If I can give a personal opinion about sound levels, It seems to me that all what we read about is partial.
Concerning the "comfortable" max SPL level, it depends greatly of the harmonic content and the dynamic, and the time we are exposed. We can afford more high level if basses are present in the musical content than if it is only high medium/treble. We can afford high levels if they are transients.
In the same time, the feeling of distance really depends of the harmonic content of each instrument in the mix. Adding low medium to a male voice, by example, makes-you feel the singer is closer at the same level.
Using a Fletcher and Munson curve to continuously adapt the sound to the position of the volume control, and you will not feel any change, both on the balances and distances of the instruments whatever this volume. But to have to adjust the max volume, depending of the source. I used, in my previous preamp a double volume control in serial: one flat to adjust the volume of the source, and one with the F&M curves to adjust my listening level.
It depends of the age too: I cannot afford and enjoy such high levels than when I was young. And it looks strnage for me, as I probably has lost some "Audibility" with age. Like my eyes don't appreciate high luminosity any more, while my vision of low lights is greatly reduced.
Concerning the "comfortable" max SPL level, it depends greatly of the harmonic content and the dynamic, and the time we are exposed. We can afford more high level if basses are present in the musical content than if it is only high medium/treble. We can afford high levels if they are transients.
In the same time, the feeling of distance really depends of the harmonic content of each instrument in the mix. Adding low medium to a male voice, by example, makes-you feel the singer is closer at the same level.
Using a Fletcher and Munson curve to continuously adapt the sound to the position of the volume control, and you will not feel any change, both on the balances and distances of the instruments whatever this volume. But to have to adjust the max volume, depending of the source. I used, in my previous preamp a double volume control in serial: one flat to adjust the volume of the source, and one with the F&M curves to adjust my listening level.
It depends of the age too: I cannot afford and enjoy such high levels than when I was young. And it looks strnage for me, as I probably has lost some "Audibility" with age. Like my eyes don't appreciate high luminosity any more, while my vision of low lights is greatly reduced.
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Lung power the only rival for a Saturn V... interesting.
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Sat V weighed 2700 tons and produced 3700 tons at lift-off.
So, when the fat lady sings . . . We have lift- off.
For those of you that are interested, I have on my website a report on the Sat V control system and flight dynamic performance written by Walter Haeussermann - one of Von Braun's people.
http://klabs.org/history/reports/tn_d-5869_1970023342.pdf
Amplifier compensation? Try stabilizing a 365 foot 2700 ton rocket with fuel sloshing around in the tanks while the whole assembly is resonating at about 0.1 Hz. Oh, and there 3 guys sitting on the top . . .
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Calibrating an SPL meter is hard to do at home. Just had a look at what was only for modding the radio shack meter and although there are changes to flatten the FR it's not clear what the absolute accuracy is. Suspect my Umik, although it has a cal file is really no better.
Having the closest anyone will ever come to unlimited budget also helped
For those of us who were not there the scale of the achievement is almost unbelievable. They knew that technology was 30 years behind where they really needed it to be, but still went for it and succeeded.Who wants to bother with mechanical VU/peak meters nowadays anyway? Why depend on mechanics when you can do it just as well, and better, with LEDs? If anyone still remembers BGW amps, the display can actually look like a mechnical scale.
Velleman kits produces such meters at very reaspectable prices, 15 LEDs in total. form -40 dB to +6 dB if memory serves.
Velleman kits produces such meters at very reaspectable prices, 15 LEDs in total. form -40 dB to +6 dB if memory serves.
Another crucial distance cue is the recorded material's capture (or synthesis) of reverberation characteristics. In the early days of electronic/tape music, Stockhausen used this quite effectively, e.g. in his Kontakte, using variable reverb to have a "sound object" move from the apparent background to the foreground, or vice versa.
Check out circa 30:30 into this: https://www.youtube.com/watch?v=Y1Psx24n3rM (a particularly blatant example, although he's playing with reverb and lots of panning throughout).
I have no expertise in this but I would have to say from the days of using a tape machine, Revox A77, and other tape machines, at least when looking at a traditional Vu meter you had some intuition of the upper level from the velocity of the needle movement. Now what a series of leds would mean in that respect i can't compare, they could be slow responding or fast but how would you know and how would you have that visual clue of the velocity rate like you did with a true VU meter?
I could understand an led array if it had a measure and hold function that showed a true peak reading or an average reading choice. That would seem to be a more informative type of display, sort of like you have on a read and hold on a DMM where you can capture the peak reading and take a look.
I could understand an led array if it had a measure and hold function that showed a true peak reading or an average reading choice. That would seem to be a more informative type of display, sort of like you have on a read and hold on a DMM where you can capture the peak reading and take a look.
The actual method to calibrate level is to use a pistonphone. This is a sealed chamber with a moving piston. As you know the size of the chamber, the diameter and motion of the piston the SPL can be calculated quite precisely. It will vary a bit with barometric pressure.
You can buy the Bruel and Kjaer version on eBay for around $1,200.00. As this is a standard it does not require calibration.
I bought three of them, they all read exactly the same so I sold two of them as known to be in calibration.
Now with a pistonphone you can calibrate a class 1 sound level meter. This may then be used to calibrate the electronic version of sound level calibrators.
