I just revisited my tweaks to the DSE A2667 speaker (an OK quality cheap speaker commonly available second hand in Australia for about $20). This is because I had the loan of a WooferTester 3 unit from Col, so I could measure the drivers properly, and also had been given an extra pair to experiment with (thanks Gavin!).
TLDR summaryI made one additional adjustment to the crossover that made the response even flatter, by adding a 4.4uF capacitor to the LF portion to make it a 2nd order filter, while inverting the polarity of the tweeter.. but at the cost of an increase in measured distortion at about 3.5khz.
I was also able to save the impedance data of the two drivers as a .ZMA file for later use.
This done at 2M distant, indoors, with a measurement taken every 7.5 degrees to 60 degrees, smoothed to 12/octave.
mic 2M distant
measurement done indoors. smoothed to 12/octave.
As can be seen the tweaked version considerably flatter in response, a huge dip at 8khz has been considerably reduced by the 4.4uF capacitor lowering the crossover frequency compared to the original 2.2uF capacitor.
Did this at 1M and 2M
I also exported these as text (.FRD) files from REW so I could import the data into the PCD spreadsheet.
Also while I was searching around for solutions to this I found the most excellent WinPCD package – not all the features of the PCD spreadsheet are implemented, but it is standalone software that does not require MS-Excel to be installed, and it has a seperate resisable window for the system calculated frequency response which makes it easier to work with.
Jagged summed response caused by bad phase in the REW data, WinPCD screenshot:
Smooth summed response using Holmumpulse measurements with coherent data:
The author of the WinPCD package was quite helpful on the DIYaudio forums in sussing this out as well, by this time I’d been going in circles trying different smoothing of the data files before the messy phase in REW occured to me
I tried a few other values, but without bumping up the cost of the crossover considerably (e.g. an addition inductor for a 2nd order high pass filter) this seemed to be the best adjustment with the components I had readily available.
Here is the WinPC screenshot with the seperate driver responses plus summed response (remember some HF loss due to damaged tweeter:
Then measured it and loaded the measured response into WinPCD:
There is some variation (apart from the HF loss due to tweeter damage), but this could be due to component and driver tolerance, but measured and calculated fairly close. Whats more the response is now much flatter than the “Mk I tweak” (for future reference I’ll call this the “Mk II tweak”.
Mk I tweak:
Mk II tweak:
So what the above graphs tell me is I have much flatter frequency response – but at the expense of a 15dB increase in harmonic distortion clumped around the 1.5khz – 4khz area.
I’ve got one pair of speakers with the MkII tweak done, so I’ll have a listen, but so far I suspect this tweak has made some improvements in response at the expense of distortion.
Note that the final measurements were done on a different speaker to the one I did some damage to the tweeter while measuring.
REW plots of the individual driver response, with distortion info (all on axis, 2M):
tweeter only, WITHOUT protection cap, but trying from 1Khz.. this is where I think I damaged the HF response: