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Dj Vishnu
03-27-2012, 02:37 AM
Good Day All,

As a technical noobie, but hungry for sound knowledge (pun intended), everything learnt on these forums I apply to my mobile disco....to deliver the highest quality sound experience to my clients.

My thread is similar to the post yesterday by Unsafe8989, as I have also being pondering about it for some time now.

Often I page through this forum & the BFM forum, wherein it is advised that a 2.8V is used on the BFM subs.

I am assuming that 2.8V input into the subs equates to the max volume (before clip) output from the amplifer and that the sub is now performing at its full potential.

If so, does this same principal apply to full range speaker cabinets.

Further, how much bearing does line signal from the mixer into the amplifer, have on sound quality output or is this not relevant.

Reason is that, I use the Behringer DDM4000 and I set the channel levels & master output gains to the point where only the 1st set of red LED's just light up. I was told that whenever the signal exceeds & goes way into the red, the sound quality is not of the highest audible quality & gets somewhat distorted.

Bill Fitzmaurice
03-27-2012, 09:13 AM
Often I page through this forum & the BFM forum, wherein it is advised that a 2.8V is used on the BFM subs.
2.83v is the equivalent of 1 watt into an 8 ohm nominal load, and is the standard for SPL measurement.

Dj Vishnu
03-27-2012, 10:05 AM
Thanks for that Mr. Fitzmaurice,

Excuse me, if this might seem as a dumb a$$ question as I am totally new to the technical side things, but how would I establish the max input voltage that can go into a sub/ full range speaker.

Also, how do I go about measuring the voltage using a multi meter.

Bill Fitzmaurice
03-27-2012, 10:23 AM
Thanks for that Mr. Fitzmaurice,

Excuse me, if this might seem as a dumb a$$ question as I am totally new to the technical side things, but how would I establish the max input voltage that can go into a sub/ full range speaker.
You must know the driver specs, model it in the enclosure with driver modeling software, then use the excursion plot to see how much voltage may be safely applied without pushing the driver past either Pe or xmax, whichever comes first. In short, if you're not an expert in loudspeaker design, you can't. This information should be included in the speaker owner's manual, but is not. With tops one can generally get away with using Pe and Ohms Law to figure the safe voltage, with subs 1/2 of Pe is usually safe, as tops are usually power limited, subs usually displacement limited.

Also, how do I go about measuring the voltage using a multi meter. Put the testing leads on either the amp output or speaker input. But you can't adjust an amp to a maximum voltage output. That can only be done with a limiter.

Gjhowe1
03-27-2012, 10:31 AM
Reason is that, I use the Behringer DDM4000 and I set the channel levels & master output gains to the point where only the 1st set of red LED's just light up. I was told that whenever the signal exceeds & goes way into the red, the sound quality is not of the highest audible quality & gets somewhat distorted.

Its my understanding that when the mixer is in the red your trying to push to much power through the transistors, which results in loss of signal quality. Think it has something to do with driving them to saturation?

Bill please correct me if I'm wrong, as I think you know more about this then I do.

I think your clipping the signal inside the mixer before it even gets to the amp.

Bill Fitzmaurice
03-27-2012, 10:35 AM
Its my understanding that when the mixer is in the red your trying to push to much power through the transistors, which results in loss of signal quality. Think it has something to do with driving them to saturation?

Bill please correct me if I'm wrong, as I think you know more about this then I do.

I think your clipping the signal inside the mixer before it even gets to the amp.+1. Clipping can occur at any point in the signal chain, starting at the mixer input, ending with the speaker. It's never a good thing.

DTR
03-27-2012, 01:25 PM
Its my understanding that when the mixer is in the red your trying to push to much power through the transistors, which results in loss of signal quality. Think it has something to do with driving them to saturation?

It's not saturating the transistors, it's saturating the power available to them. Say an amp has a power supply that produces +/-30V. The amp can output a wave form that peaks at anywhere up to 30V (actually slightly less due to the inherent drop across the transistors). The amp cannot output anything greater than +/-30V. If you push the amp too far, it will output the wave form up to the 30V limit, but anything above that gets "clipped off". Hence the term clipping.

I hope that made sense, it's better explained with a diagram or two.

Bill Fitzmaurice
03-27-2012, 01:53 PM
It's not saturating the transistors, it's saturating the power available to them. Both views are correct. For the most part clipping occurs when the rail voltage cannot deliver what's being demanded, but transistors can in effect 'saturate' as well. In most cases it's the power supply that comes up short, as transistors tend to be sized so that they won't run out of headroom before the power supply does. But they can. That's how germanium transistor fuzz boxes work.

DTR
03-28-2012, 06:13 AM
Ah, thanks for the info