Two unmatched Subs, Phase control & Audyssey - AVS Forum
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post #1 of 24 Old 02-17-2013, 02:45 PM - Thread Starter
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I'm seeking some advice on my current subwoofer setup.

I currently have a PSA XS15 (sealed) and a ED A2-300 (ported). I was going to get rid of the A2-300, but I decided to try and add it to the system since I'm able to localize the XS15 at times. I think this is because I sit about 8' away from the sub and my display. I was hoping the A2-300 would help diminish some of the localization. I currently have an Onkyo TX-NR818 with a crossover set to 80 Hz. My mains are Ascend Acoustic CMT-340 SEs.

My issue: I can still localize each sub at times.

Here is how I've set everything up:
1. Gain matched the subs (middle of room using SPL meter. Both subs and mic in the same place).
2. Used REW to place the XS15
3. Added in the A2-300 and used REW to find the spot with the smoothest response (every place had some kind of null).
4. Set phase on the A2-300 to approximately 160 degrees (this gave me the smoothest response)
5. Run Audyssey XT 32 (NO SUB EQ HT on my Onkyo)

I'm guessing my issue has to do with messing with the phase on the A2-300. The XS15 actually has a smoother overall response in my room. Adding the A2-300 created a decent null around 30Hz and 50Hz. Adjusting the phase got rid of both nulls, but I'm afraid it is causing my localization problem again.

Audyssey states that I should leave the phase at 0 on both subs, but the null at 30Hz is so big that I don't think XT32 can fix it. I've read that Audyssey can adjust smaller drops and spikes, but not a null like the one created by the A2-300.

Am I fighting a losing battle trying to integrate the A2-300? I know integrating a non matching sub is a challenge, but I thought I may be able to get things good enough for my listening tastes. Am I improperly adjusting the phase?

Any help is extremely appreciated. I've read and researched a ton. Ultimately, I realize another XS15 may be my best option, but I'm not ready to go there just yet.

Thanks!
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post #2 of 24 Old 02-17-2013, 03:02 PM
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Audyssey is not foolproof, so don't feel badly about having to "tweak." Room nulls are not usually fixable with eq. Room treatments and repositioning are usually the only solutions, and practicality often dictates limits to those.

Stay with REW (and follow the threads there for advice). I have two mismatched subs (neither as good as yours) and have gotten +/- 3dB from 20 - 100Hz with a 1124P DSP, patience, and time. I think the phase is at 0 for both, but I wouldn't swear for it. 

Try moving the subs a little in each direction in their current positions. Try facing them in different directions. They should not be easy to localize if your crossover is at 80Hz.

If you're still that sensitive to it, you may want to try a lower crossover (especially with those mains).


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post #3 of 24 Old 02-17-2013, 08:44 PM - Thread Starter
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Thanks for the advice. I worked with rew for a couple more hours and found another spot to place the a2-300. It's not far off from the original spot and I could have sworn that I tested it before in this same spot. Nonetheless, I found I was able to get a smoother response without having to adjust the phase control. I also moved my couch back 8-12 inches which may also have made a difference. Now I'm going to rerun audyssey and tst the results.

Thanks again,
Nick
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post #4 of 24 Old 02-18-2013, 05:52 AM - Thread Starter
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Looks like I have some more tweaking to do. After running Audyssey again, a valley around 25Hz was made worse. I know Audyssey cannot fix nulls, but I thought it was able correct a large peak or valley. When playing back the sweep in REW, I could definitely notice the lack of bass at 25Hz...
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post #5 of 24 Old 02-18-2013, 05:54 AM
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Peaks, yes. Valleys, no. Search for "room null" and get help from those more experienced than I.

Good luck, and don't give up!

Michael


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post #6 of 24 Old 02-18-2013, 06:05 AM
 
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Quote:
Originally Posted by CincyNick View Post

Looks like I have some more tweaking to do. After running Audyssey again, a valley around 25Hz was made worse. I know Audyssey cannot fix nulls, but I thought it was able correct a large peak or valley. When playing back the sweep in REW, I could definitely notice the lack of bass at 25Hz...

Just a thought, as you're tweaking your system, have you set Audyssey to factory specs? If not then while trying to integrate your system, you're compounding your efforts as you're fighting what ever Audyssey has introduced into the the sonic information stream.

