Building the Fidelio Speakers

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Reffc
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#1 Building the Fidelio Speakers

Post by Reffc »

As some of will know (and a few have even popped over for a listen!) my Tannoy based floor standers have been finished a while now although I've spent a good few months fine-tuning cabinet damping, port lengths and crossovers. After starting off with the maths and modelling, extensive listening tests using many different amps has been undertaken to get these right and it's been quite a learning curve! I have to declare from the outset, that whilst I do offer to custom build these now, they remain my own DIY project nonetheless.

Project was based on getting the best out of some 12 inch Tannoy HPDs of 1974 vintage. The idea behind the cabinet construction was to produce something of minimal colouration and which minimised internal reflections for reduced driver distortion particularly through the crucial mid range area. The drivers were completely refurbed by Nick at Lockwood for me with uprated voice coils, new suspension and new cones. The cabs I designed myself, taking note of what Alex Gardiner of Tannoy suggested for the MGs but then doing a little more research and testing for the HPDs which I reckoned needed a slightly larger cabinet. I ended up at 178 litres gross (157 net).

A major consideration was to balance the low Qts of the driver with a cabinet that would exhibit sufficiently higher Q to result in a flat and clean response without over or under-damping the design. Smaller enclosures tend to lower Q and create higher peaks so Tannoy I think compensated with under-damped lossy boxes but this gave anything but a neutral sound so I plumped for a larger volume with inherently stiff box, tuning it for getting the best LF response.

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The shape is designed to minimise standing waves and provide inherent stiffness. I experimented with various ways to try and form the curved sides and working with an expert cabinet maker came up with a way of doing it using a DIY vacuum former (1HP motor driving the air pump!).

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The sides were mated to internal formers, hand cut from solid Birch Ply, spaced such that the distance between them was not the same for any two formers:

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The sides were veneered in the vacuum former using high quality Ripple Sycamore (sometimes called Flame Maple) veneer:

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Internally, the walls were damped with 1mm bitumen followed on the rear and side panels by 12mm dense wool felt then 40mm acoustic foam (C=0.7):

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The modelled response is shown here in WinISD for the original port tuning:

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This doesn't account for room gain and doing the calculations long-hand suggested slightly longer port lengths may be needed for the EBS tuning of 28 to 30Hz aimed for although i later changed the design (during later development) for tuning closer to 32 Hz.

Front baffles constructed from 24mm birch ply laminated with 6mm MDF board, then damped in bitumen following veneering and cutting of the driver mounting holes:

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I've used 3mm thick 10mm diameter Neodymium magnets beneath the veneer as a neater way to secure the grill frames than the usual plastic pegs which eventually snap!

Edging applied to the front baffle to provide a recess for the grill. 15mm solid American Black Walnut to accentuate the vertical profile of the cabinets and to provide a contrast with the light veneer:

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I designed the crossovers and mounted the components to PCBs kindly provided by Mark Pitcher, although my chosen components and values differ from the ones that he uses quite significantly. I have stuck with the later Tannoy design but had to compensate for the loss of the autoformer by using the electrically flat circuit values and adding the corrected value for the resistor off the back of the HF inductor to match the autoformer setting (Tannoy use a 50 ohm resistor but the reflected impedance value for the autoformer is a ratio of 2.0 in the electrically flat setting so a 25R resistor is the correct value for a fixed inductor crossover). The result is excellent control through the crossover region and combined with the cabinet design and internal damping, these are the cleanest, most coherent sounding Tannoy based speakers I've ever heard...almost a total absence of the famous Tannoy "honk"...these just don't do it.

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Completed speakers prior to fine tuning:

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I ended up removing some of the lambswool placed in the central chamber behind the drivers as it was over-kill and the sloping internal bases and shape seem to control standing waves very well indeed. rear reflections are also very well controlled behind the drive units and with the crossover design, the result is very clean linear response to around 15khz. As with all Tannoy DCs it gets a little ragged above this. In room response was initially very good all the way to 22 Hz(!!) but lacked slam. This was traced to conservative predictions from calcs for port length so a reduction in length of 20mm was used and response now has weight and authority with real slam. This also increased bass efficiency by bringing the tuning from resistive back into reactive so it meant an easier amplifier load. In room measurements are almost flat to 30 Hz so a good deal better than most traditional Tannoy cabinets and f6 is around 27-28Hz in room. They sound my more dynamic and smoother than most Tannoys I've heard and I prefer them to my previous Tannoy Turnberry prestige speakers.

