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Post by teaman on Dec 16, 2012 16:04:30 GMT -5
Hi guys, just trying to find an accurate power rating for the XPA-2. In the specs it is rated as 300wpc @ 8ohms x 2.
In the test rating it looks like it is rated as 250 wpc x 2.
I am sure someone can provide the answer. Thanks!
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Post by boomzilla on Dec 16, 2012 16:14:29 GMT -5
I don't know, but most commercial amplifier makers (and ALL receiver makers) specify power output at 1 KHz and with only one channel driven. This is an inherently dishonest way to measure, IMHO, but it IS the industry average. If Emo has done this, then that might account for the discrepancy.
Well designed amplifiers should also be able to double their wattage at half the impedance (i.e. a 100 watt amplifier @ 8 ohms should deliver 200 watts @ 4 ohms). VERY few amplifiers (and absolutely no receiver that I know of) can do this. A robust power supply is required, and few manufacturers spend the $$$ for that stout a transformer.
I notice that Emo amps (despite being better than most) don't double their wattage at half impedance either. As I recall, Nelson Pass Aleph amps can do it, but most fail.
Sorry I can't be of more use.
Boomzilla
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Post by Porscheguy on Dec 16, 2012 16:40:08 GMT -5
300wpc is correct but it matters not. There is no real world difference between 300wpc and 250wpc......
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Post by AudioHTIT on Dec 16, 2012 18:44:45 GMT -5
Often times its also a matter of correlating with the distortion spec, you get more power with higher distortion. The product page says 300 WPC @ 0.1% THD which is quite respectable. The 8 ohm test report shows 265 W @ 0.02 THD+N which correlates well and is excellent. The graph however looks like it's up to 1% at 300 W but they're not easy to read.
As mentioned, in use it's less than 1dB SPL difference, and we don't listen to test tones.
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Post by charlie7 on Dec 16, 2012 22:20:08 GMT -5
Home Theater Hi-Fi had this to say upon measuring this amp on their test bench:
"Power output at 8 ohms is very solid up to 300 watts (0.04% THD+N), before a rapid rise to clipping (1% THD+N) at 340 watts. At 4 ohms, output reached 400 watts (0.07% THD+N) before the rise to clipping at 480 watts. No question, the XPA-2 will really put out some juice."
Charlie7
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Post by Jim on Dec 16, 2012 22:24:21 GMT -5
The reason why 1% is sometimes used is because even at that level, the distortion isn't normally audible. I think even 10% isn't audible in some cases.
The Audio Precision data normally provides plenty of info...... even if the real high end is sometimes hard to read... Nice to see Home Theater Hi-fi push it and provide their bench test results.
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Post by knucklehead on Dec 16, 2012 23:09:51 GMT -5
10% distortion on a sub at 30hz isn't real audible but it certainly is at higher frequencies. The best ears in the business can detect audible distortion at 1% or so - depending on the frequency. The higher the frequency the more noticeable it becomes.
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Post by ocezam on Dec 17, 2012 10:27:00 GMT -5
According to Audioholics:
the XPA-2 exceeded its power specifications by considerable margins. Into 8 ohms it was rated to 250 watts at 1% THD , yet I measured 312 watts at 0.1% THD. Into 4 ohm loads it was rated to 500 watts at 1% THD while again my measurements exceeded this rating producing 512 watts at 0.1% THD. Make no mistake folks this is one POWERFUL amplifier and most definitely the most power for the money amplifier that has ever come across my test bench since I launched Audioholics nearly 10 years ago!
I own one. Hell of an amp!
...
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Post by teaman on Dec 21, 2012 0:09:43 GMT -5
Thank you guys. I also got a reply from Emo and they stated that the test report was done on a pre production model which has since been tweaked to up the ante a bit. I appreciate all the help!
