"Jim Lesurf" wrote in message

In article , Arny Krueger
wrote:


My point with the fishing line example is that the box doesn't move
that much, especially compared to the cone. If the box were
suspended, the rule of equal and opposite reactions would hold. Then
motion of the box and the motion of the cone would be proportional
to their respective weights or masses.

It turns out that the moving mass of a woofer cone is often
specified, and it's on the order of 15 grams for a large woofer. A
subwoofer and its enclosure weighs at least 15 kilograms, so the
mass ratio is at least 1000:1. Often it is more, far more.

That means that the box moves a thousandth of a millimeter or less
for every millimeter that the cone moves. Got the picture? The box
moves so little that its motion is practically irrelevant to sound
quality.

I agree with most of the above, but have a slight uncertainty about a
few points... :-)

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?

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

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.

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?

Another point is that the cone/motor is not the entire mass against
which the motor applies force as this must include the moving air
mass loading. That said, I'd expect this to become a tiny
contribution at LF for a typical boxed speaker.

Yes, we know that the air mass contributes very little to the loading on the
cone except in horns. That's why horns show the benefits that they do.

However I also wonder
how heavy the cones and motors are for subwoofers as they may need to
be very stiff/strong if the speaker is an infinite baffle.

The mass number I cited was for a driver that could easily be used in a
subwoofer.

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?

;-)