# High Frequency Null at 4500



## bommers (Oct 30, 2010)

Hi - 

Just starting do to some room treatments for 25 ft wide by 15 ft deep by 7.5 feet tall Home Theater/Music room. Just added a couple of front wall lower corner chunks, and a rear wall full corner chunk with Safe n' Sound. Got a pretty good idea what to do with corners and soffits, and first reflections. The REW graph taken from sweet spot, two thirds way back from front wall center. No clouds, or first reflective panels up yet. 

What's up with the huge suckout at 4500 and 14,000? I replaced my new speakers with some older towers, exact same curve. Can room effects create this huge null? I did a nearfield miking of one speaker at one foot, also same curve. 

Thanks for help, will keep working on bass traps as you can see my waterfall show lots of low end greater than 300ms.


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## bpape (Sep 14, 2006)

With a dip that wide it's not all one thing. Could be any number of things. Are the speakers set up really close to a hard surface? or surfaces/

Bass level of the sub appears to be too high by at least 10db.

When looking at the waterfall, set the left scale so that the bottom number is approx 40db < the average level. In your case that would be 80-85. That will give you a better feel for where the decay stands in the room.


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## bommers (Oct 30, 2010)

Sorry about the elevated sub, had shut off emotive correction, yes it hot. The speakers are "The Statements" DIY that come well recommended. The Front face is 28 inches from rear wall, the back side is 18 inches from wall. It's a split wall, bottom half sheetrock over framed cement half wall, top is 2x4 sheetrocked. Sidewalls are over 10 feet away. I can start working on some small placement changes, but they're pretty close to where they need to be. Any suggestions for areas of treatment? The sidewalls have a sliding glass door on one side and a large picture window on other. I'm thinking rear wall might be best place to start, am planning on absorptive panels. Played a 4500 hz test tone, its a very small wave, changes from peaks to null every few inches, but I obviously have a very large and wide dip there.

Thanks for your reply Bryan


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## bommers (Oct 30, 2010)

Speaker picture...Sorry not adding my pics.....


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## bommers (Oct 30, 2010)

Sorry had to resize picture...............


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## bpape (Sep 14, 2006)

Do you know the xover point between the mids and ribbon? Could be that one is wired out of phase. If you measure very close to the mid and tweeter, like maybe a foot, look and see if the dip is still there.


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## bommers (Oct 30, 2010)

Ribbon - mids crossover is 3500 hz. I thought of that and flipped the polarity of the ribbon tweeter, and exact waveform. Then I swapped the speakers next, thinking there was a crossover mistake, same waveform with my old Klipshes. So either a bad room response, or problem with emotiva pre or crown amps. Will swap out with old denon amp for fun to rule that out. Really surprised near field measurement was the same, but not used to working with these higher frequency problems.


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## atledreier (Mar 2, 2007)

Mic or measurement system artefact?


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## bommers (Oct 30, 2010)

Got a mini dsp USB mike. Gonna try throwing a big heavy blanket over speaker and do another near field measurement... I would think that should be flat if it's all room effect.


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## bpape (Sep 14, 2006)

If the problem is the same in the nearfield, it's likely not all room. Could be an issue with the baffle step in the xover.


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## bommers (Oct 30, 2010)

Solved the deep 4500hz mystery. When I switched from two sweeps to a single sweep with measurement it went away. Not sure why, but back to building traps and clouds....


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## Cali (Feb 24, 2011)

bommers said:


> same waveform with my old Klipshes. .


Mic problem?

Never mind..I just saw you resolved it


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