Total time invested runs to 100's of hours. Design and construction came to close on 380hrs total with many more hours spent on testing and tuning. Surprisingly, a lot of that time was preliminary design and modelling, detailed design, materials selection, trials (including the lamination trials where I settled on 4nr 6mm thick sections of Birch ply for the sides). The expense was considerable. Was it worth it? Definitely. Anyone who fancies a visit to darkest Gloucestershire is welcome to pop in for a listen.
Last edited by Reffc on Sun Sep 22, 2013 8:16 pm, edited 1 time in total.
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Paul Barker
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#2

Post by Paul Barker »

What a beautiful air cored inductor.
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andrew Ivimey
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#3

Post by andrew Ivimey »

Tannoy honk! ????? never heard of it and I've heard a few Tannoys down the years.

I'd like to know more ...
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#4

Post by Graeme »

Very nice.
I tried a few cabinets for my 10's, including ported, but couldnt get them to sound how i wanted.

Ended up with a cabinet designed by a friend which is sort of TL/rear horn but apparantly doesnt really conform to either. Uses a slightly different approach to damping too.
They sound amazing in these cabs.

http://img.photobucket.com/albums/v242/ ... noy004.jpg
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Dave the bass
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#5

Post by Dave the bass »

Is it like the Fostex Honk but not as good (naturally)...

Nice build there Mr Reffc.

DTB
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andrew Ivimey
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#6

Post by andrew Ivimey »

Beautiful wood!
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#7

Post by Greg »

Very, very nice build. I'm looking forward to hearing them fairly soon :thumbleft:
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Dave the bass
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#8

Post by Dave the bass »

andrew Ivimey wrote:Beautiful wood!
...but her Sister wouldn't?

Ha! SWIDT?

DTB
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Reffc
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#9

Post by Reffc »

andrew Ivimey wrote:Tannoy honk! ????? never heard of it and I've heard a few Tannoys down the years.

I'd like to know more ...
Its to do with the lift at the crossover point combined with distortion created by cone break-up just below the crossover point. Tannoy use a notch filter to try and reduce the peak but some cabinets seem to accentuate it. I had a new pair of Prestige speakers for 6 months in the system and they exhibited this trait very strongly. They seem to be super-critical of the amplification driving them so great care is sometimes needed when amp matching. I've tried to deal with the issue by both crossover design and minimising cabinet colourations which otherwise might add to distortion. I have to say that the speakers in the project detailed above are almost absent of it now, but it's taken a lot of work. Greg no doubt will report back his findings!
Reffc
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#10

Post by Reffc »

Dave the bass wrote:Is it like the Fostex Honk but not as good (naturally)...

Nice build there Mr Reffc.

DTB
Thanks Dave...of course, nothing's as nice as the Fostex Honk, except perhaps for the Lowther Honk! :lol:
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#11

Post by andrew Ivimey »

I thought that was the Sidcup screech!
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#12

Post by Dave the bass »

andrew Ivimey wrote:I thought that was the Sidcup screech!
Aha! Good point (well made).

For future reference...

Tannoy = Honk
Lowther = Screech
Fostex = Shout (so I'm told).

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#13

Post by andrew Ivimey »

It's your shout our Dave the bike!
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#14

Post by andrew Ivimey »

It's your shout our Dave the bike!
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
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#15

Post by Paul Barker »

Dave the bass wrote: For future reference...

Tannoy = Honk
Lowther = Screech
Fostex = Shout (so I'm told).

DTB
No it's

Tannoy trumpet
Lowther Shout

and Fostex weren't rated when these terms were first used. Latecomers to the party.
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