Need Help: Home Theater Acoustics

[ak47]

Hi!

I had recently decided on making a dedicated home theater in my basement. Since it was more of a hall, I put a wooden partition filled with glass wool sheets to cordon off an area for my home theater. I plan to carpet the entire floor. Where I am stuck is the room acoustics and panels for sound reflection, reverberation control etc. I am completely clueless about these, but would like to make the panels etc on my own. I will be using the Denon+Paradigm setup mentioned in my signature for the home theater. As seen in the diagram, the back side of the room is the wooden partition(which is completely bare as of now). The sides are normal plastered brick walls finished with POP. The false ceiling is parallel to the floor. I did some reading online and everywhere it was suggested to have panels which are made out of egg-crate shaped foam. But I still could not figure it out. I hope fellow FM's would shed some light on this and help me out with the same.

 

[sdurani]

Egg crate foam is a waste (doesn't absorb much and barely diffuses). You'd be better off with using rockwool or the same glasswool that you already used for the partition. Good starting points for the panels are across the front wall (improves imaging) and across the middle of the back wall (to cut down centre channel reflections and improve dialogue intelligibility).

Can you post a larger version of your diagram? The numbers on there are difficult to read.

Also, any chance of moving your sofa forward?

 

[ak47]

Egg crate foam is a waste (doesn't absorb much and barely diffuses). You'd be better off with using rockwool or the same glasswool that you already used for the partition. Good starting points for the panels are across the front wall (improves imaging) and across the middle of the back wall (to cut down centre channel reflections and improve dialogue intelligibility).

Can you post a larger version of your diagram? The numbers on there are difficult to read.

Also, any chance of moving your sofa forward?

Here is a better and more illustrated image:
http://s24.postimg.org/dd8ke9i05/image.jpg

I cannot move the sofa forward, as the viewing distance would not be desirable. I can use rockwool sheets. The ones I have are 50mm thick. What size panels should I make and where do I put them. Also, I was planing to cover the panes with leather or leatherette. Is that okay, or should I use any other fabric?

 

[sdurani]

Good starting points for the panels are across the front wall (improves imaging) and across the middle of the back wall (to cut down centre channel reflections and improve dialogue intelligibility).

What size panels should I make and where do I put them.

Make them as large as possible and put the panels across the front wall (improves imaging) and across the middle of the back wall (to cut down centre channel reflections and improve dialogue intelligibility).

Also, I was planing to cover the panes with leather or leatherette. Is that okay, or should I use any other fabric?

They're useless if you cover them with leather or leatherette. If you can blow air easily through the fabric, then it is good for covering the panels. If you can find a source of speaker grille cloth, that is the best acoustically transparent fabric to wrap panels in. If not, you can use burlap.

I cannot move the sofa forward, as the viewing distance would not be desirable.

The only reason I asked is because roughly 7 feet from your back wall is where there is the least variation in frequency response (fewest/smallest peaks & dips).

 

[ak47]

Make them as large as possible and put the panels across the front wall (improves imaging) and across the middle of the back wall (to cut down centre channel reflections and improve dialogue intelligibility). They're useless if you cover them with leather or leatherette. If you can blow air easily through the fabric, then it is good for covering the panels. If you can find a source of speaker grille cloth, that is the best acoustically transparent fabric to wrap panels in. If not, you can use burlap.

Is it advisable to cover the whole front and back wall with the panels or should I cover just a portion of the walls? Also, do I need anything for the side walls?

 

[sdurani]

If you're willing, cover the entire front and back walls.

To absorb broadband (full range down to the subwoofer frequencies), make your panels 150mm thick. If you don't want to spend that much, make them 100mm thick and mount them 100mm from the wall. The air gap behind the 100mm panels will make them almost as effective as 150mm panels placed on the wall.

The problem with making panels too thin (50mm) is that they will only absorb higher frequencies. That's the equivalent of turning down the treble knob on your receiver. Will result in dull, lifeless sound.

Treatments on the side walls comes down to your preference. Sit in your main listening position and have someone walk a hand mirror up each side wall. Where ever you see a reflection of one of your front speakers, mark that spot on the wall.

I would put a 2'x2' or 3'x3' absorber panel where the left speaker reflects off the right wall and where the right speaker reflects off the left wall. This will keep sounds from the left side of the soundstage from coming at you from the right side of the room and vice-versa.

 

[ak47]

If you're willing, cover the entire front and back walls.

To absorb broadband (full range down to the subwoofer frequencies), make your panels 150mm thick. If you don't want to spend that much, make them 100mm thick and mount them 100mm from the wall. The air gap behind the 100mm panels will make them almost as effective as 150mm panels placed on the wall.

The problem with making panels too thin (50mm) is that they will only absorb higher frequencies. That's the equivalent of turning down the treble knob on your receiver. Will result in dull, lifeless sound.

Treatments on the side walls comes down to your preference. Sit in your main listening position and have someone walk a hand mirror up each side wall. Where ever you see a reflection of one of your front speakers, mark that spot on the wall.

I would put a 2'x2' or 3'x3' absorber panel where the left speaker reflects off the right wall and where the right speaker reflects off the left wall. This will keep sounds from the left side of the soundstage from coming at you from the right side of the room and vice-versa.

