For your 8 ohm speakers efficiency=sensitivity. Driven by 1W they will deliver 86dB sound level. 30W (30:1 ratio) should give you about 15dB more resulting in 101dB. It should cover even symphony orchestra (EU directive limits level to 85dB in order to protect musicians).
Efficiency is defined as loudness at 1W power at 1m distance in open space. Since average room is not an open space (sound is amplified by reflections) it can be assumed to be the same in whole room (unless room is very large).
No to "are they enough power for inefficient speakers?".
Yes to "is this a bad move?".
Used KEFs still get a good price, unless you absolutely love them, I would sell them, get a pair of efficient speakers (no ports), and plan on adding a small self powered sub for a bit more fullness. Not too much extra bass, just enough that you notice when you turn it off.
Efficient speakers set you up to try 30 watt tube amps, and very efficient speakers allow even lower power, and, self-powered subs take the bass load off the lower powered amps.
I have the 30.8 and I would be shocked if the 30.5 couldn’t completely drive the heck out of those KEF’s. You will never see a more power-underrated amp than these Pass Class A’s. Those speakers are 8 ohm and only dip down 4.2 ohms. The Pass amp can drive 4 ohm speakers with authority. John Atkinson’s measurements showed that it could deliver 195 watts per channel into a 4 ohm load before clipping. And overall it delivers 6dB higher in power. The sound won’t be as magical as say paired with a 90dB speaker (like what I use) but it will get the job done and then some IMO.
The first point I would make is that your speakers can’t handle more power than the XA30.5 can provide.
John Atkinson’s measurements of your speakers indicate a sensitivity of 85.5 db/2.83 volts/1 meter, close to the published spec. Based on the impedance magnitude and phase angle curves he measured I would consider it to be a 4 ohm speaker **for purposes of SPL (sound pressure level) calculations.**
It should also be noted that the specs for the speaker which are quoted in that review indicate it to be capable of generating a maximum SPL (presumably at 1 meter) of 110 db, and amplifier power of 50 to 150 watts is recommended.
As noted by Three_Easy_Payments in the post just above measurements of the XA30.5 show it to be capable of providing 195 watts into 4 ohms. It will leave class A operation at considerably lower power levels than that, of course. But I wouldn’t be concerned about that, in part because those high power levels are likely to be required, if at all, only during very brief dynamic peaks in the music, and in part because of what is said about "Leaving Class A" by Nelson Pass in this excellent paper.
For a non-planar non-line source speaker, especially a relatively small bookshelf speaker, putting aside the effects of room reflections SPL will fall off at 6 db per doubling of distance. Using the following calculator ...
... it can be seen that depending on what assumptions are made about placement and room effects the amp/speaker combination will be able to generate SPLs of between 101.7 and 107.7 db at a listening distance of 10 feet, **if** the speaker would not be overdriven and hence caused to perform in a non-linear manner (or worse) by 195 watts. However given the speaker’s limitations I referred to in the third paragraph of this post I would consider slightly more than 101.7 db at 10 feet to be a practical upper limit.
My perception is that many members here are satisfied with equipment providing maximum SPL capabilities at their listening positions that are in the mid-90s, or even less in some cases. However if one’s listening includes recordings having particularly wide dynamic range (i.e., large **differences** in volume between the loudest notes and the softest notes, such as many classical symphonic recordings), that may not be satisfactory. For example, my listening includes some classical symphonic recordings which have been engineered with minimal or no dynamic compression that can generate 105 db at my 12 foot listening distance, while being listened to at average levels of around 75 db or so.
In any event, given the limitations imposed by the speaker’s power handling capability (which is typical of many bookshelf speakers), if 102 or 103 db or so at a distance of 10 feet is not adequate for your purposes the solution would be to change speakers rather than going to a more powerful amp.
For a non-planar non-line source speaker, especially a relatively small bookshelf speaker, putting aside the effects of room reflections SPL will fall off at 6 db per doubling of distance.
Al, yes but doesn't it apply to open space or anechoic chamber only?
I found this published by Benchmark Media (Rules of Thumb)
Rule 13: In a home environment, the SPL at the listening position is about the same as the 1m response of the speaker in an anechoic chamber.
If a speaker has a measured output of 90 dB SPL at 1 meter when fed with one watt, you can expect about 90 dB SPL at your listening position when driving your speaker with one watt. Room reflections supplement the output of the speakers and compensate for the fact that you are more than 1 meter from your speakers. If you are outdoors, this rule does not apply. But, in a typical home listening room, the rule works reasonably well for a quick approximation.
