BE718,
Thanks for conducting your vibration analysis and presenting the results here.
Your use of a shaker with accelerometers to measure the transfer function would be of interest (although exactly what to measure could be an interesting discussion as I was really thinking about the amplifier support system as I am interested in this and have no kit to measure with).
As others have stated, please could you put your measurement posts in a separate thread as they are far too good to be lost in this thread.
Thanks,
Ian
No worries......... omg I have been over here too long to saying things like that...
OK, can you clarify what your amplifier "support system" is?
There are going to be two major routes for vibration into an amplifier, directly through the surface/stand it is sat on and acoustically induced.
A stand (or the amp itself) will have also its own natural frequencies it resonates at. If excited at those frequencies they will, in simple terms, get amplified. You can bump test to identify those frequencies. The structure can then be modified if necessary to move those frequencies and or reduce their amplitude.
The question is what sort of vibration input is appropriate - I'm a little unconvinced about using a shaker because it's just not representative of the real world vibration going into the system.
different floors will also respond/conduct vibration differently (concrete/wood).
However All this can be measured and amp outputs measured to see what gets through at what level.
You could well be right in that a shaker may not be the best way to do this, especially as the ground is part of the mechanical system through the energy sinking process. But I am struggling to see how to put the energy into the stand at the required energy level, across the frequency range required.
Thanks Robert, interesting stuff. BTW the reason I used tones instead of pink noise on this test was so that it would be easy to identify them in the noise floor.
What about one of those bluetooth 'speakers which use a resonant coupling to produce the sound?
They make quite good if variable portable 'speakers!
http://www.ebuyer.com/582698-adin-d...=51630194939&gclid=COfLnKTq_cUCFUjnwgodxnQALA.
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?
OK, the measurements only took about 15 minutes, I suspect writing this post may take longer.
I placed an accelerometer on the amps top (Onkyo NR5010 in the theatre room speakers are Usher BE718 with paradigm sub12). The amp is sitting on 20mm mdf shelf with a reinforcing bit of ali angle cos the amp weighs a tonne. Nothing sophisticated in any way. Concrete floor, brick walls.
The first problem here is that if you are not familiar vibration or its terms the plots could be a bit meaningless. So what I did first was take two measurements that put put some context into this for people. 1st was tapping the amp top gently, second is dropping a tennis ball on it multiple times from a height of 10 cm. Both minimal vibration inputs. All plots are provided in velocity and acceleration.
Next plot is the amp off and silent room. If you are wondering what the low frequency ski ramp is, it's a bit of accelerometer noise plus the inherent integration errors from converting to velocity from acceleration.
Next is amp on. Wow, you can see the harmonics of the mains transformer buzzing (its not electrical pick up).
OK, now a 60Hz tone playing at 85 dB
250Hz
500Hz
Daft Punk - ignore the FFT, just look at the waveform. The transient nature of the music will not be truly captured by the FFT
OK, so whats the conclusion? Just look at the numbers. The induced vibration is spectacularly low. Note this is on the amps top cover which is essentially a thin sheet easy to excite. The vibration on the internal components may be even lower.
So anything solid state just dont worry about it. Valves are a little bit different, they are more microphonic. Steven give one of the valves a flick. Do you hear it ring? Well its possible that if you play notes loud enough at that frequency it may resonate, but for general music again I wouldnt say it would have much effect. You going to have try real hard to get it to be a problem. All of this and its effects can be measured if you want to know for sure and just how much. Oh and btw this will have no effect on the room resonances.
Now, I suppose some are saying, well this doesnt tell me if this tiny vibration is actually affecting the output of the amplifier. The next test is to bring home a Bruel & Kjaer measurement system and measure the noise floor of the amplifier with and without music / tones playing from a separate amp and speakers playing in the same room.
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.
It would be interesting to see if induced vibration had a more dramatic effect on stylus tracking and cart distortion whilst playing an LP.