# Standing Waves?



## airpiratehkg (May 27, 2008)

Hello, I am running Yamaha RX-V2600, a pair of Mythos One's and a Super Cube I sub (sub is just in line and just left of my right main speaker.. Listen position sofa pushed all the way to back wall (no choice) I do have a HT setup but, my main listening pleasure is 2 channel. I live in a concrete high rise tower in Hong Kong. My room is nearly a perfect rectangle with a hallway that can not be closed off and a small closet in the far corner (the door in the pic is not the closet). It's a rental that means tile floors, concrete walls (no treatments) one wall is glass (left of my system and I am closest to the glass wall) and of course concrete ceiling. Short story I have never had any luck with subs. This is especially that case here. I have run the YPAO and in order to not get W3 error (sub gain higher than YPAO can adjust +/- 10dB) I have to adjust the sub gain to less than 1/4 to almost 1/8th volume and the YPAO puts the LFE output at -9!! So.. Dave Koz, sounds good, Steely Dan and The Police zero bass. Proven club music which should have enough bass to cause an avalanche nada. Speakers set small / large crossover 80Hz to 160Hz no help. Put the sub in my listening position and crawled on the floor. I did not find one place that really sounded better than any other. Certain recordings at certain frequencies sound quite good and others not. So I am thinking standing waves?? I realize one CD to the next will have a different base response but, the differences I am hearing are huge and others have noticed it as well. That said my experience in other locations with standard full range speakers (JBL L100 Century 1971 vintage) offered a pleasing (not perfect but with good consitancy) over all sound with very little messing about. If it is standing waves is there anyway I can measure it and see it on REW? Even though my speakers are from the same manufacturer and the Mythos Ones are meant to go with the Super Cubes could there be a phase issue because of my room acoustics and can phase be measured and corrected with an SPL meter? Something has got to be amiss or why would the YPAO want to almost completly deactivate my sub? (by the way I turned my sub back up to 50% and LFE to 0 but still no joy. Feeling I should have stuck with genuine full range mains and steered well clear of subs. Oh and corner placement was no joy and a bit boomy as well:hissyfit:

See attached pics of my room.


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## kermyb123 (May 21, 2008)

:huh:I'm not as seasoned as a lot of the people who I'm sure will reply to your post, however, I would say your room is a three sided acoustic mirror!

I would start with a nice plush carpet/area rug over that tile. Some traps could help you also. HEAVY drapes?

Just some ideas.


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## JCD (Apr 20, 2006)

I'm not sure about the standing waves idea -- I'll admit this isn't my area of expertise, but I'd think that if you moved around, or moved the sub around, the standing waves move within the room.

I do agree that you have an acoustical nightmare with your room -- hard refelctive surfaces, reinforcement on the left side but not the right, coffee table in front of you, couch right against the wall, speakers right up against the wall.. all of those issues are going to affect the imaging and frequency response of your system.

Hmm.. I just thought of something. I know this might be a huge pain, but what if you set up a 2.1 setup somewhere in your apartment so that your speaker, sub and sitting position are all at least ~1 meter away from any wall and see if you get the same low bass problem. I THINK the bass issues you're having are related to your couch being right against the wall more than anything else.. so maybe not a standing wave per se, but acoustic regardless. You might actually want to pose this same question in the acoustic sub-forum. There are some wicked smart people in there.

JCD


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## Wayne A. Pflughaupt (Apr 13, 2006)

Welcome to the Forum, airpiratehkg!


> Short story I have never had any luck with subs. This is especially that case here.
> 
> If it is standing waves is there anyway I can measure it and see it on REW?


I suggest visiting our REW and BFD Forums. REW can identify what and where your low frequency problems are, and a parametric EQ can probably deal with most of them. You might not be able to get perfection in your room, but you'll at the very least see a noticible improement.

Regards,
Wayne


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## andru (Aug 19, 2008)

Hi,
Your room sounds like a cube.. and a concrete cube!!! uuurgh! which is the worst environment for listening to music. If you scan your room with the REW you will probably notice huge peaks and dips... standing waves. I'm thinking you need to control the bottom end, not really enhance it. Bass traps, helmholtz resonators, wall damping... I think you might need the lot... could be cheaper to move to a different apartment.... or accept a lesser expectation of
quality from your listening environment. (perhaps use less volume..?)
Unfortunately... as the price of good equipment falls... especially in China, the physics of acoustics don't change one bit, except perhaps for temperature.

What I suggest, for the sake of experiment... would be to add some absorbent... behind paintings or any where it might not seem intrusive... try open cell fibre stacks in the corners of the room.
use the mirror method to kill early reflections hitting your listening position. Which means...
Getting a friend or your wife to hold a mirror on the walls either side of your listening position, when you can see the speaker drivers in the mirror add some absorbent material there... 
what about your ceiling? If it's a false ceiling ,load the void with acoustic absorbent...
Good luck
Andru


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## andru (Aug 19, 2008)

_I'm not sure about the standing waves idea -- I'll admit this isn't my area of expertise, but I'd think that if you moved around, or moved the sub around, the standing waves move within the room._

Hi again,
Standing waves and room modes are a product of the room dimension and nothing to do with where you place the speaker. They are based on the dimensions of the room... sure.. placing a subwoofer on a node or where it will excite a mode can make it louder or softer... (simple acoustic theory), but it doesn't change the room modes or standing waves.
Alton F. Everest has a great book on Acoustics... called from memory... The Handbook of Acoustics" or similar, it really is worth the read, you might get it from your library but it's definitely at Amazon.

