Delay

[tommysb]

What is the path length difference (in feet or ms) between a dr250 and tuba 36?

I would like all the sound to be cohesive at x-over frequencies, and want to make sure i buy a lms with enough delay on it.

Out of interest, has anyone seen the bbe ds48 or have experience with it?

I wondered if the parametric eq on this would be enough to compensate for the bumpy response curve on the dr250, or is a 31 band graphic going to be much better?

[DAVID_L_PERRY]

Setting delay on subs depends where you have your subs, and also where you are stood in the room....each and every venue will be different if you locate your subs to suit the room. The quick check to try out that I do at every gig is to swap polarity of the subs, sometimes its better with them inverted....depends where you are stood...At very low freq's the delay is pretty much impossibly to notice.

The biggest difference I find is delaying the whole rig to suit the stage backline....but again it depends where you are stood...

Its all about making the best of a situation.

[tommysb]

Ok, lets assume the dr250 is stood on top of the tuba 36 and there's a path length difference of 1.5m.

Where the wavelength is 3m, (~100hz), there'll be a cancellation if both speakers are producing this frequency.

so delay the tops so that ouput from them comes out in phase with the subs. Not so much for the PERCEIVED timing of it all, just so that energy isn't being wasted!

[Alan Star]

Ok, lets assume the dr250 is stood on top of the tuba 36 and there's a path length difference of 1.5m.

Where the wavelength is 3m, (~100hz), there'll be a cancellation if both speakers are producing this frequency.

so delay the tops so that ouput from them comes out in phase with the subs. Not so much for the PERCEIVED timing of it all, just so that energy isn't being wasted!

Good point if you are splitting your subs, but in smaller venues it seems more beneficial to cluster your subs together, ideally centrally, where in that case the need to delay the tops will not be necessary.

[tommysb]

Why would it make a difference if the subs were split or stacked together?

[DAVID_L_PERRY]

Its a massive difference........
Read this http://billfitzmaurice.com/phpBB2/viewtopic.php?t=398
And this:- http://www.prosoundweb.com/live/articles/jbrusi/pa.php

And as your subs are now placed meters away from your tops the whole delay thing goes out the window unless you are static..

[tommysb]

Why would it make a difference if the subs were split or stacked together?

Sorry, no i understand that dave, but I'm saying, the subs/tops cancelation still occurs when you stack subs together.

If you were running one big mono stack, the same cancellations between tops/subs could occur. do this twice, you still get the same effect, regardless of whether seperate bass stacks are now cancelling AS WELL.

[gdougherty]

The difference is that now your tops and subs are in different locations and suddenly you can't just control a single alignment variable. Hypotehical: Tops 30ft apart, subs clustered in the center 15ft from each. Path length on the T36 is something like 13ft I think, ~3ft on a DR250. So at any point with roughly a 10 ft difference between the two you'd need no delay to align them. At all other points you'd need a different delay value to perfectly align the two sources. Then you also get into backline alignment issues which for the same reasons are just as difficult to chase, especially if the bass rig is located at the back of a 20ft stage but a keyboard or guitar amp is 15ft closer for some reason. You can try to delay the sources, but IMO it's not of any real benefit unless you're running a huge setup with two speaker stacks on either side of a large stage. Still, with a massive set of T48's and a huge stage I'd possibly consider just lining them all up across the front of the stage and coupling them as one huge 50ft wide T48. I'd imagine the output from a wall of 20 30" wide T48's would be pretty massive.

[hclague]

In order for 2 drivers to be properly time aligned through crossover, The two drivers must be less than 1/4 wavelength ( crossover freq) apart. Therefore aligning for smooth transition through crossover of Center clustered subs with flown or split tops is not likely. as an alternative, many choose to align for arrival which creates a "sweet spot" some where in the listening area. This 'sweet spot' can be rather large when you are talking about sub frequencies.

Before, programs like SMAART, SIM, PRAXIS, etc. people used to try to align with a simple RTA. The process is this:

1. Play a test tone ( sine wave ) at the crossover frequency through the system.
2. Invert the polarity of the component being delayed ( usually the tops )
3. slowly add delay and watch your RTA readout at the crossover freq, eventually a dip will start to form, when the dip reaches it's lowest point, you have aligned for the mic position.
4. return polarity back to normal on the delayed component.

This is not as accurate as alignment through crossover with SMAART etc..but in the Sub area it can be affective.

Hal

[Bill Fitzmaurice]

This 'sweet spot' can be rather large when you are talking about sub frequencies.Hal

The good thing is that it takes a huge amount of time differential to be audible at 100 Hz and lower, so time aligning between the tops and bottoms usually isn't critical as far as the sound goes. What is problematic is the potential for both constructive and destructive phase interactions within the overlapping bandwidths in the vicinity of the crossover frequency. That is best controlled by minimizing the overlap with no less than a 24dB/4th order crossover slope.

[gdougherty]

This 'sweet spot' can be rather large when you are talking about sub frequencies.Hal

The good thing is that it takes a huge amount of time differential to be audible at 100 Hz and lower, so time aligning between the tops and bottoms usually isn't critical as far as the sound goes. What is problematic is the potential for both constructive and destructive phase interactions within the overlapping bandwidths in the vicinity of the crossover frequency. That is best controlled by minimizing the overlap with no less than a 24dB/4th order crossover slope.

So would you recommend a 48db slope if you've got it?

[Bill Fitzmaurice]

This 'sweet spot' can be rather large when you are talking about sub frequencies.Hal

The good thing is that it takes a huge amount of time differential to be audible at 100 Hz and lower, so time aligning between the tops and bottoms usually isn't critical as far as the sound goes. What is problematic is the potential for both constructive and destructive phase interactions within the overlapping bandwidths in the vicinity of the crossover frequency. That is best controlled by minimizing the overlap with no less than a 24dB/4th order crossover slope.

So would you recommend a 48db slope if you've got it?

Yes.

[gdougherty]

So would you recommend a 48db slope if you've got it?

Yes.

Coolness, will do.