What Speakers SOUND GREAT with Moderate-Powered Tube Amps (27 -85 WPC)? SET or Push -Pull is fine! What are those Speaker Designers doing differently?

caesar

Well-Known Member
May 30, 2010
4,290
767
1,698
Mid-powered tube amps - 27-85 WPC - seem to be the red-headed bastard children in this hobby.

The popular fare (such as Wilson, Magico, Sonus Faber, YG, etc.,) really come fully alive with the big Boulders, Soulutions, CH Precisions, etc. (I am NOT talking about soft, syrupy, anemic, fake-warmish, less-resolving sound of pairing moderately -powered amps with popular, hard-to-drive box speakers).

And, of course, many of the hard-core horn guys are after 10 wpc or less SETs.

The only speakers I can think of that sound great with mid-powered tube amps off the top of my head are Scaena with ARC Ref 75, Nola with 85 wpc VAC integrated, and possibly Alsyvox can sound good with 50 wpc or higher.

What other speakers have you heard that sound great with mid-powered tube amplifiers, SET or PP?

What design choices did their creators make to make for their speakers to work great with moderately powered amps?

(Interestingly, CJ seems to have a new amp out with 27 wpc, but I can't think of too many speakers it would work well with.)
 

Al M.

VIP/Donor
Sep 10, 2013
8,682
4,470
963
Greater Boston
That's easy, my speakers: Reference 3A Reflector.

They are 92 dB sensitive and feature a crossover-less design. The mid-woofer is directly coupled to the amp, the tweeter is coupled to the amp simply via a capacitor. I have 15 wpc push-pull triode monoblocks, and they could drive the speakers very dynamically, to maybe 85-90 % of their enormous dynamic potential as judged by my current amp.

Now I drive them with a tube amp that has 100 wpc into the speaker impedance of 8 Ohm (130 wpc into 4 Ohm), and that is complete overkill, as I like it. I'm sure 85 wpc as in your upper limit would be complete overkill for these speakers as well.

As to be expected, these speakers sound just as much alive at low volume levels as at high ones.
 
  • Like
Reactions: Andrew S.

Duke LeJeune

[Industry Expert]/Member Sponsor
Jul 22, 2013
747
1,200
435
Princeton, Texas
What design choices did their creators make to make for their speakers to work... with moderately powered amps?

In my case I was an Atma-Sphere dealer with ideas about speaker design. Since I love what Atma-Sphere amps can do it made sense to build speakers which would work well with them, in particular the 30-watt S-30 and 60-watt M-60.

Among the design choices were taking steps to keep the impedance curve generally fairly high and smooth, which results in a speaker that works well with a wide variety of amps.

The efficiency needed to be fairly high, but not super high. Since there is a tradeoff relationship between bass extension and efficiency (for a given box size), this made it possible to still get good bass extension without needing a huge enclosure.

The interaction between a low-damping-factor tube amp and a speaker presents both challenge and opportunity in the bass region. (The low damping factor shows up as in increase in woofer's electrical Q.) The challenge is to not make the speaker a one-trick pony that needs a particular amplifier type, and the opportunity is that the amplifier's low damping factor can translate into a worthwhile increase in bass extension. The solution I use includes adjustable port tuning, which also happens to make the speaker more adaptable to different room acoustic situations.

The increased bass extension with the enclosure sized and tuned for the low-damping-factor amp is about as close to a "free lunch" as it gets in speaker design, and when tuned higher the speaker still works normally with a solid-state amp.
 
Last edited:

spiritofmusic

Well-Known Member
Jun 13, 2013
14,604
5,413
1,278
E. England
Um Keith, you've missed out a brand you know quite well...
 
  • Haha
Reactions: bonzo75

steve59

Well-Known Member
Jan 7, 2018
356
110
150
persona 7f is 92 db sensitive and benefits from a little mid range tube warmth, 30 watts is enough volume for rock.
 

VerdantAudio

VIP/Donor
Jul 2, 2020
51
60
350
46
My experience is your looking for relatively flat impedance and either the speakers is a limited range (monitor??) or the speaker is relatively efficient. Take my speakers, they have a minimum impedance of 7.3ohms and although not efficient (84 or 85dB depending on model) they are limited range starting to roll off around 60hz.

Thus I would say my speakers (Verdant Audio) do quite well in this range. They were designed and voiced using 45w 845 based amps and can be driven at reference levels without issue. Other brands that I am certain do well:

Scansonic and Raidho, particularly their speakers that aren't full range like their monitors (X/XT, C and TD) and X series and other small floor standers.
Zu and Tekton do very well as they are efficient
Vivids particularly the Kayas, Ovals (discontinued) or Giya G4s are going to be fine in a medium sized room
Joseph Audio Pulsar - even as inefficient as it is (83.5dB) it is a very easy to drive speaker and does well with a 50-70w amp.

