I started collecting GenRad equipment as a sort of tribute to proper analog measurement, and as a specific apology to GenRad itself for favoring Bruel & Kjaer during my time in academia. GenRad equipment was solid, rugged, easy to handle. BK was Danish, with the typical Kraut qualities. More precise than anything else under precise conditions, but brittle and fussy. At Penn State we had a dozen BK capacitor mics, and all but one had shorted out from PA humidity, which is similar to Danish weather.
First I bought this 1565B sound level meter:
Only $50 from Ebay. IETlabs, the successor to GenRad, still sells it for $3500, so $50 is a pretty good discount. As I noted before, the extreme overprice is really paying for legal support of the calibration, not paying for the device itself.
Made in the ’90s, it doesn’t have the classic GenRad styling but it was MADE IN AMERICA, and it’s still solid and fully functional. I didn’t use it much until 2020 when I started doing ‘real science’ as a form of prayer against the NAZI FAKE SCIENCE THAT IS KILLING THE WORLD.
I’m mainly using it as a microphone. It’s a cheap way to get a wide-range mic with a built-in preamp and tone control. Changing the dB setting changes the amplification, and changing the weighting alters the filtering.
The 1565A and 1565B should have been given distinct model numbers since they’re totally different in every way, not just the same innards in square and round cases. Since GenRad chose to number them confusingly, I’m going to call them square and round. Here’s the abstract tribute to the square:
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In 1970 GenRad published a lively little handbook of sound measurements.
IETlabs continues to make and calibrate derivatives of GenRad products, and performs a tremendous service by maintaining old GenRad publications online. Maintaining old records of old technology is an even more important form of calibration in an era of Github memoryholing. Clearly they were using the original booklet from GenRad files, not one of the 20,000 printed copies that were ordered by the original form. Calibration at all levels! Thanks, IETlabs.
The book was aimed at industrial tech types who were suddenly required to deal with noise measurements by new OSHA regs in 1970. GenRad’s simple sound level meter at that time (the 1565A) looked like this:
The artist took full advantage of the meter’s face, turning it into a character.
Decibels don’t add like apples and oranges.
Meters and humans don’t work the same way. Human hearing is totally oriented toward filtering OUT stuff that doesn’t matter, and bringing IN new information in the strict sense. If a sound is meaningful and new, we focus on it, starting with the remarkable tip-link mechanism in the cochlea, and continuing all the way into the higher language centers.
The meter has no idea which sounds are meaningful. It just picks up waves of air pressure and filters them by frequency.
Here’s how the GenRad book balances out the human and meter perceptions:
You have been told, correctly, that measurement is the first step in the solution of a noise problem, and you have made your measurements. The noise, meanwhile, continues, apparently unintimidated by your bulging data book. But your day is near; you have the facts you need to act intelligently. An effective noise-reduction program requires careful planning. The man who finds a noise level too high and immediately says, “We’ll just slap some acoustical tile here and there; that ought to take care of it,” will probably be disappointed at the results.
Not that acoustical tile isn’t a good way to reduce noise – it often is. But this approach is like shooting a person full of penicillin at the first sign of a cold.** The more prudent course is to analyze the noise (either roughly with the sound-level meter, as discussed on page 74, or in detail with a sound analyzer), decide from this analysis what to do about it, and check results by further analysis. This procedure ensures that you’re reducing the noise at the frequencies you’re most concerned with – usually, those frequencies that are about the same as speech frequencies.
The meter can filter by freq, so you have to use those filters as a crude approximation of our PURPOSE filters. The A-weighting filter is closest to the spectrum of speech, so the A is the best setting to measure interference with meaningful communication. The B weighting tends to focus on the upper freq range that is likely to cause damage to the cochlea. C is broadest, covering the whole range of hearing while ignoring freqs that don’t affect the ears at all.
Here Polistra is using a pistonphone to calibrate her 1565A.
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The handbook ends with a poem!
With so much sound-measuring equipment and counsel available, there is no longer any need to suffer the annoyance and hazards of excessive noise. Ry acquiring a sound-level meter, you will take the first step on that golden stairway to the promised land where …
Like beacons on a sea of silence
Life’s silver sounds invade the air:
The wind plays tunes upon the trees,
The stream sighs and from the mountain flees,
The rain’s beat, the phoebe’s call –
Ears were made for sounds like these.
The author isn’t credited, and I can’t find the text online, so it might have been written at GenRad. Do any modern industries have poets on staff, or use poetry in their handbooks? Especially poetry that says ears were MADE? Not even worth asking.
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** Shoot everyone full of penicillin at the first sign of cold: Neanderthal primitive analogy. As we know now, the CORRECT SCIENTIFIC MEDICAL approach is to shoot everyone full of fear and panic and isolation and depression and starvation and darkness and unemployment and screeching hopeless desperation, and then strangle them to death, in order to PREVENT people who were already dying from catching colds in the middle of dying. This is SCIENCE. Back in those primitive Neanderthal times, the primitive Neanderthal knuckle-draggers called our modern progressive methods “human sacrifice” because they were completely uneducated and stupid.
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