Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How... - Page 27

Quote:

Originally Posted by dstew100 


pages 7-18 here
http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/LoudspeakersandRoomsPt3.pdf

Were sufficiently difficult to make me stop reading but should provide some insights.

Def gunna attempt to read that a couple times.

Edit: fixed link

Typical, a 33-page technical document to slog through looking for an answer.

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Originally Posted by jevansoh 

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Originally Posted by kbarnes701 

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Originally Posted by jevansoh 

However, a lot of people that follow this philosophy stop there. The fact is, all reflections are NOT bad! In fact, they are necessary! Depending on the size of your room and your level of commitment, anywhere from about 12-20ms (larger rooms up to 25ms) should have a termination of the effectively anechoic space we are creating by reducing the early reflections to -20db in gain relative to the direct sound. There should be reflections after somewhere between 12-20ms but they should be diffuse and dense and not just one or two here and there.

 

J, there's one thing I have never understood wrt to the above. I can see that some reflections can be a good thing for stereo setups because without them one will never get the sensation of a large room and so on. But why are some reflections necessary when we have 7 or 9 or even 11 channels of sound in a HT room?  Isn't any required ambience already recorded into the track and reproduced through the appropriate speakers as required?

I remember Max referencing a movie I am familiar with - Cliffhanger. At the beginning of this movie there is a helicopter scene. If you engage Audyssey DSX Wide, which attempts to simulate reflections in order to attempt to recreate a 'concert hall' space, the helicopter sounds perfect for a helicopter recorded in a large hangar. The problem is, the helicopter is actually outdoors. The additional reflections (simulated here, but would it be any different if they were real reflections?) destroy the intended effect of a helicopter flying outdoors.

I can see the benefit of having some reflections for music and for stereo - but cannot understand why the ambiance recorded into the material is not all we need when we have multiple channels for movie sound reproduction. I am only concerned with movie sound as I do not play music in my HT room. If this is regarded as OT, please PM me if you have time. Many thanks.

PS. I followed and understood all the rest of your post, so I am making progress!

Well Keith, I suppose if 100% of the content you listen to is multi-channel (5 channel or more) and the majority of that content keeps the surrounds active providing that ambiance, then you have a point and I concur that the model which we've been discussing thus far (LEDE/RFZ) is the most suitable and a model approaching NE (Non-Environment) would probably be most suitable.

In this case we'd simply suppress all the reflections to a minimum of -20db from 0ms to infinity without a termination or return.

We'd have an effectively anechoic room at this point and it would not be enjoyable to listen to 2-channel music or even movies that didn't provide ambiance/content in the surrounds, in my opinion.

Your case is a bit different. You actually DO have a dedicated 2 channel room and a dedicated room where you ONLY watch movies.

So... In your case, which I doubt we'll come across very often in this thread, I might recommend just that for you! You won't achieve a true NE room, but you can approach it, which is all we're trying to accomplish in this thread anyway...Getting people on the right path, provide the info and the tools necessary to achieve the goal, but realizing few will take it all the way.

For most folks though, they either don't have a dedicated room at all, in which case it would be pretty boring and lifeless and wouldn't work at all if, for instance, it was a living room where you hoped to have quiet conversation, or they are lucky enough to have ONE dedicated room which must serve a mixture of 2-channel and HT.

When you're listening to two channel and only have those 2 speakers and the room itself to do all the work, in my experience, it's best to account for the needs of those two channels and let the HT fall into place, especially if the ratio of music listening to movie watching approaches 50/50.

This is why there is no one right answer though. Everyone's situation, needs, and goals are different.

This is what makes it difficult if not impossible to put a nice pretty bow on this because we don't start with a neatly wrapped package.

There are different models to get different results and what works for one doesn't work for the other, which is why I hesitate to do what Nyal did and say, This should be your target. Period.

I know he means well, but I just don't believe it can be summed up that easily because of different uses for the rooms and different tastes, not to mention WAF, budget, etc.

So a more one on one approach is probably needed.

There are, however, certain things all the models have in common and only a few of which are drastically different, one of which is this talk about reflections.

Even in the industry there is a wide variance on what is "right" with Floyd Toole himself going against what has been pretty standard for decades now and basically saying there aren't bad reflections and most people prefer them.

