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Author Topic: Lab Subwoofer Delay Time Offset Question  (Read 2415 times)

Mr.Nightro

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Lab Subwoofer Delay Time Offset Question
« on: September 29, 2004, 04:31:35 pm »

I know about the 10.5 millisecond delay needed to time align these subs to the tops but seeing as I only have a Drive Rack P.A. that only gives a maximum delay time of 10.00 milliseconds whould the half a millisecond make THAT much of a REAL difference in real world use? If the answer is yes then couldn't I make up for this half a millisecond shortfall by placing my tops end cabs further to the back of the Labs while they are sitting on top of the labs to make up this difference (there is after all four feet to play with up there)? I would also like to know if anybody has used anyother type of plywood for this project with good results in substitution of the Baltic Birch that is speced? Baltic Birch costs $175.00 a sheet here because they only carry grade A Veneer Baltic Birch for finish furniture applications, I was thinking of using Mahogony ply that costs $65.00 a sheet.

If it makes a difference this is going to be used for small to medium sized outdoor sets with people in the 500-1000 range as a dj rig to compete against other P.A.systems.(though I plan to just start out with two so I can A-B test them against the garbage subs my partner sold our good subs to get)I am tired of waiting for my partner to go half & half on building our own rig of 8 Labs so I am going to bite the bullet & finish building the ones I started to collect the parts for over a year ago. My problem is that I don't wish to purchase any more rack equipment since I spent 90% of my budget from last year revAMPing the racks thus the reason why I wish to keep the Drive Rack P.A. My wish is to get rid of this garbage collection of subs we have collected over the years that are just full of boom at high SPL & get back to the quality sound we once had with our EAW BH800 rig or the Servo Drive rig we used to have access to.

Thanxx in advance.


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Peter Sylvester

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Re: Lab Subwoofer Delay Time Offset Question
« Reply #1 on: September 29, 2004, 09:54:54 pm »

The speed of sound is roughly 1.1 feet per millisecond, so you would need to move the tops back about 6.6" to get another 0.5ms delay.

As for plywood, as long as it is fairly solid (void free) and flat you can se other than BB. I used "shop birch" and it works fine.

--Peter

http://home.comcast.net/~labhorn/
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Mr.Nightro

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Re: Lab Subwoofer Delay Time Offset Question
« Reply #2 on: September 29, 2004, 10:26:23 pm »

Thanxx Peters that was exactly the information I was looking for. Very Happy
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Tim Padrick

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Re: Lab Subwoofer Delay Time Offset Question
« Reply #3 on: October 01, 2004, 02:36:43 am »

That 10ms is for the box, and does not take into account the delay in the filters (protective high pass, crossover low pass).  My tops and subs are front loaded, and it takes a delay of 12.5' on the tops to align them with the subs.

Mike Pyle

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Re: Lab Subwoofer Delay Time Offset Question
« Reply #4 on: October 01, 2004, 04:22:00 am »

TimmyP wrote on Thu, 30 September 2004 23:36

That 10ms is for the box, and does not take into account the delay in the filters (protective high pass, crossover low pass).  My tops and subs are front loaded, and it takes a delay of 12.5' on the tops to align them with the subs.


I'm curious... Is there a rule of thumb for estimating delay time for different filter orders at different frequencies?
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Mike Pyle
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