rzdz@fluke.UUCP (Rick Chinn) (02/14/85)
Since this old subject has reared its ugly once more, I feel compelled to
add my 3 cents worth.
First, kudos to Dick Grantges (hound!rfg) for his comments on phase shift,
etc. It's nice to see the horse pulling the cart.
Now its time to dispell some myths:
1. yes, an equalizer will help you flatten the frequency response of
your system.
2. yes, a real-time-analyzer (rta) will help you adjust your equalizer
to attain flatness.
3. both #1 and #2 can improve the loudspeaker/room/listener interface.
4. contrary to popular belief, flat is not beautiful, nor desireable.
5. if you simply equalize your system to flat using an rta and an
equalizer, you won't like the sound.
Here's what you need to do (if you feel you must):
1. hook everything up. turn it all on.
2. pick a reasonable volume level for the pink noise. it should be
high enough to overcome any local ambient noise.
3. use the crossover controls on your speakers to level the curve out
as best you can.
4. now use the equalizer to further smooth the curve. Start at the
largest peak (note *PEAK*). You may have to use two adjacent
sliders to remove it if it's bandwidth is greater than the
bandwidth of an individual band on your equalizer.
5. ignore any dips in the response if they're greater than 6 dB.
fortunately (for you), the human ear hears excesses better than it
hears absences. Going after huge dips wastes power and causes
excessive phase shift. If the dip is caused by diaphragmatic
absorption in your room, then you could pour tons of energy at it
without appreciable benefit. (the dbx automated equalizer doesn't
know this.)
6. now that your system is relatively flat, introduce a controlled hf
rollof into the overall response. there is a lot of discussion over
where to begin the curve. I'd say between 3 and 8 khz, around 1 to
3 dB/octave. Try using the tweeter level control on the speaker
first. If your crossover is in the midrange, then this could be an
easy way to introduce the required rolloff. Otherwise, do it on the
equalizer.
7. Remember flat isn't beautiful, but smooth is the name of the game.
8. If your listening room is an acoustical toilet (cesspool, etc.)
then what you need is dynamite rather than an equalizer.
Sorry to burst the bubble, but someone had to. I have many equalizers and a
spectrum analyzer (rta). I use the equalizers to "fix" bad recordings and
the specrum analyzer to observe the spectral balance of program material. I
don't really care if it is *flat*, just smooth and listenable (and
occasionally very loud).
Rick Chinn
John Fluke Mfg. Co MS 232E
PO Box C9090 Everett WA 98206
{ihnp4!uw-beaver, ucbvax!lbl-csam, microsoft, allegra, ssc-vax}!fluke!rzdz
(206) 356-5232
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