"Suppressed Mids" and tweeter / woofer phase?

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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;

ZBM4-crossover.gif


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
 
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.
 
GordonW said:
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;
An externally hosted image should be here but it was not working when we last tested it.


Tweeter;
An externally hosted image should be here but it was not working when we last tested it.
 
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
 
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;

An externally hosted image should be here but it was not working when we last tested it.


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

Sam T
 
Ex-Moderator R.I.P.
Joined 2005
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
 
tinitus said:
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 said:
Does the sub have a phase adjustment or polarity switch? Try that and see how it sounds.

Yep it has a 180 switch, tried that, unfortunately with the exact same result.

tinitus said:
Or you may try and reverse polarity between main amps and main speakers

Are there active subfilter on your subout from surroundamp as well as in the subs...I know Rythmik sells subamps with 12db lowpass fore that reason

My surroundamp does have an active lowpass filter, in addition to the filter on the sub itself. I've played with this (the amp filter), running it from 60hz to 150hz trying to reduce the problem, but no help there :(.

Jay_WJ said:
I agree that this issue may be a null due to phase errors between your subwoofer and speakers.

My current theory is it is actually a *level* problem, perceived by myself as a dropout of the mids, but really my sub is just overpowering the ZBM4's. Maybe :confused:. The level overall does drop when activating the surround / sub on the amp, I believe this is part of the amp's compensation for the relative inefficiency of these speakers. Anyhow tomorrow when I am less sleepy I'll try turning the level knob on the sub down and re-doing the auto-calibration on the amp, see if the issue is reduced.

Still having fun listening to these things in 2 channel mode, they just sound great.

Thanks for all the suggestions, if anyone has any other ideas I'd surely appreciate hearing them,

Sam T
 
Hi Sam T.

I have a theory on your problem.

If you have the amp setup with centre and rear speakers enabled, but you don't actually have those speakers, this could cause the symptoms you are describing.

What can happen is that when you tell it to run 2CH ST mode, the amp sends all the sound just to the front two speakers and they will sound fine.

If however, you switch on some sound field mode and the amp thinks it has more speakers than whats actually connected (particularly the centre channel) the amp will process the sound for these extra speakers. For example, it may pump out a lot of the vocal range through the centre channel, as this is used for mainly dialogue during movies.

Make sure you have any other speakers disabled in the amp setup before you go digging any deeper.

Apologies if you have it set up correctly, sometimes we all miss the obvious stuff ;)

Mark
 
Ex-Moderator R.I.P.
Joined 2005
samtny said:


My surroundamp does have an active lowpass filter, in addition to the filter on the sub itself. I've played with this (the amp filter), running it from 60hz to 150hz trying to reduce the problem, but no help there :(.

Sam T



Bikeman may be on to something about your setup(surround)

Subs with 2/channel(stereo)
If possible, try to use the "high level" signal to sub...meaning using the main speaker terminals feeding the sub with speaker wire ;) that is if your sub has this option
 
Bikeman said:
If you have the amp setup with centre and rear speakers enabled, but you don't actually have those speakers, this could cause the symptoms you are describing.

What can happen is that when you tell it to run 2CH ST mode, the amp sends all the sound just to the front two speakers and they will sound fine.

If however, you switch on some sound field mode and the amp thinks it has more speakers than whats actually connected (particularly the centre channel) the amp will process the sound for these extra speakers. For example, it may pump out a lot of the vocal range through the centre channel, as this is used for mainly dialogue during movies.

Thanks Bikeman; Although I do have a center channel and rear channel speakers connected, the "Auto Field Direct" mode on the amp does not direct any output to them from a 2-channel source unless I select, as you say, a "sound field mode" such as "Hall" or "Jazz Club", etc. I generally eschew these sound field modes, they're interesting as magic tricks but don't produce what I would call an improvement in sound quality.

The display on the amp also conveniently highlights which speakers are currently active, so I can see clearly it only has the sub + L + R channels activated in the AFD mode. When I flip back to "2CH ST" mode its just L + R.

Another thing I will try today is turning off the sub completely and flipping between the AFD / 2CH ST modes to see if there really is an interference / phase problem between sub / mains, or if its just something wacky the amp is doing to my L + R channels.

Sam T
 
tinitus said:
Bikeman may be on to something about your setup(surround)

Subs with 2/channel(stereo)
If possible, try to use the "high level" signal to sub...meaning using the main speaker terminals feeding the sub with speaker wire ;) that is if your sub has this option

You mean connect the sub to the same terminals on the amp as my R + L mains? Yes, my sub does have high-level ins as an option. If I do this, though, don't I have to worry about impedance, etc, differences between sub and mains?

I see advantages and disadvantages to this approach; one advantage is I can use the controls on the sub to set crossover freq., etc., without concerning myself with the amp's active xover weirdness. This would establish once and for all whether I am having sub "phase" issues or whether it is something else, i.e. my amp, since I can really play around with just the sub leaving the amp in "2CH ST" mode.

One disadvantage seems to me however to be that the amp will no longer be able to send a discrete LFE signal when decoding multi-channel source material, DTS, Dolby Digital, etc.

Hmm. Not sure if I should try this, or what to try next, frankly. :xeye:

Sam T
 
Ex-Moderator R.I.P.
Joined 2005
I suppose that the "high level" input on your sub is high impedant as it goes to subamp input somehow and not directly to speakers...it should not be a problem

I have seen som reports on this option actually being better than line level input...makes me wonder if some gain curcuit is bypassed in subamp ?

Do you feed sub with a stereo signal ?
 
tinitus said:
I suppose that the "high level" input on your sub is high impedant as it goes to subamp input somehow and not directly to speakers...it should not be a problem

I have seen som reports on this option actually being better than line level input...makes me wonder if some gain curcuit is bypassed in subamp ?

Do you feed sub with a stereo signal ?

Currently the sub is fed with mono, line level signal from the amp.

Before I switch over to the high-level inputs I think I am going to "reset" the amp to factory defaults and start over, it seems to me there is something really wacky with the sound field processing going on right now. Also I will disconnect center channel and surrounds and just focus on my 2-channel setup until its either right, or I decide to give up and try with a different amp.

Sam T
 
Problem solved; it was the amp.

Basically I turned off the "auto calibration" feature of the amp and set levels, crossover freq by hand.

Now switching between "2CH ST" and "AFD" gives the desired effect; the first directs output to my mains only, the second "adds in" the sub without changing output to the mains.

Whew.

Thanks everyone who gave me suggestions,

Sam T
 
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