OK, we know that simple on axis, straight into the speaker frequency measurements aren’t the whole story – getting a range of measurements at different angles gives a better idea for speakers getting general use, not the whole glued to the magic sweetspot that a lot of hifi has.

So it was time to do some directivity measurements. I don’t have the a licensed copy of ARTA so I can’t do the heatmaps ala Gainphile’s site – but at least Room EQ Wizard is a nice free package that makes it fairly easy to overlay lots of frequency response graphs in different colours.

To do the directivity plots, I took the entire speaker (box + waveguide) outside and sat them on a turntable made (with help from Col) from 2 bits of marine ply attached together by a lazy susan bearing purchased from Ebay. My backyard isnt huge so I could still have some environmental effects – but there is no ceiling and it should be bigger and less obstructed than the loungeroom.

The below measurements were done with the mic @ 2 metres distance, pointing direct into the compression driver. Then the turntable was rotated 7.5 degrees and another measurement taken, up until 60 degrees off axis. I then smoothed the response graphs to 12/octave to make them more readable.

I turned off the crossover, so lower frequency was only being attenuated by the 66uF protection capacitor – which gives a single order high pass filter @ about 400hz

I did leave in the miniDSP correction I was using for the PH916.. this was set up to give as flat as possible on axis response:

First I measured the PH916, with the following response:

Then I measured the LTH142, with the following response:

Now one gotcha here is I used the same EQ settings, and the LTH142 measures a bit brighter above 7khz than the PH916, so its a bit harder to eyeball and compare directly.
But the results are interesting, the PH916 has a closer spread below 10khz, so better directivity. But more chaotic dips above 10Khz. The EQ I am using has a big notch at 11.5khz – looking at the graphs this only helps on axis, and maybe makes things worse with the PH916 off axis.
For starters I’m now crossing over at 700hz to avoid the first dip at 600hz.

Also as a comparison I took a measurement of the Lorantz woofer the same way:

though this is using a 2khz LR24 cutoff. as expected, no directivity issues. Not sure what the huge dip at 280hz is??

Also to measure the angles properly I purchased a CRAFTRIGHT 300MM DIGITAL ANGLE FINDER (i.e. protractor) from Bunnings – this is a handy but of gear, I’ve used it to toe in the speakers in the loungeroom so they are 22.5 degrees off axis pointed at the couch (about 3M away) – this translates to a very slight toe in. For now I’ll use the 22.5 degree toe in as the basis for measurements.