The amps will do fine on the Lowthers. You don't need that much power, and will only turn up the volume slightly to get plenty of sound. You can do better with a low power SET, but you can do that later.
The main concern would be accidentally turning the system on with the volume cranked wide-open, or driving the speakers into compression at loud volumes for a long period and heating up the voice coils. They will do 108db peak, or so, without much compression, so limit the listening levels to that or below, and you'll be fine.
So long as one uses a reasonable amount of caution, too much power in an amp is typically not as much of a problem as not enough power. Having said that, my thoughts are that Lowther's are more fragile than most "hi-fi" type drivers, so treat them with a little more respect than you might normally bestow on a bigger, more rugged beast.
As far as power amps go, so long as speed, bandwidth, linearity, stability and class of operation ( bias level ) remain consistent, the amp with more power will typically sound better and work in a wider variety of situations. When one of the factors that i mentioned differs between comparable models, what you like best is strictly a matter of personal preference.
Twl: When you mention 108 dB peaks, are you talking at 1 meter, at a random listening position X feet away from the pair of speakers, etc... ? Sean
Yes, Sean, that is based on the 1 meter testing position, on peak. They start to suffer from compression above that level. They may have some compression below that also, but not real noticeable. Of course, SPL drops off as you get further away.
Which Lowther drivers are these and what are they rated at in terms of 1w / 1m in stock form ? Sean
Why not look into oris horns? voight pipes are nice but not a real horn also look into other drivers AER ,PHY ,Fostex, lowthers do have there own character so..also smaller amps work best on horns. Later you may want to try a SET .Happy listening .JK
Sean, these are the EX3 drivers which are rated at 98db at 1w/1meter, and in a suitable enclosure, they gain about 2db, which puts them at about 100db/1w/1m. With 2 watts, they do about 103db and with 4 they do about 106db. At 8 watts they are hitting about as high as they will go before some noticeable compression, due to to 8" driver size. They are rated to take 100w, but it really just doesn't make any sense to give them more than about 6 or 8 watts max. These are peak figures for music applications. They are not average SPL figures, nor are these figures relevant at the listening position. The much more expensive EX4 driver is rated at 99.5db/1w/1m and should do a little better, but it will still enter compression around the same point, because it is still an 8" driver, and starts to lose the ability to move enough air at around the same point. These are not long-throw drivers.
Also, it should be noted that these speakers don't go below 40 Hz, so there is not as much air for them to move at the frequencies they produce.In addition, the typical rear-horn enclosure will augment the bass response to help the driver out, when the freq's get lower. And, it should be noted that if the cabinet is narrow, the baffle-step losses will cause a 5db shelving-down at the 375Hz point, or thereabouts, depending on the width of the cabinet. This is why I added the mod to my Voigt Pipes. Many designers will just put in an electronic baffle-step compensating network and cut 5db off everything above 375Hz, but I didn't have the power to lose that 5db of efficiency, so I acoustically reinforced the frequencies below 375Hz with a wider, swinging baffle to keep the 1/2-space radiation much further down into the bass. I was a little concerned about edge-diffraction problems, but with the swinging baffle-extensions angled slightly backward, it doesn't seem to be any problem at all. So, I managed to squeeze all the efficiency of the drivers out of them, all the way down to about 48Hz, where much of the sound is coming out of the port mouth at the bottom, and has floor reinforcement. Simple and quite effective.
When these speakers are loaded into a front horn, then they can produce higher SPL, if the horn is properly designed, and they also generally have multiple drivers in these applications, due to the unacceptable size of bass horn cabinets. The Oris Horns mentioned above are good ones which provide about 104.5db/1w/1m, if I remember correctly. They use a powered subwoofer to handle the freq's below 150Hz.
Lowther claims the most efficient drivers in the world, but I think that there are a few others that can match them, and Loth-X is supposed to have one that is more efficient.
Part of the problem with these is probably due to their limited X max ( excursion ). Then again, drivers with a longer X max will also typically be of higher mass, hurting their high frequency extension and transient response.
