# pretty big dip, can not move IB sub



## kjgarrison (Nov 17, 2007)

Hello everybody. I'll post some graphs from REW and ask for your expertise. But first: my equipment and environment. DIY IB (2x18" Fi Audio line array centered within a half inch of floor level right under the center channel and the TV, powered by Behringer EP1500); Denon 4308 AVR with Audyssey Multi EQ XT; PSB Synchrony Two floorstanders and center speaker; large (~7000 cu ft), "bright" room (hardwood floors, lots of windows, right floorstander within inches of right wall and about 2 feet out from front wall, left floorstander 25' from left wall across dining room and 2 feet out from front wall); seating position ~9 feet from center and sub and about 20 feet from back wall.

First graph: Nearfield of subwoofer with no EQ (Audyssey off)

Next: Listening position, subwoofer, EQ on (Audyssey)

Third: Listening position, subwoofer, no EQ

can only get three attachments .. next post for the real issue and question.


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## kjgarrison (Nov 17, 2007)

Here is the graph of the whole thing.

This is full range, with EQ (Audyssey) Some dips that are main/subwoofer interaction. What do I (you) need to measure, or do, next?

[Edit:] I removed the extraneous graph that was there before.


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## hjones4841 (Jan 21, 2009)

Your LF response with Audyssey on looks quite good, especially the extension below 20Hz. A BFE would help smooth response, but it rolls off below 20Hz, which is something you might not want. I suggest doing and posting some waterfall plots from your listening position to see what is going on in your room and if treatments might help.


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## bpape (Sep 14, 2006)

Exactly. Waterfalls will help determining modal interactions as well as potential seating/speaker location issues. 

As for interaction with subs/speakers - some may be fixed with moving speakers, some may be helped with adjusting phase if it's infinitely adjustable vs just a 0/180 switch.

Sub positioning can also help.

Bryan


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## kjgarrison (Nov 17, 2007)

hjones4841 said:


> Your LF response with Audyssey on looks quite good, especially the extension below 20Hz. A BFE would help smooth response, but it rolls off below 20Hz, which is something you might not want. I suggest doing and posting some waterfall plots from your listening position to see what is going on in your room and if treatments might help.





bpape said:


> Exactly. Waterfalls will help determining modal interactions as well as potential seating/speaker location issues.
> 
> As for interaction with subs/speakers - some may be fixed with moving speakers, some may be helped with adjusting phase if it's infinitely adjustable vs just a 0/180 switch.
> 
> ...


Thanks guys. I'll post the waterfall for the full range. (As soon as I figure out how ...)

As to moving the sub: it's an IB.

Re adjusting phase: I don't have a control for that. Just my AVR and the sub's amp (EP1500). However, I was told that changing the sub's distance in the AVR is an alternative way to accomplish the same thing. Doing that is possible, but the distance has been set by Audyssey for the sub and all the speakers (5.1) so that sound arrives at the listening position in sync. Hopefully a small tweak one way or the other wouldn't mess anything up.

OK, here is a waterfall. Not sure if the many settings are what is needed; they are all defaults. The graph spans several screens if I do the whole range, so this is just 0-200 part of the 0-20,000 measurement. The crossover is set to 60Hz. Let me know if other settings should be used and/or how to post the whole waterfall if that's what you need. Meantime I'll be reading up on proper waterfall settings.

[EDIT:] I forgot to mention some things that have been talked about using REW in the (extensive) AVS Audyssey thread. Chris (Audyssey) points out that Audyssey takes 8 measurements at and around the primary listening position and then does it's thing. I see in the REW tabs a place to average multiple measurements. Would it be a good idea to take measurements at the same places where the Audyssey measurements are taken and then average them in REW before we decide that anything needs to be fixed? This ONE measurement is centered in front of the sub and between the mains ... fwiw


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## kjgarrison (Nov 17, 2007)

Here is another waterfall spanning the second dip at around 1800Hz. This one is 1k-3k


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## hjones4841 (Jan 21, 2009)

Looks like your mains are on - not seeing the rolloff above 60Hz crossover point. Power up just the sub and re-run the waterfall plots. Looks like your REW settings are OK.

Lots of LF energy bouncing around your room. Also seems to be several significant room modes (the valleys in the freq response). Do you have any room treatments/bass traps? I suggest posting a simple sketch of the room with dimensions. That will give Bryan something to work with for suggested treatments. 

Your IB certainly has potential looking at the LF extension, just need to smooth out the FR and tame the room ringing - you will be amazed at the difference bass traps make.


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## bpape (Sep 14, 2006)

Run a plot from 20-300 Hz. The rest is what it is for all practical purposes. In all honestly, 99% of the time, you'll get better EQ manually than letting Audyssey set it other than position times - which again, can be used to your advantage.

Bryan


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## kjgarrison (Nov 17, 2007)

hjones4841 said:


> Looks like your mains are on - not seeing the rolloff above 60Hz crossover point. Power up just the sub and re-run the waterfall plots. Looks like your REW settings are OK.
> 
> Lots of LF energy bouncing around your room. Also seems to be several significant room modes (the valleys in the freq response). Do you have any room treatments/bass traps? I suggest posting a simple sketch of the room with dimensions. That will give Bryan something to work with for suggested treatments.
> 
> Your IB certainly has potential looking at the LF extension, just need to smooth out the FR and tame the room ringing - you will be amazed at the difference bass traps make.


