Why is an XA30.5 a bad match for Revel Ultima Salon II speakers?


I actually own Revel M106 speakers right now, but some day, I intend to replace them with full range speakers like the Wilson Sophia II or Revel Salon II.

People say you need a lot of power to drive the Salons. The M106 and Salon II have almost the same sensitivity, and the XA30.5 can play the M106 louder than I prefer to listen (FYI I have a Velodyne powered sub). I guess my ears are pretty sensitive to loud volumes.

Does having all the mass of driving full range woofers into the 20hz range increase or complicate the workload on the amp significantly?

What is it about these speakers and many others that would demand a larger amp even at moderate volumes? My XA30.5 is supposed to be good for about 190W into 4 ohms, but nobody, including Pass Labs, seems to recommend an amp of that size for the Revel Salon II.

If I were to buy the Salons but had no amp budget, would I be better off trading for a more powerful but somewhat lesser quality amp than the XA30.5 such as a Parasound?
sboje

Showing 10 responses by bombaywalla

Thanks for the link, it was a nifty tool for discovering I needed to tighten up an air conditioning duct cover when my Salon 2s made it buzz at 20.1 Hz!
welcome! good to read it was useful....
good question! The specs for the XA30.5 are pretty good (not surprising since it's a Pass Labs product):

Description: Solid-state stereo power amplifier. Inputs: 1 pair unbalanced (RCA), 1 pair balanced (XLR). Outputs: 2 pairs binding posts. Rated power output: 30W into 8 ohms, 60W into 4 ohms (both 14.8dBW). Maximum output voltage: ±35V. Maximum output current: ±20A. Voltage gain: 26dB. Input sensitivity: 0.77V at 26dB gain. Frequency response: 1.5Hz–100kHz, –3dB at 1.5Hz, –2dB at 100kHz. Signal/noise: 150dB at full power. Distortion: 0.01% at 3W, 0.1% at 30W. Input impedance: 30k ohms balanced, 15k ohms unbalanced. Damping factor: 150 at 8 ohms. Slew rate: ±50V/µs. Power consumption: 238W.
Read more at http://www.stereophile.com/content/pass-labs-xa305-power-amplifier-specifications#pFvKLDoXoFb0JoE8.9...
with it's ability to output +/- 20A my calculations show that it should be able to double in power for each halving of the speaker load impedance (I expected nothing less from Pass who's been a major contributor to writing the book on how to make a class-A amp).

But, let's look at the Revel Ultima Salon II impedance & phase plots (Fig1 in the link below):
http://www.stereophile.com/content/revel-ultima-salon2-loudspeaker-measurements#fm6YgtoIdAOUp14u.97

IMO a tough impedance & phase plot - large swings in phase swinging from capacitive in the deep bass to inductive in the upper bass & lower midrange, rather low impedance (4 Ohms) in the bass. This is a hard speaker to drive for any amp. Definitely bring a high current amp to this party (which the XA30.5 seems to be).
The thing to remember is that with non-zero phase angles, the impedance is actually much lower than what is plotted. For example, at 50Hz, the phase angle is approx -20 degrees. My calculations show that the resistive part of the speaker impedance (which is the part used by the amp to create a voltage to drive the speaker cone) is actually 3.57 Ohms (not 3.8 Ohms as plotted in Fig 1). Having a reactive component to the speaker impedance exacerbates speaker impedance i.e. makes a low impedance appear lower to the amp. Thus, the amp struggles more as it has to dump current into a (further) lower impedance.
For a moment forget the brand & model of your power amp.
A 30W power amp (no matter which brand) can output 1.9A into 8 Ohms.
A 60W power amp can output 3.8A into 4 Ohms
A 120W power amp can output 7.75A into 2 Ohms.
All of the above ASSUMING the output voltage does not violate the max output voltage capability of the amp + the AC power xformer is capable of delivering this sort of current.

