In article , Arny Krueger
wrote:
"Jim Lesurf" wrote in message



I'd agree that the action and reaction forces will tend to be equal
and opposite (Newton). However although the movements of the box/floor
will be small in terms of amplitude compared with the speaker cone I
wonder about the radiation efficiency once the floor area is coupled
to the box.

If you couple the floor to the box, then that increases the effective
mass of the box, right?

Agreed.

Increase the effective mass of the speaker box and you further decrease
its motion.

OK.

In the end it comes down to the mass/area ratio of the floor versus the
mass/area ratio of the speaker box presuming the coupling to the floor
is perfectly rigid. Based on what I know about how speaker boxes and
floors are made, I'd say that floors are more massive per unit area than
your typical speaker box.

I'm not sure of this, or of the relative flexibilities, radiation
efficiencies, etc. I am also not sure of how/if it may matter changing
from one form of speaker to another - e.g. a downward firing IB sub
to/from a ported side-firing design.

Although the displacements are small, the area moving may be much
larger than the area of the speaker cone. Hence I am not yet sure that
the sound levels radiated are simply in proportion with the masses.

Per my analysis above, adding in the floor probably strenghtens my
argument, no?

I am not sure of this. I would need to do a proper analysis or measurements
to decide. Your argument is perfectly plausible, but I am not certain it is
the whole story.


Not seen any figures / calculations / models of this, but I do wonder
about it. When I fitted spikes to the stands of my ESL63's I did form
the view that the bass was altered. That said, an ESL is a very
different case to a boxed subwoofer, and the ESL63 is pretty light
compared with a typical large boxed speaker, so this might not be a
reliable guide to the general situations.

I'd agree that you had the perception that the bass was altered.
However, was the bass *actually* altered?

;-)

Pass. :-) Certainly possible that my impression was misleading.

FWIW I did do some before and after measurements and they showed a
difference in response. However I am not at all sure these measurements
were reliable enough as it is very hard to measure such things in a real
room situation and I am not sure I did this well enough at the time.

The ESL63 is something of a special case in this area as both the diaphragm
and the body have quite low masses, and the speaker is dipolar. Hence the
situation is very different to using an IB subwoofer. As a result, even if
it did make a change I am not sure this means a similar change would be
audible with a conventional speaker or subwoofer.

Slainte,

Jim

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