22 replies to this topic

[stazed]

:tony:

"That is why clipping sounds distorted. The speaker doesn't magically stop moving therefore there won't even be any reduction in cooling due to less coil movement."

Well what I've read disagrees with you on that, and I haven't seen anywhere (yet) that states "The part at the top of the wave actually contains odd order harmonics (ie, higher frequency sound). "

And lets not forget that the guy was rattle testing, so sine sweeps aren't out of the question.

I've seen the blown speaker, that's enough proof for me! That said, you present a very good argument, I'm guessing that this guy was just doing everything wrong all at once. That said the speaker was definitely not receiving enough pure power to burn the coil - this is a 600W RMS sub.

Well anyway, what's your final point then:
You can underpower a subwoofer, clip the signal it as much as you want, and the only thing that will get damaged is the amplifier?

Where I got my opinion from:
" If a relatively low powered amplifier is driven into clipping (to a full square wave for a lot of people), a relatively large portion of the time, the voltage delivered to the voice coil no longer resembles a sine wave as it would with an unclipped signal. While the amplifier's output is clipped, the voice coil is not being motivated to move as far as it should for the power that's being delivered to it and therefore is likely not being cooled sufficiently"

We're talking 50W RMS, 600W RMS subwoofer, bass testing at very high volumes, and probably for a long period of time.

Either way, I won't underpower mine nor will I clip my amp. And yeah, sorry for not agreeing with you, but the more complex calculations you've presented don't make too much sense at 3am, and I've got two sources which disagree with each other (you and the article).

If someone could just make a final adjudication I'm happy to be wrong I'd just like to know!

[Blackrazor]

I have NO idea where the whole beleif that the minor change in coil movement during clipping is going to make a massive difference to cooling came from... its an old wives tale...

I'll let Mr Dan Wiggins explain it, because he has more experience and way with words than i...

"Dan Wiggins" said:

Now, you might say, what about the increase in heat? After all, most subwoofers rely on the conversion of electrical power to acoustic power to lower the dissipation in the driver, right?

Again, wrong. Look at the parameters of a typical subwoofer. Look specifically at N0 (eta naught). This is the parameter that gives the electrical-to-acoustical power conversion efficiency of the driver.

This number, for most dynamic cone subwoofers, is less than 0.5%. In a FEW cases, it may be as high as 3%. But, for the most part, you'll see N0 well below 1%. What N0 represents is the percentage of electrical power that's transformed into acoustical power. For example, let's take a driver with an N0 of 1%. Apply 100W to the driver. Of the 100W electrical power delivered, 1%, or 1W, is converted to acoustic power (1%). The other 99%, or 99W, is converted to heat.

Look at a typical dual voice coil sub, such as Shiva. It's N0 is ~0.4%. This number is VERY comparable to other 12" DIY high-end subs out there, and represents a driver with an 88 dB SPL rating. Now, apply 300W electrical power. Wire the voice coils in parallel, in the same electrical phase. We'll get
our acoustical output, or (300 * 0.004) 1.2 acoustical Watts of power out. The other 298.8W of electrical power is dissipated as heat.

Now wire the two voice coils out of phase. What will happen? Well, we know from the above that the two magnetic fields from the voice coils cancel each other out, so there's no net cone motion. Thus our acoustic power output is zero (can't have any, if the cone doesn't move). That means ALL the power is dissipated as heat within the driver. How much? 300W. Compare this to the
situation where the two voice coils are connected in the same polarity: 298.8W. Net difference? 1.2W of dissipation.

Now, is that 1.2W extra heat going to be a problem? Most likely, no. If a driver is rated to handle 300W, chances are it's not going to have a problem with 301.2W. 400W, sure, but a 0.4% increase in power dissipated? Well, the temperature of the voice coils may raise another 0.1 degree C, but that's about it.

I'd like to see any of you try and claim 1.2w of extra heat dissipation in the coil is going to make a huge difference...

