What exactly does power handling mean? - AVS Forum
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post #1 of 38 Old 10-20-2012, 07:42 PM - Thread Starter
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I tried to google but could not find exactly my question.

Using the driver I am using as an example.
Say it is speced at 500rms/800 peak.

Does this say anything about the wattage the coils can handle at various displacements?
As far as I understand excursion is needed for cooling. So running a sine wave at a very low displacement frequency could over heat the coils very quickly.

The reason I ask this is according to horn resp for my sub it produces the loudest noise at about 71hz. It also is able to handle a lot of power at that frequency before excursion becomes a problem.

Basically I want to hear 130+db biggrin.gif.

Another question, is there anyway to determine the amount of wattage an amp is using by voltage across the driver.

Thanks.


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post #2 of 38 Old 10-20-2012, 07:50 PM
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Quote:
Originally Posted by Shinyav View Post

Does this say anything about the wattage the coils can handle at various displacements?
No. It's a thermal rating measured with pink noise.
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As far as I understand excursion is needed for cooling. So running a sign wave at a very low displacement frequency could over heat the coils very quickly.
That conceivably could be a problem if one only listened to a sine wave at the excursion null frequency, but one would never do so.
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Another question, is there anyway to determine the amount of wattage an amp is using by voltage across the driver.
No. Since power varies with impedance and impedance is not a constant there's no viable method of measuring power. For that reason when pro systems set the limiter to allow the amp to only deliver a set maximum voltage output that voltage is calculated at the frequency within the passband where driver excursion is at the maximum.
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Basically I want to hear 130+db
Not for long, doing so will render you deaf in fairly short order.
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post #3 of 38 Old 10-20-2012, 08:23 PM - Thread Starter
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Awesome reply. Thank you.

Definitely don't plan on 130 as background noise.. Just a "whats that like"

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post #4 of 38 Old 10-20-2012, 09:58 PM
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A bit technical, but a great resource on power handling:
http://www.klippel.de/uploads/media/Nonlinear_Modeling_of_Heat_Transfer_03.pdf

With subwoofers you usually end up excursion limited with broad band signals (which most of the source material is). As long as you keep the volume low enough to where you don't hear distortion, then you should usually be fine.

Btw, I've never seen any published research showing that large SPL's (130dB) at very low frequencies causes hearing damage. I've seen mention of respiratory damage, but never damage to the ears. 130dB at 20Hz is only 100phon, and all the hearing damage studies performed use A-Weighting or CCIR weighting, both of which have the relative weighting below 100Hz at <<20dB.

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post #5 of 38 Old 10-20-2012, 10:00 PM - Thread Starter
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well the frequency I am thinking of would be 71hz, so really don't plan on anything more than 5 seconds. Thanks for the link.

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post #6 of 38 Old 10-20-2012, 10:03 PM
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Quote:
Originally Posted by Shinyav View Post

Say it is speced at 500rms/800 peak.
Ignore the peak number as it's marketing. Depending upon the manufacturer and the test methodology, the 'RMS' number might have no merit either.
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Originally Posted by Shinyav View Post

Does this say anything about the wattage the coils can handle at various displacements?
Nope. To expand a bit on what Bill answered, power handling is determined by how much heat the coil/former assembly can take before it fails in some way. Providing that Xmech isn't exceeded in the test, excursion isn't important.

When power is applied to a coil, it heats very quickly, proportional to the energy flowing through it. When that energy is removed, most of the heat must be dissipated by convection across the air gap to the magnet and frame assembly, not an efficient method of transfer. The frame /magnet then dissipates it to the surrounding air, usually the inside of a box.
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As far as I understand excursion is needed for cooling.
I'm very dubious about the real efficacy of cone driven cooling.
Parnham's heatsinking and Bosso's forced air cooling will be far more effective.
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Basically I want to hear 130+db biggrin.gif.
Not for long you don't.
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Originally Posted by Shinyav View Post

Another question, is there anyway to determine the amount of wattage an amp is using by voltage across the driver.
For a sinewave at a single frequency you can easily if you know the impedance at that frequency.