I am sure there are countless others. These are just ones I have direct experience with or am very familiar with.
 

Kingrex

Well-Known Member
Feb 3, 2019
2,802
2,310
350
PAP Trio 15 horn and any Daedalus.
 
  • Like
Reactions: morricab

bonzo75

Member Sponsor
Feb 26, 2014
22,442
13,471
2,710
London
Mid-powered tube amps - 27-85 WPC - seem to be the red-headed bastard children in this hobby.

The popular fare (such as Wilson, Magico, Sonus Faber, YG, etc.,) really come fully alive with the big Boulders, Soulutions, CH Precisions, etc. (I am NOT talking about soft, syrupy, anemic, fake-warmish, less-resolving sound of pairing moderately -powered amps with popular, hard-to-drive box speakers).

And, of course, many of the hard-core horn guys are after 10 wpc or less SETs.

The only speakers I can think of that sound great with mid-powered tube amps off the top of my head are Scaena with ARC Ref 75, Nola with 85 wpc VAC integrated, and possibly Alsyvox can sound good with 50 wpc or higher.

What other speakers have you heard that sound great with mid-powered tube amplifiers, SET or PP?

What design choices did their creators make to make for their speakers to work great with moderately powered amps?

(Interestingly, CJ seems to have a new amp out with 27 wpc, but I can't think of too many speakers it would work well with.)


the only thing that separates it from Tang's speaker is the bass horn, which can be made by the designer or Bert from Netherlands.
 

ACHiPo

Well-Known Member
Feb 22, 2015
518
309
310
Pleasanton, CA
My Kef Reference 207/2 speakers are 91 dB and they sound great with AtmaSphere M60 monoblocks.
 

morricab

Well-Known Member
Apr 25, 2014
9,391
4,986
978
Switzerland
Mid-powered tube amps - 27-85 WPC - seem to be the red-headed bastard children in this hobby.

The popular fare (such as Wilson, Magico, Sonus Faber, YG, etc.,) really come fully alive with the big Boulders, Soulutions, CH Precisions, etc. (I am NOT talking about soft, syrupy, anemic, fake-warmish, less-resolving sound of pairing moderately -powered amps with popular, hard-to-drive box speakers).

And, of course, many of the hard-core horn guys are after 10 wpc or less SETs.

The only speakers I can think of that sound great with mid-powered tube amps off the top of my head are Scaena with ARC Ref 75, Nola with 85 wpc VAC integrated, and possibly Alsyvox can sound good with 50 wpc or higher.

What other speakers have you heard that sound great with mid-powered tube amplifiers, SET or PP?

What design choices did their creators make to make for their speakers to work great with moderately powered amps?

(Interestingly, CJ seems to have a new amp out with 27 wpc, but I can't think of too many speakers it would work well with.)
Are you talking triode or only UL or Pentode amps? Class A?

The Class A triode PP amp is probably the best sounding of PP tube amps.

Odeon, Dynamikks, Live Act Audio, Zingali, JBL K2 all should work well.
 

morricab

Well-Known Member
Apr 25, 2014
9,391
4,986
978
Switzerland
Mid-powered tube amps - 27-85 WPC - seem to be the red-headed bastard children in this hobby.

The popular fare (such as Wilson, Magico, Sonus Faber, YG, etc.,) really come fully alive with the big Boulders, Soulutions, CH Precisions, etc. (I am NOT talking about soft, syrupy, anemic, fake-warmish, less-resolving sound of pairing moderately -powered amps with popular, hard-to-drive box speakers).

And, of course, many of the hard-core horn guys are after 10 wpc or less SETs.

The only speakers I can think of that sound great with mid-powered tube amps off the top of my head are Scaena with ARC Ref 75, Nola with 85 wpc VAC integrated, and possibly Alsyvox can sound good with 50 wpc or higher.

What other speakers have you heard that sound great with mid-powered tube amplifiers, SET or PP?

What design choices did their creators make to make for their speakers to work great with moderately powered amps?

(Interestingly, CJ seems to have a new amp out with 27 wpc, but I can't think of too many speakers it would work well with.)
Of course mid powered SETs, like Aries Cerat, will work great with full blown horns or the speakers I have mentioned above. Oh and I would also suggest the Supravox Zelia, which is a moderately large open baffle with 96db sensitivity.
 

morricab

Well-Known Member
Apr 25, 2014
9,391
4,986
978
Switzerland
In my case I was an Atma-Sphere dealer with ideas about speaker design. Since I love what Atma-Sphere amps can do it made sense to build speakers which would work well with them, in particular the 30-watt S-30 and 60-watt M-60.

Among the design choices were taking steps to keep the impedance curve generally fairly high and smooth, which results in a speaker that works well with a wide variety of amps.

