Column speaker design

[Kay Pirinha]

Hi,

two or three weeks ago I picked up a new carpet for our living room. It came on a large and rather beefy cardboard roll, 185 cm (6'1") long, internal diameter 30 cm (12"), wall thickness 1 cm (~3/8"). I immediately came to the idea to cut it in half (that leaves about 85 litres net volume per unit) and build a pair of round, coloumn-shaped 3-way speakers into them. As the volume isn't that large, I'm thinking of building vented enclosures. Now several questions arise:

1)Which is the best way to get the roll precisely cut?2)One way to do the speaker is to install the woofer into the upper opening (so that it radiates upward) by use of an appropriate board, close the lower opening and get the vent somewhere at the backside, next to the bottom. Another way is to get the whole unit on stand-offs (about 5 cm/2") and to mount the vent into the bottom, using a donut-shaped round board. The third way is to close the upper opening completely, mount the woofer to the bottom one (still using stand-offs) and get the vent to the backside.

Are there any objections against any of these ideas?

Last but not least, which speaker combo do I have to look for? May it be a good idea to use one designed for a common prismatic enclosure of a similar volume?

Best regards!

 

[ctrlx]

take a look at el-pipo by nelson pass.
although its a TL, it may give you some ideas on driver mounting etc.

 

[jplesset]

Also look at the LXmini on Linkwitz' site:
LXmini Challenge

 

[scottjoplin]

What's a "common prismatic enclosure"? Googled it unsuccessfully

 

[Kay Pirinha]

Rectangular edges.

Best regards!

 

[scottjoplin]

Eh? sorry Kay, I'm none the wiser.....😕

 

[Kay Pirinha]

Take a box with rectangular planes. That's what is commonly done.

Best regards!

 

[scottjoplin]

I feel I'm being really thick here, do you mean a normal rectangular box, I've just never heard it described that way?

 

[Kay Pirinha]

Yes, that is it. Maybe I was wrong in using this term that I derived from batteries, which can be cylindrical cells, such as AA, AAA etc., or prismatic ones, such as LR6.

Best regards!

 

[scottjoplin]

Thanks Kay, ha ha yes when I googled it I was taken to batteries, now all is clear. They are a nice size tube, have you thought of using them for a simple TL sub?

 

[Kay Pirinha]

I do not have enough space for installing a sub, and I don't like it, btw, as I use tube amplifiers - DIY, of course

. So each one should be a complete speaker in a design that isn't very common.

Meanwhile I've got some advice from Visaton, a German manufacturer (or just dealer, I don't know). Maybe it is best to use stand-offs and install the woofer in the bottom board, radiating downwards, with the top closed. The woofer/squawker xover frequency has to be rather low then for good spacial impression.

Best regards!

 

[scottjoplin]

This looks like it might give you some ideas SpeakerBuilding.com - Speakers from the sewer - Print

 

[Kay Pirinha]

This looks like it might give you some ideas SpeakerBuilding.com - Speakers from the sewer - Print

Very impressive, thanks! That's a concrete tube, isn't it?

Unfortunately it's dimensions are very different from my carboard roll/tube, and I do prefer a comparably simple vented »box« (eh, rather a cylinder...) over this complicated design. But I might pick up the idea of mounting the squawker and the tweeter outside the tube instead of integrating them.

Best regards!

Edit: My online dictionary (LE😵rg - Ihr Sprachangebot im Web) names »prismatic«, »ashlar-formed«, »box-shaped« and »rectangular block« as synonyms, with emphasis for »prismatic« in electrotechnical context.

 

[scottjoplin]

I think so, to be honest I didn't read it all, but I was thinking about the problem of mounting midrange and tweeter, and thought some of the drawings might give you inspiration. In that regard, the other one that caught my eye was this 6moons audio reviews: Lenard Audio Sarabande

 

[Kay Pirinha]

Thanks again, Scott. Very appreciated!

I'll have a look at it when at home again, as I'm not allowed here to visit most web sites.

Any advice on cutting my cardboard tube precisely, i.e. exactly perpendicular to it's axis and leaving clean cutting edges? I'm afraid that neither a hand saw or a jigsaw will do...

Best regards!

 

[scottjoplin]

I think you are right, very tricky to get good clean cut. Nothing springs to mind at the moment, except a very sharp knife, like a Stanley knife and a hell of a lot of patience. Sorry can't be more helpful

 

[Kay Pirinha]

Perhaps it's better to have it done by a woodworker (on his table or band saw) instead of ruining it by myself 🙂.

Best regards!

 

[scottjoplin]

Yep, they would have experience with fibreboard and hardboard and suchlike....hopefully!

 

[GM]

Having used hand, jig, radial arm, table saws, most any way will work, just have to use a fine finish [high tooth count] veneer/plastic blade, some low tack tape and however elaborate a jig required to ensure a straight/perpendicular cut, though for the casual DIYer I too recommend having a cabinet/furniture builder cut them on their typically very large table saw with high end fine finish blades that cost more than all mine combined.

GM

 

[BWRX]

Having used hand, jig, radial arm, table saws, most any way will work

I would use a table saw. You just need to have X (horizontal, perpendicular to the blade) and Y (vertical, like a table saw fence) fences so that you can slide the tube into the blade linearly while contacting the Y fence, have the tube hit the X fence, then you slowly rotate the tube so you get a nice straight cut the whole way around the tube. You may have to do this with the other half of the tube if your blade isn't perfectly square with the table, so plan to have some waste for at least a couple of blade widths. It should be obvious that you might want to have another person help holding the tube while doing this!