Open Baffle Project

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Paul Barker
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#31 Re: Open Baffle Project

Post by Paul Barker »

Hpw the poundstretcher ob worked. bass he;per was the limit to the quality. drivers sold. The small sigmas as full range went into a OB dimensions of a sheet of 6f by 3ft plasterboard plywood sandwitch wiht a far better bass helper which I brought to Owsen maybe 3 or 4 years ago. Those I like a lot, but they cant be used in a normal house. Bass helper was a European (German?) 12" vintage driver that I cant remember the name of, but very expensive, Alnico. Mike those inductors I wound myself with very very thick winding wire, which was speced for 5kw inverter I wound for my Milling Machine. Cost me £100 for enough to wind the inverteer and these coils. I used an online calculator to come up with the number of turns and on test at Island Pink's house on his bridge they came out cock on. I didnt have a bridge at the time I wound them. It is vert hard wire to wind with. Dont know where they are now though.
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#32 Re: Open Baffle Project

Post by MJK »

Ali Tait wrote: Fri Apr 14, 2017 5:28 pm Martin, I'm currently using one of your OB designs - B200 and twin Alphas per side. I'm looking for a bit more detail in the bass. Would It be a good idea to go for Betas, or would you have another suggestion?
I have never used the Beta 15A woofers so I can't provide an absolute answer. People seem to be very divided on their feelings about the Alpha 15A woofers, some really like them and others complain the bass is too loose. Not sure what your set up is but a few things you can try before spending money on different woofers.

1. Use a SS amp and see if that tightens things up. I did not have much luck using a tube amps and my recipe/trade-offs for OB designs.

2. Take some cardboard and create a 7.5 inch deep tunnel for each woofer on each side of the OB turning them into H frames. That will lower the tuning providing deeper bass and a lower Q for the woofers.

3. Try listening to only the woofers with their crossover. Disconnect the full range driver and see if this resulting sound contains the issues you are hearing. Try it the other way around keeping only the full range driver and crossover. This might help you localize the problem to the woofers, full range driver, or the crossover integration of the two.
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Ali Tait
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#33 Re: Open Baffle Project

Post by Ali Tait »

I run the speakers actively, Alphas run up to 200hz and are driven with a 500w SS amp.

I'm not unhappy with the bass, just would like a bit more detail, the Alphas seem to mask a bit compared to others I've heard, including Betas.
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Ray P
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#34 Re: Open Baffle Project

Post by Ray P »

IslandPink wrote: Fri Apr 14, 2017 4:29 pm...that sort of plaster could be very dense and non-resonant.
Yes, that's my thinking.
IslandPink wrote: Fri Apr 14, 2017 4:29 pmHow thick do you think the material would be ?
It'll need to be a bit trial and error but my gut feeling is about 25mm around the bass unit, thinning to maybe 18mm towards the top. With the plaster bandage it's easy enough to vary the thickness pretty consistently. Obviously it has to be strong enough to support itself. I'll probably embed some wire mesh into the plaster to try and give it a little more impact resistance and maybe wrap it in a light epoxy/Kevlar or epoxy/carbon laminate - might look quite nice in Kevlar too as it has a light straw like colour.

Ray
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Ray P
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#35 Re: Open Baffle Project

Post by Ray P »

Just thinking through designing the mould to lay the plaster up on, I think I've got most of it.

Can anyone tell me how deep a rebate I would need if I chose to flush mount the Beta 15A units? I've found all the other dimensions.

Ta

Ray
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SimonC
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#36 Re: Open Baffle Project

Post by SimonC »

Ray P wrote: Fri Apr 14, 2017 7:30 am That's very kind of you Simon, I'll take up your offer if I may.
Ray
No problem, I'll pop them in the car for Owston :)
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#37 Re: Open Baffle Project

Post by Ray P »

Thanks Simon. If you get half a mo any chance you could check this out for me?
Ray P wrote: Sat Apr 15, 2017 1:18 pmCan anyone tell me how deep a rebate I would need if I chose to flush mount the Beta 15A units? I've found all the other dimensions.
Cheers

Ray
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JohnG
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#38 Re: Open Baffle Project

Post by JohnG »

The idea of trialing new baffle materials is of interest to me.
I have decided when I attempt my OB to make a baffle from Fibre Cement Board, it can be sourced locally very cheaply as off cuts or excess ordered boards. The idea is to laminate it, it can be worked with as easily as any common board substance.
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Ray P
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#39 Re: Open Baffle Project

Post by Ray P »

I've been thinking on constructing the baffle for this project and wondering about Nick's comment that was referenced in post #1, "this isn't optimum - Quasar shape is but this works pretty well and is good for starters". Someone has previously provided me with a Quasar drawing, attached, and reproducing that shape would seem to be a possibility with plaster construction, though the baffle would need to be wider to accommodate the Eminence unit. Would it be a reasonable/sensible thing to do simply build a wider Quasar baffle, based on the attached diagram, for use with the Eminence/Fostex drive units?

Cheers

Ray
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Nick
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#40 Re: Open Baffle Project

Post by Nick »

Yes, just take the size for the 15" bass and apply the same profile as the real Quasar which was based on the 12" bass driver. But my advice would be build one using MDF first and have a listen.
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Ray P
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#41 Re: Open Baffle Project

Post by Ray P »

Thanks Nick.

I note, and would normally heed, your advice about an MDF build but for this project I want to explore using plaster as well as experiencing OB sounds at home so I'll give some more thought about that before I 'cut any turf'. The main issue I'm wrestling with is the practicality of making a plaster OB, which is a large item, in one piece - I don't think joining separate sections together will be very tough so I'll probably try a small experiment or two.

Ray
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pre65
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#42 Re: Open Baffle Project

Post by pre65 »

Thing is Ray, with building in MDF to begin with you will have a reference for further experiments.

If the plaster ones don't hit the spot for you you'll not know if it's the principle (OB) or the materials (plaster) are the problem.
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Nick
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#43 Re: Open Baffle Project

Post by Nick »

Or do what James did first (and I did, it does work) build them out of cardboard and gaffa tape.
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Ray P
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#44 Re: Open Baffle Project

Post by Ray P »

Fair comments...

Hmmm

Ray
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#45 Re: Open Baffle Project

Post by Ray P »

So with the Owston meet approaching, when I collect the drive units for this project, I thought it time to start making some practical progress on this project.

I've located a FabLab type facility in Bristol that means the cost of CNC'ing the panels for a first build is very low (<£200 including the ply) so my limited woodworking skills won't be put to the test.

This weekend I'll start to work up the CAD drawings to get the panels cut. I plan to build the cabinets as per the quasar drawings, widened a little to accommodate the Beta15 units.

If this build is to my liking I'll explore the use of plaster for constructing the baffle at a later date.
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