PSW article on blown speakers, underpowering

[kevinnem]

 

Can you actually point to a thread that does that? I have been a member of that forum for more than 10 years and can't seem to recall any like that.

 

 

I can .

http://srforums.prosoundweb.com/index.php/mv/msg/54287/0/0/4392/

 

I felt bad for this guy, so I pm'ed him - I wasn't goign to say what I wanted to say in public there - would be flamed accros the country.

 

I like both websites, .. but PSW seems to have a lot of a "old boys club" feel to it. They really don't like people that don't think what they think.

 

They do however have a lot more people that make a living off sound then here - a lot more pros. Ther eis a lot of "group think" and "self justification" happening on there that sucks. I also don't like the fack that being an "a$$hole" is considered a badge of honor on that forum.

[jwlussow]

Wow. $230,000 for 700 people. I really feel like my little $15,000 system is too small to use in my living room now.

 

Kevin, did you ask him to come here and ask the same question?

[The Chinese]

I gotta say, this forum is the gentlest of all the one's I go to. I am on PSW alot as well, but I'd agree that sometimes it's a bit harder on the less knowledgeable. This forum is perfect for the guy that just wants to keep it real, and has some real crackerjacks who post here.

T

[dboomer]

 

Square wave = 2x the same amplitude sine wave (maximum). Can't exceed this.

 

 

Yes ... and remember that amps with built-in clip limiting DO NOT CLIP.

 

So yes a a 200w amp has the potential to deliver 400W. With a clip limiter engaged it will not deliver that power, it will essentially be limited to the 200Ws or so it's rated at. So this is a non issue

 

Now with the limiter off ( or if you had one of the small number of power amps without limiting) it can and will deliver 400W clipped peaks ... but it is highly unlikely that it will do it for more than milliseconds at a time with the exception of catastrophic screw ups. So playing music WELL into clipping still does not significantly raise the continuous power actually delivered to the speaker. As long as the level of clipped signal does not exceed the peak rating of the speaker and it does not continue on long enough to raise the continuous power delivered to the speaker then it doesn't become an issue for the speaker's thermal power rating.

[Vinny D]

 

I can . http://srforums.prosoundweb.com/index.php/mv/msg/54287/0/0/4392/ I felt bad for this guy, so I pm'ed him - I wasn't goign to say what I wanted to say in public there - would be flamed accros the country. I like both websites, .. but PSW seems to have a lot of a "old boys club" feel to it. They really don't like people that don't think what they think. They do however have a lot more people that make a living off sound then here - a lot more pros. Ther eis a lot of "group think" and "self justification" happening on there that sucks. I also don't like the fack that being an "a$$hole" is considered a badge of honor on that forum.

 

 

 

You do realise that the topic mentioned in the above post over at PSW was in the "Classic Live Audio Board"....the section of there forum that they try hard to reserve for *Pro's*only, it is not the forum for noobs to be posting in which is clearly spelled out on there forum rules.

I have been a member at PSW for a while now and I have made exactly (2) posts in that forum because I know I don't belong there.

They get into discussions that are way over my head and most normal *weekend warrior* types.

Noob's at PSW should be posting in the *lounge* which I find to be pretty close to this forum here.

Considering where that posting was made at that forum I don't find the responses that person recieved all that bad, they were giving suggested prices for *PRO* corporate events....not a DJ doing an event at a rented VFW hall.

 

Just my opinion.

[philw44]

Here's some posts on the Blue Rooms forum about overpowering - Why to do it and how to do it safely.

 

Rob Beech @ Cnics Audio:

 

"The input signal as a constant". Providing this is true then the controls on the amp will adjust wattage. It's not "What they do" as such, just what happens is the input level remains the same. They ARE sensitivity controls, you can get the maximum power with them turned down (there is a limit on this you know, you can overload the input stage and cause clipping here, if you haven't already from your next device back up the line, so best to leave these up and control from elsewhere as is the norm).

 

Larger amps have better control over a driver or series of drivers. This is more important and indeed more noticeable on LF drivers. particularly those with larger diameter.

 

500 watt driver (in a suitable box that allows this power without over excursion.... remember that one) with a 500 watt amp. Everyone really should be happy. But to get the maximum continuous level out of the box, you push the amp to its limit. You have no headroom so your continuous level MUST be lower than this if your program material has any dynamic range at all. So with a 500 driver on a 500 watt amp, if you want dynamics ad don't want to make your amps sweat too much, your continuous level would expect to output maybe half of this. 3dB lower in theory.

 

This is all well and good, but 3dB is useful in places. Now lets look at a 1000 watt amp on the same driver. Again, providing the driver and enclosure are suitably matched and of a passable quality, there is no reason why the driver won't handle peaks of 1000watts, if it doesn't, its poor to say the least. (John, I don't own a box that won't comfortably handle twice its rms rating (and more) for some time, significantly longer than a second). If we give ourselves the same headroom of 3dB (it's comically low but its for the sake of making sense of it all) then we get a continuous rating of around and upto 500 watts (which the driver is happy with) and peaks up to 3dB louder which again both the driver and the amplifier are happy with. You've suddenly got 3dB more headroom in the system with the same number of boxes.

 

Where it DOES go wrong is if you forget that that 3dB is HEADROOM, for occasional peaks and drive the amp into this level more continuously. The amp will be more than happy but over time the voice coil will heat up and if you carry on, eventually it will fail.

 

Most drivers have a peak rating of 4 times the RMS rating, they tend to have a program rating of 2 times the rms. The program rating on the speaker says exactly this. This is what I'll handle for short peaks and it's ideal for headroom.

 

DSP can be helpful here, you can have a slow attack compressor / limiter for when the output goes above -3dB (or equivalent within your system gain structure that makes the amp travel above -3dB) it can allow short transients but throttle anything longer and larger.

 

 

DMills

This whole subject is a can of worms, because there are at least two limits that apply to a speaker and exceeding either of them will lead to damage....

 

There is a limit on RMS Current, which if exceeded for long enough will cook the voice coil.

There is a limit on excursion, which if exceeded will run the voice coil into the magnet structure (This one is frequency dependent).

 

Now the thing is that that RMS current is taken over several seconds to several minutes, and music is dynamic, further speakers are normally voltage driven devices, and the driver impedance is complex and HIGHLY variable with frequency.

 

The overall effect, is that (given you have low and highpassed at appropriate points, so excursion limits are avoided), a power amp rated for the same RMS (they mean average!) power as the speaker will with typical programme only be running at somewhere between 1/8th and 1/3rd the of the power handling of the box with occasional ms peaks to full power. If you try to turn it up, you clip the peaks which produces lots of HF and fries the tweeters.

 

Over sizing the amp by a factor of 2 will push the average much closer to the speakers rating, and while only adding 3db to the maximum level will also make you 3db less likely to clip the peaks.

 

Many modern speaker systems are actually designed to run with massive amplifiers under control of some DSP which has a model of the driver thermal and displacement behaviour, (normally together with some EQ) so that you can actually run the thing safely WAY past the point that steady state damage would occur.

A Pair of Nexo PS15 (or even PS10!) running off something like a MA5000 or Vortex 6 is not that uncommon and you only get away with it because the processor can model the speaker for both thermal and displacement limits).

 

The point is that empirical experience is that peak/average power is almost always > 2, so an amp having twice the cont. power handling of the speaker is actually quite safe (Until you run it into clipping (which is effectively limiting and raises the average power)).

This incidentally is why most modern amps will not manage continuous rated output, think about it, most of them are plugged into 16A supplies limited to ~4KW continuous, but the short term power (~a few hundred ms maybe) could be north of 6KW. There is nothing to be gained by designing an amp that can deliver the same power as a day long sine wave as it can for a hundred ms burst, because nobody needs a day long sine wave, but having a hundred ms at a time at +3 or +6 over long term is actually very useful.

