I'm seeking some applied acoustic advice.

I am using RPG's Room Optimizer software to place a pair of
full-range speakers. From room dimensions and user's
constraints on positioning, the software suggests optimal
speaker and listener positions.

Room Optimizer tries to flatten both the "speaker boundary
interference response" and the "modal response." In the
examples of graphs I have seen (including my room), the former
gets much flatter than the latter.

Questions:

1. What do those two responses mean in practical terms? (For
example, should they be added together to produce the
perceived response?)

2. In finding optimal positions, R.O. weights the two types of
response equally, but that can be changed by the user. Given
that the room already has substantial acoustic treatments
(bass traps and absorptive/reflective panels), would one type
of response be more important than the other in determining
the sound I perceive in the room?

3. I am considering adding digital room correction (Tact
2.2X). If I added that, would the answer to the preceding
question change?

And a general comment:

R.O. gives results based on exact listener and speaker
positions to the nearest 0.1 inch (0.25 mm). Since no room is
exact, no positions are exact, and nothing is a point source,
wouldn't it be more useful to give area-averaged results over,
say, 3 or 4 inches?

Any guidance that might help me avoid moving two very heavy
speakers around, denting my pine floors with each move, would
be welcome!


Mike Prager
North Carolina, USA

Mike Prager wrote:

I'm seeking some applied acoustic advice.

I am using RPG's Room Optimizer software to place a pair of
full-range speakers. From room dimensions and user's
constraints on positioning, the software suggests optimal
speaker and listener positions.

What I have learned in a long lifetime of experimenting (and dicking
around) is that speakers are positioned for IMAGING, not for frequency
response. You position them according to all of the reflection patterns,
room surfaces, listener position, and a dash of experimentation, but you
do this for imaging, ignoring frequencies for the moment. When you're
happy with that, then you EQUALIZE for frequency response.

This little lesson seems reasonable to me, since imaging depends a lot
on geometry, and freq response depends more on the room and EQ. I mean,
what are you going to do if, after you use one of these computer
programs for speaker placement, if the freq response is smoother, but
the imaging sucks?

OK, let's talk about imaging for a moment. How do you know - that is,
what are you looking for in good imaging? Stereo is not just a clump of
sound in the left, or in the center, or in the right speaker. There
should be a smooth transition all the way across the stage. Like if you
play a solo piano, you can tell where every key is, or if there is a
jazz big band, you can place most of the instruments. Depth imaging is a
little tougher, and a loftier goal, but what you should be getting is
imaging that pools OUTSIDE of the actual speakers, in a region behind
the plane of the speakers, from left of the left speaker to right of the
right speaker. Sounds seem to be coming from virtual points in space,
fairly pinpointedly, if recorded that way, anywhere in that region. If
all of this holds as you walk around, even better, but that part is hard
to obtain in smaller rooms.

Now - a good starting point for everything would be to have the main
speakers (L, R, and C) positioned so that the L and R are 1/4 of the
room width from front and side walls. Then place subwoofers in the front
corners and never move them (!). If the main speakers are not of a
designed-in radiation pattern, then experiment with toe-in, to get an
even soundstage as you walk across the room.

Gary Eickmeier

Gary Eickmeier wrote:

What I have learned in a long lifetime of experimenting (and dicking
around) is that speakers are positioned for IMAGING, not for frequency
response. [...] When you're
happy with that, then you EQUALIZE for frequency response.

This little lesson seems reasonable to me, since imaging depends a lot
on geometry, and freq response depends more on the room and EQ. I mean,
what are you going to do if, after you use one of these computer
programs for speaker placement, if the freq response is smoother, but
the imaging sucks? [...]

Gary, thanks for an interesting perspective. By using a
computer program, I managed to get worse imaging AND worse
bass response! So I am back to positioning by trial and
error, and yes, I am planning to use some equalization to
smooth out the response if necessary.


Mike Prager
North Carolina, USA

In article ,
Gary Eickmeier wrote:

Mike Prager wrote:

I'm seeking some applied acoustic advice.

I am using RPG's Room Optimizer software to place a pair of
full-range speakers. From room dimensions and user's
constraints on positioning, the software suggests optimal
speaker and listener positions.

What I have learned in a long lifetime of experimenting (and dicking
around) is that speakers are positioned for IMAGING, not for frequency
response. You position them according to all of the reflection patterns,
room surfaces, listener position, and a dash of experimentation, but you
do this for imaging, ignoring frequencies for the moment. When you're
happy with that, then you EQUALIZE for frequency response.

I use Apogee speakers and the RPG program. I found that when I
positioned the speakers to smooth out the humps the imaging also
improved. Box speakers may be different.

Robert Peirce wrote:

I use Apogee speakers and the RPG program. I found that when I
positioned the speakers to smooth out the humps the imaging also
improved. Box speakers may be different.

To be fair to RPG, I should add that my room has features that
their program just can't model (and is not claimed to model),
and that undoubtedly influences the results. However, when I
took a look at CARA (the more complex alternative), I found it
too complex for the amount of time I have available for
tweaking. For those who put in the time, it is said to give
remarkably good results.


Mike Prager
North Carolina, USA

Mike Prager wrote:

To be fair to RPG, I should add that my room has features that
their program just can't model (and is not claimed to model),
and that undoubtedly influences the results. However, when I
took a look at CARA (the more complex alternative), I found it
too complex for the amount of time I have available for
tweaking. For those who put in the time, it is said to give
remarkably good results.

But still, these effects (of computer aided room positioning) operate
only at the bass frequencies, and what you want to do is position the
main speakers for imaging and place the subs in the corners (ref. Tom
Nousaine and a few others) and then adjust gains and EQs to taste. The
actual effects of positioning the main speakers will be relatively minor
in this scenario. So save a little money and trouble.

Gary Eickmeier

Mike Prager wrote:
I'm seeking some applied acoustic advice.

I am using RPG's Room Optimizer software to place a pair of
full-range speakers. From room dimensions and user's
constraints on positioning, the software suggests optimal
speaker and listener positions.

Room Optimizer tries to flatten both the "speaker boundary
interference response" and the "modal response." In the
examples of graphs I have seen (including my room), the former
gets much flatter than the latter.

Questions:

1. What do those two responses mean in practical terms? (For
example, should they be added together to produce the
perceived response?)

2. In finding optimal positions, R.O. weights the two types of
response equally, but that can be changed by the user. Given
that the room already has substantial acoustic treatments
(bass traps and absorptive/reflective panels), would one type
of response be more important than the other in determining
the sound I perceive in the room?

3. I am considering adding digital room correction (Tact
2.2X). If I added that, would the answer to the preceding
question change?

And a general comment:

R.O. gives results based on exact listener and speaker
positions to the nearest 0.1 inch (0.25 mm). Since no room is
exact, no positions are exact, and nothing is a point source,
wouldn't it be more useful to give area-averaged results over,
say, 3 or 4 inches?

Any guidance that might help me avoid moving two very heavy
speakers around, denting my pine floors with each move, would
be welcome!


Mike Prager
North Carolina, USA

Mike, hello from North Carolina.
There is a lot of useful information on room setup he
http://www.linkwitzlab.com
(check out "room acoustics" and "toneburst cd", the website gives you
enough information to be able to generate the tonebursts yourself in
CoolEdit or code them in C, MATLAB or similar)
Room-analysis software doesn't take into account the frequency response
of the speakers or their radiation patterns.
There is no substitute to measring the in-room response, which
is neither hard nor expensive. I use a system consisting of Behringer
ECM8000 microphone - mixer - computer sound card (Echo Gina) and
CoolEdit software. I found this particularly helpful in matching a
subwoofer to my monitors. It is also helpful in detecting early
reflections (you can actually see the early reflections on the computer
screen and know exactly how early they are). As far as frequency
response is concerned, one should try to do as good a job as possible
without equalization. However, some resonances (peaks) can be tamed
with an equalizer. Averaging over the "listening area" is a good idea,
since one never sits in exactly the same spot all the time.

wrote:

Mike, hello from North Carolina.
There is a lot of useful information on room setup he
http://www.linkwitzlab.com
.....and more..

Friend,

Thanks for the interesting and useful information!


Mike Prager
North Carolina, USA

Mike Prager wrote:

3. I am considering adding digital room correction (Tact
2.2X). If I added that, would the answer to the preceding
question change?

I would just use classic setup techniques, such as dividing the
room up in thirds and avoiding early reflections from the side
walls and use the Tact to fine tune the raw setup before correction.
Tact recomends that you strip the room off treatment and put the
speakers in the corners, but imo this is a marketing gimmick to
maximize the difference between a corrected setting and 'bypass.'
I think you will find RO fairly useless once you start using the
Tact, which is a very versatile piece of work.

wrote in message
...
Tact recomends that you strip the room off treatment
and put the
speakers in the corners, but imo this is a marketing
gimmick to
maximize the difference between a corrected setting
and 'bypass.'

Moving the speakers closer to the corners can make a
huge improvement in the low frequencies in terms of
clarity and impact, especially when used with DSP
correction. There are speakers that are designed to be
placed in the corners; e.g., the Allison One and the
Tact W210. Of course, moving the speakers back
towards the walls will increase the room gain (i.e.,
more bass) as the low frequencies' reflections from the
walls become more in sync with the direct sound. The
Tact RCS will EQ-out the added room gain but retain the
improved time behavior, resulting in tighter, clearer
bass with greater impact. I believe Tact has an
explanation on their website for their recommendation.

I also was skeptical until I moved my B&W801's half the
distance back towards the front corners and was
astounded by the improvement in the bass, even with the
same target frequency response curve in my Tact RCS
(when it comes to low frequencies, time response is as
important as frequency response). If you have an RCS,
I recommend that you give it a try. Or if you at
least have a tone control, move the speakers back and
use the tone control to reduce the added bass. If you
don't have corners, moving the speakers back towards
the front wall will have a lesser effect.

Regards,
Tip

Tip wrote [and I shortened]:

Moving the speakers closer to the corners can make a
huge improvement in the low frequencies in terms of
clarity and impact, especially when used with DSP
correction. [...] the low frequencies' reflections from the
walls become more in sync with the direct sound. The
Tact RCS will EQ-out the added room gain but retain the
improved time behavior, resulting in tighter, clearer
bass with greater impact.

As you said, Tact does offer the same explanation on their Web
site. Still, it is useful to hear from a disinterested party
who has done it.

The conventional recommendation to keep the speakers away from
the front is to improve imageing, particularly depth of image.
What was your experience in moving your speakers towards the
corners -- was there a tradeoff between better bass and less
soundstage illusion?


Mike Prager
North Carolina, USA

Hi Mike,

"Mike Prager" wrote in message
...
Tip wrote [and I shortened]:

Moving the speakers closer to the corners can make a
huge improvement in the low frequencies in terms of
clarity and impact, especially when used with DSP
correction. [...] the low frequencies' reflections
from the
walls become more in sync with the direct sound.
The
Tact RCS will EQ-out the added room gain but retain
the
improved time behavior, resulting in tighter,
clearer
bass with greater impact.

As you said, Tact does offer the same explanation on
their Web
site. Still, it is useful to hear from a
disinterested party
who has done it.

The conventional recommendation to keep the speakers
away from
the front is to improve imageing, particularly depth
of image.
What was your experience in moving your speakers
towards the
corners -- was there a tradeoff between better bass
and less
soundstage illusion?

Yes, there definitely is a tradeoff, and you have to
hit a happy median. I guess it depends on what's more
important to you - imaging or bass (I'm a bass player
;^). But this is the idea behind the Tact W210 & W410
"corner-woofers": put the woofers where they sound the
best (in the corners), the main speakers where they
sound the best (away from the walls), and integrate the
mains and the subs with the RCS 2.2X, which provides
the digital crossovers, level matching, and time
alignment in addition to room correction (needed for
the corner placement). Diffuser panels on the walls
near the speakers may provide a solution, but I decided
to go the 2.2X/W410 route instead.

Regards,
Tip