For wideband it's not technically difficult, but not something the average DIYer can do.
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post #7 of 38 Old 10-20-2012, 10:05 PM
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Quote:
Originally Posted by Shinyav View Post

well the frequency I am thinking of would be 71hz, so really don't plan on anything more than 5 seconds. Thanks for the link.
If you're going to do it for 5 secs, then you can't conceivably heat the coil enough to cause damage. Just make sure you don't exceed Xmax.
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post #8 of 38 Old 10-20-2012, 10:09 PM - Thread Starter
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Alright perfect. I will be well below xmax. Will try it out tomorrow.

Thanks everyone.

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post #9 of 38 Old 10-21-2012, 09:10 PM - Thread Starter
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Yep.. definitely never need something that loud ever.
Also was a good way to clear off one of my shelves/moved my center speaker/avr fell of ledge/lamp fell off dresser breaking bulb/ceiling cracked....
Still put a smile on my face.

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post #10 of 38 Old 10-21-2012, 09:42 PM
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Quote:
Originally Posted by Shinyav View Post

Yep.. definitely never need something that loud ever.
Also was a good way to clear off one of my shelves/moved my center speaker/avr fell of ledge/lamp fell off dresser breaking bulb/ceiling cracked....
Still put a smile on my face.

So - you fed the F-20 a full 500 watts, at the SPL peak

Sounds like it left a mark or two.

Nice.
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post #11 of 38 Old 10-21-2012, 10:25 PM - Thread Starter
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Originally Posted by lilmike View Post

So - you fed the F-20 a full 500 watts, at the SPL peak
Sounds like it left a mark or two.
Nice.

Only 300, 40 volts. Still was plenty. biggrin.gif

For some reason increasing my AVRs sub level didn't go above 40volts.

hmmm.. Hornresp says I should be able to get more like 55volts into it with 300 watts... 3 more db... Must resist.

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post #12 of 38 Old 10-22-2012, 07:47 AM
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Here's a link to a Myth Busters show they did on "The Brown Note". It's part 2 of a 2 parter.


dbl

Let's all go to the lobby
....Let's all go to the lobby
........Let's all go to the lobby
............To get ourselves a treat!
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post #13 of 38 Old 10-25-2012, 07:16 PM
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to calculate power across the voice coil, use a flavor of ohm's law:

power = voltage squared / resistance (impedance for ac)

the catch is that for subs, there is a large impedance spike at the in-box resonant frequency. for subs, this is typically somewhere between about 30hz and 60hz.

a typical impedance spike might be 5 times as high or higher than the minimum value that is in the specification sheets.

as a result, you can nail the driver right on the impedance spike frequency with a ton of voltage and not generate a ton of current/power/or heating. if the impedance peak is 5x, then the power would be 1/5th, even though the spl would hold.

this is one technique used in spl drag racing to achieve the highest possible spl without cooking the coil.

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post #14 of 38 Old 10-25-2012, 10:20 PM - Thread Starter
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Cool, thank you for the reply.

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post #15 of 38 Old 10-26-2012, 12:11 AM
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What about those sub videos on youtube in the cars, the ones where the girls hair blows so hard it goes almost all the way up? What kind of dB are they hitting, and shouldn't it cause hearing loss? It doesn't appear to be painful.
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post #16 of 38 Old 10-26-2012, 01:53 AM
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Quote:
Originally Posted by Subjga View Post

What about those sub videos on youtube in the cars, the ones where the girls hair blows so hard it goes almost all the way up? What kind of dB are they hitting, and shouldn't it cause hearing loss? It doesn't appear to be painful.

I'm guessing 150+ DB. 130DB is pretty average far a car audio system.
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post #17 of 38 Old 10-26-2012, 05:36 AM
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Quote:
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What kind of dB are they hitting
20 to 30dB less than the measurements claim. The pressurization of the cabin fools the meter; that's why the ones that win are the ones that are most successful in sealing the car airtight. As a frame of reference, even with a large grouping of direct radiators system sensitivity of 110dB/watt is about the best you can realize. To get 160dB from said system would require 100,000 watts.

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post #18 of 38 Old 10-26-2012, 05:37 AM
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Quote:
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..... shouldn't it cause hearing loss? It doesn't appear to be painful.

