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 AP2 8th October 2011 04:53 PM

AudioPower (DPA-400) Sound pressure improvements?

1 Attachment(s)
Hi,
yes, it is possible.some shape of signal contains geometry that increase acceleration of air particle. this is not new for me,it is used in military aeronautical and other (some are secret).
Preface of story:
During development of the DPA-400 (with PSU rips) I tried to get a lot of realism on percussion. when it was heard, it seems that we have achieved this performance perfectly, very fast attack on the sound of the bass drum.(with good spl)
To the latest listening tests, we found a significant warming of the woofer. At this point, along with other collaborators, it was ruled a fault on the amplifier, has taken the study of this phenomenon.
Theory :
Particle Velocity : v Particle Velocity is the distance travelled by a particle per unit time in a medium that is displaced from its equilibrium state by the passage of a sound or vibration wave. the units are m/sec. When applied to a sound wave through the medium of air, particle velocity would be the physical speed of an air molecule as it moves back and forth in the direction the sound wave is travelling as it passes.

Particle Velocity v = I/p = ξ·ω = ξ(2·π·f) = a/ω
where
I is the instantaneous acoustic intensity
p is the instantaneous sound pressure
ξ is the particle displacement
ω is the angular frequency
f is the frequency
a is the particle acceleration
In acoustics particle velocity is sometimes denoted by u
Particle Velocity Level : Lv = 20 log (v/vo) dB re 5 x 10-8 m/s - also known as dB SVL, sound velocity level

Particle velocity should not to be confused with the speed of sound.
It is obvious that I'm not changing the dynamic structure of sound.
so we are talking about eg. an envelope (bass drum).
The shape of this pulse, contains the parameters of acceleration.
10 people have measured up to 123dB SPL at 1m of bass drums (real drums)
Then, they measured with 2x800w max .. 115dB (118dB with 5000w JBL speakers system).in both cases, the timbre is not dry as fast as the original.
Independant of my job on Amplifier, this problem have an scientific explanations.
--------------------
This is the test bed, we have equipped for these measures.
As soon as possible, put all the charts. and, reason becouse dpa-400 can increase the sound pressure at constant watts rms and speaker than another amp.

Regards

 AP2 8th October 2011 11:32 PM

1 Attachment(s)
Hi,
This diagram illustrates the relationship between the geometry of the electrical signal and the pressure / depresión produced. a signal very fast (if it is reproduced with the same speed) can produce high sound pressure levels peak. as in the case of the bass drum.

Continue..

Regards

 ChocoHolic 11th October 2011 09:55 PM

Are you really sure that the bottleneck is in the amp?
Usually amps reproduce signal envelopes and even transients pretty good, while woofers are slowish mass&spring resonators which tend to mess up things.

 AP2 11th October 2011 11:18 PM

Hi,
After the measures as the pic "Current Test", the error is impossible.
I mean: we sent a continuous signal at 60hz (SIN) in MosAmplifier adjusting the gain for a clip, we measure 58vP (this is our reference amp, with very big psu). we set the DPA-400 for the same value (identical).
that's ok. Now we change the signal pattern with triple-burst. repeat the steps for one minute (ref amp and DPA-400). output voltage in both the amp is the same but the dpa-400 increased the output current. at this point with some colleagues from the CNR, we have tried to study the phenomenon.
Increase in current is also testified by the increase in temperature on the woofers. also, that during test, when the burst was on the DPA-400, he was a very different sound. (MDI has set up this laboratory measures in an anechoic chamber).
I can confirm in this moment: the woofer impendance change when in acceleration. this is correct, the mass changes in relation to speed.
the speaker and bass reflex determines the pressure / depresion internal, this is a factor in the calculation of the dynamical mass.
End, not all amps can follow sequentially the speed of a sound envelope containing accelerations.
I wait all the curves to show the differences between a mospower 700w (2R) and our DPA-400 750W (2R).
I can not show a company name of mospower.it's a prestige model big case.

Regards

 ChocoHolic 15th October 2011 10:57 AM

Really strange that you get such different results, while the voltages are identical.

Also wondering about your model of changing mass as a function of velocity.
Isn't this effect neglectible under normal conditions?
A speaker cone of a sub might typically move with velocities between 1m/s...5m/s.
That's eight decades below the speed of light, so I would not expect that mass is changing in any noticeable way.

