Class D sub questions...

[greatdavide]

I was following this conversation betwen Jinjuku and RichB who know way more than me on this stuff:
http://forums.audioholics.com/forums/amps-pre-pros-receivers/89236-iq-audio-m300-monoblock-amplifier-review.html

and one of the things pointed out by the pros was that class D subs have no headroom. Which is interesting and good to know.
But subs with Class D amps still state power at peak and RMS. What does that mean then?
For instance, here is the power rating for the class D amp in paradigms sub 12:
"total output: 3,400 watts of Dynamic Peak Power; 1,700 watts (850 watts each amplifier) of RMS Sustained Power. "
How is it possible to have different peak and RMS with class D if they have no headroom? It makes sense that Class D would not have headroom but then what are these guys claiming? Is this just marketing and the subs actually handle 3.4kW? Or are they not really class D amps?

I read the amp class article and the class D article and while helpful I still feel pretty unsure on Class D amps.

Funny side note, Paradigm refers to these as "ultra-class-D" amps
Here's the product page I was looking at:
Paradigm® | Subwoofer | SUB 12 | Overview

 

[Nestor]

I was following this conversation betwen Jinjuku and RichB who know way more than me on this stuff:
http://forums.audioholics.com/forums/amps-pre-pros-receivers/89236-iq-audio-m300-monoblock-amplifier-review.html

and one of the things pointed out by the pros was that class D subs have no headroom. Which is interesting and good to know.
But subs with Class D amps still state power at peak and RMS. What does that mean then?
For instance, here is the power rating for the class D amp in paradigms sub 12:
"total output: 3,400 watts of Dynamic Peak Power; 1,700 watts (850 watts each amplifier) of RMS Sustained Power. "
How is it possible to have different peak and RMS with class D if they have no headroom? It makes sense that Class D would not have headroom but then what are these guys claiming? Is this just marketing and the subs actually handle 3.4kW? Or are they not really class D amps?

I read the amp class article and the class D article and while helpful I still feel pretty unsure on Class D amps.

Funny side note, Paradigm refers to these as "ultra-class-D" amps
Here's the product page I was looking at:
Paradigm® | Subwoofer | SUB 12 | Overview

It's a calculation. P(peak)= 2 X P (rms).

If you're looking for a powered sub, you'd be hard pressed not to find a Class D amp inside. Look at the sub's performance as a total package.

 

[lsiberian]

Class D is a type of amp not a type of sub. They are used for subs typically because they are small and easier to put in a plate amp. These days they are also taking over the market in other areas because they are very efficient.

 

[Steve81]

Since pictures are worth 1000 words:

Suffice it to say, RMS vs peak is different from discussions on short term output headroom relative to continuous output.

 

[slipperybidness]

Since pictures are worth 1000 words:

Suffice it to say, RMS vs peak is different from discussions on short term output headroom relative to continuous output.

OK. Vp = Vrms * sqaure root (2). The calculation presented previously had an error in that it omitted the "square root" part of the equation. Edit: I see that the equation previously was for RMS Power.....see my response about RMS power:

Second (and I'm probably gonna get a lot of nonsense flak for this statement), RMS Power is kind of a shady term. RMS is really only a calculation that is valid for the sin wave. When you multiply out the Voltage by Current to get the Power, the "RMS" term loses all meaning. This error has become so common that it has now generally been accepted in the electronics field as a way to represent power with the RMS subscript. It is accepted, but it is technically not correct at all.

A better way to look at power is instantaneous power and continuous power. Sorry if this adds more confusion to the original post.

Before the RMS Power argument begins, take a quick read of an excerpt from wiki:
Continuous power ratings are a staple of performance specifications for audio amplifiers and, sometimes, loudspeakers. Continuous power is sometimes referred to as RMS power, this term signifying Root mean square (RMS), a method for measuring AC voltage or current.

 

[mtrycrafts]

OK. Vp = Vrms * sqaure root (2). The calculation presented previously had an error in that it omitted the "square root" part of the equation. .

Yes but, try the experiment with this. When Vrms goes to Vp, check the current with that peak voltage and same resistance. Current goes up by 1.414. Then P= IE will be 2 X what the power was with Vrms. It works since I just went through that calc.

 

[mtrycrafts]

It's a calculation. P(peak)= 2 X P (rms).

If you're looking for a powered sub, you'd be hard pressed not to find a Class D amp inside. Look at the sub's performance as a total package.

While power indeed doubles when Vrms goes to Vp, the power terminology is not correct as per the slippery. It is one of those terminologies that stuck over time.
Not sure what would be universally relearned

 

[slipperybidness]

Yes but, try the experiment with this. When Vrms goes to Vp, check the current with that peak voltage and same resistance. Current goes up by 1.414. Then P= IE will be 2 X what the power was with Vrms. It works since I just went through that calc.

Yeah, that's part of why I came back and made the comment about your power equation. Obviously, sqrt 2x sqrt 2 = 2

 

[Nestor]

While power indeed doubles when Vrms goes to Vp, the power terminology is not correct as per the slippery. It is one of those terminologies that stuck over time.
Not sure what would be universally relearned

I was trying to provide some insight for the op without being pedantic.


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