phase vs. distance? - Page 4 - AVS | Home Theater Discussions And Reviews
Baselworld is only a few weeks away. Getting the latest news is easy, Click Here for info on how to join the Watchuseek.com newsletter list. Follow our team for updates featuring event coverage, new product unveilings, watch industry news & more!


Forum Jump: 
 1Likes
Reply
 
Thread Tools
post #91 of 98 Old 07-18-2013, 03:21 PM
AVS Special Member
 
Luke Kamp's Avatar
 
Join Date: Aug 2010
Location: Kansas City
Posts: 1,273
Mentioned: 23 Post(s)
Tagged: 0 Thread(s)
Quoted: 72 Post(s)
Liked: 138
Quote:
Originally Posted by Larry L View Post

Since the Bass FR at a given listening position is influenced by the sub phase relationship with all speakers in the room, it seems the goal would be to flatten out the FR around the XO freq with all speakers fed a single source tone during a frequency sweep. What I have observed doing tis is that I was able to flatten out the respons of the entire system by just shifting the sub distance one foot. from where the peak output was obtained at the XO freq.

However, I do agree that the phasing with the CC is most important if I am mostly watching movies. So, now I am thinking I should remeasure and re-tweak with just the CC for best FR. I believe that gave me a difference of 6 feet from what I have now.

My understanding is that dicrete audio channels that are getting different content need to be looked at individually. If they were all getting the same signal all the time i would think calibrating with a mono signal of all speakers would be the way to go. Acoustic measurement standards for stereo listening is a good resource.

http://www.acousticfrontiers.com/whats-new/2011/10/13/acoustic-measurement-standards-for-stereo-listening-rooms-pu.html
Luke Kamp is offline  
Sponsored Links
Advertisement
 
post #92 of 98 Old 07-18-2013, 04:16 PM
AVS Special Member
 
JHAz's Avatar
 
Join Date: Mar 2009
Posts: 4,207
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 173 Post(s)
Liked: 194
regardless of the specific content, each speaker stays in the same place, so its delay from acoustic transimission through the air stays the same, and their native phase (non)linearity stays the same at any given frequency. IOW the splice at 80 Hz is the same regardless of what content contains 80 Hz information for any given speaker. I think. Of course when there are different crossovers for different speakers, the talsk of maximizing the response in what is now multiple crossover frequency regions becomes more complex.
JHAz is online now  
post #93 of 98 Old 07-18-2013, 07:14 PM
AVS Special Member
 
Luke Kamp's Avatar
 
Join Date: Aug 2010
Location: Kansas City
Posts: 1,273
Mentioned: 23 Post(s)
Tagged: 0 Thread(s)
Quoted: 72 Post(s)
Liked: 138
I might be wrong here, but I think that would be the case outdoors as the only boundary is the ground and all same distance from it, but I think when we add boundaries and differing distances to them and there influence in the modal region and the longer wavelengths and the acoustic summation it changes things. So if speakers same distance from mlp, probably not same distance from front wall. And I think this would be happening at 80hz. Also besides different crossovers, what if you don't have three matching fronts? Unfortunately I don't have an acoustic transparent screen and have to use a compromised horizontal center at this time. I also have right side of room open to basement but left speaker is within 1/4 wavelength of 80hz. Do have 4in treatment with 4in air gap though to try and balance room. Here are some quotes from earlier in the thread.

Bill-
"That would be it. Keep in mind that every response dip and peak is caused by time/phase interactions, and that not only does every source introduce time/phase issues, but so does every boundary within the room, each acting differently with every source, and with every listening position. The more sources you have the more they tend to even each other out, but you still have to make compromises in trying to get the best overall result."

Mark-
"Subwoofer distance is a very fuzzy setting with such long wavelengths and the interaction with the main speakers of various types. The selected crossover frequency can often shift the optimal setting. Just remember that at 80Hz, ~3.5' is only 1/4 wavelength. Impulse measurements from a main speaker make sharp spikes with the first sound arrival. With a subwoofer an impulse is measured as a ramp/mound of energy as high frequencies are required to make any sharp shapes. The peak of that mound is not always the best setting, especially when the bass from the main speakers always lags the high frequencies they use to set the distances."