My recommendation, based on personal experience, is to "FIRST" get the best out of a room system as one can. No Audyssey in the sonic loop. And verified by a room analyzing program, when satisfied you've gotten the very best out of your system, run Audyssey and then do final tweaks. If done in any other fashion, my experience, one will be fighting any compounded loopiness Audyssey has introduced into a system using badly set parametric controls in a poorly placed subwoofer system.
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post #7 of 24 Old 02-18-2013, 06:27 AM - Thread Starter
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Originally Posted by LastButNotLeast View Post

Peaks, yes. Valleys, no. Search for "room null" and get help from those more experienced than I.
Good luck, and don't give up!
Michael

Thanks again. I'm heading home at lunch (close to my work) and I'm going to spend a good hour with the XS15 while the kids are out just to make sure that I've got it in the best place. Then I'm going to work on the A2-300 again tonight.

I've been disconnecting the mains when placing the XS15. I've found a great spot that offers pretty smooth response. However, as soon as I reconnect the mains a few large valleys stand out. Should I keep the mains connected when placing the sub(s)? I've seen it recommended both ways here and other forums.
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post #8 of 24 Old 02-18-2013, 06:31 AM - Thread Starter
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Originally Posted by BeeMan458 View Post

Just a thought, as you're tweaking your system, have you set Audyssey to factory specs? If not then while trying to integrate your system, you're compounding your efforts as you're fighting what ever Audyssey has introduced into the the sonic information stream.

My recommendation, based on personal experience, is to "FIRST" get the best out of a room system as one can. No Audyssey in the sonic loop. And verified by a room analyzing program, when satisfied you've gotten the very best out of your system, run Audyssey and then do final tweaks. If done in any other fashion, my experience, one will be fighting any compounded loopiness Audyssey has introduced into a system using badly set parametric controls in a poorly placed subwoofer system.

I always turn off Audyssey & Dyn EQ and then reset the levels to 0 prior to running REW. Is this what you're talking about?

Thanks!
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post #9 of 24 Old 02-18-2013, 06:32 AM
 
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Have you told the room analyzing program to only use the subwoofer channel?
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post #10 of 24 Old 02-18-2013, 06:51 AM - Thread Starter
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Quote:
Originally Posted by BeeMan458 View Post

Have you told the room analyzing program to only use the subwoofer channel?

You know what, I'm not. I'm going to have to figure out how to do that in REW at lunch. I think I'm going to have to start all over and work on the mains first, and then move to the subs. Thanks again!
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You'll find this REW parameter in the "Preference" menu. Look to the upper right corner of the main page and click on the open end wrench. And in the "levels" let down menu box, you'll see two choices, mains or subwoofer.
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post #12 of 24 Old 02-19-2013, 04:49 AM
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Quote:
Originally Posted by CincyNick View Post

Thanks again. I'm heading home at lunch (close to my work) and I'm going to spend a good hour with the XS15 while the kids are out just to make sure that I've got it in the best place. Then I'm going to work on the A2-300 again tonight.

I've been disconnecting the mains when placing the XS15. I've found a great spot that offers pretty smooth response. However, as soon as I reconnect the mains a few large valleys stand out. Should I keep the mains connected when placing the sub(s)? I've seen it recommended both ways here and other forums.
Those "valleys" are caused by the destructive interaction of the subs and speakers in the ranges where they are both outputting the same frequencies, (around the crossover point.) The way to treat them is to adjust the subwoofer Distance setting until the destructive interference goes away. Here is an example:



The cyan trace is the "physical" subwoofer distance. The green trace is with the subwoofer Distance setting adjusted to the proper "acoustic" distance.

I suggest you place the sub while playing it in isolation, then turn on the speakers and adjust the subwoofer Distance setting to get the best blend of the sub and speakers.

In addition, I suggest you consider selling the A2-300 and using the funds towards the purchase of a second XS-15.

Good luck.

Craig

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post #13 of 24 Old 02-19-2013, 05:54 AM - Thread Starter
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Quote:
Originally Posted by craig john View Post

Those "valleys" are caused by the destructive interaction of the subs and speakers in the ranges where they are both outputting the same frequencies, (around the crossover point.) The way to treat them is to adjust the subwoofer Distance setting until the destructive interference goes away. Here is an example:



The cyan trace is the "physical" subwoofer distance. The green trace is with the subwoofer Distance setting adjusted to the proper "acoustic" distance.