Next, how much power do you need to generate the SPL at your listening position?
Assume you listen at 3m (10') from the speakers.
The Ultima Salon II is 86dB/2.83V/1m from the Stereophile review.
Thus at 3m the SPL would be 86dB - 6dB - 3dB = 77dB. This includes the detrimental effects of sound absorption due to walls, furniture, drapes, etc + the positive effects of having stereo playback. Essentially these 2 effects wash out.
So, 1W gives you 77dB SPL at your 10' away listening position
10W will give you 87dB SPL at 10'
100W will give you 97dB SPL at 10'
200W will give you 100dB SPL at 10'
400W will give you 103dB SPL at 10'

103dB SPL for transients is not very loud - it's decent tho' but on the lower side. If you want your listening experience to be realistic & you want to get the feeling that the music flows effortlessly, you are going to need atleast 400W of power.
With the Ultima Salon II having an impedance in the 3 Ohms range your XA30.5 is going to operate like a 70-80W power amp. If you reference this to the above SPL table you'll see that you'll get an approx 97dB SPL max out of it. This is not going to be very loud nor realistic. It's going to feel that the amp is reigned in & that the music doesn't have that sparkle or that effortless flow.
For this speaker if one wants realistic levels of SPL for the transients then power begins to increase rapidly, as you can see. 
That's why the XA30.5 is not a suitable amp for the Revel Ultima Salon II speakers.
Hope this helps. FWIW.




So in simplest terms, I can think of the impedance curve as an inverse current requirement curve?
yes, in the simplest terms that is correct.

Thanks for helping me understand that!
welcome! glad I could help.
here is a link to the imp & phase plots for your Revel M106 stand mounts:
http://www.stereophile.com/content/revel-performa3-m106-loudspeaker-measurements#ljf3ojqamBz1KzED.97

tough imp & phase plots once again...
And, here is a synopsis of its specs:

http://www.stereophile.com/content/revel-performa3-m106-loudspeaker-specifications#usPtaevBJxpkUyqE.97

with a -3dB at 59Hz, it's easy to see why the 1812 Overture canons are lacking. Your stand mounts just don't have the capacity to reproduce such a low freq. When we say -3dB at 59Hz the SPL/volume is half (-3dB) at 59Hz. The SPL is probably back to 100% at a much higher frequency such as 90-100Hz. So, essentially, you have very bass coming from your M106 speakers & I think you wrote that you use a Velodyne sub - I can see why. 
The XA30.5 "sees" the x-over of the M106 & this x-over is providing a high impedance to the bass frequencies so the XA30.5 is probably sending very little power to those low frequencies. IOW the XA30.5 is probably not taxed much at these low freq due to the M106 design.

For the Ultima Salon II speaker, it's a different ball-game. The -3dB freq is 23Hz & 23Hz is in the deep bass region (unlike the M106). Now the XA30.5 will "see" the Ultima Salon II x-over & this x-over will demand lots of power into these low bass frequencies. I expect the XA30.5 to run much hotter temp wise as it tries to deliver power into these low frequencies & the XA30.5 will get taxed much more than it ever was with the M106.
So, yes, I expect the dynamics to worsen at 80dB SPL with the Ultima Salon II.

One more thing to remember (that many forget) - even if the Ultima Salon II are 23Hz capable, does not mean you will be able to reproduce 23Hz in your room. Based on your room dimensions you will be able to support a certain min frequency.
Here is a room modes calculator that will show you what the min freq your room can support:
http://amroc.andymel.eu/?l=19&w=17&h=9&ft=true&r60=0.6  
 
Bombaywalla,

How do you think my ARC Ref 150 SE tube amp would fare with the Ultima Salons?

My amp has 4, 8 and 16 ohm output taps. I surmise that the 4 ohm taps would work best with the Salons given its lowish impedance in the low frequencies. I seem to recall that the output impedance off the 4 ohm taps is about a half an ohm. Rated power off the 4 ohm tap is well north of 150 watts if driving a 4 ohm load.

Reason for question: I’ve had Salons on my radar screen for a while.
Bifwynne,
good to see you are still lurking around these forums - haven’t heard much from you since you installed DEQX in your system.... :-)

well, we have discussed your ARC 150W/ch amp many times in these forums. I remember that it has a pretty stiff power supply (I seem to remember 1000+ Joules) & being a tube amp it’s going to maintain its output wattage more or less.
What does "Rated power off the 4 ohm tap is well north of 150 watts if driving a 4 ohm load" mean? Is it 200W/ch into 4 Ohms?
I believe it will be much better than the XA30.5 driving the Salons as you will have atleast 2X the output wattage.....
.....but, man, I think you’ll need an even bigger amp to make the Salons sing. I’m thinking atleast 300W/ch (which is going to get expensive!).
You’ll get average sonics from your 150W/ch & like xti16 wrote it depends on how hard you want to drive the Salons. If you settle for less & drive it to lower average SPLs then you should be good but it you want more realistic listening levels, i think you’ll find that you will want a bigger amp.
I once had a speaker that could handle 105dB SPL peaks & it was really very good sonically but on rock & blues there were times I wished it could hit higher peaks.
You might be different - you might be happy with lower peak SPL???

