amp question

A good guide is to get an amp rated at about 50% higher than the speakers you will be driving. This will give you extra headroom when needed, avoid running the amp into clipping, and leave room for expansion, if you wish to add another set of speakers.

i don't get what your saying...i should get and amp that outputs more power than the speakers can handle...wouldn't that blow out the speakers?
i'm confused
DJ Borris

quote:

Originally posted by borris123:
[qb] wouldn't that blow out the speakers?
i'm confused
DJ Borris [/qb]

Not really. Clipping an amp does more to damage a speaker, than having too much poswer. Just because you have the extra power, does not mean you should throttle it out. Besides, many manufacturers specs are best case scenarios or WLS (When Lightning Strikes). Most quality brands label their amps pretty well. But as a rule of thumb it is always better to have more power then just enough, or not enough power.

50% might be a bit overkill. . . anyting around 15 -25% more power than the speaker handling will provide headroom.

If you are looking at a speaker that's 250 watts RMS 1000 watts PEAK, your best bet, would be to find an amp that can safely deliver anywhere from 350 - 600watts @8ohms. A speaker will only take as much power as it is capable of handling, as long as you keep your mixer out of the RED and you make sure you aren't clipping your amp channels you will be safe.

quote:

Originally posted by Mr. Clipuptags:
[qb] 50% might be a bit overkill. . . anyting around 15 -25% more power than the speaker handling will provide headroom.

If you are looking at a speaker that's 250 watts RMS 1000 watts PEAK, your best bet, would be to find an amp that can safely deliver anywhere from 350 - 600watts @8ohms. [/qb]

aye clips, 350 - 600watts to a 250watt speaker will still be 50% headroom wont it?? ((well actually the 600w will be around 130%))...

ok thanks a ton that helps but what exactly is clipping...i'm not too educated in speakers and amps and what works with what. so the speakers are only going take what they can eat? so i could give the speakers 15-20% more power than they can handle and it'll all be fine?
thanks a ton
DJ Borris

quote:

Originally posted by dj fobster:
[qb] [QUOTE]Originally posted by Mr. Clipuptags:
[qb] 50% might be a bit overkill. . . anyting around 15 -25% more power than the speaker handling will provide headroom.

[/qb]

Math was never my strong subject

In answer to Borris123, yes that is fine, more power/headroom is good. Clipping on the other hand is what your amp does when it is pushed beyond its electrical capabilites. Most amps have a clip LED to indicate this. If an amp is clipping it is sending raw DC on top of your audio signal to your speakers, its the RAW DC current that heats up the voice coils in your speakers. Enough clipping will eventually burn the protective enamel coating the voice coil. The coil will eventually loosen from its mount and start touching up against the housing. Once this happens the speaker travel along the coil will be rough making the output sound like somone has dropped a bucket of sand in your speaker - time to buy new speakers.

So you see why clipping is so bad. If your system is intermittently clipping, you should be ok but you'll need to keep an eye on it constantly. The best solution is no clipping at all.

ROQ out

General rule of thumb is to match the amp and speaker, apples to apples, and never allow the amp to go into serious clipping. If you stick with this your chances of damaged a speaker is extremely unlikely. You will not achieve the maximum output from your system, but you will be safe.
Using an amp that has more power than the speaker is rated at will give you headroom, but you have no way to really monitor how much power you are actually delivering to the speaker. And you can definetly toast a speaker with too much power.
It's also important to pay attention to the specs on an amp when you are changing the number of speakers you are using. The amount of power available at 8 or 4 ohms can very widely from amp to amp, and the power available is divided between the speakers on each channel.
An amp that specs out at 200w @ 8 ohms may only deliver 300w @ 4 ohms. This would decrease the amount of power to each speaker. Some amps will do better than this, but a lot of amps will do worse. It's also normal for an amp to clip easier as the load increases (impedance goes down).
Most importantly,listen! If it sounds bad or distorted, turn it down. Your ears are more sensitive than any measuring device.

ok since we're talkin about amps....would it matter much if u use an amp with a low damping factor to power just the "highs"...(damping factor being 200)....and can u relly tell a difference??...

1st, a speaker has no power...it only represents a load to an amplifier.

2nd, why so much more power than the speaker rating? Simple really, getting the most from your system. It's all about dynamics, the peaks in the music we listen to and play. Lets use this 250 watt speaker as an example. It is rated at 250 watts continous. If we use an amp rated at 250 watts continous, we don't come anywhere near the potential of the speaker. Music is not a constant, it's merely amplification over time...and this means we have dynamic range. Lets say you're playing with a average output of 40 watts and you have a 10db peak, not at all uncommon. You need on the order of 350 watts to cleanly reproduce this dynamic peak without distortion. For most decent quality 250wpc amps with even 1.5db of headroom, you can handle this peak without distortion...but you're right on the edge.

Now, lets crank it up a little more and say we're now playing at 75watts continous and another 10db peak comes along...now we need 700 watts to accurately reproduce this peak cleanly...uh oh, our little 250wpc amp just went well into clipping...ouch.

