artto, here is my results with a jpg of a basic room layout.

[artto]

Now, measure the response at all eight primary trihedral corners, (by this I mean the very CORNER, where two walls & the ceiling, or two walls & the floor meet)(you can skip the floor/corner by the subs for now).

After this we'll move on to some midrange exercises to find out what the room is like for things like echo flutter and 'slap'.

And while you at it, could you also provide the height of the ceiling sections where they intersect the front & rear walls, and each other. Also the height of the floor riser sections.

Another question: Are the two side speakers reproducing the same thing? Seems there are too many speakers for discrete 5.1, 6.1 or 7.1 surround sound from each speaker.

[m00n]

WB Asynchronous Pink Noise tests.

===============================================

Volume: -35

Channels: 5

Top left corner of front wall: 85db

Bottom left corner front wall: 88db

Top right corner of front wall: 85~86db

Bottom right corner front wall: N/A

Top left corner of back wall: 83db

Bottom left corner back wall: 81db

Top right corner of back wall: 83db

Bottom right corner back wall: 81

I updated the room image. Sorry for the bad dimensioning. I am using Visio and it's not the best... Also the dimensions along the top will not be as accurate as the ones on the bottom. The ones that are trying to show how long the rise is on the ceiling slope is a guestimate. However, the 8' flat ceiling span is accurate, just not the slope lenghts.

As far as the hight of the floor, I used 2x4 on end for the first, 2x8 on end for the second and 2x12 on end for the third with 1" flooring covering them.

The side surrounds are receiving the exact same signal on each side respectivly. Meaning the two left surrounds get the exact same signal, the two rights get the same signal. I am using the main surround outputs as well as the surround pre-outs to power the second set of surrounds. The two rears are being powered via the 6th and 7th channel outs on the receiver. Every speaker has 100 watts.

[artto]

OK, good. As Im sure you can see, the sound levels are highest in the trihedral corners of the room. And that it is predominantly in the bass range. The next highest sound levels are in the vertical corners, also predominantly in the bass range. Because of the excessive length to width ratio of your room, this is expected, although most 'rooms' exhibit these properties (the difference is in the 'degree' ).

There are several things that need to be discussed here. So please be patient & try & follow along until the end. I may have to make several posts due to time available.

First I would like to point out the locations of some of the bass traps you were building. The room sound level measurements, confirmed by listening, seem to indicate that there is a fairly substantial increase in sound pressure level, in the room corners, particularly in the bass range.

The places you were building the bass traps are near areas of the room that already have decreased sound pressure level, particularly in the bass range.

The way to increase the sound pressure level and improve overall system definition & clarity at ALL FREQUENCIES, but particularly in the bass range, at those better listening/viewing positions, which are more to the middle of the room, is to trap (capture) the higher pressure levels in the corners of the room. Those sound pressure level build-ups (standing waves), in the corners of the room, are also causing the cancellation at other areas. If you put the bass traps where you originally intended, you would be basically trying to absorb more bass response (as well as other higher frequencies), in or near the area that you need to increase it. Its counter-intuitive. Until you understand some wave theory (which we will not go into now).

[m00n]

One thing you may need to be aware of and I suppose I should have reminded you of is that I started one column's absorbtion treatment before we started working on all this. I am not sure if you had noticed by the previous pics I had posted up in the tech questions. Here is another image of that. It's the right rear surround column.

[m00n]

artto, I have included this zip file with more images of my room from different angles. Sorry that some of them are so dark. Guess that's what I get for making my room flat black. I cranked up the flash on my digital camera as high as it would go.

Images.zip

[artto]

Yes, I'm aware that you've started building those 'bass traps'. However, as I previously stated, they are located in precisely (ok, well, close to) the wrong locations. You are trying to absorb more bass in the location which it needs it the least.

From the photos (helpful, thanks) I notice that the rear doors to the room are basically in the corners. This is where you should be placing bass trapping. And their present location also interferes with walking around in the room. With all the time & money you've already got into this, I still STRONGLY SUGGEST that you obtain some manufactured modular corner bass traps such as those made by Auralex. You need to do this just from the standpoint of being able to experiment freely & quickly be able to experience/observe the results. I beleive I paid about $200 for eight 2' long, 12" deep (at corner) sections in one of their 'custom' colors.

I also think the entire seating area needs to be moved forward. Those rear seats are right up against the rear wall where all the bass piles up. And they are basically under the speaker shelve so very little, if any direct sound from the rear speakers can have any impact on those seats.

