MY own OB speaker project

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Toppsy
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#1 MY own OB speaker project

Post by Toppsy »

For a while I had been thinking of building a pair of OB speakers but couldn't find anything I liked that had a certain WAF and appeal to me until I came across the PureAudioProjects web site and their Trio 15 range of open baffle commercial speakers, http://www.pureaudioproject.com/trio15- ... ioproject/, then Max posting up his own version of these using the MarkAudio Aplair 12P and a pair of Eminence 15" woofers inspired me to start checking out suitable alternative drivers. I wanted however to do something a little different to the normal 2 -way baffles with a full-range driver with bass helper and came across a new range of professional 2-way coaxial PA drivers from Monacor as part of their 'Stage Line' range of offerings. These come in 12", 10" and 8" versions. I asked Scott to check these out and he suggested the 10" version would be best suited for our purposes. This has a 96dB bass unit with a coaxially arranged horn tweeter with a 1" voice coil and 105dB efficiency.

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Before progressing a design further I purchased a pair the coax drivers for testing purposes and Scott came up with a test baffle design and a suitable 2-way XO.

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These are the baffles I took along to the last Yorkshire Hi Fi Club meet at David's in Huddersfield as NickG had expressed an interest in hearing the driver as a possible replacement for his Fostex FE167/FT17H drivers on his own OB speakers. It was at this meet that Nick commented he liked what it was doing, but beyond a volume level something was breaking up badly, I would guess it was around the 2k area, can't say if it was the cone or the horn, but it was a clear something is far from happy noise. This led to a revised filter for the HF horn of the XO and best I can tell has resolved the issue.

With the results of the coax confirming this is a very nice driver 2-pair of 15" Monacor woofers were purchased and I started to draft up plans based on the said PureAudioProjects Trio15 OB's. Here the PAP web site came in very handy as they provide dimensions for the individual baffles and plenty of photos of the frames and base plate and the finished speakers.

So I set about making up some routing templates from 6mm birch ply, and making up a set of baffles from 25mm chipboard.

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These side frames are made from 9mm birch ply and the bases from 15mm birch ply. These were painted matt black and the 6No baffles skinned in Tamo Ash veneer and given 3-coats of satin acrylic varnish.

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The speaker build is now finished but only the coax drivers are wired to the revised 2-way XO at the moment. These are still driven full range and as is sound rather good. There is something that these coax drivers with a horn tweeter do that is rather special. In the final XO design they will however only be doing midrange and HF duties. Here are some photos of the finished speakers.

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Though I did investigate the use of miniDSP's for an active filter set up I took the decision to stay with a passive filter for this project for the following reasons:

1. The initial cost of the DSP's for a 3-way speaker.
2. The thought of having to use 6 quality amplifers
3. My LDA P6 amps are making some wonderful sounds with the coax drivers I doubt I can find 6 smaller chip amps that will give me the same sound quality.
4. There has been some criticism of the sound quality of the DSP modules.
5. I have faith in Scott's ability to design a passive filter that will be at least as good as any active setup and I can use the P6 amps to drive the speakers.

These speakers can very easily be a DIY project though it is recommended one have a router to cut the holes for the drivers and a straight cutting bit with ball race template follower for cutting the side frames and bases. The frames are simply bolted to the base using M6 furniture joint bolts & Cap nuts as are the baffles similarly bolted to the vertical frames. The speakers sit on M6 x 12mm adjustable tilt levelling feet.

I'm not sure these will be added to the Reiver Acoustics range as really the DIY ply bases and side frames really need to be professionally CNC laser cut from sheet aluminium and then professionally powder coated. My initial investigations suggest these will cost in the region of £600 - £700 for the machining and then there is the added cost of the powder coating. Still depending on interest..............?

Anyone interested in making a pair of these baffle speakers can get in touch with me and I will provide a copy my draft CAD plan for the panels and the frames/base.