While I don't agree, I do agree it's possible that a certain subset of folks that are only used to hearing rooms with lots of reflections and haven't truly experienced a well treated critical listening room might think they want that because they don't know anything else.

There isn't a line in the sand answer here, though, Keith.

What's right for you isn't for the next guy and this was a great question to bring up early on because it shows just how diverse we and our needs truly are.

I'm more than willing to help you achieve whatever model you decide though, to the best of my ability, and as time permits.

To sum it up though, yes, I do believe for you, you need to either decide to try it both ways (depending on how much time/patience you have) or read up on the difference between LEDE and NE and pick one, stop thinking about it, and start working towards it.

Hope this helps,

--J

Great help thanks, J. My room has quite a lot of treatment and it definitely sounds 'deader' than the sitting room next door, but the clarity and imaging is amazing since I installed the treatments. Whenever I demo it to anyone, the one thing they all say in common is "it is so clear".  I don't mind a dryer room I think - remember it is just for HT. When my mic arrives I will be able to take some measurements and see what the decay times etc really are. Thanks for all your help so far - it is truly appreciated.

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Originally Posted by jevansoh 

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Originally Posted by kbarnes701 

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Originally Posted by jevansoh 

 
I'd like to see your FR and Waterfall with and without Audyssey, Keith.


 

And you will, J, once my mic arrives and I have learned how to use REW, at least the basics. 

Although I do measure without Audyssey, to try to get the room as good as I can without MultEQ, I always make my final graphs with Audyssey and these are the ones I rely on for my ultimate judgement of the SQ. The reason is I would never listen without Audyssey, so shouldn't my 'final' graphs be those that have Audyssey engaged - that is what I will listen to.

It's important to see both. Always. You need to know what Audyssey is doing. Unfortunately, there are times where Audyssey makes certain things worse and at times even pushes drivers beyond their limits. We won't know that without both graphs.

Also, once you get into this, who knows, you may find that you no longer need Audyssey, or at least that it doesn't make "as huge of" a difference as it used to, but most likely still "better."

We just don't know enough about your room, your goals, and what you're willing to commit to making it better yet, Keith.

I suspect pretty great things for you and your room though.

I only wish you were close enough for me to meet you and hear it in person, though.

--J

Since I installed my room treatments, I do find that the difference between using the system with Audussey ON and Audyssey OFF has diminished a lot. Before, the system was unlistenable with Audyssey OFF - now it is listenable but not as good as with Audyssey ON. But the difference is definitely smaller.

I wish you were close enough for you to hear it in person too!!  Oh boy, yes. I am all alone on this - no friends are interested to any serious extent, there is no available professional help locally and the UK forums don't go into anything like the depth we are experiencing here. But we're doing OK by remote control so far... ;)

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Originally Posted by AustinJerry 

 

I am considering adding a dedicated section in the guide covering how to configure REW measurements, and how to post the results.  I'm not sure if I have it all correct now, but we can review and correct the guidelines once they are captured.

Excellent Jerry!  On page 1 of the thread I posted the HTS guidelines for REW measurements. At one stage there was talk of sticking with their guidelines for compatibility. I think we may have moved from that position though.

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Originally Posted by AustinJerry 

@ Amir

 

So am I correct in concluding that there is no hope and we should all stop generating ETC graphs?

 

And regarding your reference to the link on Whatsbestforum, yes, I have attempted to comprehend the theory that you presented in the thread, but it is over my head.  Perhaps we are moving in the direction of comprehension, but we aren't there yet. 

Remember, Jerry, you are talking to someone who argued about ETCs for page after page in another thread. And then it was discovered he didn't even know what the E stood for ;) I guess the cut and paste let him down.

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Originally Posted by jkasanic 

 

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Originally Posted by AustinJerry 

 

Thanks for the quick response.  You had me worried there for a minute.  The 0.5ms reflections are a concern but until I get my UMM-6 mic and load the proper calibration file, I'll reserve changes to simply adjusting the L/R speakers inward and modifying the toe-in to avoid the screen frame or removing the grilles (although I can't remember exactly what these foam blocks do but I recall something about leaving the grilles installed as a result?!):

 

 

 Where's Keith when you need him?  Probably went to bed early!

Time differences!  :)  I leave the grilles on on my S150s - they are pig-ugly enough without peaking under their skirt. I'm not sure it matters much - you can run a sweep with and without grilles and see if you are finding any notice difference in FR. I would doubt it would be audible.

