Dual Sub Calibration Q's - Home Theater Forum and Systems - HomeTheaterShack.com

 
Thread Tools
post #1 of 5 Old 12-15-07, 09:41 AM Thread Starter
Shackster
GT
 
Join Date: Dec 2007
Location: Atlanta
Posts: 49
Dual Sub Calibration Q's

Hi. I have two subs: and DIY SS RL-P15 & a SVS Ultra. Both are tuned to 17hz. I've been moving the subs to different locations to get the best response, but have a few questions as to the best way to take the measurements. I'm using a Radio Shack meter w/ correction values.

1. Should I measure the response of both subs with or without the other speakers?
2. Should I measure the subs individually or together?
3. I took measurements from 3 listening spots...should I calibrate based on the average of the three or from 1 prime listening spot?
gary thomas is offline  
Sponsored Links
Advertisement
 
post #2 of 5 Old 12-15-07, 10:30 AM
Elite Shackster
brucek
 
Join Date: Apr 2006
Posts: 7,514
Re: Dual Sub Calibration Q's

Quote:
have a few questions as to the best way to take the measurements
I would certainly forget about the 'other' speakers until I had found the best spot for the two subs.

If you have them in different positions, presumably this is to produce an overall response at the listening area that neither single position provided.

Alternatively, if you've found a single position in the room that provides a fairly smooth response, then I would co-locate the two subs.

Once you've found the best position(s) for the two, then it's really a bit of trial and error when equalizing. In the end, the two subs are acting as a single unit, but you may have to measure each at the same time and offer each a bit of equalization to end up with the two creating an overall satisfying result.

You can certainly measure and equalize for a single listening position, but if you have more than one person listening, it's best to spread out the measures to a bit of a wider area and average the equalization.

brucek
brucek is offline  
post #3 of 5 Old 12-15-07, 02:26 PM Thread Starter
Shackster
GT
 
Join Date: Dec 2007
Location: Atlanta
Posts: 49
Re: Dual Sub Calibration Q's

Thanks Bruce. The reason I asked about the other speakers is that I'm getting an upward trend on SPL between 80 & 100...I'm thinking that it may be caused when my mains (crossover @ 80) and center/surrounds (crossover at 100) kick in.

I initially had both subs stacked in the corner when I added the DIY sub & output become a non-issue. The levels were great in the center room listening area & at my main listening area, but the couch seats along the wall were blown away. Separating the subs gave me a tighter response when averaging my three main listening areas. (I also tried 1 of the subs along a side wall, but things got worse)

I had a BFD at one time, but sold it. My goal is to get a good average response in all three listening positions by deteriming ideal position.

The picture shows the stacked position...I now have 1 located behind & outside each main speaker. I plan to experiment by placing them behind & inside the mains...or 1 inside & 1 outside the mains. If possible, I'd like to keep them on the stage.

After finding this great forum...and reading about subwoofer calibration, I'm wondering if using the Rat Shack w/ correction values is even worth it. I wanted to make sure I'm taking the proper measurements. I'm considering jumping in w/ REW...mostly because I get bored without a home theater project!
Attached Thumbnails
Dual Sub Calibration Q's-dsc01137.jpg  

gary thomas is offline  
post #4 of 5 Old 12-15-07, 02:46 PM
Elite Shackster
brucek
 
Join Date: Apr 2006
Posts: 7,514
Re: Dual Sub Calibration Q's

Quote:
I'm getting an upward trend on SPL between 80 & 100...I'm thinking that it may be caused when my mains (crossover @ 80) and center/surrounds (crossover at 100) kick in.
Absolutely. This where REW can help show the best sub phase and distance setting to get that rise down.

Quote:
I had a BFD at one time, but sold it.
Not many people can get by without it..

Quote:
I'm wondering if using the Rat Shack w/ correction values is even worth it. I wanted to make sure I'm taking the proper measurements. I'm considering jumping in w/ REW
The Radio Shack meter combined with REW and our downloadable correction factors is perfectly suitable for subwoofer measurements. REW is light years ahead of simple tone measuring......

Better start reading

brucek
brucek is offline  
post #5 of 5 Old 12-15-07, 03:31 PM
Senior Shackster
 
DrWho's Avatar
Mike Bentz
 
Join Date: Sep 2006
Location: Chicago
Posts: 438
Re: Dual Sub Calibration Q's

Quote:
brucek wrote: View Post
Absolutely. This where REW can help show the best sub phase and distance setting to get that rise down.
I'm not sure that is the approach I'd pursue...

Generally speaking, you're trying to optimize acoustic summation through the crossover frequency so that you can also maintain a flat power response. I would be willing to wager that the rise might be the result of processing inside the receiver. For example, the difference between "Direct" and "Stereo" on my Denon AVR is a 3dB rise at the crossover frequency. I've seen this show up on other systems too.

Nevertheless, if the rise is in fact the result of acoustic summation, then the best approach would be to implement a cascaded filter on the subwoofer, which would increase the steepness of the crossover, thus reducing the polar lobing that occurs from the subs' interaction with the mains. In other words, this should improve the power response of the system.

In order to know what kinds of interactions are going on, you'll need to measure each speaker separately, then do a final combined system response. If your phase and time-alignment is correct, you should see a 6dB rise at the crossover intersection, which indicates perfect summation.

Rane has an interesting article that addresses some of the concerns for crossovers:
http://www.rane.com/note160.html
Of interest here is the notion that mis-aligning the phase (like what occurs with a butterworth filter) results in the main lobe being redirected - not attenuated. This means that somewhere else in the room you have more bass, which is rarely ever going to be conducive when trying to optimize the sound over various listening positions.

Likewise, you should think of the subs' positions in the room as a line-array, where the physical offset between drivers changes the shape of the lobe (note that it is also frequency dependent). Here's a picture that describes the change in shape of the polar lobes, which is shown as a ratio of wavelength so that you can calculate the different lobe at each frequency for a fixed distance between sources:


-Mike Bentz
~It's all about compromise~


"It's territorial with the soundboard. So you're mixing and some dude comes by spewing opinions and trying to turn knobs. It's akin to going up to an artist and painting over his unfinished masterpiece. You just want to shove your paint brush up his nose and throw the soundboard out the window!"
DrWho is offline  
Reply

Bookmarks

Tags
calibration , dual

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









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



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