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My Ikea Blanda Bowl Build Diary

Posted 6th April 2013 at 07:56 PM by mondogenerator

So upon seeing many nice Blanda bowl projects here on DIYAudio I thought it about time I had a try and see what all the fuss is about!

About a year or so past I went through a phase of buying the nicest small wide-band drivers I could. Whether I achieved this is subject to the readers' opinion

So I have a pair of Mark Audio Alpair 5, and a pair of Tangband W3-1285SG. Both of these drivers were available to me in the UK at a very similar price-point and they both fall roughly into the 3" wide-band category. (Shown in the following picture alongside some Tangband 2" drivers)

Click the image to open in full size.

I chose to buy the 20cm Blanda bowls in bamboo. Gross volume works out at ~2 litres. Factor in stuffing or denser absorbent and I guesstimate a 1 litre volume.

This is really too small for the Alpairs, but the 2 dB rise towards the cut-off wasn't thought of as hugely detrimental especially as I accounted for half the volume as absorbent material, i.e. net volume of only just 1 litre.

F3 is at around 140 Hz (unless you consider the rise at resonance as in the WinISD plot, in which case it is ~160 Hz)

In any case, the aim would be to integrate with a 'helper' woofer, and the rise in the wide-band output would help contribute to Baffle Step Compensation.

The volume of 2 litres is too large for the Tangband, but again this was ignored. I can lose volume easily enough

In this case there is no Baffle Step Compensation, and despite the lower F3 the 'helper' woofer would need to contribute the greater part of any BSC applied.

Due to the 20cm diameter, I expect to need BSC from around 500 Hz.

Click the image to open in full size.

I still haven't totally decided which to use, but I'm going to start with the Tangbands, the logic being that their cut out is a few mm smaller (again I can lose, but not re-gain).

With this I sanded the varnish from the Blanda bowls using 180 grit glass-paper first, then 320 and 600 grit, and a 'wet' sand with spirit and a final sand.

I was surprised quite how well the varnish was removed and how nicely the bamboo material polishes up with a good sand.
It really took me next to no time at all, which I why I don't have a picture showing the prepared bowls.......
....... I just got carried away with the work.

Firstly, I sealed with a thinned coat of exterior varnish, before leaving 12 hours to dry.

The next day, A light sand to denib/de-dust, followed by a clean with spirit, allowing time to dry, and then another coat of the varnish.

The following photograph shows the bowls at this stage, with the 1st real coat of varnish:

Click the image to open in full size.

The WinISD port calculation spat out a reasonable 65mm long 23mm diameter port.

It just so happened I had a small scrap of Stainless piping

Click the image to open in full size.

Ill see how that pipe goes, but I may just opt for a plastic pipe (even though the port will be more or less hidden)

The next part involves cutting the driver cut out. Ive got a dremel and I expect I will need it!

However joining the two near hemispheres is something I am also not fully decided upon.

Ive seen the disc in the middle approach, to make the finished sphere-ish shape more spherical. I could use some birch ply to to the task, but im not sure that it would look right.

Either way, I intend to have some type of additional internal structure within the finished sphere, to strengthen the structure, and to diffuse the rear wave reflection.

Firstly, on to the driver cutouts...
..... Back when Ive done them.
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