Making loudspeaker stands - joining steel tube to wood panels

I plan on making loudspeaker stands using 4"/100mm steel pipe and 20mm ply wood.
The speakers themselves are heavy at approx. 15Kg each hence the use of steel pipe.
They will look fairly basic with square ply panels fixed to each end of the pipe.
The problem is how to fix the pipe to wood so no bolts or screws will be visible.
I've considered pvc pipe flanges but these are far too expensive at around £12.00 each; four would be needed.
Thanks

What steel pipe, thickness , finish etc. Is this for convenience or to enhance sound quallity by using ground spikes and filling with shot?

4" steel is way OTT.
Normal tripod portable speaker stands are made from 35mm aluminium.

But if it's a question of design, cut circles of wood to the internal diameter of the pipe, secure it well enough in the base for bushes to be secure. The top could use screws through the pipe sides as the speaker tops would hide them.

Thanks Tigercubrider, I actually bought speaker tripods but they don't sit low enough.
The idea of 4" steel tube came from DIY designs for stands. I may actually adopt your suggestions.
Lostinthelight - your suggestion of ground spikes, thickness, filling are irrelevant.
It's a mechanical projectbuilt for stability and nothing more.

if the design is an I shape (platform top and bottom)
You could cut your ply and also cut some ply discs.
Bond/screw the ply circles to the dead centre of the square(?) ply top and bottom so they plug into your pipes.

If the concept is to have the speakers supported on cylinders, cut the ply circles and use 2x2 as spacers so that the tube slides over but is a tight fit. You probably need feet. Use something like mastic/gripfil to secure the wood to the metal.

Might be an idea to include a couple of 25mm holes top and bottom through the ply and connect with some plastic pipe/conduit so cables can run through?