Help Please, need advice on bi-amping La Scalas for live sound reinforcement.

[dbreggin]

My biggest question is whether or not I need to modify the type AA x-over when I detach the woofer from the network?

• If so, in what manner? Re-load the network with an 8 Ohm resistive sink?
• Should I just go for an aftermarket xover for just the mid-tweet network?

Here is the proposed set-up:

• 2 stacks each with a La Scala full range cab plus an additional La Scala woofer cabinet. All 4 cabs are circa 1976.
• The tweeters are K-77s.
• Mids are original horns with new drivers: EV 1832 (2" voice coil, 110W continuous, 4 Ohm DC, 7 Ohm AC 800Hz- 1300Hz pink noise).
• Woofers are Peavey Black Widow 15", 8 Ohm, 400 Watt. specs below [8-|]

Re

is DC resistance of the voice coil in ohms

Fs

is free air resonance of the speaker cone assembly in Hz

QTS

is total quality factor in free air

QMS

is mechanical quality factory

QES

is electrical quality factor

VAS

is equivalent volume compliance of suspension in liters

No

is efficiency in percents

VD

is volume of air displaced in milliliters

Xmax

is T peak-to-peak maximum cone excursion in millimeters

Model#	Re	Fs	QTS	QMS	QES	VAS	No	Xmax	VD
1505-8DT	5.2	44.2	.37	7.8	.39	198	3.9%	+/-4.8	385

Power is

• 2 ea. Crown XLS 802 (500 watts @ 8 Ohms direct to each woofer driver),
• Crown XLS 202 (200 watts per channel for mids and tweets through the type AA passive x-over).
• DBX DriveRack PA+ for the crossover

My next questions are about the port-mod. Since I have more than enough power to withstand the reduction in efficiency [6], I'd like to port-mod (at least) the woofer only cabs. Based on the driver I am using, is there a different CU IN volume to be used, or just build as designed? I ask this because of the large volume displaced by the driver, and I remember this being mentioned in a thread as one of the variables in the calculations.

• How about tuning the ports? Anything different here?
• If I also port-mod the full-range cabinets, How should I deal with the 2 ported cabs in one stack? Ports in the middle, ports below each woofer?
• Another thought is to tri-amp the system, port only the woofer cabs, and x-over at around 125 Hz, perhaps in mono at these low freqs.

Your thoughts on this could be most helpful and influential...

[djk]

"Since I have more than enough power to withstand the reduction in
efficiency"

There is a 6dB increase in efficiency in the 40hz~50hz region (LSI with K43 shown in sim)

I'll post some more tomorrow.

[Coytee]

"Since I have more than enough power to withstand the reduction in efficiency"

There is a 6dB increase in efficiency in the 40hz~50hz region (LSI with K43 shown in sim)

My suspicion is he's aware of that and was perhaps being a bit tongue in cheek? (evidenced by his little devil face iocn next to the comment)

[JohnA]

I have similar Black Widow woofers, 1504-4, in n FH-1 bass horn. The distortion is audible and exceeds the input signal somewhere below 80 Hz (can't remember anymore). I'd say the Peavey woofer is a mistake.

Your squawker AND woofer will require a crossover change. The squawker's power limit will be much lower whan you start running it an octave below it's rating. The K-55-V is rated to full power down to 110 Hz.

If you want more performance, restore the La Scalas, buy some MWM woofers, KP-480s, or other GOOD pro subwoofers and biamp those crossed to your La Scalas at 120 HZ. I *think* that raises the La Scala's power rating to 400 watts and you will get the deeper bass you want without excessive distorton you now have.

[dbreggin]

There is a 6dB increase in efficiency in the 40hz~50hz region (LSI with K43 shown in sim)

DJK, Thanks for the feedback (pardon the pun). I know there is a boost in the lower frequencies (that's why I am looking to port), however a ported horn is less efficient overall than a true horn, to the point of some posters padding down their squawkers up to 6dB in reaction to thier porting activities. That is the loss I was referring to... and I think 2kw in the low end will allow me to make up the difference without padding down my squawkers.

Are you able to run a sim with the Black Widow's spec to see how it might work?

[dbreggin]

Your squawker AND woofer will require a crossover change. The squawker's power limit will be much lower whan you start running it an octave below it's rating. The K-55-V is rated to full power down to 110 Hz.

John, Thank you for your response. Duly noted as things to look out for, and perhaps things to go and buy.

In the mean time I have what I have (purchased as such at a really good price) and I am looking to make the most of it with what I already have.

I may not have expressed myself clearly in my original post reagarding some points about what I am trying to do and my specific questions related to that.

Tri-amping the system. From the top down it would look like this (XO in DBX DriveRack PA+):

• tweeter / squawker (200 Watts) Hi passed at 400 Hz
• 15' woofer (500 Watts) band passed between 125 and 400 Hz (this box not ported)
• 15" woofer (500 Watts) low passed at 125 hz (this box ported)

Bi-amping the system.

• tweeter / squawker (200 Watts) shelved at 400 Hz
• 15" woofer (500 Watts) low passed at 400 Hz (this box maybe ported)
• 15" woofer (500 Watts) low passed at 400 Hz (this box ported)

Note that the DBX DriveRack has a 28 band Real Time Analyzer and multiple eq's (28 band graphic and multiband parametric eq's) to start the fine tuning. it also has compressor / limiter functions, sub harmonic synth. I also will be using a Aphex 104 Aural Exciter in the chain just ahead of the DBX. The usual venue will be 300-500 seat theatres (high schools). The music will be live Bollywood dance music (think pop- top 40 instrumentation & vocals and effects), as well as some pre-recorded music for classical dance performances.

Here are my most pressing questions:

1. When I detach the 15" woofer from the crossover network, and change the injected signal from full range (to the hi pass 400Hz and up signal), is there anything I need to do to preserve the integrity of the passive crossover behavior for the squawker / tweeter pair still attached to it?
2. How would anyone recommend the physical layout of stacked FH-1's if they are both ported.
3. What else do you think I should know, or how else should I consider setting up the system?

[djk]

"to the point of some posters padding down their squawkers up to 6dB in reaction to thier porting activities. "

Not so, again, look at the simulation. I think what is happening is that the tonal balance is just so far out that people are trying to get it better.

"Are you able to run a sim with the Black Widow's spec to see how it might work?"

Two BW 15s with the T/S parameters given, each in a vented LS cabinet (40V input, subtract 23dB for 2.83V/1M).

Recommended network for mids and HF, requires a LR24 at 400hz, and a 35hz 'garbage' filter.

The 30uF is not a crossover, just a DC protection cap. The other components are to make it the correct level for the tweeter, and flatten the response in the 4Khz region.

The tweeter crossover is a new design to match the EV driver.

I would either run both LS vented from 35hz~400hz, or use one stock (non-vented) from 100hz~400hz and a very big sub below there. You would be suprised how much bass a pair of vented LS have (see plot).

[dbreggin]

DJK,

WOW, and Thanks for the great info! Its a lot for me to digest at one quick sitting. [8-|]

I do have a question about what you meant by this:

requires a LR24 at 400hz, and a 35hz 'garbage' filter

Is this the XO spec for the low end? 35 to 400 Hz as follows: 400 Hz XO w/ 24 db/octave slope and 35 Hz Hi pass filter?

Dan

[djk]

"Is this the XO spec for the low end? 35 to 400 Hz as follows: 400 Hz XO w/ 24 db/octave slope and 35 Hz Hi pass filter?"

Correct.