Class A 30 Watt Amps: Are they enough to drive my book shelfs?

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).

Regards,
-- Al

@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.

Best regards,
-- Al

@kijanki

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.

Best regards,
-- Al

@kijanki

Hi Kijanki,

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.

Best regards,
-- Al

@kijanki

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.

Best regards,
-- Al

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.

Best regards,
-- Al

Hi Kijanki,

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.

Best regards,
-- Al
 

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 ...

https://myhometheater.homestead.com/splcalculator.html

... 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.

Good luck. Regards,
-- Al