Microphony

[Blzebub]

I tried some of Buns old mana a couple of years ago, I recal it sounded fantastic.
Loads more detail, loads more everything.
Took it out to check.
Still sounded fantastic. All the detail and everything was still there!
Whoah
And guess what?

Still sounding fantastic with different equipment. In a different house.
Freaky. Man.

The stuff just completely bucking woerks.

In the absence of actually getting off our arses all we have are graphs and measurements to show the girth of our weenies. I'm terrified to share my graphs for fear y'all might tsk at its weenielessness.

There's no way you wanted the Mana to work. And now you have a French iPod with some really bad monitors.

 

[Tony L]

Aha, so you have to "want it to work"! File under 'faith based system'!

 

[PsB]

I've ever understood how microphony could appear in solid state amps or pre-amps unless there is a duff solder joint somewhere, and nobody has ever demonstrated it to me. I have heard plenty of microphony effects in HF or VHF applications, but that is a completely different environment. I don't think a properly built valve amp should be sensitive to it either at normal listening levels, provided the valves are secure in their sockets.
Turntables, cartridges, tone arms and tuners are a different matter.

 

[davidsrsb]

I've ever understood how microphony could appear in solid state amps or pre-amps unless there is a duff solder joint somewhere, and nobody has ever demonstrated it to me

Strain gauges - bend a pcb track with current running through it and the resistance varies. Some chips can get input offset shifts by stress on the lead frame.

It happens and is a pain measuring low frequency signals in industrial environments. Actually happening in a well layed out audio pcb is unlikely

 

[MartinC]

I've ever understood how microphony could appear in solid state amps or pre-amps unless there is a duff solder joint somewhere, and nobody has ever demonstrated it to me. I have heard plenty of microphony effects in HF or VHF applications, but that is a completely different environment. I don't think a properly built valve amp should be sensitive to it either at normal listening levels, provided the valves are secure in their sockets.
Turntables, cartridges, tone arms and tuners are a different matter.

Capacitors can be quite microphonic. Years ago when testing a Naim preamp with a sine wave input, the interstage coupling caps (tatalums) would mechanically emit the same frequency. I am guessing that the solid tantalum caps may exhibit some piezoelectric behavior.

 

[bownose]

Yay for French iPods... I use four screws to hang my Devialet securely to a wall: all that is needed. Stand religion in this day and age... Keep bashing those rocks together, guys.

 

[PsB]

Capacitors can be quite microphonic. Years ago when testing a Naim preamp with a sine wave input, the interstage coupling caps (tatalums) would mechanically emit the same frequency. I am guessing that the solid tantalum caps may exhibit some piezoelectric behavior.

Interesting, but the test would be to subject said capacitors to a sound wave (say a loudspeaker blaring a sine sound wave) without any signal into the preamp: do you get an electric signal at the pre-amp output? If so, what sort of signal and is it strong enough to be of concern?

 

[PsB]

Strain gauges - bend a pcb track with current running through it and the resistance varies. Some chips can get input offset shifts by stress on the lead frame.

It happens and is a pain measuring low frequency signals in industrial environments. Actually happening in a well layed out audio pcb is unlikely

Quite.

 

[davidsrsb]

Capacitors can be quite microphonic. Years ago when testing a Naim preamp with a sine wave input, the interstage coupling caps (tatalums) would mechanically emit the same frequency. I am guessing that the solid tantalum caps may exhibit some piezoelectric behavior.

I have heard singing capacitors in switched mode power supplies many times, but the ripple currents involved are in Amps. To work as a microphone, the capacitor must have a significant dc bias. The effect is very inefficient, so only likely to happen in phono preamps, especially single ended designs with a large dc shift right at the input

 

[BE718]

Could vibration affect the interconnects - not the cables, but the pin/socket interface? Naim seem to think it does, but has anyone looked at this?

