Room Acoustics Question

[mace]

Greetings,

I've been playing with a tone generator (straight sine wave) which can go from 1 to 10,000 Hz. I've got a 10 year old NAD amp with KLF 30's. Speakers are about 50 cm from each side wall, 20 cm from back wall with about 15 degree toe in. Speakers are about 250 cm apart. The room is about 5 m wide by 8 m long. Speakers are along the 5 m long wide. Carpet in room is berber on concrete, speakers are spiked.

Well with this tone generator I can vary the pitch continously. Upon starting at 2000Hz and just slowly going down I noticed distinct drops in sound volume at various pitches (100, 1500 Hz were very noticable). I then just put the pitch at 1500 Hz, turned balance to left speaker only and slowly walked around the room a bit. As I did it was like a sonic strobe, I could hear the pitch go up and down in volume very distinctly as I moved both laterally and up and down. I then sat in my sweet spot and with subtle movements in my head, like on the order of a cm or two, would make a tremendous difference in pitch volume. At one point I had my head tilted such that the volume was almost very soft in my right ear but I could hear a much higher, quieter tone in my left ear. This sort of thing happened with pitch I tried. I'd set it to 70 Hz, 100 Hz, 250 , 440 etc. and as I moved a bit I got the sonic strobe effect. The strobe effect seemed worse with just one speaker playing than with both.

Anyway, is this normal for home room acoustics or is something else going on here?

What can I do to improve it? I am hesitant to place the speakers in different positions and check out the spectrum response in the sweet spot as it would be rather time consuming. I don't think speaker placement will improve this sonic strobe effect. Plus, I don't want to go to so much trouble just to get an optimized sweet spot which is lies within a range of about 3 mm for one ear only.

Any tips are appreciated!!

Mace

Klipsch Speakers

Denon CD Player

NAD amp

and that's it.

[lynnm]

My room dimensions are similar to yours,(yours 16'x24' mine to 15' x 25'). Given that you have placed your KLF's very close to the wall (8"+/-) and very close to the corners in a room,(which like mine - that has a rather unfortunate width to length ratio - I suggest that the poor sonic experience you describe is inevitable. This is especially true with the rather severe toe in you describe - remember horns tend to be highly directional in the mid and upper end. You are fighting standing wave phenomena and mid/hi beaming.

I moved my KLF 30's to the long wall.I then drew an equilateral triangle between my speakers and the centre of the point where I wished my sweet spot to be. I then experimented with varying degrees of toe-in and distance between the back of my 30's and the wall as I wished to avoid that effect you describe in which the sweet spot was so tight that I could not move my head a little without experiencing a major change in sonic character.

In any event as it stands at the moment my positioning is approximately:

Left about 3' in from the corner and 2 1/2' out from the 25' long wall

Right about 10 1/2 feet from the left speaker.

Toe-in minimal - I have no way of measuring and lack the mathematical savvy to do so but an eye-ball estimate would be somewhere between 5-10 degrees and more likely at the low end of that range.

Sweet spot centred about 10 1/2 feet from the speakers.

Result: More experimentation will be needed but at present I have a very forgiving sweet spot and the sound stage on certain pieces sounds as if it were 20' wide. - Works for me!!

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It is meet to recall that the Great Green Heron rarely flies upside down in the moonlight - (Foo Ling ca. 1304 BCE)

[WMcD]

Very good work.

Nope, there is nothing much you can do about it short of doing a lot of acoustic treatment to the room. The only time this doesn't occur is when the treatment is so absortive that the room is an anechoic chamber.

What you're hearing is the constructive and destructive interference of waves directly from the speaker and those reflected off the walls.

These reflections would be heard as distinct echoes (sp?) in time if the distance was really great. Like a mountain side across the valley. However they certainly exist in rooms with hard walls. The only exception is the anechoic chamber which is without echoes. An-echo-ic. This takes a lot of wedge shaped absorbers to increase the absorbing surface area.

In a real world room, a given set of waves, at a given listening spot, may be out of phase when they arrive. So they add to zero. Called a node. At another spot, they are in phase and add. Called an anti-node.

When you have two speakers working the patterns are less pronounced in some ways; mostly because the pattern of nodes and antinode caused by each speaker overlay on each other.

I did a similar experiment in a room with two speakers and the generator set to about 100 Hz or 200 Hz (as I recall). Moving around, there were a couple of phenomenon. In some spots, almost no tone could be heard. In others it seemed like only the left, only the right, or both were working.

This all takes some appreciation of the wavelengths involved and wave mechanics. E.g. if you find a spot with a null, try adjusting the frequency by 10 or 20 percent. You'll find the null there has disappeared and you might find a new one a few feet away.

I think most people are skeptical about this without a demo like you've given yourself.

The funny thing is that we don't hear these nodes and antinode with most music and rooms. E.g. we don't say that the bass player disappeared entirely.

On the other hand, the reflections can gang up with certain room dimensions at certain frequencies. There might be so much treble reflection that the bass sounds weak. In others, there is so much reinforcement of bass at some frequencies that the room sounds "tubby". Room treatment and relocation of speakers can help. However, it is more a matter of exploiting the phenomenon you hear rather than eliminating it.

I'm not diagreeing with lynnm. Moving stuff around can result in a better sweet spot. However, I think you'll find the same interference patterns at high frequencies.

Gil

This message has been edited by William F. Gil McDermott on 11-20-2001 at 11:32 PM

[RossVTaylor]

Mace,

It sounds like you're suffering from room modes: high-pressure points/locations at certain frequencies. Room acoustics have a HUGE effect on sound and it would be worthwhile working to tame these modes. You can make resonators of your own (there are various plans on the net for both tube-type traps and pegboard-type perforated panels) to absorb energy at your trouble frequencies. You could also try some of the pre-made foam egg-crate or spiked panels, but these may not absorb the frequencies you need. The whole process of determining exactly what you need, and where to place it, is way above my head. But, with the right stuff your "strobe effect" should be controlable.

For materials, you could try Acoustic Sciences or Acoustics First.

If you want professional guidance, I'd suggest someone like Denise Erskine who gets rave reviews on the AVS Forum site.

Ross

Edit: When I started typing this, there were no replies. Gosh, had I known that Gil was gonna respond so quickly I wouldn't have attempted my feeble explanation... whew!

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My System's Stuff

This message has been edited by RossVTaylor on 11-20-2001 at 11:21 PM

[soundog]

Ross-

Interesting sites ... thanks. Some of the material seen on these sites can be had quite reasonably from : www.partsexpress.com

search under: acoustic foam, acoustic tiles, bass traps

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Soundog's HT Systems

This message has been edited by soundog on 11-24-2001 at 07:22 AM

[Marvel]

Believe it or not, recording studios face the same problem, it's just that they spend big bucks for the design ahead of time, or they spend big bucks for fixing it all later. The '70s had most studios killing the room acoustics as much as possible, and then adding reverb, echo, etc., back in electronically. Explains some of the dullness of those albums. Listen to early Elvis recordings (I'm not THAT old) done at Sam Phillips Sun Records, and they are remarkably alive. The floors had linoleum and lots of reflections. Most new studios have a balance of recording areas to control the reflections and ensuing problems. The 'sound' of an instrument is more than the note it actually produces. All the overtones, harmonics, and room reflections give it is sonic character. Humidity and air pressure in a room also make a difference. Is there no end to this madness?

Marvel

[mace]

Happy Thanksgiving all. I'm travelling and thus haven't been able to check in often.

Thanks for all the replies. Just some quick comments. I've been playing around at my parents house with this tone generator and the node/anti-node phenomenon (I like the term "sonic strobing" much better ) is present with their set-up as well, but not nearly to the extreme as in my room at home.

I'll experiment some more and let you know how it comes out. I'm also going to try and see if the room dimensions correspond to any of my problem frequencies wavelengths and such. I copied some tables from my trusty CRC handbook which has sound speeds for all different frequencies and humidity levels and temperatures and such... although those effects are pretty minimal, to say the least. I'm hoping for a decibel meter for Christmas.

