[Stylus]

I am just getting going on putting together what I need to effectively treat my room.  I know that I need to address the first reflection points and adequate amount of bass absorption.  My first few questions are:

For first reflection points, how much would I lose, if any, using just 1" board rather than 2"?

I have corner space above a bookshelf that I thought would be perfect for hiding some bass trapping (bookshelf ends roughly 2' below ceiling and is bordered on one side and back).  For this spot, would it be more effective filling the entire void, or bordering the void leaving an air gap behind?

Lastly, I am still confused as to where I should use 703 vs. 705 board.

Thanks in advance!

[Nyal Mellor]

On the subject of 1" vs 2":

1" doesn't have flat attenuation down to the transition frequency (where sound stops acting like a ray; around 200Hz or so). This basically means that it absorbs more of the incident sound at high frequencies than at low frequencies. Say the absorption is 100% at 1kHz and 60% at 200Hz. Since what you listen to is as much reflected as direct sound, you'll be listening to sound that has been distorted in the frequency domain. Some authorities now recommend 3" of fibreglass rather than 2" BTW.

On the subject of airgap vs not:

People use airgap to get more low frequency absorption from a given depth of fibreglass. 3" will give better absoption that 2" spaced 1" off the wall, but obviously you don't the same material costs with 2"!

[planet10]

You don't want to absorb the 1st reflection, it is beneficial. It does need to retain asflat a frequency reponse (reflection should have similar FR to the speakers)

dave

[TRADERXFAN]

Could you flesh out your point a bit more?
 Are you suggesting to diffuse the first reflection, or what? 

I didn't see mention of controlled directivity speakers, which is the only case that I have heard of before, where first reflection points were deliberately untreated.

Thanks.

Tony

[planet10]

The least expensive thing you can do to make your hifi work better in your room is to buy a copy of Floyd Tool's new book. He shows a substantial benefit for keeping a 1st reflection with flat FR & not a lot of diffusivity.

He also knocks a couple other common beliefs on their butts.

dave

[bpape]

The problem is that very very very few speakers have 'flat' off axis response and it's the off axis dispersion that ends up being reflected back at the listener.  There's also a matter of the timing of the reflections thats a factor in determining whether they're harmful or not.

1" vs 2" - I personally prefer 2" as it will reach farther down into the vocal range and the fundamentals of many instruments where 1" will not.

The space above your bookcase will make a nice place for broadband bass control - though not likely enough to properly treat the room, it's a start and one that's out of the way.

Bryan

[Nyal Mellor]

1st reflection:

If you have speakers that have reasonable off axis response then there is no strong need to treat the lateral (i.e. side wall) first reflection point.

Whether you treat or not is basically personal preference; what you are optimizing is the balance between focus (e.g. pin point imaging) and envelopment. Floyd Toole noted in his book that the average listener preferred untreated lateral reflections whereas recording engineers preferred treated.

There are a few different options you can go for: untreated (i.e. reflective), absorptive or diffusive. You can even go further and opt for a hybrid solution e.g. some reflection, some absorption at the lateral mirror points. All you are doing is balancing between focus and envelopment, there is no right answer!

My personal preference is either fully reflective or putting up some combined absorptive/diffusive panels e.g. those made by RPG.

[planet10]

Whether you treat or not is basically personal preference; what you are optimizing is the balance between focus (e.g. pin point imaging) and envelopment. Floyd Toole noted in his book that the average listener preferred untreated lateral reflections whereas recording engineers preferred treated.
.

He also noted that if the 1st reflection is not a fairly flat representation of the on-axis, it is probably worse than either of the above.

Essentially his research shows that the 1st derivative of the on-axis, 1st reflection, power reponse, and directivity should approach a horizontal line.

dave

[Stylus]

That Toole books seems to have really shook up the opinions on this matter!  From everything I have heard, I think I will start with just a bunch of broadband absorption throughout the room, and see then if I still want to try side wall reflection spots.  I am hoping I won?t find the need since due to my room, the side wall reflections will be the most awkward to get something in the right spot that won?t look like crap.

My current plan:

3 4? panels placed horizontally along the bottom of the front wall behind the speakers.  Due to windows on the right side of this wall vertical placement won?t work well.

3 4? panels mounted to the rear wall behind the listening position.

A floor to ceiling ?super chunk? corner bass trap in the rear right corner of the room (the only corner that really lends itself to corner trapping).

Fill in the space above the bookshelf as mentioned.


To do all this it will be 4 full packages of Corning 705 board (equivalent of 24 2? panels).  I guess (hope) this is enough bass trapping for the room, we?ll see.  (The room is approximately 16?W x 22?L x 8?H but has some asymmetrical attributes).

I just recently moved the system into this room after having it previously hooked up in the living room which is open to one side and has tall vaulted ceilings.  The big problem I have hearing in the new tighter space is a ringing and ?echoy? sound.  The midrange has also lost some clarity as well.

I found boxes of the 705 (6 2? boards) for $120.00.  Is this a good buy?

[bpape]

Save your money.  You can use OC703 for half the cost and it will give you 99% of the same performance in this application.

Bryan

[Stylus]

Save your money.  You can use OC703 for half the cost and it will give you 99% of the same performance in this application.

Bryan

Wow, that is good to know, I didn't know it was that close.  Thanks! 

[Stylus]

So I went to order and realized shipping on this stuff is going to be $160!  Any tips on how to find this stuff locally (ie what kind of place would carry it)?

[pjchappy]

So I went to order and realized shipping on this stuff is going to be $160!  Any tips on how to find this stuff locally (ie what kind of place would carry it)?

See if you have an SPI close by.  Luckily, there is one north of KC where I live.  Not only did I save on shipping, but it's pretty cheap.  If I remember correctly, $.78 / sq. ft. for normal 703 and $1.14 (maybe a few cents more) / sq. ft. for 703 with the backing (both 2" thick).

If there is not one close by, at least the one here said they'll ship anywhere.  So, if you have to have it shipped, they will likely have much cheaper prices than other places you've seen it for online.

Hope that helps! 

[Stylus]

So I went to order and realized shipping on this stuff is going to be $160!  Any tips on how to find this stuff locally (ie what kind of place would carry it)?

See if you have an SPI close by.  Luckily, there is one north of KC where I live.  Not only did I save on shipping, but it's pretty cheap.  If I remember correctly, $.78 / sq. ft. for normal 703 and $1.14 (maybe a few cents more) / sq. ft. for 703 with the backing (both 2" thick).

If there is not one close by, at least the one here said they'll ship anywhere.  So, if you have to have it shipped, they will likely have much cheaper prices than other places you've seen it for online.

Hope that helps!

You rock!  Found one in the Bay Area a couple hours from me.  The price is slightly cheaper than online and for $25 (less than gas!) they are delivering it to me.  Out the door I am saving about $140!!!  Thanks!!! 

[pjchappy]

Awesome!   

Here's my very recent and ongoing journey.