Four Subwoofers - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

Reply
 
Thread Tools
post #11 of 31 Old 06-30-06, 01:14 PM Thread Starter
Moderator Emeritus
 
Ayreonaut's Avatar
Naut
 
Join Date: Apr 2006
Location: Richmond, VA
Posts: 606
Re: Four Subwoofers

Sonnie,

I've been doing a lot of research on sub positioning lately, as you know. I discovered this article: link

Its a bit complicated, but after carefully going over it I was able to do the math. The gist of it is that for one sub in a rectangular room the best sub placement to avoid room resonances is in a quarter point. 1/4 of the room width off the side wall and 1/4 of the room length off of the end wall.

That may not be practical is some living rooms, but sonically its the best spot. Fourtuantely I can put mine very near one of the quarter points. I moved my sub there last night, and measured. I lost a few dB comapred to corner placement, but I got the most even FR (pre EQed) of any position I've tried. It really works.

Why does this matter? Can't I just EQ for any position? Well, I recently tried corner loading and then EQing out the ensuing resonances. Even though I gained a few dB abnd the EQed output measured flat, the sub still sounded boomy. I don't really know why. My guess is that the decay times come in to play since the room continues to ring after the sub stops. If you position in a quarter point, those modes get much less excited.

Theoretically, the only thing better for dealing with room modes is to use multiple subs in every quarter point. Instead of mitigating the LF axial room modes, it elimintes them. (I should add that two subs in the two front quarter points will eliminate the width modes and mitigate the length modes.)

I suggest poisitioning your two subs on the two front quarter points and measuring at all of your listening positions. Obviously this isn't a practical set up to keep, but it should give you the same response as subs mounted in the same poisitions in the ceiling above.

Please let us know!

We are the Shack. Existence as you know it is over.
We will add your biological and technological distinctiveness to our own.
You will be assimilated. Resistance is futile.
Ayreonaut is offline  
Sponsored Links
Advertisement
 
post #12 of 31 Old 06-30-06, 02:26 PM
Elite Shackster
brucek
 
Join Date: Apr 2006
Posts: 7,514
Re: Four Subwoofers

Quote:
The gist of it is that for one sub in a rectangular room the best sub placement to avoid room resonances is in a quarter point. 1/4 of the room width off the side wall and 1/4 of the room length off of the end wall.
Interesting stuff. Wish I knew more about it. I have certainly read opposing views to the theory and article you site though.

Floyd Toole seems to support the theory that if we have proper room dimensions where we can spread the axial modes (and lesser so the tangential and oblique modes) evenly, then the optimum position would be corner loaded so as to most efficiently acoustically couple to the room modes.

This provides us with added gain and headroom. Hopefully the resulting first order harmonics are evenly spread and not much equalization is required. That's the rub for sure - many are dealing with fixed room dimensions designed for ascetics and not subwoofer placement.

Your method essentially is in direct opposition to that theory in that you're trying to locate the dead zones so as to basically place the sub in a null and not generate any resonances. Fine, but unfortunately you're trying to power your way out of the null - you'll need a large amp. I suspect for optimum placement for a true null of the ceiling fundamental with your method, you'd have to mount the sub in the air about a quarter way between the floor and ceiling. Not possible with an IB or really very practical for any sub. Although the ceiling harmonic would be considerably higher than the other dimensions.

Who knows.....

brucek
brucek is offline  
post #13 of 31 Old 06-30-06, 03:02 PM
Elite Shackster
 
Sonnie's Avatar
 
Join Date: Apr 2006
Location: L.A. (Lower Alabama)
Posts: 22,577
My System
Re: Four Subwoofers

I can see it now... four hanging subs... who will be the first to try it? heeheehe

I'm gonna be doing some experimenting this evening with moving one of my SVS subs around the room some. The 1/4 point definitely couldn't be the permanent spot, but it would be interesting to see the different response compared with each other.

Last night when I was measuring the different spots in the ceiling I noticed the response was not a lot different from where my subs are now. There was a tad better extension down to 15hz and the dip I have moved from 40hz to 35hz.

What I'm thinkin' is moving the left sub down the left wall in various locations while leaving the other sub in check. I'll test the subs jointly as I have previously and also adjust phase on the one I'm moving and retest. I can stand to move that one sub to a couple of different spots along that wall... so I might pick up that weak spot at 40hz... or move the weak spot with that sub to another frequency area.

