Personally then I would discount the results as this near field response can be anything and does not necessarily propagate to the far field. A plane wave tube would have been better, but admittedly difficult.
Horns and drivers couple in different ways. Much of this does not propagate to the far field, but is present at the mouth. This mouth measurement is common, but it is wrong, just as measuring a 15" woofer in the plane of its mounting would not yield accurate results at higher frequencies because of near field effects.
Horns and drivers couple in different ways. Much of this does not propagate to the far field, but is present at the mouth. This mouth measurement is common, but it is wrong, just as measuring a 15" woofer in the plane of its mounting would not yield accurate results at higher frequencies because of near field effects.
It was about 5cm or 10cm from the mouth horn if I can recall correctly. I have to look at my original files to be sure. But definitely not farfield (e.g. 1m-2m).
They horn was that 12" square JBL clone. Looks like this
The problem is I don't have an anaechoic chamber for accurate farfield measurements
.Have you investigated these farfield fidelity before, and how? E.g. why did you choose DE250 and not other drivers for the GedLee speakers series.
The drivers and horns do couple in different ways. DE250+JBL provided the most beautiful sonogram compared to D220Ti+JBL
DE250 Polar
D220Ti Polar
Absolutely I do. Very different in fact. Just think about the differences in mouth diffraction in the mouth plane and in the far field.
I have done this for woofers, but not in detail for waveguides. I just know that they will be different and only do far field as a result. That's not possible with a woofer so I have looked into how the near and far fields differ, and there the differences are quite significant.
I choose the DE250 because of my connections with B&C and the belief that the drivers do not make much difference when the systems are optimized. This stems from the large multi-listener blind test we did between the B&C's and TADs (ten times difference in price). The two were statistically the same while both of these designs were statistically different from other designs. So basically I don't believe that there is much audible difference between drivers in identical systems when each system is optimized. Hence I don't spend much time on this issue.
Would the mouth diffraction be different near and far from one driver vs the other on the same horn? I can understand it being different near and far, but for that difference to change with the driver swap is what worries me.
I can imagine some differences in drivers that "might" make a difference in mouth diffraction at the far field, but I'm not sure my guess would be right. Thus the question.
Right. But how or why would that happen?
And how far do we need to measure for far field? 1 meter, 2?
When you consider the source location of diffraction that is to be included in the measurements, measuring close to the mouth can give significant path length differences from further away. So this might turn out to be more than say a mouths width away along the measurement axis, but maybe further if higher frequencies are involved. I suspect that overall (polars) things will balance. For one thing though, I'd prefer the shots close to the listening axis to be at such a distance.
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They could be because the wave front shape could be different for the two drivers. Some of this would not propagate to the far field and some would not.
I agree that sorting it out would take a study - not really worth the time.
I do think that for the most part if two compression drivers are optimized on the same horn then they will sound the same. In our study of compression drivers we found frequency response was statistically audible but nonlinear distortion was not. Hence if your get the frequency response the same then they should sound the same.
Since the systems are basically linear, the pulse testing cannot tell us anything that the frequency response does not. If I have the impulse response of he device then I can create the pulse test from that impulse response without even doing the test. So if you see a difference in the pulse test at some frequency then you have to see this in the frequency response as well. So looking at a pulse at a certain frequency is very similar to looking at the frequency response at a single frequency. We know that this can be very different even for frequencies very close together.
I prefer not to look at any test that is so dependent on a single frequency. One needs to look at and excite the system in a broad band sense and do some form of averaging to get meaningful data. Single frequencies are not highly important.
It can't, but the opposite is true. You can see something at 10 cm that you will not see at 1 m.
I know this is an old thread,, but I just stumbled on it looking for some comparisons between lower end 1 inch drivers. I'd like to share that I also came to the same conclusion as the OP regarding the D220 and DE250. To my ears the D220 just sounds more "correct" and accurate than the DE250, especially when the D220 back chamber has wool felt added for better damping. The DE250 is smoother sounding and less fatiguing at the expense of resolution, giving you a more euphoric listening experience, but it falls short when you are wanting accuracy, sort of like comparing an average soft dome to a metal dome tweeter.
I've used various versions of the D205, D210 and D220. They were all very similar and there are various revisions to the diaphragm assembly. Some of the early D205 and D210 have slots cut into the diaphragm surround. The later replacements for D205s and D210s don't have this anymore and are identical to the D220 except for the connection terminals, which are push/pinch type on the D205 and D210 and fast-on for the D220.
My success with the D220 is based mostly on the result of modifications I've done to the rear chamber and diaphragm surround. I'll dig up some of my research on this and try to share it with you guys. The D220 is a fantastic 1 inch CD that can keep up with alot of 100+ dollar CDs when tweaked a bit.
I've used various versions of the D205, D210 and D220. They were all very similar and there are various revisions to the diaphragm assembly. Some of the early D205 and D210 have slots cut into the diaphragm surround. The later replacements for D205s and D210s don't have this anymore and are identical to the D220 except for the connection terminals, which are push/pinch type on the D205 and D210 and fast-on for the D220.
My success with the D220 is based mostly on the result of modifications I've done to the rear chamber and diaphragm surround. I'll dig up some of my research on this and try to share it with you guys. The D220 is a fantastic 1 inch CD that can keep up with alot of 100+ dollar CDs when tweaked a bit.
