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Discussion Starter #1
What is the proper way to time multiple subs? I have a 4x18" horizontal IB in the center front and 2 15" subs one in each rear corner and they are definetly out of sinc. The IB is running through one channel of my FBQ and the two rears are running through the other. Please advise.

Thanks, Rick
 

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You could measure the distance from the subs to the listening position and then delay 0.9ms for every foot, but that won't account for the phase response differences between the dissimilar units...and it's not likely to be non-trivial.

There are also other forms of delay you could use to address room mode related issues.

Do you have any means to measure what you're doing?
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You do need some way to measure what is going on in order to diagnose and treat things. Do you have an SPL meter?
 

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Discussion Starter #6
DrWho, I think your questions assume I know something about subs, unfortunately I don't even know how to answer your questions but I will do my best.

I can run the rear subs through a dcx unit for a delay, we are talking about the rears right?

As far as phase response goes I need some real specific advice on what to do.

I have an spl meter and have purchased everything to do the REW but none of that is hooked up yet. I am still busy trying to finish my HT room.

Thanks, Rick
 

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To create the same displacement of air, a 15" driver needs to move further than an 18" driver....it takes extra time for the smaller driver to move further which shows up as more phase rotation. Simply accounting for the distance and speed of sound doesn't take into account the extra "delay" (phase) from what the individual drivers are doing.

If you want to do some reading on room modes, Floyd E. Tool has an awesome book called "Sound Reproduction". It's a bit in depth, but very practical. You don't 'need' to get creative with the delay to address room modes, but it's essentially free performance if you've already got a dsp involved.

Every room is different so learning how to take good measurements becomes an invaluable tool.
 

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Thats a loud dilemma you have there. Has the issue you are hearing always been there? Is this setup completely new or have you just recently added the 15's?

If you have only recently added the 15's try isolating them and disabling the 4x18. They may have a phase/reflection issue on their own that you can't detect with the front firing active.
 

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Discussion Starter #9
The set up is new and I have had many teething problems, this is just the next one on the list. With the rear 15's off there is no problem, when they are on I can hear two distinct beats instead of one.
 

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The set up is new and I have had many teething problems, this is just the next one on the list. With the rear 15's off there is no problem, when they are on I can hear two distinct beats instead of one.
If there is a DISTINCT double beat that is an amazing amount of delay for 16 vs 6 feet, The 10 foot difference is negligible. How are the two setups powered/signal sent? I assume the two 15's are each self powered, What is powering the front array? Are they sharing the exact same mono source through the FBQ?
 

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Discussion Starter #11 (Edited)
Both subs were getting the same signal (mono), the fronts are powered with a EP4000 and the rears are powered with an EP1500.

I solved the problem last night by running the rear sub line through one of the DCX2496 channels that I was not using, then running it through the FBQ and on to the amp. The DCX is very easy to use as far as the delay goes, the unit displays meters and milliseconds of delay, I think I ended up with a 7.?ms delay. Now the bass is nice and tight!

For music (2 channel) the 2 mains and the rear subs sound great, and the none of the speakers have been eq-ed yet. When the 2 mains with the front IB sub running the bass sounds a bit like one of those cars with the 30" wheels and a super matallic bass boat paint job. For movies all speakers with front and rear subs firing are pretty good, actually I can not tell if the rear subs are doing much of anything with the IB running.

So all is well for today, I probably won't start eq-ing anything until I get the rest of my sound absorbers up and carpet in.
 
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