The Equal Loudness Curves, illustrate that we at not equally sensitive to all frequencies. This is particularly true in the deep bass, as the threshold of hearing for 20hz is approx. 70dB. However, as the freq lowers to 16hz, the threshold is 90dB, lowering further to 8-9hz, our threshold requires 100dB merely to be perceptible. Plunging all the way to 5hz, the threshold raises to approx. 110dB.

But, to your point of how dangerous ..... it's hard to say. My experiences would dictate it's clearly not nearly a damaging as 3khz energy, and that makes total sense. But it's quite dificult to get good information on the subject.

That's the inherent beauty of HT, limited exposure to sustained high spls. Being involved in FOH engineering, I've had my share of sustained, full tilt, live PA levels.

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post #19 of 38 Old 10-26-2012, 07:32 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

20 to 30dB less than the measurements claim. The pressurization of the cabin fools the meter; that's why the ones that win are the ones that are most successful in sealing the car airtight. As a frame of reference, even with a large grouping of direct radiators system sensitivity of 110dB/watt is about the best you can realize. To get 160dB from said system would require 100,000 watts.


Bill I have heard you say this before but it doesn't hold up against any of the evidence. The maximum system efficiency ceiling does not hold up within the confines of a small vessel such as a vehicle based on all evidence that I have seen. I measured 108dB 2.0V sensitivity at 57Hz with a single sealed LMS 18" driver inside of a mid sized SUV. I have the same measurement outdoor ground plane from moments before that shows the expected 90dB sensitivity at 1 meter halfspace. Nothing was changed in between other than putting the sub in the back of the vehicle and moving the mic to the interior. A gain of over 32dB was realized at some sub 20Hz frequencies. Add an additional 6dB if comparing to 1m quasi anechoic /2m gp.

"The pressurization of the cabin fools the meter" ???? confused.gif Now the microphones and measurement devices are being tricked? How so? Have you ever sat in a vehicle with a powerful sub system? Heard the same system outside of the vehicle? There can be no denying the huge amount of gain that happens through semantics. Its effect on your ears and body is clear and the measurements show the difference. If you are asserting that placing a large bass horn that is already 105dB sensitive at 57Hz in a 1m halfspace setting into the back would realize much less gain from the vehicle cabin than the 18dB shown by the sealed system due to it already having much higher sensitivity, this does not hold up either. It will get the same 18+dB in gain. That has been tried too.
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post #20 of 38 Old 10-26-2012, 10:34 AM
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Maximum sensitivity/efficiency of direct radiating drivers was long ago quantified by Don Keele:
http://www.xlrtechs.com/dbkeele.com/PDF/Keele%20(1991-10%20AES%20Preprint)%20%20-%20Max%20Efficiency%20of%20Speakers.pdf

Typical increase due to cabin gain is shown in this data sheet:
http://www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/BoxesandParameters/GTO1014DTD.pdf

The math simply doesn't support the apparent SPLs achieved in auto sound. OTOH I can peg my meter by simply blowing on the mic element, and while I may be full of hit air it's not 150dB worth.

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post #21 of 38 Old 10-26-2012, 11:38 AM
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Sorry Bill but all of the real world evidence says otherwise. I'm well aware of Keele's work on that subject but there is no violation of Keele's mathematics at work in car audio SPL You are just assuming there is. The efficiency noted in the article is 25% for a direct radiator but that is only based on nominal power input not true efficiency or input.

Quoted example below.

"This relatively low value of absolute maximum efficiency (rather than 50% which would be
expected for a load connected to a generator with the load resistance equal to the generator's source
resistance) is a direct result of the definition of nominal electrical input power used in the definition
of efficiency. If the input resistance of the driver were defined as being ?.RErather than RE, as it is
in the definition of efficiency for horn loaded drivers [10], the maximum efficiency would be 50%
rather than 25%, as it is here. Alternately, efficiency could be defined as relating true output power
versus true input power (rather than nominal input power), which would remove this limitation and
would allow efficiency to rise to 100%. Unfortunately, this would mean that the efficiency
frequency response function would differ from the response function measured with constant input
voltage, and thus the efficiency frequency response would differ greatly from the response under
normal operating conditions. As an example, the true efficiency of a closed box system at box
resonance can approach 100%, because the input impedance could be very high at resonance, thus
making the input power quite low. This would reflect as a peak in the efficiency frequency
response that would not be representative of the frequency response as the system is normally
used, with a constant voltage drive source.
This power transfer condition is exactly the same as a generator having a source resistance of
R1 driving a load of resistance R2. Maximum power is transferred when the load resistance is
equal to the source resistance. In this case, however, the efficiency is reduced by a factor of 2,
because the input power is twice as high due to the definition of nominal electrical input power."




