Decca DK 30

Aug

Member
2005-07-24 11:30 am
London
Hi Guys, just a quick question to anyone who has experience of Decca Ribbon Horn
I picked a pair up recently and noticed the Red and Black Terminals are reversed. I would guess the Negative terminal would be the un-insulated one, but would just like confirmation.
Can some one confirm for me?

Thanks

Aug
 
Could be an error or can be clever .... it depends on the magnet position.. if the magnet s in the original position black knob should be on non isulated bolt ... if magnet is reverse red knob on non isulated bolt ... there is a sticker on the magnet .....IF ... my memory dont fool me it is supposed to be toward tranformer ..... I did use these 20years ago ..
 
Some factories are sloppy. I'd test them.

BTW, you do want all left and right pairings to be in phase. Quite important. But not crucial about phasing mids and tweeters (or sometimes even woofers and subs and mids).

I've messed with phasing tests lots of times and using a mic. Inevitably, phase and anti-phase will have distinct frequency responses but often hard to say which is the more desirable one.

Yes, I know how saying that will irritate some readers.

Ben
 

SoundRight

Member
2010-07-28 10:47 am
I had pairs of these to go between stacked quads. As I recall the earth was negative. By the way, it is essential to ensure this contact is absolutely clean. It is also essential to ensure they have a capacitor to protect from dc and a steep network. If the ribbon looks slack it needs replacing. Believe somebody is remanufacturing them. Fantastic design for its age...but you probably could do better with modern ribbon/horn options.

I also agree with an earlier post. Depending on crossover configuration polarity choice will depend on filter slope. 2nd Order you would usually invert and 3rd order will give you +/-15 degrees polar tilt depending on polarity connection. As it's a horn if you are not time aligning acoustic centres frankly I would go by audition!
 
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A few notes on them.

They were designed to have two spots one third down and two thirds down, left and right of the ribbon, of silicone goo between the ribbon and the edge of the phenolic carrier, for damping the ribbon itself.

Also, they are NOT going to handle much power, especially power below their nominal roll off freq. Use properly matched power (or a suitable divider/pad) and higher order filter than the simple cap that is in the unit. Replacing the cap with a more modern polypropylene cap (if you can fit it) is a good idea. I seem to remember and internal cap, right?

The purpose of the horn was to extend the LF response a bit...not that it goes low.

They're not really up to the performance of some modern ribbon drivers, imho.
Fun though. Exotic too. :D

_-_-
 

Aug

Member
2005-07-24 11:30 am
London
Dk30 Phase

Hi Guys, thanks for all your great responses.
I intended to get back on to it today but got waylaid again. I'm sort of rebuilding a pair of Mordaunt Short MS700. I've replaced the Bass and Mid Units with Monacor 12 inch Kevlar Bass Unit and Kevlar 5 inch Mid Unit. All very much experimental. Hoping to modify existing X-Over to suit.

I'll let you know how it all pans out.

Many Thanks