Ok, so we've easily surpassed the limits of a "matching" amp and we're not even close to running anywhere near 250 watts continous into it. So lets say we really want to get loud for a school dance so we introduce some compression so we can get that average level up and still keep the peaks under control. Even with heavy handed compression, you still need on the order of 6db for clean peaks. So now we're kicking out the door jams and giving the speaker an average level of 250 watts...the speakers rating. A mere 6db peak means you better have an amp capable of 1000watts to pull it off without clipping.

But you say wait, the speakers peak rating is only 500 watts...NONSENSE! Any speaker will usually handle 4 times the continous rating short term, or in other words, for dynamic peaks.

We clearly now see that matching apples to apples might be fine in the kitchen, but in the real world it's a very bad idea and will seriously underpower your speakers if you play them at very high levels. Will it work? Absolutely! You'll just not get anywhere near the speakers capabilities.

3rd, Personally, I recommend 1.5 to 2.5 times the speakers continous rating for full range and mid high cabinets and 1.5 to 3 times the rating for subwoofer cabinets. It's all about good clean power. I've NEVER had a cabinet failure due to overpowering, but I've seen so many drivers toasted due to underpowering it'll make your head spin.

4th and finally, for this 250watt speaker, the V-4000plus is really the perfect match powerwise...nope, it ain't apples to apples, it's simply good science.

Bob Dietrich

quote:

Originally posted by dj fobster:
[qb] ok since we're talkin about amps....would it matter much if u use an amp with a low damping factor to power just the "highs"...(damping factor being 200)....and can u relly tell a difference??... [/qb]

Damping factor is such a highly overated spec you really shouldn't read too much into it. I'm reposting this from a post at ProDJ.com:

"Slew factor is measured by driving an amplifier to its rated output at 1000Hz and increasing the frequency (at a constant input level) until the waveform shows 1% distortion. The ratio of that frequency to 20kHz is the slew factor. Any number greater than 1 effectively guarantees negligible slewing distortion in hi-fi listening. In my experience, over hundreds of amplifier tests, the slew factor is rarely less than 4 or 5 and is usually greater than 25."

"There is another specification, rarely found these days outside the world of high-end audio, that is, and always has been, of little or no practical significance to the user. I refer to damping factor, the ratio of 8 ohms (a standard loudspeaker impedance rating) to the internal source impedance of the amplifier. The effect of a low impedance (typically a small fraction of an ohm) is to damp, or surpress, certain resonances in a speaker, especially low-frequency cone resonance."

"There is no question that damping is desireable, but there is a catch. The damping resistance includes not only the source impedance of the amplifier but also the resistance of the connecting speaker cables, the speaker's crossover inductor(s), and the voice coil. So if the amplifier's source impedance is 0.01-ohm, the cable resistance is 0.1-ohm, and the speaker's internal resistance is 4 ohms (a typical value), the damping factor is not 800, or even 80, but a mere 2. Spending extra money for an amplifier with a 0.001-ohm impedance, or a cable the size of a garden hose with a 0.01-ohm resistance, will not have the slightest effect on a speaker's damping."

"The myth that extremely high damping factors are beneficial has been with us for many decades, and it was as nonsensical forty years ago, when I first became active in high fidelity, as it is today. Most such fads fades away with time, and almost all respond well to a dose of common sense. In the meantime, they are good for a chuckle or two."

This was taken from a Julian Hirsch Technical Talk article entitled "Obsolete Specifications" from 1992.

For those who might not know, Mr. Hirsch was a well respected reviewer of equipment for many, many years with Stereo Review magazine. He also opened his own testing laboratory in the '80's for conducting many facets of testing and was sought out from many manufacturers for his testing expertise, recommendations and common sense. I had the good fortune to meet Mr. Hirsch in the early '90's and was pleased that he took almost an hour of his time to talk with me about audio. I found him to be incredibly knowlegeable of course, but also with a very quick wit and unsurpassed common sense...along with the ability to translate things most audio engineers and designers can only understand into language I could easily follow. I always enjoyed reading his columns and reviews.

One thing he didn't speak about in this article, but I did personally speak with him about as well as the designer for Coda amplifiers some years later, was how damping factor actually plays a very insignificant role in controlling bass drivers due to the inherent distortion of the large drivers it takes to reproduce such frequencies. At anything over just a percent or two of distortion, any advantage gained from a very high damping factor is totally lost through this distortion. And as most is aware, as levels and SPL increases, so does distortion...and greatly!

Some have touted certain amplifiers for being far superior for driving low frequencies, when in fact, this too has been proven a myth in levels matched true double blind testing with an amplifier of very high damping factor and an amplifier of average damping factor at anything other than extremely low level (SPL) listening. For PA use, it has no discernable advantages or sonic attributes.
_________________
Bob Dietrich Technical/Gear Board Moderator ProDJ.com
Acoustic Dreams & Lightbeams
Professional Disc Jockey Entertainment

Thanks for backing me up Bob. For those that don't know Bob has forgotten more about pro audio then most of us will ever know. I was going to try to contact him to put in his .02 but he already made his way over here.

PS Bob. It's good to see you back, I hope your feeling well.

i wanna be just like Bob when i grow up..lol
infact how does dj-Bobster sound??..lol..juss kidding, great stuff Bob...(another new thing learnt for the day)

Awsome! thanks for all your help especially bob. i think i get it now.
DJ Borris