Scott has designed me the passive filter and the components have been ordered. However as the transformer core inductors for the bass units have to be made to order these shall not be available until after 16th October. I'll report further when I made up the filters and my mate Chris, Scott and me have had time to listen and make any adjustments to the filter for optimum listening and driver integration. I have high hopes for these speakers.
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Ali Tait
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#2 Re: MY own OB speaker project

Post by Ali Tait »

Looking good Colin, look forward to hearing them.
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#3 Re: MY own OB speaker project

Post by pre65 »

I like the look Colin, well done (as usual). :)
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#4 Re: MY own OB speaker project

Post by Cressy Snr »

Shoddy as fewk! :D
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#5 Re: MY own OB speaker project

Post by Dave the bass »

Shoddy, but bring 'em to Owston please Colin.
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Nick
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#6 Re: MY own OB speaker project

Post by Nick »

I look forward to hearing them.
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#7 Re: MY own OB speaker project

Post by IslandPink »

Nice work, Colin !
I'd heard a rumour something was brewing.
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#8 Re: MY own OB speaker project

Post by ed »

awesome!
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#9 Re: MY own OB speaker project

Post by gninnam »

Likey 8)
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Ray P
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#10 Re: MY own OB speaker project

Post by Ray P »

Excellent project - thanks for sharing. Watching with interest.
Sorry, I couldn't resist!
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Toppsy
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#11 Re: MY own OB speaker project

Post by Toppsy »

Thanks for the kind comments on the finished look, much appreciated. However, I'm sure most you guys can achieve a similar look and finish. If you don't fancy veneering the baffles then simply use 25mm MDF and paint them in a colour to match your room settings. However, Flexi-veneer (which I haven't used here) is so easy to use and apply and comes in 8'x4' sheets so only one sheet is required. Perhaps this will inspire you OB guys to more than just bolt some drivers to a bare sheet of any old wood, hey. :)

Dave,
Sure I'll bring these along to the next Owston meet. Just need to make up the first iteration 3-way XO, measure the speakers response and make any changes to fully integrate the sound. Simples.
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Ray P
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#12 Re: MY own OB speaker project

Post by Ray P »

Why do you think these need expensive machined aluminium supports Colin? I'm thinking a simple aluminium angle section fabrication, perhaps disguised by some nice hardwood support sections similar to the ones you've made up, would serve just as well? Could be drilled/tapped at intervals to accept various sized baffle panels.
Sorry, I couldn't resist!
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Toppsy
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#13 Re: MY own OB speaker project

Post by Toppsy »

Ray,
I was more thinking for a full on commercial offering.
There is a small degree of flex using the 9mm plywood for the vertical frames and 15mm plywood for the bases. To overcome this in wood one would have to use thicker ply and that to my eyes would detract from the aesthetic appeal. 6mm aluminium or steel side frames with (say) 10mm thick metal base would stiffen up the whole and add to the looks. There is also a lot of work to seal the end grain of the wood and then several coats of paint to get a finish acceptable for general sale. To be commercially acceptable laser cutting would to me be the obvious way to get consistent repeatable frame members. The panels have a 6-deg lean to aim the horn tweeter at seated ear level 3m distance from the speaker, otherwise if the panels are vertical there is a loss of ambiance and soundstage between seated and standing. Hand making consistent side frames with a guaranteed and consistent 6-deg angle is not easy. To get the price down for the frames I would have to order around 10 units, and I doubt I would be able to sell that many speakers. For DIY and my own prototype purposes the simple plywood frames suffice.
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#14 Re: MY own OB speaker project

Post by steve s »

Those look really nice Colin can't wait to hear them
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#15 Re: MY own OB speaker project

Post by Ray P »

Toppsy wrote: Sun Oct 08, 2017 2:14 pm I was more thinking for a full on commercial offering.
Ah, understood. Thanks for the explanation.
Sorry, I couldn't resist!
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