Mace

[mace]

Hello Again,

I've now had some time to experiment a bit and I've found some new things out. Thanks for the advice about speaker placement lynnm and Dr. Gil for the background info. And, your comments were spot on and I didn't read them through until after I did some more experimenting. You can move the bass nodes around but the high freq. nodes are everywhere.

For the following, "sonic strobing" is the phenomenon where you play a continous sine wave (30-10,000 Hz) through the speaker or speakers and move about the room and the sound volume gets noticably louder and softer as you move.

My observations:

1) I tried different toe in angles with the old placement (close to back wall) and the sonic strobing still very present all over in room and in sweet spot.

2) I pulled speakers out to 44 cm from back wall and used 5 degree toe in, which do not point speakers directly at the sweet spot. The room is still filled with sonic strobing. The sweet spot has less strobing under 2500 Hz but still much strobing above 2500 Hz (i.e. small movements in head really move the tone from left to right ear or produce great changes in volume).

3) I've reproduced the sonic strobing in two other rooms with two different kinds of speakers (EPI's and Boston's), both traditional radiating types. The sonic strobing was just as extreme to my ear (no actual dB measurements made). These rooms were very different than mine (size, shape etc.).

4) When listening to something bassy where bass walks up a scale I do notice the volume change depending on where I'm at in room.

Conclusions:

1) Wavelength of higher frequencies is on order of 2-14 cm (above 2500 Hz). Therefore, if there are room reflections the strobing effect (nodes and anti-nodes) will be present like a lattice with spacing of 2-14 cm (or less for higher frequencies) thorughout room, including sweet spot, regardless of speaker placement.

2) For frequencies 30-2500 Hz (14 - 1,150 cm wavelength) speaker placement can effective remove sonic strobing from sweet spot by placing nodes and anti-nodes away from sweet spot.

3) Probably have to get some sound dampening in room to get good acoustics.

Questions:

1) It was mentioned that 5 degree toe in was good (which I find good for my current speaker placement) and 15 degree toe in was bad. However, I've read on this board that the speakers should be pointed right at the sweet spot. Typically, from what I've gathered here, you want the speakers and sweet spot to make an isolese triangle with speakers on short end. With this situation the toe in angle would generally be much more than 5 degrees, more like 15-25 degrees. As a general rule, which should one follow? Aim speakers at sweet spot? Aim speakers to point at some point behind sweet spot.

2) By putting the speakers on the long wall, don't you get a "stereo hole"?

3) Has anyone else tried to run continuous sine waves and walk around in room? I got a decibel meter (radio shack) and the stobing effect was up to 20 dB by just moving the meter about 5-10 cm.

To-do:

1) Measure frequency response curves at sweet spot for different speaker placements to optimize sweet spot. This is what I wanted to avoid but there is no avoiding it. I think tblasing put up a post a while back outlining this in detail. The dB meter is pretty cool. I played with my amp settings like bass EQ, loudness and low level, and sound was within 1 dB of what the amp was doing

electronically.

Mace

PS At one of the above sites they had an interesting report on sound dampening of egg crates.. see attached .pdf.

[lynnm]

Further mucking about W/O test equipment has resulted in my moving my right speaker about 18" closer to the left speaker and the soundstage seems tighter without any tendency toward creating a left speaker/right speaker effect.

Thus when sounds that are recorded/produced/intended to be perceived to be coming from the extremes of the sound stage are heard as coming from the extremes.

I do not question the value of measurements but given that we all have major differences in how each of our ears respond to various audible sounds - the best I can offer is that one should strive to find the speaker placement that is most sonically pleasing to ourselves and accept that no test instrument can ever be designed to account for the infinite variety of our individual reception equipment. Test instruments however can very definitely assist us in that approximating the optimal placement which we can tweak according to our needs.

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It is meet to recall that the Great Green Heron rarely flies upside down in the moonlight - (Foo Ling ca. 1304 BCE)

[avman]

i found too narrow a sweet spot for my appplication was remedied by toeing the speakers in a little less. as far as the other issues are concerned, i'll leave that can of worms to other forum members.let us know...avman.