I believe this to be true, since I hear pretty much constant loudness walking in my room. What do you think?
Al, yes but doesn't it apply to open space or anechoic chamber only?
Yes, as I indicated the 6 db of falloff per doubling of distance applies if the effects of room reflections are put aside, i.e., if they are not included.
I hear pretty much constant loudness walking in my room. What do you think?
I've seen a number of references over the years indicating that "room gain" typically adds something like 3 db or so to the SPL that is heard at typical distances in typical rooms, for non-planar non-line source speakers. Obviously that number will vary somewhat depending on the room, its acoustic characteristics, the dispersion characteristics of the speaker at various frequencies, and other variables.
I drive a pair of Vandersteen 5As with a Class A 30wpc amp. They are 87db but have powered subs. Should not be an issue as Class A is high current. Happy Listening.
P.S. to my previous post, regarding the Benchmark statement that was quoted by Kijanki:
Looking at it quantitatively, and choosing a listening distance of 10 feet as an example, and putting aside room effects for the moment, an SPL reduction of 6 db per doubling of distance can be calculated to result in a reduction of 9.68 db at a listening distance of 10 feet, compared to a distance of 1 meter.
A difference of 9.68 db corresponds to a difference of 9.28 times in terms of power. So at that 10 foot listening distance only 1/9.28th as much acoustic power would reach the listener’s ears via the direct path from the speaker compared to what would reach the listener’s ears at 1 meter, in the absence of room reflections.
So for room reflections to compensate for the distance-related loss of 9.68 db it would mean that 8.28 times as much acoustic power would have to be reaching the listener’s ears as a result of room reflections than would be reaching the listener’s ears via the direct path from the speakers. And that would seem to be much too large an effect to be expectable under usual conditions. Especially under conditions that are conducive to good sonics.
I just bought that same amp here. I have Sonus faber Chameleon B's, 4 ohm 87 db, and was worried about driving them. But I can tell you it drives them well beyond my listening needs and never once has left Class A. Fantastic amp.
What I suggest sinc3 I use Stand mounts sometimes is a very good Subwoofer like the SVS -sb3000 which is superb and not that expensive ,it allows your speakers ,as well as your Amplifier to run much more efficient from 70 hz or so on down the sub handles all the heavy duty current , 30 wpc in class A ,no sweat. i run a 25 watt pass Labs at 14 ftaway into the mid 90 dB range with 4 ohm 86 dB Loudspeakers with my Svs 3000 sub.
I believe John Atkinson (Stereophile) measured the Pass Labs 25 watt amp at 80+ watts in to 8 ohms, and 130 watts in to 4 ohms.. The amp in question should have no problem with the KEFs.
For those folks with experience listening to 30watt class A amps, how would the Pass Labs XA 30.5 compare sonically to the pass labs 150.5 A/B amp? Other than more power & better bass control (with the 150.5) is there a unique listening experience (with pure class A) worth chasing?
Since it looks like nobody asked this question, why would you want to invest in a class A amp to drive KEF bookshelf speakers? Dynaudio or the equivalent maybe, but KEF? Better off to invest in better speakers and live with a class AB amp; much better bang for your buck.
@almarg Al, remember that there are two speakers, not one (+3dB). Room gain adds +3dB (or more) and I'm sitting at about 3m from the speakers equal to loss of a little more than 6dB (9.5dB?). Rule of thumb has -3.5dB error here, but works perfectly for 2m listening distance. Almost constant loudness in my room is likely because of listening angle to the speaker. When I get close to one of them the other is at an angle and when I get closer to front wall between the speakers both are at angle.
Yes, I of course realize that there are two speakers. But for a listener at a centered position that is equidistant from the two speakers the calculation I provided, involving the difference in SPL at 10 feet vs. 1 meter, applies just as well. Obviously it is not usually possible to be 1 meter in front of both speakers at the same time, but if we hypothetically assume that to be possible (so that we can use the speaker’s specified or measured sensitivity, which of course is based on 1 meter) my calculation of the **difference** in SPL between 1 meter and 10 feet is not affected. All that would be affected is the absolute value of the SPL at the two distances, which the second speaker would cause to increase by the same amount at both distances.
In other words, the second speaker does not compensate for 3 db of the distance-related loss. It just increases the reference point to which that loss applies.
I’m sitting at about 3m from the speakers equal to loss of a little more than 6dB (9.5dB?). Rule of thumb has -3.5dB error here, but works perfectly for 2m listening distance.
Here is the calculation of the 9.68 db difference in SPL that I stated occurs between listening distances of 1 meter and 10 feet, putting aside the effects of room reflections:
If we denote the two distances as D1 and D2 a loss of 6 db per doubling of distance corresponds to a loss of 20 x log(D1/D2).
