In article , Scott Dorsey
wrote:
In article , Jim Lesurf
wrote:
In article , Wally
wrote:
Powell wrote:

Allthough the sonic effects of spikes may vary from speaker to
speaker and from room to room, they do move the resonnance of the
speaker-floor combo up in frequency. Sometimes it improves overall
sound, sometimes it doesn't. But the effects have a very natural
explanation.

Care to explain the mechanism that causes the resonant frequency to
move up?

FWIW I decided not to comment on the bulk of the items asserted most
recently as I didn't want to widen the issues. But a number of
questions like the above did occur to me. The problem is that with no
measurements, details of experimental arrangements, etc, it is often
hard to assess the assertions people make.

I believe that Mr. Powell is a troll.

I can't say that I am astonished to be told that. :-)

However, I do suggest looking at
the following:

1. A system with two masses, one very large and one very small, which
are loosely coupled by a flexible joint.

2. A system with two masses, one very large and one very small, which
are more tightly coupled.

If the masses are the same in these two examples, and you look at the
response to excitation of the smaller mass, what happens to the main
resonance as the coupling is increased? Hint: both the resonant
frequency and the Q are changed.

This stuff is easy to model as a two mass spring system, in the simplest
cases. --scott

I agree with some provisos. The snags in applying that to the assertions
made by Powell seem many and various. Mainly due to the combination of
'vague and sweeping' and 'ambiguous' as features of his assertions, plus a
series of apparent muddles like using 'mass' when he perhaps meant
something else, etc. Does he not know that 'concrete' and 'wood' both come
with wide ranges in their mechanical/acoustic properties? And so on...

They key one for your comments though is, Are the 'spikes' either '1' or
'2' where the 'speaker set down on the same substrate with no spikes' the
other? Or do the two specific situations you describe not accurately
reflect comparing spikes with simply sitting on a floor? ... or a carpeted
floor? And how do you then establish any of this has any audible
significance? Is it the case that only the simple 'two masses with a
spring' longitudinal vibration matters here? Or do none of these things
matter at all?

Of course, you or I can guess which choice above is more plausible, and may
well be right. But we then need data to see if our surmise stands up in
practice. if you look around consumer audio you see all kinds of claims
made, presented in apparently technical language and seeming quite
plausible... until you start asking if they really make sense. :-)

So yes, you can model things. But you do need to be able to choose
appropriate parameter values to do so. And establish your model is the
relevant one for producing conclusions about what is relevant in real
applications.

Also, what kind of mode(s) of vibration is he talking about? Vertical
longitundinal? Rocking? Or various other possibilities. Again, that would
affect the choice of model.

Hence the need for some actual measurements to establish the relevant
parameter values which would then be used to verify the model against
observations.

I don't know the answers here, even if you or I could make good guesses.
But I have read enough to realise that people make conflicting assertions,
and then don't present checkable evidence in the form of measurements
*plus* a decent description of how those measurements were obtained.

Alas, lacking these things it is easy for people to be mislead by what
seems plausible given only what is asserted. A nice example of this is
something I looked at a few years ago. I put the results at

http://www.st-andrews.ac.uk/~www_pa/...eshift/cp.html

if anyone is interested.

It shows how a series of published articles presented 'evidence' for a
radical discovery which would be quite significant... if true.

I had doubts that so many EEs any physicists over the years had missed
something so obvious. So I looked carefully at what they'd done. This was
hard as some of the critical details were only quite tiny features in their
diagrams. But the outcome was that their results were consistent with a
simple flaw in their measurement arrangements.

FWIW I keep resisting the temptation to do similar examinations of various
other sets of 'data and claims' I find. But I may give in shortly... it is
fun. 8-] However I can't do this when the person(s) making the claims
avoid giving any data or details of how it was obtained, though. I can then
only proceed on the basis of being cautious of being expected to accept
whatever I've been told simply because the person expects that.

TBH my real regret is that a journal like the JAES does not have any
interest in publishing such 'forensic analysis' on some of the claims
people make and the 'data' they sometimes present. No doubt it would annoy
some people, though. ;-

Slainte,

Jim


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