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PA Systems A forum for discussion of all parts of a sound reinforcement or DJ system: loudspeakers, mixers (desks) etc.

Letting amps clip or running a limiter?
Letting amps clip or running a limiter?
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Old 25th February 2020, 01:58 PM   #21
Damo s is offline Damo s  United Kingdom
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could you measure the output to the tweeter from the xover? Might be that they are getting nowhere near damaging voltage anyway even with the amp on full chat
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Old 25th February 2020, 03:24 PM   #22
1hiep0 is offline 1hiep0  United States
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base on my experience occasionally clipping on the amp is fine, best is no clipping and having good gain structures.
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Old 26th February 2020, 08:49 PM   #23
CipiSound is offline CipiSound  Romania
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what value of RMS from a poweramp is just perfect for b&c 15NW100 ? limited with DSP and highpass filter at 42Hz with 48db/oct.
thanks!
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Old 27th February 2020, 09:31 PM   #24
CipiSound is offline CipiSound  Romania
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I am using a DSP with limiter (some live situation are too dangerous) and I am using a "rise up" from Ecler alma 26, and the amplifier class D I think it has an integrated limiter. all are very discreet, and when the clip red led is blinking I know that is fine, the limiter is working, speakers are safe.
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Old 29th February 2020, 06:26 PM   #25
kipman725 is offline kipman725  United Kingdom
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Party was a great success. Ended up using peak limiters on all output channels set to just before clip and an input compressor set to medium knee with 300ms attack and release set to the point where pink noise was just triggering the peak limiters. On live music the input compressor basicly didn't activate but transients from the kick where hitting the midbass and sub limiting. On dj material the compressor was invaluable, I found the rearly good DJs just instinctively rode the edge of the compressor which changed the tone of the bass heavy passages in a rearlly pleasing way. I'm thinking that a possibility for improvement could be a split band input compressor to avoid the sparkles getting squashed during bass heavy pasaages but overall fantastic sound was achived for a relatively modest system.
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Old 2nd March 2020, 03:30 PM   #26
Damo s is offline Damo s  United Kingdom
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The input compressor works a treat I've found. The release time Ive used is far shorter than yours which I think makes it less transparent to a point, but then sounds overly crushed and perhaps a bit nasty when really pushed. Hopefully the DJ will hear this and turn it down a bit, although at this point they would have to be lighting up 2 or more reds which would eat up 1 of their 3 strikes (and they are off, or the system goes off).
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Old 10th March 2020, 08:58 AM   #27
jaddie is offline jaddie
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Several things:

Speakers are damaged in two ways: overheating and over-excursion. Tweeters are mostly damaged by overheating, as excursion is generally small. Woofers are generally damaged by over-excursion where the voice coil slams agains the magnet.

Heat damage is an RMS function, not a peak function. Pushing a signal above clipping limits the peak value (to the clipping point) but allows the RMS value to rise in a way that is not dissimilar to what you'd have if you raised the signal but did not clip, at lest for the first few dB above clip threshold.

Excursion damage is a peak function, and the voltage threshold of the excursion limit drops with rising frequency until it intersects with the heat damage point, then you have an RMS function.

Peak limiting with a zero attack is not the same as clipping because of the release time. Both clipping and peak limiting with fast release limit peaks but raise RMS. Peak limiting can result in less distortion than clipping, depending on release time and frequency. The slower release time, the less RMS increase above threshold. Taken to extreme, a zero attack and very long release will cause instantaneous downward gain change on a peak, but no other change (no distortion, no RMS increase) until the limiter recovers enough to attack the next peak above threshold. Taken to the opposite extreme, zero attack and extremely short release, the effect approaches that of clipping. So you dial in recover time to minimize (or maximize) audible artifact balanced against desired peak control. Remembering that once over-excursion has been dealt with, speakers are damaged by RMS (heating value) level, thus time is a factor.

A compressor with slower attack and release should not be assumed to use an RMS detector. Many use simple average detectors, others just us a peak detector that is very slow. Neither is an accurate RMS processor. Make sure you are getting true RMS response.

Separate limiters post crossover is a nice way to get away with increased limiting action with less audible artifact. However, maximum power handling of tweeters is generally about 1/10th as high as woofers and mid-range. Thresholds and response times for each band would vary significantly, as does the spectral density in music for each band.

Ideally a tweeter protection processor would be based on the thermal damage time vs RMS level curve of a specific driver. Have fun finding that on anything but pro drivers.

The ideal woofer protection processor would be based on both peak limiting and RMS limiting. The peak limiter would use a frequency variable threshold, lower frequencies cause higher excursions, thus should limit sooner. A straight, flat threshold peak limiter would be hyper-active for upper bass frequencies, and inadequate for very low ones. The RMS limiter would follow the heat damage curve of the driver.

Peak limiter distortion is a function of release time, faster results in higher distortion. Some hardware peak limiters use a complex release time where small amounts of gain reduction are released more quickly than large ones, as a distortion reduction method. Any release time stated in dB/ms is not doing this, and will produce the same amount of distortion regardless of how far above threshold it is operating.

A slow attack peak limiter isn't actually a peak limiter at all, as peaks above threshold will get right through.
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Old 12th March 2020, 03:48 PM   #28
chris661 is offline chris661  United Kingdom
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Hey Jaddie,

Good to see you back around this side of the forum. I'd been looking for your posts a little while ago - found them here: Calculating power required for bi-amped 2 way system

Realised I never said thanks for taking the time to present the data. So, thank-you for that. I can see it was a lot of work.

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Old 18th March 2020, 08:12 AM   #29
jaddie is offline jaddie
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Quote:
Originally Posted by chris661 View Post
Hey Jaddie,

Good to see you back around this side of the forum. I'd been looking for your posts a little while ago - found them here: Calculating power required for bi-amped 2 way system

Realised I never said thanks for taking the time to present the data. So, thank-you for that. I can see it was a lot of work.

Chris
Thanks.

When I looked over that thread I felt again that every time I post the clipping/spectral analysis, it's like tilting at windmills. It always generates a fight with people who have swallowed the "other" idea. When I went after the clipping-burning-drivers problem I expected to find clear evidence contrary to what I found. If there was even a little bit of vagueness about the result, I'd have backed off a long time ago. It's a case where the popular understanding isn't really an understanding, its a belief.
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Old 18th March 2020, 08:41 AM   #30
kipman725 is offline kipman725  United Kingdom
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Quote:
Originally Posted by jaddie View Post
Thanks.

When I looked over that thread I felt again that every time I post the clipping/spectral analysis, it's like tilting at windmills. It always generates a fight with people who have swallowed the "other" idea. When I went after the clipping-burning-drivers problem I expected to find clear evidence contrary to what I found. If there was even a little bit of vagueness about the result, I'd have backed off a long time ago. It's a case where the popular understanding isn't really an understanding, its a belief.
Don't worry its pretty obvious when you consider real power is the integral of the current voltage product W.R.T time and clipping is just chopping the peaks off. Considering a drivers complex impedance the only real limiting would be voice coil temprature sensing and peak limiting to prevent over excursion. Powersoft have amplifiers which can measure the real power delivered to the load and perform limiting based on that which is most of the way there.

For a custom sub amp design it would be possible to introduce a small DC offset and use that that measure the voice coil temperature but the amp would have to be a plate amp as the composition of the wiring to the VC would have to be known (also you would have to know the voice coil wire temperature coefficient - which would probably require testing on a re-cone kit).
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