# How to reduce standing waves in room?



## papomaster

Hey all!

 I'm trying to set my newly bought subwoofer, but I think there might be some resonances around 30-35 Hz in my room since it seems to overboost one frequency with every kind of bass note being played. I have made a test tones cd with 1 Hz jumps, so I will be able to note if there is indeed a standing wave in my room or if the sub is just boomy (it's a B&W sub, so I really doubt that).

 My question is : if it is the room, how do I fix it? Can I just put some objects (like chairs) to make the room asymmetrical and remove the standing wave? Or move the sub in order to reduce the problem?


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## 883dave

Quote:


  Originally Posted by *papomaster* /img/forum/go_quote.gif 
_Hey all!

 I'm trying to set my newly bought subwoofer, but I think there might be some resonances around 30-35 Hz in my room since it seems to overboost one frequency with every kind of bass note being played. I have made a test tones cd with 1 Hz jumps, so I will be able to note if there is indeed a standing wave in my room or if the sub is just boomy (it's a B&W sub, so I really doubt that).

 My question is : if it is the room, how do I fix it? Can I just put some objects (like chairs) to make the room asymmetrical and remove the standing wave? Or move the sub in order to reduce the problem?_

 

Start your research at sites like ASC (acoustic science corporation), Rives Audio...


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## gregorio

Quote:


  Originally Posted by *papomaster* /img/forum/go_quote.gif 
_Hey all!

 I'm trying to set my newly bought subwoofer, but I think there might be some resonances around 30-35 Hz in my room since it seems to overboost one frequency with every kind of bass note being played. I have made a test tones cd with 1 Hz jumps, so I will be able to note if there is indeed a standing wave in my room or if the sub is just boomy (it's a B&W sub, so I really doubt that).

 My question is : if it is the room, how do I fix it? Can I just put some objects (like chairs) to make the room asymmetrical and remove the standing wave? Or move the sub in order to reduce the problem?_

 

If you are getting a standing wave at a particular frequency you could make a helmholtz resonator which is tuned to the problem frequency. Chances are that your problem is not just a single standing wave, in which case you could do with some decent bass trapping. A simple solution would be some rolls of loft insulation in the corners of your room. A chair is not going to fix the problem.

 Although making your room asymetrical will help with the standing waves, you will almost certainly need some bass trapping as well. There are many quite expensive commercial solutions to bass frequency problems, as a general rule, DIY solutions work just as well at a fraction of the cost.

 Here's a good article to start you off: Acoustic Treatment and Design for Recording Studios and Listening Rooms

 G


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## NightOwl

Here's another link to some inexpensive diy acoustic treatments.

Jon_Risch's Web Site, Cable Main Page


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## twylight

Bass traps, do first reflections while you are making the traps - a great upgrade than possible electronic thing for a theater or listening room - DIY if you can buy stuff and use a hot glue gun...and a stapler.


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## papomaster

If I use some fiberglass, there seems to be two ways of doing corner bass traps:

 - A layer of heavy fiberglass put at 45 degrees to cover the whole corner.

 - a large (1 foot diameter) cylinder of fiberglass just standing close from the corner.

 Am I wrong?


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## Bmac

The only thing I don't like about DIY room treatment is it usually doesn't look as good as something you would buy, and depending on how much you consider your time worth it may be cheaper to just buy a treatment.

 My suggestion is to buy some cheap corner bass traps from Ebay. You can get 8 lineal feet with a claimed NRC of 1.35 for around $50. It's probably just as cheap as DIY and you save all the time and hassle and end up with IMO better looking results.

 If you're looking for broadband sound absorption I would recommend looking at something like Sonex acoustical foam. I think it looks better than rigid fibreglass panels (DIY or not), and offers comparable NRC. At $37 per 2' x 4' panel if you buy 8, it's not that much more expensive than the cost of DIY. Here's a link:

Sonex™ Classic Colortec is the only architectural foam product offered by Sonex™ that is Class 1 Fire Rated yet charcoal or light grey color throughout.


