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Author Topic: Bi-Amplification Gain Attenuation  (Read 2051 times)

bennygreen1

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Bi-Amplification Gain Attenuation
« on: June 08, 2016, 12:46:58 am »

Hi guys,

This might seem like a bit of a rookie question but I can't really find any guidance on this online.

Say you have a loudspeaker with a 500 watt low/mid and a 200 watt high and no passive crossover. If you have 2 amplifiers, one 500 watts per channel and the other 200 watts then you can set the amp input sensitivity and crossover gains at 0dB and you should have a good relative level between the low/mid and the horn.

But if you only have 500 watt per channel amplifiers then surely you would need to apply some attention, either at the amp input or crossover, for the 200 watt horn.

Am I right in thinking that you would need -4dB attenuation as the difference between 500 and 200 in decibels is -4?

Thank you for your time!
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Tim McCulloch

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Re: Bi-Amplification Gain Attenuation
« Reply #1 on: June 08, 2016, 07:53:13 am »

Watts do not move speaker cones, rather the application of voltage does.
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Keith Broughton

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Re: Bi-Amplification Gain Attenuation
« Reply #2 on: June 08, 2016, 08:08:29 am »

Watts do not move speaker cones, rather the application of voltage does.
The question that follows is, are the sensitivity of the amps the same?
Should be available in the specs and read something like "sensitivity 32 db"
Generally, with horn highs and front loaded speakers for lows, the horn would be louder and that amp would have to be attenuated.
You can just adjust until it sounds right or use something like SMAART.
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Robert Piascik

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Re: Bi-Amplification Gain Attenuation
« Reply #3 on: June 08, 2016, 09:16:50 am »

I subscribe to the highly scientific "adjust until it sounds correct" method.
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Scott Carneval

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Re: Bi-Amplification Gain Attenuation
« Reply #4 on: June 08, 2016, 09:45:14 am »

A speaker with a woofer rated for 500 watts is probably going to have a HF rated for about 60-100 watts. That said, the HF sensitivity is likely to be much higher than the LF, usually by 10db or more. So usually the HF requires a good deal of attenuation to match it to the LF. 

You can calculate the difference by starting with the sensitivity rating of each driver, factor in the voltage gain of the amplifier, and then adjust the drive level to match. Or you can use the easier and arguably more accurate method of just measuring the speaker with SMAART and adjusting the drive levels of each channel until they match. You could probably get close enough using just an RTA if that's all you had available.

Is this a hypothetical question or do you have a speaker you're trying to set up? Don't forget you'll need to add delay (usually to the LF, especially if the HF is horn loaded) and you must set the proper limiting.
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bennygreen1

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Re: Bi-Amplification Gain Attenuation
« Reply #5 on: June 08, 2016, 10:13:08 am »

Is this a hypothetical question or do you have a speaker you're trying to set up? Don't forget you'll need to add delay (usually to the LF, especially if the HF is horn loaded) and you must set the proper limiting.
[/quote]

Until recently I have been working with d&b so never really needed to know but I was recently doing monitors in a club and they had EAW wedges that claimed to have 500 watt lows and 200 watt highs. They were running off 450 watt per channel amps for the lows and 300 watt for the highs with a bss active crossover. All levels on amps and crossovers were at unity and they sounded well balanced to my ears. I'll take my smaart kit next time I'm there. I guess there more to it than just matching the power ratings.
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Kevin Maxwell

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Re: Bi-Amplification Gain Attenuation
« Reply #6 on: June 08, 2016, 12:21:37 pm »

Is this a hypothetical question or do you have a speaker you're trying to set up? Don't forget you'll need to add delay (usually to the LF, especially if the HF is horn loaded) and you must set the proper limiting.


Until recently I have been working with d&b so never really needed to know but I was recently doing monitors in a club and they had EAW wedges that claimed to have 500 watt lows and 200 watt highs. They were running off 450 watt per channel amps for the lows and 300 watt for the highs with a bss active crossover. All levels on amps and crossovers were at unity and they sounded well balanced to my ears. I'll take my smaart kit next time I'm there. I guess there more to it than just matching the power ratings.

I and a lot of other people I know like to run the amps open all the way and take down the sensitivity in the active crossover, digital or analog. This way someone canít turn the amp up any more and mess up your settings or blow up your horns. If there was a way to lock the controls on the amp I might be inclined to set them other than full up. Even if the amps are in a locked room I still prefer to have them up all the way then I donít have to guess if someone messed with them. If they are anything other than full up I know they have been messed with. It is a really good idea to set up a limiter properly to hopefully protect the horns. But it is extremely difficult to idiot proof a system they keep making more idiots. I have considered using negative compression like in the DBX 160x to try and protect a system. Set it to a point that after they pass the threshold the more they push it the softer it gets. 

If it sounds good I wouldnít worry.
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Don Boomer

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Re: Bi-Amplification Gain Attenuation
« Reply #7 on: June 08, 2016, 08:42:15 pm »


Am I right in thinking that you would need -4dB attenuation as the difference between 500 and 200 in decibels is -4?

Probably not. You have to consider the sensitivity differences between amplifiers and between drivers.

Check the sensitivity of your power amps. If you were using Peavey/Crest amps you will get the same output from any of them for a given input voltage. For these constant gain amps if you want more output you drive them harder.  If you were using QSC amps then you get more output from big amps than little amps. Personally I don't like this style as you have to reconfigure your crossover parameters if you have to swap an amp.

But probably an even bigger factor is that HF drivers are likely 10dB hotter than cone drivers and you'll have to account for that.
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Ivan Beaver

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Re: Bi-Amplification Gain Attenuation
« Reply #8 on: June 08, 2016, 11:28:23 pm »

As other have already pointed out-IT DEPENDS.

In this case-the depends include: gain of the particular amps, sensitivity of the particular drivers, how/where the sensitivity of the particular drivers was measured etc.

Without knowing that information there is NO WAY to even start to make a guess to answer the question.

And any guess would more than likely be wrong.
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Ivan Beaver
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Re: Bi-Amplification Gain Attenuation
¬ę Reply #8 on: June 08, 2016, 11:28:23 pm ¬Ľ


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