Mains not on. For sub alone plots, I set crossover up to 250.

Sub alone, Audyssey EQ:

I'll work up a diagram.


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## kjgarrison (Nov 17, 2007)

bpape said:


> Run a plot from 20-300 Hz. The rest is what it is for all practical purposes. In all honestly, 99% of the time, you'll get better EQ manually than letting Audyssey set it other than position times - which again, can be used to your advantage.
> 
> Bryan


Here is the 20-300 plot. Manually, eh? So I need a BFD? What do you mean by "position times - which again, can be used to your advantage?"


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## hjones4841 (Jan 21, 2009)

To give you an idea of the goal, here is the waterfall of my room after LOTS of bass trapping. Not that my room is perfect, but it sure sounds much better than before. The goal is to time-shorten the room's reflections (the right hand axis on the plot), reducing the rooms' acoustic ringing. Ringing is the room continuing to "echo" the sound after the sub's cone stops moving. When ringing is controlled, the FR of the sub is smoother and its transient response is much improved.


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## bpape (Sep 14, 2006)

Sorry for not being clear. Audyssey can be used to set distance (position times) relatively accurately, though you'll want to check the sub distance. It seems to get that wrong quite often. 

IMO, EQ is good on the sub channel and you really don't need it elsewhere if you pay attention to locations, how you treat the room, and if your speakers naturally sound the way you want them to.

Bryan


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## kjgarrison (Nov 17, 2007)

bpape said:


> Sorry for not being clear. Audyssey can be used to set distance (position times) relatively accurately, though you'll want to check the sub distance. It seems to get that wrong quite often.
> 
> IMO, EQ is good on the sub channel and you really don't need it elsewhere if you *pay attention to locations, how you treat the room, and if your speakers naturally sound the way you want them to*.
> 
> Bryan


Thanks.


Location: Sub is an IB and can't be moved.
Location: R&L floorstanders can be moved a little
Location: I have only measured at one location. Should I measure several and average them, or at least show them?
Treat the room: I have read only a little bit about this. Is there a way to figure out what treatments will yield the most benefit? Would a diagram or a specific measurement help? WAF issues :explode:
My speakers: Sound fantastic to me.


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## bpape (Sep 14, 2006)

Understood on the sub positioning - just more of a general statement for those following along at home... On the other hand, you can change the phase of the sub - as you said, by tweaking distance settings. Not as good as phase itself but it can help a bit.

R+L positioning can help blend things, change frequency response, tweak things by using SBIR to your advantage, etc. 

Measure at seating positions. Other positions don't matter. Take several sets, just primary seats, all seats, etc.

Treating a room can help a ton in terms of FR and ringing. A diagram of the space will help a lot and please include dimensions

Good deal on the speakers. So many people buy something and then try to change the sound with EQ when it's much better to just get what sounds good to you, works with your room, works with your equipment, etc.

Bryan


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## kjgarrison (Nov 17, 2007)

Here's a capture of a Google Sketchup. Looks busy, but viewing/listening area in upper right. See the blind cubby behind the R MAIN. Oh, and these mains are rear ported.
I'll be doing more measurements.

EDIT: problem with image


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## bpape (Sep 14, 2006)

Pic? :scratch:


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## kjgarrison (Nov 17, 2007)

bpape said:


> Pic? :scratch:


It's there now. Had probs with formatting.

There are some fabric chairs, loveseat, and throw rugs not shown.


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## bpape (Sep 14, 2006)

OK. Definitely a couple of issues there. 

That big cabinet is effectively putting both speakers right against a boundary.

Lack of symmetry left to right is going to skew bass through dialog response so L and R are very different sounding.

Right speaker being right against the wall and against the cabinet is effectively like putting it in a box that has all of it's own resonances.

Treatments on the right wall for reflections, right next to the speaker for boundary control, and killing the right corner would all be great places to start to deal with the issues above.

Bryan


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## kjgarrison (Nov 17, 2007)

I have a question regarding a specific use of REW. It relates to setting my subwoofer's distance as you suggested.

Is there a way, using REW, to send an extremely brief spike of sound at a specific frequency, say 80Hz, and measuring/recording the output?

I want to enable "LFE+Mains" to see if this spike of sound arrives at the same time from the mains as it does from the subwoofer. I have discovered that Audyssey set the distance to my sub too close. I've been experimenting with this distance setting.


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## bpape (Sep 14, 2006)

Not that I'm aware of.

Remember that Audyssey is also trying to correct for phase issues. If the phase is off, then Audyssey (as I understand it), will adjust distance to try to compensate.

Bryan


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## weverb (Aug 15, 2008)

Can't you use the Generator and play a sine wave at any given frequency?


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## kjgarrison (Nov 17, 2007)

weverb said:


> Can't you use the Generator and play a sine wave at any given frequency?


Well, I guess I could, but how would I see a few milliseconds difference coming from the sub vs the mains? Would it just look fuzzy?

I just want to ping the system.

Honestly, though, I don't know enough about using REW.


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