Alex from Oz said:
It's mechanical.
Airbourne is mechanical itself because requires a moving mass to propagate.
Unlike the e.m. field, no vibration will exist in vacuum. The only way to excite the electrodes are the pins.
Airbourne will go through the glass and then to the pins. The lower the frequency the lower the attenuation along the travel.
It is true that the vacuum in the tubes is not absolute but that is a second (or third, possibly) order effect for sure.
Alex from Oz said:
Almost useless if you really want to sort out the problem. At low frequencies you need a damped oscillator loaded with a certain mass (from several hundred grams to several Kilos, depending on the elasticity of practical suspensions) so
that the system can be tuned at the lowest possible frequency and will not pass the higher ones and dissipating the energy only at (actually nearby, depending on the damping) or below its resonant frequency.
45
Exactly.smoking-amp said:
smoking-amp said:
No, it will be even better.
Damping doesn't need to be massive. It is more important you have an elastic suspension, then damping needs just to be minimal. Otherwise the energy dissipation extends in a wider range and you cannot "heal" the lowest frequencies.
45
A few more observations.
I tried the acoustic speaker excitation of the Type 19 tube at a couple of non resonant frequencies to see how much feedthru occurs there (ie. to find the background feedthru level in the previous tracking plots). The spectrum analyser was set to sweep the whole freq. range.
At around 400 Hz, I see a 30 dB peak (above noise) at 400 Hz when the speaker is set to an almost painful volume level. About half that peak at the previous testing level (used for the tracking plots). Around 1500 Hz, I see a 20 dB peak at 1500 Hz with a painful sound level, and about half that at the previous test level.
That should give some indication of tube sensitivity as a general microphone. What I was also interested in seeing was whether a peak would occur at twice the test frequency. I did not find this. At very loud levels I could get a 3rd harmonic peak to rise.
The reason I was interested in checking the 2nd harmonic, is that it seems to me that the filament should be vibrating symmetrically around it's rest position. One would expect that to cause the same affect on the tube current for either direction of filament deflection, since the plate is symmetrically surrounding it. This would then produce the 2nd harmonic of the acoustic signal.
Why it doesn't do this is a mystery to me. Of course the filament could be off center to begin with, so the vibration would be effectively polarized then to give 1st harmonic as it vibrates toward center or away from center position. But I checked the alignment of the filament visually, and it seems pretty well centered to me. But I guess the vibration could be so microscopic, and the off centeredness necessary to polarize to the 1st harmonic would then be too small to see visually.
Don
I tried the acoustic speaker excitation of the Type 19 tube at a couple of non resonant frequencies to see how much feedthru occurs there (ie. to find the background feedthru level in the previous tracking plots). The spectrum analyser was set to sweep the whole freq. range.
At around 400 Hz, I see a 30 dB peak (above noise) at 400 Hz when the speaker is set to an almost painful volume level. About half that peak at the previous testing level (used for the tracking plots). Around 1500 Hz, I see a 20 dB peak at 1500 Hz with a painful sound level, and about half that at the previous test level.
That should give some indication of tube sensitivity as a general microphone. What I was also interested in seeing was whether a peak would occur at twice the test frequency. I did not find this. At very loud levels I could get a 3rd harmonic peak to rise.
The reason I was interested in checking the 2nd harmonic, is that it seems to me that the filament should be vibrating symmetrically around it's rest position. One would expect that to cause the same affect on the tube current for either direction of filament deflection, since the plate is symmetrically surrounding it. This would then produce the 2nd harmonic of the acoustic signal.
Why it doesn't do this is a mystery to me. Of course the filament could be off center to begin with, so the vibration would be effectively polarized then to give 1st harmonic as it vibrates toward center or away from center position. But I checked the alignment of the filament visually, and it seems pretty well centered to me. But I guess the vibration could be so microscopic, and the off centeredness necessary to polarize to the 1st harmonic would then be too small to see visually.
Don
Originally posted by smoking-amp:
"It still needs to be tested whether a headphone (instead of a speaker) affects the sound of the DHT or not. If it does, then maybe sound damping will just kill the magic DHT effect too."
45:
No, it will be even better.
Damping doesn't need to be massive. It is more important you have an elastic suspension, then damping needs just to be minimal. Otherwise the energy dissipation extends in a wider range and you cannot "heal" the lowest frequencies.
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OK, poor choice of words on my part here. The damping should be helpful at reducing the resonances. But the elastic suspension should be effective at eliminating broadband microphone-like pickup. Too much damping would likely conduct more sound thru the suspension.
