BillFitzmaurice.info

Hi everyone!

Just read bills Placement Guide again and was wondering in which case a differing phase between subs will lead to a blown driver ? (Feeling too quiet thru cancellation and then feeding more power ?)

Phase, no. Polarity, yes. You always need to make sure your subs are polarity matched.

If you're blowing sub drivers then you aren't properly limited.

Thank you both !

Was referring on this part of the Placement guide :

"Using Tubas with other subs:
Mixing horn subs with direct radiators is a recipe for disaster. The response of the two formats is so different that it's impossible to EQ either one of them properly, while differing phase can easily lead to blown drivers. Never mix even different models of subs, including Titans or Tubas, let alone different formats."

What it refers to is the time and phase shift of a signal passing through a long horn compared to a direct radiator. If that phase shift amounts to 180 degrees within the sub pass band the effect is as if they had opposite polarity at that frequency, cancelling each other out.

Noclu wrote:Thank you both !

Was referring on this part of the Placement guide :

"Using Tubas with other subs:
Mixing horn subs with direct radiators is a recipe for disaster. The response of the two formats is so different that it's impossible to EQ either one of them properly, while differing phase can easily lead to blown drivers. Never mix even different models of subs, including Titans or Tubas, let alone different formats."

Arrrrr that bit. I'll have a crack at it for you.
Phase is a beast, and so many people either don't know of it, or, even if they study it, don't understand it.
I have tried to research it, and read some great articles, but still don't understand.
Rule number one is that phase is frequency dependant.

Even if you take the same driver, and place that driver in two different designs, then, at any given frequency, the phase response at that frequency will be different in the two cabs.
If you now use those two cabs together at a gig, because the two drivers are in different cabs, at different distances relative to each other, and have different phase, they will interactive negatively with each other, creating a null due to phase induced cancellation. That cancellation could be so severe, that in one cab, you are taking the driver beyond it's limitations, and it blows, either to over excursion, bottoming out, etc.

In the above scenario, the first thing most people do is go, "right, I can hear a hole at X frequency, let's bump EQ to fill the hole". In cab phase hasn't been altered, so you are simply increasing driver stress directly proportional to the amount of boost you apply, because you haven't addressed the null. Result, blow a driver, more quickly.
EQ does alter phase however, so when you boost one frequency, you alter phase at another.

So, EQ doesn't fix the problem, maybe delay (time alignment) will?
One might be tempted to add delay to one of the two cabs, which will shift phase, and may lead to a result at a given frequency. However, adding delay will also alter phase by 180 degrees one octave above and one octave below as well, so while you have addressed the issue at one frequency, you now have two nulls at other frequencies.

What else affects phase?
The "order"/slope and type of crossovers. eg BW v LR etc.

I could go on, but won't.

In the real world, the rules are simple;
1. Always use the same design in a single band pass at any one gig. Select one type of design, and use it in sufficient numbers to achieve the desired SPL.
2. Always check that subs and mains are in phase at the crossover point when you set up.

There is some high end gear in existence that lets you address phase issues, but it is beyond many of us to justify it financially.

The most significant stage that phase has to be addressed is at the design stage of any cab.
Thanks Bill

Thank you !

I was wondering if there is any physical effect I don't know of, that's could do harm if speakers are not on phase, haha!

Yeah...Same pass band, but that makes sense.

As our Horns won't be playing much lower than 45Hz, Id simply use the two t60s we built for 45-30 ...Or maybe cut the other horns even higher. So we won't run into phase problems.

Thank you !

Noclu wrote:Thank you !

I was wondering if there is any physical effect I don't know of, that's could do harm if speakers are not on phase, haha!

Yeah...Same pass band, but that makes sense.

As our Horns won't be playing much lower than 45Hz, Id simply use the two t60s we built for 45-30 ...Or maybe cut the other horns even higher. So we won't run into phase problems.

Thank you !

Why?
It is pointless having a sub like T60's, and using them for only response from 30-45Hz, when they can go up to 100Hz with ease, just so you can use some other cabs...

because we use the other ones together with the two t60s until we have four of them.

Edit: and it's easier to get the rest of our system stacked like this

Noclu wrote:because we use the other ones together with the two t60s until we have four of them.

You're not gaining anything doing that.

it's easier to get the rest of our system stacked like this

Uh oh.

I assume the "stack the kick bins on top of the subs" is not best practice?
(Should I open another thread?)
But as we have a Soundsystem currently consisting of 4 * q15" scoops , kicks, mids/highs we thaught that we could improve the low-end by using the two t60s.
At least until we have more of them.

What would you do ?

Noclu wrote:What would you do ?

Not what you're doing. You should run subs to between 80 and 100Hz, clustered and boundary loaded, with the mains out front to either side, pole mounted if necessary to get the HF elements above head height. Sell the scoops if you can, throw them away if you can't, but whatever you do, don't use them. They're possibly the worst excuse for a speaker ever conceived.

Noted!
Working on it!

Thank you!