Somewhere else on this site some guys have built a HT platform... you could use the same idea to lift up your sofa and use the underneath as a huge bass trap or helmholtz resonator.
Have you measured your room with REW?
That is probably the logical first step. Then change things around and keep measuring... and trying
new acoustic treatments.
Having a print out or picture of the response of your room will help you more than you can imagine.

Just another thought, in the recording world... if a control room has really, really bad acoustics and you really have to use it (no choice).... try to deaden the room right down as much as you can, especially the bottom end, then set your speakers away from the wall in an equidistant triangle with you, your listening couch at the "sharp end"....(move your couch away from the wall too...) and hopefully you will capture the magic of the stereo mix... 

depending on the size of your speakers... about a 2 metre by 2 metre by 2 metre triangle might do it... but adjust to taste. You shouldn't be able to identify the sound coming from any particular speaker... if you can... you are too close... and not getting the "true" mix. But if you change one dimension you must expand or contract the whole triangle... so if you move back half a metre you must keep the relative shape of the triangle...so everything moves. Depending on your speakers you might need to angle them up or down so that the tweeters are pointed at your ears. 
(stereo imaging)

Unfortunately in an apartment you have to live in the space too, so that may not work so well as in a studio...
Andru


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## Guest (Aug 21, 2008)

Hey, I've done quite a few set ups for Home Theater, every room has pros and cons to it. If your room is cement (so is my studio). The problem with low frequencies is that it just refracts around most items in the room. Where as high frequencies don’t have a long enough wavelength to bend around things. The same reason why you can hear more bass through a door way but high frequencies tend to get lost. The least expensive way to diminish problem frequencies is an EQ. My studio use to emphasize 125Hz by almost 15dB depending on where you are standing. I used my Graphic EQ to level it out a bit and it helps. Hanging heavy fabrics from the walls can also help. You read on the internet that some people say "doesn’t help for frequencies below 500Hz" from my experience those opinions don't always hold true. Cement reflects a high percentage of the acoustic energy that hits it so any type of material that has a lower percentage of reflective energy transfer it will help a bit. Again depending on your room sometimes a material to disperse the sound can help with bass problems sometimes it doesn’t.

I recently re-vamped a studio and they wanted to add a sub. The room was also a rectangle and they had cement blocks for 3 out of 4 walls. We used a combination of black cloth 3ft wide along the ceiling that helped reduce our bass problems by about 2dB. We then used 2X4’s to act as a bass trap. Finally two bass traps in the corners closest to the mixing board. We still had some bass problems in the room but with careful placement of the sub the area in front of the mixing board was almost perfectly flat. So all the engineer had to do was understand that the bass at the mixing spot had about 1.5dB of extra energy. 

I don't know if any of this will give you an idea for your place but it might help. If you end up still having a problem and really want a good room you can do the same thing I did with my studio. I built a room in a room. I have a floating floor, double stud walls, and a ceiling that isolates my room in a room from the cement room outside it. If you have the money and own your place you can do that as a last resort. With careful designing you can tailor the room to exactly what you want.

Hope it works out.

K:1eye:


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## tenzip (May 4, 2007)

You might also want to take a look at the Home Audio Acousitics forum, I don't know if you have SAF to consider, or if you can hang anything you want on the walls, ceiling, etc.

I would suggest starting with that, and then EQ for problems that remain.


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## drf (Oct 22, 2006)

Just a thought I had, if it is all getting too complicated why not put your sub in the listening position then move your ahead around the room until you find the best sounding spot. Place your sub there and see if it doesn't sound any better.

Of course this may not work at all but at least you have got nothing to lose.


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## DIGIT (Aug 19, 2008)

When sound waves hit the walls they bounce back and collide with the waves coming directly from the speaker. Depending on the room dimension and freq (wavelength)... this collision of pos/neg air pressure can cause either a dip or a boost, as the reflected pressure either adds or subtracts from the original. Usually dips are much more severe than the boosts and in some cases you may even have a near cancellation of certain freq (for example, a huge hole in the 80hz region..., etc...) This will/can change as you walk around the room, in some areas certain low freq. will sound louder, in other softer, etc... So, the room will be full of dips and boosts which change drastically as you move about the space, making the bass response very uneven, not a good thing!

The quickest and cheapest way to have some control over this issue is to either buy or make some good BASS TRAPS and place them in each corner of the room, as well as in other appropriate areas (tri-corners, wall(s), door, ceiling..). This will not make a really badly designed/constructed room perfect but, it WILL improve it significantly, if properly done.


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