What I meant was that the reverberation effects would be eliminated by a good isolation or suspension. This might eliminate the DHT effect, especially if the tube has a shield or cage around it to prevent direct airborne pickup. Unknown to me so far.
Don
"It still needs to be tested whether a headphone (instead of a speaker) affects the sound of the DHT or not. If it does, then maybe sound damping will just kill the magic DHT effect too."
45:
No, it will be even better.
Damping doesn't need to be massive. It is more important you have an elastic suspension, then damping needs just to be minimal. Otherwise the energy dissipation extends in a wider range and you cannot "heal" the lowest frequencies.
-------------------------
OK, poor choice of words on my part here. The damping should be helpful at reducing the resonances. But the elastic suspension should be effective at eliminating broadband microphone-like pickup. Too much damping would likely conduct more sound thru the suspension.
What I meant was that the reverberation effects would be eliminated by a good isolation or suspension. This might eliminate the DHT effect, especially if the tube has a shield or cage around it to prevent direct airborne pickup. Unknown to me so far.
Don
Don,
look at the whole thing as a 2nd order low pass filter. If you have less damping you will have more peaking at resonance, however the effective 2nd order filtering will start just above.
If you have more damping the peak will drop but the slope will be smoother and will become 2nd order only at higher frequency.
45
look at the whole thing as a 2nd order low pass filter. If you have less damping you will have more peaking at resonance, however the effective 2nd order filtering will start just above.
If you have more damping the peak will drop but the slope will be smoother and will become 2nd order only at higher frequency.
45
Don,
As you have your testcircuit up and running why don´t do a simple test with both triodes parallelled:
Human flesh is extremely good at damping vibrations
!
The 19 will not be warm so just wrap your hand around it and do the same test as you initially did.
If it makes things a lot better wrt the resonances we just have to find a good damping material that isn´t alive.
As you have your testcircuit up and running why don´t do a simple test with both triodes parallelled:
Human flesh is extremely good at damping vibrations
!The 19 will not be warm so just wrap your hand around it and do the same test as you initially did.
If it makes things a lot better wrt the resonances we just have to find a good damping material that isn´t alive
.
If we go with the idea that some sort of self resonance is creating the "DHT effect", then we find that the more we damp the DHT the better it sounds, and yet it STILL retains that DHT magic - then where does that leave us?
I use two O rings on my 3a5s but I haven't done a careful listening comparison with or without. I also use a massive chassis and there's no buzz on the toroids I use for mains transformers - this is a preampn stage, not an output stage.
So some sort of measurements with different damping would be useful, e.g.
mass - put the socket in a heavy piece of metal
elastic - rubber damping, elastic suspension
Holding the tube in your hand sounds a good idea - they're not hot.
This is a fascinating thread - thanks so much for the measurements
andy
I use two O rings on my 3a5s but I haven't done a careful listening comparison with or without. I also use a massive chassis and there's no buzz on the toroids I use for mains transformers - this is a preampn stage, not an output stage.
So some sort of measurements with different damping would be useful, e.g.
mass - put the socket in a heavy piece of metal
elastic - rubber damping, elastic suspension
Holding the tube in your hand sounds a good idea - they're not hot.
This is a fascinating thread - thanks so much for the measurements
andy
This also argues for building the amp in a soundproof box. Even with chassis-borne vibrations damped, airborne excitation of the tube envelope could certainly be an issue, especially with broadband signals and intermod- this is why I suggested an MLS rather than a swept sine.
Given my speakers' bass capabilities, I'd worry about intermod from seismic excitation. Even with damping, it's like putting the amp on a shake table. Probably not an issue if you're using ESL 57s...
Given my speakers' bass capabilities, I'd worry about intermod from seismic excitation. Even with damping, it's like putting the amp on a shake table. Probably not an issue if you're using ESL 57s...
andyjevans said:
Damping alone is no great improvement, you have to shift the overall damping frequency out of the audio band. The lower the frequency the better it is.
The best air springs can be tuned at 0.5 Hz and are fully effective from 1-3 Hz depending on the other parameters!
If you put the rubber ring on the glass the best you can do is attenuate some of the vibration but not preventing the pins to transfer energy in the audio range to the electrodes, yet.
SY said:
That's why the mass and the lowest possible resonance of the system are required. If you have a massive preamp (in comparison to the single valve) the energy transfer can be only a very tiny fraction of the whole. Whatever it is.....it's a bit like having 1% THD instead of 10% from you amp...actually even better.
