[nodiak]

Any experience with curtains for large front wall window? It's 36" x 96" ! From reading my understanding is that typical curtains are good and bad - as they're not broadband.   
I will be putting absorption right above it, and diffusion on the ceiling ~12" out from front wall.
I've thought about using blinds and adding layer of flannel or ? to them. Could cut wavy pattern end pieces the blinds would rest on and shape to (does that idea come across?  Not sure how to write it).
Open to any ideas.

Don

[bpape]

At least it's the front wall and not on one side.  You can make curtains more broadband by making them thicker and also by making sure you have enough so that even when they're closed, they still hang 'full' (not flat but stil lots of waves back and forth front to back).  This adds to the apparent thickness of the material and will better broaden their absorbtion range.

The other option is to ditch the curtains all together and use larger wooden horizontal blinds so it's more of a diffusive effect.

Bryan

[nodiak]

Bryan, I like the slat style blinds idea for diffusion. Going to look around , and think about building some too.

[Russell Dawkins]

My wife teaches music at the local university and the faculty all have studio/offices that were well designed acoustically at the outset to permit the playing of various instruments from strings to brass and woodwinds in these smallish rooms without driving the musicians nuts. By this I refer to the fact that many of these instruments, heard live and at close quarters are surprisingly LOUD.

The acoustic approach here is highish ceilings, serious angles on opposing walls (minimal parallel reflecting surfaces) and two walls of adjustable heavy curtains. These are moved back and forth, depending on how live a sound is wanted, and they make a huge difference.

On inspection, these look like stage curtains, i.e., conventional but just plain heavy! They are generously oversize, as bpape suggested and not right against the wall. The heavier they are, the more the absorption will extend into the bass frequencies, as I understand it.

I would go with heavy curtains instead of diffusion, as I favor absorption at the front of the room, based on my priorizing imaging precision and tight bass in the list of qualities I value.  I think most home rooms are more reverberent in the bass than the treble, and the way to correct the balance is to absorb bass energy more than treble energy.

[bpape]

Agreed on the absorbtion up front - but no matter what you do with curtains, they're not going to work from 100Hz down - unless they're 2-3" thick and fullness of 6-8" when closed.    We can still deal with the window via the large blinds (like 2" wide slats) in the middle and then deal with the bass and some absorbtion via corner absorbers.

My assumption is that this is a multi-use area that people have to live in and use for other things so we need to be somewhat visually friendly.

Bryan

[nodiak]

The room is 11.5' wide and 7.5' high, but 26.5' long which helps alot. It has a full carpet and padding which seems to absorb alot of the highs, and maybe mids. However it has hard plaster walls and ceiling which caused alot of treble reflections and confusion in the soundstage.
I didn't want to change the amount of treble in the room untill the reflections were calmed down. So I've been going with diffusion first, and so far it's working well to stabilize imaging and cut down on overhang. After hanging 4 large diffusers on the walls the amount of treble seems to balance out pretty well. And the "sproing" from the clap test has been almost removed. There's definitely still some excess reverb and sustain. I have 2 more wall diffusers to go and 1 or 2 for the ceiling.
I'm beginning to understand the value of diffusion, and am liking it. I like a room that's a little bit lively, but hate echoes, diffusion so far seems to be the answer for me. 
As for absorption on the front wall there will be full length 24" wide absorbers in each front corner in a few days, and 1st reflection absorbers on walls and ceiling. For me I'm guessing that will be enough adbsorption in this room. Then I'll have a better idea on how to treat the window in between them - curtain or slat type blinds. My issue is to not let the room get too dead while controlling reflections.
It's a living room, but my apartment. It's people friendly but audio is a big part of it's function.
Don

[bpape]

I'd guess that would likely be enough to suit your taste.  The only other thing I'd consider would be some thicker absorbtion on the rear wall centered behind the seating to kill the deep null that usually exists off the rear wall.  Also, you may want to consider some additional bass absorbers in the rear corner - but with FSK facing on them so the amount of highs absorbed is seriously reduced.

Bryan

[nodiak]

The listening seat is 9' from the rear wall, which almost isn't there, kinda. The middle 4' is open to steps that drop ~3' to a dining room. My plan is to use a curved diffuser/reflector above the steps that should direct much of the music into the dining area, and some down to the floor in the main room. Could try absorption too to see what works best. Anyway the opening should help avoid some of the typical rear wall reflection problems.
The corners of the rear wall are closets with doors removed. One is for this computer station, and will have it'stop half filled with fiberglass in bags. The other gets the fiberglass in bags in top half too, and may put a panel trap in front where the door would go...or get some more of the cotton bass buster instead.
The upper rear corners get small diffusers.
Funny this diffuser thing got going before I got to the rear wall, so things aren't happening in the best sequence I imagine.
After living with it a week or so I'll start taking out diffusers and see what their doing.
Don

[bpape]

Sounds like you've got a good plan going.  The opening in the rear may certainly prove to be a benefit other than making it harder to pressurize the space for deep deep bass.

