And now for more uncontrolled test.

The metal bracket probably doesn't help with diffractions etc but at least it should effect all the tweeters the same and after all, this is not meant to be a frequency response test as such.   After a 2 KHz measurement comparing the RS with the Millennium didn't seem to support the theoretical efficiency difference I tried a new approach...

Dark blue = RS,  Lt Blue, = Millennium, Red = TDFC

From the frequency response it seems the tweeters don't have such a large efficiency difference after all.   The RS is a couple db more efficient than the Millennium below 1800 Hz or so but above that they are pretty similar.  That being the case, measuring the distortion with the same input voltage probably produced an adequate approximation.   My general conclusion is that all three are very good tweeters at least based on these limited results.  No measurement is all inclusive however and thus can not fully evaluate any driver.  All these measurements can really do is make suggestions as to the relative quality of these drivers.  If one had significantly higher distortion components than the others then it would be strong evidence this driver might be inferior.  Given the similarity of the results the measurement is at best, inconclusive.  It does tend to suggest they are all of similar quality but it does not conclude this in total.   An infinite amount of data would be required to be 100%.  Or you could just listen to them;-)

Note:  These measurement methods do not meet the "Halladay Measurement Standard" now generally accepted by one individual to be the industry standard. 

Here is what the, "Hitch Hikers Guide to the Galaxy" has to say on the subject of the Halladay Measurement Standard..."Mostly Harmless"...Or was it, "Mostly Useless"?

(BTW, total change of subject here...the movie sucks!  Get the DVD of the original mini series or better yet, read the book.)

Millennium T25CF

2.5 Khz am modulated tone.

1 vrms	3 vrms	6 vrms	10 vrms

5 Khz am modulated tone.

1 vrms	3 vrms	6 vrms

TDFC

2.5 Khz am modulated tone.

1 v rms	3 vrms	6 vrms	10 vrms

5 Khz am modulated tone.

1 vrms	3 vrms	6 vrms

Dayton RS

2.5 Khz am modulated tone.

1 vrms	3 vrms	6 vrms	10 vrms

5 Khz am modulated tone.

1 vrms	3 vrms	6 vrms

As requested, I have just done some quick test at a lower frequency.   As for posting screen size images instead of thumbnails I tried creating another page like this as a test but the time to download indicator started going up very fast.   The best way to view files like these is to save the ones you want to compare in a folder and then view them with something like ACDSee.  That way you can toggle between any two of them instantly and see the differences.  Also, its better to just note the relative difference between the fundamental peak and then compare that to the same test on the other driver.   The peak of the fundamental tone varies slightly between the test not so much due to efficiency differences but in slight variations in microphone placement.   For these test the microphone is placed very near the tweeter so very small differences in distance can shift the curve up or down.   Between the test of any given frequency and voltage, nothing is changed, the wires are just pulled off one tweeter and connected to another so while the curve may slide up or down due to microphone distance, the relative difference between the fundamental and the harmonics is not effected.   So, the best way to really evaluate and compare is to note how many db down relative to the fundamental one harmonic is in one tweeter compared to another.  Odd harmonics are worse than even, and higher harmonics are worse than lower.   If one tweeter generally has slightly higher even harmonics but significantly lower odd harmonics, I would rate it higher than a tweeter with lower even harmonics and higher odd. 

1500 Hz 3 vrms.

TDFC   Millennium    RS

1500 Hz 6 vrms

TDFC    Millennium    RS

At 1500 Hz @ 6 vrms the overall harmonic content in the RS is coming up slightly whereas in the 3 vrms test it is in line with the other two.   Still, the RS is a very good tweeter and I will probably be using it in some projects as soon as I find time to get any more projects going.  All three of these tweeters are very good on these test.   I think as level goes up the Millennium is probably the best of the lot but at 6 vrms on a modulated tone like these, it's pretty darn loud.   At lower levels it's probably going to be harder to tell the difference but it is an easy matter to tell the difference in your wallet after spending $159.00 ea for the Millennium compared with $28 ea for the TDFC or $46 for the RS.