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Influence of curtains on room acoustics

voodooless

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a 1.5 cm thick curtain will not do anything to frequencies below 100Hz so I didn’t bother turning the subwoofer on.
Well, you do have an air gap between curtain and window. That should help a bit down low.

Any idea why now the standing wave is more pronounced than before? Is it the fact that one way you damped a mode, which leads to increase of another?
 

Absolute

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Curtain will not do anything below 400-500Hz.

Unfortunately single point measurement is pretty much useless to get a relevant picture of anything, unless measuring direct sound of the speaker from close distance using gating.
The measurements shown disagrees with you. And I disagree with you on the second part.

A single point measurement shows exactly what happens on that specific microphone position. Nothing more, nothing less.

@abdo123 A fun function of the newer REW versions is the RT60 decay mode where you can choose any frequency and get the decay for that frequency alone. Would be nice if you could pick a few random frequencies and show before and after just to see how the relative decay changes. Say you pick frequencies where the frequency response is most similar between with and without curtains.

Easier to visualize than the whole waterfall :)
 

thorvat

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Well take it or leave it. The good thing about data is that it's not determined by either of our opinions.

What I stated is not an "opinion" but a fact supported by science called physics.

For example, you may have an "opinion" that room doesn't affect freqeucies below 100Hz so no need to EQ above that, but the fact is that in typical room transition frequency is somewhere in the 300-400Hz range, and even beyond that (up to app 900Hz) room is influencing the response, just not that much. This can easilly be seen by taking sweeps from mulitple points around center of the LP and overlaying them. This way one can easilly identify all 3 ranges (room, mixed and speaker dominated) where each component is dominating the response.
 
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abdo123

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Well, you do have an air gap between curtain and window. That should help a bit down low.

Any idea why now the standing wave is more pronounced than before? Is it the fact that one way you damped a mode, which leads to increase of another?
it's common that you gain back energy when you use bass traps, since this is in no way an evenly spread treatment across the room it makes some sense. I probably removed the canceling mode but not the boosting one.

I'm not very concerned by it.
 

thorvat

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The measurements shown disagrees with you. And I disagree with you on the second part.

A single point measurement shows exactly what happens on that specific microphone position. Nothing more, nothing less.

Move mic 15cm on one side and both graphs would differ. Move it 15 cm on any side and no 2 graphs would be the same. Move it 30cm and you'll get even more different picture.

The best what you can do is to take spatially averaged measurement and then judge the difference. That was stated at least 100 hundred times on this forum, with quotes from Toole's book and with multiple examples, but obviously some folks just refuse to elarn..
 
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abdo123

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The measurements shown disagrees with you. And I disagree with you on the second part.

A single point measurement shows exactly what happens on that specific microphone position. Nothing more, nothing less.

@abdo123 A fun function of the newer REW versions is the RT60 decay mode where you can choose any frequency and get the decay for that frequency alone. Would be nice if you could pick a few random frequencies and show before and after just to see how the relative decay changes. Say you pick frequencies where the frequency response is most similar between with and without curtains.

Easier to visualize than the whole waterfall :)

Sounds cool! How do i use this feature?
 

Absolute

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Sounds cool! How do i use this feature?
It's this curve;

1661184156114.png

 

Absolute

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Move mic 15cm on one side and both graphs would differ. Move it 15 cm on any side and no 2 graphs would be the same. Move it 30cm and you'll get even more different picture.

The best what you can do is to take spatially averaged measurement and then judge the difference. That was stated at least 100 hundred times on this forum, with quotes from Toole's book and with multiple examples, but obviously some folks just refuse to elarn..
Although you're correct in one sense, you're missing the point of this experiment/measurements.

This has nothing to do with sound quality or sound analysis, it's just a demonstration of acoustical differences before and after a certain change measured at the same exact spot. If you move the mic the response will change, but in each different spot there will still be differences with and without.

If you wanted to find the average difference with and without curtains or try to quantify the effect on sound quality you would need to take many measurements, but that's certainly not the goal here. Having seen abdo123's knowledge and insight over time I have no doubt whatsoever that he's fully aware of all of this. Please, give people the benefit of the doubt :)
 

thorvat

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Although you're correct in one sense, you're missing the point of this experiment/measurements.

This has nothing to do with sound quality or sound analysis, it's just a demonstration of acoustical differences before and after a certain change measured at the same exact spot. If you move the mic the response will change, but in each different spot there will still be differences with and without.

If you wanted to find the average difference with and without curtains or try to quantify the effect on sound quality you would need to take many measurements, but that's certainly not the goal here. Having seen abdo123's knowledge and insight over time I have no doubt whatsoever that he's fully aware of all of this. Please, give people the benefit of the doubt :)

I'm affraid you're missing the point - in each different spot there will be different differences with and without, so the only way to estimate the difference with vs without the listener will perceive is to use the spatially averaged measurement.

As I already commented on abdo123's "opinions" I won't do it twice. But I can offer one more piece of information: when you consider how much of the sound energy on which frequencies will get reflected vs how much will pass through when it hits the barrier (being it a steel reinforced concrete wall 30cm thick, plaster wall 8 cm thick or curtain) - it pretty much depends only the weight of the barrier. Claiming that the barrier comprising of such low weight material as curtain will affects frequencies down to 100Hz is, well, uninformed..
 

Frgirard

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I'm affraid you're missing the point - in each different spot there will be different differences with and without, so the only way to estimate the difference with vs without the listener will perceive is to use the spatially averaged measurement.

As I already commented on abdo123's "opinions" I won't do it twice. But I can offer one more piece of information: when you consider how much of the sound energy on which frequencies will get reflected vs how much will pass through when it hits the barrier (being it a steel reinforced concrete wall 30cm thick, plaster wall 8 cm thick or curtain) - it pretty much depends only the weight of the barrier. Claiming that the barrier comprising of such low weight material as curtain will affects frequencies down to 100Hz is, well, uninformed..
+1
 

thorvat

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@thorvat Are you done putting words in my mouth?

Let me rephrase: if your measurements were done properly curtain vs no curtain graphs should differ from app 400Hz upward while below that the 2 FR graphs should be identical. As this is not the case it is impossible to tell the frequency where your curtain starts to alter the response. So, until you get the measurements right it is pointles to draw any conclusions from it.
 
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abdo123

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Let me rephrase: if your measurements were done properly curtain vs no curtain graphs should differ from app 400Hz upward while below that the 2 FR graphs should be identical. As this is not the case it is impossible to tell the frequency where your curtain starts to alter the response. So, until you get the measurements right it is pointles to draw any conclusions from it.

So you wishfully ignored the post where I literally did nothing except open and close the curtains between the two measurements?

Your responses are no longer welcome.
 

thorvat

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So you wishfully ignored the post where I literally did nothing except open and close the curtains between the two measurements?

Your responses are no longer welcome.

If your measurement was taken properly than it would reflect that, but as it was not there are differences in the response below app 400Hz which shouldn't be there.

I am writing my responses for the sake of expressing the facts to be available to other people reading this thread, and as far as I'm concerned you can keep your "opinions" unchanged as long as you like.

If you ever become admin on this forum you will have a chance to judge which responses are welcome and which are not, but until that happens I suggest you refrain yourself from that judgement.
 

Erici

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So you wishfully ignored the post where I literally did nothing except open and close the curtains between the two measurements?

Your responses are no longer welcome.
I think the point is that the curtains do not have enough mass to alter the low frequencies. So the low frequency response should be about the same with open or closed drapes.

EDIT: Can we agree on that?
 

thorvat

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I think the point is that the curtains do not have enough mass to alter the low frequencies. So the low frequency response should be about the same with open or closed drapes.

EDIT: Can we agree on that?

That is exactly my point.

Consequently, the only explanation for the existence of the diffferences in LF response is unprecise measurement, which makes impossible drawing any conclusions from it.
 
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abdo123

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I think the point is that the curtains do not have enough mass to alter the low frequencies. So the low frequency response should be about the same with open or closed drapes.

EDIT: Can we agree on that?

You really think I wasn’t surprised as well?

I have never made claims of anything, all i did was share my measurements of before and after a particular change in my room that involves nothing but closing and opening curtains.

Yet my measurements are questioned and claims are being made in my name that i have never actually made myself.

All i did was share my personal preference of not EQing frequencies above 100Hz and know there is a whole unlawful extrapolation of that statement.

It’s petty at best, disrespectful at worst.
 

Erici

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You really think I wasn’t surprised as well?

