Axiom Home Page Forums General Discussion Stereo Maximum SPL at 1kHz

I am an engineer developing a microphone system for a cockpit voice recorder. One of the tests required is microphone distortion at 1kHz at 120dB SPL. The distance from the loudspeaker source is not specified. I am not sure if your everyday commercial off the shelf loudspeaker would be capable of delivering this level of pressure at the microphone. If I had a typical sensitivity level of 92dB SPL at 1m what sort of level would one expect at 3" from the loudspeaker? At 1m I would need to drive 1000 watts into the speaker. Any suggestions as to the speaker to use? Must be under 5% distortion.

I also need a speaker that is relatively flat in response, 150Hz to 10kHz capable of producing 94dB SPL with about 2% distortion max.

I'm pretty sure an Axiom M80 driven by a capable amp could easily hit 120db at 3" with low distortion. And, as luck would have it, an M80 can handle 1000 watts, too.

Seriously, the M80 is what you're looking for. Buy two, and keep them for music and movies after you're done with the microphone.

Peter, master of the questionable requisition.

Axiom stress tests the M80's at over 1400 Watts.

I'm sure Ian or Alan can chime in and give you some serious statistics on how the axioms perform, distortion and soforth.

They have their own testing chamber, so they may even run a quick test just for you to verify what you are asking. :-)

Hello weekendwally,

Tests of endurance, sensitivity and maximum output levels in dB SPL of domestic loudspeakers are not performed with single-frequency test tones, but with what's known as a "broadband noise signal" with weighting applied. It's a simulated program signal (much like pink noise with equal energy octave to octave) but intended to simulate the bulk of energy content of a complex music signal.

One example used for years during tests of loudspeakers at the Canadian National Research Council had a uniform output between 200 Hz and 1 kHz, rolling off above and below those points at rates that resulted in -10 dB points at 25 Hz and 9 kHz.

If you wanted to try using a fixed-tone 1-kHz signal at extremely high SPLs like 120 dB, I'd suggest you use a big horn-loaded system with very high sensitivity (over 100 dB SPL, 1 watt/ 1 meter). Such speakers exist for concert sound reinforcement. They do not have flat frequency responses (unless carefully equalized) but typically distortion is very low and they are designed to be indestructible at such high SPLs.

Using a fixed-tone test signal at 120 dB with domestic Hi-fi speakers would risk damaging individual drivers. I'll check with Ian, the owner and designer of Axiom speakers, on the broadband noise signal used for our tests of the M80. The specification for the broadband noise signal used at the NRC used weighting according to IEC 268-1 (International Electro-technical Commission).

Regards,

Thank you Alan,

The specific test I am trying to meet is an Eurocae standard ED-112. The microphone is to be used in a cockpit voice recorder aplication. ED-112 wants to ensure that the distortion at 120 dB does not exceed 10% at 1 kHz. It is probably not the most up to date standard in terms of testing, but it is what the FAA says I have to meet. Do you have suggestions for a manufacturer of large horn-loaded speakers? I have taken a look at Mackie as they have some impressive SPL numbers in a relatively small encosure, but I would prefer just to buy the horn and not the entire loudspeaker as I have to fit it in an environmental chamber.

Also, could you advise on an Axiom product that has the flattest frequency response between 150Hz and 10kHz? The SPL for the frequency response test is 60dB and 94dB.

Appreciate the input.

Thanks
Trevor

The m80 would have the flattest response for that range. Axiom posts frequency graphs for almost every speaker on the left side.

Here is the frequency graph for the M80:

At 3" you are inside the diameter of some of the drivers. I'm not sure that the sound field would be fully developed so close in.

Hi,

Ian will be doing some measurements with our M80 in Axiom's large anechoic chamber, so I should have some data for you in a day or so.

Of the Axiom line, the M80, M60, M22 and M2 are very linear, and the M60 and M80 would have very low distortion (under 2%) in the 94 dB SPL range.

