What is your take on high efficient speakers vs. low efficient speakers?

Hi @sns ,

You mentioned a very important question.
Most low power DSET (45, 2a3, 300b,...) made today and before designed for very easy load and very hight sensitivity speakers file full range Lowther, Fostex, Voxativ,...
But in therm of pik volume these amplifiers can work for midsize room and ~95dB sensitivity speakers like big JBLs and Tannoys. But in the real live they don’t work properly even with more sensitive Klipsch and vintage Altec speakers.
The main design issue is weak power supply and weak driver tubes. The only SET amplifier I know (probably there are another) that don’t have these issues is Coincident Frankenstein.

I have been using a good DIY 300B DSET (6sn7 input, 6f6 driver) since 2006 with Altec 604E. This combination played nice but it had pronounced genre preferences. It was good for small jazz and classical groups, great for vocals but disaster for any kind of electronic music, rock, fusion jazz.
When I increased capacitors value and quality (oil capacitors) in the power supply and divided the right and left channels PS by resistors. It dramatically improved bass, dynamics and separation on bass heavy complicated, congested music. My solution is not optimal as my stereo amplifier uses one power transformer, rectifier and choke. Monoblock solution should be significantly better.
But the bottom line - the main issue in DSET in combination with big woofer 15" speakers is not lack of power but lack of ability to produce enough current. And the reason for this is not enough powerful power supplies. To drive 15" speakers some audiophiles go in the direction of big 845, 211 DSETs, but I’m not sure that this solution is the only one. 2a3 or 300B with a good big power supply can be another very good and more affordable one.

Regards,

Alex.

The critical distance for medium size room at 1KHz less then 2m. Actually 2m is the worst case. 

So, the pik volume can generate the system with 300B amplifier is -

spikers sensitivity + 9db (8w) - 3db (2m critical distance) + 3db (two speakers).

For example for 95dB speakers we get at least 104dB.

You can get "absolutely sound" with SET.

For example, 300B SET and ~95dB sensitivity 15" JBL or Tannoy in medium size room. If 300B SET build properly you can get enough dynamic headroom for any kind of music. From small jazz to symphonic music and rock.

The problem is - 99% of SET amplifiers designed and built for Lowther like speakers.

Hi @bache ,

The question: what is high sensitivity? Yes I agree. For real high sensitivity let say 98dB and up it is an issue. For a 15" driver with 94dB sensitivity bass can be good down to 35-40Hz. 

Regards,

Alex.

Hi @bache ,

Yes, sensitive speakers do not play bass below 30-40Hz. But this is a compromise with the texture in the middle bass and lower mids, which is absent in dull speakers with low sensitivity.

Regards,

Alex.

Hi @mijostyn ,

My SET amp plays down to 7Hz -3dB. And plays bass much more in real, natural way compared to any other amplifier I had before.

Experience DIYer can built SET amplifier that sounds better than most of amplifiers available on the market. It wouldn't be cheap but such amplifier can't be bought by any money and it will be tweaked and tuned to special speakers and person.
It's way more effective than cable lifters (despite cable lifter works).

Regards,

Alex.

My friend is a DIY speakers builder. He also fixes drivers.

He had and measured dozens different 15' driver JBL, Tannoy, Altec,... He says the maximal sensitivity of 15' driver in vented box (of any size) at 100Hz is 94-95dB. Some 15' drivers like Altec have higher sensitivity around 200-300Hz but it drops to 95dB at 100Hz. 10'-12' have even smaller sensitivity at 100Hz.

In my experience, each pair of speakers that isn't driven easily by 30 Watt amplifier - sounds too compressed to me.

And it easy to explain. When you put dozens watts on speakers voice coil - it overheats that leads to very sever and clearly listened compression.