Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 109 - AVS Forum
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post #3241 of 11895 Old 06-02-2013, 11:56 AM
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No. You just gate the response. Yes, you sacrifice the low end in doing so, but seeing 500hz (guess??) and up compared is still quite telling.


Jim,

To ensure I understand "Gate the response", are you saying that you set the pink noise signal to 500 Hz - 20 kHz instead of 0 Hz - 20 kHz when measuring? Usually, we measure full-range and window (filter) the impulse response, if I understand correctly.

Thanks.

Mark


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post #3242 of 11895 Old 06-02-2013, 12:09 PM
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Jim,

To ensure I understand "Gate the response", are you saying that you set the pink noise signal to 500 Hz - 20 kHz instead of 0 Hz - 20 kHz when measuring? Usually, we measure full-range and window (filter) the impulse response, if I understand correctly.

Thanks.

Mark

No.

Firstly, I recommend sine sweeps over pink noise testing.

Secondly, I am talking about the time domain, not the frequency domain when speaking of gating. My 500hz reference was that a gated response 3-4ms, doesnt give enough detail to lower frequencies to gain anything from the graph, so I was suggesting just to ignore the data below a certain frequency.


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post #3243 of 11895 Old 06-03-2013, 02:23 AM
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Jim,

To ensure I understand "Gate the response", are you saying that you set the pink noise signal to 500 Hz - 20 kHz instead of 0 Hz - 20 kHz when measuring? Usually, we measure full-range and window (filter) the impulse response, if I understand correctly.

Thanks.

Mark

No.

Firstly, I recommend sine sweeps over pink noise testing.

Secondly, I am talking about the time domain, not the frequency domain when speaking of gating. My 500hz reference was that a gated response 3-4ms, doesnt give enough detail to lower frequencies to gain anything from the graph, so I was suggesting just to ignore the data below a certain frequency.

And just to clarify further, you 'gate' the response by imposing a short time limit so the mic doesn't (is much less likely to) capture reflections that can potentially skew the measured response.

BTW, Dennis Murphy is another whose speakers (Philharmonic line) show the rare 'on and off axis' measurement data.

That was one of the things I liked about Stereophile's speaker reviews: John Atkinson's lateral response measurements out to 90-degrees. Really shows how well the speakers are designed (or not).


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post #3244 of 11895 Old 06-03-2013, 04:06 AM - Thread Starter
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BTW, it "IS" important to use the ETC properly. To do that, you MUST band filter (using the IR window and selecting 1/3rd octave filtering starting at 500hz up to at least 8khz or so) the ETC measurements, in addition to looking at the full unfiltered ETC for each individual channel to get an accurate picture and verify you are not just EQ'ing your response by not using broadband absorption (IE: Only taking care of reflections from 1000hz to 20khz by using too thin of an absorber).


If you use this method you will be using the ETC to the fullest and it will never let you down. smile.gif There is no better tool to use, no more comprehensive or accurate tool in the cookbook either.

 

J (or anyone) - can you elaborate for me please? When I open the IR Window, I see this, which doesn't gell with your remark bolded above:



Where are the controls you mention?  Thanks.

Hi Keith et al,

I'm behind a few days due to a frost freeze spigot bursting in my basement which houses my dedicated theater I'm building. (Luckily I don't have carpet yet) and woke up Friday to several inches of water! It's been a mess.

Of course I didn't find out it had its own shutoff valve on it until much much later after I shut off the main water to the house. Ahhhh... Live and learn, I suppose.

Now I know what people who are just stumbling on acoustics must think and how they feel as I was utterly overwhelmed and didn't even know what a "frost freeze spigot" was until I started calling plumbers to come fix it.

Anyway... Back on topic, and sorry for the delay.

When you have a measurement open in REW, simply click the 5th tab from the left that says "Filtered IR" and from there you can put a check in "ETC" at the bottom of the screen.

Then, on the bottom left side you'll see a default of "No Filter" which is where you can change it to filter the ETC to 1/3rd at 8000hz for instance.

I suggest doing this, for each channel (never view ETC's, filtered or unfiltered, with more than one channel at a time) from 500hz to 8khz, concentrating especially on 1khz to 8khz.

Looking at the ETC this way will verify that your acoustic panels are taming the entire broadband specular reflection(s) and not just the higher frequencies, or even just lower frequencies if for instance you have a membrane on some panels so you don't over absorb the higher frequencies.

We'll talk more later about why, when, and where to use membranes on panels but for now, just know that to fully utilize the ETC and verify you have tamed all early High Gain reflections, you must look at the measurements properly; in this case filtered at 1/3rd octave.

Don't bother looking at anything under 500hz as you're no longer in the specular region. For below 500hz concentrate on the Waterfall and Spectogram.

Hope this helps, and again, sorry for the delayed response.

--J

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post #3245 of 11895 Old 06-03-2013, 04:09 AM - Thread Starter
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Local, this is the second time you have advised me regarding the "Use Loopback as Timing Reference" setting for the impulse response measurements, and I appreciate your advice.  For others who are not familiar with where this setting is, open the Analysis tab on the Preferences screen:





I am familiar with how to configure the hardware loopback when using the "legacy" REW gear, but am not sure whether it is even possible when using the USB Mic + HDMI connection to the AVR.  Can you (or anyone else who knows the answer) comment on whether this is possible or not?  If not, does this mean that if we are using the HDMI connection, the impulse measurement is wrong, or meaningless?

I'm going to ask this question over on HTS as well.

I didn't receive any feedback WRT the accuracy of ETC measurements without the hardware loopback enabled, and how the loopback could be accomplished using HDMI connections.  A similar posting over on HTS received one reply, pointing me to a discussion on how to enable the loopback.  I read it, but didn't understand it completely.

http://www.hometheatershack.com/forums/rew-forum/67726-how-configure-hardware-loopback-when-using-asio-hdmi.html#post615095

Jerry,

I don't think there is any way possible to use the loopback for timing reference with USB Mics and since that's what 99.9% of the folks are using here, I'd hate to complicate the thread especially since we're starting to talk about advanced topics.

Just don't want to turn anyone off by confusing them even more. wink.gif

I'd be happy to help you via PM or in another thread but just note that as of now (and I don't see how it would/could change, but John has worked miracles before!) this isn't an option with USB mics.

I wouldn't worry about it too much though because your relative measurements will still be accurate.

You won't know total time of flight for direct sound and each reflection, but you don't really need to know that with the string method we've taught here.

Even the string method shouldn't be something you have to do for every reflection as soon you'll find you're able to eyeball it and get pretty close once you get involved tracking them down.

--J

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post #3246 of 11895 Old 06-03-2013, 04:14 AM
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Hi Keith et al,

I'm behind a few days due to a frost freeze spigot bursting in my basement which houses my dedicated theater I'm building. (Luckily I don't have carpet yet) and woke up Friday to several inches of water! It's been a mess.

Of course I didn't find out it had its own shutoff valve on it until much much later after I shut off the main water to the house. Ahhhh... Live and learn, I suppose.

Now I know what people who are just stumbling on acoustics must think and how they feel as I was utterly overwhelmed and didn't even know what a "frost freeze spigot" was until I started calling plumbers to come fix it.

Anyway... Back on topic, and sorry for the delay.

When you have a measurement open in REW, simply click the 5th tab from the left that says "Filtered IR" and from there you can put a check in "ETC" at the bottom of the screen.

Then, on the bottom left side you'll see a default of "No Filter" which is where you can change it to filter the ETC to 1/3rd at 8000hz for instance.

I suggest doing this, for each channel (never view ETC's, filtered or unfiltered, with more than one channel at a time) from 500hz to 8khz, concentrating especially on 1khz to 8khz.

Looking at the ETC this way will verify that your acoustic panels are taming the entire broadband specular reflection(s) and not just the higher frequencies, or even just lower frequencies if for instance you have a membrane on some panels so you don't over absorb the higher frequencies.

We'll talk more later about why, when, and where to use membranes on panels but for now, just know that to fully utilize the ETC and verify you have tamed all early High Gain reflections, you must look at the measurements properly; in this case filtered at 1/3rd octave.

Don't bother looking at anything under 500hz as you're no longer in the specular region. For below 500hz concentrate on the Waterfall and Spectogram.

Hope this helps, and again, sorry for the delayed response.

--J

 

Hi J, really sorry to hear of the problem with the flooding. Hope no big damage was done and all is OK now.

 

Thanks for the instructions. Got it!  What ideally should I be seeing in the graphs when I filter them at the different settings?



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post #3247 of 11895 Old 06-03-2013, 04:15 AM - Thread Starter
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The vertical axis should extend from 0dB to the noise floor, at least -40dB.  I set it at -60dB.  I set the horizontal axis right limit to 40ms.  The first 20ms is critical, and you should see most (if not all) peaks below -20dB beyond 20ms.  This should be especially true in your well-treated room.  I set the left limit for the horizontal axis at -1ms, which allows the initial impulse at T=0 to be more easily "grabbed" using the CTRL-Right Click technique to display peak distances.



Thanks Jerry. Appreciated. I am at least -25dB down beyond 20ms.

But remember Keith, BEFORE 20ms is more important... Also, (haven't looked myself) do you have any sparse high gain reflections after 20ms? Those should be taken care of, too.

Look to see that your ETC decays evenly and doesn't have hills and valleys right down into the noise floor.

Always filter at different bands to make sure you're not looking at only the highest frequencies as the ETC, unfiltered, can cover up all but the highest frequencies if you're taking a full bandwidth 20-20k measurement.

If you pass all these tests, then in your room at least, you may be done with the specular region! Now to concentrate on the modal region. wink.gif

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post #3248 of 11895 Old 06-03-2013, 04:23 AM - Thread Starter
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OK, time for a bit of instruction for us neophytes: what does the term "terminator" mean?


They say a picture is worth a thousand words. Well, here is a pic from a Don Davis paper.




Here is the same pic, but I put a grid into for more precise interpretation.




And here is my attempt to emulate it.



Interesting. I am nowhere near your level of expertise and I am striving towards the NE model. Here is my ETC set to the same time/dB parameters as you have used.  As you can see, by 140ms (before in fact)the graph in my case has disappeared off the radar. Is this because of the model I am trying to emulate, or is it some sort of basic error I am making, or have I misunderstood something?  I am very pleased with the sound BTW. The graph shows my left speaker, but the right and centre are essentially similar.



Keith,

The difference is that Jim (and the text he referenced) is going for a LEDE room. (BTW Very nice, Jim, you're well on your way!!)

So his ETC will terminate at around 20ms (meaning the effectively anechoic response [-20db or more] ends and he reintroduces high gain diffuse/dense reflections at around 20ms then steadily decaying into his noise floor.

In your case, since your ETC disappears at around 140ms that means your true decay time is .14 seconds and whether or not this matches with what the TOPT on the RT60 tab shows, well, who knows, since that's not something we should be concentrating on since it doesn't apply to small acoustical spaces.

You've now learned and understand how to properly view an ETC and viewing it this way gives you all the details and is accurate so there is NO REASON to use the RT60 tab. It simply tries to approximate the data and again, doesn't even apply to your (or anyone else's) room.

.14s is VERY dead/dry but since you use it for Multi-Channel movies only, if you like it, that's all that counts.

For anyone using the room for music or movies/music mixed, I would NOT recommend anything less than .2s and really .25 seconds should be the goal at a MINIMUM unless using a lot of diffusion. If using absorption ONLY, then .25 seconds should be the minimum.

Again, find this like Keith did by using the ETC and DO NOT USE THE RT60 TAB!!

--J

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post #3249 of 11895 Old 06-03-2013, 04:34 AM - Thread Starter
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Interesting. I am nowhere near your level of expertise and I am striving towards the NE model. Here is my ETC set to the same time/dB parameters as you have used.  As you can see, by 140ms (before in fact)the graph in my case has disappeared off the radar. Is this because of the model I am trying to emulate, or is it some sort of basic error I am making, or have I misunderstood something?  I am very pleased with the sound BTW. The graph shows my left speaker, but the right and centre are essentially similar.



Firstly, the models you and I are trying to emulate are different. Mine the LEDE / RFZ and yours the NE model. So comparing our ETC's is a bit apples and oranges.

I am no expert on NE rooms, so take anything I say, and verify it with someone who knows more than I about the NE model, but from what I understand, the ETC on a NE room should look relatively anechoic. In your case, those first 10ms need some reflection attenuation. But what makes the model work is a reflective floor and a reflective front wall in order to establish necessary psycho-acoustic room cues. I also believe it incorporates some ceiling diffusion aimed back at the front reflective wall for bringing up the level of those cues.

Again, look into this yourself, but I think all these criteria must be there for a NE room to sound like it should. Its much more than just emulating a anechoic ETC response.

Jim,

You are exactly right!

It's important to note that thus far we've only talked about ONE aspect of both LEDE and NE in this thread.

If I/We put ALL the details out there all at once, it'd become nothing more than a book of which there are already plenty of and of much more substance and quality than I can write.

This thread is intended to be a step by step tutorial and interactive hands-on learning process so I can assure you we'll get there, but to reiterate, you are correct.

There are a lot of criteria that go into these acoustic models and I doubt anyone, including myself, will actually get our rooms certified, but it is important for us to learn all the criteria (in due time and when everyone is comfortable/ready) so we as individuals can decide how far we wish to take our rooms.

Good points and thanks for the clarification that getting rid of reflections isn't the only step.

--J

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post #3250 of 11895 Old 06-03-2013, 04:41 AM - Thread Starter
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Interesting. I am nowhere near your level of expertise and I am striving towards the NE model. Here is my ETC set to the same time/dB parameters as you have used.  As you can see, by 140ms (before in fact)the graph in my case has disappeared off the radar. Is this because of the model I am trying to emulate, or is it some sort of basic error I am making, or have I misunderstood something?  I am very pleased with the sound BTW. The graph shows my left speaker, but the right and centre are essentially similar.



I see some significant reflections above -20dB and below 20ms.  Have you been able to identify what those are?

In your case Keith, it will be ALL the reflections.

However, MOST of us are going for more of a LEDE/RFZ design and most of us will be concentrating on taming (not necessarily just absorbing) the high gain EARLY reflections which means the reflections BEFORE 20ms.

All the reflections from the direct signal out to around 20ms need to be at least -20db.

Starting at around 20ms and moving ahead/forward in time is where the room models differ and where most of us will want to reintroduce higher gain dense/diffuse reflections, but again, in your case, you shouldn't see ANY reflections at ANY TIME over -20db.

You should ALSO not use any more absorption than absolutely necessary to accomplish this so you don't make your room so uncomfortable to live in/speak in.

An NE model doesn't mean Anechoic (without reflection) and you (and all of us) should be surgically implementing absorption only where necessary.

Also, if you don't sit too close to your back walls, you should consider 2D diffusion for your room model.

For MOST of us, 2D diffusion is the wrong choice unless we have huge rooms and/or very high ceilings, we should be looking at 1D QRD type diffusers for the back wall and back side walls.

Getting ahead of myself a bit with diffuser talk, but for now, just note that you definitely need to do something about the light fixture and anything/everything else causing sparse reflections before 20ms (and after in your case as there will be no termination of your ISD Gap) at a gain of -20db or higher.

--J

I thought that the aim was to get -20dB *after* 20ms?  I am fairly sure that one of the earlier reflections is from a light fitting in the centre of the ceiling, about which I can do nothing at all. Not a thing unfortunately. I have mooted removing it (it is rarely used) but Mrs K is against it, and I am not going to antagonise her over it given how co-operative she is in 'most all other ways. When I did the string thing it landed right on the light fitment. There may be other things that are issues too. 

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post #3251 of 11895 Old 06-03-2013, 04:44 AM
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Keith,

The difference is that Jim (and the text he referenced) is going for a LEDE room. (BTW Very nice, Jim, you're well on your way!!)

So his ETC will terminate at around 20ms (meaning the effectively anechoic response [-20db or more] ends and he reintroduces high gain diffuse/dense reflections at around 20ms then steadily decaying into his noise floor.

In your case, since your ETC disappears at around 140ms that means your true decay time is .14 seconds and whether or not this matches with what the TOPT on the RT60 tab shows, well, who knows, since that's not something we should be concentrating on since it doesn't apply to small acoustical spaces.

You've now learned and understand how to properly view an ETC and viewing it this way gives you all the details and is accurate so there is NO REASON to use the RT60 tab. It simply tries to approximate the data and again, doesn't even apply to your (or anyone else's) room.

.14s is VERY dead/dry but since you use it for Multi-Channel movies only, if you like it, that's all that counts.

For anyone using the room for music or movies/music mixed, I would NOT recommend anything less than .2s and really .25 seconds should be the goal at a MINIMUM unless using a lot of diffusion. If using absorption ONLY, then .25 seconds should be the minimum.

Again, find this like Keith did by using the ETC and DO NOT USE THE RT60 TAB!!

--J

 

Thanks J. The strange thing is that, to me, .14s doesn't seem all that 'dead' or 'dry'. Certainly no more so than all those editing suites I used to hang out in for work. But yes, I do like the result, and as you say, the room is used solely for m/ch movies. I wouldn't want a normal living room to be as dry as my HT room is - it does feel a little odd to hold a conversation in the room - but then that just doesn’t happen. I go in there to watch a movie, not to have a chat, or even to listen to my 2ch music.

 

I've never used the RT60 tab. My 'contrarian' says to use it, so that tells me not to :)  I've also read from numerous, highly respected posters that RT60 has no validity for small rooms - and my room is definitely small! :)



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post #3252 of 11895 Old 06-03-2013, 04:44 AM - Thread Starter
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This thread is for REW with HDMI and USB mics, so you won't get any support here if you buy the EMM-6 because it will be off topic.  If you decide to go with the EMM-6, there are various dedicated threads to 'legacy' REW, used with outboard soundcards and so on.

Of the two USB mics, the UMM-6 is the one most of us in this thread have opted for. 

Yes, it seems that will be the one. Thanks again KB

I HIGHLY recommend the UMM-6. wink.gif

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Too many self-proclaimed "experts" using this forum as a marketing tool.

Not that this post was directed towards me (at least I hope not tongue.gif ) but just to reiterate, as the creator of this thread, I am NOT in the acoustics business or any related field, have NO agenda other than to help folks understand this very difficult subject to the best of my ability because I enjoy the topic immensely and spend MOST of my free time reading, learning, and applying what I've learned about the field of acoustics and psychoacoustics to my own dedicated HT build, and dare I say I actually enjoy this process and the field of acoustics MORE SO than I enjoy watching movies/listening to music!

Also, I don't consider myself an expert, however I do strive one day to be just that. wink.gif

The goal here is for us, as a community, to learn about acoustics and psychoacoustics then apply what we've learned to our own rooms.