 AP2 15th October 2011 02:53 PM

Quote:
 Originally Posted by ChocoHolic (http://www.diyaudio.com/forums/class-d/198134-audiopower-dpa-400-sound-pressure-improvements-post2746424.html#post2746424) Really strange that you get such different results, while the voltages are identical. Also wondering about your model of changing mass as a function of velocity. Isn't this effect neglectible under normal conditions? A speaker cone of a sub might typically move with velocities between 1m/s...5m/s. That's eight decades below the speed of light, so I would not expect that mass is changing in any noticeable way.
----
Depends on what we call as mass.
on relativity theory, you will come across rest mass and relativistic mass.
Rest mass does not change with velocity.
Relativistic mass changes with velocity.
A part this,I called "Mass" Mms - the mobile mass (g). (sorry for my english and...very absurd google traductor).
The friction is given by the diameter of the cone, the density of air particles and the resonance structure (a project of the box). this to calculate the electrical power needed. or inverse,that spl produces.
During the tests (they are still in progress with another speaker), I agree that the behavior is new (it all started with the heat of the woofer). Now, as you can not increase the acceleration speed, in addition to that determined by mechanical structure of the woofer, it is clear that the (r) decreases during acceleration (pressure/depression). I have not at this time all the test data.
the only thing certain now is that the temperature increases the woofer, listen, the drums are very hard and that ,speed of accelleration create a big instantaneus peak pressure that our we ear.
I do not worry, the truth will come out.

Regards

 ChocoHolic 15th October 2011 04:57 PM

Quote:
 Originally Posted by AP2 (http://www.diyaudio.com/forums/class-d/198134-audiopower-dpa-400-sound-pressure-improvements-post2746570.html#post2746570) ---- Relativistic mass changes with velocity. Regards
You didn't get my point.
The relativistic mass of a speaker cone, which moves with some single m/s is almost identical to the mass of a non moving cone. The difference is far in the sub ppm range.
Therefore I am not convinced that this is the key effect of your phenomenon.

mrel= m / sqrt(1-(v˛/c˛))

 AP2 15th October 2011 05:30 PM

Quote:
 Originally Posted by ChocoHolic (http://www.diyaudio.com/forums/class-d/198134-audiopower-dpa-400-sound-pressure-improvements-post2746678.html#post2746678) You didn't get my point. The relativistic mass of a speaker cone, which moves with some single m/s is almost identical to the mass of a non moving cone. The difference is far in the sub ppm range. Therefore I am not convinced that this is the key effect of your phenomenon. mrel= m / sqrt(1-(v˛/c˛))
---
yes, I agree, I know these formulas (not in all). in my last post, I wanted to correct that "mass" in the "energy needed to accelerate an object",but ..what "friction"? ahah! I think may be the kinetic energy. if I remember correctly, in this case KE. but in this case back to the "R" that has to change. given that V on coils not change. So why change "R"?
On resistive load, Both amps have the same current.
very interesting phenomenon, change power only with speakers and fast signal.
with sinusoidal signal have little difference. amplifier was measured in all ways ... is perfect, clean output, no sub oscillation.
the measures we have moved, so it's not in my lab.
I'm sure we will have a physical explanation of the phenomenon.
you have an idea in the meantime?

Regards

 ChocoHolic 15th October 2011 07:28 PM

I guess I would spend the next nights on the measurement of output voltages and currents in comparison with both amps, because it does not fit into my world that a speaker does something different while getting the same voltage. It is not likely that the speaker changes its parameters and draws more current when seeing the same voltage from a different amp.
May be a slight shift of DC operating point under certain repeated bursts or similar?
A slight DC portion would lead to both effects.
Hotter voice coil and changed sound.

...but I guess my ideas are not new to you and I can imagine your findings did also not fit into your world and you already have spend these nights in the lab...

 AP2 15th October 2011 09:25 PM

Quote:
 Originally Posted by ChocoHolic (http://www.diyaudio.com/forums/class-d/198134-audiopower-dpa-400-sound-pressure-improvements-post2746786.html#post2746786) I guess I would spend the next nights on the measurement of output voltages and currents in comparison with both amps, because it does not fit into my world that a speaker does something different while getting the same voltage. It is not likely that the speaker changes its parameters and draws more current when seeing the same voltage from a different amp. May be a slight shift of DC operating point under certain repeated bursts or similar? A slight DC portion would lead to both effects. Hotter voice coil and changed sound. ...but I guess my ideas are not new to you and I can imagine your findings did also not fit into your world and you already have spend these nights in the lab...
Hi, I thank you ChocoHolic for time I've spent.
In fact, after the first 4 measures crossed, I did not understand anything. then (because I have a lot of work), some friends are doing all the measurements. some are physical CNR. yes, I agree that speakers not change "R" during acceleration. i know that can change the impedance in relation to the box, as frequency response. but that's another thing.
I suspect that the integrated psu (this is new topology, and is able to respond with "zero" theoretical loss at dc pinout) provides instant absorption peaks, can increasing the amplitude of peak. This dynamic is clearly visible on the tracks when ready, I'll put them on this thread. this is the only thing that would explain perfectly the behavior with burst (and not with continuos signal). not have other idea at the time.
remains, however, the theory that the instantaneous pressure produced is inversely proportional of the angle of the peak. This in theory would explain the change of timbre when we call "fast bass" on a good amp.
In fact, even if we have an amp with more watts, the bass can be soft and not fast rap. near to real drums.This is a nice realism that I have listen.

Regards

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