I also think you will get better performance in terms of smoother frequency response if you reduce the number of speakers for the sides & rear. Running the same signal through two similar or identical speakers in close proximity to each other causes all kinds of phase (time difference) anomolies which make the sound less coherent and the frequency response very bumpy.

Have you considered making the seating risers some form of bass trap?

[m00n]

Couple of things:

The side traps where not really supposed to be for extreme low frequencies but rather for mids and highs.

Doors? Yeah, I... Well... hmmm... They aint moving man.

Moving the seats? see directly above (Doors?). Not only that, but it's not going to be very often that I have 9 people in my theater all at once. And when I do, the people that will fill the room will be blown away regardless.

Surrounds? The reason for them is because I didn't like sitting behind them. My room is too narrow and when I sat behind them I was not getting very good surround affects.

Making traps from seats? Sure, I would be game for that. What do you have in mind.

One thing I would like to express as I have before, I know this is never going to be perfect. Too many things keeping it from being perfect... Room dimensions, you name it. As I have said, I just want to make it better than it is. Remove as much of the standing waves as possible, and put some absorbtion and diffusion in place to help out.

I will see what I can do about affording some professional accoustic material, however, I am not going to hold my breath... I think my moonlighting job may be coming to an end. And unless I can find some other evening software/web development, I am going to be back on a limited budget.

[Deang]

Rick, how big of a job would it be just to move the back row seating to the front? Just leap-frog that row to the front so what is now the front row, would be the second row.

I wouldn't be so much concerned about bass bunching up in the corners where people aren't sitting, as I would be about the bass standing up in the corners where people are sitting.

Bass traps are also treble traps, so be careful here, and follow what Artto is saying very closely.

Artto,

Since the bass is being generated by subwoofers (that can be easily moved), wouldn't it be more practical to move the subs around a little to smooth out the bass response?

I'm curious about your concerns regarding wave cancellation issues. The surrounds don't seem to be that much closer together than the RF-7's in the front. How far apart should the drivers be from each other to avoid this?

Neat thread.

[artto]

Dean, moving the subs (& even the RF7s) is a good suggestion and is another thing I was going to get to eventually. In Moons room, I think he might get better performance by placing the subs between the RF7s. I think I would also use two that are the same, or even just one. Two may look impressive, but in a room this size & proportion its probably just overkill considering all the other speakers in there. While moving the subs around can help, there is still a fairly large amount of bass piling up in the room corners (on the order of 50%+ increase, 5 or more dB). In order to obtain better sound in the listening/viewing positions, these standing waves need to be controlled. It will greatly improve how deep the system seems to go while at the same time improving detail, definition & clarity not only in the low end, but in the midrange as well.

Regarding the surrounds, the problem here is similar to what happens when you put two speakers close together playing a monaural signal. Here, the two side or two rear speakers are being fed exactly the same signal. They are still relatively close together. The fact of the matter is, the extra speaker is not required. And it does interfere with the sound quality. The effect, albeit to a much smaller degree, is similar to the intelligibility one experiences in, a large stadium for instance, where there are many speakers spread around at different distances, all playing the same signal. Ever notice the changes taking place in newer large scale systems of this sort? They have the bulk, if not all, of the speakers in an array from one location so all the sound arrives at a similar time interval relative to the distance from the speakers to your ear, compared to that between any speaker. Granted, Rick is not going to experience this to that degree. The distances & time intervals are too small. But thats sort of the other extreme to the same problem. The ear/brain can no longer discern them as completely separate sounds/sources (remember, both side speakers on one side (or the rear pair) are reproducing the same signal, not a separate discrete channel for each speaker). But the ear/brain can still perceive the effects of this time/distance differential which is basically a loss of clarity and imaging. I really think this is a case of less is more. This is not a large room. And it has known (predicable) acoustic problems already. So its not really a matter of How far apart should the drivers be from each other to avoid this? It has more to do with reproducing the same signal from two different speakers in a small enclosed space, with the relative distances between each speaker & that of your ears, all being relatively different, not enough to discern them as indvidual sources. But still enough to cause emphasis and cancellations in frequency response in a small space such as this, as well as the resulting phase anomolies that cause a loss of clarity & imaging. All multiple driver systems will exhibit these effects. The problem is how do I minimize this? And this case its easy. Get rid of the extra components that are not contributing anything substantial while at the same time actually degrading the overall system performance. They are not needed for acoustic output requirements. And they are not needed for audience coverage or reach.