If I happen to know something through my years of reading and research that someone else doesn't, I'm more than happy to share that knowledge by answering questions related to the topic of this thread in the amount of free time I have available.

Hope this clears things up for anyone wondering about my own agenda/objective here.

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post #3254 of 11895 Old 06-03-2013, 04:54 AM - Thread Starter
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I thought that the aim was to get -20dB *after* 20ms?  I am fairly sure that one of the earlier reflections is from a light fitting in the centre of the ceiling, about which I can do nothing at all. Not a thing unfortunately. I have mooted removing it (it is rarely used) but Mrs K is against it, and I am not going to antagonise her over it given how co-operative she is in 'most all other ways. When I did the string thing it landed right on the light fitment. There may be other things that are issues too. 

No, the objective is to reduce all early reflections (<20ms) to a level of at least -15dB, preferably -20dB.

All mine are below -15dB (except for one at 0.8ms) and they are all below -20dB after 10ms. That is the best I can do in this room I think. I believe that chasing a better result will involve a huge amount of additional time and effort for not a lot of benefit.  I have tried to wean myself off chasing perfect graphs, but I freely admit I am no perfectionist. The time required to get the last few percent of pretty much anything is always difficult to justify (in my world) - it means that, when time is limited, as it always is, I don't have enough left to pursue all the other things I want to do.  If there is something relatively easy that I could do to get the last remaining reflections down by a further 5dB between 0 and 10ms I would do it.


 

If you're happy, then you're done! smile.gif

I know you though, and know you're not done.

So... Get those that are only -15db down to -20db THEN start REMOVING panels and only keep the ones you need that are actually in the right spots to take down only the reflections that are sticking up above -20db because you really need to try to get your room to .2 seconds instead of .14 as honestly, that really is way too dead of a room. (That IS considering your personal goals and how you use your room, too, BTW wink.gif )

--J

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post #3255 of 11895 Old 06-03-2013, 05:06 AM - Thread Starter
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All mine are below -15dB (except for one at 0.8ms) and they are all below -20dB after 10ms. That is the best I can do in this room I think. I believe that chasing a better result will involve a huge amount of additional time and effort for not a lot of benefit.  I have tried to wean myself off chasing perfect graphs, but I freely admit I am no perfectionist. The time required to get the last few percent of pretty much anything is always difficult to justify (in my world) - it means that, when time is limited, as it always is, I don't have enough left to pursue all the other things I want to do.  If there is something relatively easy that I could do to get the last remaining reflections down by a further 5dB between 0 and 10ms I would do it.



 


It is always a matter of what your willing to do vs the perceived return. What you have (based solely on your ETC) could sound nice. May even be enough of what you want to call it a day. Certainly, there is no rule or expectation that room treatment is a all or nothing affair.


But dont underestimate what taking things all the way would be until you have heard a room taken to that point.

I agree with that. The main problem I have is that the room I have is very poor. It is far too small and almost square. Overall it comes in at well under 1000 cu feet. I don't think it will ever be a room that can be 'taken all the way' no matter how much time and energy I expend on it. In fact, I am amazed that I have got it to sound as good as it does. 

But my main priority isn't acoustics or AV. It is movies. The only reason I ever got this far down the rabbit hole is because of my passion for movies and the desire to see and hear them at their best. I believe I have already surpassed the audio-visual experience that is on offer in all the cinemas that are within a sensible drive of here, all except for screen size. The crappy room means I cannot install a PJ (too small) so I cannot experience the truly 'big screen'. But the audio is actually better than in local cinemas by a good margin.

There is a good AV dealer about 100 miles from where I live and he has two fabulous demo rooms. I have heard both and they are without question superior to my own. But I will never be able to emulate what he has done simply because of the physical size constraints imposed on me. That is the only reason I have said that the future effort may not be worthwhile (for me). If I had a better space to work with, and room to install a 120 inch screen, I am sure that I would be prepared to 'go all the way'. But we all have to compromise and currently I have over 150 movies on the 'unwatched' shelf and every hour I spend on trying to extract that last few percent is an hour not watching a movie. I never really wanted another hobby (I also spend a lot of time on photography, which is another passion of mine) - I just became fascinated by the pursuit of great HT sound, and the many, many great guys I have 'met' on these threads have encouraged me to 'go down the rabbit hole'. I am not complaining - I have (and continue to) enjoyed the journey!

Sorry for the OT, but...

I have a few ideas for you, Keith.

First, a projector is NOT out of the question for your room.

I just bought a BenQ w1070 that sells for under $1000 and I have to say, having owned technically much superior projectors, it is NICE and I'm using it now as my MAIN 2d and 3d projector.

It has a pretty short throw but they also make the exact same projector, called a BenQ w1080 short throw version that would be perfect for your room! It has pretty good black levels, is extremely bright, and can project a huge image from just a few feet!

So it is definitely possible. I know a few folks that have nicer projectors, such as the highly acclaimed Epson 5010/5020 projectors (which is what I was going to buy) and bought the BenQ for its 3D only, since it's DLP and DLP has no ghosting issues and they've actually decided to use the BenQ for everything as it is just that good. It also has a 6000 hour bulb life, almost perfect color out of the box, etc.

As for all those movies, how are you handling those? Do you have a Blu-Ray changer, like the Sony (I have one and like most other folks it has been repaired TWICE already, just died again, and is getting ready to go back a 3RD time!) that holds 400 discs, or do you have them all stored on a NAS (I'm just starting to do that now as I'm tired of fooling with the Sony) or, heaven forbid, are you getting up and down for each and every disc each and every time you want to watch something, lol? biggrin.gif

I found once I got the changer (and now especially that I'm starting to view everything over a NAS hooked up to an OPPO 103) I actually watch much more content since I can literally play anything I want at the click of a button.

To get back on topic, now that your ETC is looking much better and you know what you need to do to fix it up, have you posted a recent waterfall for your modal region?

When you change (add, remove, move) panels to get your ETC in line for the specular region, it can affect the modal region and since you have a small/square room, I'd say the modal region is where you should be concentrating most, especially since you have those awesome (wish I had the budget for those) Seaton F2's.

In fact, I honestly feel like this thread moved too fast past getting modal/bass issues taken care of and we never really talked about any type of absorbers other than fuzzy stuff (and you can only make it so thick before it doesn't help any more) and there are so many other ways to combat bad/muddy bass due to modes/nodes.

