Quote:
Originally Posted by
Roger Dressler /forum/post/17222579
W
TW!
Some sample WOTW waterfall measurements were made a short while back. Playback levels are given with each waterfal, but -10 dB from reference level is not bad for WOTW DTS.
Comparison of simultaneous electrical signal and in room speaker waterfalls of various scenes of WOTW are shown in the following thread. Some Apollo-13, Transformers and Incredible Hulk scenes also. That comparison was kind of fun to do. Kind of interesting to see how close the electrical and acoustic responses are for various scenes.
Start at page 11 to get a feel for the discussion about Spectrum Lab waterfalls.
http://www.avsforum.com/avs-vb/showt...163329&page=11
Quote:
Originally Posted by Roger Dressler /forum/post/17222579
At the moment I have the bass crossover set for 80 Hz. I have not yet checked to see what happens when shifting that to higher frequencies. In my case all the subs run pure mono, so I didn't want to narrow the spatial effect by going much higher. I believe you run yours in stereo groups, so can avoid that limitation. I'm also wondering about having mid-freq bass coming from the rear of the room, where rear-seated folks might pick up on it. Currently, it's easy to hear the midbass coming from the rear speakers when I walk right next to them, but in the seats it's not noticable. I'm not sure how much higher I could go with the crossover and not cause imaging/pulling problems. I guess I should try it!
We are working a different part of the modal area. You probably are familiar with all of this, but I was not familiar with the difference between modal acoustics and geometric acoustics before that Geddes thread. The Schroeder frequency divides the two areas. For small rooms this frequency is around the 150 Hz area depending of the room. Section 4.1.b for reference.
http://www.gedlee.com/downloads/Chapter%204.pdf
The major problem with room modes in my room is not in area that you are working with your setup (below 80 Hz). Geddes suggested that the modal area that needs work in all small rooms is between 50 Hz to about the 150 Hz or so area.
Geddes and HSU recommend a VLF subwoofer in a single location with a crossover around 50 Hz or so. That is the subwoofer crossover frequency area that I have settled on over the years, but HSU and Geddes put some detail in why that is a good subwoofer frequency.
HSU and Geddes try to work the 50 to 150 hz modal area by different means. That is the same frequency area that I am working on. I don't think the exact method of working this frequency area makes a huge difference, but I do think that you have to work up to the 150 Hz area (plus or minus).
I you get the basic concept, then you can try many different technical tricks to deal with the problem frequency area that applies to your own specific room.
Quote:
Originally Posted by Roger Dressler /forum/post/17222579
Flat in deed. A thing of beauty. You may have said before--but how was thos plot made--single point, average of several, weighted to any one position, filter BW?
Each color covers about a 6 dB signal level. My main seating area is better than I expected to see when I made that measurement. That Spectrum Lab program is way cool once you figure out how to work it.
The Spectrum Lab waterfall plot is very informative but the options are very restrictive. One or two locations at a time can be waterfalled, but no averages or smoothing. You can do a bit of smoothing between adjacent bins, but that is about it.
However, if you move the microphone around you can see changes in the waterfall. In the past I have made a seating area waterfall by moving the microphone in a football type of shape (up, down, forward, back). I then slowly shift the microphone left to right in the seating area. The waterfall then shows a spatial average over the area that you swept the microphone over. Kind of a cool measurement tool when you get right down to it.
