Ok. So it's not wood, but I thought I'd share anyway

[flanajb]

Recently I have been experimenting with making items out of GFRC (glass fibre reinforced concrete) and ornate veneers. My latest project was to take my black nasty veneered mission speaker cases and make something a little different.

So here is the end result. Just need to make a wood tube for the lower hole and they are done.

I used white portland cement and then polished them up to 1200

 

[Woodchips2]

They look good =D>

Are you going to tell us how you made them ?

Regards Keith

 

[Karl]

Look great. I'd also be interested to hear how you did them.

I've wanted to make some speakers for a long time. I am going to make a sub for home first.

Always loved the Sonus Faber speakers

Cheers

Karl

 

[n0legs]

They look great =D>
What else at home is going to get that treatment ?

 

[flanajb]

They look good =D>

Are you going to tell us how you made them ?

Regards Keith

Thanks.

I am terrible for taking photos as I go, but I will try and explain the process

1. I made the mold out of white faced melamine and then routed a couple of circles out of chipboard.
2. I then used a fillet ball and modelling clay to create the radius on the edges.
3. Once that was done, I made the GRFC mix. It is basically a 1:1 sand / cement with super plasticiser and 15mm fibre glass added.
4. I poured a small amount into the mold until it was 18mm deep and to the top of the 3 melamine circles that were screwed to the inside face.
5. I then placed a block of foam that I had made using 25mm polystyrene sheet into the mold and clamped it down
6. With the foam block in place I just had to then fill the mold to the top
7. Once filled I gave the mold a quick vibrate using an old orbital sander
8. Left for a day and then dug out the polystyrene and removed the cured unit from the mold
9. The face came out very polished as it was, and I used a wet 1200 diamond grit to finish polish the face and side.
10. The speaker units have been bonded into the cases using epoxy. I think I could have designed a better way so that in the event I need to replace one I don't have to make a right mess getting the old unit out, but as this was a proof of concept I thought I'd just get on with it

I am really looking forward to testing them to see how they sound

 

[Woodchips2]

Fascinating, thanks flanajb.

How do you prevent the GRFC sticking to the former?

Regards Keith

 

[Stimpi]

Thanks for showing us your speakers, interesting, do let us know how they sound.

Regards
Mike B

 

[flanajb]

Fascinating, thanks flanajb.

How do you prevent the GRFC sticking to the former?

Regards Keith

As melamine is pretty polished and smooth I have not had problems with it bonding to the melamine. Some people do apply a thin layer of bees wax to the melamine. I did give the melamine a rub over with acetone before pouring the GFRC.

It's actually pretty straight forward. You just need to make sure you design your molds so that you can remove them post cure. That is why I used foam on the inside as I knew that trying to remove melamine from an internal cured concrete box would be impossible without having to cut the melamine out

 

[Bradshaw Joinery]

Love that!

 

[xy mosian]

The first pair of stereo speakers I owned were concrete. 12" spun concrete columns to be exact with an upward pointing Wharfedale 10" double diaphram speaker in each. To me, young in '67, they sounded great. They certainly didn't move around when I turned the wick up.
xy

 

[Eric The Viking]

Wasn't that a Linsley Hood design? We had a single drainpipe one too (mono system) - I think the plans were in Wireless World.

I replaced the bass drivers of my Monitor Audio MA7s just before Christmas. On a whim I took a rounding-over router cutter round the bass port (the drivers are mounted to the front of the baffle). It's hardly visible, but it made a significant and very welcome difference - the bass is a lot smoother and less 'lumpy' than it used to be.

Back on topic, Flanjab's cases look very nice. I'd be a little nervous about recessing the tweeter to that extent though. You might find it's a bit oddly resonant because of the thickness of the front.

There's an old trick: for the best stereo image, arrange them so the two axes cross around 1 or 2ft in front of your nose (equilateral triangle made by the two speakers and you, the listener). As you move your head, physically away from one speaker, you come more on-axis to it and off-axis to the one you're moving nearer to. It stabilizes the image remarkably, especially with bookshelf speakers in my experience, but it's also good for larger ones too.

 

[xy mosian]

Hi Eric,
I cannot say whether I was using a Linsley Hood design, the whole lot, apart from the columns, came as a kit. There seemed to be a lot a shared information about in those days. Perhaps the Wireless World article kicked off the kit?
I am not familiar with the Monitor speakers, or any others these days, it sounds as if the bass port is only cabinet front thickness in length. That of course will lead to a short organ pipe resonance as well as a standing wave effect across the port. In rounding over the edge you have obviously changed, or eliminated, either or both of those effects. Perhaps something Monitor would have done had it been easier in a production environment? Either way if the sound pleases you more, Great!

xy.

 

[Eric The Viking]

It's the classic toilet roll, goes about 3/4 to the back. I couldn't match the original bass drivers, which frankly weren't very good. The new ones are Monacor IIRC, and not bad. I replaced the tweeters long ago with Audax soft dome ones, and re-capped the crossovers, so they're a bit likethe classic axe that's had three new heads and five new handles - only the wires, the foam inside and the outer woodwork are original now.

I think the port did indeed 'honk' nastily. The bottom end is smoother now, and, I think, slightly more extended than before. It's not much of a roundover either.

 

[xy mosian]

Thanks for the extra information Eric. As with many other things there is no one correct answer. You are obviously pleased with the results, great!
An update on your question about concrete column speakers. In Briggs book 'Loudspeakers', my edition 1969, but could have been earlier, he gives dimensions for a plywood column cabinet. In the text he credits the design as being of Dutch origin to which he was guide by a Mr. Bach, a distributor of the Ronette Binofluid cartridge. The first stereo pickup cartridge he used for demonstration purposes.
The concrete column variation was clearly for those who were not able to do the woodwork, must pre-date this forum.

xy