As far as Lowther claiming these to be the most efficient drivers, they are WAY off their rocker. Sean
I'd say before you settle on Lowthers, see what other drivers and horns are out there. See also what other high sensitivity speakers are out there.
While I like Lowthers and other full-range drivers, I find them too "small" sounding and a bit restricted frequency-wise.
I advocate a compromise between multi-way systems and full-range drivers: coaxials. I use Altec and Tannoy, but there are others.
For me, after 30 years in hi-fi, the all-time best speaker buy is the Tannoy System 15 DMT mk II professional studio monitor, still a current model, which you can usually find used for $1500-2000: 15" dual concentric, 1.1 kHz crossover, 6 cu. ft., 100 lbs., 98 dB, 38 Hz to 25 kHz +/- 3 dB, 90° conical dispersion, fabulous detail and dynamics with famed dual concentric imaging. . . .
Just my two cents' worth.
Sean, just out of curiosity, what are the most efficient fullrange drivers? The highest I've heard of is the Loth-X "Stamm" driver, which is 104db/1w/1m. I've never heard them though. Is there something that is higher than that, which is not front-horn loaded? I'd be very interested in learning about anything higher than that, that could sound good in a fullrange direct radiator configuration, even with a back-horn loading.
My response is of a different nature. I live in the US and have a pair of Lumley Signature Reference 150 monoblocks. Could you PLEASE help me and tell me if anyone is still selling these and if there is any chance of getting a part I really need. One of my rack handles broke and the partial handle really detracts from the ability to move these (they are heavy as I am sure you know) and also it detracts from the beauty of these amps.
I would also love to get a schematic to help with any parts problem diagnosis, if there is someone who still carries/sells Lumley.
I truly appreciate any and all help. Thanks in advance.
Your MFA 120's are very fine amplifiers especially in triode.You should compare them head on with a set amp "before" you make any amp change.Like push/pull amps,not all set amps are created equal and many have inherent liabilities.Driving my very efficient Tannoy Westminsters...my old mfa's[wired in triode]bested a whole slew of set amps. That said....MY preference is SET, however..I auditioned quite a few set amps that were not really in the same league as the MFA's
The proacs are very set friendly speakers.My system was very similiar to yours..... proac response 3's driven by mfa 120b's[in triode]and the luminescence preamp.You can certainly audition most set amps with your proacs before the speaker change to get a voice on the amps... with the possible exception of the [fabulous sounding]1.5 watt directly heated triode amps that employ the 45 tiode tube.I would think that any of the 300b based amps at 7 0r 8 watts would certainly drive the proacs.Any of the 811 or 845 based set amps will drive the proacs to live volume levels if you room isn't to large.The lowthers will allow you the luxury of mating a set amp that does use the fabulous 45 triode tube and most definately an amp you will want to hear with the Lowthers.
I agree that the DHT SET amps with the 45 triode work very well on Lowthers. I've been running that combination for almost a year now, and am extremely impressed with the results. I think a 45 amp is about optimum for the best results from Lowthers. Not all 45 based SET amps are created equal, and auditioning is a must. Take care to ensure a very good quality output transformer, which will be quite expensive, but worth it.
FYI, I am using a modified version of the Voigt Pipe speakers, and I like them quite well. Some people claim that there are serious flaws in this design, but from my experience, this is a broad overstatement. I'm getting excellent sound from mine. They are easy to make and give good results if made correctly. Get the highest efficiency Lowther drivers that you can afford.
Twl: Your first post regarding Lowther's claim made no mention of "full range" drivers. As such, my response was based on that info. I don't know what is out there in terms of "wide bandwidth" drivers, but there are surely many, many drivers that are WAY more efficient than what you stated. They just don't cover the full frequency range. Sorry for the confusion. Sean
i have just got back from holiday and looked at this thread.
there is a guy in the UK called John Jeffries, of Metropolis Music on 0044 1892 539245 who may be able to help you.
i asked him for the input impedence of the M120 power amps, and he has put me onto the guy who designed them ! so give John a try - if you have no joy, i'll follow it up on your behalf with the designer.