Modified Cambridge R50 Transmission Line Speakers

[snip]

Your welcome, they really do look nice!

What always frightens me about veneering is how to go about edges, how do you trim it so that it looks good?
Well, I have tried doing woodworking before, building speakers as well, I always end up with slightly wonky results and getting frustrated, I think it's best if I stick to Electronics and working with mild steel and aluminium enclosures.

I did have a router once, funny story about that.

So I bought this Ryobi router, came with a stand thingy to turn it into a high speed spindle moulder. So I go about setting it up, putting a bit in and so forth, the time comes to try moulding something, yay! I put the goggles on and all that and about 2 minutes later 'Ziiiiip' a small piece of wood is yanked from my hand and propelled across my garage where it is embedded into a breeze block. I stand there looking at the piece of wood, looking at the router, looking back and forth, mapping out the trajectory and then realising that it missed my head by about 9Cms..

Then I turned the router off, dismantled it, put it in the box and stowed it. Two years later my (now ex) Wife sold it to some guy seeing as how I was too scared to take it out the box anyway.

:-) I don't scare easy, but that machine scared the living daylights out of me, I don't really think I will ever be using such a device again.


//Jan

[moggy58]

Keith, they look pretty smart nice job.
You could paint the polystyrene middle and the metal outer part of the b139 drive unit
without effecting the sound quality. Would make it look more tidy, just a thaught

[MF 1000]

Keith, they look pretty smart nice job.
You could paint the polystyrene middle and the metal outer part of the b139 drive unit
without effecting the sound quality. Would make it look more tidy, just a thaught

Im going to apply copper leaf to the metal rim and polystyrene middle...watch this space...lol

[MF 1000]

Ive just finished veneering and oiling the second bass cabinet, just the carbon effect vinyl to fix now. Today I received some isolation supports from the USA that will go between the base spikes and my laminated floor. I'm hoping these will isolate any low fequency vibrations from the cabinets disturbing my neighbours downstairs

I found them on the intenet at www.simplyphysics.com

Here are some pics of them supporting the cabinets







They have certainly reduced the level of vibrations I feel along the laminate floor....think ill try putting a piece of that Draper vibe mat under them too see if that helps even more

[I like valves.]

Have you thought of trying the bass units upside down? I was always of the opinion that TLs work best with the port nearer to the floor so this might be interesting.

Btw, I have IMF Professional Monitor IIIs driven by a pair of Jolida Music Envoys and I don't live far from you either!

[MF 1000]

Hi Simon

These are a faithfull copy of the Cambridge R50 speakers which had the bass port in the middle. Turning them updaide down wouldnt change the vertical location of the port much ...and I havnt veneered the base ...lol

I aslo have a pair of cloned IMF TLS80's that will be given some TLC and offered for sale later this year. Myabe we could have a mini bake off some time too

Keith

[I like valves.]

I must admit I'm more interested in your cloned IMFs. I've always been into IMFs right from the beginning of my hifi journey so I'd certainly like to hear those. I also have a pair of TDL Studio 4s in the system upstairs which I doubt I'll ever part with. You might find them interesting.

[MF 1000]

New Additions to the R50 set up

Those of you that attended Bob C's bake off saw and listened to the combination of my R50 transmission line bass units combined with some newly aquired Fostex 127FE full range drivers in a bass port enclosure. I had cobbled together an open baffle twin KEF tweeter combo to partner these two but felt after the bake off that the top end could be crisper and better defined.

So ive made a start and firstly built my own stronger enclosures than those that I had that day (they have been donated to my daughter with another set of Fostex drivres fitted)

One problem i'd noticed with the 17mm birch ply originals is that the cabinet suffered from vibrations when driven to reasonable listening labels. So ive built 15L enclosures using 25mm MDF sides, 18mm front & rear baffle and 36mm base & top plates. This has eliminated any cabinet 'ringing' whilst starting on a style match to the bass cabinets




I modified the open baffle tweeter mount to match the width of the new cabinet so it looks better on top of the new cabinet rather than on top of the bass units as they were demo'd at the bake off.



The tweeters are KEF T15 and T27 units which run from around 3000 Hz upwards. At the bake off they were being fed from the tweeter output on my Wilmslow Audio R50 crossover, but I fet they were somewhat restrained and lacking in clarity compared to the tweeters in the Snells we listen to aswell. A bit of searching in the KEF Celeste cabinets that the T15's came from and I found the original crossovers.... the tweeter being fed from a simple circuit using a 8uF capacitor as the high range filter.

I 'borrowed' the cap from the 40 yr old crossovers and tested it out on the tweeter assembly....what a revelation

A quick trip to my local Maplin for their Audio Grade caps and the difference was s step change again

I ended up with a 6.7uF assembly for each set of tweeters



The top end is now much crisper and defined.....the tamborines on tracks that we played in the Snells at the bake off now sound the same on my speakers combination.

Here is an overall view of the 'family'



The next step is to look at a simple low range filter for the R50 Transmission Lines...rolling them off below around 175Hz or maybe lower.

[awkwardbydesign]

"I 'borrowed' the cap from the 40 yr old crossovers and tested it out on the tweeter assembly....what a revelation
A quick trip to my local Maplin for their Audio Grade caps and the difference was s step change again
I ended up with a 6.7uF assembly for each set of tweeters"

I have been playing with Russian PIO caps for my speakers and my DAC. I rather like them, don't you know.

