Opinions on limiting for speaker protection

J

Jeff Hague

Freshman
Jan 12, 2011
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Mechanicsville, Virginia, United States
www.richmondproaudio.com
Since I now have the ability to use peak voltage and RMS limiters in my Itechs I have been doing a lot of research, asking questions and trying different settings to try to get a good handle on it.
Through research here and other boards I have noticed that opinions on how to use limiters vary widely (imagine that! :D~:-D~:grin:) and a fair # of folks seem to think that they really aren't necessary.
I thought it might be helpful to ask what your opinions are.

Should limiting be used for speaker protection?
If not, why not?
If so, what kind(s) of limiters do you prefer and how do you determine the settings?

Thanks!
 
Re: Opinions on limiting for speaker protection

A good idea would be to ask the speaker manufacturer of they have any specific recommendations. Just like matching amps to speakers is a little fuzzy using a limiter for speaker protection is not a simple science.

Loudspeakers fail from different mechanisms, over-heating and over excursion... Overheating involves heat input over time so is not a simple spot threshold but involves integration over time and knowledge of how fast the heat build up dissipates. Likewise excursion is not a simple spot voltage threshold but another different voltage and time calculation, not to mention interaction with cabinet tuning.

A manufacturer may have some practical advice. There is always a trade-off that you may forgo some short term power output to insure longer term reliability.

Sorry, nothing is simple in this area.

JR
 
Re: Opinions on limiting for speaker protection

John Roberts said:
A good idea would be to ask the speaker manufacturer of they have any specific recommendations. Just like matching amps to speakers is a little fuzzy using a limiter for speaker protection is not a simple science.

Loudspeakers fail from different mechanisms, over-heating and over excursion... Overheating involves heat input over time so is not a simple spot threshold but involves integration over time and knowledge of how fast the heat build up dissipates. Likewise excursion is not a simple spot voltage threshold but another different voltage and time calculation, not to mention interaction with cabinet tuning.

A manufacturer may have some practical advice. There is always a trade-off that you may forgo some short term power output to insure longer term reliability.

Sorry, nothing is simple in this area.

JR
Click to expand...

Thanks JR! I'm not looking for simple or even answers, just opinions. I am assuming from your post that you believe in using limiters for speaker protection?
I have pieced together recommendations from JBL and other sources so I think I have decent settings and an idea of what might need to be changed depending on the gig.
What I am wondering now I guess is should I bother - it is pretty complicated and time consuming after all - and I have very rarely had a speaker fail over 30 years doing live shows, during most of which I didn't have these options.
 
Re: Opinions on limiting for speaker protection

Hello

Isn´t it wonderful, that when we get older - yes, you young shots, too - we realize, that there is so much more, that we hardly ever dreamed of, that we do not have a clue...

In early days without ANY processing we simply tried to watch out and observe - and respect meters - and yes - I did not blow any speakers either.

Oh well - there WAS processing - low-cut filter 18dB@ 40Hz ...

I have this pair of JBL EVO speakers - quite nice things - they have a built in processor that measures voice-coil temperature and predicts what will happen if I keep the pace and starts limiting SLOWLY - perhaps 3dB/hour or so - which brings back the old wisdom - if your speakers can handle 1000W then drive them with 500W - thermal load is only 50%, while SPL is THEORETICALLY only 3dB less - in real life 0.5-2dB less ( supposing someone makes a speaker with only 1dB thermal compression at full power ) - so WHO is going to really hear the difference of driving the rack up to it´s last 3dB ???

And if you keep average round -6dB then you can let the transients go through freely - result : dynamic music with powerful peaks without having to worry about speakers blowing up. Perhaps not quite today´s trend, though.... so much compression everywhere - some singers are louder inhaling than "singing"...
 
Re: Opinions on limiting for speaker protection

Jeff Hague said:
Thanks JR! I'm not looking for simple or even answers, just opinions. I am assuming from your post that you believe in using limiters for speaker protection?
Click to expand...
"Limiter" or more accurately voltage limiters are fairly crude forms of protection. Ideally we should measure, model, or impute voice coil temperature and manage that to avoid failure or even avoid power compression which occurs before thermal failure. Likewise DSP can estimate or predict excursion from the audio waveform and reduce gain if needed to thwart that.

So yes my opinion is that smart speaker protection is useful.
I have pieced together recommendations from JBL and other sources so I think I have decent settings and an idea of what might need to be changed depending on the gig.
Click to expand...
Speaker protection is about the speakers, not the gig (or amp), so when set to protect the drivers it should not need to be changed ever.
What I am wondering now I guess is should I bother - it is pretty complicated and time consuming after all - and I have very rarely had a speaker fail over 30 years doing live shows, during most of which I didn't have these options.
Click to expand...

If you rarely lose drivers in 30 years maybe you don't need to change anything, unless you already changed something like amps or boxes.

My personal preference is for the speaker design engineers to dial in the protection and to do that well involves powered speakers where the design engineers have access to more data and full system control. A close second is something like the protection circuitry that is built into the drivers (DFEND?) but that is more expensive than the whole system approach of a powered cabinet.

JR
 
Re: Opinions on limiting for speaker protection

Crown has a new (at least to me) excel sheet on their website that helps with limiter settings for itech, macro tech, and HD's
 
Re: Opinions on limiting for speaker protection

I believe you should have 3 "basic": limiter settings (if possible) for loudspeakers.

But you should also keep the amp out of clip.

1: A peak limiter-set for as fast attack as possible and set for the loudspeakers peak rating (or just below it). If the amp is not large enough-then set this for the limit of the amp.

2: A "continuous" limiter that is set for the loudspeakers continuous rating. Attach time could be in the range of 1-10ms-depending on the freq range of the loudspeaker being used. This will allow for normal short peaks to come through without being affected and still give some "control" over "average" heating.

3: A slow attack/heating limiter that is set of about 1/2 to 1/3rd the continuous (not program) rating of the loudspeaker with a slow attack (2-3 seconds or so). This will protect against long term sine wave type signals and still allow normal program material to come through. Not everybody needs this type of limiter-but for rap or EDM/dance type material it is HIGHLY suggested.

Are these essential? no-proper operation of the system is the most important thing to keep from blowing speakers.

however if you have these in place you can "walk away" from the system with a bit of peace of mind about not blowing anything.

But this ALSO assumes proper high pass filters, proper (read non excessive) eq and so forth.
 
Re: Opinions on limiting for speaker protection

Hey Jeff,

I think a big part of the problem with public conception of limiting is that many people assume all limiters are created equal. If the only limiter available to me is a fast limiter in a DSP that isn't integrated into my amplifiers I will probably leave it off, fast limiting is for media that only cares about peaks (like CDs and other recording gear) not loudspeakers. My desert island limiter would be one that measures actual delivered power to the loudspeaker and lets me limit based on that using a pretty long attack and release (many seconds at least). Lots of powered speakers have this built in, and some amps as well like the Powersoft KDSP series and Crown iTech HD series to name two.

Here's an article I wrote on this subject a while back:
http://bennettprescott.com/downloads/LoudspeakerFundamentals.pdf
 
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