Wednesday, 22 January 2014

A Tannoy 15'' Enclosure for the Enthusiast – The Realisation III


                  "Never change a winning team!"

Hi to everybody interested to follow on. Today I am writing from the position of complete frustration about the first audible results. Before I was absolutely save about my knowledge and new ideas which lead to the realizing of my new enclosures. As I already said, I have realized in the past several other enclosure projects for two decades, so I was absolutely safe about the most constructive details evolving with loudspeaker cabinet making. I did not expect to end my first listening evaluation last week with a complete disaster, the new enclosures did not work at all! These cabinets were not able to show any low frequency response at all. I had the impression below 300 hz all tonality has lost any lower support, below 100 hz it seemed to be like cut off. It sounded like with a low frequency control knob in contradictive position. The former evaluation cases performed very well in this discipline, otherwise I never would have been convinced to overtake the open baffle principle for the new enclosures. One more time it can be said: "never change a winning team…!"It was again one of the moments in life were I was absolutely stroked back from a unexpected effect…!

The new enclosure

For more than a half of a year I did use my former evaluation enclosures to work out almost any option for the final design. How can it be, that the perfectly made new cabinets didn't work almost in a similar way, when all constructive detail have been tested before with the dummies? All? I made some basic new experiences during the evaluation, first time in my life I did use a 15'' Tannoy Dual Concentric speaker in a open baffle cabinet. As the attentive might remember, my first impression was as well a  bit thin sound structure, which I needed to accommodate, when coming from a former reflex cabinet with big boost in the 100 hz area. After a while I learned to assess the faster, leaner and undistorted bass response of the open baffle to be superior to any other principle I had used with 15'' Tannoy speakers. With a good horn or in the open baffle the bass response can reach almost natural accuracy and timing, were other principles mostly suffer from a wooly and always slow thick bellied lf-extension, typical for ported designs. A lot of people do prefer this unnatural sound and get confused meaning the attribute of "warmth" and "rounded".

During evaluation I tested the mechanic extending of the cabinets in order to improve the lf-response with longing boards. These thin boards had been screwed to the back frame. This sort of simplest extension showed me the effect how such a extension will influence the lower frequency response. As a result I decided to built a extendable cabinet. Second I had already evaluated the front loaded horn with other cabinets and did know about its big advantage. So I have realized two wooden funnels and just screwed these in front of my evaluation cabinets. In the past I did learn to fear massive thick double walled baffle boards, they will not work well with a fullrange speaker of the heavy weight class of the Tannoy. The middle frequency response get hardened and does not sound very refined and musical. But here now the double baffle did do quite well, even when the evaluating design was almost 40mm of plywood with both layers in sandwich. I did not know why? The drivers had been mounted very tight from behind the original baffle boards, which were a solid part of the open box type construction, the funnels just added up as a additional front part.

The evaluation enclosure with double baffle boards

The implementation of this horn funnels into the  final enclosures made several changes in the construction of their mounting necessary in respect to the free sides for the sliding inside cases. At the end I did use a mitered frame design to incorporate the funnel into the housing. The completed object got screwed from the back using the strengthening frames at the front. The heavy driver is mounted directly to the end board of the funnel. Only the funnel itself supports the 10 kg of the driver and conducts as well its energy input to the whole system (resonances). My former experiences with Tannoy drivers have always made the baffle board construction, its material choice and its dimension to a delicate decision in order to find the best resonant voice for the full tonal spectrum.

Special constuction to keep the space free for the sliding cases

For two days I tried almost everything possible to make a change. I did seal the speaker to the funnel with mod rubber stripes. I did seal the interior cases with felt lips to the main frame, both in order to prevent any early unwanted shortcut of the lowest radiated waves. I did check my electronics for any defects, particular in the regulation of several power supplies (In the past a defective regulator tube did drive me crazy by its compromising sound). I did check tubes and tried very different first changes with the enclosures itself. The slideable interior frames did not show any positive effect at all (how could they do without lf-response). So I just made a quick reflex conversion, I did close and seal them and I did fill them with wool. All changes showed the same result, no low frequency response! I did run desperate not knowing what to do.

