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Letting amps clip or running a limiter?
Letting amps clip or running a limiter?
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Old 31st March 2020, 07:26 PM   #31
Just Dave is offline Just Dave  United States
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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,
Hey jaddie, when I read that, it was like deja vu all over again. Way back in about 1979, I wrote an article about that exact topic: overheating and over-excursion. Thanks for your post describing it to folks who are just now learning about such things.
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Old 31st March 2020, 08:20 PM   #32
HumbleDeer is offline HumbleDeer  Belgium
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I set my limiters to about 5% below the maximum output of the amp. The limiter will not completely stop signal from going louder, as that would also be practically clipping. Using a very high ratio compression like limiter (15 to 1) means that it functions more like an analog rounding clipper.
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Old 1st April 2020, 08:51 AM   #33
jaddie is offline jaddie
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Originally Posted by HumbleDeer View Post
I set my limiters to about 5% below the maximum output of the amp. The limiter will not completely stop signal from going louder, as that would also be practically clipping. Using a very high ratio compression like limiter (15 to 1) means that it functions more like an analog rounding clipper.
SOOO much more to it than that. A limiter is not practically clipping, even at infinite ratio, primarily when you consider release time. A good technical peak limiter will fully limit on the leading edge of a peak, then not distort because its release time doesn't allow the gain increase to track the waveform, only the envelope. Additionally, attack time can actually be slowed to permit a slightly smoother sound so long as the threshold is appropriately lowered as well. Release time can also be made complex, as a function of peak duration, or gated to freeze during the peak to effectively reduce gain change induced distortion to zero. Then there's the DSP based peak limiter with look-ahead, which totally eliminates attach envelope distortion.

By definition a peak limiter has an infinite slope and will completely stop peaks over threshold. However, that's not a loudness function, that's a peak function. Very different, and not completely related. Advancing the input to a peak limiter with fast release will result in a range of proportionally increased loudness at the expense of short-term dynamic range. If the peak limiter isn't stopping peaks, it's a terrible peak limiter, or is deliberately slowed for other reasons, at which point the threshold can be lowered to maintain maximum peak control.

Nah, nothin' like clipping. At all.
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Old 15th April 2020, 06:43 PM   #34
nigelwright7557 is offline nigelwright7557  United Kingdom
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If your hitting a limiter then the amp/speakers simply aren't loud enough.
I worked in an audio shop for a while and the amount of overdriven stuff we got in was amazing. Just people not buying the right gear in the first place.
You wouldn't flog your car at full revs all day long so why do the same with an audio system ?
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Old 16th April 2020, 03:22 PM   #35
kipman725 is online now kipman725  United Kingdom
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In an ideal world we would all have the rig for the gig per say. However I'm not sure your aware of the kind of gear I regularly see limiting. I see things like 14 FLH subs running on MA5002VZ's hitting limiters on bass heavy passages (large lossy indoor space). If you have the capability in the sub bass people will use it. Having correctly set limiters is essential to protect the system.

My system always sounds great and nothing like some wedding DJ clipping the amps, I keep an eye on levels and adjust if needed, correctly set limiters just reduce the effort and provide protection.

I'm always working on making my system better since this gig I have another P7000s which will allow me to run my subs with 4* the input power as I can run each P7000 bridged. Admittedly I will have to peak limit at around 90V due to running out of excursion on these particular subs so the actual dB increase will be small. However the amps will now not clip before the excursion protection limiter has to kick in. I have also replaced the tops amp with a CTS4200 which should give a few more dB.

current projects are:
1) 4 new subs using 15TBX100, these will have ~4dB more output per sub than my current subs if given enough amp. I will probably use all 8 though in order to get more directivity from my sub woofer array.
2) New top amp, I have been fixing amps to save up spare cash for a high end quad channel amp ~500W/channel, I don't expect to put more average power through the tops but this will eliminate any clipping.
3) entirely new large system using front loaded horns for outdoor use (see Mega midbass straight horn 139dB)
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Old 16th April 2020, 04:07 PM   #36
chris661 is online now chris661  United Kingdom
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Sounds like you're keeping busy!