Then eq'ing them might be more of a challenge too... being they will no longer be symmetrically located.
Sonnie is offline  
 
post #14 of 31 Old 06-30-06, 04:59 PM Thread Starter
Moderator Emeritus
 
Ayreonaut's Avatar
Naut
 
Join Date: Apr 2006
Location: Richmond, VA
Posts: 606
Re: Four Subwoofers

Quote:
brucek wrote:
Interesting stuff. Wish I knew more about it. I have certainly read opposing views to the theory and article you site though.
So have I. I've tried it both ways now.
Quote:
brucek wrote:
Floyd Toole seems to support the theory that if we have proper room dimensions where we can spread the axial modes (and lesser so the tangential and oblique modes) evenly, then the optimum position would be corner loaded so as to most efficiently acoustically couple to the room modes.

This provides us with added gain and headroom. Hopefully the resulting first order harmonics are evenly spread and not much equalization is required. That's the rub for sure - many are dealing with fixed room dimensions designed for ascetics and not subwoofer placement.
Floyd Toole has a list of rules for good sound in rooms, and what we are coming up against is a conflict between two of them. Maximize the output from the subwoofer(s), but achieve a uniform performance over the listening area. For maximizing the output, corner loading is a good idea.
Quote:
brucek wrote:
Your method essentially is in direct opposition to that theory in that you're trying to locate the dead zones so as to basically place the sub in a null and not generate any resonances.
Exactly. When we are trying to "achieve a uniform performance over the listening area" we can use what Toole calls Selective Mode Cancellation.
Quote:
Floyd Toole wrote:
So, why would we want to do this? Aha! Would it not be a good idea for everybody in each row of a home theater to hear the same bass sounds? Would it not be a good idea for a recording engineer to be able to move from one end of the console to the other without experiencing huge changes in bass? Well, this is how it can be accomplished. We are not saying, yet, that it is good sound, merely that it is the same sound. Once things are equalized in the sense of getting everybody hearing more or less the same sound, we then may need to equalize in the sense of changing the frequency response of the system.
I’ve tried it both ways. I equalized both responses and set the volumes the same. What I found was that in my room the position employing Selective Mode Cancellation does yield a more uniform response over several listening positions and a lower total level. But I also found that it sounds much cleaner. Tighter, or damped. That’s what I prefer. Many might prefer the higher output of corner loading and excited modes. It’s probably a misnomer, but some might call the difference HT sound vs. Musical sound.
Quote:
brucek wrote:
Fine, but unfortunately you're trying to power your way out of the null - you'll need a large amp.
You’re right. To achieve the same output level you might need more sub and amp. Do you think Sonnie’s eight woofer IB and two amps will do the trick?
Quote:
brucek wrote:
I suspect for optimum placement for a true null of the ceiling fundamental with your method, you'd have to mount the sub in the air about a quarter way between the floor and ceiling. Not possible with an IB or really very practical for any sub. Although the ceiling harmonic would be considerably higher than the other dimensions.
Yes, a sub on the floor or in the ceiling will excite all the vertical axial modes. Fortunately only the first resonance will be in the subwoofer range for a typical room height. In my room with an eight foot ceiling it falls at 70 Hz. But since all of the listeners in a room will be seated at about the same height, one band of EQ will correct it for all positions, if it proves to be a problem.

We are the Shack. Existence as you know it is over.
We will add your biological and technological distinctiveness to our own.
You will be assimilated. Resistance is futile.
Ayreonaut is offline  
post #15 of 31 Old 06-30-06, 05:07 PM Thread Starter
Moderator Emeritus
 
Ayreonaut's Avatar
Naut
 
Join Date: Apr 2006
Location: Richmond, VA
Posts: 606
Re: Four Subwoofers

Quote:
Sonnie wrote:
I can see it now... four hanging subs... who will be the first to try it? heeheehe
I think that to cancel the mechanical vibrations, he'll have to build four boxes and use eight woofers. Wait a minute ... weren't you going to buy eight woofers?

Quote:
Sonnie wrote:
I'm gonna be doing some experimenting this evening with moving one of my SVS subs around the room some. The 1/4 point definitely couldn't be the permanent spot, but it would be interesting to see the different response compared with each other.
That spot worked for me with one sub, but be sure to try two in the quarter points some time.

Quote:
Sonnie wrote:
Last night when I was measuring the different spots in the ceiling I noticed the response was not a lot different from where my subs are now. There was a tad better extension down to 15hz and the dip I have moved from 40hz to 35hz.
A spot on the floor and the one above it on the ceiling should measure very much the same.