Re stands - yes, the official M&K stands are rarer than hen's teeth. You can wall-mount the speakers using Omnimounts you know.

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Originally Posted by kbarnes701 

 

Time differences!  :)  I leave the grilles on on my S150s - they are pig-ugly enough without peaking under their skirt. I'm not sure it matters much - you can run a sweep with and without grilles and see if you are finding any notice difference in FR. I would doubt it would be audible.

 

Re stands - yes, the official M&K stands are rarer than hen's teeth. You can wall-mount the speakers using Omnimounts you know.

Thanks Keith!  The question about the grilles was regarding some early reflections (0.5ms) that showed up in my measurements and whether or not the cabinet was the source.  I suppose we'll answer this soon enough once you start measuring.

Quote:

Originally Posted by sdurani 


I would look for where pressure is at a minimum (nulls) and place my sources of pressure (subs/speakers) at those locations for cancellation. Like slicing off the top of a mountain (peak) and flipping it over into a valley (null) to get a flat landscape (high pressure meet low pressure).

Since you're using 2 subs on the front wall, from your chart it looks like placing them at 1/4 and 3/4 of room width will help deal with the 2nd width mode at 58Hz (within the subwoofer's range). But you've already placed your subs there.

Above the crossover point you're using 3 speakers on the front wall, so from your chart it looks like placing them at the 1/6, 3/6 and 5/6 points of room width will help you deal with the mode at 87Hz (might want to try lowering the crossover to 70Hz so it doesn't interfere).

This assumes that both subs will be playing the same bass (which they will be) and all three speakers will be playing the same bass (should be, most of the time, depending on how it was mixed, and other caveats). OK, so you can't cancel all the problems with placement alone, but at least it helps address a couple of the most audible ones.
Chances are you'd get smoother frequency response sitting at 1/3 and 2/3 of room width. But who wants to do that. I prefer to sit in the middle, probably sacrificing some smoothness for left-vs-right consistency in soundstage and imaging. Not having the latter would bother me more than the former (which can be addressed with treatments and EQ).

Sanjay, thank you for your input.  Your assessment is very accurate.  I placed the front subs at 1/4 and 3/4 several months ago, which indeed resulted in smoothing the 58Hz mode. 

However, placing the left and right speakers at 1/6 and 5/6 would represent a compromise that I am not quite ready to do.  I have a DSX 11.1 configuration, and have limited space for the placement of the DSX Wide speakers.  The Audyssey guidelines are to place the mains at a 30-degree angle from the MLP, and the wides at 60 degrees.  In my current configuration, the mains are at 26.5 degrees, and the wides are at 50 degrees, which is already somewhat less than ideal.  If I were to move the mains out to the 1/6 and 5/6 positions, they would be practically next to the wide speakers, thus impacting the DSX effect.  I could temporarily move the mains and take a fresh measurement, just to see the effect it would have on the 87Hz mode, which I probably will do when the USB mic arrives.  It is unfortunate that we are faced with these compromises.  Perhaps it's time to build a new listening room! 

Note that the last measurement that I took clearly shows the mode at 87Hz, although I guess it could have been worse than down 5dB.  Note also the 170Hz null associated with the ceiling height.  Based on the model, I guess I could try raising one or more of the subs 1.75 feet off the floor, but I'm not sure that raising the subs (which are crossed over at 80Hz) would address this issue.

Now that I understand the Room Mode Calculator spreadsheet better, I does seem like a useful tool.  Perhaps others in the thread will try it out as well.  Thanks again.

Quote:

Originally Posted by dstew100 


OK my brain won't stop toying with this even when I try to stop so lemme take a very wild swing into the dark at this. It's fine to point and laugh but helping me understand is preferable. First off I will point out what I know is blatantly obviously missing from this thought process I'm about to lay out... It does not take into account ear height which clearly matters, I'm just not understanding how to account for it.