My expertise is in domestic hi-fi speakers, not concert and pro sound reinforcement. Some well-known past brands include Meyer and JBL, and there may be new players on the block. Axiom does have a consultant on digital design who used to do the live on-tour concert mixes and setups for Led Zeppelin way back when, so I'll see if I can get some feedback from him.

Regards,

In reply to:

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Axiom does have a consultant on digital design who used to do the live on-tour concert mixes and setups for Led Zeppelin way back when

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Cool!

He should definitely know a thing or two about volume!

I said....
"HE SHOULD DEFINITELY KNOW SOMETHING ABOUT VOLUME! No, VOLUME!!!!!

Mark,

Yes, indeedy. He's a really interesting guy and his ears seem to still be in good shape. He told me he can be seen scurrying about the stage in a DVD reissue of an Isle of Wight concert, but I've forgotten which one. I'll find out.

Regards,

Any chance this is Bob Heil? He did concert work for several notables including the Dead. He may still be doing that sort of thing, but I know him mainly from ham radio where he has an impressive line of microphones and other audio gear. Good guy!

-Brian n8wrl

Hi n8wrl,

No, he's not Bob Heil. But, interestingly, Steve is also a ham radio buff who has a system in his Mini Cooper. So far as I know, he does not do concert sound anymore. He develops custom "codes" for digital algorithms.

Regards,

Hi,

Ian Colquhoun did some fixed-tone SPL measurements on the M80 in our anechoic chamber yesterday. He reports that by placing the mic between the tweeter and midrange drivers 10 inches away he achieved 120 dB SPL at 1 kHz at 15.15 volts input. The distortion was well under 1%.

Regards,

He must have been grinning from ear to ear.

In reply to:

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He must have been grinning from ear to ear.

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Or, at least he would have been, if his ears hadn't fallen off his head moments before!

LOL! Mighty good to have you posting regularly again, my friend.

Thanks Jack!
But currently, the ratio of PMs I'm receiving are 6-to-1 in favor of me posting less!

Trevor, excellent information from Alan describing Ian's test, which again illustrates the quality of the M80s at a level approaching the threshold of pain. Also noteworthy is that the 15.15 volts input used equated(P=V[squared]/R)to only about 57 watts. The problem apparently is the size of speaker that you can fit in your testing chamber.

WOW!!!! The M80s must be super rugged.

Not a chance that I would listen to mine at that level.

C'mon, you know you want to...

You probably could listen.....




once.

JohnK, the wattage being consumed here is by a single tone.
Add in another several thousand and the power usage may climb.

The numbers put forth by the speaker are impressive, but then again, i have never seen equivalent specs posted on any other brand either.

Chess, the SPL level would determine the power usage, regardless of the number of individual tones which combined to reach a given SPL.

16,000 or so tones managed to reach a Db level of 110 several times during the hockey game here in Edmonton tonight.

Ok, I haven't read this thread yet and am shamelessly plugging my hockey team. Ignore me and play on through.

I was thinking in more simple terms John where a hump or dip in a frequency response will produce a different dB level compared to the dB with the same power given to the 1kHz; but yes it makes sense that the overall sum of SPL would total that of the highest dB at whichever frequency that may be.
The sum dB of all frequencies are not additive and cumulative otherwise our ears would be in big trouble.

Right, chess; e.g. 90dB+90dB(of the same sound)=93dB, etc.

Now could you imagine additive and cumulative sound?
90dB + 90dB from only TWO frequencies equating to 180dB!!!!
(Disregard the fact that the dB scale is not a linear one).

So the math, at 1kHz with x power input we have 90dB.
At 500Hz with x power with a dip in the response of -2 dB we have 88dB.
At 3kHz we have a peak of +4dB over 1kHz, thus 94dB (for that tone).
What is the total SPL of the three?

instantaneous or averaged?

Nope, not even once. I want to keep my hearing!

Wonder what sort of ear protection is used when measurements like that are made?

When I go to the NASCAR races, I take the soft, rubber earplugs that you can buy at the drug store. I think that they knock off 20 dB of the sound.