The efficiency needed to be fairly high, but not super high. Since there is a tradeoff relationship between bass extension and efficiency (for a given box size), this made it possible to still get good bass extension without needing a huge enclosure.

The interaction between a low-damping-factor tube amp and a speaker presents both challenge and opportunity in the bass region. (The low damping factor shows up as in increase in woofer's electrical Q.) The challenge is to not make the speaker a one-trick pony that needs a particular amplifier type, and the opportunity is that the amplifier's low damping factor can translate into a worthwhile increase in bass extension. The solution I use includes adjustable port tuning, which also happens to make the speaker more adaptable to different room acoustic situations.

The increased bass extension with the enclosure sized and tuned for the low-damping-factor amp is about as close to a "free lunch" as it gets in speaker design, and when tuned higher the speaker still works normally with a solid-state amp.
Nice post Duke. With regard to damping factor of the amp, are you then critically damping (Q < 0.7) your speakers to work well with low damping factor amps? My Odeons, being horn loaded in the bass, do not respond well at all to high damping factor amps...the bass disappears completely. With low damping tube amps the bass is wonderful.
 
  • Like
Reactions: Duke LeJeune

Duke LeJeune

[Industry Expert]/Member Sponsor
Jul 22, 2013
747
1,200
435
Princeton, Texas
Nice post Duke. With regard to damping factor of the amp, are you then critically damping (Q < 0.7) your speakers to work well with low damping factor amps?
The short answer is, unfortunately it's not that simple.

The effective electrical Q, or Qes, of a woofer is modified by not only the amplifier's output impedance, but also by the series resistance of everything in between the amp and the woofer (wires and crossover).

Add up the amp's output impedance and all other series resistances, and then divide that number by the woofer's DC resistance, add 1 to the result, and that is our "fudge factor". Then multiply the woofer's Qes by this "fudge factor" to get the effective Qes. For example:

Suppose a solid state amp has an output impedance of .008 ohms (damping factor of 1000) and the wiring + crossover adds .5 ohm of series resistance. And suppose the woofer's DC resistance is 6.3 ohms, and its Qes is .25. Our fudge factor is (.008 + .5)/6.3 + 1 = 1.08. Multiply our Qes, .25, by this fudge factor and we get .26. So we use THAT as our effective Qes when modelling the speaker system's bass response.

Now if we use a low damping factor tube amp like the Atma-Sphere M-60, whose output impedance is 4.1 ohms, our fudge factor becomes (4.1 + .5)/6.3 + 1 = 1.73, and our effective Qes is 1.73 x .25 = .43.

So if we KNOW in advance what the amp's output impedance will be, we can take it into account and choose our woofer and optimize our box accordingly.

The challenge for me as a speaker designer who wants compatibility with a wide range of amps would be to come up with an enclosure which can work well whether the woofer's effective Qes is .26 or .43. I use vented boxes with multiple pluggable ports, because the shape of the low end can be adjusted by plugging ports (which can also help adapt to the specific boundary reinforcement situation). In some cases plugging all of the ports makes sense.

If you are designing a sealed box, you are pretty much stuck with whatever response THAT woofer + box + amp gives you in THAT room. Vented boxes have an additional degree of freedom (by varying the box tuning frequency). In either case a specialty amp's effect on Qes should be taken into account from the beginning, in the woofer selection stage.

If the speaker system uses TWO such woofers in series, the change in effective electrical Q in going from the solid state amp to the Atma-Sphere amp is greatly reduced: .25 with the solid state amp, and .34 with the Atma-Sphere amp. So this is one argument in favor of high impedance speakers: They are more likely to behave similarly with a wider range of amplifier types.

There are two other tricks I have up my sleeve which reduce the bumpage in the upper bass region that can arise from a using a woofer with a relatively high effective Qes in a vented box. I'd rather keep the specifics to myself for now.
 
Last edited:
  • Like
Reactions: ACHiPo

Atmasphere

Industry Expert
May 4, 2010
2,336
1,837
1,760
St. Paul, MN
www.atma-sphere.com
If you want to know what those speaker designers are doing differently, they are designing for an amp that they know has a fairly high output impedance by today's standards. Not only that, but they are not assuming that the amp behaves as a voltage source (IOW, the amp can't make constant voltage regardless of the impedance of the speaker; if it could it could double power as the speaker load is halved and you know what that means....)

