My personal Open Baffle speaker project [Archive]

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Toppsy

08-10-2017, 08:07

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-open-baffle-speakers-pureaudioproject/, and then MaxN posting up on Audio-Talk forum http://www.audio-talk.co.uk/phpBB3/viewtopic.php?f=4&t=6916 his own version of these using the MarkAudio Alpair 12P full ranger and a pair of Eminence 15" woofers inspired me to start checking out suitable alternative drivers for my own project.

I wanted however to do something a little different to the normal 2-way baffles using a full-range driver with bass helper(s) 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 (Scottmoose) to check these out for me and he suggested, based on the published datasheets, 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. Scott and I have found in the past the published data of the Monacor drivers has been pretty accurate to be relied on so this gave some degree of confidence.

http://www.audio-talk.co.uk/colin/OB_01.JPG

Before progressing a design further I decided to purchase a pair the coax drivers for testing purposes and Scott came up with a test baffle design and a suitable 2-way XO to get me started.

http://www.audio-talk.co.uk/colin/OB_02.JPG

http://www.audio-talk.co.uk/colin/OB_03.JPG

These are the baffles I took along to the last 'Yorkshire HiFi Club' meet at David's (MCRU) premises in Huddersfield since Nick Gorham had expressed an interest in hearing the driver as a possible replacement for his Fostex FE167/FT17H drivers on his own OB speakers that he has not been 100% happy with. It was at this meet that Nick commented he liked what it was doing, but noted that 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. I should say David's listening room is quite large and not any easy room to drive speakers and perhaps we had the baffles placed too close to the rear boundary wall but the volumes we were having to use in that room are far in excess what one would be listening in a home environment. However, there is a ragged rise in response in the driver FR published plot from 2.5K - 3.5K that likely is the causes of this issue. This led to a revised filter for the 2-way 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, base plate and the finished speakers. With some judicious interpolating this led me to CAD up the baffles and frames to something akin to the originals.

So I set about making up some routing templates from 6mm birch ply,, to make up duplicate copies of the side frames and bases and then making up a set of baffles from 25mm chipboard.

http://www.audio-talk.co.uk/colin/OB_04.JPG

http://www.audio-talk.co.uk/colin/OB_05.JPG

The side frames I made from 9mm birch ply and the bases from 15mm birch ply. These were painted matt black and the six individual baffles covered in some rather nice Tamo Ash veneer and given 3-coats of satin acrylic varnish.

http://www.audio-talk.co.uk/colin/OB_06.JPG

The speaker build is now finished but currently only the coax drivers are wired to the revised 2-way XO whilst awaiting the full 3-way filter make up. The coax drivers 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.

http://www.audio-talk.co.uk/colin/OB_07.JPG

http://www.audio-talk.co.uk/colin/OB_08.JPG

http://www.audio-talk.co.uk/colin/OB_09.JPG

http://www.audio-talk.co.uk/colin/OB_10.JPG

http://www.audio-talk.co.uk/colin/OB_11.JPG

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 router bit with ball race template follower for cutting the side frames and bases from the 6mm ply templates. The templates are best cut with a jig saw and finished by hand to final shape. 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.

These are a personal build project and 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..............?

As said earlier these are not that difficult a build and are suited to DIY build and so I thought I'd share the design with you folk if anyone has fancied building a pair of OB's but have not got WAF appeal. These can be made to look more domestically acceptable than a lot of other DIY baffle projects. 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.

Macca

08-10-2017, 08:41

If they sound as good as they look then you've cracked it there, Colin.

struth

08-10-2017, 08:42

Very nice.. Very nice indeed.

brian2957

08-10-2017, 08:45

rubber duck

08-10-2017, 08:49

Toppsy

08-10-2017, 09:48

Very nice Colin. I'm assuming running just the single coax driver would not be sufficient for decent bass extension? How efficient are the speakers with the 2x15in drivers? And what sort of freg response are we looking at? Thanks.

