A Guide to Subwoofers (Part II): Standing Waves & Room Modes

[Big Daddy]

Originally Posted by grod777

I understand what you are saying. I only have it hooked up the way I do because it states in the manual I can. And an email to Def Tech recently replied back with "Using both will give you a bit stronger output from the subwoofer, which may or may not be desirable". I will try it with the low level connection only. Do you think I should use the calibration program in the AR or calibrate with a test meter?

You don't need the extra output as you can always adjust the subwoofer level in the receiver's menu.

Initially, use the AVR to calibrate your speakers. After that, use an SPL meter to fine tune the system. The first part of A Guide to Subwoofers has guidelines on how to adjust the phase and crossover frequency.

[hagar852]

first time reading post.. I would just add the only thing not discussed is the temperature of the room is not factored in. The temperature also affects the speed the sound travels at which will then affect its wavelength.

[Big Daddy]

Originally Posted by hagar852

first time reading post.. I would just add the only thing not discussed is the temperature of the room is not factored in. The temperature also affects the speed the sound travels at which will then affect its wavelength.

Normally, I assume most people keep the temperature of their home theater room at a reasonable consant level. Otherwise, we would need different setups for Summer, Winter, Outdoor, Indoor, etc., etc. etc. I don't think I have the strength and the back to move my heavy subwoofers around.

[saprano]

Originally Posted by hagar852

first time reading post.. I would just add the only thing not discussed is the temperature of the room is not factored in. The temperature also affects the speed the sound travels at which will then affect its wavelength.

So which is better hot or cold?

[Big Daddy]

Originally Posted by saprano

So which is better hot or cold?

The speed of sound varies with the temperature and humidity such that sound travels slower on cold days. You really need a huge difference in temperature in your home theater room to notice any difference.

Most probably, your equipment and your ears will freeze before the temperature affects the sound quality.

[welwynnick]

Those are the best couple of posts I have seen in any forum anywhere - ever.

Kudos, BD!

[STARSCREAM]

Astounding posts!!!

[jaejw1]

great read..

[Big Daddy]

Originally Posted by jaejw1

great read..

Thank you. I spent a couple of months researching the material, creating the graphs, and putting the information in Posts #1 & 2 together. When I hear that someone found the information useful, it makes me very happy.

[crazyBLUE]

Well I just learned Quit A bit from the first 2 posts ! Thanks Big Daddy for the information that explains questains I had on A couple of different things pertaining to multiple (4) subwoofers .

[sheedoe]

I cannot remember where, but I've read somewhere that cylinder subwoofer does not produce standing waves. Is this true?

[Big Daddy]

Originally Posted by sheedoe

I cannot remember where, but I've read somewhere that cylinder subwoofer does not produce standing waves. Is this true?

Standing waves do not depend on the shape of the subwoofer. They are caused by the interaction of low frequency sound waves and the room boundaries. It is pure Physics.

Cylindrical subwoofers like all other subwoofers generate low frequency sound waves. All low frequency waves love the walls, ceiling, and floor too much.

[sheedoe]

Originally Posted by Big Daddy

Standing waves do not depend on the shape of the subwoofer. They are caused by the interaction of low frequency sound waves and the room boundaries. It is pure Physics.

Cylindrical subwoofers like all other subwoofers generate low frequency sound waves. All low frequency waves love the walls, ceiling, and floor too much.

Thanks Big Daddy! But here's a quote from this site that suggests that cylinder enclosure does reduce standing waves.
"In a square enclosure, standing waves are easily generated, and these become a problem. That is why there are so many designs on the market that move away from a simple square box. By making the sides and/or top non-parallel with the opposite side, standing wave production is reduced. So, you can see all kinds of shapes in speaker enclosures, some with sloping front, sides, top, and so on. The cylinder is ideal for minimizing standing waves, because the sides (a cylinder) are totally non-parallel. In fact, this is the fundamental reason Dr. Poh Hsu designs his subwoofers with cylindrical enclosures"

[Big Daddy]