How does your response look between 5 and 300hz in your room, Keith? Care to share?

--J

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post #3256 of 11895 Old 06-03-2013, 05:11 AM - Thread Starter
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Yep. It's about 10% of the total collection. They are not necessarily all unseen - I will have seen quite a few in the past - but they have been bought on BD or DVD and not yet watched. Crazy isn’t it?

Say you watch three-four movies a day. Do that for every day and you'll be back to measuring within five or six weeks, if you watch them in their entirety. Time to get busy LOL...tongue.gif

Jerry should be done with his A/B of treatments by then, and I might even make a little progress on finding about pricing of acoustic blinds, to see if they're remotely doable or not.

Hi Stuart,

I haven't forgotten about you, your questions/room, I promise. tongue.gif

Just had some major water issues due to a frost freeze valve (didn't even know I had one of those or what it was until I woke up to several inches of water in my basement Friday) and am very behind.

The blinds aren't necessarily a "bad" idea, but they are very expensive and would be better for light leakage (if you use a projector for instance) than sound.

I cannot imagine them doing anything much below 1000hz and depending on the amount of windows/amount of coverage you may do more harm than good by effectively eq'ing your response and neglecting everything below 1000hz which is where the majority of the problems are to begin with.

This would cause a very uneven decay rate and your highs wouldn't sound right at all compared to the still boomy/muddy mids/lows and you do have a very reflective room from what I recall with a T60 around .5s, right?

I'll try to find your post again and comment on the specifics again, but I would definitely look into other forms of treatment besides the blinds.

I'm not saying you shouldn't get them, just don't spend all your budget on them, as again, they sound expensive and I'm not quite sure how effective they'd be.

If you're looking at getting a specific model, be sure to check and see if they've had them independently tested/measured and feel free to post the NRC data here so we can see if they'll help your room or not.

Thanks,

--J

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post #3257 of 11895 Old 06-03-2013, 05:16 AM - Thread Starter
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Yep. It's about 10% of the total collection. They are not necessarily all unseen - I will have seen quite a few in the past - but they have been bought on BD or DVD and not yet watched. Crazy isn’t it?


Well, after my less than stellar results with my measurements today, perhaps you could box some of those movies up and send them to me. I'm tired of measuring and need more relaxation and enjoyment.

smile.gif  Sorry to hear of the frustration you must be feeling, Jerry. I know this feeling too. Regardless of that, I think many of us would be interested in your journey though and to see the graphic results. The measurement of the untreated room must surely be a very interesting comparison with the measurement of the room fully treated and all tweaks added?  And surely we can learn something from all those in between too?  I’d love to see them, especially the 'before' and 'after'. Then when someone asks 'do treatments really make that much difference?', all that is required is to post your two graphs and to say "look". I never made any graphs of my room before the treatments started to go in unfortunately and, unlike you, I don't have the patience and/or the energy to take them all down, measure, and put them all back up again.

A big +1 to all of this!

I would LOVE to have a before of my room. I have some before's but they are "before" the walls were even up, lol, so not exactly useful.

Jerry, with true before data, and along the way (adding things back) data, we can analyze your room so much better and help you get exactly where you're going.

Please don't give up! I know it's not fun and individually, you're right, it's easy to get disappointed thinking the darn things aren't doing much, but when everything comes together and everything is in the right place (and YOU/MLP are in the right place, too) I promise you it will be well worth it. Who knows, you may find out you have too much, not enough, or most likely not the right combination of treatments. There's a lot more to it than absorption, and your room is still very lively.

I think you probably need more treatments and more than absorption, as you definitely aren't too close to overdoing it yet.

Keep on,

--J

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post #3258 of 11895 Old 06-03-2013, 06:02 AM - Thread Starter
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Hi Keith et al,


I'm behind a few days due to a frost freeze spigot bursting in my basement which houses my dedicated theater I'm building. (Luckily I don't have carpet yet) and woke up Friday to several inches of water! It's been a mess.


Of course I didn't find out it had its own shutoff valve on it until much much later after I shut off the main water to the house. Ahhhh... Live and learn, I suppose.


Now I know what people who are just stumbling on acoustics must think and how they feel as I was utterly overwhelmed and didn't even know what a "frost freeze spigot" was until I started calling plumbers to come fix it.


Anyway... Back on topic, and sorry for the delay.


When you have a measurement open in REW, simply click the 5th tab from the left that says "Filtered IR" and from there you can put a check in "ETC" at the bottom of the screen.


Then, on the bottom left side you'll see a default of "No Filter" which is where you can change it to filter the ETC to 1/3rd at 8000hz for instance.


I suggest doing this, for each channel (never view ETC's, filtered or unfiltered, with more than one channel at a time) from 500hz to 8khz, concentrating especially on 1khz to 8khz.


Looking at the ETC this way will verify that your acoustic panels are taming the entire broadband specular reflection(s) and not just the higher frequencies, or even just lower frequencies if for instance you have a membrane on some panels so you don't over absorb the higher frequencies.


We'll talk more later about why, when, and where to use membranes on panels but for now, just know that to fully utilize the ETC and verify you have tamed all early High Gain reflections, you must look at the measurements properly; in this case filtered at 1/3rd octave.


Don't bother looking at anything under 500hz as you're no longer in the specular region. For below 500hz concentrate on the Waterfall and Spectogram.


Hope this helps, and again, sorry for the delayed response.


--J

Hi J, really sorry to hear of the problem with the flooding. Hope no big damage was done and all is OK now.

Thanks for the instructions. Got it!  What ideally should I be seeing in the graphs when I filter them at the different settings?

No huge damage, but if it happened 6 months (hopefully I'll be done by then but probably not) from now, it would've cost thousands more and meant redoing this theater all over frown.gif

When you filter the ETC it should look exactly the same as the unfiltered.

For instance, if you look at the unfiltered ETC, as you have been doing, and find all your reflections are under -20db then at first glance, you'd be done.

However, if you look at a 1/3rd filter at 1khz, for instance, and find it shows reflections that are indeed above -20db, it means your treatment is only eq'ing your response and isn't truly broadband/absorbing all the frequencies in the specular region.

This means either the treatment isn't in the right place or isn't thick enough/the right type.

The unfiltered ETC is going to be biased towards the higher frequencies.

If, let's say, you take a measurement from 20hz to 8khz and look at the unfiltered ETC it will/should look the same (or very close) as the normal full bandwidth measurement you take but filter the ETC 1/3rd at 8khz.