Normally driving a car for some hours is the perfect situation for me to let my brain play and find the clearest thoughts. Since I did not have any traveling at my timetable at the moment, I had to find other states of concentration. Waking up early in the morning and lying in bed is another excellent option to find deeper ideas. Here I realized some days ago, that the mechanical support of the driver, i.e. funnel might bring the problem. I did know from former realizations that the strong stiffening of an enclosure is a absolute basic to get good tight bass response. If you bring the conjuncted construction even further under tension (like instruments are made), it can even improve in this competence.
So I did know that the sliding mechanism does prevent any rigid inside constructions since its needs to keep all four side walls free of space. I decided to take the inner enclosures out and instead to introduce  massive panels to connect the holding backboard of the funnel to all sides of the cabinet. Additionally  to the precisely adjusted boards I did use wooden cotters to bring the whole construction into controlled tension and used some more massive screws to hold the boards into tight position. The revised construction has tightened up the whole design with a main attention to avoid the suspending effect of the funnel to the driver mounting. The classic knocking test with the finger at the outer case showed immediately a completely different resonant ability.

Wooden cotters bring the interconnected boards with the outer frame into controlled tension

Stiffening board underneath the backboard of the funnel
Two hours later I started again to listen to this enclosures. I remember the first moment last week. I just placed the diamond in the first groove and even without any music I did directly realize, that there was something going wrong. But now the inlet groove test sounded promising. From the first moment everything was better than right. The sound was completely different now. The tonal spectrum was very well supported with perfect balanced lower frequencies and all other frequencies seemed so much better integrated, that from the first moment on pure relaxing was on set. The lower frequencies have got fast, tight and deep, with a wonderful creaky ability to reproduce the best wooden instruments from the "Cremona School". Some records of Benjamin Britten with Rostropovich at his cello, Jaqueline du Pré and Pablo Casals made me immediately to find home in the absolute "gourmet class" of music reproduction.

But as well brass instruments did profit a lot from the improved integrity of the low frequencies. My absolutely favorite record of modal jazz music "Kind of blue" is always a very good test. A highly improved soundstage without any compression, but with extra space and air as a result of the front loading mechanism. I was sitting in front of my new speakers and more than happy with the result. Now they did match my highest expectations and they are performing even better now. They are the best Tannoy speakers I have heard till now – by far, no exception.
They have the ability to perform in the best possible manner being a true natural music instrument with well balanced harmonies as foremost attitude. They can work free of the usual compression effects and typical electrical artifacts with a wide open soundstage of almost holographic depth. Even after four hours of intensive listening no signs of tiring occurs, which is always a result of well balanced homogenous refinement. The speaker is able to produce exceptional fine micro dynamics, which is a more common character of electrostatic speaker designs, than with heavy weight champions of the paper cone class. The dynamic abilities of such drivers form the attraction to use a 15'' speaker, the combination with the refined abilities give such combinations a highly addictive dimension.

Only a handful other systems are in competition with such elaborated audio transducers. But this question is a purely theoretical one, who is able to make a direct comparison between let's say a JBL-Paragon, -Hartsfield, -Everest to Jensen Imperials, to EV-Partricians, or to Tannoy Westminsters, to  Altec's A7, to Western Electric WE15a's with WE TA7331a's or to a Klangfilm Euronor?  Nobody (I know, Dr. Takeshi Mikami, he has them all) is able to do such a comparison and I do think it is as well not necessary. It is much more on demand for the most of us, to find a good match for the own preferences and our personal taste. Mine was and is the Tannoy Dual Concentric speaker and I have realized now a longtime captured idea, to design a very good set of audio enclosures to bring them in the foremost line.

Some horn funnels on delivery in Japan

Other people would do now a recording/movie with an iphone and upload it to youtube to show the properties of the new speakers. I have never understand for what reason this little films about high end equipment are made, may be I am to old to understand?
But right now, it needs to improve the craftsmanship of the new changes in the enclosures as next step, before the last function will be implemented, the variable blinds as back of the baffle. We will see, if other unexpected things will happen?

Read on soon, Volker

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