My question is what frequency point does the impulse stop having a sharp spike with the first sound arrival and transition into a ramp/mound of energy and does this relate to the schroeder frequency? If the distance were set by 80hz arrival time instead of the high frequencies, would the distances readings between high frequency and 80hz be different if speaker set to differing boundary distances but still same distance from mlp?
Luke Kamp is offline  
post #94 of 98 Old 07-18-2013, 08:23 PM
AVS Addicted Member
 
Bill Fitzmaurice's Avatar
 
Join Date: Nov 2009
Location: New Hampshire
Posts: 10,995
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 1992
Quote:
Originally Posted by Luke Kamp View Post

I might be wrong here, but I think that would be the case outdoors as the only boundary is the ground and all same distance from it, but I think when we add boundaries and differing distances to them and there influence in the modal region and the longer wavelengths and the acoustic summation it changes things.
You're not wrong at all, especially with subs. Since they radiate omni-directionally even the wall behind them is a boundary that has its own influence. When software tries to calculate the sub distance from the mic it doesn't have one source to consider, in the average room it has at least seven. It's not a wonder that Audyssey doesn't always get it right, it's a wonder that it ever does.

Bill Fitzmaurice Loudspeaker Design

The Laws of Physics aren't swayed by opinion.
Bill Fitzmaurice is online now  
post #95 of 98 Old 11-10-2013, 04:07 PM
Member
 
josh1233's Avatar
 
Join Date: Jan 2007
Location: Central PA
Posts: 89
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Just remember using a tape measure and doing the math to set the delay on a sub will never be correct. It can get you close with mains and rears. Time delay should be used to match the phase between the sub and mains at the crossover frequency.

This is fairly simple to accomplish. If you do not have an RTA you can get close with your ears.

To simplify this procedure I will discuss how to set the mains and sub. As in a 2 way setup with a sub added.

With ears:
-Set your crossover point on both the sub and mains, lets say 50 Hz.
-Put either your mains, or sub 180 deg out of phase. This can be done either physically or mechanically. If reversing the mains (L/R), reverse + and - on both speakers, so they are both out of phase with sub, but in phase with each other.
-Play a sign wave that is the same as the x-over frequency. In this case, 50 hZ
-Sit in the main seating position and have an assistant slowly adjust the time delay on the sub (or do it yourself via remote). You want to listen carefully to 50 Hz tone. You are trying to find the point at which the tone is at its lowest dB level. You may find that once it hits its lowest level a few more ms of delay will not change anything, but after those few ms the volume will increase. Mark down where the first ms number and last ms number right before and right after this lowest point. Set the ms delay between these two settings.

With RTA:
--Set your crossover point on both the sub and mains, lets say 50 Hz.
-Put either your mains, or sub 180 deg out of phase. This can be done either physically or mechanically. If reversing the mains (L/R), reverse + and - on both speakers, so they are both out of phase with sub, but in phase with each other.
-Play a sign wave that is the same as the x-over frequency. In this case, 50 hZ
-Place your mic in the main seating position.
-change the display resolution on TrueRTA so it is only showing 20 Hz for the low frequency limit and 100 Hz for the high frequency limit. You can and should also limit the upper and lower dB limits so you can magnify the peak of the 50 Hz frequency. Change the speed trade off to 40 Hz (med), and the sampling to 2. Turn of the bar graph so that you are only seeing the line graph.
-Wait for the peak to settle, then hit stop and save the graph (Alt-1). Now hit Go again.
-Turn the delay until the peak reaches its lowest point. The peak will lower in amplitude on the display. If the peak gets to its lowest point and stays there for a few more clicks of delay find the middle ms number and leave it there.
-Put the speakers back in phase.
-You are done.

