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waterfall questions: comparing monitor stands

1K views 8 replies 2 participants last post by  cporro 
#1 ·
I just finished construction of a new set of monitor stands. my old stands were cinder blocks and i wondered if the new stands might effect the sound. so i took some readings with REW. i used the program maybe a year ago and found the waterfall chart to be the most helpful. correct me if i'm wrong but isn't the waterfall about all you need? it charts the way frequencies decay over time.

anyway, as you can see the 2 stands appear quite similar. i took 8 readings for each. made sure the speaker (i only tested one) was in the same position for the 2 stands. green is the new stand. red is the cinder blocks.

but i can't figure out what the window parameter is for. you know the one right above generate waterfall. can someone explain? thx
 

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#2 ·

correct me if i'm wrong but isn't the waterfall about all you need?
Waterfalls are best utilized in the low frequency area. It would be a great tool to determine any improvement you might get from room treatments like bass traps, measuring before and after installation, but I don’t think a waterfall is what you want to be using to compare your two speaker stands. If the new ones register any difference at all, it’d probably show up with a normal frequency response reading.

Regards,
Wayne
 
#3 ·
thx wayne. i am in fact looking mostly at low freq issues. i'm sure you know they are the hardest things to correct in rooms.

do you know what that window setting is for in waterfalls? i'm just asking because most of this stuff makes sense but not the window.

shouldn't the first few slices of the waterfall be the direct speaker sound? so i could use the water fall to look at the freq response. is that what you are saying?

oh wait...that would occur in the first 7 ms by my calcs. that's a thin slice. ha! anyway i'll take a look.

thx
 
#4 ·
ah wait...maybe i got it. the window is the thickness of the slice of time?

so on a waterfall you have 30 slices. the time range dictates the range over which the slices are taken. the window is thickness of each slice.

eg. if you had 2 slices over the range of 200ms with a window of 50ms... the first slice would be 0-50ms the second 150-200ms.

there is a freq reading beside the window parameter. at those low freq you need a decent chunk of time to determine freq...so that makes sense. 1/20hz = 50ms.

am i getting it? or insane. either is possible.
 
#5 ·

do you know what that window setting is for in waterfalls? i'm just asking because most of this stuff makes sense but not the window.


am i getting it? or insane. either is possible.
Maybe John can help you with what the Window setting does. The only parameter I ever change is the Time Range setting.


so i could use the water fall to look at the freq response. is that what you are saying?
For your basic frequency response graph, click the “Filter Adjust” tab.

Regards,
Wayne
 
#6 ·
wow. the filter adjust tab is completely different for these two measurements. huh? so different i think something is wrong. the wood stands look like a the curve on a waterfall. the cinderblocks look almost like a horizontal line that bows down a bit in the first 20ms.

i'm confused. is the freq response the intital direct sound form the speakers? like 0-6ms? no room sound? the waterfalls are so similar and these measurements are so different.
 
#8 ·

is the freq response the intital direct sound form the speakers?
Yes, the initial response. With the waterfall, if you reduce it to a single slice (instead of 30 or whatever), it’s the same as the frequency response plot you see with the “Filter Adjust” tab.

wow. the filter adjust tab is completely different for these two measurements. huh? so different i think something is wrong.
I’d agree. :(

Regards,
Wayne
 
#9 ·
thx for the help. i feel less crazy now. or, if crazy, i feel less lonesome.

i'm going with what the waterfall says. it's a lot more in line with common sense. i have no idea why the freq response is so different. but i don't think any speaker is that flat. not mine for sure.

some people can make a huge deal out of speaker stands. what makes sense to me is that if they hold the speaker in the same position, don't resonate, and are roughly the same construction and mass they should sound very similar.

hmm, just re-opened REW and now things look right. i'm using spectral decay with a window of 50ms and a slice of 5. here i can see when the direct sound is being measured and when room modes start setting up. nice. and the wood stands and cinder blocks are super similar in both.

i'm new to this forum...perhaps there is a REW bug i don't know about. anyway here is the spectral decay. note where modes start setting up.

why i spend so much time on this is a mystery.
 

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