A tube amp that uses no feedback will tend to act as a power source rather than a voltage source. That is to say it will attempt to have the same power output with all load impedances (4-16 ohms). No amp can do that but some are better at it than others. At any rate this requires a different set of rules when designing the speaker and its crossover (if it has one).

for more on this see The Power Paradigm vs. the Voltage Paradigm

What becomes important here is how the ear/brain system perceives tonality due to frequency response errors as opposed to tonality due to distortion. Apparently the ear puts more attention on tonality induced by distortion (the ear assigns a tonality to all forms of it BTW) than it does to errors of frequency response. For this simple reason an amplifier that makes most lower ordered harmonic distortion (such as an SET or our OTLs at a lower overall distortion level) can sound quite neutral even though the FR isn't perfectly flat. The idea here (in modern design of the last 30-40 years anyway) is to avoid the brightness and harshness caused by the application of negative feedback. To do that though you have to have speakers that are easy to drive and don't need a lot of 'damping factor'. Since you really can't apply enough feedback to any tube amp without it getting harsher and brighter (due to distortion added by the feedback) to be pragmatic some designers don't use it at all.

Full range drivers, most horns, magnetic planars ESLs usually conform to the Power Paradigm. The world's first acoustic suspension loudspeaker, the AR-1, was designed in this manner as well- so were most of the KLH speakers made in the 1960 (despite the fact that KLH made some solid state amplifier products during that time...). One clue that a given speaker might be designed for the Power Paradigm is that there will be adjustments in the back for the midrange and/or high frequencies. The controls are there not to adjust the speaker to the room but to adjust it to match the voltage response to the amp, which is considered to be an unknown. At any rate the intention of the speaker designer plays an enourmous role in making the speaker work with amps like this of higher output impedance.
 

DasguteOhr

Well-Known Member
Sep 26, 2013
2,354
2,513
645
Germany

Musicman

Member
May 30, 2021
10
11
8
60
New Mexico
The Alon Lotus SE mk ll was specifically designed to work with low powered tube amps and that included a 14 ohm woofer to maximize amplifier power efficiency in the low octaves. There were many options that could be had including AlniCo magnets on the tweeter and woofer in the Signature series or just AlNiCo magnets on the tweeter. The Lotus came stock with AlNiCo magnets on the midrange driver but all versions came with outboard crossovers with premium components at the time.

 

LL21

Well-Known Member
Dec 26, 2010
14,411
2,509
1,448
...What other speakers have you heard that sound great with mid-powered tube amplifiers, SET or PP?

What design choices did their creators make to make for their speakers to work great with moderately powered amps?

(Interestingly, CJ seems to have a new amp out with 27 wpc, but I can't think of too many speakers it would work well with.)
I used to own CJ MV60 (60 watts/channel), and at the time CJ was very supportive of creating a monoblock configuration out of them by getting a 2nd MV60. I wonder if one could do the same with their current reference level ART 27a amp which is an SET Triode at 36 watts/channel into 4ohms and apparently sensational. That takes it to 72 watts per channel, but as I understand because the amp sees half the impedance load (or something like that?), it actually becomes 144 watts/channel?
 

Atmasphere

Industry Expert
May 4, 2010
2,336
1,837
1,760
St. Paul, MN
www.atma-sphere.com
I wonder if one could do the same with their current reference level ART 27a amp which is an SET Triode at 36 watts/channel into 4ohms and apparently sensational. That takes it to 72 watts per channel, but as I understand because the amp sees half the impedance load (or something like that?), it actually becomes 144 watts/channel?
No. If you monostrap a 36 watt tube amp to be 72 watts, if you have it matched properly to the speaker it will be 72 watts. Tube amps do not double power as the load impedance is halved; if they are behaving as a voltage source then they might halve power as the impedance is doubled. Not quite the same.
 

bonzo75

Member Sponsor
Feb 26, 2014
22,442
13,471
2,710
London
I used to own CJ MV60 (60 watts/channel), and at the time CJ was very supportive of creating a monoblock configuration out of them by getting a 2nd MV60. I wonder if one could do the same with their current reference level ART 27a amp which is an SET Triode at 36 watts/channel into 4ohms and apparently sensational. That takes it to 72 watts per channel, but as I understand because the amp sees half the impedance load (or something like that?), it actually becomes 144 watts/channel?

It is just a KT88 amp. At 36 watts they are not using better valves
 

About us

  • What’s Best Forum is THE forum for high end audio, product reviews, advice and sharing experiences on the best of everything else. This is THE place where audiophiles and audio companies discuss vintage, contemporary and new audio products, music servers, music streamers, computer audio, digital-to-analog converters, turntables, phono stages, cartridges, reel-to-reel tape machines, speakers, headphones and tube and solid-state amplification. Founded in 2010 What’s Best Forum invites intelligent and courteous people of all interests and backgrounds to describe and discuss the best of everything. From beginners to life-long hobbyists to industry professionals, we enjoy learning about new things and meeting new people, and participating in spirited debates.

Quick Navigation

User Menu

Steve Williams
Site Founder | Site Owner | Administrator
Ron Resnick
Site Co-Owner | Administrator
Julian (The Fixer)
Website Build | Marketing Managersing