Treating slap echo

[Stuart E. Weiner]

Hi,

I¹d appreciate your views on treating slap echo in a large, narrow
listening room. I recently had my basement finished, in large part to
use as a listening room. I am about to set up my gear but am troubled
by the slap echo I get when I clap my hands. So I want to experiment
with some inexpensive room/wall treatments first. The room is about 12
feet by 50 feet, with a few juts and entries along the way, i.e., not
perfectly rectangular. The foundation is 9 foot high. Because of the
configuration of the room, I will have to place the speakers on the
short wall. The room is fully carpeted, full of bookcases, with a sofa
and 3 stuffed chairs. So it is not overly lively, expect for the slap
echo. If I can get rid of the slap echo, my sense is it might turn out
fairly good.

However, right now there are plenty of bare walls (all drywall), which
are no doubt contributing to the slap echo. I have at my disposal 8
fabric fiberglass panels, each 2 ft by 2ft, and 8 junior Sonex panels,
each 2 ft by 2 ft. I also have a couple of ceiling corner triangles.

My questions are:

1. Is there a difference between slap echo and flutter echo, or are they
different terms for the same thing?
2. I¹ve read that slap echo is caused by parallel, bare walls. But I¹ve
also read that it is caused by adjoining bare walls. Which is it? It
will make a difference, of course, in how I hang my panels.
3. I¹ve read that slap echo is often caused by bare walls near the
ceiling. Is this true? If so, does that imply that one should place
panels higher to the ceiling, rather than at the speaker/listener¹s ear
level?
4. Are the two bare, parallel walls roughly 50 feet apart likely
contributing to the slap echo? Or is it more likely coming from
interaction among the parallel surfaces that are roughly 12 feet apart?
(Assuming it¹s a parallel, not adjoining, wall issue.)
5. Worst case, I could break the room up into two rooms by adding a
wall. Would that help, i.e,, is the narrrowness of the room an
untreatable problem? Of course, I would want to try wall treatment
approaches first!

Sorry for the lengthy post. Thanks for any input.

[Harry Lavo]

"Stuart E. Weiner" > wrote in message
...
>
>
> Hi,
>
> I¹d appreciate your views on treating slap echo in a large, narrow
> listening room. I recently had my basement finished, in large part to
> use as a listening room. I am about to set up my gear but am troubled
> by the slap echo I get when I clap my hands. So I want to experiment
> with some inexpensive room/wall treatments first. The room is about 12
> feet by 50 feet, with a few juts and entries along the way, i.e., not
> perfectly rectangular. The foundation is 9 foot high. Because of the
> configuration of the room, I will have to place the speakers on the
> short wall. The room is fully carpeted, full of bookcases, with a sofa
> and 3 stuffed chairs. So it is not overly lively, expect for the slap
> echo. If I can get rid of the slap echo, my sense is it might turn out
> fairly good.
>
> However, right now there are plenty of bare walls (all drywall), which
> are no doubt contributing to the slap echo. I have at my disposal 8
> fabric fiberglass panels, each 2 ft by 2ft, and 8 junior Sonex panels,
> each 2 ft by 2 ft. I also have a couple of ceiling corner triangles.
>
> My questions are:
>
> 1. Is there a difference between slap echo and flutter echo, or are they
> different terms for the same thing?

Not sure, but different frequencies and reverb times, I believe. Slap echo
is centered in the upper-midrange frequencies and is worst off of solid
masonery walls.

> 2. I¹ve read that slap echo is caused by parallel, bare walls. But I¹ve
> also read that it is caused by adjoining bare walls. Which is it? It
> will make a difference, of course, in how I hang my panels.

It is caused mostly by opposing walls, floors, ceilings, etc. But they have
to be far enough apart for the echo times to be perceived as a separate
entity, not just "reverb".

> 3. I¹ve read that slap echo is often caused by bare walls near the
> ceiling. Is this true? If so, does that imply that one should place
> panels higher to the ceiling, rather than at the speaker/listener¹s ear
> level?

Ceiling or floor could contribut simply by bounding/focusing the sound and
thus intensifying it. But the base problem is the opposing walls.

> 4. Are the two bare, parallel walls roughly 50 feet apart likely
> contributing to the slap echo? Or is it more likely coming from
> interaction among the parallel surfaces that are roughly 12 feet apart?
> (Assuming it¹s a parallel, not adjoining, wall issue.)

Almost certainly the 50 foot opposing walls are the main culprit...the 12'
walls and 9' ceiling are probably too close together to contribute much, if
any.

> 5. Worst case, I could break the room up into two rooms by adding a
> wall. Would that help, i.e,, is the narrrowness of the room an
> untreatable problem?

Yes, that would help. But you do want to avoid cerain ratios. The 12'
width to 9' height is already not opimum, and a wall 25' away would be
periously close to 2x the 12' dimension. If you ever do add a wall, make it
an odd distance like perhaps 22' or so.

> Of course, I would want to try wall treatment
> approaches first!
>

I'd suggest before you do anything else, you hang the far end wall with
woolen blankets, either on wall or perhaps six inches in front. See if this
eliminates the slap. If you still get slap, try this side to side, floor to
ceiling at various points where the slap seems severe. This will help you
locate the source that needs to be treated.

Another trick, if you have them, is to pile large boxes one on top the
other, floor to ceiling and turn them so one corner points "out" into the
room. For a twelve foot wall, you might need three such stacks. These
serve as diffusers and tend to reduce echo. You can also use these
particularly effectively as corner and center diffusers near the front of
the room, behind the speakers. Of course, they don't look like
much.......but the price is right.

> Sorry for the lengthy post. Thanks for any input.

Hope this helps you tackle it.

[Arny Krueger]

"Stuart E. Weiner" > wrote in message


> 1. Is there a difference between slap echo and flutter
> echo, or are they different terms for the same thing?

Slap echo is more like the short form and flutter echo is more like the long
form. Flutter echoes arise when a slap echo bounces around a while before
it dies.

> 2. I¹ve read that slap echo is caused by parallel, bare
> walls. But I¹ve also read that it is caused by adjoining
> bare walls. Which is it? It will make a difference, of
> course, in how I hang my panels.

You can have a slap echo from one wall. A slap echo is just a bounce that is
loaded with high frequencies. Bare flat plaster is good for making slap
echoes, and corners make better reflectors.

> 3. I¹ve read that slap echo is often caused by bare walls
> near the ceiling. Is this true?

They aren't so common at lower levels due to the popularity of carpets and
rugs. But you can definately have them near the floor with hardwood floors.

> If so, does that imply
> that one should place panels higher to the ceiling,
> rather than at the speaker/listener¹s ear level?

Absorbtive panels work best when closest to either the listener to block or
near the reflecting surface to absorb.


> 4. Are the two bare, parallel walls roughly 50 feet apart
> likely contributing to the slap echo?

That would be more likely to be a flutter echo with flutter at about 20
times a second.

> Or is it more
> likely coming from interaction among the parallel
> surfaces that are roughly 12 feet apart? (Assuming it¹s a
> parallel, not adjoining, wall issue.)

You should be able to suss this out by walking around clapping and
listening.

> 5. Worst case, I could break the room up into two rooms
> by adding a wall. Would that help, i.e,, is the
> narrrowness of the room an untreatable problem?

Smaller rooms are less likely to have distinct echos with long periods. They
are easier to make bass in.