left right and center setup questions - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 16 Old 04-03-08, 03:13 PM Thread Starter
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left right and center setup questions

I have two Polk Rti70s tower speakers as left and right (surrounds also) channels, a Polk Csi40 center channel, and a subwoofer I recently eqalized. I am using the bass management on my XA2 and PCM analog out to my amplifiers. A problem I have is when I setup all channels, inculding the subwoofer, to thesame level, the front speakers are very aggressive when they face inwards. I have them set to small right now and I have faced the drivers forward to prevent them from causing what feels like somewhat shouting about 3 inches away from eather side of my head. I am not sure if this is realated to the distance setting but I have those setup as I have meausred them. When I face the left and right channels forward, sounds seem to be flying past me and have very little impact in comparison to the subwoofer. The speakers are 8.5 feet away.

Do I face the drivers towards the main listening position?
Do I set them to large?
Do I leave the center channel set as small? It also sounds kind of midrange aggressive.
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post #2 of 16 Old 04-03-08, 05:19 PM Thread Starter
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Re: left right and center setup questions

I took 13' width of my room and divided it by 3 until I got 1.4'. Then I took the 1.4 and coverted that to 16.8". I placed the left and right speakers furthermost corner closest to the left or right wall 16.8" which is divisible by the odd number of the room width. I meausred the distance from the front wall which is 17". I took 20.5', the length of the room and converted that to 246". I took the 246" and divided that by 17" and got 14.5. They sit in front of bass traps so I'm not sure that matters. I centered the couch in the room and aimed the drivers towards the middle of the room or the center seat but I faced them slightly away from the center (or behind the center seat) giving a larger sweet spot. I measured them to be sure that the distance was eqaul for the center channel.

I set the three front speakers to large and checked the levels in DVE. Will this solve my problem and am I doing this incrorrectly?
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post #3 of 16 Old 04-04-08, 07:46 AM
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Re: left right and center setup questions

Have you set the levels using an SPL meter or the auto setup routine? Also, what cross-over are you using?
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post #4 of 16 Old 04-04-08, 04:56 PM Thread Starter
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Re: left right and center setup questions

I use a 80Hz crossover and I set it up manually with the SPL meter. My receiver quit working awhile ago because I played pink noise through it from my XA2 at full level. I conctacted the manufactor yesterday about the problem and they have told me that the ampliifers are damaged and it is the cause why my reciever will not turn back on. I recently replied explaining that I don't use the amplifiers to see if there is a way to bypass them. The reciever in the auto-setup routine used to recommend a 50Hz XO or a 80Hz XO. It started recommending the 80 after I began installing room treatments. It always set my speakers to large although occassionally it set my center to small.

Setting them to large, moving them slightly, and pointing them less inwards seemed to have helped. I bridged my left and right speakers with other mono ampfliers the other day for 360W each. I have DVE setup for 71dB pink noise at all channels and HD-DVD is very nice. DVD is loud and I have another list of settings for a 65dB reference point if it is not a loud movie, or I just set all the levels to -12 or -10,except for the subwoofer which I have just been adjusting manually on the back.

It seems more even now accross the front stage now and the sound seems more natural.

When I had these speakers setup in my last HT, I had them set to large after lots of tweeking and expermentation, but my older subwoofer was less capable then.

I think there still is something I could adjust for speaker timing, and I am not sure that the speakers being set to large is right still although it sounds right. I think I remember someone once telling me that setting towers to small could damage them, but I also remember someone else telling me that speakers should always be set to small.
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post #5 of 16 Old 04-04-08, 07:22 PM Thread Starter
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Re: left right and center setup questions

With the large setting I was able to set the limited banwidth pink noise to 67dB around the room. The Full Bandwidth Pink noise is 74dB on the SPL meter so I set the SPL meter in REW using that and telling REW to use a full range test...

Then I ran sweeps from 15Hz to 22Khz on the disk and recorded it in the spectrum anylizer and calculated distortion. Speakers are 9 feet from the mic on the couch. Speaker distance is set to 8.5 feet.

Results for large setting -

Sweep
left right and center setup questions-large-settings_sweep.jpg

65536-point spectrum using Rectangular window and no averaging
Input RMS -13.0dB FS
Distortion at 4.3Hz, -29.8dB FS
Based on 8 harmonics
THD 18.462%
THD+N 98.944%
2nd harmonic 14.613%
3rd harmonic 6.378%
4th harmonic 4.774%
5th harmonic 5.081%
6th harmonic 3.277%

440Hz Tone
left right and center setup questions-large-settings_440hz-tone.jpg

65536-point spectrum using Rectangular window and no averaging
Input RMS -12.6dB FS
Distortion at 440.1Hz, -12.7dB FS
Based on 8 harmonics
THD 0.267%
THD+N 14.662%
2nd harmonic 0.189%
3rd harmonic 0.179%
4th harmonic 0.033%
5th harmonic 0.035%
6th harmonic 0.022%

I repeated the steps for the small settings after I wrote down the large. The difference for the level was +6dB for the limited bandwidth pink noise on the mains, and the same for the subwoofer. I adjusted the settings on the XA2 -6dB and it came to 67dB again. The full bandwidth pink noise was now at 73dB but I did not need to adjust the SPL meter calibration in REW becuase this ran the same.