I doubt whether acoustic vibration has any significant effect on anything at all, but there's structure-borne environmental vibration, and intrinsic vibration generated inside the various boxes. The most extreme form of this is the stylus in the groove.

Its possible, but a competently designed connector should not have a problem. Cables can and do have problems, do a search on triboelectric noise.

This can be a big pain in instrumentation (specifically charge type accelerometers I used a lot in aero engine testing) but less so in other simple voltage signals (as per hifi)

However its got to be said that the vibration levels youll experience in a domestic environment are so low that no-one should consider even thinking about either of these, connector or cable, as a problem.

Its simply a non issue.

edit: I will add one caveat to that - high level signals. Turntables cables have more potential to be problematic. BTW you can buy cable that is specifically designed to overcome this issue with very tightly constrained conductor/insulator geometry.

 

[BE718]

I'd say you need more extreme conditions, because simply measuring the effects in normal use at normal listening levels will invite the myriad cares of 'yeah but if you did this' the results would be different.

You need to show that typical usage conditions fall below the threshold of results obtained from a more extreme test. For that reason I used a pre amp with lots of gain, (and lots of components in the signal path), recorded into a digital recorder using maximum gain, and then applied further gain in software. All tied to a music signal at a painfully high SPL. If under these conditions there is no output, we can safely conclude that no output would also be the result in all normal domestic conditions.

The signal source needs to be wide-band IMO, both noise and music.

Have to say I'm not sure where you are all going with this.

What are your vibration limits? ie what is the maximum and at what frequency?

Its not a question that can be answered. Different equipment will be affected differently.

Each stand will have its own vibration response. This will depend an a number of factors including the size and weight of equipment it supports.

Different floors will transfer vibration differently etc etc etc - too many variables.

The vibration levels I measured at the start of the thread are so spectacularly low that I have little doubt there will be zero effect on the amplifier when I test its electrical output later in the week. For competently designed solid state kit its just a non issue.

Turntables and valves will be more susceptible.

 

[BE718]

That would definitely be worth trying.

The addition of 2 accelerometers and logging equipment could allow us to measure some interesting results.

BE 718, is there any cheap(?) logging equipment available for purchase?

well.......in a word..... no....


you are talking thousands for something basic and low performance with accelerometers.

I used a CSI 2130 to take those measurements, its actually discontinued now. Its replacement, the 2140 starts at around $30000.

 

[cooky1257]

I'm looking forward to the results.

 

[BE718]

I would like to echo others in thanking BE718 for his efforts.

Why I think the use of a shaker plate might be useful is to demonstrate an effect in extreme circumstances. If no effect can be detected then the theory (of the damage microphony can do to a signal) is flawed.

If microphony has no effect on what we hear, how then do isolation products work, if indeed they do. By isolation products I mean anything from cones, sorbothane, equipment feet, racks etc..

indeed...perhaps they dont

Hard cones dont isolate anything. Any rubber type device will only operate over a certain range of frequencies, which will also be effected by the mass of the object on top........

None of that, even if it does work, will stop the directly induced acoustic vibration...........

 

[Purité Audio]

Isolation can be effective, a visco elastic material of the correct durometer and 'height' ,properly loaded ,or active tables designed for nuclear force microscopes, under the correct conditions.
The rolling air diaphragm platform I use here under my turntable, is effective from a handful of hertz up.
Keith.

 

[BE718]

One thing I'd be interested in proving/disproving is the notion of a "feedback loop" as mentioned in the other thread, i.e. try to establish if the energising frequency can be found at all on the sound output (assuming of course any effect was present at all). As an example if one were to place say a tube preamp on an upturned bass amp or sub-woofer and run a loud 50Hz sin wave through it would you actually measure any 50Hz signal on the preamp's output? A feedback loop occurs when a microphone is able to hear it's own output which is then reamplified, i.e. the input must hear and respond to the output frequency it is generating. I very much suspect that equipment "microphony" doesn't work in this manner, especially not at anything that could be classed as room-node frequencies (again as suggested in the other thread) - if you tap a tube you'll get a high-pitch 'tink' or 'ting' sound, not a bass frequency, so I don't see how this could ever howl-round/feedback.