Does that make sense?

No matter what, whether looking at a full bandwidth unfiltered ETC or a filtered ETC at different 1/3rd bands (frequencies) your goal is the same. No reflections greater than -20db UP TO (meaning before) 20ms or so. (In your case this extends to infinity/noise floor)

If you see reflections above -20db when looking at a filtered ETC, depending on the frequency it's filtered at, it shows you where you need more absorption.

So the most common thing to happen is the unfiltered ETC shows you're good and you've gotten all the reflections down to -20db or more.

Then you filter at 16khz and it's the same, 8khz same, 4khz same, get down to around 2khz or 1khz filtered and you may start seeing reflections popping up above -20db. That's where you need to adjust your absorption, reflection, or diffusion.

This means you may need to move it, supplement it, or replace it with better performing treatments, which in most cases means thicker.

Once you get it right, then ONE BY ONE (never more than one change at a time so you know exactly what is making the difference) you start removing treatments, remeasure and look at all the frequencies filtered, and if you're still good (all reflections -20db or more) then don't replace that panel.

Remove one by one until you only have what you NEED, surgically implemented, and your room won't be so dead.

Then... You look back at your modal region again. Look at the Waterfall and the Spectogram as the Frequency Response will only show you the frequency domain and only indirectly affects the time domain. If you have a lumpy/bumpy modal response, which ONLY the waterfall/spectogram will show you, then you need to reintroduce SPECIALIZED absorption panels that have a membrane of Mass Loaded Vinyl, Plastic, or Wood, (or even specially tuned bass traps such as Helmholtz traps if you only have one or two specific frequencies to tame) so as not to mess with the specular region that you just spent so much time on to get perfect.

This way you're treating the whole response, full bandwidth, frequency domain, and time domain and not leaving anything out.

--J

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I thought that the aim was to get -20dB *after* 20ms?  I am fairly sure that one of the earlier reflections is from a light fitting in the centre of the ceiling, about which I can do nothing at all. Not a thing unfortunately. I have mooted removing it (it is rarely used) but Mrs K is against it, and I am not going to antagonise her over it given how co-operative she is in 'most all other ways. When I did the string thing it landed right on the light fitment. There may be other things that are issues too. 

No, the objective is to reduce all early reflections (<20ms) to a level of at least -15dB, preferably -20dB.

All mine are below -15dB (except for one at 0.8ms) and they are all below -20dB after 10ms. That is the best I can do in this room I think. I believe that chasing a better result will involve a huge amount of additional time and effort for not a lot of benefit.  I have tried to wean myself off chasing perfect graphs, but I freely admit I am no perfectionist. The time required to get the last few percent of pretty much anything is always difficult to justify (in my world) - it means that, when time is limited, as it always is, I don't have enough left to pursue all the other things I want to do.  If there is something relatively easy that I could do to get the last remaining reflections down by a further 5dB between 0 and 10ms I would do it.


 

If you're happy, then you're done! smile.gif

I know you though, and know you're not done.

So... Get those that are only -15db down to -20db THEN start REMOVING panels and only keep the ones you need that are actually in the right spots to take down only the reflections that are sticking up above -20db because you really need to try to get your room to .2 seconds instead of .14 as honestly, that really is way too dead of a room. (That IS considering your personal goals and how you use your room, too, BTW wink.gif )

--J

 

:)  OK - when I start measuring again, soon, I will do as you say. IDK how I will get rid of those reflections that are only -15dB down as I have tried everything I can think of and they are persistent. I can easily remove treatments and re-measure - that seems like a worthwhile objective. Are you saying that even using a NE model I should still be aiming for 0.2s then? Why would making the room more 'live' help when all the ambiance I require is already recorded into the content and reproduced by the m.ch speaker array?



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post #3260 of 11895 Old 06-03-2013, 07:47 AM
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Sorry for the OT, but...

I have a few ideas for you, Keith.

First, a projector is NOT out of the question for your room.

I just bought a BenQ w1070 that sells for under $1000 and I have to say, having owned technically much superior projectors, it is NICE and I'm using it now as my MAIN 2d and 3d projector.

It has a pretty short throw but they also make the exact same projector, called a BenQ w1080 short throw version that would be perfect for your room! It has pretty good black levels, is extremely bright, and can project a huge image from just a few feet!

So it is definitely possible. I know a few folks that have nicer projectors, such as the highly acclaimed Epson 5010/5020 projectors (which is what I was going to buy) and bought the BenQ for its 3D only, since it's DLP and DLP has no ghosting issues and they've actually decided to use the BenQ for everything as it is just that good. It also has a 6000 hour bulb life, almost perfect color out of the box, etc.

 

Thanks. I have considered such a PJ before. The problem I have is that I am as obsessive about PQ as I am about SQ. You should have seen the agonising that went with the decision to get rid of the Kuro in favour of a much bigger (65 inch) Panasonic VT50. I am not sure I can live with 'pretty good' black levels. If I went for a PJ it would have to be one of the SOTA jobs, and hence very expensive. I am not sure I could find one suitable for my room and/or that would do the PJ justice.   I have all the Calman calibration s/w and a colorimeter so calibrating the screen isn't a problem for me. I will check out the BenQ short throw version. 

 

 

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As for all those movies, how are you handling those? Do you have a Blu-Ray changer, like the Sony (I have one and like most other folks it has been repaired TWICE already, just died again, and is getting ready to go back a 3RD time!) that holds 400 discs, or do you have them all stored on a NAS (I'm just starting to do that now as I'm tired of fooling with the Sony) or, heaven forbid, are you getting up and down for each and every disc each and every time you want to watch something, lol? biggrin.gif

I found once I got the changer (and now especially that I'm starting to view everything over a NAS hooked up to an OPPO 103) I actually watch much more content since I can literally play anything I want at the click of a button.

 

All my legacy DVDs are ripped to disc and played back via Plex  -- a formidable open source front end. But my BDs are just played via my Oppo 93, one at a time. I hear what you are saying but I haven’t got the heart to rip 600 blu-ray discs!  I only watch one movie a day so getting up and down isn't all that arduous - LOL.

 

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To get back on topic, now that your ETC is looking much better and you know what you need to do to fix it up, have you posted a recent waterfall for your modal region?

