Emo XPA-100

[Hobbit]

If you read the follow up posts, you may have the answer. .

LOL! There were only a couple of follow ups when I started writing.... This is what happens when I try and post while at work.

BTW, are we talking RMS?

 

[Steve81]

With respect to the XPA-100 and 200, one thing I will say is that I'm less than thrilled that they're rating output into <1% distortion as opposed to the usual 0.1% or less. Looking at the Audio Precision tests they ran on the XPA-200 for example, I'd probably rate it as a 100W @ 8 ohms / 200W @ 4 ohms amplifier with under 0.1% THD+N, which is still nothing to sneeze at by any means.

 

[PENG]

LOL! There were only a couple of follow ups when I started writing.... This is what happens when I try and post while at work.

BTW, are we talking RMS?

Purely mathematically speaking, RMS power is a misnomer, but yes, the term seem to have been widely accepted though some people still insist to talk in terms of average power (caution:Average Voltage or current does not equal their RMS value). I do think the term average power is more technically correct than the so call RMS power.

 

[Hobbit]

Purely mathematically speaking, RMS power is a misnomer, but yes, the term seem to have been widely accepted though some people still insist to talk in terms of average power (caution:Average Voltage or current does not equal their RMS value). I do think the term average power is more technically correct than the so call RMS power.

I
Lol! This time I was being funny. I am an EE... by day anyway!

 

[slipperybidness]

Purely mathematically speaking, RMS power is a misnomer, but yes, the term seem to have been widely accepted though some people still insist to talk in terms of average power (caution:Average Voltage or current does not equal their RMS value). I do think the term average power is more technically correct than the so call RMS power.

You are 100% correct. I prof actually made a point of this a couple days ago in my AC circuit analysis class.

 

[CraigV]

OK, I have some questions for all you amp guru’s;

1. Am I right in saying that the ohms drop when there is more demand put on the amp, and usually in the lower frequencies?
2. Is there a point when the average setup will have enough watts to adequately power the speakers, no matter the volume & program material?
3. Do we enter the realm of amperage/current over wattage at a certain point?

The reasons I ask is because I’m thinking for some people, even in a two channel setup, they might enlist the use of a subwoofer. Indeed in home theater setups, subs are common. Depending on where you cross over the main/surround speakers, do you also off-load some of the power requirements from the main amplifier to the speakers (assuming of course you have a good sub/amp combo)?

 

[Steve81]

I'm not an amp guru by any means, but I'll see if I can take a crack at your questions:

Am I right in saying that the ohms drop when there is more demand put on the amp, and usually in the lower frequencies?

A drop in impedance (ohms) will demand more current from an amplifier. This holds true regardless of frequency. However, a dip around 100Hz is more of a problem than 20kHz simply due to the fact that there's not much real world content that stresses 20kHz, whereas 100Hz is in pretty active territory.

Is there a point when the average setup will have enough watts to adequately power the speakers, no matter the volume & program material?

I'll use myself as an example: I've got a set of speakers that are likely to be at least 95dB sensitive w/ 2.83V at 1m, and I've got them hooked up to an Emotiva XPA-200. I also use bass management to cross them over at 80Hz, and I sit a tad under 9 feet away from them. I've been informed by the manufacturer that these speakers have a minimum impedance of 4 ohms. With these variables accounted for, I reckon that I've got enough power to drive my speakers to any volume I'd care for. However, I still set a maximum master volume level in my receiver's setup, both for the protection of my own ears and for the protection of my equipment.

Do we enter the realm of amperage/current over wattage at a certain point?

Not exactly given the relationship between watts and amperage. However, a receiver's watt output into an 8 ohm resistive load doesn't mean much if your speakers present a 4 ohm reactive load.

The reasons I ask is because I’m thinking for some people, even in a two channel setup, they might enlist the use of a subwoofer...do you also off-load some of the power requirements from the main amplifier to the speakers (assuming of course you have a good sub/amp combo)?

Yes, a subwoofer can be quite useful in a two channel setup. How much is offloaded of course depends on the material itself.

 

[Irvrobinson]

OK, I have some questions for all you amp guru’s;

1. Am I right in saying that the ohms drop when there is more demand put on the amp, and usually in the lower frequencies?

You have this backwards. When impedance drops, maintaining the same voltage level takes more current, and that increases the output demand on the amplifier. Your statement implies that when you turn up the volume control on the pre-amp that impedance drops, which is not the case. Low frequencies do tend to represent more amplifier power demand than other parts of the audio spectrum in the balance of most music and movies.

2. there a point when the average setup will have enough watts to adequately power the speakers, no matter the volume & program material?

I'm not sure what "average setup" means.

3. we enter the realm of amperage/current over wattage at a certain point?
The reasons I ask is because I’m thinking for some people, even in a two channel setup, they might enlist the use of a subwoofer. Indeed in home theater setups, subs are common. Depending on where you cross over the main/surround speakers, do you also off-load some of the power requirements from the main amplifier to the speakers (assuming of course you have a good sub/amp combo)?

