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Cs7 with BD139 passive radiator for deeper bass?

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Joined: 25 Feb 2018
Posts: 9
Location: Berlin, DE

PostPosted: Fri Aug 16, 2019 9:01 am    Post subject: Cs7 with BD139 passive radiator for deeper bass? Reply with quote

dear forum members,

Originally I had a pair of B110's, B300B's and T33's, having in mind to create a speaker resembling the CS9, but with the tweeter section of the R105.4. Thanks so much for all the advice you have given me here.

This plan is now obsolete however, having found wonderful used R105's (see my thread below). Still, my curiosity is wide awake. And I still have the B110s and T33s lying around (I sold the B300Bs).

So I am wondering if I should try to build a CS7 instead. I'd need two B139's which seem to be relatively easily available (used or new, but expensive, at Falcon).

Looking at the CS7 construction leaflet, I see the bass rolloff begins already at 70Hz. So I wondered if I could expand the box volume and help the bass with a passive BD 139, put at the back. I have a pair of those lying around, too. Following common opinion I should use two per box. But maybe one would suffice?

I'd slightly raise the height of the box (to about 1 meter, making its appearance resemble more that of a C80, albeit bigger in its overall dimensions) and build it a bit deeper, so I should be able to reach a volume of 120 liters.

Would one BD139 per box work? Could I use the CS7 crossover? Is this a good idea at all, or should I opt for just building a CS7 and raising the lower bass by selectively enhancing the region below 50Hz, in order to get it more or less flat down to 30Hz?

I am in no need to replace my 105's and surely won't, but I am curious how the CS7 sounds, and I'd like to experiment a bit. and there is still some space left in the flat.

I am desperate for advice, so thanks in advance! does my plan sound like a good idea... or am I headed towards frustration county (vented design difficult to tune, wrong size of now slightly elongated baffle, two BD139 needed per box, better to put in a simpla port like in the Concerto)?

There could be a reason why KEF did not come up with the design I have in mind. I have heard of an obscure studio monitor by swiss builder ACR, with Fostex FT3 RP tweeter, Audax Norme C.E.L. mid driver, KEF B139 bass and B139D SP 1042 on the back. but I cannot confirm this information anywhere. And the design might not have sounded good anyway Smile

thanks so much for your input, andreas
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