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Old 19th September 2005, 02:48 PM   #1
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Default Getting a feeling for bass-resonance

For years I have had a pet-hate for bass-resonance, but only recently have I begun to think about it a bit, so I am interested whether others have too.

The late John Linsley-Hood, in his article about his new hi-fi amplifier design in the early '70's (?) mentioned how inadequate a simple "sine-wave" view of high-frequency response is, preferring to see how good an amplifier was at, say, handling a 10KHz square-wave.

I think that sine-wave response of loudspeakers at the bottom end, is also very limited in it's information.

I tried a simple sine-wave sweep on my very old KEF Concord III's which, I think, have a bass-resonance at about 68Hz. You can hear a bit of a peak around about 68Hz as the sine-wave sweeps past it, but it is not very noticeable. However, if you listen to music, you can much more obviously detect bass-resonance. Why is this?

Consider the simple tuning-fork. This resonates at a particular frequency. But you don't have to "excite" a tuning fork by subjecting it to sine-wave excitation -- you simply have to strike it on a table, and then it resonates. I think that bass-resonance in speakers is similar to this: it can be set off, i.e., induced, by simply a "thump". And like a tuning fork, it carries-on resonating for a while, and THESE TWO REASONS are why it is so noticeable when listening to music, but not when simply applying sine-waves.
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Old 19th September 2005, 03:20 PM   #2
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Room resonances are by far the biggest problem.

I'm not sure if your talking about the room or speaker design introducing coloured bass.

What you say about resonances effecting other portions of the freq. spectrum is true.

Music also contains lots of sounds that will constantly excite that 60hz peak you have despite not being entirely centered around it.

If you run an RTA and watch the line level signal, you'll notice that there's a broad wash of response throughout the frequency range that means problems are rarely isolated to a particular bass drum sound.

If you want to tackle the problem you need to first determine if its the speakers or the room causing the problem. Its almost certainly the room IMO. From there you can fix room related bass inconsitancies quite easily using EQ.
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