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Author Topic: Amps/Limiters/speakers... again...  (Read 1312 times)

Steve-White

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Re: Amps/Limiters/speakers... again...
« Reply #10 on: August 17, 2022, 11:27:48 PM »

The quickest and easiest way is to DISCONNECT the speaker and put a volt meter on the output of the amp

Then use a sine wave input (60Hz is generally best) and drive it until it is above the voltage rating of the loudspeaker.

Then turn down the limiter threshold until you get the voltage you want.

That is the short version, but quick and easy.

The attack time should be related to the high pass filter freq.

"The attack time should be related to the high pass filter freq."

What would be a proper relationship between attack time for a limiter and the high pass frequency?
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Ivan Beaver

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Re: Amps/Limiters/speakers... again...
« Reply #11 on: August 18, 2022, 11:23:21 AM »

"The attack time should be related to the high pass filter freq."

What would be a proper relationship between attack time for a limiter and the high pass frequency?
It varies on the type of limiter.  And different people have different opinions.  Below are my "go to" times.

For a normal "music/program limiter" around 1-2x (NOTE:Edited the attack time) the time interval of the high pass filter.  The release should be around 15x attack time

For thermal type limiter. around 100x the time interval of the high pass filter

A peak limiter should as fast as possible.

The formula is 1/freq=time in seconds.  If you want it in milliseconds: 1/freq x 1000=time in milliseconds
« Last Edit: August 18, 2022, 04:12:05 PM by Ivan Beaver »
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Russell Ault

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Re: Amps/Limiters/speakers... again...
« Reply #12 on: August 18, 2022, 12:36:03 PM »

{...} Then all of sudden everything was fine.

Just when I thought your story couldn't get in worse...I feel like the only thing worse that 70V wall power is intermittently-70V wall power.

-Russ
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Minka Matikainen

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Re: Amps/Limiters/speakers... again...
« Reply #13 on: August 18, 2022, 01:51:30 PM »

Good discussion and tips. I should have mentioned that this is going to be a fixed installation on a night club.

Someone asked for the models of speakers and amps, but as far as the limiter calculation and setup those details have very little to do with it. And also as an asnwer to question on DSP, it will be separate DSP with dedicated speaker processing capabilities, including RMS and Peak limiting.

And yes, I totally agree with Ivan on measuring the voltage, but my idea was to setup somekind of ballpark for limiters before getting the system up and running.

And yes, the question rised exactly because in this particular case amp manufacturer tells the input sensitivity as window between -19,5 to 27 dB and that just doesn't make any sense to me how to use that information.
 
I know that I will be driving the amp "fully open", because then the risk that someone touches the knob and blows a speaker (or ears) is a lot smaller... ...but also because of that, and the fact that the amp is rated for [email protected] (bridged) and the speakers have RMS rating of [email protected], I need to get the limiters setup. One could aske why I would use the amp in bridged mode? That is because the amp will give in "normal mode" only [email protected] which might end up to a situation where amp is driven to clip and speakers are blown because of that.

I would have loved to have some other manufacturers amp, which has it's gain written down on spec sheet to avoid the confusion, but you work with the ones the customer buys if you can't affect the purchase process, right?

Referring to the discussion and all the things I've written above myself, I think I don't have any other route with the given information than measuring the voltage... ...or if I do, please point me to correct direction.

Thanks!
-Minka-
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Russell Ault

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Re: Amps/Limiters/speakers... again...
« Reply #14 on: August 18, 2022, 02:46:07 PM »

{...}  ...but also because of that, and the fact that the amp is rated for [email protected] (bridged) and the speakers have RMS rating of [email protected], I need to get the limiters setup. One could aske why I would use the amp in bridged mode? That is because the amp will give in "normal mode" only [email protected] which might end up to a situation where amp is driven to clip and speakers are blown because of that. {...}

I think there's a typo in here: in your original post you mentioned the speakers wanting [email protected]Ω, not 4Ω. (Incidentally, this is one of the reasons why we ask for equipment model numbers: everyone can make typos, but if we're all looking at the same manufacturer's spec sheet then the typos don't have to happen.)

In that case, I think you're overthinking it some. First, 630W is only ~0.5 dB less than 700W, which is not typically considered to be an audible difference, so you should have no trouble safely powering those speakers in non-bridged mode.

Second, putting a pair of [email protected]Ω speakers across a bridged amplifier rated for [email protected]Ω is roughly equivalent to powering a single speaker rated for [email protected]Ω. 1400W is only ~2.5dB less than 2500W, so the speakers aren't going to be grossly overpowered (although protection limiting will still be important, as it always is).

-Russ
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Tim McCulloch

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Re: Amps/Limiters/speakers... again...
« Reply #15 on: August 18, 2022, 03:24:22 PM »

Has anyone asked the loudspeaker manufacturer for their input?
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Steve-White

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Re: Amps/Limiters/speakers... again...
« Reply #16 on: August 18, 2022, 07:22:11 PM »

I think there's a typo in here: in your original post you mentioned the speakers wanting [email protected]Ω, not 4Ω. (Incidentally, this is one of the reasons why we ask for equipment model numbers: everyone can make typos, but if we're all looking at the same manufacturer's spec sheet then the typos don't have to happen.)

In that case, I think you're overthinking it some. First, 630W is only ~0.5 dB less than 700W, which is not typically considered to be an audible difference, so you should have no trouble safely powering those speakers in non-bridged mode.

Second, putting a pair of [email protected]Ω speakers across a bridged amplifier rated for [email protected]Ω is roughly equivalent to powering a single speaker rated for [email protected]Ω. 1400W is only ~2.5dB less than 2500W, so the speakers aren't going to be grossly overpowered (although protection limiting will still be important, as it always is).

-Russ

That.
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Minka Matikainen

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Re: Amps/Limiters/speakers... again...
« Reply #17 on: August 22, 2022, 08:10:42 AM »

I think there's a typo in here: in your original post you mentioned the speakers wanting [email protected]Ω, not 4Ω. (Incidentally, this is one of the reasons why we ask for equipment model numbers: everyone can make typos, but if we're all looking at the same manufacturer's spec sheet then the typos don't have to happen.)

In that case, I think you're overthinking it some. First, 630W is only ~0.5 dB less than 700W, which is not typically considered to be an audible difference, so you should have no trouble safely powering those speakers in non-bridged mode.

Second, putting a pair of [email protected]Ω speakers across a bridged amplifier rated for [email protected]Ω is roughly equivalent to powering a single speaker rated for [email protected]Ω. 1400W is only ~2.5dB less than 2500W, so the speakers aren't going to be grossly overpowered (although protection limiting will still be important, as it always is).

-Russ

Sorry for my mistyping. All should be 8ohm, speaker [email protected], amp [email protected] bridged / [email protected] "normal". Dunno why I wrote 4ohm, might be that I was just tired while writing that and didn't double check.

And yes, I see the point you have, but like said earlier in my post, this is going to be a night club, where one could imagine that the system might be run every now and then to it's limits, and I would like to be sure that no speaker is blown because of that...

But I guess the only "safe way" is to actually measure the output of the amp with voltage meter.

Br,
-Minka-
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Riley Casey

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Re: Amps/Limiters/speakers... again...
« Reply #18 on: August 22, 2022, 01:00:53 PM »

A couple of caveats for those who don't spend inordinate amounts of time with test equipment. Many if not most digital volt meters are designed for use in the 60 to 400 hz range and are not flat outside that range. Check that your meter is going to provide useful measurements for say setting voltage limiters on compression drivers operating above 1500hz. Ideally you'd be using an audio range AC volt meter with an analog meter and / or  using an oscilloscope across the amp output to confirm that nothing is clipping. Oscilloscope computer apps would be fine in this application as long as you are using an input device that will survive the voltage swing in question.

Caveat two is that a great many amplifiers will not produce proportional voltage swings across loads lower than 8 ohms. In essence they are limited in their current capacity and clip at lower voltage output than the double voltage that the math says a 4 ohm load would require. Check the amp specs and derate your measurements accordingly when setting up for lower impedance loads.

Steve-White

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Re: Amps/Limiters/speakers... again...
« Reply #19 on: August 22, 2022, 03:39:14 PM »

My weapon of choice for amplifier testing, in addition to the dummy load and 4ch scope is a Simpson 260 VOM - virtually flat throughout the full audio spectrum and beyond.

One can find used Simpson 269's in decent condition for ~$75-$125 on eBay.  I also have a Simpson 260 VOM that works great, but the 7" meter face on the 269 is fabulous.
« Last Edit: August 22, 2022, 03:42:43 PM by Steve-White »
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Re: Amps/Limiters/speakers... again...
« Reply #19 on: August 22, 2022, 03:39:14 PM »


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