Small setting results -

Sweep
left right and center setup questions-small-settings_sweep.jpg

65536-point spectrum using Rectangular window and no averaging
Input RMS -15.6dB FS
Distortion at 5.1Hz, -29.5dB FS
Based on 8 harmonics
THD 16.375%
THD+N 97.959%
2nd harmonic 12.961%
3rd harmonic 6.387%
4th harmonic 3.835%
5th harmonic 4.146%
6th harmonic 2.018%

440 Hz tone
left right and center setup questions-small-settings_440hz-tone.jpg


65536-point spectrum using Rectangular window and no averaging
Input RMS -12.7dB FS
Distortion at 440.1Hz, -12.8dB FS
Based on 8 harmonics
THD 0.268%
THD+N 17.761%
2nd harmonic 0.196%
3rd harmonic 0.171%
4th harmonic 0.024%
5th harmonic 0.050%
6th harmonic 0.019%
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post #6 of 16 Old 04-04-08, 08:46 PM
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Re: left right and center setup questions

Quote:
thewire wrote: View Post
I think I remember someone once telling me that setting towers to small could damage them, but I also remember someone else telling me that speakers should always be set to small.
How on earth could setting speakers of any type ever damage them? Makes no sense at all.

I believe that setting all speakers to small is a rule of thumb, to be used as a guide, as not many speakers are capable of playing very low frequencies ie 50hz and lower. I have noticed when I set my mains to small, my sub gets worked much harder. I have heard claims that when all speakers are set to small the amp doesn't have to work as hard(which makes sense) to produce those lower frequencies so it is easier on it and allows the speakers to be more efficient at the higher notes as the subwoofer is designed specifically for the lower frequencies. What it really comes down to is you just have to set your system the way you like it, that is all that matters.
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post #7 of 16 Old 04-04-08, 09:17 PM Thread Starter
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Re: left right and center setup questions

Quote:
jakewash wrote: View Post
How on earth could setting speakers of any type ever damage them? Makes no sense at all.

I believe that setting all speakers to small is a rule of thumb, to be used as a guide, as not many speakers are capable of playing very low frequencies ie 50hz and lower. I have noticed when I set my mains to small, my sub gets worked much harder. I have heard claims that when all speakers are set to small the amp doesn't have to work as hard(which makes sense) to produce those lower frequencies so it is easier on it and allows the speakers to be more efficient at the higher notes as the subwoofer is designed specifically for the lower frequencies. What it really comes down to is you just have to set your system the way you like it, that is all that matters.
I don't know about that harming of a speaker and size settings. I'm reading at Polk and they have no mention of my model speaker on the page about bass management. Setting the speakers to large seems to cause some crown molding on my wall that I found loose to shake and make a rattle noise. I would be happier with a small setting then but I will ask what Polk recommends since I would like to see what others do or recommend. Need to fix that crown molding also.

http://www.polkaudio.com/homeaudio/p...ers/?helpid=52
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post #8 of 16 Old 04-04-08, 11:42 PM Thread Starter
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Re: left right and center setup questions

I have asked the people at Polk what they recommend but here is what I have figured so far.

1. My speakers were aimed to close before and I had poor stereo imaging. Spreading them out has helped.
2. The bass in my mains don't sound very transparent, or it is something to do with SBIR.
3. Adding more power to the mains seems to have helped...I think.
4. My target settings were low and I need volume controls again.
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post #9 of 16 Old 04-05-08, 04:03 AM
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Re: left right and center setup questions

Adding more power to the mains should help because it takes alot of power to produce the lower frequencies properly, that is why there are seperate powered subwoofers.

Just curious, how far apart are the speakers and how far back are you from them? It is usually suggested that you should be making an equilateral triangle between you and the mains. If the mains are 8 ft apart then you should be 8 ft from them. I know of a few people that had their mains toed in and once they went to pretty much neutral or ever so slightly toed in the imaging was much better and less aggressive.
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post #10 of 16 Old 04-05-08, 01:15 PM Thread Starter
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Re: left right and center setup questions

My screen is 8' wide and I have been trying to keep them close as possible to the triangle. The center seat is 8.5' from the screen and the headrest is like 9'. They recline also. Reading that having the speakers slightly towed in, as you say, becoming less aggressive this way being a proven solution is very good news. The reply I got at club Polk says I can set all of them to Large as they are somewhat capable of playing lower frequencies. I tried this and I needed to put more insualtion in the ceiling in a particular spot to be able to do so, but it seems to help for a few reasons I mentioned already. I also have less problems with the volume this way. I called the store I got the AVR at this morning and they said my extended warranty was not over until next year and to bring in the AVR for inspection, so hopefully I will get the part sorted out also.
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