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## linuxworks

standing waves?

 I think you're using your waterbed incorrectly!


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## mulveling

The treatment suggestions have been mentioned, and rightly so. They're necessary, to at least some degree, for achieving maximum sound quality in the overwhelming vast majority of rooms. However, they are a difficult/expensive route. 

 One thing that is _cheap_ and _easy_ (assuming you have full control over decor & layout), with equally great effect, is to vigorously experiment with positioning of your seating, the main speakers, and the subwoofer. Avoid stuff like sitting in the middle along any room dimensions (bass peaks/nulls), and try to avoid stuff like having yourself or the speakers very close to any hard boundary (though I realize that can be tricky). Try weird stuff like firing down the diagonal of the room, perhaps even in a slightly asymmetrical manner.


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## papomaster

I have already tried a lot of different positions for the speakers, and they all give huge dips with huge peaks, and sometimes moving an inch sideways can reverse everything : a dip becomes a peak and a peak becomes a dip. That's why I will try asap to do bass traps at least to help with those HUGE peaks somewhere in the 35 Hz region.

 I've found these designs, and they seem interesting since they only involve a cardboard tube, two pieces of plywood and sand, and they seem quite easy to raise very high (those tubes can be bought up to 8', do only one can cover floor to ceiling).

Build an awesome bass trap

 Would these work just as right?


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## Bmac

Whoever wrote that has no idea what they are doing. That will not absorb sound. For good sound absorption you need acoustic foam or rigid fibreglass. Even carpets hung on walls can work, but a cardboard sonotube will not absorb sound. It may look like a real bass trap but real bass traps are full of rigid fibreglass, not cardboard.


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## gregorio

Quote:


  Originally Posted by *Bmac* /img/forum/go_quote.gif 
_Whoever wrote that has no idea what they are doing. That will not absorb sound. For good sound absorption you need acoustic foam or rigid fibreglass. Even carpets hung on walls can work, but a cardboard sonotube will not absorb sound. It may look like a real bass trap but real bass traps are full of rigid fibreglass, not cardboard._

 

Not true unfortunately. Carpets on walls will absorb mid/high frequencies but will have no effect on low frequencies. Ideally, place dense rockwool triangles in the corners. If you want to make it pretty, just build a stud frame for them and then cover, still relatively cheap. If your problem is specifically at 35Hz and nowhere else, have a look at a helmholtz resonator. 

 You could easily make acoustic panels yourself, make a rectangle out of 1x4 wood, put thin plywood on the back, fill with rockwool, cover with material and hang on the wall. Bare in mind though that treating the corners is particularly important when treating a room for bass freq problems. Unfortunately, low freq problems are the most difficult to solve.

 G


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## linuxworks

standing waves?

 sounds like you are not using your waterbed properly.


 (sorry)


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## Bmac

Quote:


  Originally Posted by *gregorio* /img/forum/go_quote.gif 
_Not true unfortunately. Carpets on walls will absorb mid/high frequencies but will have no effect on low frequencies.
 G_

 

I wasn't implying that carpets will absorb bass, just that they will absorb sound as opposed to dense cardboard, which will absorb very little.


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## gregorio

Quote:


  Originally Posted by *Bmac* /img/forum/go_quote.gif 
_I wasn't implying that carpets will absorb bass, just that they will absorb sound as opposed to dense cardboard, which will absorb very little._

 

I haven't tested dense cardboard but I imagine it would be quite absorptive in the higher frequencies, it may even be effective at lower freqs but without knowing the absorption co-efficient I can't be sure. Bare in mind that even solid wood absorbs high frequencies. 