To check the frequency response of the sound level meter you can use a capacitive coupler and a simple sine wave oscillator and NIST or equal calibrated meter.
Now in house we do our semi-annual upkeep, inventory etc. every year on July 4th weekend or between Christmas and New Years.
This summer I did nine sound level meters and two calibrators.
Now the popular low cost condenser microphones are quite temperature sensitive, so they must be calibrated before and often during use. But since you probably aren't measuring a stadium, you might not need to.
Hi Ed,
Sounds like a fair amount of work, depending on the calibrator. Also, many thanks on the condenser mic information. I wasn't aware that they were sensitive to temperature. Thousands are in use, sometimes to determine health and safety sound pressure levels in industrial spaces. The temperatures could vary a lot.
-Chris
Multi-function calibrators or something else. I'm thinking Fluke 5500A,5520A, 5700A or the current model?
Sounds like a fair amount of work, depending on the calibrator. Also, many thanks on the condenser mic information. I wasn't aware that they were sensitive to temperature. Thousands are in use, sometimes to determine health and safety sound pressure levels in industrial spaces. The temperatures could vary a lot.
-Chris
My multimeter is done to NIST traceable by a local cal lab.
Sound level calibrators that go out with the meters. One a General Radio, the other Bruel & Kjaer. Actually have enough junk to build some!
Just got in a new to me HP 54542A 4 ch 500 MHz 2 GS scope. Input 1 had a bad attenuator step. Exercise cleaned it. Once I learn how to use it, should be able to finish my power supply article. Stole it for a bit under $350.00 including delivery. Missing a foot and a chipped plastic front, all easily fixed.
Years ago Harman had a division known as Harman Applied Technology, renamed after Harman Applied Research sounded too unlikely to make money (my surmise but plausible). The division started with funding from Ford, where someone had made a mistaken calculation about the fuel economy attendant on an active muffler system, using a high-temperature-withstanding loudspeaker.
But the august crew ventured into other noise cancellation activities, including auto interiors. When a reorganization put HAT under the management of Harman-Becker, the president of the latter came out to Northridge for a review. He was given a demo of one of the cabin noise cancellation systems. Unfortunately, the vehicle had been sitting out in the sun for quite a while. The sensitivity of the condenser mics drifted a lot, and the system didn't work, in fact I believe oscillated like the proverbial house-a-fire. A bad scene.
The division was shut down not long thereafter, with a clue to this coming beforehand, when that one president referred to it as The Toy Factory to one of the VPs. The latter found another position before the ax fell.
All I can say is that on my Signl Status board, reaction time of the LEDs is 7...9 mS. I strongly doubt one could find analog meters with that kind of response time which wouldn't cost an arm and a leg.
For a full bar meter, this would probably take somewhat longer, but not by much. Not with dedicated circuits like LM 3915/3916 and half baked buffer op amps like TLO7x. Some like them, some hate them, so it's your choice. In my view, the lower the output power of an amp, the more you need them for fear of overdriving the amp input. Also, I find them to very convenient to measure the output of a preamp, also a nice reference to check for overdriving the power amp.
An acquired taste, no doubt, I still love the looks of the old SAE amps. Also, I am very curious, I always love to know what's going on, so in my home made Yugo I installed a slew of gauges: fuel level, engine temp, oil temp, voltage level, oil pressure, a mix of Italian Veglia-Borletti and German VDO instruments.
For a full bar meter, this would probably take somewhat longer, but not by much. Not with dedicated circuits like LM 3915/3916 and half baked buffer op amps like TLO7x. Some like them, some hate them, so it's your choice. In my view, the lower the output power of an amp, the more you need them for fear of overdriving the amp input. Also, I find them to very convenient to measure the output of a preamp, also a nice reference to check for overdriving the power amp.
An acquired taste, no doubt, I still love the looks of the old SAE amps. Also, I am very curious, I always love to know what's going on, so in my home made Yugo I installed a slew of gauges: fuel level, engine temp, oil temp, voltage level, oil pressure, a mix of Italian Veglia-Borletti and German VDO instruments.
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Hi Brad,
Nice 'scope. I recently acquired an Agilent 54642D, so we are looking at similar displays. It's the same sampling as yours, but only two channel. Mine cost me 3X what yours cost you, so you got an excellent deal for sure!
What do you use for a multimeter?
As for the calibrations, I used to work at a lab that accepted that kind of work, but not SPL, everything else that was DC, AC, frequency, pressure, humidity, temperature and resistance. Oh yeah, we checked oscillators too (Distortion). The place was called Transcat.
-Chris
Nice 'scope. I recently acquired an Agilent 54642D, so we are looking at similar displays. It's the same sampling as yours, but only two channel. Mine cost me 3X what yours cost you, so you got an excellent deal for sure!
What do you use for a multimeter?
As for the calibrations, I used to work at a lab that accepted that kind of work, but not SPL, everything else that was DC, AC, frequency, pressure, humidity, temperature and resistance. Oh yeah, we checked oscillators too (Distortion). The place was called Transcat.
-Chris
But as described that is certainly not an 'at home' procedure for the average user! Then again I am sure there is someone on here that has one just for personal use
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