Unquestionably an issue, this is an area where microphony is a given. Record decks do all suffer from feedback to some greater or lesser degree dependant on design and installation. In fact I suspect most of the differences between decks that rotate at the right speed are down to their stability and isolation. Many ways to skin that particular cat.

PS LOL at CG's '+1' post!

In you example with tube amp and sub, then yes you absolutely would. I dont need to test this, we know microphony is real. But that would be an extreme and fairly unrealistic test.

I think this really needs to be broken down into three discrete sections :-

• solid state amps
• Tube amps
• Turntables

 

[BE718]

Isolation can be effective, a visco elastic material of the correct durometer and 'height' ,properly loaded ,or active tables designed for nuclear force microscopes, under the correct conditions.
The rolling air diaphragm platform I use here under my turntable, is effective from a handful of hertz up.
Keith.

Correct, the point is the device has to be properly designed for the object (mass) it is isolating and the frequency range of operation. I have seen an incorrectly designed isolation device (not hifi )at resonance - thats pretty funny, it does quite the opposite of what you want!

 

[BE718]

Surely one only needs to recreate real world events, e.g. whether a typical audio sound pressure level in-room is likely/capable of having any impact on the equipment's output? Banging, tapping etc is just not what is happening in this scenario. What we have is a constant yet varying full-range sound pressure, the sound of the music in-room. As such I'd have thought a loudspeaker speaker playing something should be the energy force - if I was doing it here I'd use my Moog into my bass amp and see if that could upset the output of a preamp/CD player or whatever.

To my mind whether the equipment casework resonates is irrelevant, what matters is if there is any measurable change to the output, e.g. record the analogue outs playing a track in total silence, then do the same in a room with a series of say 95db LF pulses, intermittent pink noise etc, then do a null-text on the two files and see if there is a change. Try the test with a few different things less/more likely to be microphonic, e.g. a modern surface mount technology DAC and a old valve amp.

As an example I know I can hear the effect of tapping certain tubes in high-gain positions through the speakers, but I tend not to tap them whilst listening to music and I very much doubt the SPL I put into the room us going to worry them much as the energy actually reaching them will be miniscule fraction that of physically tapping the tube with my finger! Even so I'd be interested to see this measured and even more to see if any of the usually reassuringly expensive support "solutions" available had even the slightest effect (baring in mind we are dealing with airborne energy here).

I mostly agree with this.

Regarding the resonance, dont discount it as an issue. For example, what are the resonant frequencies of a tonearm? Any excitation force at a resonant frequency will (in simple terms) be amplified, so a vibration level that may normally not be a problem suddenly becomes a problem at the wrong frequency.

Here is a bump test of the pictured hifi stand. If you are worried about vibration you really dont want to excite the stand at 62.5 Hz, 85 Hz and 150 Hz. But guess what, put different kit on it and the frequencies will change

 

[clivem2]

For a while I ran my valve power amps next to my speakers. The speakers are OBs with 18inch bass drivers - being OBs there's bass cancellation so the bass drivers run harder than box speakers and hence more more air. I found when I hit mute the music of course stopped but the valve amps continued with a "boeng" sound effect. Microphony is this case was very real and it resulted in some frequencies (esp piano) sounding harsh. All fixed by moving the amps.

 

[cooky1257]

Can I just point out that;
1. You will test the wrong SS amp.
2.You will test the wrong TT.
3. You will test the wrong Tube amp.
4. All your results will be unrealistic because you didn't test on mdf shelf, glass shelf, pine shelf, acrylic shelf, wood table, glass table, etc etc etc.
5. The anecdotal circumstance will always trump your empirical research.

Anti science, anti knowledge, anti data the holy trinity of the audio creationists.