High efficiency systems :

Today's trend is toward high efficiency and as usual many things happen in the commercial world of tube mania, for 1, single ended triodes have established themselves as top performers and are being successfully build and sold by many companies and many do it you're self folks.
The main reason they enjoy such big success is the common belief that low powered SE tube amplifiers are much less complex then their Solid State counterparts. The more simple the design, the less electrical components are used in the signal path, the less harm can be done.
Common belief is that each extra electrical component is changing the original signal and corrupting the upper harmonics or replacing them by something else or completely losing them!
Feedback is mostly used to correct something that went wrong in previous amplifying stages somewhere in the amplifier.
Properly designed amplifiers don't need feedback ,without they sound more open, transparent, spatial, softer etc. commercial amplifiers have more power , marketing and product image obliged but then more components must be used (paralleling of tubes and/or transistors, more powerful drivers and therefore more Capacitors and Resistors, etc.).
Okay, the most simple designs like SE tube amplifiers do not have a lot of Watts to give so with these small gems comes a new problem , speakers .
If you use high sensitive loudspeakers, no problem!
But finding the right high sensitive loudspeaker isn't that simple.
Most are big and ugly and expensive AND not that good!!!
Here I present a very good alternative to the problem , the problem of most high efficiency speakers is the fact that they are not homogenous , they offer high sensitivity only for a limited bandwidth.

What I mean here is the following :

It is absolutely not a problem to obtain high efficiency with increased frequency, the main problem will always be the bass .plenty of good mid range horns are available and plenty of tweeters are also available at relative low cost.

A small list of past and present top system components :

JBL motors and horns
Altec and Electro voice and Gauss
TAD & Radian
Beyma & RCF & Selenium

These brands main markets are the pro audio use, movie theatre and studio monitors .
Unfortunately their best products come from a period in electronic history when amplifiers didn't deliver the power that today is available .
Today we live in a world of consumption and quantity , therefore good sound systems are measured by how many dB's they produce and how much power they can handle. The big change is not big for the high frequency motor and tweeter assemblies but more for the woofers, those have increased in weight and moving masses, hence heavier voice coils, less BL is needed and the air gap is bigger for better cooling , hence for the audiophile they are not interesting enough anymore, 40 years ago 100Watts was awesome, 20 years ago a 300 Watt RMS speaker was already phenomenal, today 1000Watt RMS exists, and 300Watts is considered a minimum in pro audio .

Example of efficiencies of horns :

Beyma CP22 super tweeter (a copy ? of the JBL bullit tweeter) has 107 dB/w/m from 4Khz upwards , usable above 6Khz 6dB filtering
Beyma CP650Ti + TD460N horn has 108dB/w/m average between 500Hz and 10Khz although I don't recommend that, 500Hz to 6Khz 6dB is plenty already.

This shows how easy it is to make a high efficiency system above 500Hz

With a custom made horn of the Iwata style we can easily go down to 350Hz with the same driver for high end applications = low power.

BUT what do we use under this frequency ?
This is the main problem of the question, many solutions are available :

Bass at 107 dB/w/m is highly unlikely to happen , it is possible with many drivers
And a huge horn we can get there. But you're wife is likely to file for divorce if you mention that you have such a speaker in mind .

What is already commercially available = reasonable size ?

Klipsch horn , is a fairly decent bass horn using the corner of the room as part of its design and a high efficiency 15 inch speaker
This combination has about 40Hz-200Hz bandwidth and approx 101dB/w/m .
Another known problem of such combination is that the horn only comes alive from a certain dB spl, mainly due to speaker parameters and the ear ( loudness effect ) then the horn itself.

JBL has many horns, the Disco 100 & 200 being quite popular , with their double 15 inch speakers but needed a quite few watts to come alive, 55Hz-500Hz 6dB useable at approx 97dB/w/m .And I can confirm you that only once we pass the 20 watt mark then only they become alive!!!!!!

Altec has the voice of the Theatre, this is a bass reflex using a 15 inch speaker of the old days, one with decent BL factor, light voice coil and good efficiency but low power handling with a small front horn to increase sensitivity even further.
This speaker has no horn for the function below 100Hz, above it's 101dB/w/m is easily attainable, but below it's a standard big bass reflex cabinet, going extremely deep but not very efficient.

So why haven't these systems conquered the world ?

