GoodSoundClub - Romy the Cat's Audio Site - Suggestion for teting acoustic feedback

Analog Playback
Topic: Suggestion for teting acoustic feedback

Page 1 of 1 (5 items)

Posted by Romy the Cat on 11-01-2010

The lower bass configuration in my room is a bit interesting below is the bass diagram (under 50Hz)

As you can see the allocation of hot bass sports is superbly favorable in the room. There is pretty much no bass anywhere in the room, in fact in the hoarse, besides an area in close proximity to my listening spot. Walking around the room I feel not bass but sitting in my listening chair I get it on fill bloom. That is a pure lack and I did absolutely nothing to get this result – it just came with the room.

Currently the lower bass is produced by two bass towers (marked with number 1 on the schematic), each of them has 4 10” drivers; they are crossed at 28 Hz. I am planning to ad two more drivers per channel and put the bass modules in the second active location (marked with number 2 on the schematic). This would substantially reduce the exertion of each driver and will work very well in the room. The location of the bass section #1 and #2 are not too abstractive and even though they are large modules but they are not truly demanding in the room. They are for instance not visible from the listening position…

So, from bass perspective the room turning out to be very comfy but there is one ugly moment. The maximum bass pressure my room develops at the very precise location where my turntable setup lives (red things in the left corner). The turntable is atop Vibriplane, Vibriplane is atop fo 1000 point stand and the TT itself has a LOT of mass but I am sure that this concentration of airborne pressure do affect tonearms. So, does anyone know any methodology that would allow me to test the exposure of my analog setup to airborne vibrations? I can invent my methodology but I think some know-how shall exist already. I wonder if measuring the tonearm resonance frequency with ULF channel on and off might be a valuable test? When my analog will output 9Hz then in the space around TT will be a good +30dB at 25Hz and it has to affect something….

The Cat

Posted by JJ Triode on 11-02-2010

Romy,Choose an LP with considerable low bass information, and record it to digital the best way you know how, but with the Melqs not even turned on (or running at very low SPL.) Then compare play of the LP at high SPL with the digital playback at the same volume. The LP will now get feedback effects to the TT but the digital will be largely immune. The delta between them will be a measure of the TT microphonics (I assume the delta due to your best digital record/playback cycle is negligible, I think you said so.)Cheers,JJ

Posted by Romy the Cat on 11-02-2010

Very good idea, I like it. I had the similar idea but liseniing you I think I come up with better then I had before idea how to compare the results. This is not so simple question.

I am sure one can just listening the samples but I think this is what I do not want to do this time but I would rather have objective evidence. I might get two digital files made as you proposeed and then to built from them a 3D spectrum analyses.

I can change the viewing angle in the 3D spectrum analyses and to perform analyses dedicated over any bandwidth. This is very indicative tool and it will show all difference, it is what I most like will be doing. Again, I like this approach.

My own idea how to do detect the auburn pressure was similar but different. I was thinking to record two dual mono samples as you proposed and then run them to a scope. Right and left channels with a dual channel scope with viewing subtraction one from another will essentially visualize antiscating. So, my presumption was that airborne pressure will blow antiscating and rock the tonearm that shall be viewable on the scope.

The Cat

Posted by rowuk on 10-04-2014

I recorded the LPs (Bruckner7-TeDeum Concertgebouw/Haitink, Also Sprach Zarathustra Chicago/Reiner - 1954) to digital. Then I lowered the stylus on to the record, but did not have the turntable turning. I played the digital copy at a bit more than my usual volume. The output from the stylus is the resonance picked up at the TT. I repeated this for various positions on the record. The highest resonance was at about 30% from the outside edge of the record.
Moving the TT on the rack changed nothing. Moving the speakers a couple of inches helped quite a bit. What I measured/changed did not have a BIG effect on the sound on most of the program that I listened to. I suspect that the "improvement" at the turntable moved the standing waves in the room and masked the effect at my listening seat.

Posted by mem916 on 10-14-2014

I recorded the output of my cartridge/ phono stage/ line stage with the stylus resting in a groove of a stationary record while playing a CD at high volume with heavy bass through another path. Since my system uses tubes I was also getting tube microphonics of course.
One of these days I will re-do this test and play an unmodulated test track as I suspect that is more realistic. Comparing the spectrum analyzer plots of an unmodulated track with and without the high volume air and floor born vibration hitting the system should reveal the degree of the problem.

Page 1 of 1 (5 items)