Newbie question on wattage rating of speaker drivers

[coffee412]

Iam looking to build my fronts/centers/rears for my ht. Im going to start with the fronts but I also want to be able to use them for music too. I do have a paradigm PDR10 sub that works great so I will keep that in the HT.

My question is: Alot of designs that I looked at for HT and also music show specs on speakers around the 50 watt rms area. My thinking is: If you were to build for example a 3 way WMT system using Oh, a 100 watt reciever wouldnt you run the risk of blowing drivers? One build I saw showed drivers rms of around 50 or so and were qouted as being able to handle 300 watts after building the speakers. How is that possible?

Thanks in advance for helping a newbie.

coffee

[Geoff St. Germain]

The power handling (thermal) of the speaker is going to mostly depend on the power handling of the individual drivers, the crossover, and the number of drivers in each band.

It's somewhat complicated and I'm sure that the 300 W rating is mostly a guess. Without seeing the design it's hard to say if it could handle that much power but it is conceivable depending on the specific setup of the speaker.

[looneybomber]

Well the thing is, you're playing music/movies/animal sounds ect. You're not playing test tones. A snare drum will bang out some massive peaks, but will only last a couple dozen milliseconds. That power is then split between the woofer, mid and tweeter, so with a clean 200w spike of power, maybe only 50w or so will go to the tweeter, with the majority possibly going to the woofer. A woofer is typically more durable (thermally) than a tweeter is, so that's ok.

[coffee412]

http://www.partsexpress.com/projects...=MagnaCumLaude

The above is the link to the speaker system that I was baseing my question on.

Thank you,

coffee

[Zembonez]

I've seen and heard some Parts Express builds that didn't sound half bad! As with anything you buy, quality trumps quantity every time.

Keep in mind... Overdriving your amplification, clipping, excessive distortion are all enemies of even a well designed driver. Basing your "system" on rated power handling is an iffy proposition. The finest driver can be blown by the cheapest amplifier much quicker than a poorly designed driver would be on a high end amp... Power handling of your speaker build will be dependent on a lot of factors... drivers, enclosures, crossovers, etc.

Many manufacturers of mainstream (inexpensive) components seem to grab their highly optimistic wattage ratings from the "Marketing Fairy". If it sounds good in print, it sells their stuff. It's about as much fact as that cheese the moon was supposed to be made of.

My 2 cents worth.

[superchad]

What most times will blow speakers is too little power, sure there is overkill but in general too many watts is a good thing as the amp will drive speakers easily with plenty of "headroom", when an amp runs out of power it clips and drivers overheat or loose control......there is your blown speaker. If you are going to use an amp of lower power make sure you run an efficient design,like in the 90+ db range.

[Geoff St. Germain]

This underpowering myth seems pretty rampant on the internet. You are either overpowering a driver or you are not.

[Zembonez]

Geoff... I don't think that is a true representation.

The underpowered myth is somewhat misunderstood. Underpowered systems typically get driven well beyond their capability and the distortion and/or clipping results in excess heat... causing driver damage. These failures are not caused by excessive current delivered to the drivers. I've seen this happen time and time again with inefficient speaker systems being driven by low powered "receivers".

[Geoff St. Germain]

Can you explain how this would result in this excess heat? I contend that even though you're using a "low powered receiver" that you are still exceeding the thermal power limit of the driver. Otherwise how do you physically damage the driver?

[Zembonez]

First... I don't claim to be a scientist on the subject but I have had quite a lot of experience dealing with such matters. My opinion is only worth as much as the next guy's.

As I understand it from my tech, the distortion the driver is trying to reproduce (the square wave or clipping) is what creates excessive heat in the driver's voice coil.. eventually resulting in the burning of that coil.

I have personally sold people quality speaker systems capable of handling hundreds of clean watts that sustained voice coil damage from being overdriven by a 50 watt inexpensive receiver. Most times, this damage was covered once by the manufacturer's warranty but if the same results were duplicated the warranty was void.

On the flip side, I have run 70 watt rated Polk Audio (I believe they were A70s?) in my garage with some vintage Harmon Kardon Citation stuff and they never faltered... even after being driven at high volume for long periods of time. I used that pair of speakers in my garage / workshop for at least 5 years without damage.

[Otto]

If you severely clip a signal, and it becomes a square wave, the square wave will have high frequency components (Fourier analysis) that are perhaps not representative of the original signal. If there becomes too much high frequency content, the tweeter may receive more power than it can handle.

I haven't done all the math out (and I surely won't), but I know that the above can happen. I've blown speakers by massively underpowering them, and then trying to play them loudly (when I was a kid).

Indeed, Geoff, in this case, you are overpowering the tweeter, but it comes from underpowering the system.

[Geoff St. Germain]

It isn't from underpowering the system unless you are simply relying on what the amp's spec says the RMS power output is at 0.05% THD or whatever the manufacturer specs. With substantial amounts of THD (ie clipping) the amplifiers output can easily be double the spec'd output (ie a square wave contains twice the power of a square wave of the same amplitude). Then we have short term power to consider as well. IMO underpowering is a misnomer and some people will take it much to far. The better thing IMO is to understand that the amplifier's spec'd power (RMS @ 0.0X% THD) is not the same as the peak power and sometimes the peak power can be many times higher.

On a bass amplifier forum I frequent there's pretty much a question a week on this subject and a lot of people think that if you drive a cabinet capable of handling 1200 W with a 50 W amp that you have a substantial risk of damaging the driver. This simply isn't the case, and that's the consensus of some amplifier engineers and speaker designers on that board (ie QSC).

[Zembonez]

I think we basically agree on the fact that using an amp beyond its designed range of operation can be detrimental to driver longevity. We may not agree 100% on the cause of such destruction, but the end result is the same. we don't all have to agree... it would be boring!

I think the bass driver comparo is a little bit "apples to oranges"

Bass amps and drivers are a little different breed of animal. Bass drivers are quite heavily designed units with heavy voice coil windings and long excursion cones. They are extremely tough drivers and therefore much less likely to be damaged by ANY amp IMO.

[superchad]

Not over-powering...under controlling them....an amp that runs out of reserves clips and looses any ability to control the driver.

[Otto]

Zembonez wrote:

I think we basically agree on the fact that using an amp beyond its designed range of operation can be detrimental to driver longevity.

Agreed.

[Geoff St. Germain]

Zembonez wrote:

I think the bass driver comparo is a little bit "apples to oranges"

Bass amps and drivers are a little different breed of animal. Bass drivers are quite heavily designed units with heavy voice coil windings and long excursion cones. They are extremely tough drivers and therefore much less likely to be damaged by ANY amp IMO.

Not really. Bass drivers don't typically have very long excursion. Typically the driver's Xmax is in the range of 3 - 5 mm. Also, the voice coil windings typically aren't that heavy as you want Le to be low on such a driver as a typical driver will be used out to 2 to 5 kHz. IME they're pretty easy to damage.

I agree that the argument is a bit of semantics.

[Zembonez]

Yes. I admit to dragging it on a bit. Sorry. I shall now cease!

Cheers, man!