You are correct that in OB use from my and Chris's (Stratmangler) listening experience of the 10" coax driver on the test baffles and finished speakers does not give sufficient bass extension. However, Klang+Ton do a vented box speaker for the 10" coax driver called the 'Studio 10' that can be found on the web and is in kit form. This quotes bass extension to 60Hz. But having spoken to Scott (Scottmoose) given the right type of floor standing speaker design that could be extended down to a reasonable 40Hz. Top end extension is to 20kHz.

The final speakers coupled with 2 x 15" bass units wired in parallel with the coax driver it is hoped for a frequency response between 29 to*32hz – 19Khz (in a typical room)

Toppsy

08-10-2017, 09:52

Hi Colin , hope you are well .

These look absolutely beautiful , as does all your work . I wish I had the required skill to build something like this . Also I have to be careful because my listening room is small and I have limited space .

Looks like a fantastic project for those who can do these things .

I really enjoyed reading this post , thanks for sharing :)

Brian,
There is a 10" OB version that has much smaller single baffle and can use the same side frames but with a narrower base. This would suit smaller rooms and has 16.5" wide baffles.

brian2957

08-10-2017, 09:59

That sounds interesting Colin . I'll measure later . Thanks .

Toppsy

09-10-2017, 09:58

How efficient are the speakers with the 2x15in drivers?
Apologies Jeff didn't answer your efficiency question. Without measuring the final speakers and making allowance for baffle losses the simple answer is the expected efficiency of the speakers is 93dB - 94dB. perhaps a little higher so could be driven by 300B SET amps.

rubber duck

09-10-2017, 21:43

Thanks Colin, that's good to know. And I imagine it will be an easy load as well?

Toppsy

10-10-2017, 06:57

Thanks Colin, that's good to know. And I imagine it will be an easy load as well?
Yes. That is one of the design goals.

Bass driver transformer core inductors should arrive Monday next week, I already have all the other components, so I should have the 3-way filter built early next week and can report back initial listening review. I'll invite Chris (Stratmangler) around to give feedback. Watch this space..........

Toppsy

22-10-2017, 08:59

The Transformer core inductors finally arrived from Germany earlier in the week

http://www.audio-talk.co.uk/colin/INDUCTORS.JPG

I have just finished the 3-way XO'ers temporary lash-ups for testing purposes for when Scott and Chris come over this afternoon. Should be an interesting tweaking of the filters session. To add to the mix I have also the 2-way modified XO that Scott designed for the Coax drivers as standalone speakers that on the baffles and without any added bass help do sound rather good but as one would expect lack bottom end extension but nevertheless are an engaging listen.

As an aside earlier in the week I did try the twin 15" drivers driven direct with no filter and they are surprisingly good. The spec sheet states the FR for these drivers is F3-4000Hz and I don't doubt this listening to the drivers alone. This suggests to me that they will work rather well in a 2-way configuration replacing the 2-way coax driver with a horn loaded compression driver. Depending how this 3-way configuration set-up works out I reckon this could be worth further experimentation. I have in mind a rather nice Monacor 1.4" compression driver (MRD-300) that when coupled with their MRH-300 mid-high range horn has the capability of a 1kHz - 20kHz FR and the driver a recommended minimum XO of 1.2kHz. This however, will require a slightly larger central baffle to accommodate the horn, so a complete new speaker build.

I'll report back later our initial listening findings and any fine tuning mods.

Toppsy

23-10-2017, 17:17

Well Sunday afternoon proved to be a very fruitful and successful afternoon.

I have to give my thanks to Scott for coming over from Hull even though he was not well. However I think he left feeling a lot better in himself than when he arrived, thanks perhaps to Lynn's home cooked pastry's and good few Stepsils to calm his evil chesty cough and sore throat.

