R-e/p: What docs it? Is it the thin cone?
GA: It’s hard to know. Theoretically, yes, it’s the fact that the speaker is not as well behaved as another kind of speaker. But how well behaved any monitor is at the levels some mixers run is a moot point in itself.
R-e/p: What role docs the floor play, insofar as low end is concerned, at least the area of the floor that the console and mixer are on? Do you do any thing special with that, or are there special problems that can develop with it?
GA: Problems can develop. Although it’s not really as serious as a lot of guys like to think. There seems to be a lot of mystique about the platform. And engineers will go in and thump 011 the floor, and if they feel it give, or if they hear it resonate, they figure, “Well, this is bad.”
“We’re not going to get any bass.” Well, maybe, maybe not. If it absorbs some bass you’ll really get more, at the console location. In general, we try to keep the platforms rigid; we try to keep them non- absorptive. In this case there was no change made in the existing platform. It was solid, it was well done, so it was left alone.
R-e/p: What about the decision to use bi- amplification? Is it necessary?
GA: The system is bi-amplified using a specially designed, phase-compensated low-level crossover circuit.
It helps give us a smooth transition from woofers to mid- range drivers, and avoids the common sag in power response through the 300 Hz region exhibited by many studio monitors.
R-e/p: George, thank you very much for going into this kind of detail with us. There are a few general questions we have. Everybody talks about a sound pressure of 100dB or 110dB. What scale are you using?
GA: Ok. The accepted scale on which all these SPL figures are given is basically simple, and it’s a standardized one. It starts from 0, and 0 is about the softest sound that a very young person with very good hearing can possibly hear.
For most of us, in real life, the softest sound that we are apt to be able to hear is somewhere around 10, +15dB. In terms of actual power, 0dB is 0.0002 dynes/square cm., which is now called 20 micronewtons/ square meter.
Everything is based on that, all the sound level meters are calibrated to that. Now, there’s one other thing. You can either throw in a weighting factor or not. In community noise measurements, it’s almost always used with an “A” weighting characteristic, which tends to emphasize the middle frequencies where your ear is more sensitive.
For most studio use, where you’re talking about monitors, we use the broad band spectrum, since this is what you’re reproducing. In this room for example, any one of those speakers can develop something over 110dB SPL at the console on musical material.
R-e/p: Another subject. Can distortion in the program material adversely affect speakers at high power levels?
GA: It can. I can think of a couple of situations in which it might. One is the situation in which, let’s say, all the low frequency distortion products get transferred to the higher frequencies and help blow out the tweeter.
The other is sort of the inverse, and that’s the kind of wild gyrations a given amplifier may go through once it’s been driven into clipping and has to recover.
If, as some of the famous old hi-fi amplifiers that we remember, the thing goes into a 5 cycle oscillation and starts sending horrendous currents through the whole speaker system while it’s settling back down again, it might very well do some funny things to the speaker.
R-e/p: Is there any sort of circuit that doesn’t distort your sound or limit levels, where you still have full protection from blowout?
GA: To the best of my knowledge, it’s like putting a governor on the car, there is no way that you can protect the speaker without limiting the level that you might otherwise get out of it. So what I much prefer to do is the same thing we did here. You just build in enough overload margin that, unless something literally blows up in the place, they simply are not going to blow out the speakers.
R-e/p: Thank you again George for contributing some very informative background on control room IS, and on room design in general.
Editor’s Note: This is a series of articles from Recording Engineer/Producer (RE/P) magazine, which began publishing in 1970 under the direction of Publisher/Editor Martin Gallay. After a great run, RE/P ceased publishing in the early 1990s, yet its content is still much revered in the professional audio community. RE/P also published the first issues of Live Sound International magazine as a quarterly supplement, beginning in the late 1980s, and LSI has grown to a monthly publication that continues to thrive to this day.
Our sincere thanks to Mark Gander of JBL Professional for his considerable support on this archive project.
