Inexpensive wavguide for 1" drivers

[ralphs99]

On the tail of the excellent work published by Zilch and others, I've been testing a cheapo waveguide that might be of interest.

MCM sell a $10 circular 6.5" waveguide that fits on 1" screw mount compression drivers. Part number 54-580. http://www.mcminone.com/product.asp?catalog%5Fname=MCMProducts&product%5Fid=54%2D580

It works very well with a nominal directivity of 90 degrees circular.
Cut-off frequency is about 1.5kHz and it starts to lose direction control below about 2.5kHz although still useable down to a least 2kHz. Could be a good option for something like a 2407 driver.

Note that some rough EQ has been added to the on axis response to make it easier to see the what's happening.

Cheers,
Ralph.

[Ian Mackenzie]

There are similar devices on Parts Express.

Ian

[Zilch]

I'm always a little confused when doing similar testing.

The specs are usually "included" angle, i.e., "90°" being +/- 45° from axis.

Is your 45° "off-axis" or included angle?

Nice measurements, in any case. :thmbsup:

[ralphs99]

Hi Zilch,


My plots show the degrees off axis, so the 45 degree plot has an included angle of 90 degrees.

Cheers,
Ralph

[GordonW]

What's the "rough EQ" entail? Top end lift? Could you post a curve of on-axis without the EQ?

Looks like a pretty "linear" curve, though. No real discontinuities. Very good performance, from that standpoint...

Regards,
Gordon.

[Zilch]

Let's try and guess the driver Ralph used from the curve.

Not a 2407, apparently.

Zilch guesses 2416 or 2426.

Only one? 2426, then.... ;)

[ralphs99]

Zilch is right on the money. 2426 with the snout removed.

I can't offer a plot of the driver plus waveguide before EQ.

The purpose of the tests were just to get an idea of the off-axis response of the wave guide. I wasn't too worried about the actual frequency response, just how it changed as I measured at increasing angles.

But I can give you the EQ settings I used with my driverack:

MCM waveguide on 2426 with baffle approximately 270mm x 500mm.
Equalised for flat on axis. Measurement distance= 0.5m, 1/24th smooth.
EQ: HP Shelf 5.6kHz, 10.5dB, S=9; 2.12kHz, 6dB, Q=1.57;
3.15kHz=-3.5dB, 4kHz= +3.5dB, 5kHz= -1dB, from here just tried to add HF boost as the HF Shelf ran out of gain, 10kHz= +0.5dB, 12.5kHz= +2.5dB, 16kHz= +6dB.

From my notes it says I ran out of parametric HF EQ and so I just boosted a bunch of frequencies in the top octave with the graphic. Hence the response is a bit rougher than could be achieved with more parametric bands.

Below is the on axis response on its own:

[ralphs99]

The response isn't as smooth as the first plot I posted 'cause it doesn't have as much smoothing, 1/24th octave vs 1/6th octave.

Here is the original set of plots with the same 1/24th octave smoothing applied.

Cheers,
Ralph