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Post by Deleted on Dec 21, 2012 3:09:52 GMT -5
I notice that Emo amps (despite being better than most) don't double their wattage at half impedance either. As I recall, Nelson Pass Aleph amps can do it, but most fail. Boomzilla Look again Boomzilla!  Emotiva XPA-1: Power output (all channels driven):
1,000 watts RMS @ 4 ohm (0.1% THD)
500 watts RMS @ 8 ohm (0.1% THD)MSRP $999, currently on sale $849 (Note that not only does Emotiva claim 500/1000 watts into 8/4 ohms in their specifications, but they publish the actual AP test results on their website.) All quality power amps produce higher power into 4 ohms than 8 ohms (this does not apply to the amps in receivers). Most of the entry to mid level amps are up about 25-50% power into 4 ohms over the 8 ohm output. As one observes the top half of the line in some brands including Emotiva you might find a 67%-100% increase into 4 ohms versus 8 ohms. There is only one amp model in the entire Emotiva line that is less than a 50%-100% increase from 8 ohms to 4 ohms range, very impressive! Speaking of Pass Labs, their amps are very impressive in construction quality and very high prices. They seem to blindly specify all of their amps at double power output into 4 ohms. Just don't always believe what the manufacturer claims, even from amps that cost $5000-$15,000 or so. I could not find one review that confirmed the 4 ohm output of any Pass amp doubled the 8 ohm output or even close. I think they simply post all of their amps as double on the 4 ohm spec and presume we all will believe that as gospel. As far as Emotiva specs, I think occasionally they have made an unintentional mistake or two. However, it does look like the XPA-2 is one beast of an amp with very high power/channel into 4 ohms with both channels operating and at 0.1% distortion and not 1.0% distortion (clipping) as Pass Labs uses. Some folks can hear down to about 0.25-0.5% THD at certain frequencies. I think any company that uses 1.0% clipping level for their specs is trying to fool this old nut! I'll take a Pass, thank you. The 312/512 watts that Audioholics tested sounds great, but even 260/500 is fine with me. Most folks who look at the XPA-2 for driving their 8 ohm speakers would actually find if they have review test measurements that their 8 ohm speakers are usually closer to 4 ohms as a nominal rating. |
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Post by creimes on Dec 21, 2012 3:17:47 GMT -5
So my Monitor Audio RX6's are 6 ohms so does that mean an XPA-1 could push out 750 Watts, the in between of 8ohm 500 watt and 4ohm 1000 watt  ? |
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Post by garbulky on Dec 21, 2012 3:52:33 GMT -5
Creimes, this won't answer your question. But impedance also tends to dip as the power used goes up. So your 6ohms may dip down to 4 ohms during high power passages.
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Post by creimes on Dec 21, 2012 5:11:12 GMT -5
Creimes, this won't answer your question. But impedance also tends to dip as the power used goes up. So your 6ohms may dip down to 4 ohms during high power passages. Yeah I've heard of the ohm rating changing during listening just hard to understand the whole ohm into watts calculations |
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Post by willcycle on Dec 21, 2012 5:49:43 GMT -5
I think if you look at the simple math the relationship between power and impedance becomes clearer. Power (P) is defined as the product of current (I) and Voltage (V), or P=VI. For any given amplifier input signal voltage a correspondingly larger output voltage will be delivered to the speakers. The amount of current drawn by the speaker is proportional to its impedance (R). By Ohm's law V=RI or I=V/R. From this equation we can see if the impedance is halved - say from 8 to 4 Ohms - the current draw will double and substituting twice the current into our power equation above results in a doubling of power to the speaker.
For various reasons all real world amplifiers do not quiet track this perfect relationship so some manufacturers chose to rate their amplifier power lower into 8 ohms to appear as a perfect voltage source into 4 ohms.