When you change (add, remove, move) panels to get your ETC in line for the specular region, it can affect the modal region and since you have a small/square room, I'd say the modal region is where you should be concentrating most, especially since you have those awesome (wish I had the budget for those) Seaton F2's.

In fact, I honestly feel like this thread moved too fast past getting modal/bass issues taken care of and we never really talked about any type of absorbers other than fuzzy stuff (and you can only make it so thick before it doesn't help any more) and there are so many other ways to combat bad/muddy bass due to modes/nodes.

How does your response look between 5 and 300hz in your room, Keith? Care to share?

 

Sure.  

 

Ooops - I did them at 15 - 300 Hz, sorry. That is the measurement range I usually use so it's all there is on the graphs.

 

 

 

 

 

Any suggestions for improving these?  By 'improving' I mean audible improvements not just nicer looking waterfalls of course. Down low it's hard to hear the initial impulse let alone any overhang that is 20 or 30dB below it in level.  What's going on in that 20-30Hz area when measuring the subs with L plus R as opposed to L or ~R or C on its own?

 

Here are the decay graphs for the same as above:

 

 

 

 

 



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post #3261 of 11895 Old 06-03-2013, 09:55 AM
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Hi Stuart,

I haven't forgotten about you, your questions/room, I promise. tongue.gif

Just had some major water issues due to a frost freeze valve (didn't even know I had one of those or what it was until I woke up to several inches of water in my basement Friday) and am very behind.

The blinds aren't necessarily a "bad" idea, but they are very expensive and would be better for light leakage (if you use a projector for instance) than sound.

I cannot imagine them doing anything much below 1000hz and depending on the amount of windows/amount of coverage you may do more harm than good by effectively eq'ing your response and neglecting everything below 1000hz which is where the majority of the problems are to begin with.

This would cause a very uneven decay rate and your highs wouldn't sound right at all compared to the still boomy/muddy mids/lows and you do have a very reflective room from what I recall with a T60 around .5s, right?

I'll try to find your post again and comment on the specifics again, but I would definitely look into other forms of treatment besides the blinds.

I'm not saying you shouldn't get them, just don't spend all your budget on them, as again, they sound expensive and I'm not quite sure how effective they'd be.

If you're looking at getting a specific model, be sure to check and see if they've had them independently tested/measured and feel free to post the NRC data here so we can see if they'll help your room or not.

Thanks,

--J

Jason,
I figured that you hadn't forgotten. No problem about not getting back to me urgently - right now I certainly have my hands full with projects at the office, as well as minor things like planning a possible one-week trip for our 15 year old and me in middish July.

Yes, I'm quite aware that our room is highly reflective by audio nirvana standards, with T60 around 0.5 and that I've heavily relied on Audyssey XT32 to address FR in a informally treated room, at best. I haven't said otherwise. Our HT has been progressively built around an existing living room and some dedicated furniture, and while I think the electronic EQ has done a reasonable job for FR by itself (and I've placed speakers as best I could given the multipurpose room with measurement tools), obviously it's not addressing early reflections < 20 ms, let alone the more rigorous standard of a declining ETC curve that we're starting to recommend here as the best practice. We all know now that Audyssey by itself is inadequate except for improving FR as an objective, assuming it's properly used. Certainly not after the conclusions that Keith and others have drawn lately (best described as "whither Audyssey"?!

Originally, I'd planned on not even getting seriously into the treatment world until we moved in a year or so after the newborn (kid 2.0, due in mid-September), and wasn't going to put much energy and time into this room until I could start from the POV of a room from scratch. But since we're diving into REW specifically to address room issues...maybe I'm a good case study of what is or isn't possible with resource constraints LOL.

To your point: since I have an entire side of our living room/HT that's windows, blinds seemed like a more practical solution than covering a southern view of Lake Michigan with acoustic panels. Curtains (which Jerry mentioned as one idea) won't fly in our house due to WAF and because, well, they'd look ugly. However, one idea I'd gotten from a CI for automated Lutron blinds was indeed prohibitively expensive - $3K per window eek.gif - so efficacy or not, they're a moot point.

Actually, the one kind of blind I was thinking of are Sound Elite acoustic blinds, which according to their chart, focuses on improvement in roughly the 400 Hz range on up, particularly 500 Hz to 2K (blinds closed):
http://www.controlnoise.com/sound-elite-window-blinds/

Still need to get pricing to see if this is remotely doable financially, though. A thousand or so is one thing (it actually would help resale value for us a little, and offer some utilitarian value too for cutting outside nose): the equivalent of a Trinnov TEQ for window treatments isn't!

If this SoundElite data is "correct", and the blinds were affordable, it might go some way toward addressing reflections more evenly above 400 Hz, at least. And while I agree that without room correction, bass is certainly boomy and mids/highs are muddy - - that's where Audyssey does make some discernible (to listeners as well as chart) improvement, for what it does accomplish. it's also why I went to a Mythos ST supertowers mains over my old Klipsch References set in the first place: better dispersion of mids/highs and a larger spatial presence than what the more 'rock-oriented' Klipsch could do. Even if I'm doing the 'abomination' of EQing without treating first - remember, retrospective cart before horse, at least for some of us in our learning curve.

Would it help if I PM'd you some room pictures so you could see why I consider the HT area problematic for treatments - on all four sides of the room?

Stuart

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post #3262 of 11895 Old 06-03-2013, 10:03 AM
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Originally Posted by sdrucker View Post

Jason,
I figured that you hadn't forgotten. No problem about not getting back to me urgently - right now I certainly have my hands full with projects at the office, as well as minor things like planning a possible one-week trip for our 15 year old and me in middish July.

Yes, I'm quite aware that our room is highly reflective by audio nirvana standards, with T60 around 0.5 and that I've heavily relied on Audyssey XT32 to address FR in a informally treated room, at best. I haven't said otherwise. Our HT has been progressively built around an existing living room and some dedicated furniture, and while I think the electronic EQ has done a reasonable job for FR by itself (and I've placed speakers as best I could given the multipurpose room with measurement tools), obviously it's not addressing early reflections < 20 ms, let alone the more rigorous standard of a declining ETC curve that we're starting to recommend here as the best practice. We all know now that Audyssey by itself is inadequate except for improving FR as an objective, assuming it's properly used. Certainly not after the conclusions that Keith and others have drawn lately (best described as "whither Audyssey"?!

