Reply To: Phase Issue???

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dpdan
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“When standing about 30 to 40ft away right in the middle the sound would nearly cut out”
“Lean left and you could hear the left stack, lean right and you could hear the right stack”
There has to be a reversed polarity (phase) cable for this to happen in the center of the system,…
if it is happening between the two top speakers on each side, then it is most likely a comb filtering issue.

Provided all the gear is indeed “in-phase” electrically, everything in the center of the system will sound nice and punchy.
I am impressed that strokerRED recognized this issue with the system. So many sound guys would be asleep at the wheel and not even notice.

StrokerRED, the problem is most likely not what I am going to discuss here but something to experiiment with the next time you set up your system. If you have two top cabinets on each side and they are not pointing away from each other enough this causes a serious bad sounding issue called comb filtering. Even if the cabinets are trapezoid design, the angle is usually not enough. You can test this by setting up just two top cabinets, sitting side by side as they would for lets say,… the left side. Angle them away from each other instead of allowing the insides of the cabinets to be flush with each other. Those Yamaha SV115 cabinets claim to have a 90 degree horizontal dispersion so we can not allow them to interfere with each other. Yes, they can sit side by side, but there needs to be a pretty big gap between them. I am only going to guess that they probably need somewhere between 10 and 16 inches between them, I am talking about this gap being in the front of the cabinets with the backs touching each other… spreading the front outward.

When speakers overlap, (conflict with each other) certain frequencies double up and become “HONKY” and other frequencies get cancelled out.
The advice that Gcumbee and Dick Rees have given is good, and what they have offered is a good starting place to make sure that everything has the same polarity.

Here is a picture of some of my Altec and JBL gear set up outside for a concert.

speakers

You can see that even though the top cabinets are not identical, they are spread out, the amount of spread or angle between the two cabinets on each side will always be determined by your keen ears and a pretty short listening test after setup.

Experiment with this and the lights will come on and you will say WOW! I had no idea something so simple could make so much of a difference.

Now on a different topic… sometime we can discuss the fact that for most of JBL’s existance, their components were “out of phase” from virtually all other brands of speaker components. It was always stated very clear though…
Positive voltage applied to the BLACK terminal creates a forward cone movement. JBL recently changed this otherwise (stupid)
design and now their components are in phase with most all other brands. Even if we discovered that the subs were out of phase from the top Yamaha cabinets, it would not cause the sound to practically disappear in the center.

Somewhere, ONE of the cables feeding the DBX inputs is reversed polarity, or ONE cable feeding the Crown amp for mains is reversed polarity, OR…..
the Crown amp is set in Bridge mode. That will cause this symptom too.

Alright, enough of me rambling 🙂