ProMedia 4.1 RMS Rating and Subwoofer Setup

[MarkM]

This is as question posted here for DanF as per his request. There is a somewhat heated discussion ongoing in the 3DSS forum, part of which involves the RMS ratings of the ProMedia 4.1. As you know there are no standards for how multimedia speaker RMS rating are measured and it's clearly different than how the hi-fi amps/subs are measured in many if not all cases.

The question is simple. Exactly what does the 400 Watts RMS rating mean. I.e. is it one channel driven, two channels driven, all channels driven? What test frequency was used and if it was the FCC frequency how does that account for the subwoofer rating? I.e was the sub and sats driven at the same time? What was the THD cutoff for the rating? Was it somewhere less than 1 percent, 1 percent or the 10 percent that many (most) multimedia speaker specifications use? You get the idea

Part two of the question is the sub setup. I have been working with the ProMedia 2.1 and 4.1 sub and I had an easy time flattening out the ProMedia 2.1 for far field frequency response testing and I can't do it for the 4.1 sub (there is a big spike in the 50-70 Hz range in my room). What's the recommended placement in a 12 x 12 room to get performance that is as neutral possible and ideally as neutral as the Promedia 2.1 subwoofer.

That's it for now. For anyone wanting to join in the discussion (but keep it sane please!) the original thread is at http://www.3dsoundsurge.com/ubb/Forum4/HTML/001700.html

Mark Muschett

3DsoundSurge

www.3dsoundsurge.com

[Dan F]

Thanks, Mark.

>>Exactly what does the 400 Watts RMS rating mean. I.e. is it one channel driven, two channels driven, all channels driven? <<

First, a point of clarification. The term "RMS Watts" has no engineering meaning; however it is usually interpreted to mean Average Watts based on RMS voltage measurements into a reference impedence. As a practical matter, the measurements are usually done into a standard resistor.

Klipsch's rating is based on this method with the following conditions:

- The system is hooked up to 120 V.

- All channels are driven simultaneously; the satellites into 3.6 ohm loads; and the sub into 1.8 ohms.

- the satellite channels get 1 kHz input signal, the sub channel gets 100 Hz.

- the output voltage on each channel is recorded at the onset of clipping.

- The resulting calculation for each channel is added together to give the final result.

If each channel is driven separately, you are likely to see voltages that allow up to 75 Watts at each satellite.

Note that these are RMS values,and for sine waves, RMS is about 1/2 of peak power ratings. If the amplifier were rated for peak values, it would be about 800 Watts.

The "onset of clipping" is around 1% THD. Not a lot more power is observed at higher distortion levels.

A few additional clarifications:

There are some speaker protection circuits in the system, which would make independent measurements a little tricky; however sine-pulse testing would confirm these levels.

Some audio gear is rated at long-term continuous as opposed to short term continuous. This component is rated for short term, which relates more directly to how audio gear is actually used (i.e., unless your program IS in fact 8 hours of sine waves, the difference between the two methods is not significant, audio-wise). The difference in hardware, between a system that would be long-term continuous (and this one) is about $50 worth of aluminum.

Since this is a switching power supply, the size of the power supply has no relation to the power output, as it might in conventional audio gear. We're just going to have to get used to our audio equipment getting lighter weight, and higher performance...

The combination of efficient power supply and optimum power design is what allows a 400 Watt amplifier in such a small space in the first place.

>>What's the recommended placement in a 12 x 12 room to get performance that is as neutral possible<<

Corner placement almost always reveals the nominal character of the subwoofer. This is where the room effects are minimal, and the gain of the three reflecting surfaces is as uniform as possible. That said, if I were trying to knock down a 70 Hz bump in a square room, I would try to find a point along the diagonal that coincided with a null, to get the smoothest possible response. Could be two feet from the corner, could be five. It can be calculated, but I'm late for work <g>.

Mark, thanks for facilitating the dialog. I'll be happy to answer any followup questions you may have.

-djf

[Swerv]

Thanks for the Information Dan. Glad you cleared all that up.

[Dan F]

No problem, Swerv. Thanks for highlighting the discussion. The more people know about audio, the better they enjoy their Klipsch speakers and the audio hobby in general. Glad to help.

-djf

[MarkM]

Thanks Dan

One quick followup for now. Is the impedance ratings of the satellie test an exact match to the combined satellites impedance? When I look at the tests that Sound and Vision using on the amplifiers it's 4 and 8 to generally match the common impedance ratings of the hi-fi speaker system, hence my question. I also wonder about the rationale of using such a low impedance on the sub channel under test. Is the sub driver impedance that low or some other more realistic real world simulation?

Thanks!

------------------

Mark Muschett

3DsoundSurge

www.3dsoundsurge.com

[Dan F]

Good questions, Mark.

In the case of the subwoofer rating, the 1.8 ohm reference impedence is derived from the minimum impedence specification (2 ohms -10%)for two four-ohm subwoofer drivers hooked in parallel.

The reference impedence of the amplifier is in fact different from the impedence typically measured on the speakers.

