The Once and Future Theater - Page 39 - AVS Forum
Forum Jump: 
 12Likes
Reply
 
Thread Tools
post #1141 of 1152 Old 07-17-2014, 09:10 AM
AnalysisParalysis Analyst
 
TMcG's Avatar
 
Join Date: Mar 2010
Location: North Carolina
Posts: 2,478
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 95 Post(s)
Liked: 236
Quote:
Originally Posted by hopefulfred View Post
you've got books, right? Get on it!

moar reading!!!!

:d
J_P_A likes this.
TMcG is online now  
Sponsored Links
Advertisement
 
post #1142 of 1152 Old 07-17-2014, 09:11 AM
AVS Special Member
 
J_P_A's Avatar
 
Join Date: Dec 2008
Location: L.A. - Lower Alabama
Posts: 3,896
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 105 Post(s)
Liked: 201
Quote:
Originally Posted by TMcG View Post
MOAR READING!!!! :d
HAHA!

Dude, are you made of leprechauns? Cause that was awesome!

The Plains Theater Has Begun
J_P_A is online now  
post #1143 of 1152 Old 07-17-2014, 09:25 AM - Thread Starter
AVS Special Member
 
HopefulFred's Avatar
 
Join Date: Mar 2007
Location: Atlanta, GA
Posts: 2,687
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Liked: 183
Yes.
HopefulFred is online now  
post #1144 of 1152 Old 07-17-2014, 10:31 AM
Advanced Member
 
KNKKNK's Avatar
 
Join Date: Feb 2009
Location: AZ
Posts: 859
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 22 Post(s)
Liked: 64
Fred, WRT the earlier post regarding the resonance and what being measured below ~ 60hz.
I was looking for the fly in the ointment regarding the measurement setup and the differential between the predictions and the actual results.. particullarly your readings for the first 2 length modes, which should be fairly predicatble regardless of changes in width/ height, soffit to soffit, floor to soffit, soffit to riser etc...
I cant see the short face of the riser or even the entry impacting these modes to the extent that it would shift the 1st or second length mode signifigantly from the predictions. These should be the most predicable and eaisest to correlate with even seemingly substantial changes.... Ie if your room measured shorter by 10% or longer by 10% to account for the face of the riser/ entrance etc.. the 1st and 2nd modes would still be 29/58 and 24/48 respectfully... Heres a quick graphic overlaying the predictions with a +/- 10% band compared to actual measurements:



Basically I was throwing darts at the 35Hz peak.. which I couldnt account for with what I thought were reasonable assumptions on the 1 or 2nd length or 1st width modes...... it just seems "out there" so to speak...
now that I read it,, this may not make sense to anyone else.....hmmm

as Albert said 'In theory, theory and practice are the same. In practice, they are not.'

My Basement HT Construction ~ Faster than the speed of Dark

"I've cut that piece 3 times and its still too short..."
KNKKNK is offline  
post #1145 of 1152 Old 07-17-2014, 10:59 AM - Thread Starter
AVS Special Member
 
HopefulFred's Avatar
 
Join Date: Mar 2007
Location: Atlanta, GA
Posts: 2,687
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Liked: 183
I'm going to keep looking, and I appreciate all ideas. Thanks, and don't hold back.

Where did you get that image?
HopefulFred is online now  
post #1146 of 1152 Old 07-17-2014, 03:07 PM
Member
 
xjagox's Avatar
 
Join Date: Aug 2005
Location: Maryland
Posts: 182
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 13
Quote:
Originally Posted by HopefulFred View Post
Here's a surprise. I placed my order with HVACQuick on the afternoon of July 6. The grills arrived at work yesterday. That's super-quick, especially given that the website and order confirmation email say standard production is 3-4 weeks.

The blue is the protective film, the grills are brown, as expected.

I also ordered some right around the same time and was shocked at fast they came in. I paid the $4 each or whatever for the two week as opposed to the 4 week lead time, but I'm not convinced that there's really any difference.
ellisr63 likes this.
xjagox is online now  
post #1147 of 1152 Old 07-17-2014, 06:47 PM - Thread Starter
AVS Special Member
 
HopefulFred's Avatar
 
Join Date: Mar 2007
Location: Atlanta, GA
Posts: 2,687
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Liked: 183
Remember how I started taking measurements saying that it was confounding? yeah...

Here's the frequency response plots for the three measurements I kept the first time, as a reminder:


And the list of predicted modes:


I went back downstairs today to pour out two more bags of sand (looks like one more will be the last one) and consider some of the things that came up in the discussion of the first set of measurements. In the process, I measured the diagonal that J_P_A mentioned in reference to the mid-30s peaks - it is about 14 feet as predicted. When I did that, I may have nudged the mic an inch or two, but I can't believe that the small movement of the mic will have changed the measurements to look like the new ones. I figured I would start with duplicating yesterday's work, just to verify set up. Well, the levels got adjusted again, so not only are these levels not absolutely right, they can't be compared directly to the first set (in terms of level).


Here's the two sets of measurements on the same plot:


I don't know what to say about that.


