Audio Dandy LS3/5a
DIY open hardware loudspeaker

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

Part 2 - Building the front baffle & External XO

Building the front baffle

Be the LS3/5a has a closed loudspeaker design, so it's very important that the cabinets are air tight.
Therefore I spend a lot of energy in creating a airtight front baffle.
First of all I use bolts with metal plugs in my design instead of wood screws, and also I used rubber foam on the entire back of the front baffle.
On the the beech braces frame inside the cabinet I used the same foam, but this foam is cut out of one piece of rubber.
So in the edges there are no little gaps.

Photo above: this was my first design, using straight rubber strips, you see you get little gaps in the corners were air could leak out...

Now the sealing foam is made out of one piece of rubber, so no more leaking air from
around the edges!

This is my first design with the Mundorf AMT tweeter and Monacor 135C Carbon mid/woofer.
later I decided to go for Audax mid/woofer instead.
In this drawing I wanted to use velco tape to hold the front speaker grill.
later I decided to not use velco tape...
The Stirling LS3/5a V2 also doesn't have the velcro tape anymore instead they choose
for 4 small velcro circles in the cornes to hold the speaker grill.


I glued a piece of paper on the black front baffle so it was easier to draw were the holes would be drilled

Drilling holes for holding the speaker units

The Mundorf tweeter fits in the front baffle


This is the backside of the front panel, the rubber foam covers the entire surface.
The foam has one self-adhesive side.

The rubber foam is glued on the front baffle, now the speaker-units can be mounted.


I used self-locking nuts to attach the speaker units to the front baffle

On the frontbaffle I used the same rubber foam to make sure to also no air could escape were the Mundorf tweeter was mounted.
I found that the original rubber of the Mundorf tweeter was too hard, so I removed it
and I glued of big piece of rubber foam on the front, then I carefully cutted away the
excess edges.


Gently pulling the remaining rubber foam away.
Now the Mundorf tweeter is totally airtight mounted.

Around the edges of the Mundorf tweeter will come a felt square to control the diffraction effects of the tweeter.
Just like the original LS3/5a design.

I will do these "felt square diffraction" tests later, so for now, I leave it how it is.
I first want to experience how it sounds without, to have a starting point.

I used a big hole drill to make the holes for the mid/woofers

Now it almost starts to look like a loudspeaker :-)


I used this tool to make sure that the bolts don't stick out on the front baffle


I used standard "Pritex" damping foam

You cannot see it on this photo but on the each side of were the subwoofer is located,
I cutted away the foam on both sides, so the foam couldn't touch the back of the subwoofer membrane.

To connect the internal speaker wire to the speaker units I used shrink plugs.
The cables are a bit longer, so that in case of repair the front speaker baffle can be taken off easily.

With an inbus screwdriver it's very easy to tighten the front baffle.
the idea of using bolts instead of screws works perfectly!

Time to mount the front speaker baffle onto the chassis with the inbus bolts

Creating the external XO loudspeaker cables

I decided to use XLR audio connectors for connecting my external xo to the speakers.
Not only because the original BBC LS3/5a prototype has these XLR connectors, but also
because I would leave the possibilty open to experiment with "ground" (GND) in the future.
The orginal prototype didn't use "ground" however, but I maybe would.

For the connectors I used the Neutrik "NC3MPR-HD" male chassis connector
that not only because it has gold plated contacts but also has a dust and water sealing,
so for a closed loudspeaker design this is a big plus to make it easier airtight.

For the female XLR connector I used the Neutrik "NC3FXX-14-D"
Because this was the only connector that could accept a thick 10mm speaker cable.

After a long search I found a XLR loudspeaker cable that had 4 wires, and was small enough to fit in the Neutrik XLR female connector.
The brand is: "Tasker" type: "C 268 - 2x1.50 - 2x2.50 16+13 AWG O.F.C" this cable is made in Italy.

In my current design I didn't use ground (GND) yet, so I used only the two thickest wires
for + and -

Making these cables was much harder that I expected
The rubber is stiff, and it's difficult to get the cables into the XLR connector, but after some efforts I succeeded!
The cables are now ready.


Creating the connector back plate

I also wanted a nice connector back plate, because it's important that the XLR cables are connected to the right chassis connector on the speaker.
So I draw a image of a connector back plate, and I went to a online shop that can make
aluminium name cards for houses.
I just uploaded my design and a few days later I received two nice custom made panels
They look very professional I think.

At my local woodwork shop they have many industrial machines from the original old Philips factories.
A member helped me with drilling two holes in the aluminium back plate with a very big drill.

