To my ears, this is the best speaker I've ever made - and the biggest! 150 liter brutto volume is what you have to be prepared for should you decide to follow. From the front it seems fairly modest, 28 cm wide and 105 cm high, but depth is 50 cm and it will require some 20-25 cm minimum to the rear wall to breathe. Overall sensitivity is 95 dB/2.8 volts and having a minimum impedance of 6 ohms, it can be driven by low-wattage SET amps. I do not recommend 2 watts SET; these amps need 98-100 dB minimum no matter what manufacturers may claim. I have no trouble driving the DTQWTs from my 8 wpc 300B SET amp. Deep powerful bass - and that very special 300B midrange. With a proper 300B SET amp you can play these speakers for hours and hours without listening fatigue, a clear sign of low distortion and proper balancing of drivers.

In many ways life gets easier when we make big speakers. We may have more and bigger drivers and distortion may all of a sudden be reduced significantly because none of the drivers have to move much to produce high sound levels and we don't have to rely on drivers being capable of large cone excursions either.
We may all have experienced a 6" driver being driven to high SPLs and doing its best to pump air in order to produce deep bass notes - and at the same time trying to produce a smooth upper midrange/lower treble, the 640-2560 Hz range. It's not ideal but a compromise most of us have experienced. As long as we don't push a "six + one inch" too hard, things go well.

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A study into rather nerdy high-efficiency speakers using extended range drivers, allowing point of crossover to be taken above 7-8 kHz, thus a single driver covering the entire range of basic notes plus most harmonics.
Nerdy? Well, this is not a speaker for everyone - I think. It's a speaker for those who want to explore the world of low-wattage, single-ended triodes - and not least - the delicate presentation of the very best recordings from either CD or vinyl. It's a discriminating speaker and if you have less than the best source material, this speaker will tell you. Those addicted to heavy metal or contemporary type of music having a constant "noise" level over the entire frequency band, please look elsewhere. I like music having breaks, music with low level passages, etc. How can we build up expectation and excitement if we don't have breaks? Anyway....

Driven by the best of SET amps it can bring you close to the music like only good fullrange drivers or electrostatic speakers can do - but there's a price to pay: The paper cone of the 215RTF64 is extremely thin and careful damping behind the driver is necessary to avoid rear reflections and there's a limit to loud we can play before the membrane starts breaking up and smears details. T

The 215RTF64 is a large 8" driver having a membrane area of 265 cm^2 and efficiency is around 96 dB. In commercial terms this means 98-99 dB from the usual overrating of products. In the treble range it actually does deliver some 100 dB/2.8V, but this won't help if the upper bass and lower mid does not follow - and it doesn't.

I'm always ready for surprises when it comes to speakers. The sensitivity of this panel is phenomenal, reaching a healthy 100 dB/2.8 volts in all of the midband. Actually the JBL tweeter is working hard to make up to the two other drivers, but despite the apparent sloped response towards the top octave, treble seems to be well balanced from having no attenuation on the tweeter.
Reaching ear-shredding levels, I measure no more than 5-6 volts peak RMS on speaker terminals, accounting for some 5-6 watts. This means that even flea-powered amps can be in here and I haven't been able to drive the MAE1 amp to any noticeable distortion levels.

Obviously there's no boxy sound from this panel. The bass comes out clear and punchy and listening to acoustic bass is most enjoyable. It's also obvious that the bass is not as deep as had the Goodmans been placed in an e.g. Onken vented box. So, how about the mid running so high? Well, I hear treble crisp and clean, but dispersion - or lack of the same - in upper mid and lower treble is very noticeable. In that sense it resembles electrostatic speakers. Move your head a little and the soundstage changes a lot. There's a hot spot, no doubt about it. However, due to the dipole status, this is more tolerable than expected. A dipole tweeter might be interesting to try, but where do we find a suitable planar at this level of sensitivity?

The recipe:

- 1 x JA8008/TW034 kit (= a pair)
- 2 x Eminence Deltalite II 2515 bass drivers
- 1 x electronic crossover, 24 dB L/R with variable point of crossover
- 2 x stereo power amps, anything from 20 watts and up will do. Small SET amps can easily run the mid/tweeter section.
- A decent clone of the beautiful vintage Wharfedale SFB speaker.
- Liniarise Deltalite II impedance from 15 uF + 10 ohms across terminals.
- Add baffle step loss compensation to the bass drivers from 8.2 mH bypassed by 4.7 ohms.
- Hook it all up, set point of crossover between 80 Hz and 160 Hz to your liking - and you're flying!