Thursday, 8 January 2015

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.

1 comment:

  1. Hello Neil, I see that you have experience with the 773 speakers.

    Do you have any photos of the speaker disassembled? I am wondering if the speaker housing is enclosed to the top half or it uses the whole length of the housing to generate bass?

    The reason I ask is because I am looking to convert these speakers into bookshelf size.

    I have a pair of Mission 773 floor standing speakers. They sound great, but the finish (black wood effect vinyl) has started to peel off, it is possible the previous owner let them get slightly damp or the material has over time become too tight and come off on its own. I think it's called Sheffield Oak Umbra Vinyl Fablon.

    I am thinking of rehousing them in a smaller enclosure so that I can fit them on shelves. My question is, if I maintained the distances between the different speakers in the new enclosure, will a new enclosure be detrimental to the sound? I would like to go for a black wood finish, which shows the natural wooden texture. What wood should I use and what thickness? What do I do about feet?

    How about something like Oak Crown Cut Plywood MR Veneered 1 Side Only ? Possibly in 18mm/22mm thickness.

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