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Discussion Starter #1
I am seeking advice on the best way to deal with a strong axial mode.My small room makes it neccessary to place my subs in the corners which gives me a nice little shot of room gain but on the downside it also excites a nasty 50hz mode.
I am curently using a single band of Parametric EQ to reduce its level but was wondering if corner loaded bass traps like superchunks would be an even better solution.Or is the best approach to combine both traps and EQ?
What are the pros and cons of each?
What thickness would the trap have to be for it to be effective at 50hz?

Thanks Fred
 

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Fred, what are the dimensions of the room?

if you are 'trapping a freqency' in your room, that is if exactly half of a 50hz sine wave fits into your room, then no amount of EQ can truely fix the problem (though i supposed you could notch out 50hz from your setup, which would not fix the problem, but would eliminate the source (kind of like cutting off your leg because you have a sore foot - when a padded shoe is really the best answer to let the foot do it's job))

You'll find that a reasonable size (2-4") panel will do well so long as you give it some space between the panel and the wall. A popular technique is to put one diagonally over corners.

ok now here are a few thoughts...
If you have a Radioshack sound meter, and a laptop (or a PC near your theater) - there is free software you can use to measure the response of your room. if you are capable of this, it should be the foundation of anything you do, and you should use it to validate that what you are doing is working.


Its been suggested that a compressed roll of homeowners insulation has decent absorbing properties.
Yes it is ugly. but it is also cheap. if you really want to 'hear' what the difference is in your room with some absorption, 2-6 rolls of insulation would do the trick - once you hear the results, you can decide the best way to treat the room permanently (very likely via commercial panels like GIK or realtraps). if you've used the software and measured before and after, the difference will not only be audible, but it will be documented too, and then you can post back the results here.
 

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Good advice.

Also, IMO, the best way to attack it is to determine what is causing that peak - hence the question above about your room dimensions. Also, would be nice to know the distance from the listening position to the rear wall of the room.

Corner treatments tend to deal with pretty much everything in the bottom end. That's not a bad thing, just don't expect it to only do 50Hz. You had said it's an axial mode - which dimension if you're sure? Based on that and the other answers, you may find that in addition to the corner absorbtion, it may be beneficial to specifically treat the offending dimension a bit in addition. The EQ is not a bad thing for a sub but IMO should be used in addition to proper treatment.

There is so much more than just FR to deal with that EQ just can't do over a wide range and over a wide number of seating positions.

Bryan
 

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Fred,

> What are the pros and cons of each? <

How much are you willing to read to get the answer? I'll give you the Reader's Digest version, but first HERE is a link to the unabridged version. :reading:

Okay, now that you read all that and digested it... :holycow:

The best approach is as much bass trapping as you can manage, then, if more control is still needed, a touch of EQ cut only at one or two remaining offending frequencies can finish the job. I have 40 traps in my living room (no kidding), and I also use the one-band cut-only parametric EQ on my SVS subwoofer to reduce one really low room mode peak by a few dB. That gets me flat within 10 dB, which is about as good as most domestic size rooms will ever get.

--Ethan
 

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Discussion Starter #5
Jack ,Bryan and Ethan,thanks for the great feedback.:T


Jack, my room is 19' x 11.2' x8'. Unfortunately I don't have a lap top or a PC near the HT so my only measurements are with the Rat Shack meter and test tones.Doing a mode calc indicated the presence of a 50 hz axial mode corresponding to the width dimension and the measurements and listening confirm a problem.Using the the EQ as a 50 hz notch filter certainly improves things but the three of you seem to be in agreement that corner traps will improve matters even further so I guess I should order some Rockwool.

Bryan ,Iam aware of the broadband coverage but I was wondering what kind of thickness was needed to get any benefit in the 50hz range.My space is limited but I did some checking today to see what the maximum size of trap I could squeeze into the corners.It looks like the max would be a 4' tall triangle shape with a 16" face pointing into the room.The maximum thickness would be somthing like 10 or 11 inches in the center.This is a lot smaller than the Tri Traps but will it be reasonably effective if not 50hz at least for the several modes falling around 150hz?

Ethan, thanks for the link and I will be reading that and many other sections of your very resourseful website.
Wow 40 traps ,I bet that room sounds good.

Thanks all for your help.
 

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Jack, my room is 19' x 11.2' x8'. Unfortunately I don't have a lap top or a PC near the HT so my only measurements are with the Rat Shack meter and test tones.
The good news is you don’t need to have a computer near the HT room. All you need is a cable long enough to reach from the SPL meter to the computer. You could do it easily with a regular coaxial cable with RCA adapters screwed onto both ends. :T Get a coaxial cable with an easy-to-reseal box, and you could return it after you’re done, and save a few bucks.

