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Hi Mathieu -<br>
<br>
again, sorry for the big delay. I was a bit busy the past 2 weeks.<br>
<br>
On 22.10.2010 07:35, Mathieu Bouchard wrote:
<blockquote
cite="mid:alpine.DEB.2.00.1010220005450.16612@paik.artengine.ca"
type="cite">On Thu, 21 Oct 2010, Martin Schied wrote:
<br>
<br>
<blockquote type="cite">
<br>
Isn't the heat proportional to the mean power ? Then you
just do [*~] with itself and then some kind of [rpole~] to
account for the
<br>
accumulation thereof. After that I don't really know what
to do with that.
<br>
<br>
one could feed the output of this [rpole~] into a [*~] to the
input signal (or at any place later, but then it has to be cared
for the delay of the doppler vd~ too, so better do it first).
<br>
</blockquote>
<br>
Why would you be doing the doppler first ? The heat is generated
first, in the moving coil, but the doppler is relative to the
observer, who comes at the very end in the data flow from the amp
to the ear. Thus it seems to me that the [vd~] should come at the
very end.
<br>
</blockquote>
yes, absolutely...<br>
<blockquote
cite="mid:alpine.DEB.2.00.1010220005450.16612@paik.artengine.ca"
type="cite">
<br>
How does one take the réactance into account, again ?... then we'd
have to change the first [*~] to account for ampères not following
volts, and do we have to change the other [*~] too ?
<br>
</blockquote>
I think there are 2 main factors where reactance is important. The
first is the varying current flow for heat, the second is the
varying frequency response of the speaker. However I'm not knowing
of a possibility to model the circuit so you actually have a current
and a voltage signal. To calculate the heat production the voltage
isn't used. You have to know the resistance of the coil and the
current flowing through it. And since the force on the cone relates
on the current flow (and this is what we hear) and not the voltage
we should just not care about the voltage and assume the signal in
pd is the current signal. Or expressed in other words the system
should be treated like no difference in current and voltage can
happen. At least it seems to me this makes a lot of things easier
and the audibe effects could be estimated. At least for me a
realistic modeling with verification is out of my knowlegde and also
my time capabilities are limited at the moment...<br>
<br>
<blockquote
cite="mid:alpine.DEB.2.00.1010220005450.16612@paik.artengine.ca"
type="cite">
<blockquote type="cite">I think there aren't many too. The only
case I can imagine and I heard of is for huge negative signals,
where you can't go beyond 0 pascal of air pressure and the
signal is clipped physically - but I doubt this ever happens in
small speakers. Also I'm not sure if this only happens in
compression speakers.
<br>
</blockquote>
<br>
I doubt that it (getting close to 0 pascal) happens at all. It
sounds more like a weapon of mass destruction, than like something
for listening to.
<br>
<br>
Though... in some ways, it does happens, at a very small scale.
What's the speed of air molecules, and how much time do they take
to fill the void made by the speaker moving ? What happens if the
speaker moves faster than that ?... (and is that actually the
Doppler effect said using different words ?)
<br>
</blockquote>
That's beyond my knowledge, but I think that's not the point. If you
calculate the maximum pressure before the negative peak is zero you
have an spl of approximately 135dB which is not that much for
pressure levels directly in front of a speaker - possibly I
calculated it wrong? I used: air pressure: 101.325 Pa and <i>p</i><sub>0</sub>
= 20 µPa RMS, which gave me 134.09 dB (for a wave with RMS of
101.325 Pa - so ideally I would have to take this as peak level but
that doesn't change much, only factor sqrt(2)).<br>
<blockquote
cite="mid:alpine.DEB.2.00.1010220005450.16612@paik.artengine.ca"
type="cite">I don't know what you mean here by «enclosed volume»,
«free field», nor «radiation resistance».
<br>
</blockquote>
radiation resistance is the same like impedance, but for mechanical
systems. You can treat the spring/mass system of the speaker and the
air similar to an electrical circuit driving an antenna as far as I
understood. And similar to electrical load you can have pure
reactance and pure resistance. Unfortunately the internet isn't very
wise concerning acoustics and speaker systems and is full of voodoo
and homeopathy instead using the same vocabulary, so I could not
find very much about it on a quick search.<br>
<br>
By enclosed volume I thought of an air tight wooden box with no
holes other than that for the speaker in it - just like most older
conventional speakers. Pressing the membrane into the box creates a
pressure proportional to the excitation of the cone and not
anymore to the acceleration. I think this closed volume would be
called a high radiation resistance, because the pressure (analog to
the voltage) is high for very small air flow (analog to the
current).<br>
<br>
Martin<br>
<br>
<br>
<br>
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