Adding a Second Sub to a 7.1 System - AVS Forum
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Old 03-02-2013, 02:07 AM - Thread Starter
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I have just bought a second B&W DB1 for my Classe / B&W 800 Series system.

When I se the levels using an SPL Meter, do I set the level of the second (new) sub the same as the other sub and the speakers (75db) ?

Or, should it both subs be set lower (as I am using two) ?

Thanks Tom
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Old 03-02-2013, 07:55 PM
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set both subs to 72dB if they subs are placed in separate parts of the room.

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Old 03-03-2013, 05:58 AM
 
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Do you have any room measuring capacity?

You want the subs to have similar output at the main listening position but as pointed out, independently, each sub should be in the 72dB range so when played together, their combined output equals ~75dB.

Do you have an auto-EQ feature in your preamp or AVR?

If you do, you should have the internal AVR gain setting set to zero and you should use your subwoofer's gain control to set your sound levels at the main listening position. Having internal AVR gains jacked up or down beyond zero, will squirrel your reading/gain settings by an equivalent amount.

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Old 03-03-2013, 06:11 AM
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BeeMan458,
I've veen thinking about adding a second sub as well and I was interested in your comment regarding having the AVR levels @ zero and using the sub gain to get to the desired db. That's the first time I've ever seen that mentioned. What is the disadvantage to having the AVR set the volume, it's certainly easier to do it that way? Also, and this is probably a dumb question, but by "interrnal AVR gain", you are referring to the speaker line levels, yes?

Doug

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Old 03-03-2013, 06:28 AM
 
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Originally Posted by DougReim View Post

BeeMan458,
I've veen thinking about adding a second sub as well and I was interested in your comment regarding having the AVR levels @ zero and using the sub gain to get to the desired db. That's the first time I've ever seen that mentioned. What is the disadvantage to having the AVR set the volume, it's certainly easier to do it that way? Also, and this is probably a dumb question, but by "interrnal AVR gain", you are referring to the speaker line levels, yes?

Sorry if my use of terminology causes you (or others) confusion. I find the current esoteric terminology to be confusing as it fails to accurately convey an ideal; language for the purpose of communication with "all."

That said, when one measures their room with a sound meter for the purpose of using an auto-EQ feature, the auto-EQ feature, with the permission of the AVR manufacture's license agreement, resets the internal AVR gain settings for the subwoofer pre-out; speaker line levels.

To get an accurate and useful reading that will translate over to the auto-EQ system (a standard), the @ main listening position (MLP) measurement needs to be set, using the sub's gain potentiometer with the AVR's gain set to zero so there will be no AVR influence on the set-up, @ MLP, measurement.

Also, each sub needs to have the volume level set, using the sub's gain potentiometer, independent of the other; only one sub turned on at a time. In this case, distance is not a consideration (that's the purpose of the phase control and any time domain feature the auto-EQ feature has available) as equal output, measured at the MLP, is the goal. When all subs are turned on, the combined final, @ MLP measurement, should be as close as reasonably possible to 73dB - 75dB.

From the above standard, now the auto-EQ feature can tell the AVR how to set the internal gain settings (line levels), based on auto-EQ measurements, but first, a standard has to be set for this to happen accurately. With that in mind, if this is done, one can go into "ANY" room, "ANY" system, "ANY" time and by having a dependable starting point (standard) in which to run the auto-EQ feature, despite room acoustic variables, expect to have consistent, across the board results in which to start to get the best from the system being worked with.

If my above causes you further confusion, my apologies as I've done my level headed best to accurately articulate my thought process in the above.

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Old 03-03-2013, 06:34 AM
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Quote:
Originally Posted by Tom Edge View Post

I have just bought a second B&W DB1 for my Classe / B&W 800 Series system.

When I se the levels using an SPL Meter, do I set the level of the second (new) sub the same as the other sub and the speakers (75db) ?

Or, should it both subs be set lower (as I am using two) ?
In most cases you want the two subs set to the same output level; the usual exception would be with a very large room, where the distance differential of the two subs to the LP is 20 feet or more. Two subs will be louder than one, so you probably will have to run the sub volume a bit lower to level match the system.

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Old 03-03-2013, 06:37 AM
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If my above causes you further confusion, my apologies as I've done my level headed best to articulate my thought process in my above.

No, that makes sense now, thanks for explaining. I'm glad I saw your post.

Doug

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Old 03-03-2013, 06:39 AM
 
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Originally Posted by DougReim View Post

No, that makes sense now, thanks for explaining. I'm glad I saw your post.

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Old 03-03-2013, 07:46 AM
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Originally Posted by DougReim View Post

No, that makes sense now, thanks for explaining. I'm glad I saw your post.

If the second sub you're adding is identical to your first sub, you are likely better off using the process described by Bill Fitzmaurice than the level-matching technique described by BeeMan. Level-matching can result is significant disparities in the gain settings. Consider that a 3 dB difference means that the higher-set sub is using twice the amplifier power and twice the driver excursion of the lower set sub. A 6 dB difference equates to 4x the power and excursion. If you are buying a 2nd sub because you want more output/headroom, you'll want to set them up so they both output the same SPL irrespective of their position in the room, (arbitrary), or the location of the listening position, (arbitrary.) Of course, if you are not intending to use the subs at anywhere close to their limits, then set them up any way you like. Also, if the subs are different from one another, don't use gain-matching; it only works with identical subs. In that case, use BeeMan's level-matching technique or Geddes technique: http://mehlau.net/audio/multisub_geddes/

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Old 03-03-2013, 09:29 AM
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Originally Posted by craig john View Post

Consider that a 3 dB difference means that the higher-set sub is using twice the amplifier power and twice the driver excursion of the lower set sub. A 6 dB difference equates to 4x the power and excursion.
Excursion is linear with respect to voltage swing, not power. Doubling voltage swing quadruples power, but it only doubles excursion, and results in 6dB higher output. Either way, you don't want to have one sub running hotter than the other unless absolutely necessary, otherwise the one can run out of both electrical and mechanical headroom before the other.

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Old 03-03-2013, 10:31 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Excursion is linear with respect to voltage swing, not power. Doubling voltage swing quadruples power, but it only doubles excursion, and results in 6dB higher output. Either way, you don't want to have one sub running hotter than the other unless absolutely necessary, otherwise the one can run out of both electrical and mechanical headroom before the other.
Thanks for the clarification.

Craig

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Old 03-03-2013, 12:42 PM
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Thanks for the clarification.

Craig
No problem, I wouldn't remember half of this stuff if I didn't work with it seven days a week.

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