Chris (Stratmangler) had hinted previously he knew we had a good speaker from the initial experiments with playing the 15" units full range without a XO and also playing the coax driver mounted on the finished baffles and using Scott's modified 2-way XO that resulted from my taking the test baffles over to David's Huddersfield Sunday gatherings. The end XO is a combination of using the modified coax filter with the bass filter element of Scott's first attempt 3-way filter. This gave a very cohesive and engaging sound but, though the lower bass was present it was a little muted in the mix. This was solved when Scott suggested we make the capacitor in the bass shunt CR a much smaller value. Five minutes with the soldering iron and the cap was changed and hey presto bass definition solved.

Apart from this the demo of driving the bass units direct with no filter convinced Chris and Scott they would work very well as a 2-way when coupled with a quality compression horn tweeter. I suggested the Monacor 1.4" compression driver and horn that would require a larger central baffle (it would have to be increased in size from 300 high to around 330mm to accommodate the horn). This would require a complete new speaker frame build. Scott then suggested a 1" Celestion compression horn driver and a matching mid-high range horn as a better option that from the manufacturers published data sheets and FR plots he preferred and would also fit perfectly on the existing size 300mm high baffle. So all I need to do is buy a pair the drivers and make up a couple new centre baffles that will bolt straight on the existing frames. This should also have the advantage of being more efficient, pushing the efficiency into the upper 90's dB and the XO should also (in theory) be simpler. So that's the next stage of development for these speakers.

Stratmangler

23-10-2017, 17:31

It was a very fruitful afternoon, and Scott's input was invaluable.
The elements for a really good speaker were already in place, it's just that the various elements weren't quite gelling.
A bit of alchemy happened, and base metal became gold.
It could have gone the other way, and we'd have created purest green, but thankfully it wasn't the case.

Various bits of music were played, basically trying to trip the speakers up, and we didn't once have cause to wince.
Eventually the "torture track" (Metallica - S&M - Nothing Else Matters) was retrieved from its hiding place, and for once I actually enjoyed it.
As far as I'm concerned that counts as a result.

If they weren't so big I'd be after a pair ... :)

Vinyl turner

04-11-2017, 19:26

Toppsy

05-11-2017, 13:12

Hello Colin,

I have read this post with great interest and congratulate you on creating such a great set of speakers, which look the 'bis' too.

Looking through your photos I was however more than intrigued with a particular image I spotted (which was incidental to the focus of the photo): And hope you can tell me more.

Your ninth photo is a view of the whole assembly but what caught my eye was the black & white photo montage picture on the wall above your rack.
It shows various instruments, central to which is the badge that can be seen as "Laurinat & Co Berlin"........ is this a picture you created yourself or is it one from a commercial source ?

The significance for me is that as I type this I am sitting next to Mrs. vt's piano, which was made by Laurinat & Co, Berlin !!

The World is made up of such amazing coincidences and I can't believe having spotted this in a post about DIY OB speakers :stalks:

Hi Mark,
Thanks for the interest in this thread. I started it as I believed these OB speakers could be a DIY project for all you budding speaker builders. When the development side is complete I may offer them as a kit of parts - drivers, fixings, XO components etc. with a set of plans for the home constructor to make the side cheek frames, bases and a set of baffles. However for those that just wish to source their own drivers and fixings just a set of plans. However, these are still in the development stage and from this weekends gathering and feedback from Nick Gorham and a couple of other good mates I need to make the side cheeks, frames deeper to bring up the lower bass which will also mean new bases as well. So they are a few weeks off being finished. I also learned that OB's need to be at least 1.5m away from any rear wall and some wall treatment/high frequency damping wall panels is really a requirement to fully integrated speakers with the current driver configuration.

Now as to the large picture mounted on the wall I bought this from 'The Range' multi-store in Rochdale. We happened to be passing the store on a shopping trip for other things and my wife suggested we pop in to see if they had a couple of table lamps for my then new music room. It was whilst browsing for lamps I spotted the picture and as thought what a perfect montage for my music room. I also found a couple lamps so a very fruitful diversion thanks to the missus.