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Author Topic: Better to overpower or underpower speakers?  (Read 22536 times)

Adam Schaible

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Re: Better to overpower or underpower speakers?
« Reply #60 on: June 16, 2009, 03:49:31 PM »

Ok, I should have specified.  We're only interested in the lowest frequencies we're asking the speaker to play right?

So if we're high passing our subs at 40Hz - we could calculate this for 40Hz and set our peak limiters to limit voltage below the calculated value.

Is this possible to do?
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Stephen Dranger

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Re: Better to overpower or underpower speakers?
« Reply #61 on: June 16, 2009, 03:50:16 PM »

Art Welter wrote on Tue, 16 June 2009 14:26

Stephen,

If your hearing ability is like your reading comprehension, then no, there is nothing you can listen for.

Smoke 'em if you got 'em.

Please, point me to the post in this thread where this answer was given to me. I know I didn't see it.
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Stephen Dranger

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Re: Better to overpower or underpower speakers?
« Reply #62 on: June 16, 2009, 04:01:21 PM »

Greg Cameron wrote on Tue, 16 June 2009 14:37


Stephen, if you know for a fact that you're going to be running true sine wave signals through your amp for extended periods, get an amp that has a continuous output rating that is equal to or less than the rms rating of the speakers rather than one that is 2x the rms rating and never hit the clip lights on the amps. This is the only way without an rms limiter that you can ensure you won't cook your speakers. Also be aware that a lot of amps don't like running full power sine waves for extended periods of time and will ramp the output down if you're running full tilt. This is especially true with the newer class D style amps and low impedance loads. Older designs will tend to just overheat or pop their internal breaker if you're running low impedance loads with full power sine waves.

Greg


Well, as I said in the OP, I am poor and I'm stuck with what I have Sad

From what one of the other posters wrote, if I don't ever go above 0dBu on my mixer, the amp is not going to distort that signal because its input sensitivity is 1.23V. That means I'm safe running it at 500W. This was echoed by a poster who told me exactly what you just did: run it low and just make sure you never overdrive the amp.

Some people, though, have said that I shouldn't trust that my mixer will never peak above that level, and that running my amp at 1300W would be safer because if I did have any accidental peaks, the amp wouldn't clip and therefore the speakers could handle it. My next question was: how to make sure I wasn't sending too much continuous power to the speakers if I was operating at that high a wattage.

I really appreciate everyone's help and I appreciate most of you being patient with me...hopefully you can see how confusing this is to someone doing it for the first time!
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John Roberts {JR}

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Re: Better to overpower or underpower speakers?
« Reply #63 on: June 16, 2009, 04:32:26 PM »

Stephen Dranger wrote on Tue, 16 June 2009 14:50


Please, point me to the post in this thread where this answer was given to me. I know I didn't see it.


Regrettably these threads degenerate into a this kind of dueling experts often.

Regarding audible "tells" from loudspeakers in distress, for overheating there is a mechanism before complete melt down called "power compression", where you have to turn  the amps up more than when the speakers were cold to get the same output. This is subtle and hard to hear unless you are pretty familiar with your system and the room.

For over excursion, there is no graceful audible warning. When woofers bottom there will often be a loud snap. This may be terminal on the first event, or give you a second chance if driver is robustly engineered.

For setting level, most amps will have front panel clip or limit LEDs. These will be more accurate to detect (amp) clipping than console meters or calculated gain structure.

If you amp has clip limiters make sure they are engaged.

Good luck.

JR
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Art Welter

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Re: Better to overpower or underpower speakers?
« Reply #64 on: June 16, 2009, 05:33:48 PM »

Stephen,

Messages #444077, #444087, #444251, #444275, #444286 and the linked article all point out that that when driven too hard, a speaker’s sound will change.

The changes should be apparent  before the speakers are damaged, other than exceeding Xlim.

However, some music is so distorted to start with that it is hard to tell the difference when speakers distort.
Oh well.

If you have a decent set of headphones, you can compare the sound of your speakers to them, using the phones as a reference.

As you start pushing your speakers too hard, there will be a level where they no longer sound the same.
The speakers will be out of their linear operating range.
The point where you need more rig for the gig.
As speakers  exceed Xmax, the woofers will distort.
Distortion sounds different than clean. A pure sine wave will start to sound like a sawtooth wave.
Clean vocals will start to sound like Joe Cocker, etc.
If the woofers or tweeters hit Xlim, they may make clacking, or popping noises.

The voice coils will have heated up, which causes their impedance to rise, and the speakers will now not be as loud, thermal compression has set in.
Compression sounds different than uncompressed, less dynamic. A three dB increase in drive level may only result in a one dB increase in SPL.

As the voice coils change impedance from heating, the passive crossover points and slopes will change.
This sounds different, like an EQ change, usually a “thinner”, “harsher” sound will result.

Get yourself some cheap disposable speaker from Goodwill or laying unused in some closet.
Put your amp in bridge mono mode, play music through the speaker and listen.
Continue to turn the level up a dB at a time every 3 minutes. Use earplugs so your ears don’t distort, and listen for the effects listed above. If you hear clacking noises, raise the high pass filter.

I have moderately clipped a 400 watt amp into eight  4” speakers rated 5 watts RMS apiece, 40 watts RMS total, with no problem. The musical peaks were 10 times the speaker RMS level. Same ratio as 5000 watts into a 500 watt RMS speaker.

I have also (by accident) burned up a 100 watt RMS speaker in approximately one second with a 400 watt 200 HZ sine wave. If I would have turned that speaker up slowly, (and had not been doing tests while drunk) I would have noticed the distortion well before I had exceeded the power level by six dB.
I was reading a dB meter set on “A” instead of “C”, so it read about 6 dB SPL low, using my eyes instead of my ears...