Thanks a lot for the help! I will be covering the entire front and back walls with 150mm thick panels. I wanted to know what would be the best place for my sub in the room. I normally keep it in the top right corner. Should I also have bass traps at the corners?

 

[Naturelover]

If you can find a source of speaker grille cloth, that is the best acoustically transparent fabric to wrap panels in.

Try this
Grill Cloth

 

[john_k_antony]

I recently did my HT room and I used black and red colored cotton cloth that was costing around Rs. 100/meter. The cloth was 4' wide. I used them to cover all my acoustic panels - both absorbing and reflective. They worked out to be very cheap and looks pretty nice.

As Sanjay mentioned, before you select the cloth, just blow through them to check whether they are acoustically transparent.

Here is my build thread - http://www.hifivision.com/home-theater/46258-yet-another-dedicated-home-theater-build.html

Thanks,
John.

 

[sdurani]

I wanted to know what would be the best place for my sub in the room. I normally keep it in the top right corner. Should I also have bass traps at the corners?

If using a single sub, I would put it at the midpoint of room width (middle of the front wall, below the centre speaker). If you're using two subs (highly recommended), place them at the quarter points of room width (46 inches in from the side walls). Both will help give you smoother bass (fewer peaks & dips) across the entire seating area.

For bass traps to be effective (i.e., really absorb bass, not mid-bass or midrange), they need to be thick. Like a foot or two thick. But the thicker the trap, the less dense the material inside needs to be. So instead of using rigid glasswool or rockwoll, you need to use low density fluffy fiberglass.

Rather than going through all that trouble, there is an alternative you could try: since you're building panels out of glass wool anyway, place some stradling the front corners of your room. The air gap behind the panels will help them absorb into the lower frequencies.

 

[ak47]

I recently did my HT room and I used black and red colored cotton cloth that was costing around Rs. 100/meter. The cloth was 4' wide. I used them to cover all my acoustic panels - both absorbing and reflective. They worked out to be very cheap and looks pretty nice.

As Sanjay mentioned, before you select the cloth, just blow through them to check whether they are acoustically transparent.

Here is my build thread - http://www.hifivision.com/home-theater/46258-yet-another-dedicated-home-theater-build.html

Thanks,
John.

You have one hell of a setup man! Amazing stuff...

I actually have a friend who can source me speaker grille cloth. I will use that if I'm lucky enough to get my mom's approval for black panels. If not, I'll go in for the cotton cloth as you have suggested.

If using a single sub, I would put it at the midpoint of room width (middle of the front wall, below the centre speaker). If you're using two subs (highly recommended), place them at the quarter points of room width (46 inches in from the side walls). Both will help give you smoother bass (fewer peaks & dips) across the entire seating area.

For bass traps to be effective (i.e., really absorb bass, not mid-bass or midrange), they need to be thick. Like a foot or two thick. But the thicker the trap, the less dense the material inside needs to be. So instead of using rigid glasswool or rockwoll, you need to use low density fluffy fiberglass.

Rather than going through all that trouble, there is an alternative you could try: since you're building panels out of glass wool anyway, place some stradling the front corners of your room. The air gap behind the panels will help them absorb into the lower frequencies.

Will do sir. I am using rigid rockwool for the panels. I'll use the same for making bass traps....

Thanks a lot for your help

I am gathering all the materials required as of now. Will post images when I start building the theater. And, I will bother you again at that time because I'm sure I'll be needing more help

 

[ItsMe]

Reviving an old thread - I am unable to get rockwool locally. Is it possible to order it online? Else, can I substitute it with synthetic cotton to make a panel for reverberation control ?

 

[koushik]

Reviving an old thread - I am unable to get rockwool locally. Is it possible to order it online? Else, can I substitute it with synthetic cotton to make a panel for reverberation control ?

Try to search in Just Dial for local glasswool dealers. Search for thermal insulator dealers.
I was pleasantly surprised to find so many dealers in Kolkata that I had no idea before.

 

[captrajesh]

If you're willing, cover the entire front and back walls.

To absorb broadband (full range down to the subwoofer frequencies), make your panels 150mm thick. If you don't want to spend that much, make them 100mm thick and mount them 100mm from the wall. The air gap behind the 100mm panels will make them almost as effective as 150mm panels placed on the wall.

Covering the entire front and back walls with 150mm thick panels! That would eat up not only considerable real estate but also the pocket Wouldn't it be better to do what was suggested below and go in for bass traps?

Make them as large as possible and put the panels across the front wall (improves imaging) and across the middle of the back wall

But the thicker the trap, the less dense the material inside needs to be.

Since real estate is more precious than the room treatment material, it would be apt to rephrase the above as:

Thinner the trap, denser the material inside needs to be.

 

[sdurani]

Covering the entire front and back walls with 150mm thick panels! That would eat up not only considerable real estate but also the pocket

If you don't have the real estate and/or your pocket can't afford it, then don't do it.

Wouldn't it be better to do what was suggested below and go in for bass traps?

I wouldn't replace broadband absorption with bass traps.

 

[IndianEars]

Instead of 150 mm rockwool on the wall,

Use 75 mm Rockwool and then a 75 mm air gap between the rockwool and the wall.

Cheaper and More effective.