Additionally not only is this a nominal approximation of input power but he is talking about efficiency as a % where you are making a jump to maximum SPL levels possible but have not defined what environment this data point occurs in , which directly impacts it, the distance from the radiator,etc. This has a direct impact on the SPL that will be measured and is why there is such an increase inside of a vehicle. The speaker is enclosed inside of a vessel that is very small compared to the wavelengths of interest. The environment not only modifies the sensitivity of the device but also the theoretical nominal SPL/ efficiency ceiling that you speak of. It is not the same SPL at 10m outdoors as it is at 4m or 1m is it? Why would it be the same inside of a small car? It is most definitely not. Looks like the inside of my jeep allows something near 128-130dB theoretical 1w sensitivity. No laws are being broken.
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post #22 of 38 Old 10-26-2012, 01:12 PM
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Quote:
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The environment not only modifies the sensitivity of the device but also the theoretical nominal SPL/ efficiency ceiling that you speak of.
Do the calcs, when you exceed 100% efficiency collect the appropriate prize. Do it with a Chevy Volt and you can power the car with the leftover juice.

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post #23 of 38 Old 10-26-2012, 02:08 PM
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when the size of the wavelength is large relative to the enclosure, the whole system changes. the air no longer behaves as a compressible fluid. the speed of sound increases by something like a 4-5x.

while in an environment of non-compressible fluid, the efficiency of the driver may actually rise because of better coupling to the air, it obviously will never get anywhere near 100%. that doesn't mean that the measured sensitivity of the driver can't be enormous--well in excess of 112db.

also, in an environment where pressure is pretty changing everywhere simultaneously, the 1m measurement assumption gets thrown out the window.

that is a VERY different environment than the 2pi space compressible fluid environment where the 112db@1w1m = 100% efficiency is coming from.

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post #24 of 38 Old 10-26-2012, 02:10 PM
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Bill you are missing the forest for the trees buddy. Answer these simple questions in your head.

What happens if the 110dB @ 1m in 1/2 space speaker is measured at a 10m distance instead of 1m? How about from a distance of 0.25m?

What if the measurement is now taken with the speaker and measurement device placed into confined 1/8th space instead of 1/2 space?

Has the input power changed? Has the total energy output from the speaker changed? Has it's efficiency changed? Has its basic voltage sensitivity?

This has absolutely nothing to do with the base efficiency % of the speaker system at all which does not change.

It has everything to do with the environment that the speaker is radiating into and where the measurement device is placed relative to it.

You can apply 2.83 volts to a speaker and get 100dB at 1m 1/2space. Move the mic back to 10m and read 80dB. Put it in a compact car and read 115dB. The actual efficiency % of the speaker and total energy output has not changed at all.
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post #25 of 38 Old 10-26-2012, 02:18 PM
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Quote:
Originally Posted by Ricci View Post

Additionally not only is this a nominal approximation of input power but he is talking about efficiency as a % where you are making a jump to maximum SPL levels possible but have not defined what environment this data point occurs in , which directly impacts it, the distance from the radiator,etc. This has a direct impact on the SPL that will be measured and is why there is such an increase inside of a vehicle. The speaker is enclosed inside of a vessel that is very small compared to the wavelengths of interest. The environment not only modifies the sensitivity of the device but also the theoretical nominal SPL/ efficiency ceiling that you speak of. It is not the same SPL at 10m outdoors as it is at 4m or 1m is it? Why would it be the same inside of a small car? It is most definitely not. Looks like the inside of my jeep allows something near 128-130dB theoretical 1w sensitivity. No laws are being broken.

Quote:
Originally Posted by Bill Fitzmaurice View Post

Quote:
Originally Posted by Ricci View Post

The environment not only modifies the sensitivity of the device but also the theoretical nominal SPL/ efficiency ceiling that you speak of.
Do the calcs, when you exceed 100% efficiency collect the appropriate prize. Do it with a Chevy Volt and you can power the car with the leftover juice.