You will probably be quite surprised how much peak power a  speaker will take before it finally burns up if the music has reasonable dynamics.

Art Welter
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Bennett Prescott

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Re: Better to overpower or underpower speakers?
« Reply #65 on: June 16, 2009, 05:38:12 PM »

Phil Lewandowski wrote on Tue, 16 June 2009 15:28

What slow attack and release times do you think are good points to start with?

This is not a simple issue, and it is difficult to give an accurate answer without knowing a lot about the box, its application, and the drivers. The frequency range being worked with, driver loading, driver capabilities, and excursion can all be an issue. For instance, it is perfectly possible to have a loudspeaker that is excursion, rather than thermally, limited... i.e. (usually at lower frequencies) the driver runs out of excursion before it will ever overheat.

That said, and please be aware that to really get this right takes a lot of almost certainly destructive testing, the best guess for attack and release times for a low frequency driver that I have are on the order of 5-10 dB per second attack, and .5-1 dB per second release. That should be a good starting point, adjust more or less within that range until it is inaudible. Driver overheating generally occurs on the order of 30+ seconds, so these times can be very slow because of that... but too slow and it's too audible, and too fast and it's too audible. We're talking about really very small reductions in SPL here, compared to what we normally nail compressors with. Maybe 3-6 dB, maybe as high as 9 for a really big amp and really abusive source material, but the amp's rail voltage will become the limiting factor again very quickly.

Good luck!
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Bennett Prescott

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Re: Better to overpower or underpower speakers?
« Reply #66 on: June 16, 2009, 05:39:50 PM »

Art Welter wrote on Tue, 16 June 2009 17:33

If I would have turned that speaker up slowly, (and had not been doing tests while drunk) I would have noticed the distortion well before I had exceeded the power level by six dB.

Don't give away the loudspeaker tuning secrets of the pros, Art!

Art Welter wrote on Tue, 16 June 2009 17:33

You will probably be quite surprised how much peak power a  speaker will take before it finally burns up if the music has reasonable dynamics.

Indeed!
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-- Bennett Prescott
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Phil Lewandowski

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Re: Better to overpower or underpower speakers?
« Reply #67 on: June 16, 2009, 06:33:23 PM »

Bennett Prescott wrote on Tue, 16 June 2009 17:38

Phil Lewandowski wrote on Tue, 16 June 2009 15:28

What slow attack and release times do you think are good points to start with?

This is not a simple issue, and it is difficult to give an accurate answer without knowing a lot about the box, its application, and the drivers. The frequency range being worked with, driver loading, driver capabilities, and excursion can all be an issue. For instance, it is perfectly possible to have a loudspeaker that is excursion, rather than thermally, limited... i.e. (usually at lower frequencies) the driver runs out of excursion before it will ever overheat.

That said, and please be aware that to really get this right takes a lot of almost certainly destructive testing, the best guess for attack and release times for a low frequency driver that I have are on the order of 5-10 dB per second attack, and .5-1 dB per second release. That should be a good starting point, adjust more or less within that range until it is inaudible. Driver overheating generally occurs on the order of 30+ seconds, so these times can be very slow because of that... but too slow and it's too audible, and too fast and it's too audible. We're talking about really very small reductions in SPL here, compared to what we normally nail compressors with. Maybe 3-6 dB, maybe as high as 9 for a really big amp and really abusive source material, but the amp's rail voltage will become the limiting factor again very quickly.

Good luck!


Thanks Bennett for the info,

And I do understand from other times I've asked this question that there is no one size fits all and you just have to play with it.  Which is what I would love to do!


Now I just have to find an appropriate compressor to use for a job like this...
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Stephen Dranger

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Re: Better to overpower or underpower speakers?
« Reply #68 on: June 16, 2009, 10:01:28 PM »

Art Welter wrote on Tue, 16 June 2009 16:33


I have moderately clipped a 400 watt amp into eight  4” speakers rated 5 watts RMS apiece, 40 watts RMS total, with no problem. The musical peaks were 10 times the speaker RMS level. Same ratio as 5000 watts into a 500 watt RMS speaker.

I have also (by accident) burned up a 100 watt RMS speaker in approximately one second with a 400 watt 200 HZ sine wave. If I would have turned that speaker up slowly, (and had not been doing tests while drunk) I would have noticed the distortion well before I had exceeded the power level by six dB.
I was reading a dB meter set on “A” instead of “C”, so it read about 6 dB SPL low, using my eyes instead of my ears...

You will probably be quite surprised how much peak power a  speaker will take before it finally burns up if the music has reasonable dynamics.

Art Welter


This was really helpful. I appreciate the advice, even if I don't seem to be quite understanding the plethora of information out there.
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Art Welter

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Re: Better to overpower or underpower speakers?
« Reply #69 on: June 16, 2009, 10:54:53 PM »

Stephen,

I have mixed thousands of shows on thousands of speakers.
I have burnt a total of four speakers, all on the one night I mentioned when I was testing rather than mixing.

The plethora of information boils down to:

1) Set up your system gain structure so nothing clips before the amps
2) Don’t hard clip your amps, lest they put out lots of squashed power.
3) Properly high pass your LF speakers.
4) When a speaker starts to sound different, don’t turn it up any more.
5) Have ample headroom to reproduce musical peaks.
6) If the music you are playing is really compressed or full of droning sine wave like tones, be conservative with the power ratings, as the average, not peak power is what burns coils.

I have mixed thousands of shows on thousands of speakers.
In that time I personally have destroyed a total of four speakers, all on the one night I mentioned when I was testing rather than mixing.
Make that 6, two tweeters went on another test with a mini line array that had the center tweeters getting 10 dB more power than the outside tweeters, you can view that and many other basket cases in Bennett’s request for speaker failure pictures a while back.

Art Welter
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