I have never made claims of anything, all i did was share my measurements of before and after a particular change in my room that involves nothing but closing and opening curtains.

Yet my measurements are questioned and claims are being made in my name that i have never actually made myself.

All i did was share my personal preference of not EQing frequencies above 100Hz and know there is a whole unlawful extrapolation of that statement.

It’s petty at best, disrespectful at worst.
Didn't mean to offend you abdo. Just trying or find some area of agreement....
 

thorvat

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You really think I wasn’t surprised as well?

I have never made claims of anything, all i did was share my measurements of before and after a particular change in my room that involves nothing but closing and opening curtains.

Yet my measurements are questioned and claims are being made in my name that i have never actually made myself.

All i did was share my personal preference of not EQing frequencies above 100Hz and know there is a whole unlawful extrapolation of that statement.

It’s petty at best, disrespectful at worst.

Let me explain something to you: measurements are essential step when researching something as conclusions are drawn from them. Your measurements can easilly be disputed by anybody who understands basic physics. Now, you had a chance to learn what you did wrong when making your measurements but instead you choose to accuse me as if I offended you when I proved your measurements are innacurate.

So, try to think about these 2 things:

1.) yes, your measurements are questioned, and that is how the science should work. You should be the one to question them and you should encourage others to question them if you want to prove them right to be able to draw conclusions from them. Why else did you post your measurements on this forum? To get appraisals for them without the right to question them? I repeat, that is not how science was meant to work, so I advise you to get used to your work being questioned, and also to be the first to question it instead of denying others the right to do that and to act offended like a child when nobody even thought about offending you.

2.) You should realise it is your work that is being questioned, not yourself, so there is no room here for being offended. That is how adult people should act, if they want to continue to develop themselves.
 

ernestcarl

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Regarding the green curve - you don't really need A/B test to see that it can sound better - having the 320-950Hz range playing higher than 100-320 Hz cannot possibly sound good.

A/B listening is important to me because what looks initially unacceptable in the presented steady state curve may not sound as "bad" as it looks. From time to time, what looks worse in a graph, may actually sound good to one's ears -- or, at least perceptually "neutral", or not even necessarily "worse" compared to the original (no EQ or "treatment") response.

I don’t like to EQ the response above 100Hz anyway.

If the default natural voicing of your speakers is good enough for your ears, then there's probably no further need for that... leaving it be should be fine.

But, with adequate data -- i.e. multiple measurements, filtering and/or viewing methods -- one should still be able to safely apply more detailed full-range room and speaker EQ with little cause for concern.

@abdo123 A fun function of the newer REW versions is the RT60 decay mode where you can choose any frequency and get the decay for that frequency alone. Would be nice if you could pick a few random frequencies and show before and after just to see how the relative decay changes. Say you pick frequencies where the frequency response is most similar between with and without curtains.

Easier to visualize than the whole waterfall

Besides the somewhat underutilized RT60 decay view mode in REW, wavelet spectrograms and "spectral" decay graphs can be quite revealing as well. The difficult part is connecting the dots or correlating what is seen in the graphs vs what is actually heard/perceived.

---

The ff. are measurements from a badly positioned (corner-backwall-placed) left rear surround speaker pointing directly at the opposing wall/right side surround speaker instead of my actual Desk MLP which is closer to the front half of the room. Do note, however, the room is partially already dampened from construction by default; and, I have, through the years, acoustically "treated" the space -- though, haphazardly! BTW, this is because I'm no acoustician and only half of the time know what I'm doing. It's got everything: highly reflective and heavy sound absorptive curtains, foam acoustic wedges, a ceiling cloud, and various other DIY panels.

1661191603448.png 1661191915161.png 1661191921091.png 1661191935480.png 1661191941556.gif

The speaker above is a modified (sealed and internally overstuffed) LSR305. Directivity of this small wave-guided speaker is good despite some non-linearities seen in the steady state response.

The graphs should also illustrate why, IMO, single-point measurements at the main listening position are actually not "useless" or wholly uninformative -- in fact, a lot can be garnered from that method alone. But, on the other hand, if the task also included equalizing above 500 Hz or so, I wouldn't truly be so confident of not messing things up without the additional use of other reference curves. And because this is only one speaker in a larger 7.1 MCH system, I find A/B listening between the rest of the channels (having different speaker brands/types in the mix) also very useful very important.
 
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