"Suppressed Mids" and tweeter / woofer phase?

[samtny]

Hi All,

Recently finished my first build, Zaph's ZBM4's which I am really liking.

HOWEVER, I am having a persistent problem of "suppressed mids," i.e. vocals, depending on the source material / source device / multichannel format, etc.

Question; was I supposed to connect the tweeter / woofer OUT of phase? Original crossover design here;



Currently I have them connected "in phase," i.e. the '+' leads for woofer and tweeter are connected to the terminals that have little red ink dots on them, the '-'s to the other terminals.

As I was watching tv with the wife last night (I don't know, some random Canadian comedy thing), some characters seemed to have audible voices, particularly those with low voices. But most were almost unintelligible, like their voices were "lost" somewhere between the speakers, no matter how loud I cranked the volume.

Most music sounds pretty great, but again it depends; on Thelonius Monk, Criss Cross, the drums and sax sound incredible, but the piano seems very 'distant' and/or suppressed.

Any help appreciated,

Sam T

[GordonW]

It depends on what the woofer is doing near the crossover point (ie, whether it's starting to mechanically roll off yet. Same goes for the tweeter- if it is being run near the limit of its response (where it starts to roll off on the bottom end).

If not, then yes, you should have the polarity of one of the drivers reversed, since in-polarity, the combination of second-order lowpass and third-order highpass will result in 135 degree phase shift at the crossover point... which will cause SOME cancellation (not total, but will result in a loss of power response in that area, to an extent). Usually, convention goes with reversing the tweeter polarity...

Do you have response curves for the bare drivers?

Regards,
Gordon.

[samtny]

Originally posted by GordonW
It depends on what the woofer is doing near the crossover point (ie, whether it's starting to mechanically roll off yet. Same goes for the tweeter- if it is being run near the limit of its response (where it starts to roll off on the bottom end).

<snip>

Do you have response curves for the bare drivers?

Regards,
Gordon.

Yes, courtesy Zaph's website;

Woofer response;


Tweeter;

[BlueWizard]

Just a thought, but did you use the same drivers that the Zaph website suggests?

I notice the crossover is at 3,000hz, if that is pushing the upper limit of your woofer, then that might be the problem. I think speech is roughly in the 200 to about 2000hz range (a guess), which means your woofer is carrying the bulk of speech.

Ammeded:
Just check, the fundamental range of singing voices ranges from 80hz to about 1.2khz.

If the woofer starts naturally rolling of before it hits the cross over frequency, then you are going to have a dip in the upper voice range.

Check the specs on your speakers and make sure a 3khz crossover is really practical.

Just a guess.

Steve/bluewizard

[samtny]

Originally posted by BlueWizard
Just a thought, but did you use the same drivers that the Zaph website suggests?

Yes, I am using the MCM-55-1853's and the Aura NT1 tweeter.

What's your take on reversing the polarity / phase of the tweeter? I would have thought Zaph would have mentioned this if it was desired with this crossover, but he doesn't;

http://www.zaphaudio.com/zbm4.html

[tinitus]

Phase issues because of big series inductor(BSC) ?

I would prefer a notch filter instead

[samtny]

UPDATE: After some more listening and fiddling, I am all but ruling out any "phase" issues with the drivers / speakers themselves. Rather I am now looking at the amp/subwoofer, or more likely my inept handling/configuration of same, as the culprit;

When I set the amp (Sony DGR-910) sound field to "2CH ST", suddenly *bang* my problems with suppressed vocals go away, and oddly the soundstage opens up vastly. Problem is this sound field mode disables subwoofer output. Actually these ZBM4's sound so freakin' good alone that its not a "problem" per se, however for movies I would enjoy a little more low-end punch. So then...

When I return the amp to "AFD" ("auto-field direct"), the sub (Dayton SUB-100) kicks in and instantly the soundstage also "pinches" and the midrange seems to get lost lost lost, vocals go bye-bye, become directionless, etc... Also the volume overall decreases...

No idea what is going on here, but it almost seems the amp is applying some bogus digital "enhancement" of the stereo signal in the AFD mode, when in fact according to the manual all it is supposed to be doing is enabling a crossover to the sub. I'll start a thread in one of the various amp forums, but if anyone here has a clue how I can enable my sub without compromising the sound quality of these great little speakers I'd much appreciate it.

P.S., can't resist throwing up a pic, it is my first project after all;



The offending sub and amp visible here as well...

Sam T

[tinitus]

Ahh...subs! you didnt say nothing about subs, and made me make a fool of myself

strange subs can do that, isnt it
We go through hell to get the main speakers and their filters right...and then we toss a sub randomly in a corner, and dont even care that the sub has a filter and rolloff too...hell, what can a bit of active crossover do below 100hz

Have you tried to place the sub differently...and with carefull adjustment
You may need to adjust the BR port of your mains with stuffing

[samtny]

Originally posted by tinitus
Ahh...subs! you didnt say nothing about subs, and made me make a fool of myself

strange subs can do that, isnt it
We go through hell to get the main speakers and their filters right...and then we toss a sub randomly in a corner, and dont even care that the sub has a filter and rolloff too...hell, what can a bit of active crossover do below 100hz

Have you tried to place the sub differently...and with carefull adjustment
You may need to adjust the BR port of your mains with stuffing

I believe my next steps will be lowering the low-pass filter on the sub from 180-hz where it is now, perhaps to around 100hz, and then re-trying the auto-calibration feature on the amp. The documentation on the DG-910 states to set the xover on the sub to the maximum value before doing the auto-cal, however I wonder if this is not optimum in my situation. I certainly don't have any issues with directionality of bass frequencies from the sub, which in the past led me to believe the amp is doing its job at automatically setting the proper xover frequency, but at least this is something to try.

Can't really move the sub out of the corner where it currently sits, there is just noplace else in my living room for it.

Sam T

[augerpro]

Does the sub have a phase adjustment or polarity switch? Try that and see how it sounds.