I suggest you place the sub while playing it in isolation, then turn on the speakers and adjust the subwoofer Distance setting to get the best blend of the sub and speakers.

In addition, I suggest you consider selling the A2-300 and using the funds towards the purchase of a second XS-15.

Good luck.

Craig

Thanks so much for the info. This makes perfect sense. I was playing with the crossover last night, but didn't think of changing the distance settings. I did notice that changing the crossover to 60Hz did cure one valley around 70Hz. The mains were stronger in this range and seemed to compensate for the valley caused by the sub. However, I still have a pretty nasty 12-15 dB valley/null around 25Hz that just won't go away. I'm guessing this is a room null and will only be cured with room treatment.

I've read a ton of your posts while doing my research. Thanks for all of the help and advice you give the forum.

I hear you loud and clear on the A2-300. I actually had it up for sale locally about a month ago, with zero luck. I'll have to look into again in the very near future.

Thanks again,
nick
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Originally Posted by CincyNick View Post

I'm guessing this is a room null and will only be cured with room treatment.

Moving the subwoofer or the listening position goes a long way in correcting for main listening position based nulls.

The simplest way to experience what I'm posting about, using the "Generator" feature, play a 60Hz continuous tone through the subwoofer system and slowly walk around the room. Make note of the sonic changes as you go about the room.
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post #15 of 24 Old 02-19-2013, 06:30 AM - Thread Starter
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Quote:
Originally Posted by BeeMan458 View Post

Moving the subwoofer or the listening position goes a long way in correcting for main listening position based nulls.

The simplest way to experience what I'm posting about, using the "Generator" feature, play a 60Hz continuous tone through the subwoofer system and slowly walk around the room. Make note of the sonic changes as you go about the room.

Thanks for the help. I've moved the subwoofer to every viable spot so far. The spot with the smoothest response seems to be the right wall about 3 feet away from the corner. Last night I also moved the couch back about a foot and rearranged some furniture. Like many, my HT is in a shared area of our basement surrounded by toys, so there are some places that won't work unfortunately. I can just see my son playing Star Wars guys on top of the sub while simultaneously adjusting the gain, phase and crossover smile.gif
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post #16 of 24 Old 02-19-2013, 06:33 AM
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That's how I started.

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post #17 of 24 Old 02-19-2013, 07:13 AM
 
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Originally Posted by CincyNick View Post

Thanks for the help. I've moved the subwoofer to every viable spot so far. The spot with the smoothest response seems to be the right wall about 3 feet away from the corner. Last night I also moved the couch back about a foot and rearranged some furniture. Like many, my HT is in a shared area of our basement surrounded by toys, so there are some places that won't work unfortunately. I can just see my son playing Star Wars guys on top of the sub while simultaneously adjusting the gain, phase and crossover smile.gif

As a suggestion, stop moving everything and play the test tone. Walk around the room and listen for the changes. Make note, adjust accordingly and then repeat. The idea of playing the continuous test tone is so you can familiarize yourself with changing room acoustics. It's the most graphic and simple method I've found to convey how small movements in the same room create such large changes.

As to parametric control changes, if not already doing so, one must do each, one at a time and do so incrementally, with measurements being taken and analyzed, every step of the way. It never hurts to take physical, on paper notes in which to refer back to. As I'm sure you know, as the more changes are made, the more difficult it is to accurately recall what did and didn't work.

-
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post #18 of 24 Old 02-19-2013, 10:31 AM
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Quote:
Originally Posted by CincyNick View Post

Thanks so much for the info. This makes perfect sense. I was playing with the crossover last night, but didn't think of changing the distance settings. I did notice that changing the crossover to 60Hz did cure one valley around 70Hz. The mains were stronger in this range and seemed to compensate for the valley caused by the sub. However, I still have a pretty nasty 12-15 dB valley/null around 25Hz that just won't go away. I'm guessing this is a room null and will only be cured with room treatment.

I've read a ton of your posts while doing my research. Thanks for all of the help and advice you give the forum.

I hear you loud and clear on the A2-300. I actually had it up for sale locally about a month ago, with zero luck. I'll have to look into again in the very near future.

Thanks again,
nick
A second XS-15 is probably going to be the best "cure-all" for your room induced nulls. You can move a single sub around the room all day long and never find a "perfect" spot that yields no peaks or nulls. You might cure the 25 Hz null only to find another one in another placement at 35 Hz. Having multiple sources of bass is pretty much the only way to counteract room nulls. (Peaks can be addressed with EQ, but nulls are cancellations and no EQ can correct cancellations.)