Mainly because they are not well balanced systems and perform well for one type of music but not for all types, some are just to big, and others require a corner and the main objection from audiophiles is that sound is not always what they expected, many audiophiles do believe that less components in the circuit and signal path is better, so the current stream is Full Range, no filter, smaller because full range speakers cannot full fill the whole audio spectrum completely, and anyway no one really expects them to do so.

What is available :

Lowther, very popular and very expensive.The only recommendable speaker they ever made is the PM4 and PM6. The bigger the horn usually the better the performance and this is not a good performer for the low end.

Aer, lowther like and with high prices competition arrives is the new kid on the block. They are made in Germany by a guy who is an authority on Lowthers, he finally decided to make a speaker that has all the qualities and none of the faults that Lowther is renowned of and I must say sound is very good.
Fertin woofers , Davis,Fostex , PHY-HP ect.
And many custom models.

I would like to point out to the full range enthusiast that the curves are measured at 1 watt/meter and that it is inconceivable that a woofer can produce a good quality high frequency output.
A super tweeter will all ways be much faster and better .
If only because its voice coil moving mass is only a fraction of the full range ( think in terms of a Ferrari versus a truck )
This off course doesn't show on a standard graph, but add a super tweeter and you will fall off you're chair, or measure high frequency output at 100milli watts and compare.

On analysis of basic high efficiency systems :

A few classic systems : ( usually 3 way )

Visaton has a 93dB/w/m system using 2 12inch woofers and a mid horn and the TL16H tweeter, this system is quite good, but in order to obtain this, the efficiency of the mid and tweeter had to be sacrificed, 93dB is not great but sufficient for a 10 watt amp especially if the low end is really good .

Altecs voice of the theatre is huge and is mostly popular as a 2 way system, it is also quite good but doesn't go down very deep and using a 15inch woofer up to 800Hz is tricky ( cone breaks up at this frequency ) but it is fairly popular and sounds very good.( even with the cone breaking up !!!!! )

The newer systems want to be artistic design and good sounding at the same time, this is very difficult to combine, they sacrifice the bass and its efficiency and are very unbalanced, usually with active subwoofer that has terrible low efficiency.

An example :

A certain Dutch popular design, to me sounds to thin, on classical music with lots of trumpets will shine but anything that has ground tones under 300Hz ( and most instruments and voices do ) will distort the harmonics image .
Also the plastic flower pots used as horn are not in my opinion suited for high end but the final judge should be the ears of the concerned person, but its better to be warned and to know what to listen to then to go in blind. These plastic horns appear more and more and are prone to add many distortions due to there bad shielding properties ( inside the horn the sound of a vibration or secondary reflection of the horn itself is very much amplified )

They also uses active subwoofer to produce real pressure in the bass section, on a demo this seems very good, for the demo material uses low tones with little harmonic content, but real music has tons of harmonic content and then suddenly the bass sounds very sluggish and artificial. Because the upper harmonics arrive much faster then the lower.

Very popular are the Active subwoofer using 2 10 inch speakers and horns
Mid horn using Lowther, claims are really overstated at 107dB/w/m .
And recently I even heard a system at a claimed 109dB/w/m and this is very overstated indeed. ( bass section usually if its active has a lousy 86dB/w/m )

On this : many claims of SPL of speakers are overstated usually by 3dB at least and more commonly by 6dB .

The Humfrey horn .+ tweeter shootout

This design was build from the idea that pushing for max efficiency was not the solution to go, especially at my young age !!!!!!
I like a good tight bass, and lack of it drives me up the walls .
So high efficiency yes , but good fast tight bass is a must, for me this is logic itself

Example read the article : harmonics & high end

A contra bass lowest ground tone is approx 60Hz
If we break down this into upper harmonics

1st 60Hz ground tone
2nd 120Hz
3rd 180Hz
4th 240Hz
5th 300Hz
6th 360Hz
7th 420Hz
8th 480Hz
9th 540Hz

All those upper harmonics make together the sound of the instrument .

If the bass is slower and the mid is much faster, then the brain detects something is wrong, and this results in listening fatigue.

For me this unbalanced inhomogeneous sound cannot satisfy me, even if the mid's have tremendous attack speed and decay properties.

Horn rear loaded, hyperbolic ( best for bass ) loaded and first room tuned to filter out mid going down the horn.
The front of the horn is basically just a baffle and the efficiency is determined by the speaker itself.
The first speaker I used was the Audax HT210AO, this was a horrible choice, because it did not have high efficiency at all, but it was cheap , from there on I tried a Lowhter PM6, that was much better but the Lowther even with the help of the horn didn't have proper bass output, mids where to bright and treble seemed a bit too artificial.
Then came the Fostex Fe208Sigma, this was the most coherent one, but lacked the sparkle from the Lowther ( which had plenty of sparkle ), from there I tried an old Goodmans full range unit, remarkable but not yet satisfied, I decided to try the lesser Fostex Fe204 , from the first note I knew this was the right speaker with the perfect balance, everything was just as it should be, except for sparkle , the Lowther was still the king there .
Extremely coherent, excellent bass response, excellent mid range, but dull highs not that obvious on first listening sessions, but when an extra tweeter was added the improvement was tremendous, like finding a treasure and using 6dB slopes , Jensen copperfoils and tritec coil the result is 1st class.

It is a very tough speaker to build but its worth it.(Plans will follow )

Tweeter shootout :

In this issue I discuss several tweeters from Beyma used for comparison, the most expensive costs 75 euro VAT incl .

The CP-09

This is a shy unit, no sparkle, very tame, probably also too low sensitivity ,
In this application certainly not recommendable.
Bi radial horn , on paper excellent polar pattern, irregular frequency output, between 5 & 10Khz 110dB/w/m and then steady decline 10dB/octave
High 2nd order distortion compared to others

CP-12N

Already a lot better but with an aggressive undertone more suitable for cheaper PA speakers, so also not recommendable. Polar pattern shows this is a narrow dispersion unit, average 106dB from 5Khz to 20Khz usable.

CP-21F

This is a very fine sounding tweeter, excellent 3d image , sparkling and pleasant highs , details are a lot better, much more finesse, softer and yet more present , highly recommended. Smooth frequency plot and excellent polar response curve, very low 2nd harmonic distortion, 105dB/w/m average from 5Khz -20Khz.

CP-22

This one is also excellent, it blends in, nothing to really mention, you listen to the music and relax also highly recommended. Polar pattern is far from good, this is a directive horn, 30° is still excellent but above it pressure drops fast, overall nice frequency graph, excellent sensitivity 107dB/w/m

CP-25

To our big surprise this tweeter performed excellently in this configuration not as refined as the CP-21F or the CP-22 but very close and therefore also highly recommended. Excellent polar pattern , and excellent frequency graph, harmonic distortion is slightly high , for high end seems to be usable between 3Khz and 20Khz at 101dB/w/m

Visaton TL16H

if you disassemble this one you find it has the same magnet, voice coil and membrane as the very cheap DHT-9, but its much better, probably even better then the CP-22 and CP21F although it depends on the day !!!!!!

When used for high end consider you are not going to grill it by playing loud, you're kids might so you can experiment crossing low with just 6dB, the ear should be the judge .

Next Issue Will feature the Big Mama Solution :

Preview of Big Mama :

We had custom made 15 inch bass speakers with narrow gaps and light voice coils and wanted to use an open styled cabinet .The cabinet will be as large as the Mid horn approximately .The reason to use 2 drivers for bass is the fact that the mid horn needs to sit at ear height so the stacking of 2 bass units makes sense and the increase in radiated area is certainly beneficial ( what difference in size does it make if the height is filled with 2 stacked speakers or just one ? )
They idea came after having repaired another guitar amp, as I test them with 50Hz
I am time after time amazed at the pressure these guitar amps possess, they have excellent bass response, use fairly cheap speakers and an open cabinet so I decided to try it, 2 different units will be build, one using the 15 inch speakers
And the others using eminence 12 inch units.
The theory says that acoustically the low frequencies are shorted, but I have discussed the phenomenon with other colleagues and they agree that this is not the case. So I will try it and see if theory again disagrees with reality and then we'll have to find someone that can explain this!

As a mid horn an Iwata scorpion horn or another Mid horn will be used with different motors for comparison and as a super tweeter I'll stick with the beyma CP-22 or CP-21F.

Pictures and measurements will follow and especially the appreciation of the ears .

I just hope it aint a flop , given the time and money this costs ?

Next are the Datasheets of the tweeters .
And some pictures .