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Old 20th August 2007, 03:43 AM   #1
Geoff H is offline Geoff H  Australia
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Default New OB project

After much research and maths I finally took to the saw bench. It seems to me the most discussed topic on OBs is bass response. In another thread some time ago, John (in CR) suggested an array of 6x9 car speakers on a W baffle as a bass helper.

Well, I had a couple of 6x9s laying about, so why not give em a go. The main drivers I have been working on for some time, so all that was needed was a crossover to try out the combo.

Standing 900mm high, and 450mm wide, tapering to 250mm at the top. The main drivers are 6" single cone Panasonics, with bitumen treated surrounds, several coats of PVA on the cone with a bias to stiffening the apex to extend the top end, and an extra magnet to increase sensitivity and improve transient response.

The helpers are nothing more than Sansui SB-3693s minus the pod mounted tweeters.
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Old 20th August 2007, 03:49 AM   #2
Geoff H is offline Geoff H  Australia
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The baffles at present are 10mm particle board. I expected some vibration from this, however, there is more life in the sound, compared to what I had when the drivers were mounted on 16mm MDF.

Cut from a 900x600 mm sheet, the triangular off cuts become the braces, forming a U-baffle at the floor.

This is the messy side, with prototype crossover.
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Old 20th August 2007, 03:52 AM   #3
Geoff H is offline Geoff H  Australia
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The biggest surprise was the bass response. I was planning a biamp to force the bass.
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Old 20th August 2007, 03:54 AM   #4
Geoff H is offline Geoff H  Australia
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A notch filter to kill that peak, and I was convinced it was worth proceeding.
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Old 20th August 2007, 03:57 AM   #5
Geoff H is offline Geoff H  Australia
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The crossover and notch filter, as it stands at present. The low pass inductor is a multi tapped secondary on a 30VA transformer. Once I establish the correct value, I'll hunt out a better quality unit.
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Old 20th August 2007, 04:32 AM   #6
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Closeup of the National 6"?

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Old 20th August 2007, 04:46 AM   #7
Geoff H is offline Geoff H  Australia
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Hi Dave, I think you've seen them before.

Before the surgery:
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Old 20th August 2007, 04:47 AM   #8
Geoff H is offline Geoff H  Australia
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When I grow up, I want to be an Altec.
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Old 20th August 2007, 04:51 AM   #9
Geoff H is offline Geoff H  Australia
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And as they are now, with tips from BC, thanks.
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Old 20th August 2007, 04:59 AM   #10
Geoff H is offline Geoff H  Australia
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And the extra magnet. ex microwave magnetron.
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