Moon, if those traps were supposed to be mostly for the mids & highs, you really didnt need to build anything that large & massive. And like I said before, since they are large enough to act as bass traps, they will absorb more low end exactly where you dont need it. Now think about this carefully. What is the result of this? If more bass is absorbed where you dont need it absorbed, whats going to happen to the apparent sound level of the mid & high frequencies at that location? They are going to seem louder. The sound will be even thinner & with less weight. This is why I keep saying BROADBAND. ABSORPTION. DIFFUSION. BROADBAND. And the first place to start tackling this is in the vertical corners, then the horizontal corners. And if you assume that the absorbers you made also absorb the mid & high frequencies (this is correct except we dont really know how much until after-the-fact), then youve really got problems because there will be this small area near the absorbers where the sound seems sucked out, too dead (no diffusion, too much absorption of the mids & highs).

What I had in mind for the riser bass trap, is to possibly louver or vent the front of each riser so sound can easily find its way inside. Inside the risers (underneath the seating), pack that area with a denser acoustic fiberglass like Owens Corning Quiet Zone Acoustic Batts. If you move the rear seats forward (or even the entire riser area) you could extend this bass trap up the rear wall. Your rear speakers could rest on top of it. It might even help the room proportions somewhat. While this floor bass trap is not in the vertical corners where the biggest problems often originate, it should be large & massive enough to have some impact, without intruding on your existing space.

[m00n]

Dean, to answer your question about moving the seats, I can't move the back row to the front. 2 reasons, the front row would be way too close to the screen and the line of sight to the screen would be blocked by the speakers. Secondly, there is nothing to bolt the seats down with.

artto, moving the entire riser is not really an option. I would completely have to rip it appart and start from scratch. It doesn't move, it's screwed to the walls, not to mention too much work, time and enegry. Also, this is not our final resting place. I figure we will be in this house for about 5 more years then we will sell the house.

In case you have already described it and I missied it I am sorry but what do you mean by broadband?

As far as trapping the bass in the floor? The best I could do would be to cut small little vet type holes and shove fiberglass in them. If you look at the construction, even this may not prove to be very reasonable.

.

I used a lot of bracing in the floor and there is not much space between each floor joist.

As far as the back corners, why can't I also build traps and mount them onto my doors? I can build bass traps that will cover the doors, that little side area beside the shelf as well as below the shelf. While I agree, this may not be as good as putting 100% smack dap in the corner, I would think this would still help.

[Randy Bey]

M00n,

I'll butt in here although I probably shouldn't.

A quick (and dirty) bass trap is to buy a stack of insulation at your local home improvement store. Leave it in the plastic wrap and just stack in in the corners, floor to ceiling.

You should have a cylinder about 3' in diameter with a pink panther grinning at you reaching from floor to ceiling.

This will not do the definitive job of trapping standing waves, but you will quickly see how even a little trapping will help define bass.

The 3' diameter is probably only good to about 100Hz, so don't expect it to do the low frequencies.

When I get that big bonus check I've been dreaming of I'll do the 8' sections of 1/8" masonite that Artto recommends. That and stuffing the curves with some kind of absorbtive material.

[m00n]

Randy, thank you kindly for the suggestion, but if you look at some of my pics you will be able to tell that I have absolutly no room for that. .

[rod gervais]

Moon,

I agree that you need bass trapping - probably low, mid and high trapping in fact.

Ethan weiner has some plans for home built traps - and also manufactures (at Real Traps) standard bass traps as well as mini traps......

Artt's observations are very accurate - although i would suggest (to quote Ethan) that a corner is a corner is a corner is a corner....... - and bass doesn't know the difference between corners at walls and corners at wall to ceiling.

You can decrease the effects of peaks/nulls with Low Bass corner traps at any of the room corners..... and probably some mids and highs in other locations.

I also think you want to consider taking your sweet spot and looking for reflection areas off the walls and ceiling - Artt is also correct about the problems these cause with properly hearing the stereo effects that have been programned into the system.

The potential for phase problems with the extra speakers you've added also have to be considered. Phase cancellation with speakers that close together sending the exact same signals can be a real issue.

A couple things you need to understand - more is not always better....... and what seems intuitive - even common sense - doesn't necessarily work in acoustic design.....

One comment - shy of doing things like moving the seats forward - moving the doors - those types of suggestions that have been made...... you are never ever going to get the back of the room to sound like you probably want it to.

So settle for making the sweet spot the best it can be and live with whatever is left.

By the way - i mention Real Traps not only because i know Ethan (he is a freind and co-moderator at RO)- but also because at least this way you can get some competative bids for comparision purposes.

Rod

By the way - it's nice to meet all the rest of you. This is a great forum.....