The speaker impedence is typically dialed in by the system designer based on a number of factors including several independent of the amplifier (such as optimum level and headroom matching of subs and sats).

In the case of the ProMedia systems, the satellite speakers themselves would probably get an independent impedence rating of around 6 ohms.

-djf

[Dr Sevrin]

So how does this relate to the real world? Wouldn't loads of 8 ohm (for the sub) and 4*6 ohm (for the sats) give a more realistic measurement, or am I missing something?

Also, is there any truth to the rumor that the 4.1 sub is different from the v.2-400 sub?

Thanks.

[SomeGuy15]

So if the satellites have an impedence rating of 6 ohms, why is a 3.6ohm load used when testing the amplifier?

Also was a purely resistive load used to test the amplifier or complex impedences (ie. speakers). As you know a purely resistive load is much easier to drive than a speaker's complex impedence.

And regarding the 1.8 ohm test... isn't this very low. Why is the minimum impedence used for testing instead of the "nominal" impedence?

Finally regarding the term "short term continuous". What does this actually mean? Yamaha regards the short term power rating as the PMPO rating.

Using simple electronics, if the sub amp was driven at maximum specs (160 watts into 2 ohms), it'll draw almost 9 amps. Can it actually be sustained for more than a couple of milliseconds? Wouldn't the amplifier IC overheat? ... This doesn't even include power to the satellites?

How much power can the amplifier supply to the Promedia sub and sats continously for say 30 minutes without extra cooling or a power supply upgrade?

[Dan F]

quote:

---

Originally posted by Dr Sevrin:

So how does this relate to the real world? Wouldn't loads of 8 ohm (for the sub) and 4*6 ohm (for the sats) give a more realistic measurement, or am I missing something?

Also, is there any truth to the rumor that the 4.1 sub is different from the v.2-400 sub?

(edited 04-30-2001).]

---

We rated this amplifier so that it relates more to separate/ hi-fi amplifiers. As you may know, home hi-fi amps are often rated with different standard loads. The impedence of a loudspeaker is a variable with frequency, so you have to pick a resistive value to go with. We picked these values because they were reasonable test cases for the amp.

The 4.1 amp is electrically identical tio the v.2-400; but has a different layout to facilitate manufacturing.

-djf

[Dan F]

quote:

---

Originally posted by SomeGuy15:

...was a purely resistive load used to test the amplifier or complex impedences (ie. speakers). As you know a purely resistive load is much easier to drive than a speaker's complex impedence...

---

We use a power resistor which can dissipate the high power indefinitely, which is a much more stable load than a loudspeaker. A speaker voice coil can rise in temperature (and therefore in impedence) over time.

Speakers do have a complex impedence, but a resistor equal to a minimum impedence value is a tougher load.

[Dan F]

quote:

---

Originally posted by SomeGuy15:

...Finally regarding the term "short term continuous". What does this actually mean? Yamaha regards the short term power rating as the PMPO rating.

Using simple electronics, if the sub amp was driven at maximum specs (160 watts into 2 ohms), it'll draw almost 9 amps. Can it actually be sustained for more than a couple of milliseconds? Wouldn't the amplifier IC overheat? ... This doesn't even include power to the satellites?

How much power can the amplifier supply to the Promedia sub and sats continously for say 30 minutes without extra cooling or a power supply upgrade?

---

Peak Music Power Output does refer to milliseconds of signal duration and doesn't really present a useable figure for audio signal reproduction. Short term continuous refers to 30 to 60 seconds worth of full power, after which some heating will take place. Most program material, as you probably know averages 10 dB below peak values, so the amplifier is running relatively cool. Then, a relatively long duration crescendo would test the upper limits for this short but meaningful time. This is the pattern that music and other program materials follow, and so the amplifier was tailored for optimum performance under those conditions.

A 30 minute rating would be somewhat less, but probably in the 250-300 Watt range.

-djf

[SomeGuy15]

A low resistive load is hard to drive but a capacitive or inductive load can cause instability (ring or oscillate) in the amplifier output. A resistive load won't cause this.

So the 400 watts is more for dynamic headroom as compared to continuous power. Cool. But back to the Promedia 4.1 unit itself, is the power supply sufficient to handle a 400 watt output from the amp to the Promedia sats and sub for around 30-60 seconds? How large are the filtering caps?

BTW, sorry for all the question. Its rare to see such a high power amplifier in such a cheap package.

[Dan F]

You're absolutely right about potential instability caused by severely reactive loads. Some speaker designers attempt to cure speaker phase problems by diving the capacitive reactance; and I think this is where most of the problems occur. Also some electrostatics have a hard reactance to them.

The amplifier is in fact tested at full output for a minimum of 30 seconds. I don't know the actual value of the filter caps, but since this is a Class D supply, it wouldn't compare to conventional power supplies (where it is important). The filter caps are not depleted because the power is created in proportion to the signal, and on demand; as opposed to a storage type supply.

-djf

[Swerv]

wow, im learning a lot. thanks guys!

