I had an interesting discussion with Barry Ober (www.soundoctor.com) the other day. Barry is the chief technical consultant for JL Audio, makers of some very nice subwoofers.
We discussed setup issues that affect sound quality when integrating (one or more) subwoofers into your system. Barry, who seemed immediately both personable and knowledgeable, was adamant that we consider the time element of integration first and foremost before frequency response concerns were addressed.
He stated that JL subwoofers have a group delay of 9 milliseconds (mS). Here is how the science and math work to show you the placement and setup details for optimal time alignment with your main speakers:
Speed of Sound = 1126 feet per second OR 1 foot in 0.000888 seconds
Group Delay of 9 mS = 0.009 seconds
Therefore: 0.009 divided by 0.000888 = 10.135 feet equivalent distance offset
So, you would need to place your JL sub 10.135 feet in front of your main speakers to have perfect time alignment in wave launch. Since very few folks choose this setup configuration, it stands to reason that very few people achieve optimal results with the JL subwoofers. If you cannot achieve time coherency, then frequency response tuning/adjustments will never fix what is fundamentally wrong.
Now, since many of us can't physically locate our subs 10 feet in front of the main speakers (spousal acceptance factor and other reasons), how do we achieve time coherency?
There are a couple of methods.
The end effect is that your sub is "electronically" placed 10 feet forward of your main speakers to account for its group delay.
If you tend to place your subwoofers BEHIND your main speakers, as many of us do, you must then add an extra foot of sub distance in your processor (in addition to the 10 foot offset already discussed) for each foot behind the main speakers to the sub.
I set up my system this way yesterday, and it made a large positive difference in the sound quality of my setup. Kick drums were rendered far more realistically, and bass instruments were placed in space far more precisely than before.
Once you get things oriented correctly in the time domain, then you can run the ARO (EQ) feature of the sub to improve the frequency response characteristics.
I was admittedly a bit skeptical as I listened to Barry at first, but the straightforward logic of the discussion made perfect sense to me. This short discussion is but the tip of the "bass iceberg", and I hope to invite Barry here to delve much more completely into this subject.
Lee
We discussed setup issues that affect sound quality when integrating (one or more) subwoofers into your system. Barry, who seemed immediately both personable and knowledgeable, was adamant that we consider the time element of integration first and foremost before frequency response concerns were addressed.
He stated that JL subwoofers have a group delay of 9 milliseconds (mS). Here is how the science and math work to show you the placement and setup details for optimal time alignment with your main speakers:
Speed of Sound = 1126 feet per second OR 1 foot in 0.000888 seconds
Group Delay of 9 mS = 0.009 seconds
Therefore: 0.009 divided by 0.000888 = 10.135 feet equivalent distance offset
So, you would need to place your JL sub 10.135 feet in front of your main speakers to have perfect time alignment in wave launch. Since very few folks choose this setup configuration, it stands to reason that very few people achieve optimal results with the JL subwoofers. If you cannot achieve time coherency, then frequency response tuning/adjustments will never fix what is fundamentally wrong.
Now, since many of us can't physically locate our subs 10 feet in front of the main speakers (spousal acceptance factor and other reasons), how do we achieve time coherency?
There are a couple of methods.
- Processor speaker distance settings: Most all of today's surround processors and receivers have "speaker distance" adjustments to calibrate the system for proper surround envelopment. This adjustment can also be used to "move" the subwoofer back the required 10 feet extra. So, instead of setting your subwoofer at 10 foot distance, you would use 20 feet. This setting would produce the required increase in main speaker delay to properly time integrate the JL sub with the mains. If you have an upper limit of distance for speakers, say 15 feet, then you could set the sub at the maximum distance of 15 feet and reduce the distance of all other speakers by 5 feet. This 10 foot offset for the sub would maintain the distance differentials of all the other speakers and also create the proper time offset for the sub.
- JL subwoofers have a "Phase" control (which is really just a delay). Measured at 80 Hz, 180 degrees of phase "delay" is equal to 6mS of delay. So, if processor adjustments are not feasible or adequate, you can fine tune the sub's "time position" using the phase control. If, for instance you choose to place the subs in a location that (coupled with your processor time/distance delay settings) produces a POSITIVE offset for the sub, then you can use the phase control to achieve the theoretical 10 foot offset.
The end effect is that your sub is "electronically" placed 10 feet forward of your main speakers to account for its group delay.
If you tend to place your subwoofers BEHIND your main speakers, as many of us do, you must then add an extra foot of sub distance in your processor (in addition to the 10 foot offset already discussed) for each foot behind the main speakers to the sub.
I set up my system this way yesterday, and it made a large positive difference in the sound quality of my setup. Kick drums were rendered far more realistically, and bass instruments were placed in space far more precisely than before.
Once you get things oriented correctly in the time domain, then you can run the ARO (EQ) feature of the sub to improve the frequency response characteristics.
I was admittedly a bit skeptical as I listened to Barry at first, but the straightforward logic of the discussion made perfect sense to me. This short discussion is but the tip of the "bass iceberg", and I hope to invite Barry here to delve much more completely into this subject.
Lee
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