Originally, I'd planned on not even getting seriously into the treatment world until we moved in a year or so after the newborn (kid 2.0, due in mid-September), and wasn't going to put much energy and time into this room until I could start from the POV of a room from scratch. But since we're diving into REW specifically to address room issues...maybe I'm a good case study of what is or isn't possible with resource constraints LOL.

To your point: since I have an entire side of our living room/HT that's windows, blinds seemed like a more practical solution than covering a southern view of Lake Michigan with acoustic panels. Curtains (which Jerry mentioned as one idea) won't fly in our house due to WAF and because, well, they'd look ugly. However, one idea I'd gotten from a CI for automated Lutron blinds was indeed prohibitively expensive - $3K per window eek.gif - so efficacy or not, they're a moot point.

Actually, the one kind of blind I was thinking of are Sound Elite acoustic blinds, which according to their chart, focuses on improvement in roughly the 400 Hz range on up, particularly 500 Hz to 2K (blinds closed):
http://www.controlnoise.com/sound-elite-window-blinds/

Still need to get pricing to see if this is remotely doable financially, though. A thousand or so is one thing (it actually would help resale value for us a little, and offer some utilitarian value too for cutting outside nose): the equivalent of a Trinnov TEQ for window treatments isn't!

If this SoundElite data is "correct", and the blinds were affordable, it might go some way toward addressing reflections more evenly above 400 Hz, at least. And while I agree that without room correction, bass is certainly boomy and mids/highs are muddy - - that's where Audyssey does make some discernible (to listeners as well as chart) improvement, for what it does accomplish. it's also why I went to a Mythos ST supertowers mains over my old Klipsch References set in the first place: better dispersion of mids/highs and a larger spatial presence than what the more 'rock-oriented' Klipsch could do. Even if I'm doing the 'abomination' of EQing without treating first - remember, retrospective cart before horse, at least for some of us in our learning curve.

Would it help if I PM'd you some room pictures so you could see why I consider the HT area problematic for treatments - on all four sides of the room?

Stuart

I am not sure it work, but in principal, you may be able to utilize those types of blinds that are vertical wide slats. These can be made to open at various angles. It may work out that they could be in a partially open configuration, that is at a particular angle that redirects much of the sound in a beneficial direction.



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post #3263 of 11895 Old 06-03-2013, 10:15 AM
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Originally Posted by jim19611961 View Post

I am not sure it work, but in principal, you may be able to utilize those types of blinds that are vertical wide slats. These can be made to open at various angles. It may work out that they could be in a partially open configuration, that is at a particular angle that redirects much of the sound in a beneficial direction.


These are similar to the kind of blinds I was thinking of - vertical slat/adjustable blinds. Know if these are the Sound Elite ones I mentioned? They can be opened/closed from the description, but not sure if there's any angling of sound/reflection possible.

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post #3264 of 11895 Old 06-03-2013, 10:34 AM
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Quote:
Originally Posted by sdrucker View Post

These are similar to the kind of blinds I was thinking of - vertical slat/adjustable blinds. Know if these are the Sound Elite ones I mentioned? They can be opened/closed from the description, but not sure if there's any angling of sound/reflection possible.

The pic/link was for illustration only.

I am betting that high frequency energies could be redirected by them. Obviously, the wider the slats, the lower the frequency they may affect. Ive read you can get them with up to 5" wide slats. I wouldnt expect them to have any effect below 1k or 2k though.


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post #3265 of 11895 Old 06-03-2013, 10:41 AM
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Quote:
Originally Posted by jim19611961 View Post

The pic/link was for illustration only.

I am betting that high frequency energies could be redirected by them. Obviously, the wider the slats, the lower the frequency they may affect. Ive read you can get them with up to 5" wide slats. I wouldnt expect them to have any effect below 1k or 2k though.

I didn't say I believe that chart - but they claim that their solution offers up to 80% reduction, with focus on that range if you see the graphed response on that link I'd posted.

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post #3266 of 11895 Old 06-03-2013, 11:35 AM
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For MOST of us, 2D diffusion is the wrong choice unless we have huge rooms and/or very high ceilings, we should be looking at 1D QRD type diffusers for the back wall and back side walls.
Is that in order to maximize the lateral diffused cues, or because diffused sound bouncing off the ceiling impairs the result?

I thought about this quite a while before settling for 2D diffusors, rationalizing that the ceiling returns would help movies create a better sense of a spatial bubble for the surrounds. This is done in concert with placing the surrounds/rears at a mildly elevated angles (25º and 20º deg, respectively). The other problem being that in my small room, the working distances for 2D QRD seemed too large, and I wanted to avoid potential colorations in the closest seats (1m away from the walls).

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post #3267 of 11895 Old 06-03-2013, 01:17 PM
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Originally Posted by Roger Dressler View Post

I thought about this quite a while before settling for 2D diffusors, rationalizing that the ceiling returns would help movies create a better sense of a spatial bubble for the surrounds. This is done in concert with placing the surrounds/rears at a mildly elevated angles (25º and 20º deg, respectively). The other problem being that in my small room, the working distances for 2D QRD seemed too large, and I wanted to avoid potential colorations in the closest seats (1m away from the walls).

All that, ... Plus, your implementation of said diffusors visual aesthetic, is spot on fantastic! cool.gif

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post #3268 of 11895 Old 06-04-2013, 05:58 AM
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I have a question about REW on Macbook OS-X and HDMI for doing multi-channel measurements. Any problems? Is it working for somebody? Is it working 'out of the box' or some tweaking is necessary?
Just curious about it as I am selecting a notebook...
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post #3269 of 11895 Old 06-05-2013, 04:30 AM
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It was claimed in this thread that fixing the frequency response with EQ would also fix the time behavior (modal decay, ringing). This is NOT generally true. It is only true if the response is minimum phase (or very close to MP). Here's a great article by John Mulcahy (author of REW) explaining the details:
http://www.hometheatershack.com/roomeq/wizardhelpv5/help_en-GB/html/minimumphase.html

Furthermore, even if the response is MP but varies throughout the listening area, only a single point in space will be corrected. All other points will NOT get optimized. If more than one point needs to be optimized, it's crucial to first make the response at each point as similar as possible (passive absorption, near field subs, multiple subs, SFM).
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post #3270 of 11895 Old 06-05-2013, 06:59 AM
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^^^ You can go back and forth between time and frequency domains but not if you throw away phase info in the freq domain by only looking at the magnitude plots.

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