Dahlqvist DQ-10
This QUAD ESL 57 looking speaker was designed by Jon Dahlquist and Saul Marantz some 30 years ago - twenty years after the ESL 57. As the "best speaker of all times" ESL 57 is a good role model for any speaker, but apart from the shape the DQ-10 has quite little to do with the QUAD.
The DQ-10 houses 5 dynamic drivers, four in a semi open back configuration (felt backed), and the 250mm woofer in a sealed fibreglass damped cabinet (50 L). The four mid-to-high units are spread over a large frontal area, and on varying depths relative to an imagined front baffle. The reason is "time alignment", ie. an attempt to minimize phase errors by placing the drivers so that they would act exactly as one and the same acoustic source. The front baffle of the DQ-10 is not tilted, but instead the smaller units on small baffle boards (minimizing diffraction) are set behind the deeper ones.
The 125mm lower mid-range driver covers frequencies from 400Hz to 1kHz. The 43mm upper mid/lower dome tweeter operates from 1 to 6kHz. The main tweeter is a 18mm dome unit for the range 6 to 12,5kHz, above which a piezo-electric dome works as a super tweeter. The crossover circuit board with some 20 components is behind the driver boards. The filtering of the units is not made particularly steep.
For long, DQ-10 was the company's only product. In 1979, according to a person who was present, John Dahlqvist gave a lecture at CES on how an audio company can survive with only one product.
Something good
A person who've heard the DQ-1Q long time back, described its sound by saying "It has something good." That's precisely what I'd say about the sound. The speaker doesn't sound "modern" in any way but it doesn't sound old-fashioned either by which I mean that it doesn't sound like some of the British speakers used to sound in the 1980s, ie. soft, muted, sometimes even dull. The midrange from its lower notes up to the highest midrange sounds is wholesome, with a cupboard touch tonally. The presentation is slightly forward but not aggressive. The soundstage is not hugely three dimensional, yet the sound itself is immaterial in that it does not stick to the speakers.
The weakest point in the sound may very well be the bass. The problem is not that the bass would be colored. It could be more open and purer but straighforwadly colored it's not. Nor is the problem that the bass doesn't drop particularly down; it would help if it did - it would give music more body and soul, and correct the tonal balance - but a more important problem is that there's some discrepancy between the bass and the rest of the frequency band. The listener just feels it that the two do not go together perfectly. As if your socks were of two different colors.
But overall I liked the sound, there really was something good about it. Something that made me think that I'd prefer it over many modern speakers despite that fact the latter sound better in terms of technical correctedness. I recently heard the new EAR/Yoshino dipole speaker with two 8" woofers and a horn tweeter. Notwithstanding the differences there was something similar to their sound; both sound "as speakers used to sound" and both do it in a good way.
The little I had time to audition the Dahlqvist DQ-10 proved that it's not perfect but also that it's not impossible either. How would you call something that is in the midway of being perfect and impossible?
More info on the speaker here:
http://www.stereophile.com/floorloudspeakers/174dq10/
http://www.regnar.com/dahlquist_website_042.htm
http://www.gramophone.net/Issue/Page/March%201977/124/772551/Page%C2%A0%3B124%20-...