But yeah, I agree that the DJ's demands will inflate to use all available LF headroom, no matter the rig.
What's the new 4-ch amp?

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Old 16th April 2020, 10:22 PM   #37
kipman725 is online now kipman725  United Kingdom
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Hi Chris, I hope that your also keeping busy, any projects?

I also have this mad subwoofer plate amp project which is actually taking all the time up at the moment. Basic idea is to store transient energy in an 10 mF capacitor bank to have an amp that can drive the largest 21" drivers to their limits while costing little money and running off a 13A plug: Energy storage in non isolated amplifier PFC stage
Its possible but I'm having to push the technology quite hard and the final cost might not be that low.

As per usual anything that meets the spec:
  • quiet (both electrically and acoustically)
  • if using a DSP it needs to have digital input and use 40 bit or above floating point processing. This is due to having very large dynamic range requirements from my system and needing to control the gain upstream from the amps and not liking to change the attenuation settings on my amps. While also disliking hiss.

I notice Lab Gruppen CX series amps are sometimes going cheap second hand. Another option would be to put the P7000s's on tops and get a new sub amp but its tricky working out what the fan noise situation is with high power amps. Still waiting for the great flood of cut price amps from venues going bust. In a dream world I would just run everything off an X8 ha.
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Old 17th April 2020, 08:04 AM   #38
chris661 is online now chris661  United Kingdom
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Hmmmm, looks like the Powersoft T-series only use 32-bit. I think that's enough, though, given the dynamic range available in a typical venue with an audience present.

Having a lot of storage for the big bass hits makes a lot of sense. FWIW, I'm looking to sell my Crown MA12000i. Quite a lot of energy storage in there - the caps are 220v 1200uF, and there's 20x of them. There's 10x 1KV 33uF at the primary side.
Needless to say, I didn't switch it on while I was poking around. The fan noise might be a problem for you, but I'm happy to dig it out and take some SPL measurements if you're interested.


Projects-wise, I spent yesterday in the back yard with the Powersoft rack, a measurement mic, REW and RePhase. Got the 10" coaxials and 2x10+HF speakers to have a flat phase response from about 600Hz upwards, and made the frequency response nice and flat, too.
Sounded exceptionally good - I actually spent a while just sitting on the grass and listening to music.

Apart from that, I'm fixing up an old McGregor mixer-amp from the 1980s. I'm nowhere near as good as you at electronics, so it's simple stuff for me. Also working on various mics - turns out I own over 100 of the things, so I'm fixing those that need work and will get them on eBay soon.

Hope you're keeping safe, and let me know on that Crown amp. I just checked, and there's the option to limit output power delivery according to the power ratings of the speakers. Might be handy.

Chris
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Old 17th April 2020, 08:12 AM   #39
edbarx is offline edbarx  Malta
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Clipping can burn speaker coils. This is what I was warned about when I purchased my two Wharfedale Titan 12" speakers. Even if the speakers are large, it all depends on the voice coils' resistance, amplifier rail voltage and power supply current capabilities. At clips the thermal dissipation in a speaker's coil is equal to V^2/R, just like with any resistor. So, with a rail of 30V and a coil resistance of 2 Ohms, this will be 30^2/2 = 450W of power. A few seconds are enough to destroy a voil coil.
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Old 17th April 2020, 08:52 AM   #40
jaddie is offline jaddie
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Originally Posted by edbarx View Post
Clipping can burn speaker coils. This is what I was warned about when I purchased my two Wharfedale Titan 12" speakers. Even if the speakers are large, it all depends on the voice coils' resistance, amplifier rail voltage and power supply current capabilities. At clips the thermal dissipation in a speaker's coil is equal to V^2/R, just like with any resistor. So, with a rail of 30V and a coil resistance of 2 Ohms, this will be 30^2/2 = 450W of power. A few seconds are enough to destroy a voil coil.
It's the RMS power only. Clipping has nothing to do with it.

Have you read the thread?
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