I think you mean, does high current capability at low impedance levels become more important than high watts at 8 ohm loads? Or something like that? It depends on the speakers. If you have speakers that demonstrate low impedance characteristics at important points in the audio spectrum, yes, high current can be more important than high watts at 8 ohms. And, yes, using a sub with a high-pass filter for the mains is a well-known strategy for reducing power-requirements of the main speakers.

 

[CraigV]

What I'm asking is as demand on the amp increases and the ohm level drops, is amperage more important than wattage?

 

[Grador]

What I'm asking is as demand on the amp increases and the ohm level drops, is amperage more important than wattage?

You cannot really say "demand on the amplifier increases AND the ohm level drops" as those are two separate scenarios you are lumping in together. Demand increases when you turn up the volume, but that won't effect impedance. Impedance is a modifier of demand, lower impedance requiring more current to achieve the same wattage than a higher impedance load.

Furthermore a comparison of amperage to wattage is never applicable. Amperage can be a limiting factor in wattage [along with voltage], but as it is a component of amperage (amps x volts= watts) you cannot really say it's more or less important.

 

[Irvrobinson]

lower impedance requiring more current to achieve the same wattage than a higher impedance load.

This isn't correct. Lower impedance requires more current, hence more watts, to achieve the same voltage level. This is why as you halve impedance it takes twice the power (in watts) to maintain a similar voltage. Think about volts like water pressure and impedance like water pipe diameter. As the diameter increases you need to increase the amount of water flowing to maintain the same water pressure.

 

[Grador]

This isn't correct. Lower impedance requires more current, hence more watts, to achieve the same voltage level. This is why as you halve impedance it takes twice the power (in watts) to maintain a similar voltage. Think about volts like water pressure and impedance like water pipe diameter. As the diameter increases you need to increase the amount of water flowing to maintain the same water pressure.

Everything both of us said is true, the only difference is if you're looking at maintaining wattage or voltage.

Edit: Or I think the difference in view here is one of supply vs demand. I'm looking at it on the demand said [asking for more current to keep the wattage] while you're looking at it supply side [requiring more capacity to maintain voltage].

 

[Irvrobinson]

Everything both of us said is true, the only difference is if you're looking at maintaining wattage or voltage.

Edit: Or I think the difference in view here is one of supply vs demand. I'm looking at it on the demand said [asking for more current to keep the wattage] while you're looking at it supply side [requiring more capacity to maintain voltage].

No, you're being too kind. For some reason I can't explain at the moment, I misinterpreted your post and said you were incorrect when you were actually correct. If watts are held constant and impedance drops, then voltage drops, so amps increase. Yes, what I posted is also correct, but it wasn't relevant. Sorry for the confusion.

 

[PENG]

Everything both of us said is true, the only difference is if you're looking at maintaining wattage or voltage.

Edit: Or I think the difference in view here is one of supply vs demand. I'm looking at it on the demand said [asking for more current to keep the wattage] while you're looking at it supply side [requiring more capacity to maintain voltage].

Mathematically both correct, practially, the voltage one may be easier to understand for some.
It is not hard for us sometimes to get fixated on one side of the equation. I can see that happening (just mildly though) in even notable loudspeaker designers/engineers as evidenced in Gene's new article when they commented on the 2.83V vs 1W thing.

I just want to add the obvious (to some of us) that there is a limit to what the power supply transformer can take, in terms of keeping up with the higher current demand resulted from the lower impedance without failing. Same applies the amplifier's electronic components such as the output devices.

 

[CraigV]

OK, I’m still trying to wrap my head around this. So, when I see the specs for an amp, and they read “200 watts per channel with all channels driven into an 8 ohm load” does that mean that the amp is putting out those 200 watts all the time, with the primary limiting factor being the volume control? The more I turn the volume “down” is the more resistance I’m putting in the path between the amp and the speaker? Then as I turn the volume up, I’m lowering the resistance, and when a particularly loud sound comes through, like a gun shot or explosion, the signal goes to the amp, it amplifies to the corresponding volume level, pushes that signal out to the speaker, which presents a load to the amp depending on the volume and frequency of the sound?

 

[Steve81]

So, when I see the specs for an amp, and they read “200 watts per channel with all channels driven into an 8 ohm load” does that mean that the amp is putting out those 200 watts all the time, with the primary limiting factor being the volume control?

Not exactly; simply put: an amplifier will impart a specific level of voltage gain (32dB in the case of the XPA-100) to the input signal it receives from a pre/pro. The input signal is a combination of whatever the source (say a CD player) sends (which is in and of itself variable) combined with the attenuation provided by the volume control of the pre/pro. As such, the actual voltage (and consequently power) an amplifier is putting out is not fixed.

The more I turn the volume “down” is the more resistance I’m putting in the path between the amp and the speaker?

No; the impedance of a loudspeaker is independent of the amplifier. This is the impedance curve of the NHT Classic 3 as one example: