[email protected]$#$% Nulls!!!!

[dguarnaccia]

I'm just about at my whits end. I can't seem to get rid of this frackin null. I've spent days moving crap around, playing wtih phase, and putting up bass traps. Here is the best I've managed to get with REW.



What else can I do to whack down this friggin null. I've gotten a few more bass traps from Gik, the 242's I think. They are across the back wall. It didn't seem to help. All the corners have tube bass traps floor to ceiling. 16 inch diameter in the fronts, 12 inchers in the rear corners.

Is it just a matter of just putting up enough bass traps till I kill that null? I've moved the sub everywhere, and it hasn't improved it one bit. Playing with the phase usnig the sub distance settings at one foot increments hasn't helped either.

I suppose I'm just venting, but if anyone has a good idea I'm all ears.

[HAL]

What is the crossover point for the mains to the sub? It looks like the mains are about 7dB higher than the sub. If you try matching levels does it change?

[dguarnaccia]

Sorry, forgot to mention that. The crossover is at 60 hz. I've tried moving it up to 80 and 100 and it gets worse.

I'll try lowering the mains a bit more. I can't push the mfw15 any harder, it starts making a mechanical noise when push it too hard.

Thanks for the suggestion.

[lngbruno]

Your beginning with an illogical premise....

....and proceeding perfectly, logically, to an illogical conclusion.

dguarnaccia,

Would you please provide some additional information:

1.What are the powered woofers settings set at? Have you played with the phasing on these amps? Individually?
2.Do you have the powered woofers facing inward or outward?
3.Did you verify that the woofers are phased properly?
4.Did you verify that the sub driver is phased properly?

You will find you are not alone in dealing with a conundrum wrapped in an enigma wrapped in a riddle…however, solutions do vary.

Lou

[dvenardos]

Lou,
If it is phase shouldn't he be able to tell pretty quickly my running just the sub or just one the mains? Does seem like that is the problem though doesn't it? :no clue:

Don

[dguarnaccia]

Ok, lets see:

I've been doing a lot of testing with just the sub alone, and I still see a lot of the same problems in the same region with just the sub, here is a run with just the sub:



Here are the answers to the questions you asked:

1.What are the powered woofers settings set at? Have you played with the phasing on these amps? Individually?
On the 1k's, the power is set to the 12 o clock position. Both are set to Zero phase.


2.Do you have the powered woofers facing inward or outward?
The are currently facing outward. I've tried them facing inward as well, and outward seemed better at the time according to the REW plots

3.Did you verify that the woofers are phased properly?

I'm not sure I know how to do this. Are you referring to polarity here for the speaker, or the powered woofer itself? How would I go about verifying that?

4.Did you verify that the sub driver is phased properly?
This one I've played with a ton. I've left the phase on the 1k's alone, and played with the phase on the sub. I've tried incrementing the distance setting in the recieve by 1 ft chunks to find the best phase setting.


I've also tried turning off the amps on the 1k's to see if that had an impact, and I haven't noticed much difference in the REW plots either. I would think if it's a phase problem from the 1k's, pulling the amp power would neutralize it, wouldn't it?

[HAL]

Since there is a +6dB peak at 60Hz the sub and RS1K are in-phase as they are summing.

It looks like from the second graph that moving the crossover frequency down to 40-50Hz would make the area where the problem exists much lower in level for the sub output and the summing with the RS1K's not as big an issue. Not sure if the XO will go that low is the question. Lower frequency looks better from the second graph info.

Just a thought.

[dguarnaccia]

Unfortunately, the lowest the XO will go on the marantz is 60 :(

[lngbruno]

dvenardos,

Yes, he could run the sub with either the R or L front main to see what shows up on the graph. Also, to run the mains full changing the phase to see how the room affects the signal. Experimentation is good, apathy is bad.

dguarnaccia,

Thanks for answering the questions. To test each driver you would pop them out and use a battery to test if the driver moves out or in consistently when the drivers + is on the battery +. Important to remember to do this for just a few seconds. I agree with Hal that they appear to be in the correct phase alignment based on your new chart, but something strange is happening.

Okay, have you tried measuring them the old fashion way - RS meter and test tones? Try running the mains full, and dialing in the sub starting at 80 and working down to see how that works. Don't forget to add in the RS meter corrections to get as accurate a picture as possible. This is my preferred method.

Oh, I forgot to mention this one little point, "I don't know enough to know what I don't know." :no clue:

Keep hunting, you will find the answer.

Lou

[toddbagwell]

Could it be a function of some overlapping room modes? What are your dimensions?

http://www.realtraps.com/modecalc.htm

todd

[dguarnaccia]

The room is 18' W x 23' L x 9' H

The primary listening spot is roughtly at 10' from front wall center of room.

[dguarnaccia]

Looks like a couple of nulls right in that general area between 90 and 100 hz. Anything I can do about those with trapping? Or am I just hosed?

[dguarnaccia]

dvenardos,

Yes, he could run the sub with either the R or L front main to see what shows up on the graph. Also, to run the mains full changing the phase to see how the room affects the signal. Experimentation is good, apathy is bad.

dguarnaccia,

Thanks for answering the questions. To test each driver you would pop them out and use a battery to test if the driver moves out or in consistently when the drivers + is on the battery +. Important to remember to do this for just a few seconds. I agree with Hal that they appear to be in the correct phase alignment based on your new chart, but something strange is happening.

Okay, have you tried measuring them the old fashion way - RS meter and test tones? Try running the mains full, and dialing in the sub starting at 80 and working down to see how that works. Don't forget to add in the RS meter corrections to get as accurate a picture as possible. This is my preferred method.

Oh, I forgot to mention this one little point, "I don't know enough to know what I don't know." :no clue:

Keep hunting, you will find the answer.

Lou

I've worked a little with the test tones, mostly to try to find the best placement for the sub while its in the listening position. I'll try to play with the phase some more on the woofers on the mains as well and I'll take a few more screenshots with just the mains playing full range.

[toddbagwell]

The room is 18' W x 23' L x 9' H

The primary listening spot is roughtly at 10' from front wall center of room.

Try measuring one or two feet infront or behind of your current LP to see if it is just a position related issue

[NekoAudio]

It might be a null from your room height.