cone to it. ROFLMAO! Burrrrrrrrpp. Play at tuning as well as you get so much force from those things it'd drive it to Xmax anyway

Pneumatic drill is a little harder to borrow than a traffic cone though Perhaps I should rent one and try it out just for kicks. I have a cone and a spare Basket from my currently blown mouse.... It would certainly be interesting on my CV..... Of course get it wrong and I may end up blowing out my windows as I'm not sure quite how loud it would be ..... Need a model with a high Xmax and low driving frequency.... Perhaps I should post some diagrams of how pneumatic drills work.....

Pneumatic drills use a compressed return stroke for absolute speed, having a vacumn on teh other end isn't really a problem.