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In Reply to: Isolation posted by lipmanl on May 4, 2007 at 10:44:32:
You're right! all turntables in a soundfield will reproduce acoustic feedback to one degree or another. I ran some tests on mine a while back.I had thought about putting my turntable in another room, but my house is small and I don't think it would totally eliminate the problem. However, it is easy to do this without introducing noise or other losses. Simply locate the phono section next to the turntable and run balanced interconnects from the phono section to the control preamplifier. I don't think there would be any sonic degradation in running 50-feet of Monster Cable Studio Pro 1000 from my Pass Labs XOno to my Pass Labs X1.
You're other idea:
> to put the turntable in a sonic crypt, something like a coffin that the turntable
> fits in and, when playing, closes, isolating the turntable from the sound field.This seems to me to be a bit cumbersome and impractical.
There is a third option that I use.
You can copy your vinyl to digital with the speakers turned off and then play back the recordings without the slightest hint of acoustic feedback. This method works very well for me. Furthermore, it is much more convenient to play a CD-R than to play a vinyl record. It is also kind of fun making the recordings.
This procedure does work really well. I copied some material from a Reference Recordings LP that contained substantial bass with my speakers playing and again with my speakers off. Then I played back the digital copies for comparison. The one with speakers off sounded exceptionally clear with tight, clean bass. The other sounded somewhat blurred in comparison, but still quite nice. In fact, I can see how some people might even like a bit of acoustic feedback because it tends to augment the bass. However, I prefer the added transparency and clarity when acoustic feedback is totally eliminated.
Follow Ups:
here's an even more interesting experiment. put the needle in the groove of a stationary record as you did, but send the signal into a high quality tape recorder. then walk around, clap, sing, speak loudly, etc. while you are recording with the needle in the groove.guess what you will hear when you replay the tape.
This is very cool. I would have expected the peaks from 40-150Hz as those could be caused by woofers bouncing your floor around(I have a serious problem with a suspended floor under my subs). The others are a bit bewildering, especially that whole slew of peaks from 400 to 600Hz which should be in the upper range of male vocals. Do you have any ideas? From what you are saying; there is an audible improvement from playing CD's recorded with no speakers playing vs. with the speakers? I can see that you measured such a difference.
So, is it logical to conclude:1) Recording vinyl to CD in this manner then playing the CD, assuming the equipment is good, might produce a result that is audibly better than playing vinyl directly.
2) People who prefer the sound of the vinyl directly may in some instances unknowingly like it because they like the sound of the feedback (a little bit of reverb?)
Do the measured levels of feedback indicate much about how audible an effect this is?
The feedback probably varies quite a bit with cartridge, tonearm, turntable, support, speakers, placement etc. Have you got or seen any measured data from other systems?
> So, is it logical to conclude:
>
> 1) Recording vinyl to CD in this manner then playing the CD, assuming the equipment
> is good, might produce a result that is audibly better than playing vinyl directly.Yes, from the standpoint of totally eliminating acoustic feedback.
> 2) People who prefer the sound of the vinyl directly may in some instances unknowingly
> like it because they like the sound of the feedback (a little bit of reverb?)Yes! They might also like harmonic distortion and other audible artifacts from RIAA equalization, etc. Vinyl produces significant distortion compared to digital and the characteristic sound of vinyl is based on all of these distortions.
> Do the measured levels of feedback indicate much about how audible an effect this is?
Certainly! All distortions in vinyl make an audible difference!
Unless you believe that distortions in the range of 1% to 10% are inaudible, then distortions in vinyl must make an audible difference because many of them exceed 1%.
On the other hand, distortions in digital fall below 0.01% in nearly all cases. That means the distortions are at least -80-dB, which is totally inaudible. That's why I can copy an LP on my Masterlink and hear absolutely no difference whatsoever.
> The feedback probably varies quite a bit with cartridge, tonearm, turntable, support,
> speakers, placement etc. Have you got or seen any measured data from other systems?No! Why don't you measure your system's feedback and distortion and show me the results.
Best regards,
John Elison
Thanks John. Its great that so far at least response to this thread has been pretty constructive.I'd love to measure the feedback on my system but right now all I've got is a Radio Shack SLM. Hopefully one of these days I will get set up to do it. I suspect it would quickly lead to some long nights rearranging my layout.
David
Excellent experiment. Could you please tell me what program you used to do this? Could I just use my RTA program and plug in the output of the phono stage where I usually plug in the microphone?I wonder if it would not be better to do this while tracking a blank groove. The rotating platter and bearing might affect (hopefully diminist) the feedback.
I use Sound Forge software, which contains a spectrum analyzer function. First, I copied the output from my phono preamp to 24/96 high-resolution digital using an Alesis ML-9600 Masterlink. Then I transfered the digital files to my computer for analysis in Sound Forge.I never tried this experiment while playing an unmodulated groove, but you are probably correct that the vinyl noise floor would be higher and tend to mask some of the feedback.
signal is getting in to your system?
Well, the answer is yes and no!It's obvious that the 60-Hz signal is coming from my line frequency. ;-) However, I don't know if it is introduced into the system by an external source or whether it is simply transmitted through the phono preamplifier's power supply as a result of its design. All I know is that it is totally inaudible and insignificant.
At one point I thought it might be coming from my TV cable because I do get an audible hum through my digital components, which are connected via unbalanced interconnects. When I disconnected the TV cable, the hum went away. Consequently, I made some recent measurements with my TV cable disconnected to see if it made any difference in my vinyl front-end. Unfortunately, it didn't.
Here are these more recent measurements. The first is the noise floor with my tonearm sitting in its rest.
The next is with the tonearm sitting on a stationary vinyl LP.
There is virtually no difference between these two above as can be seen from the following graph of the two superimposed upon each other.
Now, let's play a record. This is the zero-dB reference level of vinyl at 1000-Hz from a professional Denon test record. Notice the arm/cartridge resonance just below 10-Hz and also notice the 50-Hz spike from the 50-Hz line frequency in the country where the test record was made.
Okay, the finale! Here are all three curves superimposed upon each other.
nt
with a CD playing to measure the effect?
To measure what effect? If you are talking about acoustic feedback on a CD player, there is none. ;-)
.
No, I did not re-run the acoustic feedback tests like the one below. I'm sure it would look similar, thought, except in color. ;-)
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