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1-pair klf 30's

c-7 center

ksps-6 surrounds

sony strda-777ES receiver upgraded to v.2.02 including virtual matrix 6.1

sony playstation 2

dishnetwork model 7200 dishplayer satellite receiver/digital bitstream recorder

pioneer dvd player

sharp 32"tv and sharp xv-z1u lcd projector

panamax max dbs+5 surge protector/power conditioner

monster cable interconnects/12 gua.speaker wire

a 'teens' sub coming!(RSW-15 LOOKIN'GOOD!)

KLIPSCH-So Good It Hz!

[soundog]

The room is a very important and often neglected component of the system. Positioning of speakers is one element. The other elements are the proper application of absorption, diffusion and reflection principles. Either a consultant or some study and lot of trial and error can yield dramatic results. If you can describe the structure and contents of your room, I will be happy to give you the benefit of my experience (more trial and error than expert}. Perhaps some others will also.

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Soundog's HT Systems

[Guest BobG]

The toe in angle will have little to do with the nodal pattern unless the 90 degree wide dispersion pattern combined with the proximity of nearby walls and the toe in angle allows for much energy to be reflected off those walls. With lots of early arrival reflections, you get lots of interference - the summing and cancelling you've described as the strobe effect. While this causes abundance or absense of bass, in the highs, it causes ragged and annoying response. Toe in sufficient to minimize early arrival reflections from nearby walls is a great help, especially with horn-loaded speakers that are able to control dispersion.

You can do an interesting experiment by taking two small (smaller is easier but big will work) speakers and placing them side by side, fronts even. Now, play pink noise or interstation FM noise through them IN MONO (you can hook both to one channel if you don't have a mono switch). While you listen from your normal position, have a helper move ONE speaker forward (or backward) about 1". You'll hear major changes in the sound due to the interference pattern between the two sources. Every time a speaker is moved, the tonality will change - a lot. Now imagine the reflections from a nearby wall and the speaker producing the sound. It's really the same situation as with the two speakers. Every time the distance between the speaker and the reflecting surface is changed, the tonality changes. You can put up with it or you can try to minimize wall reflections. Point the speaker away from the wall, move the speaker futher from the wall or put absorptive material on the wall where the sound hits it.

The reflections that arrive at your ear less than 20 millisecconds after the direct sound are the most damaging based on human psychoacoustics. Thus, reflections from the back wall don't have much impact on tonality.

Now, about speaker spacing and toe in. If your speakers are too far apart, you'll get a hole in the middle. Sounds that should be centered in the image, will instead seem to come from Left or Right or both but not from the center. If the speakers are too close together, there will be little breadth of image (duh!) and the imaging will be very 'confused'. I start with the speakers apart about 70% of the distance from me to the speakers. If the image is bunched up in the middle, widen the distance between speakers. If there is a hole in the middle, narrow it up. If you have the speakers too wide and try to toe them in to accommodate, the image depth diminishes and everything seems on the same plane or distance from you. Ideally, you should achieve a wide sound stage, lots of layered depth and distinct lateral placement of sound sources in the image. Keep speakers at least 1-2 feet from the rear wall. Otherwise you'll get boomy bass. Too close is too boomy with little deep bass. Too far robs the reinforcement the wall provides to support deep bass. Also, too close to the rear wall or any reflecting surface interferes with depth of imaging.

Bob out.

[mace]

Hi,

I agree, our ears our the final judge as to what sounds good and what doesn't. But, I do like to quantify things... I did some tests at different frequencies (I tried to use frequencies that weren't factors of each other (2, 4, 8 etc.).

I measured the dB level of a range of tones at the sweet spot for both my left and right ear positions (20 cm apart, 8"). The amp was set to stereo mode with both speakers on. The results were pretty dramatic at some frequencies. Between 100 and 4000 Hz the sonic stage is a mess, with vast differences between my left and right ears. Of course, that range is exactly where most of the action is.