As Ricci notes above, you're confusing 1/2 or full space SPL equivalent efficiency with the results of operation in a confined space. Just as 50% efficiency results in a different SPL for 1/2 space/ground plane vs. free space, it is different for confined spaces, and at low frequencies it will even be frequency dependent.

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post #26 of 38 Old 10-26-2012, 02:23 PM
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"This has absolutely nothing to do with the base efficiency % of the speaker system at all which does not change."

it may actually increase because of better driver/air coupling as you get into the pressure vessel region.

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post #27 of 38 Old 10-26-2012, 02:24 PM
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Quote:
Originally Posted by Mark Seaton View Post

As Ricci notes above, you're confusing 1/2 or full space SPL equivalent efficiency with the results of operation in a confined space. Just as 50% efficiency results in a different SPL for 1/2 space/ground plane vs. free space, it is different for confined spaces, and at low frequencies it will even be frequency dependent.

Why do you always have answers that are so much cleaner...LOL rolleyes.gif

Right what I was trying to say is that if the efficiency is say 5% at 50 Hz it is still 5% in the vehicle however that may produce an extra 20dB of SPL to the mic position compared to outdoors.
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post #28 of 38 Old 10-26-2012, 02:38 PM
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this actually raises an interesting question though. what is the rate of sound attenuation in an incompressible fluid? if the speed of sound is increasing by a 4-5x, then by stoke's law http://en.wikipedia.org/wiki/Stokes%27_law_(sound_attenuation) which has attenuation being inversely proportional to the cube of the speed of sound, then the effective measure distance to the mic decreases by 1/(4-5)^3 which is 64-125 times. so now instead of measuring at 1 meter, the effective point is about 1/64th of a meter. 64 is six "halvings" of distance and with each halving at 6db, that is a 36db increase. at five times the speed of sound, we would add another doubling or about 6db for a 42db increase.

if ricci's speaker measured 90db 1w1m outdoors, then in this environment it would measure 126-132db 1w1m. ricci's measured results are right in that range. damn, that's pretty cool.

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post #29 of 38 Old 10-26-2012, 03:51 PM
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Quote:
Originally Posted by Ricci View Post

Bill you are missing the forest for the trees buddy. Answer these simple questions in your head.
What happens if the 110dB @ 1m in 1/2 space speaker is measured at a 10m distance instead of 1m? How about from a distance of 0.25m?
What if the measurement is now taken with the speaker and measurement device placed into confined 1/8th space instead of 1/2 space?
Has the input power changed? Has the total energy output from the speaker changed? Has it's efficiency changed? Has its basic voltage sensitivity?
This has absolutely nothing to do with the base efficiency % of the speaker system at all which does not change.
It has everything to do with the environment that the speaker is radiating into and where the measurement device is placed relative to it.
You can apply 2.83 volts to a speaker and get 100dB at 1m 1/2space. Move the mic back to 10m and read 80dB. Put it in a compact car and read 115dB. The actual efficiency % of the speaker and total energy output has not changed at all.
I'm not missing a thing. The standard for SPL measurement is at 1 meter. If the car SPL guys are getting silly high readings by measuring at a shorter distance then they've changed the rules of the game. And while cabin gain does add to sensitivity it also has its limits, you're simply not going to get 30dB of cabin gain.
Quote:
Just as 50% efficiency results in a different SPL for 1/2 space/ground plane vs. free space, it is different for confined spaces, and at low frequencies it will even be frequency dependent.
Of course, but the inference is that an ever smaller vessel results in ever higher sensitivity, meaning that eventually efficiency exceeds 100%, rather than the 25% that a large group of direct radiators can actually achieve.

Bill Fitzmaurice Loudspeaker Design

The Laws of Physics aren't swayed by opinion.
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post #30 of 38 Old 10-26-2012, 05:31 PM
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"Of course, but the inference is that an ever smaller vessel results in ever higher sensitivity, meaning that eventually efficiency exceeds 100%..."

that is exactly right. the sensitivity in a car can exceed 100% of the efficiency of a bunch of drivers in a field.

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