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Re: T39/OT12 Limit/Crossover
Posted: Mon Aug 10, 2009 12:47 pm
by djohnson573
bgavin wrote:Dennis, I am more conservative than most about my upper limits.
Most of the time, this means 50% of rated input power.
Bruce, I'm completely on board with this philosophy which is why I asked for the 50% power in the OP.
From what I can gather, it appears that I don't need to be concerned with over excursion if I follow this advice.
I'm running my stuff with xti 2000s which is too much amp. I want the redundancy of being able to run everything on one amp if one of them dies.
My main concern is not me. It is some drunk that might touch my stuff if I have to take a leak.

Re: T39/OT12 Limit/Crossover
Posted: Mon Aug 10, 2009 1:00 pm
by BrentEvans
djohnson573 wrote:
My main concern is not me. It is some drunk that might touch my stuff if I have to take a leak.

This product might just be the answer to that problem....
If you're sick, demented, and twisted, of course...
Re: T39/OT12 Limit/Crossover
Posted: Mon Aug 10, 2009 1:19 pm
by David Carter
bgavin wrote:T39/3012LF requires an active filter at 46 Hz, 24dB/octave, to be at the required -3dB point at 42 Hz.
This allows the balls-to-the-wall operator to pound this box.
Dropping from 60v to just 50v drops power consumption from 450w to 312w.
This gives you miles of headroom (safety) at very little difference in loudness.
Most of the noise comes from the first hundred watts..
So, if I limit my T39/3012 at 50V instead of 60V, can I lower the filter point or does it need to stay at 46Hz? What about if I'm using a 48dB/octave filter? Just curious as I'm not yet confident in my ability to figure this stuff out for myself.
Re: T39/OT12 Limit/Crossover
Posted: Mon Aug 10, 2009 2:00 pm
by Bill Fitzmaurice
David Carter wrote:
So, if I limit my T39/3012 at 50V instead of 60V, can I lower the filter point or does it need to stay at 46Hz?
You can, but only to 43 Hz. To lower the HP frequency to, say, 35 Hz you'd have to drop voltage to 30v.
Re: T39/OT12 Limit/Crossover
Posted: Mon Aug 10, 2009 3:25 pm
by David Carter
Bill Fitzmaurice wrote:David Carter wrote:
So, if I limit my T39/3012 at 50V instead of 60V, can I lower the filter point or does it need to stay at 46Hz?
You can, but only to 43 Hz. To lower the HP frequency to, say, 35 Hz you'd have to drop voltage to 30v.
Thanks, Bill. I didn't have a specific target number in mind. I was just trying to find out what the possibilities are. Does using a 48dB/octave filter instead of a 24dB/octave affect the HP frequency or is the difference too small to have an impact?
Re: T39/OT12 Limit/Crossover
Posted: Mon Aug 10, 2009 3:51 pm
by gdougherty
David Carter wrote:Bill Fitzmaurice wrote:David Carter wrote:
So, if I limit my T39/3012 at 50V instead of 60V, can I lower the filter point or does it need to stay at 46Hz?
You can, but only to 43 Hz. To lower the HP frequency to, say, 35 Hz you'd have to drop voltage to 30v.
Thanks, Bill. I didn't have a specific target number in mind. I was just trying to find out what the possibilities are. Does using a 48dB/octave filter instead of a 24dB/octave affect the HP frequency or is the difference too small to have an impact?
I run 48db slopes on the bottom and I personally can't tell the difference between a 40Hz HP and a 45Hz HP with rock music on my T48's. I doubt most would notice the difference between 43 and 46Hz.
Re: T39/OT12 Limit/Crossover
Posted: Tue Aug 11, 2009 9:06 am
by bgavin
The 48dB/octave slope has little effect over the range of a few Hz.
For example, the 24dB/octave filter at 46 Hz presents -3dB at 42 Hz for the 3012LF.
You might be able to set the 48dB/octave filter at 45 Hz or so. A nit.
T39 is a 42 Hz horn.
It will run lower than this, but at greatly reduced input levels.
If this is not satisfactory, build the T48 instead.
Re: T39/OT12 Limit/Crossover
Posted: Tue Aug 11, 2009 10:39 am
by David Carter
Thanks for the info everyone. Helps my slow but steady climb up the learning curve. Sorry for the hijack, Dennis.
Re: T39/OT12 Limit/Crossover
Posted: Tue Aug 11, 2009 1:45 pm
by djohnson573
David Carter wrote:Thanks for the info everyone. Helps my slow but steady climb up the learning curve. Sorry for the hijack, Dennis.
+1 A great help to my learning curve as well.