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.

FRANKENKEILIDHS - Zombie Speakers Rise Up: PART 3

PART 1 here
PART 2 here

The starting point, a set of cabinets in very good condition, but kinda missing tweeters, mid-bass drivers, wadding, crossovers, terminals and any sense of self esteem:

Empty cabs - no drivers, crossover, wadding, terminals nor bases

Inside, Linn fitted these "Kustone" blocks which are said to help with absorbing internal reflections

The Linn logo is moulded into these, but a bit tricky to see here

Its a loosely packed set of granules, held together with adhesive.  Water would probably pass through this material

Here you can see some of the internal cross-bracing and the thickness of the MDF in use.  These are suprisingly sturdy and well constructed boxes

Further internal bracing - the flat board with small holes is horizontal and the larger hoop is in the vertical

So I started with tweeters - and already there is some doubt over how to calculate the budget for this build, as I attempt to keep track of the spend.  I have decided the following (possibly dubious) rules:

- I only include the cost of what goes into the final version
- Parts tried along the way can be sold on or used in other projects, so are not included in the total
- Where I've used parts which are components of some other product or project, I've allocated a nominal value to them, based on a vague recollection of what I paid for the complete product
- Labour is not included, otherwise I'd be looking to buy a brand new pair of M140s or something...

Here were my choices of tweeters.  Why Mission?  Well, I have some lying around in the workshop, there's loads of them about and they sell at very reasonable prices.  The left hand flat faceplate driver looks very similar to other Linn drivers from earlier designs such as Isobariks and early Kabers.  But they also look very similar to a million other soft dome tweeters out there and probably originate from a limited number of manufacturing plants, regardless of the branding on the product.  Of course, there will be many subtle variations in design, materials and sonic outcome.  This particular pair are from a pair of Mission 737R speakers from the 1980s.  Sourced from a pair I had that suffered a little too much from aging cabinet glue and the mid-bass drivers having brittle rubber surrounds.  So I paid about £45 for those originally, breaking them after about 3 years of ownership.  Let's call it £15 the pair.

At the time I was looking into this, a pair of much more recent Mission 782 tweeters came up on ebay and I picked those up for £18.  As it happens, later testing revealled suprisingly little difference in the performance of these drivers - the 737R driver sounding a little more enthusiastic, the 782 smoother and more cultured, but these were very slight differences.

At £15 and £18 a pair, both options look like they're going to be within the budget.

Tweeter options.  737R (1980s) and 782 (90s - 2000s). Front

Rear views with the 737R at the top

Here they are in the original homes:

Mission 737R

Mission 782

Trial mounting these in the cabinets immediately gave the need for the use of a file (to provide clearance within the cabinet for terminals in the case of the 737R, some head scratching about the way the face plate is designed on the 782.  Much use of blu-tack too.  Mocking up stuff is a bit crude, rough and ready, but hopefully gives an approximation of the way stuff will work when finished from a sonic and physical perspective.  I had a pair of old Linn tweeters in the workshop too, but there faceplate is huge and the magnets won't go through the hole in the Keilidh baffle.  I don't have any wood routing equipment so major changes to the holes in the baffle were of the radar.  This is my first real attempt at doing stuff with speakers, so I wanted to keep it as straightforward as possible.

Mid-bass drivers:  the main challenge.  Where to get something that will fit, and at the right price.  I'm sure Monacor's drivers from the likes of Wilmslow are very good, but they're out of budget for this build.  Pretty much nothing else fits in the size and power bracket.  The size though, is common place in the car audio arena.  But then they always seem to come coupled with a matching tweeter (and a not so sophisticated single capacitor crossover, in the main).  So an ebay automated search was instigated and a couple of weeks went by.

The up popped something quite interesting from Monacor's CarPower branded speakers - a 165mm woofer, boxed, new old stock, no tweeters and 2 pairs available, model CRB-165PS.  At a buy it now price of £25.95 a pair, worth a punt.  Only 4 ohms per driver though - which is the standard in the car hifi world, but something which could present amplifiers with a load challenge.  The cones on these are polypropylene, which might fit well with the tweeters, with the 737R also using that material in its mid-bass driver.  The look like a metal cone, with their blingy sliver finish.  With their 4ohms and 35W nominal power handling, they were always going to be a bit of a gamble.  Manufacturer's details here.

The back of the Mancor CarPower mid-bass driver.  The basket is very thin steel (in line with the price of the drivers) and I added some foam pads in an attempt to damp them a little.  Pictures of the fronts come later.

More on mid-bass drivers later!

The final component is the crossover.  Another rake around in the workshop and I dug out some old Mission 773e terminal / crossover units.  The Missions, like the Keilidhs, are a 2 way design with 3 drivers - again the mid-bass drivers doing identical work and arranged vertically above and below the tweeter.  They look like this:

Mission 773e - similar to the Keilidh in concept, but newer, cheaper and a somewhat less well built cabinet.  Decent sounding for their price though.  Might be a good donator of a crossover.  Or not.

So what are these crossovers worth, when considering the budget?  They're from a pair of 773 that I bought from ebay which were described as "immaculate".  When they arrived, they'd clearly been stood in a puddle at some time and the side panels were separating from the base, with the wood de-laiminating in the way that MDF does. The cabs were good only for the wood recycling skip down at the local tip.  Fortunately a full refund was paid immediately and the speakers weren't required to be returned.  So I have 4 drive units, 2 tweeters and a pair of crossovers spare to help out with any problems I have with the pair we have in the dining room.  I'm therefore going to count the crossover costs as £0.  If you're not convinced by this logic, no worries, it all comes back to bite me later...

So the major components are selected, a few bits and pieces such as terminal posts have been sourced and build can commence.