 

Regards, Dan.

[RoadRanger]

Last I knew 115V x 15A = 1725w continuous (minus the efficiency of course)? Or is that Europe power they are talking about?

[Craig Vecchione]

Last I knew 115V x 15A = 1725w continuous (minus the efficiency of course)? Or is that Europe power they are talking about?

 

16 x 250 = 4000. Yep.

[IsildursBane]

 

I can . http://srforums.prosoundweb.com/index.php/mv/msg/54287/0/0/4392/ I felt bad for this guy, so I pm'ed him - I wasn't goign to say what I wanted to say in public there - would be flamed accros the country. I like both websites, .. but PSW seems to have a lot of a "old boys club" feel to it. They really don't like people that don't think what they think. They do however have a lot more people that make a living off sound then here - a lot more pros. Ther eis a lot of "group think" and "self justification" happening on there that sucks. I also don't like the fack that being an "a$$hole" is considered a badge of honor on that forum.

 

 

I read that thread, and I don't recall anything being out of place. In fact, a lot of people were very supportive and encouraging of him, given the fact that he's so young. But they were telling the truth when they said that the kid would be in way over his head for a 1500 person show and that he'd be smarter to rent than to buy.

 

You're right that there are a lot more professionals over there, and when you're working at a professional level for bigger-budget clients day-in and day-out, the standards are different than they are when you're working at a bar on the weekends. People in that thread spec'd out what their quarter-million dollar corporate rigs consisted of, and there was nothing extravagant or way over the top. To cover 1500 people like he wanted, you need a lot of equipment. His $15000 budget isn't going to cut it when road cases cost several hundred dollars each, a single wireless mic can cost $1000+, good speakers are a few thousand/box and up.

 

-Dan.

[agedhorse]

There are also a few folks over there who wear big power and blown drivers like a badge of honor. As the economy gets tighter and tighter, these guys are getting squeezed really hard and the added costs associated with accidents really affect the bottom line.

 

Everything is fine until you have an accident or momentary lapse of good judgemet.

[dboomer]

 

Rob Beech @ Cnics Audio: Where it DOES go wrong is if you forget that that 3dB is HEADROOM , for occasional peaks and drive the amp into this level more continuously. The amp will be more than happy but over time the voice coil will heat up and if you carry on, eventually it will fail.

 

 

I don't know who this is ... but I don't think he understands how things work in the real world. Full range music with only 3 db of headroom would sound like absolute crap. To me music with about only 10 dB is affected sonically.

 

But to be fair it is possible to have music with only 3 dB. It not possible to take that 3 dB music and drive the amp any further without the music ether becoming a test tone or completely and continuously clipping the system ... not just a couple of clips on peaks.

 

You cannot drive an amp to full continuous power with music and even then you'll need to be able to furnish continuous current at voltage from your power source. Big amps typically take something approaching 40 amps or more ... continuously!!! You cannot get that out of the wall here in the USA. You would have to have a pro distro and then maybe a Variac to make that happen. Even then ... "CONTINUOUS" to a lot of manufacturers really means only a couple of seconds before the breaker pops (some that you all know and love less than 1 second).

 

So even if you managed to get full continuous power out of your amp it would only be for seconds and the typical rating for a AES/EIA rated speaker is that continuous rating for 2 hours or more. So tell me how continuous power burns up a speaker?

 

Maybe if it gets hit by a bolt of lightening:thu:

 

Power amps do not burn up speakers Accidents and mistakes do and the only way to guarantee not to make them is to leave the power switch in the off position.

[agedhorse]

 

Power amps do not burn up speakers Accidents and mistakes do and the only way to guarantee not to make them is to leave the power switch in the off position.

 

 

Other ways are to learn how this stuff works, appropriate processing, conservative ratings, common sense, realistic expectations etc.