In addition, simple room treatments are ineffective at low frequencies like 25 Hz. A 25 Hz wave has a wavelength of about 45 feet. You would need absorption that is at least 1/4 of the wavelength to be absorptive of such a wave. IOW, you would need absorption that is 11.25 FEET thick to be effective at 25 Hz. Obviously, that is impractical. There are other types of resonant absorbers that can be tuned to a target frequency, but they are more expensive and more complex to build than simple fiberglass absorption panels.

Bottom line, the best way to correct room nulls is with multiple subs placed around the room. Welti and Geddes have different approaches to the problem, but multiple subs is the common denominator:

Welti's Paper: http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/multsubs.pdf
Geddes Paper: http://mehlau.net/audio/multisub_geddes/

You could try the Geddes technique using your A2-300, and it may help with the 25 hz null, but I would be careful that you don't overdrive it asking it to keep up with the XS-15. Also, it's a ported sub vs. the sealed PSA sub. The ported sub will roll off faster below tune, so it won't have the extension of the PSA. It won't be easy to integrate the two, but it *might* help with the 25 Hz null.

Craig

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post #19 of 24 Old 02-19-2013, 12:17 PM - Thread Starter
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That's how I started.
biggrin.gif

It's very easy to see how we go from a simple setup in the family room to dedicated theaters in our homes. It seems to happen incredibly fast. I don't know if I'm fortunate or not, but I won't be able to go the dedicated route for some time. My kids are only 4 and 6 months, and I'm in NO HURRY for them to get older smile.gif

But, when they do, our basement will be completely transformed!
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post #20 of 24 Old 02-19-2013, 12:22 PM - Thread Starter
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Originally Posted by BeeMan458 View Post

As a suggestion, stop moving everything and play the test tone. Walk around the room and listen for the changes. Make note, adjust accordingly and then repeat. The idea of playing the continuous test tone is so you can familiarize yourself with changing room acoustics. It's the most graphic and simple method I've found to convey how small movements in the same room create such large changes.

As to parametric control changes, if not already doing so, one must do each, one at a time and do so incrementally, with measurements being taken and analyzed, every step of the way. It never hurts to take physical, on paper notes in which to refer back to. As I'm sure you know, as the more changes are made, the more difficult it is to accurately recall what did and didn't work.

-

Thanks, BeeMan. I only moved the furniture after trying every place i could find for the XS15. I just wanted to hear and see the differences it would make in my system. It was actually a pretty cool exercise to get a feel for just how much objects and furniture can affect response. After all was said and done, I moved the furniture back. Right now my couch position has three great seating spots for XT32 calibration. I chose that over having an extra chair moved further into the listening area.

I'll try your suggestions out tonight or this weekend. I have to say, it's pretty fun trying to get everything dialed-in even if it's not close to perfect.
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post #21 of 24 Old 02-19-2013, 12:36 PM - Thread Starter
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Originally Posted by craig john View Post

A second XS-15 is probably going to be the best "cure-all" for your room induced nulls. You can move a single sub around the room all day long and never find a "perfect" spot that yields no peaks or nulls. You might cure the 25 Hz null only to find another one in another placement at 35 Hz. Having multiple sources of bass is pretty much the only way to counteract room nulls. (Peaks can be addressed with EQ, but nulls are cancellations and no EQ can correct cancellations.)

In addition, simple room treatments are ineffective at low frequencies like 25 Hz. A 25 Hz wave has a wavelength of about 45 feet. You would need absorption that is at least 1/4 of the wavelength to be absorptive of such a wave. IOW, you would need absorption that is 11.25 FEET thick to be effective at 25 Hz. Obviously, that is impractical. There are other types of resonant absorbers that can be tuned to a target frequency, but they are more expensive and more complex to build than simple fiberglass absorption panels.

Bottom line, the best way to correct room nulls is with multiple subs placed around the room. Welti and Geddes have different approaches to the problem, but multiple subs is the common denominator:

Welti's Paper: http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/multsubs.pdf
Geddes Paper: http://mehlau.net/audio/multisub_geddes/

You could try the Geddes technique using your A2-300, and it may help with the 25 hz null, but I would be careful that you don't overdrive it asking it to keep up with the XS-15. Also, it's a ported sub vs. the sealed PSA sub. The ported sub will roll off faster below tune, so it won't have the extension of the PSA. It won't be easy to integrate the two, but it *might* help with the 25 Hz null.