On another note, i happened to have my promedias at school during a spare and we set them up in the caf/ Auditorium, They filled the whole place with Nice audio, i was surprised it could fill such a large room with that much sound. I definatly think the numbers dont lie, ive also heard some of my friends so called "500 Watt RMS" loudspeakers, and the volume they reach is very low compared to the pros without distorting, but its true that watts rms dont mean its going to sound louder, just means it can take a lot of juice. hehe

[DwK]

wow.. this is some good stuff..

I just got my Pro Media 4.1's .. returned my v2 400's and got them replaced.

I am much happier now.

I am going to attempt at some point to get these in a BIG place to see how they sound. but I can totaly believe what Swerv is saying about it filling a room.. I expect no less.

**

question :

Will it hurt to have other speakers hooked up?

Like I have 2 Fishers hooked up to my front channel

They are Impedance of 8 ohms

Imput power of MAX 100 watts.

On the rear I have 2 fisher surround

8 ohms

Imput max of 60 watts.

thats all thanks

[SomeGuy15]

quote:

---

The amplifier is in fact tested at full output for a minimum of 30 seconds. I don't know the actual value of the filter caps, but since this is a Class D supply, it wouldn't compare to conventional power supplies (where it is important). The filter caps are not depleted because the power is created in proportion to the signal, and on demand; as opposed to a storage type supply.

---

I know little about Class D amplifier designs but even if power is created in proportional to the signal, your test impedences are extremely low. Can the Promedia's power supply handle 25 amps to amplifier?

But my main question is can the Promedia power-supply and amplifier sustain 400 watts to the Promedia sats and sub for 30-60 seconds?

What are the long-term continuous power ratings into 8 ohms?

[Dan F]

quote:

---

Originally posted by DwK:

...Will it hurt to have other speakers hooked up?

Like I have 2 Fishers hooked up to my front channel

They are Impedance of 8 ohms

Imput power of MAX 100 watts.

On the rear I have 2 fisher surround

8 ohms

Imput max of 60 watts.

...

---

There's no risk in using higher impedence speakers on these amplifiers. But because the amplifiers are limited in bandwidth, you may not get much low frequency output out of your Fishers. This itself is not a problem, because the subwoofer takes over. If the Fishers and the sub match up pretty well at the crossover frequency, it will work out okay. Chances are if it sounds good to you, then the match is reasonably good.

[Dan F]

quote:

---

Originally posted by SomeGuy15:

I know little about Class D amplifier designs but even if power is created in proportional to the signal, your test impedences are extremely low. Can the Promedia's power supply handle 25 amps to amplifier?

But my main question is can the Promedia power-supply and amplifier sustain 400 watts to the Promedia sats and sub for 30-60 seconds?

What are the long-term continuous power ratings into 8 ohms?

---

Again, the amplifier is rated separately from the speakers, (mostly because it is derived from the home theater side of the business). Thus, the resistance we use to test the amplifier is not necessarily the same as the speaker impedence. Since there is no standard "power test speaker"; it is necessary to specify a test resistor. We use the lowest specified resistance because, quite simply, that's what the amp is capable of driving.

Only for the case of the speakers matching these impedences at some frequency or set of frequencies will you be able to "see" 400 Watts delivered simultaneously to the speakers (for 30-60 seconds).

25 amps? I've never done the math, but if that's what it works out to, then yes.

I don't know what the rating at 8 ohms would be. Since it is a voltage limited system, you could estimate about 200 Watts; and this would be long term continuous.

Hope this helps.

-djf

[Swerv]

sure does!

Never really knew how they tested the Watts, all very interesting. thx again..

[Dr Sevrin]

quote:

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Posted by MarkM:

Is the impedance ratings of the satellie test an exact match to the combined satellites impedance? When I look at the tests that Sound and Vision using on the amplifiers it's 4 and 8 to generally match the common impedance ratings of the hi-fi speaker system, hence my question.

---

quote:

---

Posted by Dan F:

We rated this amplifier so that it relates more to separate/ hi-fi amplifiers. As you may know, home hi-fi amps are often rated with different standard loads. The impedence of a loudspeaker is a variable with frequency, so you have to pick a resistive value to go with. We picked these values because they were reasonable test cases for the amp.

---

quote:

---

Posted by Dan F:

Again, the amplifier is rated separately from the speakers, (mostly because it is derived from the home theater side of the business). Thus, the resistance we use to test the amplifier is not necessarily the same as the speaker impedence. Since there is no standard "power test speaker"; it is necessary to specify a test resistor. We use the lowest specified resistance because, quite simply, that's what the amp is capable of driving.

---

Maybe it's just me, but something doesn't seem to be adding up here. Based on Mark's comment, it would seem that a fair comparison to "separate/ hi-fi amplifiers" would involve using nominal speaker impedances rather than the lowest specified resistance. Perhaps there is no 'standard "power test speaker"', but there are standard nominal impedances that can provide apples to apples comparisons. What this sounds like is Klipsch picked test values that would give impressive RMS numbers. This is not to downplay the quality of the pros (I love mine), but just to say that Klipsch's 400 watts RMS doesn't seem to be equivalent to Sound and Vision's 400 watts RMS.