Power handling is power handling. You can feed a speaker rated at 300wRMS a sine wave, a saw wave, square wave, hell, whatever wave you want, and so long as the RMS power of the wave is less than the drivers thermal rating and the mechanical limit of the driver, then you'll be 100% tickedy boo fine...

[fuddbutter]

my old setup i had the amp going into clipping a little bit, never had a problem and sub is perfect..

[DrBoom]

Hey there guys and gals.

Thanks for all your comments on this subject. I shall print it out and have a through read on the train this afternoon. Interesting subject thougth, showing when it comes to subwoofers, enclosure plays a major role on its performance and power-rating.

Thank you all for your input in this matter. Hope you all are having a good day at work.

[Bassaholic]

The subwoofer wasn't damaged due to the shape of the signal (whether it was clipped or whatever) but simply due to too much RMS power. If you damage a speaker due to clipping it is not due to underpowering, but overpowering - the speaker was blown when it was given too much RMS power.

As based on my explination, technically you could blow a 400w RMS rated speaker with a 120w RMS amplifier without clipping the amplifier - but you would be playing sine waves continuously at full volume to do so. If you were to clip the amplifier it would put out even more power and would be even more likely to damage the speaker.

stazed said:

I've seen the blown speaker, that's enough proof for me! That said, you present a very good argument, I'm guessing that this guy was just doing everything wrong all at once. That said the speaker was definitely not receiving enough pure power to burn the coil - this is a 600W RMS sub.

The only proof that the seeing the blown speaker gives you, is simply that the speaker was blown. It doesn't prove anything about the how or why.

stazed said:

Well anyway, what's your final point then:
You can underpower a subwoofer, clip the signal it as much as you want, and the only thing that will get damaged is the amplifier?

Only provided the RMS power delivered by the amplifier does not exceed what the speaker can handle. Despite the 600w RMS rating, a 600w RMS speaker cannot handle 600w RMS continuously. This is why Cyberpunky says "test tones should be used with caution on any system regardless of power".

We all agree that he was most likely playing tones for extended periods of time and driving the amplifier hard into clipping - so the speaker was definitely recieving more than 50w RMS and the continuous power handling is no where near 600w RMS. Are things starting to make a bit more sense now?

stazed said:

Where I got my opinion from:
" If a relatively low powered amplifier is driven into clipping (to a full square wave for a lot of people), a relatively large portion of the time, the voltage delivered to the voice coil no longer resembles a sine wave as it would with an unclipped signal. While the amplifier's output is clipped, the voice coil is not being motivated to move as far as it should for the power that's being delivered to it and therefore is likely not being cooled sufficiently"

Ok I do understand where you are coming from. I used to believe that the clipped part of the wave would suddenly result in less movement and therefore less cooling, until I realized that it simply wasn't true. In fact it isn't really possible to have speaker produce a true squared off wave, except in theory. A speaker is in effect a band-pass filter..
The practical effect is that all oscillating waves consist oscillating entirely of sinewaves - squarewaves consist of the fundamental and third order harmonics. These harmonics are at higher frequencies - so although the physical displacement of the speaker is less, it also happens to be moving in and out more times a second so it really is a moot point. Its would be almost like saying playing music is more likely to damage a speaker than a low frequency sine wave, assuming the same average RMS power.

The reason why I want to clarify this is for a particular reason -

Often you see people saying things along the lines of clipping causes speaker damage, so get a 600w RMS amplifier instead of a 300w RMS amplifier to avoid clipping and therefore avoid damaging the speaker.

I'm sorry but it doesn't work like that. Sure if both amplifiers were used sensibly (so the RMS power handling of the speaker was not exceeded) then no damage would occur. But in all likelyhood, when used in the real world the 600w RMS amplifier will be more likely to damage the speaker as it has more power available...

[stazed]

Makes sense to me!

[bob]

Guess you wern't smarter than me after all

[stazed]

bob^ said:

Guess you wern't smarter than me after all

Ooooh rub it in go on, I dares ya!
I'll steal your points...!