Good luck and keep us up to date as things progress.

Bryan

[nodiak]

Good point about the deep bass. Hoping the Rythmik servo sub can pull through.

[HiFiJake]

Good point about the deep bass. Hoping the Rythmik servo sub can pull through.

If you have modal problems in the low frequencies in your room, you can throw all the power and speaker design at it in the world, and it still isn't going to overcome the actual physics of the room.  You NEED low frequency absorption.  That will flatten out the peaks and dips in the frequency response of your room that are caused by the phase relationships of the sound reflected from your room boundaries to the direct sound from your speakers.  At certain distances and certain positions in your room, you are going to get interference between the two sound waves that can either cancel each other out (causing dips) or enhance each the sound at given frequencies.  That's related to the dimensions of your room.  You can't defy the laws of physics.  At least not last time I checked. 

As for the "diffusion" thing, I agree with the others that you are better off with some heavy curtains instead of trying to use the slat blinds as "pseudo" diffusors.

The problem is that you won't be getting even diffusion at all the high and mid frequencies, and you may even end up with an unbalanced sound or less clarity with your imaging.

Just because something scatters sound doesn't make it a "diffusor."  Diffusors are designed according to careful calculation of acoustic principles.

Don't be afraid of absorption in a listening room.  Obviously you don't want too much absorption in the highs and mids, but for the first reflection areas, you'll do better with absorption if you want to get really clear and accurate imaging.  When you have too much mid and high frequency absorption and not enough bass absorption, that's when you end up with a room that sounds too dead and muddy.

I can tell you getting a balanced amount of absorption did wonders for my room, getting some good low frequency absorption, and then a bit of absorption for the mids and highs at the first reflection points.  The lows really tightened up and became more clear, and the imaging is now pinpoint.  And now I actually hear the reverb that's on the recording from the room the music was recorded in instead of just a jumbled mess of the reverb on the recording combined with the sound bouncing around my room!

If you are really dead set against putting heavy curtains up on that window, maybe you would be better with something like this:  http://www.rpginc.com/products/clearsorber/ClearsorberPanel.pdf   At least that would be something that is properly designed.

[bpape]

Not suggesting that he not have bass absorbtion and not suggeting that he have all diffusion.  The front wall between the speakers was the special case.  I agree that the blinds aren't true diffusors.  They're not supposed to be.  They're simply a way to isolate mids and highs in the room from bouncing directly off the glass and scatter them a little bit in the vertical direction.  They're certainly not going to disperse as evenly as a poly or as randomly as a QRD.  In a primarily 2 channel environment, this is not a bad thing.  In a multi-channel environment, yes, it should be absorbtion.  I'll agree that I prefer absorbtion at the reflection points.

The comment on the Rhythmic was to be able to pressurize the room with a large opening in the rear - nothing to do with overcoming modal issues or as a replacement for bass control inside the room. 

Bryan

[nodiak]

HiFiJake, no need to play the expert here, especially with your first post. I was enjoying no ego tripper had come into these threads as happens so often, turning everything into a power trip.The thread is just about working on a specific part of the room. Of course all parts need to work together. And each room is different, mine is a work in progress. I don't mind posting my audio/acoustic ignorance here, it's a new subject to me, and that's what the forum is for in my understanding. Just learning as I go. If you don't have the patience (maturity) to watch, don't. If you've got experience to share go for it, I'd be into hearing about it, really. If you need a target to snipe at from your hidden computer foxhole, you got me dude. (BTW, there's no guarantee I won't become the next so and so once I think I know what I'm doing!).

Modal problems weren't mentioned, pressurizing the room was - for deepest bass frequencies. I can't seal this room for that purpose. So the sub comment.
Modal-wise the bass in my room has been pretty good actually, and so far some rear corner absorption has been done.
I think the biggest factor in that MAY be (has to be?) the 8' couch located at 62% distance from front wall. It's a fat stuffed type. In this 11.5' wide room it absorbs/blocks/effects all frequency waves that come it's way. I'm not going to move it to find out, but it's gotta be doing something (alot?). Bass has been tight and clean, and although some peaks along a side wall, no deep nulls front to back in the places I listen.
BUT then last night I put up full length absorption straddling the front corners. It made the bass worse - it became softer, and wasn't as even throughout the room, sidewall peaks got stronger, and imaging was tilted way up. Because the (cotton) absorber is uncovered it is broadband and I'm guessing the midbass/upper frequency reflection was lost from the soft cotton absorber, taking away the sharpness these frequencies add...? I'll try a shorter piece later tonight to see if having some wall exposed brings back the sharpness. Also try plastic or other reflective material on it's face. Maybe need more bass absorbers to even things out...

