"What a refreshingly honest blog about listening to music through hi-fi. So happy to see views based upon the enjoyment of music rather than so-called sound 'quality'." - Peter Comeau, Director of Acoustic Design at Mission / Wharfedale

Thursday 8 January 2015

FRANKENKEILIDHS - Zombie Speakers Rise Up: PART 5

PART 1 here
PART 2 here
PART 3 here
PART 4 here

Driver installation time.

70W max it says on the back of the CRB-165PS drivers.  The spec says 35W RMS.  Enough to get a decent volume without being a PA system.  The chassis of these drivers is a perfect fit into the baffle cut-outs in the Keilidh.  Even the holes are drilled in a perfectly aligned arrangement to allow bolt to go straight into the existing threaded bushes embedded in the cabinets.

The chassis of the driver is a very thin pressed steel (at least its not moulded plastic) which pings quite nicely when flicked. So I stuck some foam pads on the legs in the hope that one of those little tweaks might help the whole.

At this point, I was using "chocolate block" connectors to connect the cables inside the cabs to short links with spade terminals.  This would allow for multiple fitting and removal without worrying about soldering - that could come later.

Rear of the mid-bass driver
Front of the mid-bass driver.  Note foam surround.  The driver looks like its metal, but actually that's a very thin film of something shiney (not sure what though) on a core of polypropylene.
It order to seal the drivers into the cabinets, gaskets are required.  These were supplied by Wilmslow Audio.  They're about 8mm thick before use.  Once clamped into the cabinets, the drivers appear tightly mounted, then about an hour later another half a turn can be applied to the bolts.  This goes on approximately another 6 times as the gasket compresses over time.  The bolts are M4 threaded.  I've chosen to use allen cap headed stainless steel bolts.

The uncompressed gasket in place on the back of the driver and held in place on the mounting bolts
All 4 mid-bass drivers were installed very quickly.  Laying the Keilidhs on their backs makes access to the internals and installing the drivers very quick.

Now to the choice of tweeters. As in the picture below, the tweeter mounting plates look like a similar diameter.  However, seen from the side they're very different.  The 737R driver (on the left) is essentially flat with the magnet protruding a small amount to the rear.  The 782 driver (on the right) has an essentially flat back panel with the chassis and magnet protruding forward - creating a very shallow horn shape.

Tweeter options

I don't have the tools, nor the confidence to think about routing the baffle nor to machine down the tweeter backplates nor faceplates.  So the 782 option almost excluded itsself immediately because the backplate is too big to fit into the recess in the baffle, but the smaller front protruding section is not deep enough to pass through from the back of the panel and be flush with the front.

However, I did want to give both options a listen, just to be sure it wasn't going to be worth the effort of finding another way.

To get the 737R tweeter to fit, a small part of the baffle opening had to be made slightly larger to allow for the terminals to sit inside the opening.  Given this wasn't going to prevent the fitting of standard tweeters again at some point in the future, the powerfile came out and some MDF dust was created.  Although the mid-bass drivers are bolted in at the moment, the tweeters need mountings that are different to the originals, so are blu-tacked in place at this point, making sure the ring of blu-tac is complete to ensure a seal.

Laying on their backs, installing the drivers was straightforward

Here the 737R tweeter is sitting slightly proud of the baffle, but not significantly so

Looking a bit more like a speaker again

Here the 782 tweeter is loosely installed (even by blu-tack standards!), clearly showing a poor alignment compared to the baffle.  To achieve time algnment, tweeters are usually mounted further back than mid-bass drivers, so this wasn't going to go well.

782 tweeter from the front view

At this point, all the drivers came out again to be able to install the internal wadding.  From converstaions, it seems the Keilidh was filled with polyester wadding.  However, it seems somewhat harder to find out how dense this should be packed.  The internal bracing in the cabinet is very solid just below the lower mid-bass driver.  It has 4 small holes in it, but I'm not sure if this should be packed with wadding or not.  I choose, at this point, not to fill this cavity, thinking that if the bass doesn't sound right, I can add some into there later, whereas extracting it again looks like it would be hard work.

So, polyester filling?  Where to get that from?  Quick chat with Mrs Musings and it seems that cheap pillows are filled with the stuff.  That's lucky as we have some of those in the garage - they've been used for packing stuff in the boot of the car, in trailers etc. to protect items in transit.  Scissors into action and 3 pillows are soon emptied of their filling.

I choose to pack the material quite tightly, remembering to feed the cables through before they get lost in amongst the wadding.

Here you can see the small areas filed out of the tweeter cut out

Labelling the cables for each driver seemed like a good idea

At this point the gaskets still rebound to a reasonable thickness when the drivers are removed.  Within a few weeks they stay pretty much compressed when the drivers are removed. so continuous re-tightening seems to become unnecessary.

Crossovers and first listening in the next part.

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