Le Cléac’h Acoustic Horns

Trade Secrets

For anyone contemplating their own acoustic horn factory........

Horn Lathe

Unless you have one of these in the garage you are going to have to make a lathe / horn mill for yourself!

Horn Mill

Horn Mill Azurah Horn Mill

Here is the azura machine – a round table on a 1” shaft driven by a Woodlathe and skateboard wheel. 

AH-160 Horn On Lathe AH-160 Horn On Turning Neck

Cutting the profile

Grinder Jig

My eureka moment: Jig up a 100mm angle grinder on a plate like this …

The angle grinder has the template follower concentric with the cutting wheel – this means the cut is not effected by the angle the grinder is held at relative to the work. This has the enormous advantage of enabling the curve to be ground exactly to the template – not hand finished to match it.  There’s a big difference.     


The Template is made from 6mm MDF.  Mount steel ruler as shown and ensure the set square runs smoothly up and down.  Plot the curve from x,y coordinates.  like this ….

Marking Out Template 160 Template    

The cutting tool fulcrum must however follow a curve equidistant from the desired curve.  This curve is achieved by the simple expedient of describing multiple arcs back from the desired curve.  The equation defeated me – but that’s what geometry is for. Offset is half the grinder wheel diameter - PLUS half the bearing diameter.

Update: Jean-Michel kindly designed me a curve calculator spreadsheet with the equidistant curve delineated. All that is now needed is to plot this onto the mdf sheet.
Horn Templates      

Making a plug mould

Turning Foam Blank

The plug mould blank is made from polyurethane foam – built up in layers from sheet, or 2-pack poured into a rough mould.  The initial shape is turned from this blank with the grinder, a few mm short of the final curve.  Next, a fibreglass layer is built up on this, and ground to just shy of the final curve.  The last layer is gel coat, or an easy sanding primer, ground to the finished profile.  Remove the grinder marks by light hand fairing, and polish.

The trick is to sand back the template in stages until achieving the final curve at the last pass.

The finished plug mould is only used once.  The first female is taken off and further finishing is done on this. From this female the production mould is made.


AH-425 009 AH-425 017

Laying up

Polish mould with releasing wax
Gel coat 1
Gel coat 2 – make thicker round the throat area
Resin / matting 1
Resin / matting 2
Resin / matting 3
Flowcoat / Q-cell mix
Break out product from mould – 3mm mdf wedges works best
Trim off edges and sand back to top of step


Images are self explanatory…

Cut throats -  jigged up angle grinder and adjustable bench
Ream to exact size with tapered sanding reamer
Cast the flange – mix resin and calc carb.
Mark up and drill driver mounting holes
Update: brass template for drilling flanges - most accurate method of drilling the mounting holes. 
Surface finish
Update:  spinner for surface finishing made from cheap Bunnings wood lathe with lay shaft and trusty skateboard wheel…

Cutting throats

Cutting Horn Throats Cutting Throats 160hz
Cutting Throats 2  

Casting AH-340 Flange
Casting AH-340 Flanges

Acoustic Horns-Marking Up Flanges Acoustic Horns - Marking Out Flange    

Horn Manafacture: Drilling 340 Horn Making Horn - Drilling Flange 160s DIY Horns - Drilling  
Drilling 160 Horn DIY Horns - Drilling DIY Horns - Drilling  

D.I.Y. Horns: Final Finish Table Ground Coated Blank Casting AH-160 Flange  


Hole Cutting Router Jig

Flange Mould With Spigot