Sound degradation

[jose99a]

Hi everyone, is it normal for sound to degrade when running more than 1 speaker per amp channel? Testing 2 ohm load on QSC RMX5050 with
4 EV SX300 (8 ohm ea. equals 2 ohm load).

[CoronaOperator]

I think what you are experiencing is called comb filtering (page 685) where the sound from all four speakers are arriving at your ears at slightly different times causing huge peaks and valleys in the response. It probable has nothing to do with your amplifier. Spread your speakers apart by 20 feet or more and have another listen.

[Bill Fitzmaurice]

I think what you are experiencing is called comb filtering

+1. Speakers that are engineered to be used in vertical arrays don't have comb filtering problems, and using more of them sounds better than using one. Those EVs are intended to be used in horizontal arrays, and can only sound worse when so arranged. You can make things better by cross-firing them, as explained here:
http://homepage.mac.com/randyhyde/webst ... Stuff.html

[jose99a]

I had the speakers horizontally 2 on the bottom and 2 on top of them, the thing is when I had them 2 per amp channel which is 4 ohms they sounded normal but once I ran all 4 to one channel the sound was horrible.
I'll try different positions to hear any difference. And thanks for the help.

[Bruce Weldy]

I had the speakers horizontally 2 on the bottom and 2 on top of them, the thing is when I had them 2 per amp channel which is 4 ohms they sounded normal but once I ran all 4 to one channel the sound was horrible.
I'll try different positions to hear any difference. And thanks for the help.

A couple of things.....

First.....were you running the first test in stereo? If so, then moving the extra two speakers to one side would only give you one side of the stereo spectrum and sound like crap..... I know this seems elementary, but sometimes goofy stuff like this happens when in a hurry.

Second....the chart below show the power available. Running two per side was giving you 800 watts per speaker. All four on one side is only 500 watts each. If you were driving them full out and trying to achieve the same volume in each test, the second configuration would be trying to do more with less and could be part of the problem. Plus THD at 1khz in 2 ohm mode is 10 times higher based on EIA.


4 ohms
FTC 20 Hz - 20 kHz, 0.1% THD 1600 W
EIA 1 kHz, 0.1% THD 1800 W


2 ohms
FTC 20 Hz-20 kHz 0.1% THD 2000 W
EIA 1 kHz 1% THD 2500 W

All of this plus comb filtering could be adding to the mess.....

[jose99a]

I believe I've found the problem, could a tweeter thats wired wrong in one of the speakers "reversed polarity" cause all of the speakers to sound bad?
I mean the sizzle part of the music?

[Bill Fitzmaurice]

I believe I've found the problem, could a tweeter thats wired wrong in one of the speakers "reversed polarity" cause all of the speakers to sound bad?
I mean the sizzle part of the music?

Yes, it can.

[jose99a]

Just opened the cab and found this...
Do I need to replace the whole xover?

[horst]

Whoa s that a cooked induction coil former I see before me?
to melt the former in a crossover you have to really put some power into them.
So new theory for the bad sound is a cooked voice coil, the insulation expands just enough to rub on the magnet.
run a frequency sweep to confirm. the Crossover may well be still okay but you may have to replace the drivers.

[LelandCrooks]

Whoa s that a cooked induction coil former I see before me?

[jose99a]

Thanks for all your help, one more thing what does the white rectangle looking thing do?

[BrentEvans]

Thanks for all your help, one more thing what does the white rectangle looking thing do?

Its a resistor.

[jose99a]

Mr. Brent is a resistor used to protect the tweeter? I'm asking because 2 of the 5 speakers I bought have the resistor knocked off and I hear no difference from the other 2.
Just to let everyone know I bought 5 ev sx300 from a bar/lounge at a ridiculus price, in the hope to resale them to fund some DR 200's.

[BrentEvans]

It could be a protection resistor, but I'm no expert in crossover design.

Are you sure the HF drivers are even working? It would be common in an environment like that for them to be blown. Removing the resistor and hearing no difference might mean you're simply hearing no HF at all.

[jose99a]

Yes, the tweeters are working fine, thats why I'm puzzeled as to what are they for " protection or sound"
The speaker that has the "cooked induction coil former" as Mr. "horst" stated is the one that sounds bad "tweeter".