Craig

I wholeheartedly agree. Maybe after I figure out how much I owe uncle Sam this year, I can add another XS15 to the system. Fantastic info about room treatments. I had NO IDEA that it would require absorption that thick. Obviously that's a no go. Where would my son put his AT-AT and snowtroopers?

I'm kind of using Geddes approach now (if I'm reading it correctly). My mains are great down to 60Hz before they start to dip. The XS15 has a valley at 70 Hz but is pretty darn smooth at 60-25 and again in the low 20's high teens. The 25Hz null is the kicker that I'm attempting to cure with the A2-300. So far, no luck.

Thanks again for all of the help. Even if I don't fix the null, I'm learning a ton and having fun doing it.

Best
Nick
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post #22 of 24 Old 02-19-2013, 06:16 PM
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I'll admit I didn't read each post thoroughly, but it seems like the conversation has shifted from being able to localize each sub to achieving the smoothest response?

 

From your first post, it sounded like you were pleased with your response, but could localize each sub. In the scenarios above, have any of them solved for the localization problem (regardless of their combined frequency response)? 

 

From a 'smoothing' your FR perspective, I'd recommend exactly what you did when integrating ported and sealed. I have both designs in my theater, and adjusted the phase on each sub where the combined response were absent of nulls. Audyssey XT's FR was pretty choppy compared to my final result. 



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post #23 of 24 Old 02-19-2013, 09:15 PM - Thread Starter
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I'll admit I didn't read each post thoroughly, but it seems like the conversation has shifted from being able to localize each sub to achieving the smoothest response?

From your first post, it sounded like you were pleased with your response, but could localize each sub. In the scenarios above, have any of them solved for the localization problem (regardless of their combined frequency response)? 

From a 'smoothing' your FR perspective, I'd recommend exactly what you did when integrating ported and sealed. I have both designs in my theater, and adjusted the phase on each sub where the combined response were absent of nulls. Audyssey XT's FR was pretty choppy compared to my final result. 

You're correct. I initially was having localization problems with my dual (mismatched) sub setup. After taking some measurements, I also found a 15dB null at 25Hz and some other smaller valleys from 0-200Hz.

Tonight I was able to find the sweet spot to integrate both subs and rid myself of the nasty null. My XS-15 ended up front and center and my A2-300 in the back right corner of the room (phase at 0). This combination offered the smoothest response in my listening area There were some valleys, but nothing in the double digits. I gain matched each sub and ran Audyssey once again.

Audyssey really smoothed things out even more. I'm +/- 3 all the way down to 20Hz until it starts to drop off a little bit. Audyssey set my mains to 40Hz though and my measurement was based on this crossover.

Now, everything I've read (forums, Audyssey zendesk) is that it's not an issue to increase the crossover after running Audyssey. I raised my mains and center to 80Hz and then measured the response. To my surprise a nice sized valley suddenly appeared around 90Hz. Lowering the crossover to 60Hz and raising the sub distance to 11.5 smoothed it out a bit, but not as nice as my initial measurement. I'd rather not keep my mains at 40Hz as I'd like the subs to deal with most of the frequencies up to 80Hz.

Honestly, I'm not going to lose sleep over this, but I'm a little disappointed after seeing the initial post Audyssey measurement. I just set the subwoofer distance back to 10 feet (per Audyssey) and my mains back to 80Hz crossover and played a couple movie scenes:
1. TDKR - Batman/Bane fight. Tons of mid bass - Sounds great
2. Transformers - Ironhide flip scene - Sounds great
3. Tron Legacy - Games scene - Just an amazing surround and sub experience
4. Kung Fu Panda - Skidoosh scene - Bam...I felt this one.

Zero localization!

All in all, I'm extremely happy and the help provided by the members of this forum has been priceless. I may mess with things a bit to see if I can rid myself of the 90Hz valley, but I don't know if it's worth it. I'm going to watch some more test scenes to see if I notice anything funky.

Thanks again for all of the help.
Nick
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post #24 of 24 Old 02-20-2013, 06:15 PM
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Congrats! Good to hear. Isn't it a great feeling to have your system tweaked?

 

I'm in Cinti too. If you ever want a demo or want to demo yours, drop me a PM.smile.gif



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