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Subsonic Filter |
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Posted: 25 Aug 2016 at 3:38am |
Well done!
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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GrahamD
New Member Joined: 13 Feb 2015 Location: Auckland NZ Status: Offline Points: 34 |
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Well, in the absence of further advice I went ahead and changed the resistor value to bring the turnover closer to 20Hz.
I had a couple of 270k resistors available and according to the advice given these in parallel with the amps 100k should result in 73k which with the 0.1uF capacitors results in 21.8Hz with a 6db/octave slope. It certainly sounds fine to my old ears as I can't detect any difference in the sound switching it on or off but a noticeable reduction in cone movement at these low frequencies. I am very pleased with outcome as I only wanted a very simple and non-intrusive filter that I could activate when required with little or no impact on the music. Cheers Graham Edited by GrahamD - 25 Aug 2016 at 2:08am |
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GrahamD
New Member Joined: 13 Feb 2015 Location: Auckland NZ Status: Offline Points: 34 |
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Thanks for the input guys.
I must admit I never considered the lack of damping provided by valve amp transformers. What value resistor do you suggest Graham to bring the turn over closer to 20Hz ? The records in question are not warped, in fact my Oracle Delphi has a record clamp, it seems to be recorded into the 'groove'. One of the culprits is a brand new pressing of Dave Gilmours Rattle That Lock. The first track on side one really gets the cones flapping. Cheers Graham |
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Richardl60
Senior Member Joined: 04 Nov 2014 Location: Yorkshire Status: Offline Points: 1468 |
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Another angle. If this relates to a small number of records are they warped? If they are can they be flattened to reduce this issue?
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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-3dB turnover frequency 37Hz, 0.1u into 43k (75k || 100k). Slope of filter 6dB/octave.
Agreed, damping factor (or should we call it driving impedance?) isn't much from an output transformer, and as such "sod all" is appropriate wording. Reflex "loading" allows the driver to resonate (pump) at its resonant frequency and a complete lack of damping will allow large cone excursions, but I would have thought the manufacturer would have taken that into consideration so as not to "bottom out" on its suspension. Then again, Chris says these are designed using amps with a stiff driving impedance. It's always a good idea to do a lot of research before buying, but some manufacturers don't give the full details these days. And therefore I should remark that the Proprius also has sod-all damping factor Based on common knowledge it is around 4 at 20Hz. I say common knowledge because some rubbish the whole idea of damping factor. Back emf is the release of inductor energy once the drive has been removed, but as the amplifier is now driving in the opposite direction the maths will be a little more complex, and a factor of 4 might be a long way off. I once connected a DC coupled amp to a drive unit and tapped the cone and then repeated it after disconnecting the amp. My ears heard no difference. No change in cone excursion. Which suggests that simple calculation is not indicative of the amplifier's control over the cone. Also being old enough to have only had analogue tape or vinyl sources, cone flap was not considered out of the ordinary. In fact one expected to see it and when not there we thought something must be wrong |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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BackinBlack
Senior Member Joined: 05 Feb 2012 Location: Hinton, N'hants Status: Offline Points: 2020 |
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Another cure - 2 x Proprius to keep them cones under control
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Just listen, if it sounds good to you, enjoy it.
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Chris Firth
Moderator Group Joined: 16 May 2013 Location: Rossendale, UK Status: Offline Points: 1529 |
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... and therein lies your problem. Cone flap occurs with bass reflex speakers, and isn't as much of an issue if your amplifier has a high electrical damping factor. MA tend to use big solid state power amps with high damping factors when they design their speaker models. Your amp effectively has sod all electrical damping factor, which in turn means that the back emf from your speaker drivers will have an effect on the signal. The cure is to get a loudspeaker that is mechanically well damped, and has a relatively benign load. |
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