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Old 23rd February 2004, 04:34 AM   #11
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If it has not been mentioned already, one of the complaints of
running prosound amplifier in a home is the noise from the heatsink
fans, most people disable the fans. I not referring to fan noise entering
the signal path, just plain ole wind noise ... /hehehe
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Old 23rd February 2004, 09:08 PM   #12
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Default tweeter damage

Bink - how can you tell if you are giving the speaker too much voltage, heat or mechanical shock? This system will probably be played at a reasonable volume 80-90% of the time, so with the exception of transients, the speakers shouldn't see all that much power with a preamp, right? How does the preamp work? Say the power on the amplifier is turned all the way up. That would be 710W per side, regardless of how much the preamp is turned up, right?

As far as damaging speakers, someone here mentioned something about a square wave being the one that will damage a speaker driver. The inter-m seems to have a light on it saying when the amp is clipping. A clipped signal is a square wave right? So what would you do if the amp was clipping? Just turn it down or what? It wouldn't be fun to toast several hundred dollars of drivers (much less damage an amp!). Oh also you mentioned that the tweeters are the most likely speakers to be damaged.. How about the mids? The power dispersion between the speakers is very different too.. Is there a way to calculate what the maximum power each speaker would be receiving?

It sounds like the amount of power from the inter-m would be safe from what you're saying so far here.. Maybe that would be adequate. Rumor has it though, that these particular Selenium woofers need to be driven hard to work well.. But i definitely don't want to have to listen to music at blaringly loud volumes all the time. It's nice to have just ambient music most of the time.

I would like to hear about the results of your amplifier tests when they come out.. How many people are you using to compare the sound of these different amplifiers? It will be some time before these speakers are pieced together, so the amplifier purchase will be down the road a ways. Also, what criteria are you using to compare the various amplifiers? Clarity? Output power? Gain? etc etc.. TIA

Dave
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Old 23rd February 2004, 09:25 PM   #13
netgeek is offline netgeek  United States
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IMHO - and based on experience - so-called "Pro" amplifiers are "better" simply because of the protection mechanisms built in. They tend to protect the stupid users (myself included 8-)... from alot of sins and keep working despite much abuse. Do they sound better? You wil have to listen and decide for yourself. But, I do know that you can drag a QSC or Crown behind vehicles, drop them off reasonable heights, stomp on them, and - generally - they continue to work! These are real benefits if you happen to be trying to make a living from their use 8-).....!!!
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Old 23rd February 2004, 09:43 PM   #14
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Well, I have a Crown K1 for use with my basement PA/hi-fi speakers and a Crown K2 for use with my HT subwoofers.

I chose the Crowns because of their high efficiency, no fans, ruggedness, power and performance in the bass. But to keep the cost down, I bought them used. I understand that they are less sonically pristine at higher frequencies than some conventional AB SS amps, let alone tube amps of which I use the latter for my serious listening.

Btw, any opinions on how the Crown Class D amps stack up against Carver Pro Tripath amps sonically?
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Old 23rd February 2004, 10:30 PM   #15
Bink is offline Bink  United States
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Default Wrong assumptions and more on Amp Shootout

Quote:
Originally posted by bonsai171
Bink - how can you tell if you are giving the speaker too much voltage, heat or mechanical shock?
Well, you burn some drivers up and find out! Or you could ask the factory what their speaker driver voltage limits are. Heat is probably not going to be a problem for you, so don't worry about it. Mechanical shock is the driver bottoming out and you can hear that as blats or farts at the point of a high-power kick drum hit or movie explosion or whatever. Back off the preamp if you hear the cones bottoming out. Before that point the distortion of your speaker will be increasing so you can listen for that as well.

Quote:
This system will probably be played at a reasonable volume 80-90% of the time, so with the exception of transients, the speakers shouldn't see all that much power with a preamp, right?
Right.

Quote:
How does the preamp work? Say the power on the amplifier is turned all the way up. That would be 710W per side, regardless of how much the preamp is turned up, right?
You make a couple of false assumptions. The speakers will see ~zero watts if there is no signal going to the amplifier. Also, the big knob on the front of the amplifier is not the POWER control or the VOLUME control, it is simply a means to match the sensitivity of the amplifier's input stage to the previous unit's output stage. Even if you turn your amp's 'volume' knob down to half, you can get maximum power out of your amplifier. It would take a much larger signal from the preamp to do so, though.

