28-2-2018

Audio Dandy LS3/5a
DIY open hardware loudspeaker



This article is about the building of my DIY Audio Dandy LS3/5a inspired loudspeaker


Part 1 - The Beginning & Building the cabinets

Part 2 - Building the front baffle & External XO

Part 3 - Listening & Conclusion








The beginning

It all began when I visited the X-Fi show High-End show in the Netherlands in 2017.
I was in general very disapointed about the quality of the loudspeakers that were demonstrated.
Personally I didn’t like the sound quality of many of them, I found them too synthetic, lifeless and also too tiresome sounding.
Then at last I visited a small room were the Stirling LS3/5a V2 were demonstrated.
I was very impressed by the sound of these little speakers.
They were sounding totally different than all the speakers I had heard that day before.
The music of these little speakers was sounding more comfortable, and also warmer.
I listened for a longer time to this speakers, because I liked them very much.
My love and respect for the LS3/5a loudspeaker was born.
I also wanted a pair of these little speakers!


Too late? …

But the fact is that manufacturer of the loudspeakers units for the original BBC LS3/5a has decided to stop producing them...
and therefore the LS3/5a cannot produced any more in it’s original form.
Therefore Stirling also had to use different loudspeakers from other manufacturers (SEAS & ScanSpeak)
and I must say they sound very good, there is a lot of bass coming out of these little woofers.
But these speakers units that are used in the Strirling LS3/5a V2 are specially designed and manufactured for the Stirling LS3/5a V2 alone, and they are not for sale for the DIY community.

So what should I do?
Should I buy a pair of Stirling speakers? or are there other options?
After visiting some DIY loudspeaker events, and DIY loudspeakers designers I felt self-insured enough to start building my own speakers.
But why should I do all this effort, when I can buy a pair of new LS3/5a V2 loudspeakers?

The answer on this question is that I find it very important that a buyer of a product in general should have full control, over her/his on own product.
This includes the right to modify, upgrade, improve, or repair it.
Nowadays these rights are taken away from us costumers.
We cannot update the firmware anymore of a lot of products we have bought, so we are forced to buy a newer version of the same product...and to throw the other (still working) product away…

Also often you cannot open or upgrade your product anymore because its so designed
that it cannot be opened without damaging your product.

Because of these reasons I wanted to make my own speaker, inspired by the original design of the legendary LS3/5a.
But then according my own personal wishes.
This way it would be my own product, build by me, so I can repair, upgrade it when I wanted.

But I had never have build speakers before, this project would be my first audio DIY project!

When I told others about my plans they laughed, or even acted irritated...
Strange because for me audio is a hobby, not a way to make money
I like to share knowledge and to help others.
By sharing our ideas we help others and also we can learn from each other.

We live in a free world, so we don’t have to share our knowledge with others, or do we?
There is license called open source hardware (OSHW) that makes sure that when you release a certain product under this license it stays open forever!
So that everybody can build it, if they want it.
This license also allows modifications and improvements, but this improvements have to released under the same licence.
So they also will be open for everybody.
This is to prevent that a company can take over the project and turn into a closed product again.

I come back about about this license in the near future, but let's first return to my idea to build my own loudspeaker.


My design criteria

So were do I start?
I met a member on the LS3/5a Yahoo group called Bert from the Netherlands that was very friendly.
He was willing to help me with my project, and he has a great knowledge about the original design criteria of the LS3/5a.
He owned a set of original 15 Ohms Rogers LS3/5a loudspeakers and he had build an identical set of LS3/5a's  himself.

After long discussions I decided to keep the outer dimensions and some typical design elements the same.
Like the rear mounting woofer, XO point around 3 kHz, removable front baffle and the special internal frame made of beech braces
But this is were the similarities stops, all other elements are totally different.

We used the DIY LS3/5a (Rogers clone) made by Bert as the starting point.


I decided to use MDF instead of plywood, also I wanted an external XO instead of an internal one, so that experimenting with other XO’s would be easier.
I didn’t wanted to use beautiful but vulnerable veneer as the finish of the speakers.
instead I wanted to use “warnex structure paint”, so that repairs can be easily done my the users themselves.
I also wanted to use XLR loudspeaker connectors like the original LS3/5 BBC prototype had.

I wanted a no-nonsense, more practical loudspeaker that would contain the best sounding loudspeaker units, and XO parts currently available.
So that this speaker would suitable for High-Resolution audio streaming.

But because the original loudspeaker units aren't produced any-more, I had free choice to find some other brand of loudspeakers.

After having listened to many loudspeaker designs in my life, I am very impressed by Mundorf AMT tweeters from Germany.
They have a very detailed and open sound character, and you will hear every micro detail of the sound recording.
Also I liked Audax loudspeaker units very much from France.
They have a very comfortable, smooth and typical sound character that I found very appealing.
So I decided to uses these two brands for my project.


The Audax HM130CO 13cm 5.25" woofer


Some specs: Zamak die cast frame, High Loss Rubber surround
Woven carbon fiber cone, Edgewound flat copper wire
Vented pole piece with protective grill
90dB Sensitivity

The handmade in Germany Mundorf AMT tweeters:
This model is specially designed for use in closed cabinets


They have very strong magnets inside, so be carefull with metal tools! so that you don't accidentally dammage your tweeters.


Building the cabinets

First I bought the wood (MDF) and I went to my local woodworkshop


Be carefull for your fingers, these machines can be dangerous
 


Here are my panels very precisely cutted.

I used black MDF bcause I thought that this way I didn't had to paint my speakers
but I didn't like the grey-black color so I had to paint the wood anyway :-)


MDF is environment friendly PEFC certified "wood"
(MDF is in fact made from recycled wood)



I glued the boards together with wood glue, and I used a special mall to make sure that the cabinets would be straight.

Then I used this machine to create nice bevels around the edges of the cabinets
because paint doesn't hold on sharp edges.

After this I glued the special beech braces frames inside.
Later the front baffle will be screwed against this frame.

 

First I used special MDF primer, which was only available in the color white :-)

After the primer I painted the front panels black with Warnex structure paint,
this paint is also often used for painting professional PA loudspeakers and flightcases.
 

I found that this paint is very easy to work with, i gives nice results when you use a roller.

Now the cabinets are black again :-)

I didn't wanted to use normal woodscrews for attaching the front baffle because if you use the woodscrews frequently they will not hold so good anymore that can lead to leakage of air.
A friend of mine found this metal plugs that can hold metal bolts.
Bolts are much better then screws.

So we drilled holes in the beech braces and then glued these plugs inside the holes with
special PU foam glue.

I used M6 metal bolts with inbus head instead of the normal woodscrews.
These metal bolts can be fastend many times without the danger that the wood of the
frame will be dammaged.

there was only a little problem...
The Audax mid/woofer was a little too wide, so I wouldn't fit inside the cabinets.
So I bought a special belt sander to cut off only 1 a 1.5 mm of wood :-)
The wood was too hard to do it manually by hand, with this device it took only a few seconds.





 


Now the Audax mid/woofer speaker fits inside the cabinet!

Time to glue the bitumen damping pads inside, the dimensions are all arcording the original specs.



The story continues:
 

Part 2 - Building the front baffle & External XO



               
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