Polar measurement rig

I'm putting together a measurement rig to take polar plots.

 

It will feature one of these stands which extends to 2.2m. I'll then build a turntable with set steps in angle.

Waveguide surrounds - drivers installed

Drivers are now installed:

Cutting the driver recess:

Template in place:

S1 point source horn - update

The compression driver needs a mounting flange, so I decided to turn it up and do it neat, using some ply scraps.

The hole flares out and is the start of the horn.

Now all the pieces are cut, firstly with square edges. Most of the time was spent getting these angles right, although the horn is 60 degree included angle, the actual angle of the cuts isn't 30 degrees. It took some time to work out what they actually should be. 

The sides need a precise angle and this was done with the "buzzer," a plane with a side fence that can be angled. The buzzer like all power tools is a very dangerous piece of equipment. My poppa chopped off part of his index finger many years ago. When I heard about his accident as a little boy, it inspired caution with power tools. 

In case you are wondering, that isn't me. That's my technical consultant aka Dad. There is nothing quite like a father-son project. 

Testing out the angles:

All pieces now cut with angles:

Holes have also been cut (ports for the mids). 

You can see the holes are quite tricky, because of where they must be placed to come to the corner on the inside. I had to cut these with a spade bit, and actually modify it because none of them were the right diameter. I filed a 19mm bit back to suit with a metal file. 

Here you can see the hole size relative to the driver.

Next step is checking everything, then glue and screw. 

Waveguide surrounds - update

Main project page >

12mm roundovers on edges:

Front corners will be done later when the baffle is glued in place. It will need to come off to work on the waveguide.

Template for flush mounting the midwoofer:

Rave horn

Here is a quick design for a HUGE horn inspired by this thread:
http://www.avsforum.com/avs-vb/showthread.php?t=1357500

Hornresp sim for 8 drivers loaded into a horn installed into a 1m high stage that is 7.5m wide. B&C 18TBX100

Now a tapped horn with the same driver.

Note that this is a single driver with 300w. Less power is required to find the excursion limits, but the efficiency is lower. The front horn has 107 db sensitivity while this has 100 db. This is 430L while the front horn is 7000L, in other words 16 x larger! However, the FLH doesn't increase much in size when more drivers are added. The mouth stays the same but the throat gets larger. The curious thing is that to match the output of the front horn, you need 16 tapped horns. The volume in the end is the same, but with the tapped horn you have twice as many drivers and 4.8kw of power.

So if the volume limit is the same, you can use 18 drivers + 4.8 kw of power, with 16 large boxes. Or 8 drivers into a single huge horn and 16 kw of power. 

Surround test boxes in progress

This is a test box for my 8" waveguide surround speakers. 

The baffle is double thickness under the driver and has a simple brace in the middle. 

Octagonal face plates are a pest! I've marked this one out in pencil but plan to flush mount using a router template. 

Drivers arrived! 2 x B&C 8PS21 & 8 x Pyle PDMR5

The drivers arrived today for my current speaker projects. Peavey Black Widow 18" shown also to give an idea of scale.

B&C 8PS21 - an 8" pro midwoofer shown in the front, Pyle PDMR5 (8x) shown in the middle along with a pair of B&C DE250 compression drivers.