MY own OB speaker project

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Toppsy
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#31 Re: MY own OB speaker project

Post by Toppsy »

Yes Indeed it was 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.

As Chris has hinted we 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 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 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 a 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). 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.
Last edited by Toppsy on Mon Oct 23, 2017 6:19 pm, edited 1 time in total.
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IslandPink
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#32 Re: MY own OB speaker project

Post by IslandPink »

Interesting stuff. Good effort all round !
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Ray P
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#33 Re: MY own OB speaker project

Post by Ray P »

Good stuff chaps and thanks again for sharing. The developments outlined maintain the interest...

Scott, if you're reading, do look after yourself.

Ray
Sorry, I couldn't resist!
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Toppsy
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#34 Re: MY own OB speaker project

Post by Toppsy »

I have just placed an order for a couple of these:
Image
Image
together with a couple of these mid-high range horns to go with the compression drivers:
Image
Image
They should arrive early next week, which should give me some time to make up a couple of new centre section baffles to mount them on for the 2-way configuration experiments.
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Toppsy
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#35 Re: MY own OB speaker project

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The compression drivers and horns were delivered earlier in the week:
Image
The horns are quite well injection moulded in glass fibre and are 8mm thick, weigh 1.3kg each and the exposed facing and inside the horn surfaces have a rather decorative speckled matt finish. They also come with black fixing bolts, nuts and spring washers for mounting the driver. The compression drivers are well made units, measure 120mm dia. x 53mm deep, and weigh a tad under 2kg each. They come complete with fixing/mounting bolts, nuts and washers which is a nice touch. They are a perfect fit on the horn mounting ring. As with a lot of drivers these days these Celestion units are labelled 'made in China'!

I should have the new 300mm wide baffles finished later today. More photos and update on progress later.
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Toppsy
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#36 Re: MY own OB speaker project

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For those that are still following this thread, I have this morning finished the new 540mm wide x 300mm high baffles for the compression horn tweeters. Panels in the same 25mm chipboard and skinned in TAMO ASH veneer and finished with 3-coats of satin acrylic varnish.
Image.

Our host NickG and AndrewL with a couple other mates are coming over my place tomorrow for a mini gathering. It is hoped to have some fun with these drivers an see how they perform as a possible alternative (and cheaper option) to the coax units currently installed on the OB's. Nick is bringing a miniDSP and some speaker measuring gear so we should have some fun and Scott will get the measurements he has been asking me for.

More photos and reporting back Sunday.
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Ali Tait
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#37 Re: MY own OB speaker project

Post by Ali Tait »

Shame I can’t be there Colin, look forward to the reports.
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#38 Re: MY own OB speaker project

Post by steve s »

Yes, best of luck with them colin hope the day goes well
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#39 Re: MY own OB speaker project

Post by pre65 »

I'm an avid reader on this topic Colin. :)
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#40 Re: MY own OB speaker project

Post by chris661 »

Watching with interest.

FWIW, it might be worth trying removing the back cover of the compression driver, if it leaves the diaphragm in place. That way, you'll have dipole for the full frequency range.
Something I didn't quite get on with when I last tried an OB was the >1kHz range was on a 60x40 horn, and the rest was dipole. The way the room was excited was very odd. Your horn looks wider, though, so it might be fine as-is.

Chris
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Ray P
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#41 Re: MY own OB speaker project

Post by Ray P »

Waiting with baited breathe Colin...
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Toppsy
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#42 Re: MY own OB speaker project

Post by Toppsy »

Thanks for the interest guys and best wishes for a successful day but, Oh dear I feel like I'm on the spot now with coming up with a positive result. But what will be will be.

Ali,
Yes your experience with OB's would have been most useful but family comes first mate so you're doing right by not travelling down.
chris661 wrote: Fri Nov 03, 2017 1:07 pm Watching with interest.

FWIW, it might be worth trying removing the back cover of the compression driver, if it leaves the diaphragm in place. That way, you'll have dipole for the full frequency range.
Something I didn't quite get on with when I last tried an OB was the >1kHz range was on a 60x40 horn, and the rest was dipole. The way the room was excited was very odd. Your horn looks wider, though, so it might be fine as-is.

Chris
Chris,
Definitely one for us to try out tomorrow and thanks for the suggestion. Having just removed the rear cover of the compression driver it may be feasible but the dome cover that has a contact ring attached to spade connectors is just held in place by magnetism. I'll take second opinions from Nick and Andrew when they have a chance of examining the rear of the driver with the cover removed.
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ed
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#43 Re: MY own OB speaker project

Post by ed »

also watching with avid breath(baited really)...

You are tempting me to have one more go at OBs after my failure with the AMTs......

good luck
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Toppsy
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#44 Re: MY own OB speaker project

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ed wrote: Fri Nov 03, 2017 1:54 pm also watching with avid breath(baited really)...

You are tempting me to have one more go at OBs after my failure with the AMTs......

good luck
Well now Ed as it happens last that Scott was over he did comment that he thought you would like these. You are most welcome to pop over to have a listen anytime that is convenient or wait till the next Owston.
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Ray P
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#45 Re: MY own OB speaker project

Post by Ray P »

Toppsy wrote: Fri Nov 03, 2017 1:38 pm ...but, Oh dear I feel like I'm on the spot now with coming up with a positive result. But what will be will be.
Sorry for that Colin; not the intention and you're right about the outcome being whatever it is.

Personally I'm enjoying you sharing your journey/adventure...
Sorry, I couldn't resist!
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