DRPA and Community SLS920 / monitors

byacey

I have a Driverack PA that I would like to setup up for subs and SLS920 passive mid high boxes. Does the parametric EQ affect both left and right channel outputs? I'm using the left in and outs for the main speakers and subs, and am using the right channel mid out for monitors. Mains are mono.

I've calibrated my Xover outputs to the power amps and set the limiters. Everything seems to be working as it should, just I'm not sure about the parametric EQ only affecting the left outputs.

Gadget

Perhaps this answers the question:
viewtopic.php?f=60&t=2228

You don't get separate PEQ's but you DO get separate GEQ's...

byacey

Thanks for the reply. I've never used this before, but to set the levels, I put dummy loads on the amps, set the Xover points, drove the left channel with +4db @ 1 Khz and adjusted the high pass xover output until the amp clipped, and then backed it down until the amp clip lights were out. Then I set the limiter threshold on the high out so it was starting to limit at +2db of input.

Then I did the same for the low output, except I fed +4db @50Hz .

This way my amp level controls are all wide open and can't exceed the maximum operating point.

Does this sound acceptable?

Dennis

byacey wrote:

. I've never used this before, but to set the levels, I put dummy loads on the amps

Interesting.....I don't remember the topic of using dummy loads coming up here before. What did you use for that?

byacey

I have some big power resistors that I wound for testing power amps, they are good for about 2000W each, and are a 4 ohm load. The reason I used the load resistors is that the amplifier rail voltages typically sag under full power output under load, and this actually lowers the clipping point of the amp compared to driving the amp to clipping without a load on the output.

Gadget

I concur... not top mention that with no idea of what kind of power is available for said speakers how do you intend to balance the sound from tops to subs?

This thread will perhaps illuminate a different train of thought:
viewtopic.php?f=60&t=2242

Dra

byacey wrote:

I have some big power resistors that I wound for testing power amps, they are good for about 2000W each, and are a 4 ohm load. The reason I used the load resistors is that the amplifier rail voltages typically sag under full power output under load, and this actually lowers the clipping point of the amp compared to driving the amp to clipping without a load on the output.

I have seen discussions using 5 gal plastic pails, I think filled with water and coils.

How much heat do you get from the coils you made? Whould you care to share the design and parts list?

DRA

byacey

My intention is to leave the subs running at maximum level available, and cut back the xover level for the high output to get the spectrum balanced. Once I arrive at a good balance, I'll reset the limiter for the high output. The Community SLS920's are a very efficient box, so I doubt they'll be running very hard.

The power resistors I made are wound on a triangle shaped soft ceramic pillar used in pottery kilns to hold up the shelves within the kiln. I drilled a hole through each end to put machine screws for the wire terminals. I wound the resistors on the form using 16 guage nichrome wire; I forget how many turns is required to make 4 ohms, perhaps 20 or 25 turns. I just measured a length at 4 ohms, then cut it and wound the length on the form. With a thousand watts RMS it glows red, and at 2000W, it's a bright orange color. I don't run it for long at these powers though, as it's hard on the amp. Very few amps are capable of running this kind of power continuous.

I wouldn't put any load resistors in water, but I have seen some old loads in a can of oil for cooling. Mine work fine in the air.

If you like, I can take some pics tomorrow.

byacey

Gadget wrote:

I concur... not top mention that with no idea of what kind of power is available for said speakers how do you intend to balance the sound from tops to subs?

This thread will perhaps illuminate a different train of thought:
viewtopic.php?f=60&t=2242

I had a look at that link. Numbers are useful, bu ultimately you want to satisfy the ears. Because the subs use the most power, they should be set for maximum level before clip. The Mid / Hi level can then be brought up to an acceptable level in keeping with the subs to create a balanced audio spectrum, and then set the limiters to clamp down on anything past this maximum level.

I'm just using the limiters to prevent amp clipping, but if you want to set a cap on the sound level to protect the drivers from exceeding maximum ratings, monitoring the voltage level across the dummy loads will tell you where the limiters need to be set according to the particular speaker specs. That's my thoughts on the subject.

The reason I would prefer to do it this way rather than marking the amp level controls as mentioned in some other posts, is because if somebody moves the controls, they can only reduce the levels at the amps, rather than over driving them and causing damage. Also, it's convenient to be able to just open the controls wide open after powering up the amps and walk away knowing they are set where they should be.

Gadget

The problem comes when you run up against the limiters and keep on going... the average power level goes up and up till the voice coils start to heat up... if you do it like we suggest, set the maximum gain structure and then use the crossover gains to set the balance to the outputs you only need the limiters for OOPS...

You do realize that the limiters on the DRPA are NOT brick wall but peak stop... and they will overshoot...

byacey

The way I presently have it set, the limiters clamp down pretty hard once you exceed the normal operating levels of the master section of the board. Some common sense has to enter the equation at some point too; for years I was fine without using any compression or limiting before the power amps, and I'm the only one using the sound rig. If someone wants to exercise above average levels of stupidity, they'll destroy things , no matter what safeguards are put in place.