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Charles

Noise at low SPL

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I'm hoping that Ricci or others with more experience with high end, high efficiency drivers can help solve an issue I am having:

My subwoofer uses B&C iPal drivers.  When there is bass content at a very low SPL level (barely audible), the bass sounds scratchy.  It is almost like there is static in the signal.  Turning the volume up to a more moderate SPL level eliminates the noise and at very spirited levels, it sounds fantastic.  Luckily, this exact scenario is very rare during normal listening but it does occur in scenes where the SPL of the bass content is very low like distant background music.

Is it possible that what I am hearing is the result of the high efficiency of the drivers themselves?  My thought is that at very low signal levels, the signal to noise ratio reaches a point where noise that usually wouldn't be heard becomes audible.  Because the drivers are very efficient, they are able to pickup this very weak signal and produce noise where lower efficiency drivers would remain silent.  If that isn't the cause, what might I look at?

I have already tried different receivers, cables, power source, amplifier, etc.

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Do you hear any scratching or feel it rubbing if you gently push in on the cones? Is the sound more similar to a tapping sound or a ticking? Myself and some others did receive some 21Ipal's which were making a tick or tap type of sound. B&C replaced mine. I suspect that it comes from a loose shorting ring, but I'm not sure. It sounds like you may have the same issue. 

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7 minutes ago, Ricci said:

Do you hear any scratching or feel it rubbing if you gently push in on the cones? Is the sound more similar to a tapping sound or a ticking? Myself and some others did receive some 21Ipal's which were making a tick or tap type of sound. B&C replaced mine. I suspect that it comes from a loose shorting ring, but I'm not sure. It sounds like you may have the same issue. 

I don't hear any noise when gently moving the cone.  In fact, when the noise occurs, the cone really isn't moving because the SPL level is very low.  The only time the noise occurs is when the driver is playing something, but at a very low level.  I wouldn't describe it as tapping or ticking, more like a slight popping like a radio station that is not quite tuned in.  These are 18 inch iPal drivers.  Do you have information on the issue you experienced that I can reference?  The sub has 2 drivers and the noise comes from both of them which is why I didn't suspect a driver issue.

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From your description, I'd be more inclined to suspect something going on with electronics.  It's almost like there is noise in the signal chain but a muting circuit is acting to stop it the noise until sound starts playing.  Then at higher levels, the sub is music enough that the noise is drowned out.

What kind of electronics are you using?  This is a bit of a stretch, but it's possible what you're experiencing could be caused by numerical precision issues in the DSP, hence it's more pronounced at lower signal levels.

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