Friday, March 1, 2013

DIY clone of Rogers LS 3/5A with replica 11ohm crossover

I initiated the DIY speaker project of the LS 3/5A clone as I was looking for an easy-to-fix and cost-less(aka lower cost) replacement for my mainstay speakers as when something does break, it would cost an arm and leg to put right again.

Searching the net for possibilities I came to realise the BBC LS 3/5A was probably the most cloned of the  (classified as a mini-)monitor class speaker . Hence one would be spoiled for choices of parts and/or alternatives from around the world!

For the curious, please refer to the following websites.

The Unofficial LS3/5A Support Site
KEF, BBC and the LS 3/5A

I shelved that realisation before I was reminded of it's potential a few weeks later. I was at a local AV show and heard the new LS 3/5A V2 being demo with the new AB2. The reproduction was acceptable to my ears but unfortunately ... the cost wasn't (would definately burn an extremely large hole in my pockets eg abt GBP1650+GBP1450 or GBP3000)!!!

Hence I decided to proceed with a DIY clone of the infamous mini-monitor.

I was prepared for the fact my resultant clone could/would be inferior to the real thing since there is a large cost difference and the review of available DIY clones on the net are close but no cigar.

My objective was not to create a 100% clone of the infamous speaker (as per many others) but to create a usable high quality drop-in substitute for my mainstay speakers which would not cost an arm and leg to repair if any component gives-in.

The following are some of the items to consider before proceeding with any such projects.

Would it be cheaper to arrange for a local carpenter to do the job or buy from overseas?
After much investigation, discovered it was much cheaper to procure a cabinet made from Birchwood ply overseas rather than to commission one locally (surprisingly!?!?)

Each cabinet was provided with a bare 23AB crossover. Will populate the 23AB once I manage to acquire the parts.

How much is required?

Found the answers at the following websites.

Explanation of difference between Soundproofing and Sound Absorbing
TNT case studies on stuffing material in speaker cabinets

Have ordered Monacor MDM-2 and felt layers but not delivered yet. Hence will use misc foam cuttings in the meantime

11ohm or 15ohm?
After reading The HiFi News LS 3/5A Shootout and discovering the fact that all new LS 3/5A are 11ohm,  I bought a replica of the 11ohm crossover. 

KEF(s) or the proper replacements, or, use modern alternatives?

History of Kef Drive Units from the 1960s and 70s
Summary of various KEF B110(s)

Since the required KEF models required are no longer in production and the objective was not to create a 100% replica, I bought a pair of original T27 SP1032 from eBay, and, an alternative replacement for the B110  as prices for the KEF B110 are getting silly. Actually the prices for the T27 SP1032 are getting silly-ier than those for the B110(s)!!!

Cabling (internal)
Thickness? Length? Silver or OFC?

The 11ohm crossover replica came with all the necessary cabling. Hence no worries. 

Cost for clone parts?
How much will it cost to DIY a clone? What is the average price for a decent USED pair?

Please perform a careful assessment for the total cost of  parts required to assemble a pair of clones vs the average cost for a decent used pair in your area/region.

Maybe hard to believe but I have came across DIY-ers who got carried away and invested over 70% of the cost of a decent used pair to build a clone!!! 

Please note it is highly unlikely you would be able to recover the cost for a DIY unit. Whilst the original speakers seem to have appreciated in value over time.

You should finalise how much you would spend on a DIY clone of the infamous speakers, before initiating such a project (or similar). Then compare against the cost to purchase a decent used pair (in your area/region) before proceeding. Otherwise your ROI (return on investment) maybe impacted.

Initial test

Most of the necessary components arrive before the cabinet.

Could not wait to test the usability of the various components!!! Hence I assembled the various components and placed them into a make-to-do cabinet from a pair of chilly bins!!!

Before sending signals from the amp, I verified the speaker setup to be about 11ohm with the T27 and woofer connected to the crossover.

Sounds (surprisingly!!!) pretty decent without any dampening except for a piece of foam on the back panel. Too bad the styrofoam cabinet was rather fragile and the screws kept popping out every once in a while!!!

Cabinet arrives

After opening the box

Cabinet internal construction

Baffle with cover

Front and back view

My DIY clone

Since I have not receive the Monacor MDM-2 yet, I redeployed various pieces of foam I had lying around for insertion into the cabinet.

Initially did not use any rubber seal between the baffle and the cabinet - just to try out a before and after scenario.

There was a definate noticable tidy-ness in the presentation with the rubber seal in-place.

T27 with the alternative woofer on the baffle and the felt layer  for  crossover mounting and dampening from tweeter

Just before sealing - with  replica 11ohm crossover

Completed  before applying cover

I then used a frequency analyser app for the iPhone to ensure the frequence coverage was to expectation (know it is rough gauge as professional equipment are expensive).
iPhone with Frequency Analyzer app

Initially the bass was non-existant. After the 1st 30mins or so, there was a hint of bass. More bass became audible after an hour later.

After 20hrs, the presentation began to open up.

At about 30hrs, bass from the woofer started marching in.

In the beginning I used my original late model 303 with my 2nd 33 to drive the new toy. After the first 40hrs or so, you could start hearing the limitations of the original late model 303. I then switched to my 2nd recapped 303 to drive the clone.

Bass from the woofer started to stamp it's authority after about 60hrs after usage.

Minimum run-in time seem to be about 100hrs for most clones on the net.

How does it sound so far?

After 60hrs of usage, the presentation is well behaved and very English in nature. Presentation of details was pretty good but lack the open-ness when I have gotten used to from my floorstander (equipped with a horn loaded tweeter).

Nevertheless the performance of the clone was impressive ... enough for me to invest in the AB1 cabinet with the required parts for it's crossover.

After doing some research on the net, I decided to try populating the 23AB crossover board which came with the cabinet to hear the difference from the KEF inspired circuitry. Will do so once I manage to locate the necessary parts for it.

Hence do keep an eye out for the 23AB crossover and AB1 in the very near future!

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