[MF 1000]

Further update

After askin questions on another thread on here about using a 1st Order crossover for the bass T/L, and potentially the perils of this with a the KEF B139, as there could be issues around the 415Hz mark with the B139's...at the weekend I took the plunge.

I was thinking of using a 3.9mh inductor to start to roll off the bass at approx 175HZ. I found a monacor inductor using 1.4mm wire on the CPC website ...and as they are only 15 miles from me ...well it had to be done.

Although not an ideal inductor as its based around a large ferrite bobbin it is certainly a large beast at 65mm dia and 40mm high and at approx £13 easch wasnt going to break the bank for an experiment. The pic below shows the test crossover board I then made to mount the inductr and the 6.7uF of caps that feed my pair of KEF tweeters



The board is fed by me biwire cables for the tweeters and bass units with a direct feed being taken through to the Fostex full range units. All components were hot glued to the 25mm mdf board.

Sound wise ...well what a revelation...the bass is now warmer and has more depth...the roll over at around 195 Hz. As regards the potential issues at 415 Hz ....an test with an audio test CD showed little output from the bass TL at 400 Hz ...so any issues at 415Hz seem to be minimal at normal listening levels.

To me the experiment has given me what I wanted ...a good sound with minimal 'colouration' etc from a multitude of caps/inductors involved in a 3rd order filter set up.

What next....well a move to better quality caps...maybe some Mundorf M caps and some nice Mundorf M Foil air cored inductors.

Keith

[Moko]

That looks some nice veneer, where did you get sheets the right size, or are there lots of carefully hidden joins?

[MF 1000]

The veneer was from IPL Acoustics.... its walnut and a good price from Ivan. There are joints on either side ...but gaps are filled in with Libron Dark Walnut wax filler

[awkwardbydesign]

The veneer was from IPL Acoustics.... its walnut and a good price from Ivan. There are joints on either side ...but gaps are filled in with Libron Dark Walnut wax filler

Ivan flies a little bit under the radar for most hifiers, but he has some good product at good prices, IMO.

[MF 1000]

What next....well a move to better quality caps...maybe some Mundorf M caps and some nice Mundorf M Foil air cored inductors.

Keith[/QUOTE]


Just ordered a new pair of inductor coils and caps



Janzen torroidal inductor using 2 mm thick copper



and Janzen silver foil caps. They should be with me in two weeks ....ill keep you updated with the progress

Keith

[Pjblakey]

What next....well a move to better quality caps...maybe some Mundorf M caps and some nice Mundorf M Foil air cored inductors.

Keith

Just ordered a new pair of inductor coils and caps



Janzen torroidal inductor using 2 mm thick copper


Keith....
Have you made ay progress on the copper leaf for the B139?
I'm very interested to find out how it is done.
Peter

and Janzen silver foil caps. They should be with me in two weeks ....ill keep you updated with the progress

Keith[/QUOTE]

[MF 1000]

Ive not made any progress yet on the copper foiling.....mainly due to the tweaking off the crossovers and currently experimenting with bi-amping them too. I will eventually get round to trying out copper foiling both the outer chassis ring of the racetrack 139's and the flat face of the driver.

Of course any progress I make will be documented and reported on this thread

Keith

[MF 1000]

At last the Jantzen torroidal coils and silver caps have arrived

Straight out of the box and get them ready to fit on my test cross over boards. First impression as I unpacked them...wow they are huge... the torriodal coils are a Jantzen C-coil 3.90mH 0.6 ohmn wire gauge 2.00 mm and weigh 2lbs (900g) each. These are a simple 1st Order filter for the transmission line bass to start to roll off around at 160 Hz. The silver caps act as a high pass filter abover 2900 Hz for my twin Kef tweeters housed above the Fostex full range drivers.

I quickly fitted them onto my basic test board made for the previous monacor/maplin crossover test along with the equally large silver capacitors u



here is a couple of pics to show the size of the components....




...and 30mm high

I know they will require some burning in ....but the intial listening had me smiling ...more detail in the bass and a crisper top end. I hope this is only the start and they reveal even more as they settle in.

[earlofsodbury]

Those look decidedly Proper

[MF 1000]

Those look decidedly Proper

I love the look of the torriods...pity you cant remove the shrink foil round them (Jantzen said the coills could relax changing the inductance value) ...would love to have them mounted ontop of a perspex cyliinder - would look lkie a mini Van Den Graaf generator ;)

[MF 1000]

Finally getting started on the copper leaf 'guilding' of the B139 bass drivers. I found a seller on eBay who has 0.15mm thick self adhesive copper sheet - think of thick baking foil. I got a 1m x 300mm length for £10 inc postage to try out.

As im also restoring my IMF TLS 80 speakers so after just finishing repainting the baffle I thought id try the foil out on the B139 driver on this speaker first.

The self adhesive is very sticky ....and once the foil is creased...thats it forever - so my 1st attempt wasnt good .... but then found if you apply the foil from one end and use the edge of a bank card to smooth the foil and push away the backing paper as you go as good finish can be acheived as you can see in the pics below. The foil is easily trimmed with a scalpel...so I just ran it over the edge then trimmed it back to the edge of the front face of the B139.





A break for lunch now and then move on to the R50 TL - more pics etc later

Keith