[m00n]

So, a few people now have told me that having my two surrounds so close together could be phase issues. What that exactly means, I don't know other than it can cause cancelations of frequencies, which I know is bad. Combing affects has also been mentioned to me. What are combing affects?

So here is my question. Lets say that removing a set of surrounds is NOT an option. What can I do to help reduce some of the issues with having two sets of surrounds? Here are some options I am curious about...

Would speading them appart help? If so, how far appart?

Would changing the type of speaker help? If so, I am thinking about the RB-75's. If I did that, would it be best to also swap out my RC7 rears?

Would absorbtion help?

Would diffusion help?

Again, I am not trying to make a concert hall here, I am simply trying to work with what I have and make it better.

[DrWho]

the comb filter effect is when the frequency response becomes extremely jagged, and becomes a larger factor as freqency increases.

http://www.prosoundweb.com/install/spotlight/bartlett/phase/phase.shtml

that article talks about the comb filter effect as it relates to microphones. the same concepts can be applied to loudspeaker placement.

(if nothing else, it shows a nice graph and explains "comb filter")

http://www.prosoundweb.com/install/sac/v28/2/interact.php

this is another article that talks about room and system interactions and is helpful in understanding what all is going on.

http://www.prosoundweb.com/install/cpm/lobes/lobes.php

this article addresses loudspeaker placement directly and also defines and explains comb filtering. (it even shows you how to deal with it). the last line on the first page says, "The only real solution is to relocate the existing loudspeakers or redesign the array." It also talks about arraying the loudspeakers and all that good stuff.

anyways, if you don't wanna read all of these, then at least read the last article. I think it's the most helpful in your situation. If possible, I would suggest moving your paired surrounds so they are 3 times away from each other as they are from the audience. The other alternative would be to move them close together so that they act like a line array (but if you did that, one speaker would be a better compromise...).

so ya, imma go back into the shadows and resume watching

[m00n]

DrWho, thanks for those links. So if I understand it correcty, comb filtering is a result of two speakers sound waves canceling out and the response pattern that it makes... Yes? They did help me out. But what they didn't tell me is how to create magic solution to my surrounds.

Will diffusion help out with comb filtering? Seems to me as though it would. Now given my room where I have 2 surrounds on teh same wall about 2 feet appart, could I put diffusers between them and if so, would it help? I am thinking about an oval shape, one that would stick out maybe 6" further than the RS7s. I am thinking something along the lines of a slatted diffuser.

If not an oval, how about a rectangular one... One that diffused from three sides?

Here is a crude drawing of what I am thinking in regards to the oval diffuser.

[DrWho]

according to the articles, there is no magical solution except for moving stuff around.

as far as the "diffusor" you mention, i am doubtful. comb-filtering deals with very sharp peaks and lulls in the frequency response. any kind of acoustical treatment would be too broad. Also, I think it would make it sound like it was coming out of pipe. however, it is interesting to think about pseudo isolation between each surround. i don't think it would work or sound good, but it's fun to think about.

btw, for your rear surrounds...have you ever considered using in-wall speakers or even soffit mounting your current speakers in the wall? from all the pics, it seems like that would do wonders for providing more present rear effects (especially in the last row).

another thing to keep in mind..."comb filtering" is also the phenomenom behind stereo imaging. because of the nature of surround content, this might end up being an improvement, or a relatively small defect. take into account the better imaging, and it might prove to be the best method. all that to say, why don't you just try unplugging the front pair of surrounds and compare the differences...maybe even experiment a bit with the placement (like toeing in the rear pair a bit). according to theory, this experiment should increase the clarity...if it doesn't, then plug em back in and don't worry about it.

and lastly, i might suggest playing around with tilting the front speakers up, and moving em side to side a bit (finding that sweet spot)...maybe move the subs around a bit while you're at it.

Ok, i know this post has almost nothin to do with treating the room, but I'm a nut about speaker placement...mostly cuz it's a free fully reversible mod that has incredible impact on the overall sound.

now back to the room...what are you floors made out of? In all the acoustically treated environments i've been in, i've found that the rooms with a "live" floor sounded the best...it's hard to describe, but it's like the whole room is dead, cept the floor (which is usually hardwood or something similar). I was thinking about how you want more of that midrange impact and a hardwood floor would be an early start (dunno how that'd fit into your grand scheme of things though...). maybe patches of hardwood might be a more feasible approach...let arto comment on that first though, cuz i wasn't the one designing these studios, just noticing a common trend. at home, we installed woodfloors and the sound is so much bigger than when we had carpet.

[artto]

If you really want to improve the sound in that room, you're going to have to do several things. How you achieve that is up to you. In order of priority, for right now, this is what you need to do.

