Ok, none it is time to dive into the practical process of tweeters alignment. Once again I presume that we are taking about monopole tweeters that use AFTER your midranges compression drivers (read my previous post). Some people use term “supertweeters” but I tend do not use that name and that concept.
I have my reasons do believe in the ability to align tweeters using methods of objective control, at least I never was successful in doing it. You might rune a high resolution RTA and move tweeters until you get max (if they are in-phase) amplitude at crossover point. You might run 2 microphones into dual trace oscilloscope (or one trace + memory) and perfectly synchronies two sinusoids. You might run impulse response synchronization and have your tweeters perfectly aligned. However all those methods of alignment contradict the auditable experience that I usually get from tweeters and therefore I discard the methods of objective tweeter alignment. Furthermore the ideal setting for the tweeters that I get from objective methods is always deterrent then the one that I get from the methods of subjective alignment. So, my methodology of tweeters alignment is a sequence of subjective actions, shaped into a methodological pattern- or something that I call “the real objective methods”.
I few word before I go further. Over the course of the 6 years that I’m working on my Macondo I had approximately two dozen of tweeters and in one way or another I my further writing is a collective experience hot to make my tweeters to sound “right”. One exception though. I never tried to stabilize the tweeter’s impedance and to write the “phase neutral crossover” against it. All my experiments were around the regular 6, 12, 18, 24 db per octave, none series, crossovers. I do not know if with subtraction crossovers satiation would be different and I have no experience with “phase neutral crossover” (in fact for HF I believe that they are bogus). Also, and it is very important to understand: that the method below juts synchronization of the HF and MF alignment and it is not responsible for the tonal attributes of HF and MF drivers.
So, below is my “Real-Objective Tweeters Alignment Survival Guide”
1) Mount your tweeter in the position where it’s diaphragm would be roughly at the same vertical and horizontal plane + 2 inches back relative to the diaphragm of your MF driver. Use juts one right of left channels. All further alignment should be done for each channel separately.
2) Regardless the time or order of the crossover you use set your tweeter in phase with your MF driver. There is a LOT of reasons or school of thought suggesting to invert the tweeter with second order as it has 180 degree phase shift and there are many other reasons. Nevertheless, do not invert tweeters under any circumstances. Tweeter and MF driver much be in-phase. (Be advised that mic of your phrase tester might not pick HF well, use alternative methods to synchronize the polarity of your MF and HF)
3) Set up a correct listening volume of your tweeter relative to MF driver. It should not be exact but it should be from exact to +2db. It is preferably to have your tweeter at this point slightly “hotter” then necessary. It is important do not set the tweeter too soft at this stage. A general perception “a little too bright” but not “aggressively bright” works well at moment.
4) Find a good quality, fill range recording of an opera with strong soprano and tenor. The opera must be recorded during 1950s, preferably before 1955 (less HF screwing global feedback was used at that time)
5) Play in a loop (do not convert it in WAV file) the soprano/tenor recording and pay attention that the highest notes of the singers have a certain “clippings” at “TH” and “S” sounds. Monitor it from the listening position.
6) Begin very gradually to move your tweeter forward, approximately 1/8” per move. At certain point the “clippings” will be minimized or disappeared. Make those locations. Continue to move the tweeter forwards at the distaste of the MF’s diaphragms, minus 2 inches.
7) Now you covered with your tweeter 4 inches and you have 2-3 spots what you feel that the “clippings” were minimized.
8) Set your tweeters in each location and find a better among those marked locations. Still do not loose the markings of the other marked locations – you will return to them.
9) Set your tweeter in the location-winner and while you listen ask someone to very gently angle the tweeter to 3-5 degrees to different directions.
10) If a very minor deviation of your tweeter form being aligned to it’s axe produce a very slight improvement in reproduction of fast sibilants or shibilants then keep moving your drivers. Your goal is to find a location where the driver will not demonstrate any improvements being angle and where it will be sitting perfectly on the axe of the MF driver.
11) After you feel that you found the correct location and the shibilants are the best you can get try further move of your driver but now the increments of the movement should be 1/32 inch or even less. At this point you should pay attention to the raise of dynamic in the singers singing and the decays of the singer voice into the background nose. The raise of dynamic (usually with frequencies doing up in sopranos) should be without any micro events (unless it justified musically) and it should be very gradual and constant. If you have little “thorns” in the dynamic raise then your have timing anomalies and be further movement of the tweeters you should be able to resolve it. The same is with voices decay to “dark”. It is very rare when voice can go to “dark” smoothly and usually at certain point you will feel a “step”. However, the softer this step would be the better time alignment of your tweeter is.
12) Now you are within 1/8”- 1/16” from the correct alignment. Take a large chorus peace recorded not “ambianic” but with more or less up-closed microphones. Play it at different volume levels. Pay attention that sometime some singers “jump” out from the chorus by having that “clippings” Move your tweeter more in order to minimize the previously mentions effect of sibilant consonant “clipping”. When the choirs hits the aerodynamicy defended letters/sound they should sound as not problematic as strident vowels. At this point the adjustment of the tweeter positioning will be very-very minor.
13) After you reach the point of perfection in the paragraphs above then begin to walk across your room listening the same things that you were listening in the paragraph #12. If your were able to detect with your “side hearing” any HF artifact of chorus reproduction when you are at 30%, 60% or 90% from your tweeter axes then you most likely have chosen a wring marked point at the step#10. Return to different marked location and start everything again.
14) After you succeed. Set the tweeter volume back to the normal level, or preferably .5dB less.
15) Listen an act or two of the opera and confirmed that your have no HF artifacts.
16) Do again the paragraph # 15 at the day with different electricity. Do not do the specific intentional listening … do something else and let the music just to play on background loud. If you pick with your “side hearing” any HF anomalies then … you have them and then your should look at them further.
17) Listen the large string groups, preferably of the orchestras that have bold and aggressive string sections. Fine adjust the volume of the tweeters…
18) Make the final location of the tweeter very precisely and do it with another channels of you’re using 2 channels Stereo. If you use 5 channels then do not worry about the tweeter alignment but kill yourself – you deserve it.
You should be all set from here. The tweeter alignment might be a pain in ass ceremony but it is a mandatory if you use tweeters. If your tweeters are crossed over 12K then you should not hear any changes ion sound when you turn you tweeters on an off. Of you by turning on the tweeters have auditable “tonal event” then only two conclusions are possible:
A) The amplitude of your tweeters set too high.
B) Your tweeters are garbage in relation to your MF channels and it is better do not use them
Romy the Cat
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche