Mitigating Acoustic Feedback in Widerange Systems

Soundminded · 14th August 2011, 01:50 PM

After rarely paying attention to them anymore, at least for the last 2 decades, I've dipped my toe again into listening to vinyl phonograph records, at least for the moment. My playback systems are very wide range equalized for flat bass output to the lowest audible frequencies and then some. My best turntable is Empire 698 which has fairly good isolation, its motor, arm, and main bearing mounted on a casting suspended from the main plinth by springs. But it's not enough. Without a bass cut there's acoustic feedback at anything more than very low gain settings. So what's the best strategy for making a platform to isolate vibrations from it? A pillar of concrete blocks? Thick rubber mats? A sandwich of both? Looking for simple practical answers, not expensive audiophile gimmicks that work for some turntables but not others. This one is fairly heavy. If you have a system that has very deep undistorted bass, do you experience this problem and how do you deal with it?

sreten · 02:09 PM

Hi,

You need a electronic rumble filter set around 20Hz, no way round it practically.
Hardly any records have any bass anywhere near 20Hz or below, groove width.
All good RIAA preamps should have one, but sometimes they are omitted.

rgds, sreten.

DSP_Geek · 19th August 2011, 06:39 PM

Just for kicks & grins, try reversing the leads on both your speakers, to see whether changing the phase might help.

Zero D · 19th August 2011, 06:49 PM

Apart from any other suggestions which may also help, a thick piece of foam under the turntable works wonders

in my experience with high powered sound systems anyway. Try it, it's cheap too

DF96 · 19th August 2011, 07:13 PM

Put your turntable on a shelf screwed to a solid brick wall, not the floor.

dangus · 23rd August 2011, 07:59 AM

I've heard that a paving slab supported on tennis balls works well. Or, in a pinch, wrap a bunch of rubber bands over rolls of duct or gaffer tape and suspend each foot separately. Enclosing the turntable in a cabinet should reduce feedback through the air, if that's a factor.

Moving the turntable to avoid room nodes ought to help.

It would be instructive to hook up a sound card or recording device that has level meters and compare the output from a needle sitting on a stopped record (with music playing from a CD), with the normal output level of record playback.

14th August 2011, 01:50 PM	#1
Soundminded diyAudio Member Join Date: Sep 2008	Mitigating Acoustic Feedback in Widerange Systems After rarely paying attention to them anymore, at least for the last 2 decades, I've dipped my toe again into listening to vinyl phonograph records, at least for the moment. My playback systems are very wide range equalized for flat bass output to the lowest audible frequencies and then some. My best turntable is Empire 698 which has fairly good isolation, its motor, arm, and main bearing mounted on a casting suspended from the main plinth by springs. But it's not enough. Without a bass cut there's acoustic feedback at anything more than very low gain settings. So what's the best strategy for making a platform to isolate vibrations from it? A pillar of concrete blocks? Thick rubber mats? A sandwich of both? Looking for simple practical answers, not expensive audiophile gimmicks that work for some turntables but not others. This one is fairly heavy. If you have a system that has very deep undistorted bass, do you experience this problem and how do you deal with it?

19th August 2011, 02:06 PM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, You need a electronic rumble filter set around 20Hz, no way round it practically. Hardly any records have any bass anywhere near 20Hz or below, groove width. All good RIAA preamps should have one, but sometimes they are omitted. rgds, sreten. __________________ There is nothing so practical as a really good theory - Ludwig Boltzmann When your only tool is a hammer, every problem looks like a nail - Abraham Maslow Last edited by sreten; 19th August 2011 at 02:09 PM.

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19th August 2011, 06:39 PM	#3
DSP_Geek diyAudio Member Join Date: Aug 2003 Location: Santa Cruz, California	Just for kicks & grins, try reversing the leads on both your speakers, to see whether changing the phase might help.

19th August 2011, 06:49 PM	#4
Zero D diyAudio Member Join Date: Aug 2009	Apart from any other suggestions which may also help, a thick piece of foam under the turntable works wonders in my experience with high powered sound systems anyway. Try it, it's cheap too

19th August 2011, 07:13 PM	#5
DF96 diyAudio Member Join Date: May 2007	Put your turntable on a shelf screwed to a solid brick wall, not the floor.

23rd August 2011, 07:59 AM	#6
dangus diyAudio Member Join Date: May 2004 Location: Vancouver Island	I've heard that a paving slab supported on tennis balls works well. Or, in a pinch, wrap a bunch of rubber bands over rolls of duct or gaffer tape and suspend each foot separately. Enclosing the turntable in a cabinet should reduce feedback through the air, if that's a factor. Moving the turntable to avoid room nodes ought to help. It would be instructive to hook up a sound card or recording device that has level meters and compare the output from a needle sitting on a stopped record (with music playing from a CD), with the normal output level of record playback.

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