Originally Posted by sheedoe

Thanks Big Daddy! But here's a quote from this site that suggests that cylinder enclosure does reduce standing waves.
"In a square enclosure, standing waves are easily generated, and these become a problem. That is why there are so many designs on the market that move away from a simple square box. By making the sides and/or top non-parallel with the opposite side, standing wave production is reduced. So, you can see all kinds of shapes in speaker enclosures, some with sloping front, sides, top, and so on. The cylinder is ideal for minimizing standing waves, because the sides (a cylinder) are totally non-parallel. In fact, this is the fundamental reason Dr. Poh Hsu designs his subwoofers with cylindrical enclosures"

What the author in that article is talking about is standing waves inside a subwoofer's enclosure and not in the room.

Contrary to all the nonsense that is repeated in most Internet forums, we do not have standing waves in a subwoofer's box, particularly in HT applications. Assuming that the vast majority of subwoofers for home audio are crossed at 80Hz to 100Hz, you can imagine the craziness of this claim. For standing waves to occur inside the box, a sound’s wavelength must be twice the size of the box. These are the approximate wavelengths of bass frequencies:

20Hz: 56.5ft
50Hz: 22.6ft
80Hz: 14.1ft
100Hz: 11.3ft

How many people have a subwoofer that big?

The article in your link discusses the HRSW12v cylindrical subwoofers from Hsu Research. I am quite familiar with the Hsu subwoofer in that article. I own two updated versions of that subwoofer, HRSW12Va. I spent several hours with Dr. Hsu and discussed the placement of the sub in the room to eliminate standing waves. That was the main reason I bought two subwoofers, instead of one. Hsu does not make cylindrical subs and they haven't made any for about 6 or 7 years.

All subwoofers, regardless of the shape or size, create standing waves. Room placement is absolutely crucial in receiveing good bass. In almost all cases, two or more subwoofers are preferred to one.

[sheedoe]

Thanks again Big Daddy for taking the time to answer my question. You are truly very resourceful.

[rpatt]

Excellent presentation Big Daddy. Is anyone using the 1/4 distance from walls position with 2-subs? I'm interested in your results.

[jerix]

Is the level of standing wave in a given room not dependent on the other materials that are present in the room like curtains, tables couches, picture frames, windows, doors. etc.?

[Big Daddy]

Originally Posted by jerix

Is the level of standing wave in a given room not dependent on the other materials that are present in the room like curtains, tables couches, picture frames, windows, doors. etc.?

Many objects affect the sound waves in the room. However, the biggest factors that affect the long wavelngths of the bass frequencies are the room dimensions and the walls, ceiling, and floor. Most of the other objects in the room affect the higher frequency waves.

[Fors*]

Originally Posted by Big Daddy

Many objects affect the sound waves in the room. However, the biggest factors that affect the long wavelngths of the bass frequencies are the room dimensions and the walls, ceiling, and floor. Most of the other objects in the room affect the higher frequency waves.

I decided to check this out and so I moved both of my subs to the first "best" location, or as the diagram shows, in the middle of the room, on the left center and right center opposite one another. I have some new surrounds coming in, so once I get them in, I will re-run MCACC (again) and then try to dial in my speakers and both subs using my SPL meter. I felt that the SVS sub in my front soundstage was cramping my right front speaker, so I decided to move them (again) and hopefully this will be a much better location for both subs. Hopefully I will have my new surrounds by Friday, and I will then re-calibrate and report back any changes I find then.

[Big Daddy]

Originally Posted by forsberg21

I decided to check this out and so I moved both of my subs to the first "best" location, or as the diagram shows, in the middle of the room, on the left center and right center opposite one another. I have some new surrounds coming in, so once I get them in, I will re-run MCACC (again) and then try to dial in my speakers and both subs using my SPL meter. I felt that the SVS sub in my front soundstage was cramping my right front speaker, so I decided to move them (again) and hopefully this will be a much better location for both subs. Hopefully I will have my new surrounds by Friday, and I will then re-calibrate and report back any changes I find then.

And your wife hasn't forced you to sleep in the living room yet?