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Old 18th July 2013, 11:15 AM   #1
DeonC is offline DeonC  South Africa
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Question What would a Leak Sandwich bass driver be like in a large cabinet?

Hi Guys

I have a pair of Leak Sandwich (ceramic magnet) bass drivers, and for my next project I would like to mount them in a relatively large sealed (or possibly ported) cabinet. I would like to know if anyone has measured them or have experience putting them in a larger box? First let me explain what I want to do. There are two versions of this story, the short version and the long version- I will post both and you can decide which to read.

The short version:
As I said above, I want to mount them in a relatively large cabinet. Relative, that is, to the cabinets they originally came in. In the original Sandwich speaker these were mounted in a 60-liter sealed cabinet. I am planning to put them in a circa 120-liter to 135-liter box (sealed, but I want to experiment with porting too). My thinking is this: in the 60-liter sealed box, the system resonance is 58Hz, but from what I have read on the forum, the driver's own Fs is a low 19Hz. That means that the 60-liter box is a peaky loading, hence the idea of the bigger box and hopefully much lower bass. What do you guys think?

The long version:
I have a pair of Kef Concertos. Overall they are not bad, and my current system is not good enough to really expose their weaknesses, except for one part- the bass. First of all it runs out of puff very quickly if you have strong low-bass. The 3mm x-max of the B139 woofers do not really help here. Furthermore, they do not do quick bass. Take a track like Rob Rock's Garden of Chaos- the quick double kickdrum of the intro is simply blurred into one long sustained bass 'wobble'. No definition at all. So, having the Leak Sandwich bass drivers on hand, I thought I would add them to the mix, and cut the lower bass from the B139s. Here is my whole idea:

I'm going to get myself a pair of the 41Hz Audio AMP9 kit (28V max) 4-channel amps, and go full active. The active XO will be Rod Elliott's Project 09 (24 dB-Octave 2-3-Way Linkwitz-Riley Electronic Crossover). I will keep the original cabinet width (and keep the existing front baffle- just add another baffle below it for the Leak driver). I'm going to chuck the outer cabinets- the veneer has started to peel and they look bad. Then I'm going to build a new outer cabinet which will be deeper and much taller, but with the same width.

There will be more changes over the standard Concertos, and they will be as follows:
1. The crossover points will be changed from the existing 400Hz (from the B139 to the B110) and 4kHz (from the B110 to T27), all 2nd-order passive, to 300Hz (from the B139 to the B110) and 3kHz (from the B110 to T27), all 4th-order active. This has an additional benefit as the baffle-step point is at 300Hz.
2. I will add a 150Hz cross-over point (from the B139 to the Leak Sandwich bass driver)
3. The existing cup behind the B110 will be replaced by a pipe of 22.6 long and 5" diameter. This pipe will be stuffed and basically be a 300Hz Ĺ-wave TL. This is because I read elsewhere on the forum that a TL like this will help smooth out some response irregularities in the B110s response, and also because it will give lower distortion that that cup.
4. The B139 will be mounted in its own 30-liter sealed cabinet. This is in line with the spec-sheet from Kef. The port on the front baffle will be removed and the hole closed (see pic). I want to keep the B139 for two reasons: a) it will be closer to original, and b) David Wilson used the B139 as a mid-bass coupler in the old WAMM systems, so I figure if it was good enough for him, it would be good enough here.

In the new cabinets, the internal volume of the Leak bass drivers will be circa 120-liters to 135-liters. I am thinking of keeping it sealed, but with a separate sub-baffle for the Leaks, I could just as easily experiment with porting. Iíll just make one baffle for the sealed version and one baffle with ports in it. My question is just this- has anybody experimented by putting these drivers in a larger box, or better yet, has anybody measured them to get their TPSs? Iím just wondering if anybody can share their experience with the bass drivers.

Thanks,
Deon
Attached Images
File Type: jpg Kef Concerto.jpg (115.2 KB, 52 views)
File Type: jpg Kef Concerto - peeling veneer.JPG (78.9 KB, 47 views)
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