I’ve a friend who has the original Salon speakers & drives it with a Gamut 200W/ch s.s. mono-block amp to a really, really, really good effect. He has a smaller room & they way that speaker pressurizes that room in the bass region is simply a treat. I’ve never heard anything like that in a long time....
Now the s.s. amps of that caliber are different - their output power jumps atleast 50% into lower impedances so I bet that he has something like 300W/ch or slightly more into 4 Ohms (which is where i was going with this in the sentences above).
Hope this helps. FWIW.
thanks stewart0722, initforthemusic - you guys just consolidated the point I was making. 

bifwynne,

thanks for the feedback re. your amp - 150W-165W/ch if the speaker is connected to the correct tap.

Magneplanars are planar (mix of ribbon & planar) speakers which tend to have (really) low impedances much like some of the extreme cone-driver speakers (think B&W). In such cases we are back to using high-current, high wattage s.s. amps. Or, in many other cases I’ve seen people using high-wattage class-D amps successfully. Unfortunately for these sort of lower sensitivity speakers with lower impedances & tough phase angles that’s the solution that works best.
In the end one can hook-up any speaker to any amp & you will get music but you wont be getting the best out of that particular speaker you paid handsomely for & it will keep you longing for more. What’s the point?

I know you really like your all-ARC system but ARC does make bigger i.e. higher wattage amps. What about spending the money on the next level up power amp rather than the latest preamp. A bigger amp will open your doors to many other speakers that are on your list but you can’t get because they might be substandard sonically due to your present amp’s output wattage.

Or, find another speaker with a more benign impedance & phase plot that will be in the sweet-spot of your present amp. I’m sure such a speaker exists....

So, the DEQX is sidelined due your philosophy of minimizing the signal chain? nothing wrong with DEQX - just that you are a minimalist w.r.t. audio gear, right?

[good thing you didn't spend anymore on it.... ;-)]

My amp drove the S8s (version 2) to ear splitting levels.
thanks again for the feedback bifwynne.
As you well know it’s the not ear-splitting levels we are trying to achieve. You could get that with a lesser amp too than your present ARC. What we want is loud without distortion - as you turn up the volume it should get louder but not distort. This is much harder to achieve than perceived....
sorry to read that the ARC 250W/ch is not in your cards....
seriously - you should look for a time-coherent speaker. Your quest for another speaker will end. Don’t waste your time with these wicked phase angle, crazy impedance curve speakers. They’ll leave you wanting for better sonics....FWIW.
Gotcha. I am aware of only 3 speaker brands that are purportedly time coherent; namely: Vandies; Green Mountain Audio; and Thiels. Am I missing something? What brand did you have in mind?
you're right - the 3 you cited are time-coherent.
additionally, older Quads, Sanders Sound Systems ESL Model 10 & Model  11, some older Martin Logans such as the CLX or CLZ or CLS (I'm forgetting the exact model number), Eminent Technology LFT-8 (I think this is the model number), Tannoy DMT xxx Mk2 series (I've the DMT10 Mk2 which is a flat 8 Ohms across the entire audio band & is being driven aplomb by my 1977 vintage Yamaha integrated amp. They don't have great WAF but they sound fantastic). 

@bombaywalla , your calculations make perfect sense. I was just wondering if there will be any improvement if the OP uses 2 x XA30.5 in a biamp configuration ? I am not talking about bridging the amps to use as monoblocks but actually using proper biamping, whats your take ? Will the amps perform better, with more headroom ?
Hi Pani,
nah, biamping will still not do it for him. It does relieve the stress on the amp in that instead of 1 amp providing bass to 2 speakers, 1 amp provides bass to 1 speaker only. 
But, this is a class-A amp - it always runs 100% bias & it's well-known that class-A amps have zero headroom. That's just the physics of class-A topology. 
His XA30.5 will still be a 70-80W/ch into the low impedance with a little more current. It will still limit the peak SPLs. It will surely give him music but not what the Ultima Salon 2's are capable of....