I've attached a graph of the results as well as a rather busy schematic of my listening room. (I thought I'd be clever and just scan in my house plans for that room and draw over it... it turned out rather poor).

I figured that with the side wall reflection the sound would only get to my ears about 2 ms later than the straight path.

Any feedback on alternate speaker placements would be welcome!! I'm very limited by fireplace, glass doors to outside and big couch.

I'm going to change the toe in and see if that helps. I also want to measure the same thing with only one speaker playing at a time. I looked at some of that acoustic foam stuff as well as acoustic panels and they are a bit expensive...

Thanks,

Mace

[soundog]

Generally speaking, the "sweet spot" would be located at about the apex of an equilateral triangle formed by the two speakers and the listening position. Perhaps a swivel chair placed about 3/5 of the distance from the wall behind the speakers and the opposite wall. A listening position against the far wall from the speakers is less than ideal. Of course, without a dedicated music room, compromises are inevitable. A heavy drape that can be drawn over the glass doors would probably help (experiment with a heavy blanket or quilt). Does the recliner block the left speaker? The back shelves if filled with books of different sizes could provide diffusion if they were not so close to the listener. You can also experiment with acoustic treatments on the walls. It appears that you room is too "alive" as is.

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Soundog's HT Systems

[mace]

Hi again,

I've uploaded a pic of the room where the speakers are. I also took some more dB measurements at a position which would make an equilateral triangle with the speakers. The response wasn't any better, but I didn't toe in the speakers either. See attached pictures. I did measurements with just left, just right and both left and right speakers. Tone was just a sine wave.

Question: Is such an extremely bad response curve typical for the average living room?? I mean, there is a 26 dB spread, which seems extreme!! Maybe my speakers are defective.

I think acoustic treatment of the room is the only option to improve things at this point.

Any tips would be appreciated!

Mace

[WMcD]

I think this is not too bad. I'd say there is nothing wrong with your speakers. You may be expecting too much from your tests.

We're used to seeing sound pressure curves which have been massaged quite a bit or at least are not done with a single tone. There are articles written about this. I.e., what is a reasonable test set up and data.

The following may seem like cheating. But the effect of sonic strobing, room effects, is so great and unpredictable, that efforts are made to find a way of averaging it and looking for underlying, general trends.

One starting point is to realize the numbers resulting from what you're calling sonic strobing. Let's assume you have a 70 dB reference. If you wind up at a node for a given frequency, the level can go down to essentially zero. However, when you are at an anti node the level can go up by a factor of two, but that is only 3 dB. Therefore, the overall effect in dB tends to be small peaks and very deep dips. So you can expect 73 dB and down to, let me say, the lowest level you can measure.

That is just the number theory. Something to keep in mind. An anti node from reflections can cause a big dip. We can recognize that it has nothing to do with the speaker at all.

The use of a single tone at a measurement frequency results in such ragged and unpredictable results that the professionals don't use it.

In speaker testing, the speakers are dragged outside where there are no room reflections. Or put in an anechoic chamber where there are no echos.

When trying to get the response of a speaker in a room, the data is massaged a bit by various techniques. Essentially, the pros look at the response of the mike over 1/3 rd octave. I don't have the math here to give you numbers. But we know that doubling the frequency is a whole octave. Like going from C to C above C on the piano. In 1/3 rd octave, you're talking about a range of 4 half notes out of 12 half notes (in an octave) on a piano scale. I think that is like C to E flat.

There are a few ways of getting this range at a frequency test point.

One is let the mike, like the RS unit, listen to everything. But the input tone to the speaker is a warble tone which moves around the center frequency by 1/3 octave. If you hear this, you'll notice this is the sound effect for a Star Trek (original) phasor pistol.

The other way is to use "band limited pink noise". There are typically recordings of this. The noise is limited in the frequency band.

Note that in the above, we're putting a test "tone" of 1/3 rd octave wide into the system and the mike is not limited. The meter will bounce around and you can approximate the average. The average setting on the RS meter can help.