At any rate, you can power your speakers with a too-large amplifier and still be fine because you will have turned something down to compensate. If it is not too loud for your ears then it is probably going to be fine for your speakers.

Quote:
As far as damaging speakers, someone here mentioned something about a square wave being the one that will damage a speaker driver. The inter-m seems to have a light on it saying when the amp is clipping. A clipped signal is a square wave right? So what would you do if the amp was clipping? Just turn it down or what?
In professional concert sound the clip lights are often engaged at every single kick drum hit. The smartest concert providers know that clipped transients add to the feeling of being loud. If you had a crazy clean and stupendously powerful concert system devoid of distortion, without that reference to the familiar concept of 'loud', the newbie band engineer will keep turning the super clean system up and up until they get the sense that it's loud. It has to have a bit of distortion or nobody will equate their auditory experience with the intense physical and emotional effort coming from the artist on stage.

Clipping the transients makes it sound loud.

Clip indicators on amps can mean you have 3dB of headroom left or they can mean there is absolutely no headroom left. You have to look at the amp specs or write to the manufacturer or test it on a bench to find out what level was selected for the indicator. Also, many pro amps have limiting or clip-softening circuits built in which means you can slam the hell out of them, make your speaker sound 'loud' and yet stay safely within speaker performance limits. HiFi home amps having some kind of soft limiting are more rare.

Clip lights at home? If you don't like the sound of clipped brief transients then turn it down and start planning for a bigger amp. If you can't hear anything wrong, then no problem. Don't do anything.

If the clip light stays mostly on you will be shopping for new speakers soon unless you turn down!

Quote:
Oh also you mentioned that the tweeters are the most likely speakers to be damaged.. How about the mids? The power dispersion between the speakers is very different too.. Is there a way to calculate what the maximum power each speaker would be receiving?
Any wave can damage any speaker driver if it is too strong. The square waves are more evil because the little square corners contain a surplus of dog-whistle bat-echo HF energy that goes far beyond the freq response of the amp or the speaker. It's this aspect of square waves that fries HF drivers first. All that HF energy is turned into heat since the HF driver can't move that fast.

If you have a passive speaker crossover feeding your three bandpasses then the whole speaker system has to be examined as a whole. The passive crossover will burn up some amplifier power as heat meaning you need a bigger amplifier.

Calculating the max per driver has been done by the mfr. Adding a crossover and putting the drivers in a box complicates things. This is not my area of skill.

Quote:
It sounds like the amount of power from the inter-m would be safe from what you're saying so far here.. Maybe that would be adequate. Rumor has it though, that these particular Selenium woofers need to be driven hard to work well.. But i definitely don't want to have to listen to music at blaringly loud volumes all the time. It's nice to have just ambient music most of the time.
Yes, if you can stand the fan noise then an amp that is rated like the Inter-M M2000 will do your speakers justice. Personally, I would go for a non-fan amp like the Crown K Series or their Studio Reference Series or similar known brands. Inter-M is a cheaper amp manufacturer whose gear is made in Korea. The model you are looking at may or may not be hiding audible problems. I hope to find out in late March.

If people say your woofers need to be driven hard then they are probably saying the woofers need more power to move the same amount. That is, they are less sensitive, possibly from having fewer wire turns in the voice coil or something like that. You don't have to make it loud to get the full benefit, you just have to have a bigger amp to get it the same volume.