Now the Neutrik XLR chassis connectors can be connected to the back connector plate.
and the  the back speaker panel can be glued to the speaker cabinet.
I made only the mistake to not solder the internal wires at this point...
Advise: it's better to solder the internal speaker wires before the back speaker panel is glued to the main speaker cabinet.
Because now you have much more space to solder.

So if you can see each speaker unit has it's own connector.
I did this to make it possible to bi-amp the speakers in the future.


The external XO designed by Leon Huijgen

Leon Huigen holding the Audio Dandy LS3/5a, and in other hand his external XO design

This is how the finished external XO looks like


I consider my very lucky that in my city also lives the famous loudspeaker designer
named: "Leon Huigen"
He is also the XO designer of the PureAudioProjects "Leonidas" XO.
What I have learned so far, is that the XO plays a very important part in the total design of a loudspeaker.
A XO can break or make the loudspeaker, and therefore I wanted the best XO for my project.
When I told Leon about my plans to make a loudspeaker inspired by the LS3/5a he liked
my adventure and he was willing to help me with designing a simple but Audiophile Grade XO for my Audio Dandy LS3/5a loudspeaker project!

So after making an appointment I went with my Audio Dandy LS3/5a speakers to
his studio.

Leon promised me to connect the XO of his “Krill XL” loudspeaker to my
Audio Dandy LS3/5a speakers one more time, so that I would at least have a first impression of how e.e.a. could sound.
When I was in Leon’s studio and were we were listening, Leon tried to get everything as good as possible by adjusting some XO parts.
Leon paid very close attention on my comments & reactions!!
So this XO is actually customized for my ears, in Leon’s studio listening room!
Therefore Leon advised my to start with cheaper parts, because my livingroom
is totally different.

So in fact this it a Maarten Starters XO :-)
But apparently Leon's first design was universal enough to also sound credible & audiophile in my livingroom and also at my friend Bert house.

There are definitely technically perfect XOs to think of, but whether that sounds better?

The result:

Leon Huijgen designed a minimalistic XO that only contains 4 parts (!)
two air(foil)coils, a capacitor and a resistor.
It uses a 6 dB order slope for the Audax mid/woofer and a 12 dB order slope for the
Mundorf tweeter.

His original design was this:

I have to admit that I have zero experience and knowledge of designing XO's
Therefore I designed a loudspeaker with an external XO so that I could outsource
this important but complex task by other talented people.
Leon realy saved me for this project, thanks to him the Audio Dandy LS3/5a has
succeeded, thank you Leon!


Building the external XO

Leon adviced me to first experiment with cheaper parts before buying audiophile
grade parts.
But I was so conviced of the sound quality of the initial design that I ordered audiophile parts right away...

This are the parts I ordered:

- Intertechnik: Tritec air coil 2.70mH 7x0.60mm

- Jantzen: 0,280 mH wax foil coil +/-2% 12 AWG Rdc 0,09  Ohm +/-5%

- Mundorf: capacitor: 10.0uF Mcap EVO Oil (Referentie: MEO-10.0T3-450)

- 10.00 Ohm 1% 10Watt Superes Resistor

Bert helped me with building the external XO's:

The Intertechnik Tritec air coil (in red) are very heavy, they weigh almost one kg per piece


I used normal "bed plate" hardboard wood for holding the XO parts together
You can buy it in every woodcraftshop, it's cheap, and it's very functional
in combination with tie-wraps.

While shopping in the Swedish shop IKEA, I found a nice little bamboo box called "DRAGAN"
I found that this box was perfect for the external XO.
Sometimes it's cheaper and also nicer looking to just buy
existing products and to use them in another concept, than try to make them yourself

The photo above is the first assemblage (with different connectors)

This is how the external Audio Dandy LS3/5a XO "Designed by Leon Huigen" looks now:

( I still have to isolate the copper ends of the Jantzen wax coil with rubber
heat shrink tubing )

We used these handy connectors called "welding clamps" of the brand "WAGO"
to connect the XO parts together.

This clamps has two advantages: it goes very easy and fast, you don't have to solder, and the connections are also very firm and solid.
Another advantage is that this way you also easily can change a part if you want to experiment with other resistors, capacitors, etc.
You don't have to solder to parts anymore.

Now the XO is ready it's time for the first listening test!

The external XO designed by Leon Huijgen connected to the Audio Dandy LS3/5a DIY
standing on the self made subwoofers of Bert (we didn't connected these subwoofers during these tests) they were just used like speaker stands.

to be continued!


Part 1 - The Beginning & Building the cabinets

Part 2 - Building the front baffle & External XO (this page)

Part 3 - Listening & Conclusion


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