 G


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## Danny Q

If you decide to go the foam route, you can get it from Parts Express for pretty cheap:
Parts Express @ Amazon.com: foam


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## papomaster

Thanks everyone for the suggestions. I did something which, although it seems crazy at first, has a pretty logical foundation to it: I put some single-bed mattresses in the two front corners (right behind the speakers), and voila! The big bass hump is almost gone! Even though there are still some little ups and downs in the bass and lower midrange, it has become ten times more enjoyable to listen to and no longer causes the whole house to vibrate when a bass note kicks in. I kept one of my other speakers in the back corner, and tried using a double mattress on the back wall:

 Corner mattress:






 Both mattresses:





 Back corners:





 But, there were two problems: first, there was an annoying treble hump that made pianos and violins sound metallic, and my amps had to be placed under my rack due to lack of space, which heated everything and made my LPs stick to the mat after a while...

 First things first, I found a big piece of carpet which fits directly on the width of the room. I can also put the speakers on it, since they were destroying my floor protectors over time. 

 After, I moved my rack on the back right corner, behind the couch, so I could have space to separate the monoblocks from the rack. 

 I haven't taken any pictures yet, but will do so anytime soon. I still need to find a solution to the treble problem.


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## gregorio

Quote:


  Originally Posted by *papomaster* /img/forum/go_quote.gif 
_But, there were two problems: first, there was an annoying treble hump that made pianos and violins sound metallic, and my amps had to be placed under my rack due to lack of space, which heated everything and made my LPs stick to the mat after a while...

 First things first, I found a big piece of carpet which fits directly on the width of the room. I can also put the speakers on it, since they were destroying my floor protectors over time._

 

Your solution doesn't look very elegant, I take it you're not married!! 
	

	
	
		
		

		
		
	


	




 If it works for you though and you like the sound...

 You have a lot of reflective walls, ceiling and floor space, this is most likely responsible for your "treble hump". You might find a strategically placed rug on the floor will solve the problem. Maybe also try a thicker curtain to cover the window and door (glass is very reflective to treble freqs). If not, also try a couple of cheap rugs hung on (or better, just away from) the walls. You won't need to cover all the walls and floor, just strategic areas.

 G


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## papomaster

Hey, I'm only 20... And this is my grand-parents' house, they own a duplex and usually rent the top floor but right now there is noone so I can use one room for my setup. I started using it when they were in vacation in florida (they stay there 6 months a year, november-april) but when they came back they told me I could keep using it since it wasn't bothering them at all.

 The only thing that I can't do is staple some carpet on the wall to reduce those high frequencies... I have to find some way to hang it _close_ to the wall but without taping it or nailing it.


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## Lead Ears

Quote:


  Originally Posted by *papomaster* /img/forum/go_quote.gif 
_Back corners:



_

 

The mattress against the back wall looks like it could have been stolen from the set of Saved by the Bell!!!


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## iriverdude

There are a few electronic parametric EQ's, from Behringer BFD, Velodyne SMS-1, and SVS EQ1. I know the responses on my two subs aren't flat (room peaks and valleys) but first you need a accurate plotted response. It makes little sense if you attempt to correct a peak, when it appears to be +10dB but in reality it's +5dB because your microphone is out.

 I'd definietly put a large rug inf front of the speakers, those wooden floors will cause lots of reflections.


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## terriblepaulz

Quote:


  Originally Posted by *papomaster* /img/forum/go_quote.gif 
_Hey, I'm only 20... And this is my grand-parents' house, they own a duplex and usually rent the top floor but right now there is noone so I can use one room for my setup. I started using it when they were in vacation in florida (they stay there 6 months a year, november-april) but when they came back they told me I could keep using it since it wasn't bothering them at all._

 

When I saw those pictures I knew there was an explanation like this. As someone who shares his house with a wife and two spawn, I can't begin to explain how jealous I am. I have several years before a child's bedroom can be converted into a dedicated listening room.

 The bonus with the mattresses is it gives your listening room an adult film-set vibe. I'm sure your grandparents would appreciate that 
	

	
	
		
		

		
		
	


	




.


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## Bmac

Quote:


  Originally Posted by *Lead Ears* /img/forum/go_quote.gif 
_The mattress against the back wall looks like it could have been stolen from the set of Saved by the Bell!!!_


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## papomaster

I built some real bass traps today!