You may find that this ms number is way off from one that would be obtained through measuring with a tape and subtracting the difference, but it will put the mains and sub in perfect phase at the given seated position where the mic was placed.

Putting one set of speakers out of phase when doing this increases the magnitude of the change (than if they were in phase) and is easier to hear and/or see on the RTA program.
I've been using this method for about 25 years and it works every time.
josh1233 is offline  
post #96 of 98 Old 03-21-2015, 08:28 AM
AVS Special Member
 
muzz's Avatar
 
Join Date: Jun 2002
Location: MA. USA
Posts: 2,711
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 151 Post(s)
Liked: 81
Thumbs up

Quote:
Originally Posted by craig john View Post
Quote: Originally Posted by Tstan7777

No prob Saturn94, it's a good question.

It's been a good discussion. No arguing either!!! While very informative, some of this goes over my head. Good news is next time, my head will be a little taller!!! How good are the room correction suites at getting all this right? I've never used Audyssey, only YPAO. Audyssy is only on/off right? You can't tweak it's results?

With Audysey, you can tweak the subwoofer Distance setting to your hearts content. Audyssey often gets the subwoofer Distance wrong, especially in multi-sub systems. I ALWAYS re-check the post Audyssey FR, concentrating on the response around the crossover. I often tweak the sub Distance to imporve the blend around the crossover. Here is the most dramatic example of this:



The blue trace is the sub Distance set by Audyssey for 3 Submersive HP's. The green trace is the exact same system with the only difference being 4 ft. added to the sub Distance setting.

Here is another system where the difference is more subtle, but still very noticeable:



The colors are reversed in this graph, but you can see that a sub Distance tweak managed to get some extra SPL around the crossover frequency.

Craig
Great examples Craig.
I just used REW with mains and subs, and dialed in the 80hz area much better than what Audessey had set it at.
I had a big hole at 80hz, went both ways to figure it out, and it's almost flat there now.

Thanks for the visual, it was a great example!

Thanks Again

m

Why waste $ on more cheap stuff, it's like challenging a dragon with a pocket knife.
muzz is offline  
post #97 of 98 Old 03-21-2015, 08:57 AM
Member
 
jsc79's Avatar
 
Join Date: Feb 2014
Posts: 63
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 35 Post(s)
Liked: 23
I dialed in my mains/sub with the method outlined above, reverse polaity on ma in speaker, etc.. I did it at 100hz. If i am switching between 80-100hz do I need to recalibrate it at each frequency?
jsc79 is offline  
post #98 of 98 Old 03-21-2015, 09:28 AM
AVS Special Member
 
coolrda's Avatar
 
Join Date: Nov 2002
Location: Bakersfield, CA
Posts: 1,284
Mentioned: 14 Post(s)
Tagged: 0 Thread(s)
Quoted: 85 Post(s)
Liked: 83
Quote:
Originally Posted by Bill Fitzmaurice View Post
Quote:Originally Posted by Tstan7777 

So how about this statement......Switching the phase will adjust the timing of the sub across all frequencies and adjusting the delay will adjust the timing of the sub at the xover frequency? Or do I have that backwards, lol?

Switching the polarity changes phase by 180 degrees globally. Adjusting delay changes phase of every frequency as well, but each by a different amount. For instance, 180 degrees shift at 80Hz is 7 feet. That same 7 feet is 90 degrees at 40Hz, 45 degrees at 20Hz.Quote:My wife pretty much hates the sub. It's not so much the look as it is the sound. Apparently she hates deep bass.

Women are genetically predisposed to not like low sounds, as in the wild they tend to warn of potential dangers, as in lightning and stampeding herds. Men are genetically predisposed to go towards low sounds, as those stampeding herds might represent dinner.
This is freakin hilarious. One of my all time favs. I had no idea the answer was so simple.
coolrda is online now  
Sponsored Links
Advertisement
 
Reply Subwoofers, Bass, and Transducers



Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off