Quote:
I would like to hear about the results of your amplifier tests when they come out.. How many people are you using to compare the sound of these different amplifiers? It will be some time before these speakers are pieced together, so the amplifier purchase will be down the road a ways. Also, what criteria are you using to compare the various amplifiers? Clarity? Output power? Gain? etc etc.. TIA
I'll post the Amp Shootout results on or before April 5. The starting page I'll use currenty has my GEQ Shootout results but I'll scoot the GEQ Shootout over and make room for the Amp Shootout. Here's where you'll be able to see the Amp Shootout results when they are ready:
Bink's Shootout homepage

I'll be testing for a bunch of stuff. I'll be using a collection of really high quality test gear. The Audio Precision 2722 is the best piece there. It will test for noise floor, dyamic range, CMRR, IMD, THD+N, frequency response and much more. We'll be running the amplifiers into a resistive load so that they are working hard while they are being tested. We'll also look at power consumption via fast ammeter and we'll look at problems with AC waveform artifacts. We'll chart the maximum rms and peak output power levels attained and under what kind of distortion spectra. We'll also test under 90% and maybe 80% voltage conditions to emulate sagging AC supplies. We'll run burst tones into the amps to get an idea of their transient response and rise time. and we'll look at low-impedance protection circuit responses and at soft-limiting circuit results. We'll examine what happens with clipping and with limiting prior to clipping. Finally, we'll have the audience listen to different amplifiers under load and rate them in a randomized double-blind sequence. The room seats 200. Anybody at all who is interested can RSVP me for a seat. Attendance is free but limited.

-Bink
binkster@binkster.net
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Old 24th February 2004, 03:59 AM   #16
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Any wave can damage any speaker driver if it is too strong. The square waves are more evil because the little square corners contain a surplus of dog-whistle bat-echo HF energy that goes far beyond the freq response of the amp or the speaker. It's this aspect of square waves that fries HF drivers first. All that HF energy is turned into heat since the HF driver can't move that fast.

This information above is the same claims written in that old JBL
document on how clipping can destroy speakers, etc. That was old
school thinking, but it has been proven by many that it's in slight
error. Many old school folks will not agree with the new because
that is all they've learned in the past. :hehe:

Exceeding power and mechanical limits is the main variables that
damages speakers. (fingers too) -- lol

A speaker doesn't care what waveform is playing, it just dissipates
heat. A clipped signal has the potential to drive the speaker with
2x more power than unclipped, hence the speaker blew up due to
extra power, not the waveform itself. I can listen to square waves
all day as long as I don't exceed the power or mechanical ratings of
the speaker. Music is a collection of complex waveforms, the speaker doesn't blow up when you play certain songs due to
unique waveforms produced by the music. /hehe

It's not good practice to clip your amplifiers, but many people do
clip on transients all the time. /hehe

If you analyze this statement
All that HF energy is turned into heat since the HF driver can't move that fast.

You have to wonder why a woofer doesn't blow up when
you send a 20khz tone. It's not going to be able to perform well
at this frequency - yet it doesn't blow up.... because you have
not exceeded it's power and mechanical rating.

Fun stuff.
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Old 24th February 2004, 04:35 AM   #17
Bink is offline Bink  United States
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Quote:
Originally posted by thylantyr
If you analyze this statement
All that HF energy is turned into heat since the HF driver can't move that fast.

You have to wonder why a woofer doesn't blow up when
you send a 20khz tone. It's not going to be able to perform well
at this frequency - yet it doesn't blow up.... because you have
not exceeded it's power and mechanical rating.
At home your woofer is protected from 20k by the passive crossover which routes nearly all the 20k to the tweeter. If there were no crossover, you would simply be heating the woofer up. It would take a massive amount of 20kHz to make your woofer fail from the heat. In that respect, you are correct; a nominal amount of 20kHz is within the mechanical and power rating specs of the woofer and passive crossover combo.

I'm sure you know that I was talking about square waves as produced by clipped amplifiers, not square waves that might be a part of the input signal. Totally different scenario... The difference is that the square waves in your music that are within power spec are softly rounded by the frequency limits of the amplifier. The square wave which results from pushing your input signal past the amp's abilities has HF power completely unrelated to and higher than the amplifier's own freq response. An amp that has RFI LPF protection above say, 30kHz, will be able to put out much higher freqs like 40k, 50k and more if forced into square wave clipping.

But you knew that.

Me, I was talking about a tweeter, not a woofer. The tweeter is able to take some heat build up, but not nearly as much as the woofer since the tweeter build is smaller. Blowing tweets is what happens with running continued clipped-amp square waves.