Another way of smoothing the response in the result is to use sophisticated devices which sweep the frequency up the band and record every point. But then every frequency point data is then "smoothed" by averaging it with nearby, in frequency, points. With computers, this is easy. This is 1/3 octave smoothing. Ragged curves become respectable curves.

There are other techniques. One is to take measurments at several points in the room, perhaps near your sweet spot, and average them.

PWK at least once spoke of a techniques which seems to honor the theory that dips are ignored and response is averaged. This was from the days when an ink plot was run on a long strip of paper in scientific events. You see this sort of plotter thing on "lie detector tests" in movies.

He'd take three or four measurement at different mike locations but put them all on the same paper chart by restarting on the same piece of paper. I'll assume he was using his "Klipsch Logarator." I'm inferring this from his few comments.

This must have resulted in a lot of ink on the chart. However, you can imagine that the dips were irregular and did not overlap. However, overall trends would be where the ink traces overlapped and traced a broad line. We may be seeing these results on the old spec sheets for the Heritage series.

The "bottom line" is that the raw data from your test has long been realized as too "noisy" to show the underlying trends.

Let me ask my friends out there. I had an excellect test CD by Alan Parsons called "Sound Check". It is now out of print and mine was lost. It has the band limited noise needed to run tests described above. If any one has it, I'd love to borrow it.

Regards,

Gil

[Colin]

I do not think that your actual listening room response was that far off, it is not extremely bad, few speakers measure very well in real world cicumstances, but I am surprized at the suck-out below 100 Hz, this is an area where speakers manufactorers try to make sure that there is some boost there as it adds to the bass,

try to move the speakers further away from the back and front walls and see if that improves them, your room dimensions are just about ideal, a rectangle instead of a square,

but try your listening spot about 50% farther back, if the two speakers are 250 cm apart then your seat should be 375 cm back, Klipsch often sound better as you get farther away from them, the image will be better and the frequency response might improve ...

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Cornwall 1s & Klispch subs; lights out & tubes glowing!

This message has been edited by Colin on 12-12-2001 at 11:19 AM

[mace]

Hi,

Colin: The suck-out around 100Hz happens to be an anti-node in the room, not the speakers... a couple of meters away the sweet spot 100 Hz gives a normal response.

Gil: I'd love to get ahold of such a test CD with the +/- 1/3 octave white noise. However, I don't fully understand how the data I've collected is "noisy"... it seems that it exposes the raw limitations of my room/speaker placement. I mean, when I listen to organ music (big old cathedral organ) some deep tones are somewhat soft and as the tone moves down lower it gets really loud... i.e. I can hear the sonic strobing in music. I approach the room acoustics problem that if a room response can be "flat" with single frequency tones then it would be "flat" with the +/- 1/3 octave white noise. If the room response was flat with +/- 1/3 octave white noise it may or may not be flat with single frequency tones. This is just my opinion, please correct me if I'm wrong!

Bob: I'm going to do some playing with speaker to sweet spot distance...

I'm surprised no-one commented how strong the 30's are below 50 Hz. Most stuff I've read here has commented how rapidly they fall off below 50 Hz. Part of the good response in this room is that I do keep the "Bass EQ" button on my amp in, this provides a +6 dB boost at 40 Hz, +3 dB at 70 Hz. I think it helps keep the bottom strong with no boominess at all... so no subwoofer really needed for 2 channel audio.

I do wonder if the blue chair in my room blocks the woofers to much in the left speaker causing some weird reflections/dispertion/absorption...

My thanks to everyone for all the help and input! Merry Christmas!!

Mace

This message has been edited by mace on 12-22-2001 at 10:54 PM

[WMcD]

I received some e-mail from a gifted and experienced engineer regarding my comments. He gave some input and suggested more reading, which I've yet to complete.

I should watch being too pedantic.

There are some overall themes which have to be appreciated. The issues are complicated and I'd like to set out why there are no clear answers, or tests leading to audio nirvana.

