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#144079 - 07/25/06 12:50 AM My Superchunk Bass Trap Project, Graphs included
SirQuack Online   shocked
shareholder in the making

Registered: 01/29/04
Posts: 13333
Loc: Iowa
As most of you know, I've gone graph crazy. Not sure what it is, but there is something that is interesting about improving your room response and overall sound.

Before I get started, I want to thank "Bridgman" for helping me become an Excel expert on graph plotting.

Ok, so I've been spending some time lately on various websites reading about the topic of improving your room response by using a combination of bass traps and mid-high treatments. Many believe this type of setup is mainly for recording studios, when in fact the same rules apply to a HT environment. There are tons of great websites out there on this subject. Audioholics even has some great articles on bass traps and acoustic treatments. Another great starting point is http://www.ethanwiner.com/acoustics.html or reading some of the other articles by Ethan's company at www.realtraps.com.

I decided to take the DIY route as usual to save a buck. What I really appreciate about people like Ethan from RealTraps, Bryan from SensibleSoundSolutions, and Glen from GIK Acoustics, is that they were willing to give me advice on building my own treatments using some of the same materials they use, versus trying to talk me into buying from them.

Based on my research I decided to purchase some Owens Corning 703 Rigid Fiberglass board from a local insulation distributor. This is a popular product that has been proven to have great absorption properties when installed correctly. Many people use foam products, but if you look at the stats, they just can't compare to Rigid Fiberglass board, Mineral Wool board, or cotton. The 703 I purchased came in 2' x 4' x 2" thick sheets. Many people will double these up and straddle a corner which provides good results for bass trapping, just ask Royce73. However, an even better method is to use superchunks, which basically are triangles that fill the entire void in the corner.

The OC 703 is very easy to cut. Just make sure you have some gloves on as it can make you itch, just like regular fiberglass. For starters you cut the 2' x 4' piece in half. This gives you two 2' x 2' pieces. You then cut these each diagonally to make triangles which are 24" x 24" x 34". Many people use this size for their corner chunks, however, I decided to make another cut to those pieces which gave me 17" x 17" x 24". This size worked better next to my screen and gave me room for my m60's.

Here is a picture of some of the precut OC703.


Once they are all cut, you basically stack them in the corner. I built a frame out of some 1 x 2 pine, and used general purpose velcro to attach the black felt I purchased at Walmart.









For low bass frequencies the material is not as important as it is for higher frequencies. With the higher frequencies you don't want a material that will reflect the sound. A good test is if you can see some light passing through or if you can feel your breath through the material you'll be fine. Muslin is another material often used.


Anyway, I know Bridgman told me not to worry about graphs, but I could not help myself. I didn't figure I would see much improvement just by adding two rear wall bass traps. In reality, it is best to have all your corners treated with some form of bass trap, this can include corners where ceilings meet walls also. I would then move onto treating some of the first reflection points with mid-high frequency traps. But one thing at a time.


Sooooooo without further ado.....Here is my most recent graph. In both situations I used the Real Traps test tone CD which covers from 10hz upto 300hz in 1hz increments. The master volume was set at 70dB's per the instructions. Prior to the tests all my speakers were calibrated for SPL, Delay, and dB levels using the Denon built in mic and setup. In addition, I verified the dB levels with my SPL meter prior to starting. M60's were set to small with a crossover of 80hZ.



Overall, I feel there is some good improvement if you compare the before/after plots across the entire graph. You can see the severe dips I had around 145hz and 235hz have improved. In addition some of the higher peaks around 40hz, 55hz, and 80hz, have been reduced slightly.

The most important thing that really suprised me is the sound has improved just with two rear traps. I've been listening to a variety of cd's in my collection and I am being 100% honest that I truely hear a positive difference. The bass is much tighter and individual notes are clearer and easier to hear versus the "one note bass" that some experience, especially in the lower range.

Sorry this has been such a long post, I hope some of you can provide some positive feedback for me.

Thanks for listening, Randy
_________________________
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#144080 - 07/25/06 01:18 AM Re: My Superchunk Bass Trap Project, Graphs included [Re: SirQuack]
bridgman Offline
axiomite

Registered: 08/25/04
Posts: 5408
Loc: Bowmanville, Ontario, Canada
Wow -- those are mighty impressive looking bass traps, and they really seem to disappear once you get the frame and grill installed. VERY nice. I'm tempted to load up the back of the Magnum with OC 703 sheets, grab a sharp knife and head over to MarkSJohnson's house.

Just a quick thought -- we look real hard at the +/-3 dB frequency response specs for speakers, ie 6 dB deviation within the listening range. Very roughly, those traps took the deviation from 42 dB (!!!) down to 26 dB. The big bass peaks came down by 5-7 dB, and in most of the other frequencies the excursions were down by a few dB.

Very interesting results. Conventional wisdom is that you need a lot more traps, but those are BIG honkin' traps. Thanks very much for taking the measurements and posting so much good information.