1 meter is 39.37 inches; 10 feet is 120 inches.
20 x log(120/39.37) = 9.68 db
For your 3 meter listening distance the result would be:
20 x log(3/1) = 9.54 db
Factoring in 3 db or so of room gain brings that loss close to the 6 db figure you cited. Although that amounts to a 6 db error in Benchmark’s rule of thumb guideline, since their guideline asserts that essentially no loss would result.
I have the 30.8 and I would be shocked if the 30.5 couldn’t completely drive the heck out of those KEF’s.
Yes but the amp will be pushed close to it’s limit to "drive the heck out of them", and no amp I know sounds it’s best when near it’s limit. Like I said the 30.5 will be enough, but if you want to go big, then you will hear the strain when compared to say the 60.5
@almarg Al, I agree, but shouldn't second speaker make a difference (both at 10' distance)? Two speakers vs. one should add +3dB making overall error 3.54dB (no error at 2m listening distance)
Two speakers vs. one will add 3 db, but both speakers will have the same distance-related loss, so as I indicated the second speaker will not compensate for the distance-related loss. It will just make the sound 3 db louder at any given distance.
If 2.83 volts is applied to one speaker rated at 90 db/2.83 volts/1 meter, neglecting room gain the SPL at 3 meters will be 90 db minus 9.54 db.
If 2.83 volts is applied to two of the same speakers, neglecting room gain the SPL at 3 meters will be 93 db minus 9.54 db.
In the second case the SPL at 3 meters will be 3 db louder than in the first case. But the distance-related loss in both cases is 9.54 db. Room gain will compensate for around 3 db of that loss, resulting in a loss of about 6.54 db in both cases. The 6.54 db subtracts from 90 db in the first case, and subtracts from 93 db in the second case. While the Benchmark statement implies that 0 db should be subtracted from 90 db in the first case, and 0 db should be subtracted from 93 db in the second case.
@almarg Yes, loss will be 6.54dB, but from rated sensitivity of one speaker it will be only 3.54dB. For 2m listening distance, that they likely assumed as an average, there will be no error. Sound level at listening position will be the same as rated sensitivity.
In case on hand each speaker sensitivity is 86dB. Two of them playing at the same time add +3dB, room adds +3dB and distance of 2m causes 6dB drop resulting in 86dB sound level at listening position when 2.83V is applied to both speakers. Am I missing something?
OK. I see what you are saying. What it comes down to is that we have been interpreting the Benchmark statement differently. And both interpretations are reasonable, IMO, as long as each interpretation is properly understood and applied.
You are interpreting their statement such that:
In case on hand each speaker sensitivity is 86dB. Two of them playing at the same time add +3dB, room adds +3dB and distance of 2m causes 6dB drop resulting in 86dB sound level at listening position when 2.83V is applied to both speakers.
I agree with this statement, but I have been interpreting Benchmark’s statement differently, with my interpretation having been indicated at the end of my previous post. As I say, though, I think neither interpretation of Benchmark’s statement (yours and mine) is unreasonable.
In any event, though, the 101.7 db and 107.7 db numbers I originally stated in my response to the OP do in fact reflect the presence of two speakers.
In my own personal experience, "enough" never does the trick with amps. Having the most quality power has always given me the most satisfaction - maybe it's the extra ability of the amp, extra headroom...or maybe it's all just in my head.
I use a Class A amp that outputs 40 watts but will drive just about anything - they were driving 1 ohm Scintillas when I bought them, and one of the currently drives a pair of speakers that are 86 dB efficient.
I don't know those Pass amps but I do know their reputation and would bet that you would have no trouble driving your speakers with them.
tubes, transistors, transformers, capacitors, ... are all relative to the rated amount of power within certain specs. All are sized to achieve a price point. Other components are designed to deal with ... heat. If an amp truly could produce more power within specs, certainly the manufacturer would publish that capacity. It ain't so. Measured distortion prevents a larger rating.
reserve power not only for instantaneous bursts, move a low efficiency woofer forward, of low and enough power to control the woofer, and, have enough reserve to make repeated instantaneous bursts. Many subs have servo control to assist with the tight control to avoid distortion.
volume controls, preamp components, pushed to high output is not sensible to me. A lifetime of too much heat from high output is also not sensible to me. pushing tubes hard, why?
Play Mickey Hart,, even at mid volume, serious amounts of power is repeatedly needed, serious amounts of control of the woofer is repeatedly needed.