1) If you want to test the speaker alone, it pretty much has to be done in anechoic conditions. The best way seems to be outdoors. This means, usually, putting it on its back in a big yard. This is half space. There are no reflections except from the "floor". The alternative is an anechoic chamber. I read that even the largest chambers have "room" effects at low frequencies.

2) Once you get an anechoic measurement of the speaker, you will find some it is non-flat. Dr. Toole of Infinity states that large, narrow peaks (high Q) are difficult to detect by ear, while little, broad trends (low Q) are easy to detect by ear. "Detect" as I use it, means that you can or can't hear them. The theory is that music does not excite them.

The bottom line on this is that a speaker can flunk a plus or minus 3 dB test because of high Q problems. Yet one with a response fitting in plus or minus 3 dB window can have audible "issues" if the anomalies are broad.

Toole's conclusion is that any frequency response curve has to be interpreted with a lot of insights which don't come without experience. The biggest problems may be the ones which are least likely to be measured.

3) The next "problem" seems to be what we are trying to measure when we test in a room with test equipment of many designs. This is not well identified.

In my reading, there are many techniques. Some, with limitation, try to minimize room effects. None are totally effective, particularly at low frequencies.

If room effects can be filtered out (perhaps simulating anechoic conditions), then we can identify problems with the speaker. A manufacturer can say, correctly, "This is a room problem, not a problem with my speaker." Treat your room.

4) Despite the above, we listen to our speakers in real rooms. Let's assume we have some agreed to source, and agreed to electronics. We're listening to the speaker, and the room, at an identifed location in the room. Those are three variables which interact.

You've identifed the sonic strobing while moving about the room (different location) with a constant frequency.

You've also identified sonic strobing with various bass frequencies as the organ notes vary (same location).

I believe this is a listening condition which is not contemplated by Toole's work. The pedal tones are long term. They may well overlap with high Q room modes at the listening position.

People playing with sub placement identify the issue of speaker placement and listening location.

5) How about our hearing? Bob G. points out that early arriving reflections are the most damaging. This is not a bass issue, but is very important.

It implies that early arriving reflections causing "sonic stobing" is bad, but late arriving ones are ignored by our hearing. None the less, both create a ragged response. How can we tell what ragged response is good or bad?, just by looking at a ragged response.

Naturally it can be done with sophisticated time domain equipment, or it wouldn't have been discovered in the first place.

He points out that directional speakers (some horns at some frequencies) can reduce early arrivals by keeping the treble off the walls. So there will be less sonic strobing. Klipsch is addressing the problem of speaker / room interactions.

Bob didn't say this, but our speakers don't have directional bass in a strict sense. Yet because of interference effects from the room (nodes and anti nodes), the listening level changes from one location to another. And from room to room. Treble can be controlled at the speaker. Bass can't be.

6) The above are all the product of very serious engineering studies. (Please appreciate why I'm not a fan of super wire upgrades. This acoustic stuff causes gross, measurable, anomalies in frequency and time response. Wire has none of these. Yet people go nuts over wire.)

7) The issue at the beginning was (if I may be presumptuous about anyone's thought processes), (a) "I want to test my set-up at my listening position to determine whether it is good or bad." ( "Now that I have the test results, does the data tell me something about whether it is good or bad?" And ©, "If I can identify what is good and bad, how do I make it better?"

8) I've been wrong to suggest that something a step or two up from a frequency generator and an RS meter is going to give a solid answer to (a), ( or ©. The most gifted engineers with the most sophisticated test equipment look for the answers.

9) The room is definitely the problem. Please note that the movie theater industry wants what is essentially the listener in an anechoic chamber with very well controlled directional speakers. Unfortunately, we don't have that at home. The horns can do some of it thought.

Gil

[soundog]

Perpetual Technologies is working on both speaker correction and room correction software for their P1A Correction Engine. It is their intention to produce sofware for specific speakers (the KLF-10 is scheduled - why they chose that Klipsch speaker before all others is a mystery to me) and a kit to measure other speakers and also to measure and correct room anomolies. Great idea, if they can pull it off. I would imagine that some acoustical treatment will be required in at least some rooms.

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Soundog's HT Systems