Crossover Outputs or Amp Attenuators

[Langston Holland]

You're absolutely correct Pepe - the amp's gain determines the limiter threshold.

Example: if a loudspeaker passband can handle a voltage of +40dBu, the amp has the ability to deliver that and the amp gain is 32dB, the limiter threshold will be +8dBu. Turn the amp gain knobs counterclockwise so that the amp's gain is reduced to 26dB and you'll want to increase the limiter threshold to +14dBu.

You'll improve the S/N by 6dB with the 26dB setting, but if someone bumps the amp's gain knob clockwise you're in trouble - not to mention upsetting the balance between passbands.

[pepe ferrer]

Hi all,

Excuse me sometimes I'm lost in translation.

From my point of view, it is always a compromise, our maximum value will always be the clip of our amplifier. if we use such a 18dBu maximum output and we match this value with the maximum peak power of our amplifier, we need to reduce the voltage gain, this means that we need more output voltage to achieve the continuous power of our speaker.

Otherwise, if we use the nominal value of our mixer (+4 dBu) to achieve continuous power our speaker, then we must increase the voltage gain.
If we use a 2:1 ratio in our amplifier, we will be +6 dB maximum peak, then do not use the full range our headoom, but then need to send less voltage.

I hope I explained correctly.

Greetings.

[Langston Holland]

A coda to the gain structure portion of this thread:

http://www.rane.com/pdf/ranenotes/Se...l_Controls.pdf

Summary:

If you have control over the entire audio system, optimized gain structure isn't subjective or hard to do and can result in significant, audible benefits.

Merry Christmas!

[James Woods]

Hey Ferrit!

Good point! Maybe this will generate into a new thread...

I don´t think it matters much since few of us use sense returns on the amp outputs much anymore. We just need to keep in mind the system gain structure and act accordingly. If I drop the amp input gain, I just drop the sensitivity not the power output. Limiter settings are set in the system processor (and on some amplifiers as well). Depending on the system, I would one thing, and on another something else.

However, if we drop the amp knobs, and they get bumped, we could run into problems. The question though ought to be, where are the amps located and who has ready access to them? They ought to be out of the way, and no possibility of any knob bumping. Also, if knobs get bumped, could they not get bumped down?

[James Woods]

Hmmm, I didn´t see the second page before sending the previous post..

I agree with Langston.

Again, if people can get access to my amps, then they out to be somewhere else!

This reminds me of when digital consoles were new, and for some jobs I had to design a fail safe system where if one console went down, the gig would still go on using another mix from a different console. How many of us pull analog multicores and wire them in paralell to the digital snake system, just in case there is some problem? I never used redundant analog snakes either for that matter.

[Ferrit37]

Hey Guys,
I can't remember the number of times I've seen systems where the processor is using "reccomended" limit points but the amp gains have been turned down totally upsetting the system.
Most gain knob settings on amps are to be taken with a "pinch_of_salt" maybe we need to implement EIA-426(A) noise in the smaart generator.....

merry xmas everyone

[gluis]

I am bringing up this topic because on some other forums where I hang there is somewhat of a debate on this. I wanted to see if any of you have dealt with this in the field and IF it even matters.

I am not partial to this one way or the other BUT I do have some questions. I currently run with my amp attenuators pulled back a bit from clipping. This means my XO outputs are all set a ZERO.

I could make the adjustments the other way around as well BUT does it matter?

Amp attenuators wide open means no one can turn them up any further. May be nice when the system is being used by several different engineers that have different view points. I could also see it being a bad thing too.

On the DR 260 (probably any DSP Device) there is signal loss after it is split into its specific frequencies range -- high, mid & lows. This is very noticeable on the output meters of the 260. They are all at different levels.

In your opinion -- should the outputs on the DSP match the inputs at this stage or does it matter as long as you aren't clipping at the amp?

This may be a completely dumb question so I will take one for the team here...

I was perusing the forum and catched this one. Hopefully I'm not repeating something already said (didn't read all of it before answering).

Your crossover outputs will always have less voltage than its inputs (assuming unity gain) as they have only part of the spectrum in them; you only have part of the energy in each output as opposed to all of it on the input.

As a long time SR company owner and system tuner, I ALWAYS set my amp gains to maximum and set gains and limiters at the processor. It might not be the best S/N ratio, but you are 100% sure no one is going to mess with amps' knobs and destroy your loudspeakers in the process (It costed me 20 DH1 diaphragms at once to learn this a long time ago). Anyway if you are using modern, high quality amps probably they have some sort of internal (or at least back paneled) means to have their gain settings adjusted. You can get them close to ideal for your system and have a good S/N ratio. In fact, I had been using Crown DSP equipped amps for about 8 years now, and you set their gains precisely to match what you need.

I rather like BSS Omnidrive family of processors metering. They are related to output limiter settings (they show your headroom before limiting).

It is important to realize that your limiter settings have to be set to protect your speakers. It seems obvious but sometimes people adjust them just to prevent amps from clipping, and sometimes your amp can destroy your loudspeakers without going into full power (i.e. big amp for compression drivers)

[Harry Brill Jr.]

Use the same amp sensitivity for every passband and leave your crossover and amp outputs alone. A lower amp sensitivity means you'll have to run the esk hotter to get to a given SPL than if you used a higher sensitivity. This has the effect of reducing system hiss.