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Post by Deleted on Dec 21, 2012 11:05:35 GMT -5
Creimes, the specified speaker impedance is only a rough estimate because the impedance changes as the frequency changes. Thus there is no set impedance figure. The spec is there only to give the buyer an approximate idea of the average or nominal impedance of the speaker so that one can choose the appropriate amplifier. The problem is that many brands of speakers tend to specify the impedance level on the high side not to scare off owners of AVR's since most of the current batch of AVR amps are not strong into 4 ohm loads. I never trust the speaker's specified impedance as gospel and I try to find an actual review that has measured and posted the nominal impedance. For example, if a review reports that an 8 ohm spec'd speaker actually dips down close to 4 ohms level and recommends an amp that is stable into 4 ohms then you should consider that an important tip. In the case of the MA Silver RX6, which is listed at 6 ohms, the test from Stereophile puts it closer to the 4.35-5 ohms range for a significant part of the frequency response range. Thus they recommend a 4 ohm rated amp. Therefore you can't say that your speakers are 6 ohms and thus can draw at least 750 watts. More correctly would be that the speakers will draw somewhere between 500 and 900 watts at rated output. You cannot pin an exact figure on it. You simply know that the XPA-1 sees the RX6 as about an 4.5 ohms speaker at part of the frequency range. Also FYI, the power rating is for continuous power which is nice for comparative evaluation of amps. However, actual music and movie tracks rarely have continuous sounds or tones and instantaneous dynamic peak sound requirements are very common. In this case the XPA-1 will exceed 1000 watts output into 4 ohms for brief periods. I hope this brief explanation of a complicated issue helps clear up this so often confusing speaker/amp impedance relationship. Below I have taken the liberty of posting the impedance graph and a quote from the Stereophile review and provided the link to the entire review. " The Silver RX6 is specified as having a voltage sensitivity of 90dB/W/m. My estimate was slightly lower, at 88dB(B)/2.83V/m, which will not be a problem. The RX6's impedance (fig.1) remained below 8 ohms over most of the audioband, with a minimum magnitude of 4.35 ohms at 160Hz; this speaker will work best with 4 ohm–rated amplifiers and receivers. Fig.1 was taken with both ports open. Closing the ports with the supplied foam bungs gave the impedance shown in fig.2; the speaker now behaves as a sealed-box design with a tuning frequency of 66Hz, which will help with optimizing the sound on boomy rooms, but there is no difference in the impedance above 100Hz."  Note from looking at this graph that the impedance (solid line) stays below 6 ohms in the 40-60Hz and 100-500Hz range. www.stereophile.com/content/monitor-audio-silver-rx6-loudspeaker-measurements |
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Post by creimes on Dec 21, 2012 13:05:41 GMT -5
Thx Chuckienut, it's such a grey area I find and makes it very hard for the average consumer especially as I know quite a bit more than my friends who are non audio enthusiasts. I guess that's why I noticed such a huge improvement when I went from my Yamaha RXV-1065 by adding my UPA-1's to power the RX6's, it was like night and day difference using "Real" power.
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Post by The Mad Norseman on Dec 22, 2012 16:38:44 GMT -5
Hi guys, just trying to find an accurate power rating for the XPA-2. In the specs it is rated as 300wpc @ 8ohms x 2. In the test rating it looks like it is rated as 250 wpc x 2. I am sure someone can provide the answer. Thanks! It was originally listed as 250w x2. Now at 300w x 2. For comparative purposes with other manufacturers amplifiers, I'd use the 250w x 2 figure as a closer approximation. |
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Post by ocezam on Dec 23, 2012 10:33:23 GMT -5
Hi guys, just trying to find an accurate power rating for the XPA-2. In the specs it is rated as 300wpc @ 8ohms x 2. In the test rating it looks like it is rated as 250 wpc x 2. I am sure someone can provide the answer. Thanks! It was originally listed as 250w x2. Now at 300w x 2. For comparative purposes with other manufacturers amplifiers, I'd use the 250w x 2 figure as a closer approximation. Why? Every 3rd party test I've seen or heard shows the XPA-2 out performs it's 300/500 watt rating. ... |
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Post by The Mad Norseman on Dec 23, 2012 17:11:48 GMT -5
It was originally listed as 250w x2. Now at 300w x 2. For comparative purposes with other manufacturers amplifiers, I'd use the 250w x 2 figure as a closer approximation. Why? Every 3rd party test I've seen or heard shows the XPA-2 out performs it's 300/500 watt rating. ... Because Emo's OWN results show about 265w x2 as thieir own measured output for this 2 channel amp. I just think people should be conservative when comparing amps... |
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