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Tannoy Cornetta replica... Beyma build 15" coaxial project


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Ok, my turn to start a thread here in the DIY corner. I'm excited to see where this goes, by all accounts this appears to be quite an addictive path to tread. I've decided to go big, given that I'm fortunate to have the space and am looking for dynamics and realism to cater to primarily classical & jazz listening. Hoping that some experienced and helpful souls will chime in when I inevitably need help! :thumb:

 

Drivers are the Beyma 15" coaxial - 15XA38nd - specs here: https://usspeaker.com/beyma 15XA38nd-1.htm . @mwhouston I've read all your experiences with these drivers (and later the 12" version) and appreciate the kind offer already to assist with crossovers. Look forward to your insight on the Beymas along the way.  

 

For cabinets, I was admiring the Shindo 604 and 360l Onken designs found online. The size of the sound that these designs provided convinced the purchase on the Beymas. This was until I found a slightly more sensible and easier-on-the-eye option by diyaudio veteran 'Billfort'. See Billfort's interesting corner facilitating build here: http://www.wardsweb.org/Billfort/

 

(Options) Shindo, Onken, XA38, and Hiraga designs -

 604_3.thumb.jpg.06312f9bb5e11ae511b9083c27b9dc03.jpg538429575_onkenfasteningtocleats.png.ecd5c5ea9c408110ffa1aa66cf032801.pngXA38.png.d0b6ed6bbbd3fc87fc8f7a3a0c6918c1.png

 

(Chosen build) Pics and plans (plans -> 604cnr.pdf ) for Billfort's 604-8G build speakers - 

billfort_cabs.jpg.74ef45f472fe4f1c206b8a6ae986ece0.jpg

 

👆👆👆

 

Current situation: waiting for drivers to arrive from France. Holding off on ordering the 24mm birch ply until they arrive and certain design queries are made clear, because the stuff is exxy!

 

First question(s):

- Regarding tuning the cabinet, obviously the Beymas are specced differently to the vintage Altec drivers, the web surfing I've done so far has led me to believe that I should see some success by tuning the port (see triangular port on bottom-inside face of Billfort's design) with cloth or amounts of speaker stuffing. I don't have a Windows PC for trying winISD but I imagine this irregular design would be difficult to model anyway. Should this design be workable, despite the differences between these two 15" coaxials? Particularly port size - which is considerably smaller than the alternatives above...

 

 

Edited by crtexcnndrm99
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Remember the port only effects low bass. Nothing else. 
 

My big 15” Beyma boxes had large short ports on the back. The problem with wide mouth ports is they allow too much mid range to come out too. This cancels this mid range from the front of the speaker.

 

To off set this more stuffing is needed inside the box to stop any mid range getting to the port and then the outside world. Note 15” and 12” Beymas can work in very small boxes. For the 12” it’s down to 30 odd ltrs. And a short fat port. Beymas don’t go super low which can be typical of a lot of high efficiency speakers. If bass is your thing you may need bass assistance or a subby.
 

This doesn’t detract from all the good things high efficiency speakers have to offer. Add to that coax drives with 2” titanium point source radiator tweeters  in their own horn and neodymium magnet assembly. 
 

 

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On 07/05/2020 at 10:37 PM, mwhouston said:

It’s funny you mention high efficiency speakers.

 

this needs a watch; 

 

Such enthusiasm! Haha. No those ''pros' to high efficiency speakers will be fun to discover for the first time, coming from speakers with 86db efficiency.

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Thanks for the point about the port only affecting low frequencies. 

 

The point about mid frequencies and front-facing ports reiterates what I've read so far about the advantages of placing ports on the bottom (e.g., Higara, Shindo 604 style) or side (Billfort). 

 

I also read that the larger cabs are more difficult to get wrong with mids and above frequencies provided there is sufficient bracing and internal damping..

 

Attempted to download WINE and my antivirus blocked the download. I'll have to retry (and watch the tutorial vids).

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I'm also considering including a rear (or I suppose 'side' mounted, compared to the Onken design where a rear-front baton is used) mounting support for the large driver. Despite using 3/4" birch ply I figure eliminating any potential strain is worth it 😄

 

1523661735_driversupportmount.jpg.b2123c0f17657f45f3492a3e1af22939.jpg

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On 09/05/2020 at 9:21 AM, crtexcnndrm99 said:

The point about mid frequencies and front-facing ports reiterates what I've read so far about the advantages of placing ports on the bottom (e.g., Higara, Shindo 604 style) or side (Billfort). 

Port placement (especially, relative to other surfaces) will have a (likely substantial) effect on it's operation.

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The big boys arrived today, all the way from France. :cool:

 

It's going to be a gradual process getting the crossovers, cabinet materials etc. but glad to see these arrive safely. 

 

IMG_2228.thumb.JPG.2f219be325dbe43fdbb85a785d778005.JPGIMG_4036.thumb.jpg.81769af81cccec427be62230e357d4ff.jpg

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  • 1 month later...
13 hours ago, bbe said:

Hi crtexcnndrm99

Hows it going..any Progress??

 

Best regards, bbe

Hi, thanks for showing interest :) 

 

Ask me again Saturday night... I should have plenty of build pics to share from that day! That’s the plan anyway

 

Cheers

Ash 

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An update:

 

09BDF8EF-3D79-4C2B-8587-E87023908992.thumb.jpeg.13045f9558768c6e853ea201c0bfe1cf.jpeg9CDE1D10-C013-4E87-BB46-841E3AE02DCA.thumb.jpeg.b3c277a50fefbd504e030cd6c78a8120.jpeg2EBAC179-7AF8-49C6-8A55-7CC6ADE2AD59.thumb.jpeg.fe05a007afe939aae2edc928422c0d7f.jpeg

 

We spent 12hrs yesterday building from scratch (using a scaled up version of the Japanese Tannoy Cornettta plans) and got probably 90% of the way there. Combination of the 24mm birch ply (damn its $$$) and the 24mm regular a grade for the rear and bottom sides. 
 

Left for last if the most finnicky part - the front loaded ‘horn’ / flare.. gave some bendy ply and a plan to get that done :D Oh and plenty more internal bracing to be done yet a la below: 


50462F78-50CE-4B07-8E9D-3983BA9A8C4B.jpeg.9e3ffe05bd4c37babcb962d8bc50f774.jpegB4924EAE-2083-4EC0-B410-D72356D4F552.jpeg.7e96c9acd9e48f5ee0bd5d6c5bb8ee0f.jpeg

 

Needless to say, am quite excited to hear these! 
 


 

 

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  • 2 weeks later...

Getting closer... 

 

Does anyone have any ideas on how to get this finish on the birch ply? Looks stunning and Shindo-like, I’d set my hopes on a finish half as nice.

 

(From an eBay seller)

6E7B25FB-917F-4098-80E8-0F99053AD5EC.thumb.png.f74ea316803528b04c4587b2986896e6.png

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You could use a tinted shellac. I know a guy close by who does real french polishing for a very very reasonable price.

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27 minutes ago, kelossus said:

You could use a tinted shellac. I know a guy close by who does real french polishing for a very very reasonable price.

That sounds very interesting. Because I wasn’t looking forward to eventually doing the finish... can you pm me the details? 

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22 minutes ago, tuyen said:

mind sharing details re the crossover?

 

I have the schematics for the Beyma FD2XA - https://usspeaker.com/beyma FD2XA-1.htm   if there is any interest.

 

(I have pair of the Beyma 12cxa400nd)

Currently the crossover is just a temporary thing until the build is settled. I’d be interested in your schematic though to have a go myself.

 

@mwhouston has been very generous in that regard - this crossover was one of the versions he tried with his Beymas. Xover at 1600Hz?.. his recommendation was clearly 1st order 1100Hz, so I’d intended to ask for some built to those specs with some extra nice parts when I finished building.

 

interesting to hear your thoughts re the Beyma 12’s

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Beymas crossover below that was designed for most of their 12-15" coaxial drivers. 
 

I built them with some scrap parts in the past.  Sounded not bad.   But I run equalization on the system so I fine tune the sound to my liking.    I dont think the beyma xo is designed to provide flat frequency (via notch circuits). 
 

not sure if first order slopes would be optimal for these drivers.  Atleast 2nd order ime. 
 

967830FD-0AF2-47AC-BBB9-2FCB3769DC1F.jpeg

E165784D-8637-4D41-AB81-D28DB734EEE3.jpeg
 

Overall, I dont mind the sound of the beymas.  I think the woofers produce really high quality mid-bass.  The treble is decent. Clear and extended.  Not as refined and 'soft' like Faital Pro in the highs. Likely due to the titanium diaphragms.  

Edited by tuyen
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Had another day to build today. 
 

definitely not finished but I wanted to hear them so badly.. 

 

Going back to small speakers is going to be difficult when the time comes ;) 

 

EA62E1DB-2FAE-4DDB-AFA6-88CED125228E.thumb.jpeg.d222cebd2255755b03cf92d08af9ee94.jpeg

 

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  • crtexcnndrm99 changed the title to Tannoy Cornetta replica... Beyma build 15" coaxial project

A few updates, as we get to around the 7month mark since first ordering the parts.

 

This weekend I knocked out a fair bit:

 

- Flare / front loaded horn finished, puttied, etc. 

- Baffle and horn painted (to

hid imperfections, also because most of the Cornetta builds on hifido have done this too)

 

Here are the speakers ready for their first coat of Tung oil today:

E4A774FF-A280-4061-A881-510B9CC53E73.thumb.jpeg.003f61aa05e5546f1409301ea46ffd5f.jpegBED150F8-D18B-49C5-853E-C44A913E5733.thumb.jpeg.0c5b3f955520c4aea4b4051605430aca.jpegDE4B05C6-9B14-47ED-8781-084C4E329126.thumb.jpeg.c1cc446e42367d9582b471cadea5971d.jpeg

(Marks on the baffle are fine sawdust.. I’m no painter but don’t worry I’m not quite that bad!)

 

Not too bad, considering this is what is being copied:

image.jpeg.5c9e6ea87db482978df774fbab7a1544.jpeg


After a few coats of the finish, last step (for now) is to build some grilles a la -> image.jpeg.b4a6d8f0abe45c6f329df33c60ce6466.jpeg

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And a shot during daylight this time. Need to add skirts around the base to cover the castors... 

 

As a just read on another members’ burgeoning build thread, “no replacement for displacement” :D 

 

After a morning of listening, having switched it up with a new to me MM cart, the punch out of these is very satisfying. FD76BFA9-C5AC-4BB3-9BAB-CBF7CEC667B4.thumb.jpeg.dd6413063090c54969adbf83418a836d.jpeg

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  • 3 weeks later...
  • 1 month later...

So much listening time that I still hadn’t decided on how to get the finish up to spec after the Tung oil coats above. With the news of QLD’s lockdown yesterday morning, I rushed to Bunnings between work yesterday to pick up some poly. 
 

Second thin coat on this morning, sanding with 202 sandpaper on a foam block in between. I chose a Satin finish, and I think a little sheen once they’re done is going to make them look even more like a (large) piece of furniture :) 

 

904BF385-0A63-4657-B54E-6CECB7BD0D6F.thumb.jpeg.4af74b661701285339a2840137d02f3f.jpegC37B1319-42DB-4A7B-B948-584A5980DC92.thumb.jpeg.27f403d5191d7c704000606433a76403.jpeg


P.S. Grille cloth ordered from a US speaker store on eBay and is on the way. Revived notification if had arrived at customs yesterday. MDF for grill frames sitting in the corner of the room waiting for their clothing 👍 

 

 

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Regarding placement, which is always an interesting topic for such large speakers, I have been liking the corner placement, pushed against sidewall but about 40cm out from the front wall. 
 

