There , solved ...! Everyone to class-d amps ....
Not everyone, but I expect the majority would live happily with a properly designed and implemented class-d or class-t amplifier.
I have one such class-t amplifier and can play with it for a period of time before I simply loose interest in listening to music. The class-a SIT JFET amplifiers can be used for months and years without such negative bi-effects.
There still is reflection, but the dimensions of the volume may become too small to sustain (and dissipate) a full wavelength at lower frequencies.
If these reflections come back to the transducer with phase shift <90 degrees, they will add constructively. This creates pressure differences inside a small volume, hence isobaric imo is not the right word. Room gain would be more appropriate to describe what happens here.
Solved?
I am hoping you are being sarcastic, I certainly didn't state there were no differences to be heard. I stated that Richard Clark's specific test, for whatever reasons didn't indicate people could hear a difference. I was merely fleshing out what Demian had referenced. Please read what I wrote carefully if you though otherwise.
My own experience leads me to think that a lot of the perceived differences between amps do indeed have to do with performance in clipping. Especially with dynamic material, having 14-20+ dB crest factor (not that much music is anywhere near that), very little average volume would be required to induce clipping.
Viewed from a different perspective, unless you use fantastically efficient speakers, or huge power and speakers that do not suffer from power compression, when one turns the volume up to the point where you can hear deep into the mix, you will will most certainly have clipping. I have proven that to myself by using limiters and repeatedly enabling and disabling them. When clipping is occurring, the sound most definitely changes to the better by enabling the limiter.
Another amp characteristic which causes sonic issues is DC stability. There have been amps made which offset when fed asymmetrical signals, like a lot of orchestral music. During these events the woofers slew in and out, causing weird image shifts. Maybe this is mostly cured these days, I don't know. My experience in this is years old.
I am sure there are a multiplicity of other factors...which is why I joined this forum, to learn from those who design the circuitry.
Cheers,
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
There , solved ...! Everyone to class-d amps ....
I am hoping you are being sarcastic, I certainly didn't state there were no differences to be heard. I stated that Richard Clark's specific test, for whatever reasons didn't indicate people could hear a difference. I was merely fleshing out what Demian had referenced. Please read what I wrote carefully if you though otherwise.
My own experience leads me to think that a lot of the perceived differences between amps do indeed have to do with performance in clipping. Especially with dynamic material, having 14-20+ dB crest factor (not that much music is anywhere near that), very little average volume would be required to induce clipping.
Viewed from a different perspective, unless you use fantastically efficient speakers, or huge power and speakers that do not suffer from power compression, when one turns the volume up to the point where you can hear deep into the mix, you will will most certainly have clipping. I have proven that to myself by using limiters and repeatedly enabling and disabling them. When clipping is occurring, the sound most definitely changes to the better by enabling the limiter.
Another amp characteristic which causes sonic issues is DC stability. There have been amps made which offset when fed asymmetrical signals, like a lot of orchestral music. During these events the woofers slew in and out, causing weird image shifts. Maybe this is mostly cured these days, I don't know. My experience in this is years old.
I am sure there are a multiplicity of other factors...which is why I joined this forum, to learn from those who design the circuitry.
Cheers,
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
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Ed's example wouldn't even support a half wavelength! The box is basically isobaric.
100% agreed if you add in recovery from clipping as well as clipping performance. My little tube amp, for example, is designed to recover essentially instantaneously, and when it's loud enough to be clipping on peaks, the clipping sound hardly noticeable. Conventional circuits will block following a clipping event, which can last on the order of hundreds of milliseconds or more and sound grossly "choked."
You are correct.
Yes, we are. Just because there is insufficient distance for an entire cycle to be created doesn't mean it's not a wave.
At LF, unless the walls have free space compliance, the internal pressure will build up as a consequence of the pressure wave. That buildup will depend entirely on the enclosed volume and the percentage of volume the fill material takes up. Any wavefront will expand outward until it hits a surface, when reflection will occur.
The pressure will build up higher as a consequence of the enclosure volume.
jn
Yes, but it will be equal everywhere within the volume. It will have a time dependence, but not a spatial dependence.
There is of course no technical reason why this can't be done. Being a
manufacturer, it is easy for me to provide a listener with two amplifiers with
identical exteriors and differing only in subtle ways. The amplifiers are
delivered blind, and the listener labels them to avoid confusion. They do not
get to see inside, and information regarding the differences is not provided.
The amplifiers are used in the listener's known system for as long as they
like, and upon returning them they tell me what is heard. Later, I can check
that using their labels. The test can be repeated, but care is taken that
the units cannot be identified by external scratches and such.
Anecdotally I can tell you that some people are reliably sensitive to things
that do not stand out in the "usual measurements". Not being very objective
myself, I try to keep these people around.
50-60 db btn loud and quiet parts, plus ~40db ambient noise = ~90-100db.
A common case with classic music CDs played in an apartment (thus the need for using headphones
)George
The internal pressure, and therefore, the back pressure the woofer sees, will be dependent on the internal volume, and the change in the internal volume as a consequence of the woofer movement.
As the internal volume increases towards infinity, the chamber will asymptotically approach the lf response of a true anechoic chamber.
As a practical, absorption will not work when the wavelength is far longer than the absorbing structure dimensions. There is no way to fully absorb bass anechoically in a cabinet of the dimensions earlier pictured. Even if the guy hitches his pants back up.
jn
At dimensions smaller than wavelengths of interest? There is no sound radiated then. is there?
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Let's take the example of a 20Hz variation in Ed's box (.8 x 3.5 x 2.4 M). The wavelength at 20Hz is 15M. So along the longest dimension, you have less than 1/4 wavelength. The transit time is 11 milliseconds, compared to the period of 50 milliseconds.
jneutron said:
True if you place the restriction that the sound must be completely absorbed within the box volume and that the absorption need be 100%.
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