Next I moved the mic to the center of the rear plane of the room. The mic was hanging from the outlet where the HDMI runs through the face of the rear soffit to where the projector will go. The mic hangs down to approximately the center of the vertical height. I didn't measure when I set it up - only just now as I write this up. It's 52 inches from the riser deck, and 40 inches from the ceiling. So it's 6" above the center of the rear air space, and maybe two or three inches to the side. Without adjusting anything in the computer or soundcard - only moving and replacing the drywall "door" I generated these three sweeps.


At this point I also generated a waterfall graph for this new set:


That's when I noticed the hum in the noise floor at 120Hz. I assumed it was because I had the laptop plugged into the wall. So I unplugged it and tried again with some sweeps. This is when the impulse error I had yesterday came back. I tried three sweeps, all with the same error. I then plugged the laptop back in, and the error went away. Magic. I also noticed that the level changed when the power cord was unplugged. There's something going on here. I don't want to get into it right now if there's anything useful to say about these new measurements; but really there may not be anything worth saying, because I am now less confident in all of these based on the weird influences of the power cord that I've noticed.

Last edited by HopefulFred; 07-17-2014 at 06:59 PM.
HopefulFred is online now  
post #1148 of 1152 Old 07-17-2014, 08:25 PM
AVS Special Member
 
J_P_A's Avatar
 
Join Date: Dec 2008
Location: L.A. - Lower Alabama
Posts: 3,896
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 105 Post(s)
Liked: 201
I feel your pain, sir! After all the measuring I did to try to figure out my fan issue, I finally decided none of the plots were correct. There's a lot to get your hands around with REW to feel like you can get repeatable measurements.

Dude, are you made of leprechauns? Cause that was awesome!

The Plains Theater Has Begun
J_P_A is online now  
post #1149 of 1152 Old 07-19-2014, 06:27 PM - Thread Starter
AVS Special Member
 
HopefulFred's Avatar
 
Join Date: Mar 2007
Location: Atlanta, GA
Posts: 2,687
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Liked: 183
Yesterday after work, my only friend with a truck was good enough to meet me at Lowe's to bring home a few more sheets of subfloor. I got one last bag of sand, which officially overfills the stage. I'm trying to stuff the sand in there so that any settling won't leave any open area (overkill, I imagine). I think I'll have to pull out a little as the last of the decking goes on. I go one 8' length of the stage covered with one layer of decking tonight, caulking along the edge. Now that I'm out of caulk, I'll wait until tomorrow to seal it up.

Meanwhile, I want to cut out the soffit face for the new grills. I held one up in a place that seemed right to me and traced around it, but chickened out before I cut it out. The face of the soffit is about 10-11", but the opening will be limited to the center portion, due to the ripped 2x4s framing it (does that make sense when I say that? do you see this?) So the hole could never be closer to the ceiling than 1.5", and could never be within 1.5 inches of the bottom (not counting the sheething on the bottom. That is the say, there's a 7" gap into which the hole can be cut. I haven't even really thought crown molding or anything up there, so I have no idea how low or high is appropriate. Should I just make it as low as possible?


Hopefully you can see the pencil mark on the drywall.

I need MOAR CUTTING!
Mfusick likes this.
HopefulFred is online now  
post #1150 of 1152 Old 07-20-2014, 09:17 AM
AVS Addicted Member
 
Mfusick's Avatar
 
Join Date: Aug 2002
Location: Western MA
Posts: 21,394
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 62 Post(s)
Liked: 649
I'd be really curious to see how your measurements compared to this calculator: http://www.bobgolds.com/Mode/RoomModes.htm

-

"Too much is almost enough. Anything in life worth doing is worth overdoing. Moderation is for cowards."
Mfusick is online now  
post #1151 of 1152 Old 07-20-2014, 06:39 PM - Thread Starter
AVS Special Member
 
HopefulFred's Avatar
 
Join Date: Mar 2007
Location: Atlanta, GA
Posts: 2,687
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Liked: 183
Mike, I think all the calculators use the same math. They all make the same predictions, given the same inputs. If they were sophisticated enough to do more, they would need a lot more input data. The differences come out in the presentation of the data. Bobgolds gives a lot of data, I just get swamped by most of it.

The stage has a top. (Pardon the mess) It will get another layer of decking in a few days.



The HVAC grill has a hole. And it fits pretty well - you'll just have to trust me on that part.



Baby steps...
HopefulFred is online now  
post #1152 of 1152 Old Today, 10:40 AM
AVS Addicted Member
 
Mfusick's Avatar
 
Join Date: Aug 2002
Location: Western MA
Posts: 21,394
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 62 Post(s)
Liked: 649
Looking good Fred!

I meant about the data was how your measured results would compare to the predictions and calculations. reality vs theory. My understanding is things are not always as they might seem.

-

"Too much is almost enough. Anything in life worth doing is worth overdoing. Moderation is for cowards."
Mfusick is online now  
Reply Dedicated Theater Design & Construction

Tags
Pioneer Electronics , Sherbourn , Dayton Audio Um18 22 18 Ultimax Dvc Subwoofer 2 Ohms Per Coil

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


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