More than enough driving my Harbeth 7es-3 (86 db 1w/1m) with my XA30.5 . As previous post just mentioned and I forgot--the amp goes into A/B at a certain point delivering more than 30 watts and I dont generally need to go past that marker on the dial which shows when leaving hard core class A.
I use a Pass Labs X150.5 on Vandersteen Model 5s. The meter has never moved out of class A. Its sounds plenty loud for me. Dance club loud, no. But plenty loud for home use.
In real life a 3 dB gain is not much (and you need to double the power to get it). 3 dBs is generally regarded as the minimum change most people need to hear a difference when playing music. Play around with an AVR with the volume calibrated in dBs. Go up and down 1 db on the dial. I doubt you will hear a difference. And when you are listening and someone asks you to "turn it up just a little" if you turn it up 1 dB they will look at you funny.
People are way too hung up on watts. In most cases it is just a marketing ploy. Why would you buy a 100 amp receiver when you can get a 160 amp receiver? But what they don’t tell you is you will never hear that difference. Doing the calculation those 60 extra watts will only give you an extra 2 dBs when playing both amps at max volume (just before clipping). If you can hear that difference you have better ears than I do.
An amp having an ample power supply and good reserves to power the peaks are way more important than published watts. From what I hear the OPs amp has a great power supply and reserves. I would prefer it to a 100 watt amp with an undersized power supply and cheap power caps. He should be fine.
I could be wrong, but I thought the Pass Labs XA 30.5 was a true Class-A amplifier, and true Class-A amplifiers don't have headroom.
elliottbnewcombjr179 posts11-08-2019 12:05pmtubes,
transistors, transformers, capacitors, ... are all relative to the
rated amount of power within certain specs. All are sized to achieve a
price point. Other components are designed to deal with ... heat. If an
amp truly could produce more power within specs, certainly the
manufacturer would publish that capacity. It ain't so. Measured
distortion prevents a larger rating.
@atdavid, the Pass XA30.5, as well as the XA25 which I use, and I believe most or all other Pass XA amps, operate in class A up to and somewhat beyond their specified power ratings. (I say "somewhat beyond" in part because those ratings are specified very conservatively in terms of distortion percentages). But at higher power levels these amps transition to class AB, resulting in much higher power capabilities than are specified, as illustrated by the reference Twoleftears provided above.
To provide an additional example, my XA25 is specified as having capabilities of 25 watts into 8 ohms and 50 watts into 4 ohms. Yet Stereophile measured 80 and 130 watts per channel into those impedances, respectively, at 1% THD + noise.
Also, the paper by Nelson Pass on "Leaving Class A" that I referenced earlier in this thread may be of interest.
Unfortunately when I was looking at them, most articles described them as "pure" Class-A, not high bias AB like they really are. Thank you for clarifying.
Will the amp run so hot that it generally becomes impractical for this space?
Since the amp will be operating in class A the great majority of the time the amount of heat it puts into the room will correspond to its 200 watt specified power consumption (assuming that spec is accurate) minus the amount of power delivered to the speakers at any given time. And since most of the power delivered to the speakers will be converted into heat by the speakers anyway, as a good approximation you can expect that the amount of heat put into the room will be similar to the heat put into the room by any device which converts the great majority of its power consumption into heat and consumes 200 watts. Such as two table lamps each using a 100 watt low efficiency incandescent light bulb (the kind that have now been mostly phased out).
My XA30.5 is in separate 10'x12'x8' room from my main system. I didn't have room for it in my media cabinet, and my wife didn't want it on the floor.I can keep my hands on the fins of the 30.5 comfortably for as long as I like.The fins are warm, but not hot to the point you have to worry about children touching it (like tubes). It's one of the cooler running class A amps out there.I get more noticeable heat generation when my Dynaco ST-70 amp is running for a few hours in that same room. That said, I live in the NY snow belt and not Arizona. Al's reasoning above is excellent. If you can handle a couple 100 watt bulbs firing away in that room without needing to crank the AC, you should be good.
If you want a similar XA30.5 sound without the class A design, the Jeff Rowland Model 2 is pretty close in sound. More delicate and finer grained. Zero heat due to it's AB design. Kind of hard to find these days though.
Does anyone have any idea of how this amp might sound at medium volume levels in comparison to a Modwright KWA 150? ( which I currently own ) I would assume a finer grain and less texture?
Does anyone have any idea of how this amp might sound at medium volume levels in comparison to a Modwright KWA 150
Never heard one, but should be ok grunt wise to handle the low loading between 70hz and 150hz for the bass, all depends on the rest of the design to how it's going to sound in the mids and highs.
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