Setting gains with multiple devices

[Sizzlechest]

I recently hooked up a subwoofer to my factory radio. I am using a MTX Re-Q as my LOC. This signal is being fed to a crossover then to my amp. I know the re-q has a built-in crossover but I wanted more flexibility so I am outputting the full-range signal from the re-q to the crossover.

So it goes: radio (full range / high level) -> re-q (full range / low level) -> crossover (lows / low level) -> amp

The re-q, crossover, and amp all have gains to be set. Can anyone help me out with how to go about setting these gains correctly? I don't have any devices, it's all by ear.

Also, what frequency do you recommend for my crossover? 80hz? And should I use the bass boost and if so what frequency?

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[fly_marlin]

It looks like the re-q has 8V max output voltage for the sub. I would set it to the highest that the crossover and amp would take. If max input voltage for your amp is 5V, set the re-q to 5v and crossover. Essentially, set it to the highest voltage that all components can tolerate.

 

[Sizzlechest]

But how can I tell what the max that the crossover and sub will take? The sub amp and crossover have to be set somewhere for me to listen for clipping.

If it helps, my amp is a PPI Art Series A600.2, crossover is Sound Storm SX310

 

[fly_marlin]

Here's the link to the manual for your amp:

http://www.precisionpower.com/Manuals/Amplifier%20Manuals/Precision_Power_Art%20Series%20Axxx.2%20Amplifiers.pdf

Its maximum input voltage should be 2.5V. Set everything to that. Note that this setting on your amp is the LEAST sensitive, meaning you are less likely to clip your signal and you also have a lower noise floor. Hope this helps.

 

[Sizzlechest]

But how to I set the gains, am I missing something? My gain knobs have no voltage listings so I cant just dial in to 2.5V. I am working with ears and dials with no numbers basically.

I do have a multimeter I could use, if that helps.

Can you give me a step-by-step procedure for how to set each device (re-q, crossover, amp)?

 

[adulbrich 5,000+ posts]

If its your first system, don't use the bass boost! There is no crossover point that is best for all systems. Play around with your EQ crossover settings until you find what sounds best to you.

To answer your question about gain: You should start off by setting your LOC and crossover gains to a little before half way. Make sure your amp gain is set to the minimum level. Play bass heavy music on your head unit. Start your head unit on 0 and slowly move it to slightly above your normal listening volume. Turn your amp gain up slowly and listen for distortion. If you max out your amp gains and there is still no distortion, back the gain down to about half way and turn your LOC and/or crossover gain(s) up slowly.

^^^If at any time you hear distortion, turn the gain down! Distortion will harm your equipment. Clipping can damage your amp, and your subs.

 

[fly_marlin]

I think you're confused because the dial doesn't have numbers on it. When this happens, take for example the minimum and maximum input voltages for your amp: 0.5V and 2.5V. Add them together to get 3V and divide by 2. This means the very middle setting is 1.5V. The "max" (most sensitive) setting would be at 0.5V - meaning your amp expects only a 0.5V signal, thus being most sensitive. Does this make sense?

 

[Sizzlechest]

Thanks adulbrich!

olegni, that makes sense sort of. Basically the gain potentiometer has a range of min to max voltage supported by the device?

I had the amp gain up pretty high last night, higher than in my previous car where I had an aftermarket head unit, and I had no distortion. So I think my LOC and crossover gains are too low. My sub (Sundown Audio SA12) handles power like a beast. Is there frequency ranges that are better for tuning\hearing distortions?

 

[adulbrich 5,000+ posts]

No problem, my friend had a similar problem when he used an LOC!

 

[Sizzlechest]

What do you guys recommend for a frequency range setting on my crossover for my sub? I read that 75-90 is good. Setting range goes from 40hz-400hz

 

[adulbrich 5,000+ posts]

What do you guys recommend for a frequency range setting on my crossover for my sub? I read that 75-90 is good. Setting range goes from 40hz-400hz

Start it somewhere, then go up or down. Really, its about what sounds good to you and what your subs can reproduce. I'd say start at 240 and go down until you don't hear any vocals whatsoever on your subs. Do you have a subsonic filter too? Or nah..

 

[fly_marlin]

There is a general vicinity that you can reference to. I like my sub's lpf to be at 80Hz and HPF for the mids/tweets at 100Hz or 125Hz, depending on the driver. My new comps have amazing midbass, so I cross them at 100Hz. It's important to remember that a crossover point is not an immediate cut off, but gradual, so you don't want your subs and mids crossed at the same point or the frequencies around the crossover point will sound too warm - meaning you have more than 1 driver reproducing the same frequencies. Play around with it, start the sub at 80 and mids at 100 and adjust as you like. You may end up at the same starting point or may end up elsewhere.

 

[Sizzlechest]

Start it somewhere, then go up or down. Really, its about what sounds good to you and what your subs can reproduce. I'd say start at 240 and go down until you don't hear any vocals whatsoever on your subs. Do you have a subsonic filter too? Or nah..

The MTX Re-Q has a subsonic setting, as well as frequency setting for subwoofer output. But, I am using the full-range output of the Re-Q and letting my crossover do the work. Should I ditch the crossover and let the Re-Q do everything? I figured my crossover would be better since it has more settings, and it's a device strictly for the purpose of filtering, whereas the Re-Q is a LOC+crossover.

What do you guys think?

 

[fly_marlin]

Does the crossover have sub-sonic filter? If so, since you're already using it for all the filters anyway, just set the subsonic filter there. If not, set it on the re-q.

 

[Sizzlechest]

Does the crossover have sub-sonic filter? If so, since you're already using it for all the filters anyway, just set the subsonic filter there. If not, set it on the re-q.

Crossover does not have subsonic filter.

The Re-Q does, but as I said in my previous post, I am using the full-range output of the Re-Q, so the signal is not hitting the subwoofer filters. The crossover is doing all of the work.

This is why I asked if I am better off with using the Re-Q with subwoofer output alone without the crossover after (Radio -> Re-Q sub output -> Amp), instead of Re-Q full-range output to crossover (Radio -> Re-Q full-range output -> Crossover -> Amp).

It was my thought that the crossover may be better at processing the signal than the Re-Q. But what do I know.