T39/OT12 Limit/Crossover

[djohnson573]

I know this was on here at one time, but I can't find it now.

4 - T39s - BP102 loaded
4 - OT12s - Deltalite 2512 loaded

Can someone give me the preferred crossover point/slope and the half power voltage limit for these speakers? Also, when running two speakers per channel in parallel, is the voltage measurement at the amp doubled, halved, or remain the same as when running one speaker per channel. Thank you for the help.

[Sydney]

when running two speakers per channel in parallel, is the voltage measurement at the amp doubled, halved, or remain the same as when running one speaker per channel

In this situation what has changed - Obey Ohm's Law Dennis:
or you can use this:
http://www.dni-inc.com/things-here/misc ... _v1.12.xls

[djohnson573]

Obey Ohm's Law Dennis:

I fought the law, and the law won. OK, so I'm going to have to think on a Friday afternoon. Syd, I love it when you make me learn.

Having just reviewed about 50 of Bruce's posts, I think I see enough of a trend to take a stab at this. But, please, someone check my reasoning (and please don't laugh).

Voltage Limit - The real unknown here for me was which watt rating to use. Comparing Bruce's often posted limits to the 0312LF, I deduced it was the lower one, so:

BP102 = 200 watts/2 = 100 watts @ 8 ohms = 28.28 volts
2512 = 250 watts/2 = 125 watts @ 8 ohms = 31.62 volts

1 vs 2 Speakers – Since the power requirements double as the resistance is cut in half, I’m guessing that the voltage requirement remains constant.

Crossover – I realize what I was really asking for here was high pass information and Bruce mentions 46Hz @ 24 db slope or higher, but this is to allow applying 450 watts to a 3012LF before reaching its excursion limit. I also read that the T39 is a 42Hz box. So at 100 watts, do I set it at 42 and forget about it?

OK, now my brain is full.

[Sydney]

Remember power is the product of voltage and current and it is opposed by resistance...
If you reduce the resistance power goes up...
If the goal is to maintain the same power limit to a driver and you reduce the opposition to it ( when you parallel and halve the impedance ) you drop the voltage to compensate.
( didja play with the spreadsheet yet? )

The analogy for electricity is water, Voltage is pressure, Current/Amperage is Volume, and Resistance is Resistance ( opposition to flow ). Small pipes have greater resistance to flow, Large pipes allow greater flow, multiple pipes in parallel allow greater flow.
Small wires have greater resistance to flow, Large wires allow greater flow, multiple wires in parallel allow greater flow.
Multiple speakers ( in parallel ) are multiple paths and less resistance, allowing more flow ( current/amperage ) so less pressure has to be applied to get the same power out.

[djohnson573]

Remember power is the product of voltage and current and it is opposed by resistance...
If you reduce the resistance power goes up...
If the goal is to maintain the same power limit to a driver and you reduce the opposition to it ( when you parallel and halve the impedance ) you drop the voltage to compensate.
( didja play with the spreadsheet yet? )

The analogy for electricity is water, Voltage is pressure, Current/Amperage is Volume, and Resistance is Resistance ( opposition to flow ). Small pipes have greater resistance to flow, Large pipes allow greater flow, multiple pipes in parallel allow greater flow.
Small wires have greater resistance to flow, Large wires allow greater flow, multiple wires in parallel allow greater flow.
Multiple speakers ( in parallel ) are multiple paths and less resistance, allowing more flow ( current/amperage ) so less pressure has to be applied to get the same power out.

Hey, I thought I asked you not to laugh.
I did play with the spreadsheet (which is very cool BTW).
I understand a lot of the above (scary, huh), but I think this is where I have the disconnect. By adding the second speaker we have cut the resistance in half, but haven't we double the amount at wattage we can apply (e.g. 2 - 100 watt speakers instead of 1) thereby allowing the voltage to remain constant? Or, when I add the second speaker do I have to reset the limiter to half of the single speaker value?

[Sydney]

I think I see where the disconnect is:
If you wire 2 drivers in parallel ( assume 4 ohm load )
* This includes a 3db Crest factor
For a 200 watt limit use 20V ( 100 watts per driver )
For a 300 watt limit use 24.49V ( 150 watts per driver )
For a 400 watt limit use 28.28V ( 200 watts per driver )
For a 500 watt limit use 31.62V ( 250 watts per driver )

Using Straight Ohm law
For 4 ohms
28.28V = 200 watts
34.6V = 300 watts
40V = 400 watts
44.7V = 500 watts

TGIF

[djohnson573]

Syd, thanks, as always, for the schoolin'. It's almost Miller time.

[Bill Fitzmaurice]

Syd, thanks, as always, for the schoolin'. It's almost Miller time.

It's always noon somewhere.

[Sydney]

And for some it's always...
"Beer-Thirty"

[Gregory East]

Now I'm confused, it's almost time to go to work and it's 12 hours to beer o'clock.

Leaving aside the actual numbers, if you're basing the voltage limit on what power an individual driver can handle isn't the voltage limit independent of the number of parallel drivers?

[Tom Smit]

Syd, thanks, as always, for the schoolin'. It's almost Miller time.

It's always noon somewhere.

"It's five o'clock somewhere" http://www.youtube.com/watch?v=ib8nH4kHjxk

[Sydney]

Sorry Gregory: I have caused the confusion:
As you said, ( and most commonly )
If you set the voltage and drop the impedance. The current goes up. the amp produces more power, per volt, and the power is distributed among the multiple drivers.

If, However the goal is to set a fixed limit on the power that the amp produces, then the voltage is reduced to compensate for the increase in current. Probably a less common goal, but useful if you are concerned with power draw and amp protection.

FYI:
http://svconline.com/mag/avinstall_better_set_limiters/

[Bill Fitzmaurice]

Now I'm confused, it's almost time to go to work and it's 12 hours to beer o'clock.

Leaving aside the actual numbers, if you're basing the voltage limit on what power an individual driver can handle isn't the voltage limit independent of the number of parallel drivers?

The 3012LF power rating and displacement limited power in the T39 is 450 watts, so a 60 volt signal is the maximum allowable; running 10 volts lower will give a higher margin of protection, and will have only a cursory effect on output. The S2012 has a 150 watt voice coil, and can run to that without exceeding xmax, so it can handle a 35 volt signal. The Delta 12LF has a higher rated voice coil, but it’s also displacement limited to 35 volts. The BP102 has a 200 watt coil, but is displacement limited to 35 volts as well. The 150 watt rated S2010 is displacement limited to 100 watts, for a 28 volt signal. With paralleled drivers or cabs voltage is the same across each load, so the voltage limit that applies to one applies to all.
Titan 39 plans page 28.

Lest I forget... :iitp:

[Gregory East]

Hey, it's beer o'clock. I see my confusion was vindicated. Different sums for limiting the amp for the amp's sake rather than the drivers'.

What about the crossover?

Probably ITP too.

[bgavin]

Dennis, I am more conservative than most about my upper limits.
Most of the time, this means 50% of rated input power.
I believe George did power compression tests on BP102/T39, and found 150w is the onset.

The real limitation in all these boxes is displacement (cone excursion).
Each box/driver combination has a unique frequency where it is most easily overdriven.
Bill includes a generic rule in the plans that offers adequate safety.

For those who live on the edge of destruction, there are steep slope crossovers (24dB or higher), and brick wall limiters.
I'd rather add more boxes and skip the worry... YMMV.
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..