In the 6moons review (https://6moons.com/audioreviews/tannoy/cornetta.html) with the original 10 & 12” driver built version, the reviewer preferred straight firing to the corner loading, however the differences in cabinet size and drivers for my scaled up version probably mean this isn’t apples to apples. Additionally, being able to tuck into the corner has a substantial impact on room appearance/feeling... 

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And back in place after 3 coats of wipe on polyurethane finish. In pic 2, a subtle satin sheen. A major win from this finish has been making those veneer stripped added more durable I think. 

D8F162F4-2903-4BE9-8B57-E1493C4A43CE.jpeg

9C31B686-613F-44DD-A3EA-D1A750175271.jpeg

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Hi Ash, looks great.  Did you sand after the final application of poly? 

I haven't finished polyurethane before, am planning a 400 grit by hand with a cork block to get it fairly even, then 1200 and 2000 wet sanding with a random orbital - am looking for a gloss finish though.   Hopefully ends up with a consistent finish (whatever that may be).

 

These speakers would be pretty imposing if you didn't have them in the corner, they'd block out the sun!  How tall do they stand off the floor?

 

Edited by Janus77
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Hi mate,

They are imposing - it was a little shocking when I first wheeled them inside! I imagine / intended them to be similar in size to the Autographs (an endgame build to DIY if there ever was one), so in that respect don’t mind so much with the size. Total height on castors is 1300 :cool:
 

I had initially finished with a few coats of Tung oil. This succeeded in giving some yellowing, making the birch less of a stark white and more vintages in appearance. However the poly IMO was well worth adding.

 

I sanded with 2xx grit after each coat, using a foam block (cut off piece of open cell foam I had lying around). No sanding following the final coat, only a rub with a sheet of paper on the foam block to remove any nibs. You definitely could buffer, use 0000 steel wool or the wet sanding you are talking about to achieve a far superior finish. However I wasn’t after a strong sheen because these are pushed into the corner, intended to have bits and pieces placed on top, and generally blend in, not showing the odd knock here or there. 
 

Perhaps give the foam sanding block a try instead of the cork? I did see one fellow on YouTube use the random orbital sander a Scotchbrite fine pad on the final coat as well. 
 

Also, I was very worried about brush marks myself (also an amateur when it comes to poly finishes) and so I used a cloth to apply it. You could also use a foam brush but I think it’s superbly simple to apply nice thin coats with a lint-free cloth.  

 

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  • 2 weeks later...

Grilles went on this morning  


7FD83B52-9963-46CC-ACC1-682A2959C0A9.thumb.jpeg.142200c9b2fc5bcaca443e23142abf96.jpegDAD51791-FEA1-4BBC-A01B-B9B2FDF51419.thumb.jpeg.4bbca8df3ce9c9b26837c55410f42fa2.jpeg487F597B-630E-4FAD-A67F-1ACA976C5ED9.thumb.jpeg.59559f7260625993eb4a5b7b98cd5944.jpeg8157CF20-370E-407A-B980-AC15F192694E.thumb.jpeg.78e910e26c847ace051854ce04b8898c.jpeg

 

I feel that I’m getting close to the original inspiration :) —> 

 

40D43E73-E445-4F1E-9913-6C2B95DD75C9.jpeg.91df15cd38c225d0c85cb306b78ab46f.jpeg

 

 

85707E6A-3829-4BCD-9BF7-34DD2BA81A17.jpeg

Apologise for the room - hadn’t realised what a mess it would look to an outside observer 👀

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If anyone has a pro audio amp for low $$ that might be suitable for LF biamping alongside the Tamarisk tube amp, let me know. Cheers, Ash 

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