SY said:
The table can shake only according to its vibration modes and if the coupling is subsonic and elastic then will stand still in the band of your interest (in the sense of relative motion)
The idea works in general: the atomic force microscope would never work without such suspension. Here you have a tip (made of no more than 2 or 3 atoms!) scanning the surface of a material down to very small distances (for tuning the tunneling effect of the electrons respect to what you want to look at).
Cheers,
45
How about an aerogel box around the tube, suspended by sorbothane. With tiny #40 flexible wire electrical connects, coiled into helixes. Or,... anyone up to doing a shuttle trip to the space station (no air, no gravity, floating....)?
I'll try holding the tube and running the speaker test again. But I don't think thats going to be too popular with listeners (150 V).
In my thinking there are two phenomena of interest. One is the tube resonances. (I HAVE to hear what that magic gong tube sounds like in a preamp.)
The other is just broadband acoustic pickup, like a microphone, which could be producing reverberation like effects from acoustic delay.
A listening test with headphones could considerably narrow the focus here. Or it could throw everything up in the air again if it has no effect.
Don
I'll try holding the tube and running the speaker test again. But I don't think thats going to be too popular with listeners (150 V).
In my thinking there are two phenomena of interest. One is the tube resonances. (I HAVE to hear what that magic gong tube sounds like in a preamp.)
The other is just broadband acoustic pickup, like a microphone, which could be producing reverberation like effects from acoustic delay.
A listening test with headphones could considerably narrow the focus here. Or it could throw everything up in the air again if it has no effect.
Don
smoking-amp said:.... tiny #40 flexible wire electrical connects. Or,... anyone up to doing a shuttle trip to the space station (no air, no gravity, floating....)?
You are almost on the right way Don!
:Wrap the tube with 2 semi-cylindrical lead plates and suspend the whole thing from the plates with the elastic wire to another very rigid support.
Remember that, except for the suspension, the higher the rigidity of the system the better it will work.
Check (the system has to work at subsonic frequency): pull down the whole thing and simply count the oscillations as long as you can do that and taking notice of the time.
This is the best thing you can do with little stuff and it certainly works as it has already been done by someone else......
Cheers,
45
"Wrap the tube with 2 semi-cylindrical lead plates (using a proper metal spring to keep them around it) and suspend the whole thing from the plates with the elastic wire to another very rigid support. ...... pull down the whole thing and simply count the oscillations as long as you can do that and taking notice of the time."
Hmmm...., gravity wave detector mounts, LIGO..... magnetic levitation of a marble slab.
As soon as I get my $10B bailout check..... Maybe a couple more weeks they'll get down the list to me.... hopefully before the $ printing press breaksdown.
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On the headphone test, I was just thinking. The listener should use headphones to listen to the preamp with the speakers still connected, then with the speakers disconnected. But always listening thru the headphones for consistency (maybe sitting in the next room).
Don
Hmmm...., gravity wave detector mounts, LIGO..... magnetic levitation of a marble slab.
As soon as I get my $10B bailout check..... Maybe a couple more weeks they'll get down the list to me.... hopefully before the $ printing press breaksdown.
-----------------------------------------------------
On the headphone test, I was just thinking. The listener should use headphones to listen to the preamp with the speakers still connected, then with the speakers disconnected. But always listening thru the headphones for consistency (maybe sitting in the next room).
Don
Well, first I put a 3/8 inch light foam pad around the tube and tied it up with a small elastic band which was used to support the assembly also. Doesn't look like it helped at all, maybe even worse.
--------------------
"Magnetic coupling doesn't work!"
after all those billions $, no gravity waves yet either.
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"Magnetic coupling doesn't work!"
after all those billions $, no gravity waves yet either.
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Next I put a wet, size 12, sock around the tube and suspended that with the foam and elastic as a sling around all. (takes like 5 minutes to scan the freq. slowly, I couldn't hold it steady that long)
Seems to have helped some, but nothing miraculous. I wonder now if the height of the resonant peaks is consistent, maybe random phase shifts between the freq. sample tests interact with the high Q resonances to alter responses. I'll try the last one again to see if its consistent.
Seems to have helped some, but nothing miraculous. I wonder now if the height of the resonant peaks is consistent, maybe random phase shifts between the freq. sample tests interact with the high Q resonances to alter responses. I'll try the last one again to see if its consistent.
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