It appears that everyone that casually quotes the results of the typical 19, 20kHz IMD test for some ambitious audio gear are suffering the same problem. Which is, what his main point is ...
And, what stops people who do know from using a combo of 8 and 9kHz ... unless, it might be too revealing ...
Frank
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I might have done this in 1980 but this is beyond my brain capacity this millenium. Yus gurus, please point to something that dun nid Higher Maths for Dummies. I'm sure there's loadsa stuff if you have done HM4D.
Harmonics and IMD both come from trigonometry. Take two sines (or cosines or one of each). Multiply them together. There are trigonometric identities which tell you how to write the result in terms of other sines and cosines involving the sum and difference of the angles. That is how harmonics and IMD are formed: multiplying sines together in non-linearity.
Yes, when you slaved over triangles as a bored teenager in school you were learning the mathematical basis for low distortion amplifier design, but unfortunately the teacher never told you because he probably did not realise this himself.
Yes, when you slaved over triangles as a bored teenager in school you were learning the mathematical basis for low distortion amplifier design, but unfortunately the teacher never told you because he probably did not realise this himself.
The guys here seem to consider mu zero constant even in the megatesla range. I'll ask one of the carpool guys about the 7 TEV collisions. (chance are, I will not understand the answer.
)I've always pondered the spl's at the throat under high power. Prop velocity in air is pressure dependent, and putting a couple of acoustic watts into a few square inches is not exactly low level.
jn
If you are playing at moderate-high levels in a large living room at listening distance, then up close to driver the spl is huge! As is distortion.
Measuring thd at 1W at 3 feet doesnt begin to tell you what you are really hearing/producing at the listening position under normal (for me) listening levels out in the room. I would imagine same for horn at throat entrance.... very high spl and distortion. Distortion is a Lot higher than typical measurement conditions/specs imply.
[Just use an SPL meter.... set up listening level out in the room's listening position and then move the spl meter to the driver up close (inch) and measure.... you get really high spl, then. What is the driver doing at such high spl?] I measured once very high thd under same real world conditions. -RNM
Measuring thd at 1W at 3 feet doesnt begin to tell you what you are really hearing/producing at the listening position under normal (for me) listening levels out in the room. I would imagine same for horn at throat entrance.... very high spl and distortion. Distortion is a Lot higher than typical measurement conditions/specs imply.
[Just use an SPL meter.... set up listening level out in the room's listening position and then move the spl meter to the driver up close (inch) and measure.... you get really high spl, then. What is the driver doing at such high spl?] I measured once very high thd under same real world conditions. -RNM
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I was more interested in the "discovery" that odd functions can only make odd harmonics.
This is signal processing 101, even Wiki summarizes it nicely.
Even and odd functions - Wikipedia, the free encyclopedia
I was told a trumpet at full throtle was about 4W at the throat. A small silicon pressure guage could be placed at the throat of the waveguide/horn, an interesting experiment.
I recall a paper by some of the Russians who Gene Cerwin hired which suggested a rearrangement of seating in big bands would produce lower acoustical IM distortion.
Of course, besides breaking up the intragroup camaraderies (and rivalries?), perhaps a bit of this IM is part of the particular arranger's sound.
Aha, what appears to be a mistake!!!
The velocity of sound is pretty much independent of pressure. However, I forgot to mention that the air, when pressurized, increases it's temperature (pv=nrt). My pondering involves the effect the acoustic power has on the gas as it traverses it. 4 watts going through a tube of roughly a square inch..
Perhaps somebody can do the math?? Heat capacity of Nitrogen is 1.040 kj/kgK.
Once I get past 10, my math skills slow down..have to unlace my shoes to get to 20..
jn
Aha, what appears to be a mistake!!!
The velocity of sound is pretty much independent of pressure. However, I forgot to mention that the air, when pressurized, increases it's temperature (pv=nrt). My pondering involves the effect the acoustic power has on the gas as it traverses it. 4 watts going through a tube of roughly a square inch..
Perhaps somebody can do the math?? Heat capacity of Nitrogen is 1.040 kj/kgK.
Once I get past 10, my math skills slow down..have to unlace my shoes to get to 20..
jn
PV=nrt raised to power gamma, there is non-linearity to consider.
How much power would need an amplifier and speaker to output 25 Watts of mechanical power?!
pain in the brain
Math Can Genuinely Make People?s Heads Hurt | News | Laboratory Equipment
Aha, what appears to be a mistake!!!
The velocity of sound is pretty much independent of pressure. However, I forgot to mention that the air, when pressurized, increases it's temperature (pv=nrt). My pondering involves the effect the acoustic power has on the gas as it traverses it. 4 watts going through a tube of roughly a square inch..
Perhaps somebody can do the math?? Heat capacity of Nitrogen is 1.040 kj/kgK.
Once I get past 10, my math skills slow down..have to unlace my shoes to get to 20..
jn
Math Can Genuinely Make People?s Heads Hurt | News | Laboratory Equipment
How much power would need an amplifier and speaker to output 25 Watts of mechanical power?!
If I remember correctly, a 99 dB 1 watt 1 meter is about 5% efficient.
500 watts.
At the low frequencies, that translates into a heck of a lot of cone excursion. You know, stun small kids and animals (a quote from the speakerlab K build instructions IIRC) . Multiple 15's or 18's at least.
If it's not bass, I wouldn't want to be in the same room.
jn
When a brass orchestra plays I can feel it by chest and other parts of the body. Down to DC probably.
An externally hosted image should be here but it was not working when we last tested it.
There are 7.9 mW/square meter at 99dB SPL. Integrated over a 1 meter radius sphere (maybe hemishere is closer), you got about 50mW acoustic power at 1W (right 5%). That's pretty good for a dynamic driver isn't it?
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