-Bink
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Old 24th February 2004, 03:43 PM   #18
sfx is offline sfx  Germany
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Again, the truth is probably somewhere in between, meaning both is true. A clipping amplifier produces squarewaves with sharp edges, and if you look at the spectrum (Fourier transformation) of a sharp edge, a lot of the energy is in the high frequency range, way above audible audio. That basically means that the tweeter gets more energy than it's supposed to get. The other thing is that an amplifier, while clipping, basically connects the output with the supply rails, without significant resistance - the transistors are fully switched through, and only the speaker limits the current.

A 100W RMS (8Ohm) Amplifier has +-40V supply rails. The RMS Wattage is calulated as follows: ( U*sqrt(2) / 2 )^2 / R_load, so in my example with 8 Ohm and 40V it's (40*0.707)^2 / 8 = 100 (W)
Now when the amp clips, it's basically DC for a short time, which means the correction factor of sqrt(2)/2 is gone. Note that this is inside the squared brackets! Basically that means the power doubles, so suddenly you have 200W DC into your speakers. Even worse, 8 Ohms means 8 Ohms impedance for AC in the audio range. The DC resistance may even be lower, again increasing the power. And, as already mentioned, if the loudspeaker can't reproduce the input frequency, then no energy can leave the system as sound, meaning it is dissipated as heat. Also, in most speakers, the tweeters have a much lower power rating. All these effects add up in the end, which has the result, that a clipping amplifier tends to destroy the tweeters first.
It is basically also possible to destroy the Woofers first (my brother tended to do that...). It's probably dependent on the speakers, and on how much you turn up the bass control.
I'm not sure how much my 'DC' argument really contributes to destroying tweeters, since they are usually coupled over a capacitor, which should keep DC away from them. It might though help to destroy woofers - suppose you crank up the bass, and clip a 20 Hz sine into a 20Hz square. That basically generates nice alternating DC pulses at 2 times full power, with 50ms duration (which is already rather long). These pulses easily travel through the woofer crossover coil, and put some stress onto the woofers.

This is my view on the whole topic. Concluding, clipping is bad. It is true, it adds to subjective loudness, but I rather prefer good sound quality, especially at home. And if I want to have the "loud" feeling, I can still use controlled compression, or better add some ground-shaking, clean bass - without clipping. And, yes, you need a lot of power for this
Comments on this are welcome
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Old 24th February 2004, 06:28 PM   #19
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Me, I was talking about a tweeter, not a woofer. The tweeter is able to take some heat build up, but not nearly as much as the woofer since the tweeter build is smaller. Blowing tweets is what happens with running continued clipped-amp square waves.

-Bink


I can operate any tweeter continous clipped-amp square waves all day without blowing them up as long as I don't exceed
thermal and mechanical ratings of the tweeter. One very simple
example is listening to music with a hand held cd player and
ordinary headphones. I can boost the headphone volume
all the way up where there is massive signal clipping, yet
my headphones do not blow up -- because I have not
exceeded thermal or mechanical ratings
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Old 24th February 2004, 07:06 PM   #20
trwh is offline trwh  United Kingdom
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Hi

A couple of posts from the LAB:

http://www.live-audio.com/messages/archive7/85620.html
http://www.live-audio.com/messages/archive7/85641.html

They both concern the same original post, unfortunately I can't seem to navigate any more levels up in the thread.

And recently in the LAB lounge:

http://srforum.prosoundweb.com/viewt...2e6d62c37ed481

I am currently choosing between the Lab.Gruppen iP450 and the Crown CE1000 to drive my Dynaudio Audience 42 speakers. The speakers are rated at 150W long term, which is equal to the output power of the iP450, while the CE1000 is rated at 450W. The iP450 is passively cooled while the CE1000 has proportional speed fans. The CE1000 is slightly cheaper in the UK.

I am currently in favour of the iP450 since its distortion at full power is much lower than the Crown; 0.08% as compared to 0.5%. Also, I am concerned that any transients from loose connections, etc may destroy my speakers if used with the CE1000. Any opinions?

Thanks,
Tim Harrison

PS - Rod Elliott's site has a good description of power compression, here: http://www.sound.westhost.com/tweeters.htm
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