1. Bass trapping in the rear corners of the room.

2. Get rid of the extra speakers. They are diluting, not enhancing, the effect that multi-channel sound produces.

3. Get that rear speaker positioned so it covers the whole listening area.

4. Bass trapping across the rear wall/ceiling horizontal corner.

5. You might also try making the whole rear wall absorbing.

These are the things you need to do first. After these things are taken care of we can move on to the next step.

Your room is so narrow it's going to be difficult to apply any significant diffusion to the side walls without making the room feel like a significant amount of space is being taken up. Instead of trying to apply sound absorption or diffusion directly to the wall, would it be possible to take a more 'ornamental' approach like they used to do in older theaters/auditoriums (this doesn't necessarily mean that it has to look ornate or traditional). For instance, a series of freestanding columns along the side walls could provide diffusion. Any 'architectural details' such as wainscots & various trim can also provide diffusion.

Dr.Who's suggestion of a hard floor is good, especially considering that you have a vaulted ceiling. Although, I'd have to disagree with it if one is using Khorns (but that's another subject that don't want to get into here).

Start with the bass trapping (oxymoron) at the rear cornes of the room. I say oxymoron because these traps should also absorb the mid & high frequencies too (broadband)(broadband=wide bandwith. ie: wide range of frequencies). The materials placed as I've suggested should give you good control down to about 75Hz. If you want to go lower than that you're going to need much larger devices.

[m00n]

artto... Hey you are back. I though you had given up on me.

as far as your suggestions,

1. Sure no problem. I will most likely use Ethans designs. This should be very straightforward

2. I am bend on this and at least do a VERY subjective test. I will unhook the frot surrounds... listen. Hook front surrounds back up and disconnect second set of surrounds.... listen. Then hook all 4 back up... listen... I will be listening to the overall quality of the sound, not how many rows it fills up with sound. If the pros outway the cons on running with one set of surrounds I will remove one row.

3. Not sure what you mean about the rears... How does it not cover the entire listening area now? Should I spread them further or bring them in closer? I am assuming you're referring to the RC7s on the back shelf...

4. I will try to figure something out, there is VERY little room behind the RC7s.

5. I have some ideas, I will ahve to draw a pic though in order to explain it...

When you refer to columns, do my RS7 colums count? My riser floor was bare wood for a while, it sounded ok, but adding the carpeting warmed the room up a bit which I really liked. Perhaps after all the other treatment is done, I will look into this.

I am not too worried about going below 75hz anyway. I can't remember exactly what frequency it was, but I read somewhere that at a certian frequency, sound waves will penetrate the sheet rock anway. Is that true? Or is that a different theory all together? Non the less, I will figure out some way to create all in one high/mid/low bass traps for my back corners.

There are two things you never mentioned...

1. You never mentioned the corners where my ceiling and side walls connect. Should I not worry about these for now?

2. Doing something to that first reflection point.

[m00n]

Ok.. so I just did a veeeerrrry small test with only one set of side surrounds, not really a fair test, but a test non the less. My findings are very preliminary and are subject to change

Ok here is what I think.

It was a bit clearer and more defined.

Adding in the second set of surrounds muddied up the sound (just a tiny bit)

A bit of history here... When I got the second set of surrounds I had a different receiver, the Harman Kardon AVR-530 which did not have DD-EX, NOR did I have the rear speakers. Because of that, sitting behind the surrounds was not as enjoyable because the surround sound ended before it got to you. Almost like there was a wall in front of you. My idea at the time was that if I added a second set of surrounds I could have better surround coverage for more seats.

Since that time I have added the two extra surrounds and two rears and a receiver that has 7.1 powered channels as well as both DD-ES and DTS-ES both formats seem to matrix in the rears.

When I turned off the second set of surrounds, the wall in front of me affect was not nearly as bad because of the rears. Thus, I think that if I remove the extra set of surrounds, and move the front set back about a foot, I will have a nice coverage for the two front rows. I am not worried about the back row to much.

You guys may be right after all. And if this is the case, I gotta figure out what to do with an extra amp and two RS7s. Sell them? Maybe... Create my own speaker boxes and use the RS7 parts? Maybe... OR... Sell all the RS7s, the amp and get a different surround all together. Either RC7s to match the back, or some RB-75s. But the RB-75s would then not tembre match the RC7s in back. OOOOOOOOR.

Is the issue you guys have a product of the type of speaker the RS7 is? Or is the issue still going to exist no matter what kind of speaker it is if I have 4 side surrounds?