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PostPosted: 15 May 2014, 07:05 
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I just took delivery of these Beyma drivers: http://www.beyma.com/products/coaxials/112XA30ND8. Boy are they heavy, the weight of efficiency. I'm thinking on making a pair of Zu copies https://www.google.com.au/search?q=Zu+speakers&client=firefox-a&hs=mIb&rls=org.mozilla:en-US:official&channel=sb&tbm=isch&tbo=u&source=univ&sa=X&ei=AKt0U8WbDIrLkAXm4YGABQ&ved=0CD0QsAQ&biw=1280&bih=736. What should I call them Zoo? Not funny.

I guess these should work well with with my low power amps. At this point I'm not sure what sort if box they will go in or where to cross the tweeter. The box only has to be about 30 to 40 ltrs (ported). The tweeter can be crossed as low as 1.2K. I'm thinking an external Xover with 1.2K, 2K and 4K selectable Xover points and 0db, -3db and -6db selectable padding. I'd like to do a Zu copy which means the box will be a lot bigger than 40ltr but I like the way they look. Also I would have the driver over hanging the baffle board.

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PostPosted: 16 May 2014, 17:27 
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Hi Mark,

Some more info on the Beyma 12XA30ND driver http://www.usspeaker.com/beyma%2012XA30nd-1.htm
They have some extra graphs and offer a crossover (1.8kHz) but no schematic.

Driver looks very interesting. Great sensitivity. Low Qts so you will need a large enclosure to get bass. Ideally a horn, double-bass reflex or a transmission line can work too. Did the driver come with any plans? The crossover might be a tricky one. The HF driver is 16 ohm and hot on the response so it will also need padding. For XO point you are prob looking in the 1.2 to 2 kHz range. Recom. crossover frequency on Beyma website 1.2 kHz or higher (12dB/oct min slope).

Cheers

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PostPosted: 16 May 2014, 18:26 
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Based on a few calcs supposedly the drivers can work in 30 to 40ltrs with a 100mm diameter port @ 150mm long. A friend is going to do some testing so see how close the posted TS specs are to the real speaker. From there we will consider a box. I'm still thinking Zu or Zoo!

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PostPosted: 21 May 2014, 02:28 
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My DIY speaker buddy Ron did a lot of testing of the Beyma drivers.There were a few critical difference between the testing and the TS figures posted by Beyma. From the test results the speaker box only needs to be 30ltr with a 100mm diameter port @ 136mm long. These speakers will not go super low but will produce weighty articulated bass.

Ron was particularly impressed with the tweeter section. He ran it up and down a number of times from 500hz to 20K listening for dips and peaks which he claims even expensive tweeters will have. The Beyma tweeter section is first class and was extremely linear right through the audible spectrum. Ron believes mid and beyond should sound particularly good.

One thing I was shocked with was the woofer section rolled-off heavily from 2K and beyond. The specs say 4K. WRONG! So now we have a Xover point - 2KHz. Also the tweeter section measured 12ohms and not 16ohms at 2K. So Xovers will be based on 12ohms.

I will have to switchable Xovers - 1st order at 2100KHz and 3rd order at 2K. When using the 0.5W amp 1st order with switchable in and out choke on the woofer. When using any other amps 3rd order.

Why third order? This is one of Ron's little tricks. 3rd order Xover image like hell. He was able to demonstrate this with small gorgeous little three-way bookshelves he made for some one else. On a live orchestral piece the speakers vanished never to return and the room filled full of music. Stunning. The secret is a 3rd order Xover.

I have a box design already and now to get the design of to my box builder - Don.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 21 May 2014, 18:22 
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Hi Mark.

Yes - measured drivers is the way to go. You are probably looking at an F3 of 60Hz. What will you do for deeper bass.

I'd be tempted to try the 3rd order crossover a little lower, perhaps 1.6 to 1.8kHz.

Cheers

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PostPosted: 21 May 2014, 18:34 
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Gio you have guessed what I intend to do. They will require support on the lower register this is where the stereo subbies I made a short time back will come in. Also I will use a 3rd order Xover @2Khz.

Last night at the Audio club we listened to some great looking speaks made by a member with a Xover and setup by Ron. Again Ron used a 3rd order Xover here. Again there was some outstanding sound staging. Ron also 'tends to apply individual Zobels to bass and midrange drivers. I feel this crushed dynamics and makes the speakers sound flat and a little boring. Bass to me did not feel right??
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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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PostPosted: 08 Jul 2014, 01:38 
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I just got the blank boxes to mount these speakers. They are 33ltr with some more of my weird vertical (in this case more diagonal) bracing. Beyma say 100 ltrs but a few other design programs claim 30ltrs. From what I understand low Q small box and must be ported. The port is 100mm X 136mm.

Here is an image of inside he box. It is more bracing on 19mm MDF than space. I have now done a final sand on the boxes and added a synthetic wadding. The primer and top coat are mixed and ready for painting. Hopefully in the next few days they will at least be primed.
Attachment:
IMG765.jpg
Attachment:
IMG766.jpg


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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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PostPosted: 20 Jul 2014, 07:50 
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It has been very wet in Southern Vic. over the last month and this made it hard to find a day I could undercoat the boxes. But finally they are done and hopefully in the next few days I can top coat. I'm also working on the Xovers. 1st order on the bass section and 2nd order on the treble section. I'm rolling at 2kHz.

For my more powerful 5W amps I'm going to make a 3rd order Xover.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 24 Jul 2014, 08:12 
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Have finished the Beyma speakers. Images to follow. They sound quite good but as ALL speakers have a sound\tone\voice and either we like its or we do not. At this point I do.

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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
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PostPosted: 25 Jul 2014, 20:31 
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All finished and now running in. Sound good currently. -6db roll on woofer at 2K and -12db on tweeter section. Xover boxes are packed with stuffing and currently a -6db L pad on tweeter section.

Plays loud with 5W 6V6 amp (Black Lace) and even 2.5W 6EM7 amp (Abstinence). Might try dropping the tweeter another 2db but OK for now.

Boxes have a my stippled paint finished and magnet grills. Boxes lightly stuffed. Louder you play them the more the bass picks-up. Boxes are now 96db efficient. Preamp now at 9 o'clock and not 11 o'clock.
Attachment:
Inside.jpg
Attachment:
Port.jpg
Attachment:
Magnet.jpg
Attachment:
Xover_1.jpg
Attachment:
Xover_2.jpg
Attachment:
VoXConcentric_1.jpg


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Projects: "Lagoon" - tube preamp with cathode follower | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic


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