Regards,
Wayne
 

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Discussion Starter #7

The good news is you don’t need to have a computer near the HT room. All you need is a cable long enough to reach from the SPL meter to the computer. You could do it easily with a regular coaxial cable with RCA adapters screwed onto both ends. :T Get a coaxial cable with an easy-to-reseal box, and you could return it after you’re done, and save a few bucks.

Regards,
Wayne
My PC is in the basement and the HT is on main floor but I guess that would be doable if I were to have an access way upstairs.I could temporarilly remove a heating duct.

I had better start spending some time at the REW thread to learn about the software.I may have to seek your assistance on the finer points of it.

Thanks Fred
 

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The good news is you don’t need to have a computer near the HT room. All you need is a cable long enough to reach from the SPL meter to the computer.
Or he could download the 1 Hz test tones from my company's site, burn a CD on his computer, and play that CD through his system with the RS meter in the same room. That SPL meter is portable, yes? :neener:

:rofl:

--Ethan
 

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Discussion Starter #9
That SPL meter is portable, yes? :neener:

:rofl:

--Ethan
yes Ethan I paid the extra and got one of the portable models :bigsmile:


:help: before I buy the supplies I would like to get the experts opinion on my planned triangle corner trap and its potential benefits and any suggestions for changes to improve on my plan.

The design I had in mind was a 40-48" tall lite wooden frame with a 16" open front facing into the room.I was thinking of using 3lb/cf mineral wool to pack it with.The front would be covered with material.

I would likely mount them in the upper half of the four corners to maybe get some additional reduction of hi frequency reflections as the top half of my room is still fairly lively.

Is this big enough to have some effect in the bass range?

Is there anything I should do different?

Thanks Fred
 

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Or he could download the 1 Hz test tones from my company's site, burn a CD on his computer, and play that CD through his system with the RS meter in the same room.

Oh, a wise guy, huh? :heehee:

Sure, he could do that, but in the time it takes to play and measure two of those tones, REW would be finished and showin' the graph on the screen! :bigsmile:

So - take that! :neener:

Just kidding, I hope you know! :joke:

Seriously, I've done the tones, I've done REW - I'm done with tones! :T

Regards,
Wayne
 

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Discussion Starter #14
Fred,

> Is this big enough to have some effect in the bass range? <

Some effect? Sure.

> Is there anything I should do different? <

Make them bigger?

--Ethan
Well I guessed someone would recommend making them bigger but WAF and placement issues limit me to that size.As long as they will have some benefit I will go ahead and build the first pair this weekend and give them a try.

Thanks Ethan.
 

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Discussion Starter #15
Ok I was able to quickly slap together 2 frames tonight .I will purchase some mineral wool tomorow.
 

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The frames look great.

I have a thought for you...

often we try and cram an acoustical solution on top of an existing room, instead of trying to design it into the room...

If you look at many high end home theaters, you'll notice that many have columns and sofits.

those are both 'room features' that can have tremendous acoustic benefits.

For example, you could build a wooden frame work for soffit - for example, on the left and right sides of the room. Cover this sofit with a neutral tight weave fabric that blends in with the ceiling color, and most people would never notice it's fabric. then under the fabric you can put what ever you want - You'll gain a **** of a lot more absorption than you will with a few corner traps, and most people won't even notice.

Columns on the sidewalls can be used for the same thing.

I made the mistake of building some tube traps... they did help, but not enough to continually answer the 'what are those' questions I get from people over and over again. If I had spent the same effort (and money!) on making acoustic sofits, I'd have a much nicer solution.
 

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The corners will not only help in general frequeny response but will also help with general decay time issues that an EQ can't deal with effectively.

If the mode is width related, consider shifting your entire setup about 6" right or left (speakers and seat so you're still centered with relation to the speakers). This assumes you're sitting dead center now. This is a freebie thing that is often a good thing to do.

Bryan
 

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Discussion Starter #19
for example, you could build a wooden frame work for soffit - for example, on the left and right sides of the room.
Jack,I like the soffit idea and had thoughts about doing something like this a while ago but I don't think I could make it look good enough to pass the WAF test in the combined living room /HT.If I had the option of building a dedicated HT room from scratch it would be easier to build in something or just buy a commericial product.


Bryan ,thanks for the tip about shifting things off center,I might give this a try.
 

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Fred,

Have you seen the program CARA before? It's an acoustic modeling program.

You design up your room in 3d and it can calculate what the frequency response will be at the listening position. It also has a cool feature that shows where peaks and valleys will be in your room for a given frequency.

You could use something like this to experiment with different options before commiting to anything.

- Jack
 
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