Edited by bridgman (07/25/06 01:22 AM)

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#144081 - 07/25/06 01:19 AM Re: My Superchunk Bass Trap Project, Graphs included [Re: SirQuack]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10388
Randy my observation is that the significant improvement appears around 140-150Hz, but the total variation around 220-250Hz seems the same or a bit greater. Maybe just that upper bass area improvement does make an audible difference.
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#144082 - 07/25/06 07:31 AM Re: My Superchunk Bass Trap Project, Graphs included [Re: SirQuack]
davidsch Offline
aficionado

Registered: 06/02/03
Posts: 678
Loc: Houston, Texas
Very professional looking job, Randy! I am glad to hear that you are pleased with the outcome as well. Keep us informed if you decide to add more traps.

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#144083 - 07/25/06 09:56 AM Re: My Superchunk Bass Trap Project, Graphs included [Re: bridgman]
SirQuack Online   shocked
shareholder in the making

Registered: 01/29/04
Posts: 13333
Loc: Iowa
Thanks guys for looking at my results. One question I have is in regards to toe in of the main speakers. Most of the acoustic websites say the best place in a room is to be 38% back from the front wall, if this is not available, 38% from the rear wall is a good second choice. By default, these locations have the least amount of modes present and a good starting point, before bass traps.

38% back from my front wall is almost 12ft. My m60's are a tad over 10ft apart. If I have the m60's aiming just slightly behind the main seating position they are toed in very much. I wonder if this excessive toe in is not a good thing and may alter the graph above? I've read you should have an equilateral triangle to the primary position, but how is this possible if the speakers are not toed in somewhat?
_________________________
M80s-VP180-QS8s-EP600-2xEP350 Denon3808 Outlaw7700
M22-OWM22-VP100-Denon2805
Audio Nirvana

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#144084 - 07/25/06 10:59 AM Re: My Superchunk Bass Trap Project, Graphs included [Re: SirQuack]
royce73 Offline
veteran

Registered: 04/20/05
Posts: 170
Loc: New Jersey
Looking good, SirQ!!

Glad to see that can tell the difference like I have. It is nice to know that it just wasn't my mind playing tricks on me. I got the day off work today and the nanny is here, so your post was has inspired me to post my RealTraps Graph as well. Once you get the time, I am sure you will see a bit more improvement with the third and fourth chunk traps

I noticed you had a dip around the 140-150 area like I have as well. Anyone have any thoughts as to improving those frequencies?

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#144085 - 07/25/06 11:56 AM Re: My Superchunk Bass Trap Project, Graphs included [Re: royce73]
royce73 Offline
veteran

Registered: 04/20/05
Posts: 170
Loc: New Jersey
Here's my first REALTrap measurement done a few weeks ago. I believe I was running my sub too hot.



Here is my room layout as well:


Any expert advice as to how to fix my highlighted problem areas?

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#144086 - 07/25/06 12:28 PM Re: My Superchunk Bass Trap Project, Graphs included [Re: royce73]
SirQuack Online   shocked
shareholder in the making

Registered: 01/29/04
Posts: 13333
Loc: Iowa
Hey Royce, nice graph and drawing. Is the room drawing to scale? To me it appears the side reflection points may be to much into the room. How did you arrive at those locations, using the mirror trick, or the equation on the RealTraps website? If you imagine making a Pool Bank shot off the wall, it does not appear you would hit the speakers. Also, I wonder if it might help if you move the sub a little closer to the corner, not sure? I'm no expert, YET.
_________________________
M80s-VP180-QS8s-EP600-2xEP350 Denon3808 Outlaw7700
M22-OWM22-VP100-Denon2805
Audio Nirvana

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#144087 - 07/25/06 12:55 PM Re: My Superchunk Bass Trap Project, Graphs includ [Re: SirQuack]
Jordan Offline
veteran

Registered: 03/29/06
Posts: 165
Loc: Ottawa, Canada
My statistics / econometric methods are a bit rusty. I'm wondering what the best way to interpret the data would be from an objective statistical standpoint. I suppose one would want to calculate and compare the standard deviation, variance and the number of outliers (and their magnitude). Oh oh, of course one should always be on guard for "heteroskedaticity".

I'm sure Chess will chime in. He will know.

Cheers,

J

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#144088 - 07/25/06 01:17 PM Re: My Superchunk Bass Trap Project, Graphs included [Re: SirQuack]
royce73 Offline
veteran

Registered: 04/20/05
Posts: 170
Loc: New Jersey
Randy,

No, the room picture is not to scale. The side traps are about two feet away from the end of the corner trap. I used the trusty mirror trick. I did also view it as a "Pool Shot" and the bank shot would hit the side trap in the real room.

I had the sub in the corner for my first measurements. There was a HUGE dip around my crossover point so I moved the sub closer to my sweet spot. The difference was noticable sonically and on the graph, so I decided to use that location. The sub is right up against the side trap like in the diagram, but os only three feet from the corner of the room.

I just finished another reading, this time I moved my CD/DVD shelf to the back wall and the table to the side. The bookshelf should be better for disfussion against the back wall. I will post soon.

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