We are the Shack. Existence as you know it is over.
We will add your biological and technological distinctiveness to our own.
You will be assimilated. Resistance is futile.
Ayreonaut is offline  
post #16 of 31 Old 06-30-06, 05:14 PM
Senior Shackster
Josuah
 
Join Date: Apr 2006
Location: San Jose, CA
Posts: 636
Re: Four Subwoofers

Hm. The article posted on Audioholics just now about room acoustics states that placing a speaker equidistant from two boundaries creates a problem. So I assume placing a subwoofer at 1/4 in from a corner would create that same problem. ???
Josuah is offline  
post #17 of 31 Old 06-30-06, 06:09 PM
SVSound
Jack
 
Join Date: May 2006
Posts: 89
Re: Four Subwoofers

Quote:
That may not be practical is some living rooms, but sonically its the best spot. Fourtuantely I can put mine very near one of the quarter points. I moved my sub there last night, and measured. I lost a few dB comapred to corner placement, but I got the most even FR (pre EQed) of any position I've tried. It really works.
Great stuff. Definitely going to give it a try. I can certainly use a front corner for this placement on a permanent basis for a single sub. Even elevating the sub to 1/4 height might be do-able, at least with one of my little sealed 12" workhorses.

Quote:
Why does this matter? Can't I just EQ for any position? Well, I recently tried corner loading and then EQing out the ensuing resonances. Even though I gained a few dB abnd the EQed output measured flat, the sub still sounded boomy. I don't really know why. My guess is that the decay times come in to play since the room continues to ring after the sub stops.
Yeah, I think you hit it. Eq-ing out some peaks isn't the same as not exciting the modal ringing in the first place.

What do you think this you linked to above...make sense?

Jack Gilvey is offline  
post #18 of 31 Old 06-30-06, 06:36 PM Thread Starter
Moderator Emeritus
 
Ayreonaut's Avatar
Naut
 
Join Date: Apr 2006
Location: Richmond, VA
Posts: 606
Re: Four Subwoofers

Quote:
Josuah wrote:
Hm. The article posted on Audioholics just now about room acoustics states that placing a speaker equidistant from two boundaries creates a problem. So I assume placing a subwoofer at 1/4 in from a corner would create that same problem. ???
Yes it will, if the room is square. If the length and width differ significantly, than the two quarter distances will be sufficiently different to avoid this.

We are the Shack. Existence as you know it is over.
We will add your biological and technological distinctiveness to our own.
You will be assimilated. Resistance is futile.
Ayreonaut is offline  
post #19 of 31 Old 06-30-06, 06:39 PM Thread Starter
Moderator Emeritus
 
Ayreonaut's Avatar
Naut
 
Join Date: Apr 2006
Location: Richmond, VA
Posts: 606
Re: Four Subwoofers

Quote:
Jack Gilvey wrote:
What do you think this you linked to above...make sense?

It would eliminate the width modes if perfectly symmetrical, but would excite all the height and length modes. You'd have to move them 1/4 of the length of the room toward you if you want to avoid exciting the first three length modes too much.

We are the Shack. Existence as you know it is over.
We will add your biological and technological distinctiveness to our own.
You will be assimilated. Resistance is futile.
Ayreonaut is offline  
post #20 of 31 Old 06-30-06, 07:39 PM
Elite Shackster
 
Sonnie's Avatar
 
Join Date: Apr 2006
Location: L.A. (Lower Alabama)
Posts: 22,577
My System
Re: Four Subwoofers

Well I just did about 12 measurements.... every which way but loose. Very interesting indeed. I'll probably start another thread for it so as I don't invade on yours and it's a little off your topic anyway. I'll say this much... I now have a different sub location for one of my subs and I can definitely live with the location but it ain't 1/4 out into the room.
Sonnie is offline  
Reply

Bookmarks

Tags
subwoofers

Quick Reply
Message:
Options

Register Now




PLEASE COMPLETE ALL REQUIRED FIELDS BELOW... THANKS!

REQUIRED FIELDS ON THIS PAGE
YOU MUST COMPLETE ALL OF THESE

Username
Password
Confirm Password
Email Address
Confirm Email Address
Random Question
Random Question #2




User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
PLEASE READ BELOW PRIOR TO ENTERING AN EMAIL ADDRESS!

ATTENTION!

YOU MUST ACTIVATE YOUR ACCOUNT!

Activation requires you reply to an email we will send you after you register... if you do not reply to this email, you will not be able to view certain areas of the forum or certain images... nor will you be able download software.

AN INVALID EMAIL ADDRESS WILL CAUSE YOUR ACCOUNT TO BE DELETED!

See our banned email list here: Banned Email List

We DO NOT respond to spamcop, boxtrapper and spamblocker emails... please add @hometheatershack DOT com to your whitelist prior to registering or you will get nowhere on your registration.


Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML is not allowed!
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 


For the best viewing experience please update your browser to Google Chrome