That's correct, as long as the wavelengths are much bigger than the source itself plus the source is a monopole, we can consider that.
But in the context here, it was just a guestimate to know what sound pressure levels we can (roughly) expect close to a speaker when reference is 94dB @ 1 meter.
The Brüel & Kjær 4004 using the 130volt power supply (type 2812 or HMA4000) is specified to haveTo be honest, the problem with standards is that everyone has their own standards.
AFAIK, Brüel & Kjær spec their capsules at 3% THD, and peak SPL at 10% THD.
Total Harmonic Distortion: 142 dB SPL peak (<0.5% THD),
148 dB SPL peak (<1% THD)
Difference frequency distortion: (DF2, DF3, Df = 80Hz) <1% at 153dB SPL peak
Frequency range: 4004: On-axis: 10Hz - 40kHz ±2dB up to 152dB SPL peak
The above is the calibration chart from one of the B&K 4004 I used to own.
For what it's worth, the pair of 4004 (1983 vintage) had around the same amount of frequency response deviation between them in the 2-16kHz range as a cheap (~ $50.00) second hand RTA 420 and a Panasonic WM62 (~ $10.00 in parts).
The chart below is of the response using the RTA 420 and a Panasonic WM62 measuring a speaker, same position for each, maximum deviation of less than +/- 2dB:
The RTA 420 response was -1 dB at 40 Hz, -2dB at 30Hz, -4 dB at 16 Hz compared to the Brüel & Kjær 4004.
At any rate, my hearing distorts so badly at high frequency high SPL, a little microphone distortion no longer concerns me
Art
This shows very well where the double distance rule ends to work. For a bigger speaker (more membrane surface) the effect is stronger.
So up to 12cm the 6dB difference works, halfing to 6cm only gives 4db rise, half again 2,5dB etc.
For real nearfield - get as close as possible (5mm is great - be carefull with high excursion drivers!). You get 20-30dB more as with 1m distance.
This is just about what I was going to say
It mostly shows that in practice the results will differ depending heavily on the practical situation.
Because of the bafflestep step, there is already a discrepancy right there.
But that's why I already said, only for monopole and when wavelengths are big, which is definitely NOT the case around 1kHz.
If I am not mistaken, the theoretical approach over estimates
Thanks Art. Great to see some historical data sheets.
Upcoming iSEMcon CPX-1212 with 48V phantom power
0.1% THD - 125dB
0.2% THD - 132dB
0.3% THD - 135dB
0.5% THD - 139dB
1% THD - 145dB
3% THD - 154dB
5% THD - 157dB
Comes with 1/2" Metal (nickel) diaphragm,
Noise floor 25dB(A)
Frequency response 20Hz to 40KHz
Interchangeable with other 1/2" IEC61094-4 compliant
(Handle/preamp 16dB(A) noise floor, 4Hz to 80KHz)
Reference:
https://cpx12.isemcon.com/
Upcoming iSEMcon CPX-1212 with 48V phantom power
0.1% THD - 125dB
0.2% THD - 132dB
0.3% THD - 135dB
0.5% THD - 139dB
1% THD - 145dB
3% THD - 154dB
5% THD - 157dB
Comes with 1/2" Metal (nickel) diaphragm,
Noise floor 25dB(A)
Frequency response 20Hz to 40KHz
Interchangeable with other 1/2" IEC61094-4 compliant
(Handle/preamp 16dB(A) noise floor, 4Hz to 80KHz)
Reference:
https://cpx12.isemcon.com/
Fundamentals of Acoustics, 4th Edition
Lawrence E. Kinsler, Austin R. Frey, Alan B. Coppens, James V. Sanders
ISBN: 978-0-471-84789-2
(It’s available online somewhere)
And while we’re on it, there’s more from Germany: https://www.akulap.de/joomla/index.php/en/en-shop/product/view/17/11
Here is a comparison of three microphones in my collection. The B&K 4135 is quite expensive even used but its specified to 100 KHz. The Girardin BP020708 is made from a Panasonic capsule mounted on a length of brass tubing Including a cal file it was quite reasonably priced. The Panasonic mikes were around $1.00 in qualtities of 100. The Nady is a typical example of the cheap pseudo measurement mike.
I used a Pioneer ribbon tweeter which was supposed to be good for maybe 70 KHz. It clearly makes it to 35 KHz. There are issues of diffration etc. that mess with the response but it still gives clear indication that the Girardin Microphone is adequate to response testing and I can keep the expensive stuff safe.
To add to the chart this is what B&K specs
I used a Pioneer ribbon tweeter which was supposed to be good for maybe 70 KHz. It clearly makes it to 35 KHz. There are issues of diffration etc. that mess with the response but it still gives clear indication that the Girardin Microphone is adequate to response testing and I can keep the expensive stuff safe.
To add to the chart this is what B&K specs
Attachments
How was this being measured?
Because most audio interfaces don't go much higher than that, even at higher sample rates
I was using Praxis with an ESI Juli@ interface. It works well at 192 KHz sample rate. (Recent updates in Win 10 have degraded it so I'm using a complicated ASIO workaround now). I'm now using an EMU 1212M (lower distortion). I usually start with loopback tests to confirm everything is working correctly.
Can you show the loopback response?
I have used a couple of EMU audio devices in the past and they most certainly didn't go above 30kHz or so.
I have actually never really seen many audio devices that will reach 70kHz.
This is mostly fixed by hardware, either the lowpass in the DAC or an analog active lowpass stage, or a combination of the two.
There are many reviews done on ASR forum where this can be seen.
I have used a couple of EMU audio devices in the past and they most certainly didn't go above 30kHz or so.
I have actually never really seen many audio devices that will reach 70kHz.
This is mostly fixed by hardware, either the lowpass in the DAC or an analog active lowpass stage, or a combination of the two.
There are many reviews done on ASR forum where this can be seen.