As for the "diffuser" issue - welcome to the mix of theories and opinions. I've read both "experts" and laymen using the term to describe curved panels and/or well type constructions. I have both types and will be experimenting with what works where in my room. So far the curved panels have helped smooth reflections, but there's still plenty to do.
I'll be trying both absorption and "diffusion" on front window.
Don 

[bpape]

Give the full height absorbers a few days.  It is a very different sound when you don't have the 'room boom'.  Also, most likely the other things that you're hearing now have always been there - just masked by the long decay times in the bottom end.  Shortening them won't help fix the other things - just mask them again. 

In all seriousness, listen with the full height ones for a few days and get used to it.  Then pull them down and listen again.  You might be surprised at your impressions at that point.  You may still prefer it with shorter ones but you owe it to yourself to hear all the nasties that come back when you take them down. 

Bryan

[nodiak]

I'll do that. I listened a bit this morning, and started to feel what you're talking about - it's just different. And my brain is used to the room untreated, so it needs to try this.
Need to use this thick material to treat the sidewall/floor spot too it seems. Chase the bass around the room, and treat?
Also, the visual effect of the corner traps threw me off too, like having stuffed polar bears standing in the corner of the dining room! "How's your soup dear?" "oh, uh, it's great, great, uh sure, soup..."
Don

[AB]

I haven't seen anyone mention a point so I will.
With every new treatment added or any change in my existing treatments, I found it necessary to adjust my speakers positioning. With less bass in the room, I discovered I could have less toe in. With diffusion behind my listening seat, I found I could have wider seperation. With first reflections absorbed, I liked a bit more toe in than without.
The various treatments and their positions impacted the tonal balance of the room so much that I needed to move the speakers around a bit to find the best sound. This effect even extended to some tweeks I use with my preamps and CDPs. With everything trapped and absorbed and diffused, I am finding now that I need more bloom in the bass and so have removed the tube dampers from one CDP.
One little thing leads to another...

[nodiak]

AB, good call, just finding out those things. Have to go back over everything and adjust again.   

[Russell Dawkins]

I just found a source I had bookmarked for "acoustic" curtains:
http://www.extremesoundproofing.com/Curtains/curtains.html

[HiFiJake]

HiFiJake, no need to play the expert here, especially with your first post. I was enjoying no ego tripper had come into these threads as happens so often, turning everything into a power trip.The thread is just about working on a specific part of the room. Of course all parts need to work together. And each room is different, mine is a work in progress. I don't mind posting my audio/acoustic ignorance here, it's a new subject to me, and that's what the forum is for in my understanding. Just learning as I go. If you don't have the patience (maturity) to watch, don't. If you've got experience to share go for it, I'd be into hearing about it, really. If you need a target to snipe at from your hidden computer foxhole, you got me dude. (BTW, there's no guarantee I won't become the next so and so once I think I know what I'm doing!).

Don,

Sorry about that.  I didn't mean for it to come off in that way at all.   I'm not here for any kind of ego trip or to take swipes at people or anything like that.  I know some things, and I've been hanging around acoustics forums a lot over the years, but I definitely don't know everything.  I was actually trying to be helpful.  I probably didn't read your post carefully enough either.

Please pardon my bull in the china shop!

But what's this thing about pressurizing the room for low frequencies Bryan is talking about?  I don't understand this concept.  You don't need to 'pressurize the room' at an outdoor concert.  I've never had a problem hearing low frequencies at an outdoor concert.  Why would you need to pressurize a room when you are indoors?

[bpape]

Being outside is a completely different thing.  First of all you have a ton more drivers moving a ton more air - and you're not trying to reproduce 20Hz outside.  Real home subs in real rooms make use of and count on room gain to do their job.  When you have 'holes' in the room, much of the sound leaves the room and is lost. 

It's a delicate balancing act to get the room to pressurize so you feel the bass instead of just hearing it but not have it so out of control that you have resonance and decay time issues - hence the bass absorbers.  Pressurize the room, feel the bass, control the resonances and decay.  That gives you the 'slam in the chest' feel of the bottom end. 

Bryan