(John Atkinson) wrote in message . com...
"Robert Morein" wrote in message ...
"John Atkinson" wrote in message
om...
Great article!

Thanks.

As I write this, I'm having a telephone conversation with my friend
Larry Zeitz, who insists there must be an escape clause for downward
pointing, carpet piercing, floor spikes on floor standing speakers, and
the interface between stands and floors.

I have responded that your article offers no implication that spikes are
useful for the floor interface. Would you be so kind as to comment?

There are 2 separate issues involved. The first is the speaker cabinet's
vibrational behavior, which is what I examined in my on-line article. The
second is the speaker's and/or stand's relationship to the floor.

There is no doubt that supporting a speaker or its stand on
downward-pointing spikes more efficiently couples vibrational energy to
the floor. This can be easily demonstrated if you have a room beneath
your listening room, or of you live in an apartment, can get access to the
apartment beneath yours. Rest the speakers or their stands on the carpet
without spikes. Play music with plenty of repetitive low frequencies and
listen from downstairs. You will hear a muffled rendition of the bass.
Now repeat the music at the same level with the speakers/stands spiked
to the floor. Again listen from downstairs and you will hear the bass
notes louder and more clearly defined, depending, of course, on your
floor construction. (Spiking your speakers to the floor is an excellent
way, BTW, of maximally annoying your downstairs neighbors, if that is
a goal. :-) )

You might also want to try wedging a pole between the back of the speaker
and the wall behind it. (The pole whould be very slightly longer than the
distance so it is under compression and the speaker is not moved forward.)
Depending on the speaker, you might hear an improvement in bass
definition. Then again, you might not. BTW, the worst case, in my
experience, is to suspend the speakers on cords of some kind, as
recommended by Arny Krueger.

What general conclusions can be drawn? From my own experience with
concrete slab floors, the speakers will sound slightly better defined
in the lower midrange and bass when they are spiked to the floor beneath
the carpet. With suspended floors, whether there is an improvement or not
will be a crapshoot.

With the cabinet itself, supporting the speaker on upturned spikes will
allow its own resonances to develop fully, as my 1992 measurements
demonstrated As I said earlier, whether or not this will degrade the
speaker's perceived sound quality or not will differ from speaker to
speaker. My measured results also show that if you want to maximally damp
cabinet resonances, you should use a lossy interface such as Blu-Tack
between the cabinet and its support.

What you _don't_ want is a compliant, non-lossy interface material, like
a typical carpet pad, or springy rubber feet. You will change the resonant
behavior rather than damping it, and you might well amplify sme of the
cabinet resonant modes. Again, this is something I examined in my 1992
articles.

So, it is relatively easy to try spikes then Blu-Tack, to determine which
(if either) you prefer. Listen to just one speaker and play something like
the half-step-spaced tonebursts on Stereophile's "Editor's Choice" CD.
Listen for overhang on some notes but not others, a "pulling" of the pitch
of some notes but not others, and a general stability or lack thereof to
pitch centers. Go with what you prefer. If you don't hear any difference,
then it is possible that your speaker cabinets are optimally braced.

John Atkinson
Editor, Stereophile

From other data I've seen the fundamental resonance frequency of the
floor-speaker interface is in the bass region (20-50 Hz) when using
spikes, and by using coupling there will be significant movement of
the speakers when the resonance is excited (up to 20 dB more). With
soft feet the fundamental resonance of the speaker-floor interface can
be reduced to under 10 Hz and will not be excited with most music
material. The resonance in the cabinet per se should IMO be dealt with
using a good cabinet construction.

Also, springy floors will be problematic using hard coupling since the
standing waves in the room will excite the floor and cause significant
speaker movement. Isolation with springy feet will make the speaker
move less.

See e.g.

http://koti.welho.com/msalone5/audio/vibra.html

Although the text is in Swedish, the graphs should not be difficult to
interpret.

T