 Got the materials yesterday:

 - 18x 3-1/2" x 15" x 48" fluffy fiberglass sheets
 - 1x 36" x 10' chicken wire, square threaded 1/2"
 - 1x 54" x 13' wool cloth
 - 2x 11"x11"x1" boards


 I cut the wire in 4, so I could have 10" diameter cylinders. I tied them using some iron wire, then connected them two by two to form a pair of 6' cylinders. Then, I took 2 sheets of fiberglass, rolled them tightly and pushed them in the cylinders. I filled the cylinders (I had to cut the last one in two to make it fit because 70"/15"=4,67) with the rolled fiberglass, then played a bit with the lower end of the cylinders to make sure it could stand up and keep its balance. 

 After that, I cut the cloth in two, wrapped it around the cylinders and hand-sew it tight enough to fit snugly on the sides but not enough to show the side imperfections due to the cylinders not fitting perfectly in each other.

 Finally, I used some metal holders that are used to stick two wood pieces together: basically, a 4"x1/2" strip with 4 wholes to put screws. I used a couple of these to hold the chicken wire firmly in place on the boards. 

 The result: a 6' x 10" fiberglass broadband absorber.

 Cost of parts:
 Fiberglass : 40$
 Chicken wire : 25$
 Cloth : 12$
 Boards : < 1$
 Screws and iron wire : < 1$

 Total : < 70$

 I installed them where the two single bed mattresses were, and moved one of them in the middle of the front wall (the other went out of the room). In short, the results are nothing short of amazing. Especially in my room, it does a really good job in reducing those pesky treble and bass peaks, and evens the frequency response throughout the room. Now, I don't have to stay perfectly still to enjoy my setup. I will post more impressions tomorrow.


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## wuwhere

How big is your listening room? I used to place cylindrical foams, floor to ceiling, that I bought from a cloth shop on the four corners of my listening room to tame standing waves.


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## gjkphd

I just got this book for father's day. It covers standing waves and many other room related issues. Might be worth the investment
Get Better Sound


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## papomaster

I listened to my setup for a while longer today, and here are my conclusions:

 - The overall tonality has improved.

 - The bass is tighter but more fluid through the midbass, so I can turn the high-pass filter on the sub from 120 Hz to 90 Hz without losing any power (and gaining some finesse).

 - The treble level has decreased overall, but there seems to be a shrillness to some high sounds, especially highly distorted guitar and high-pitched human voices (male and female). It is only harsh when there is a hard treble note that is playing, and it doesn't make every treble note harsh. Maybe it'll get fixed by burn-in, I don't know (my monoblocks and speakers both need burn-in), but I've listened to Rainmaker extensively in a treated room at an audio store and there were nowhere close from being harsh or shrill. Again, I'm not sure if it is the room or the burn-in.

 - Soundstage and imaging are way better, and depth is really easier to pick (before, I had to focus on a particular instrument to evaluate his depth but now it comes naturally).

 - Lower midrange blends better with the upper bass. It was a bit fat at first but I played with the sub and by lowering the high-pass to 90 Hz everything went back perfect.

 If anyone has heard some Totem Rainmakers prior and after burn-in, maybe they can comment on how the sound changed.


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## papomaster

I built today a set of panels with the foam I had left:

 30"x48" panels of 1/2" MDF

 2x 1"x3"x8' wood

 2x 15"x48"x3-1/2" unpressed fiberglass (the foam one, not the pressed sheets)

 I made the 30"x48" frame using the wood pieces cut 60" long, so that the panel was standing 12" above the ground. Then, I screwed the frame on the MDF panel and fixed the fiberglass onto the MDF using thick staples. Finally, I screwed 8" pieces perpendicularly to the frame to make it more stable and I stapled some cloth on the frame on all sides. Et voila!

 Tomorrow, I'll try different placements in the room to see how it affects the sound.


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## rsaavedra

A nicer approach is to use bookshelves filled with books. That way you have an extra good reason to buy good books: to make those shelves good sound dispersion surfaces. 

 Bookshelves are also generally regarded as better looking than mattresses


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