-The metric system is better then what I was taught but I did it in feet and inches anyway. I think we should poll on this topic.
-Your actual height is 10'
-The calculator assumes perfectly stiff and reflective floor/ceiling/walls, I assumed yours are not. (like the paper does in one example)
-If your room's height were 12'8" there would be a 2nd order mode at 89Hz (wow I made the tool have your null). Your "Acoustical Height" is 12'8"
-WTF, this thing is not only using U.S. customary units, it's rounding off to the nearest quarter of the foot then displaying decimal feet????
-The paper claims putting the speaker at the distance laid out by the mode calculator will make that mode not be energized
-If your floor were perfectly stiff and the added acoustical height is completely caused by the ceiling, then the correct sub height would be 3' (well with the inaccuracies and rounding maybe 3'2.5") from the floor to tame the 2nd room mode in the height dimension
-If your ceiling were perfectly stiff and reflective and the added acoustical height were entirely from the floor, then the correct sub height would be <1 foot from the floor to tame the 2nd room mode in the height dimension.
Conclusion
-Try several heights from it's current height up to 3'3" measuring along the way, if you're on a concrete slab, start at 3'3" and work down.
-Temporarily raising it up on stuff for a measurement shouldn't be that bad, finding something permanent you can live with ascetically is a different story.

OKOK, point and laugh, or help if you can help me understand.

Read my response to Sanjay.  Now that I understand the Room Mode Calculator a little better, I understand that placing a speaker at a null point is the objective.  As Sanjay observed, the sub placement at 1/4 and 3/4 addresses the 58Hz mode.  However, I don't come up with the same calculations as you do for the amount to raise the subwoofer.  If you look at the modes associated with room height, they are 113Hz, 170Hz, and 226Hz.  Of the three, only 170Hz seems to be an issue in my room, based on the published measurement.  If you look on the height graph, the speaker should be placed at a height of 1.75 feet to address the 170Hz mode, not 3.25 feet as you suggest.  However, I am not sure that the sub would help cancel a mode as high as 170Hz, but it may be worth testing.

Here's a plot of my room.  I'm not quite following the how-to on the analysis.  My only real flexibilty is with sub placement but even that's limited due to WAF.  I'm still planning to do another sub crawl when my USB mic arrives but any thoughts based on this plot?

^^ The first step would be to run fresh frequency response measurements when you get the USB mic.  Then, analyzing these measurements, we would identify dips in the response that are associated with the room modes, I.e. 40, 81, and 121Hz for the width, and 31, 62, and 93Hz for the length.  One or more of these frequencies might be an issue in your room.  After we determine that, we would look at your speaker positions to see if we could move any of them into a null associated with a problem frequency.  So, for example, in my room there was an issue at 58Hz.  I was able to move my two subs to the 1/4 and 3/4 positions along the front wall, which are the nulls associated with the 58Hz room mode.  The result was that the null at 58Hz all but disappeared.

Of course, the issue is whether you are lucky enough to be able to find speaker positions that address a room mode, and are acceptable from other perspectives, like aesthetics or the WAF.  Make sense?

Quote:

Originally Posted by JChin 


Hi Jerry, is there a recommended square size and how thick of R-30 to get?

It comes in a roll, and I believe it is ~9 inches thick.  A roll allows you to cut a piece that fits the area you are testing.  You can layer two pieces for an 18" thik test as well.  Be careful with the pink fluffy when you are handling it.  Try not to inhale any particles--it is nasty stuff.  Here is a picture of the R30 when I was testing how to treat my back wall:

Quote:

Originally Posted by JChin 


Where do I find this Axial Standing Waves graph in REW?

The Room Mode Calculator can be found here:  http://www.harman.com/EN-US/OurCompany/Innovation/Documents/Calculators/Room%20Mode%20Calculator.xls

The second screenshot in my post is just an Excel spreadsheet that I created.

Quote:

Originally Posted by AustinJerry 

^^ The first step would be to run fresh frequency response measurements when you get the USB mic.  Then, analyzing these measurements, we would identify dips in the response that are associated with the room modes, I.e. 40, 81, and 121Hz for the width, and 31, 62, and 93Hz for the length.  One or more of these frequencies might be an issue in your room.  After we determine that, we would look at your speaker positions to see if we could move any of them into a null associated with a problem frequency.  So, for example, in my room there was an issue at 58Hz.  I was able to move my two subs to the 1/4 and 3/4 positions along the front wall, which are the nulls associated with the 58Hz room mode.  The result was that the null at 58Hz all but disappeared.

 

Of course, the issue is whether you are lucky enough to be able to find speaker positions that address a room mode, and are acceptable from other perspectives, like aesthetics or the WAF.  Make sense?

Makes sense...thanks for spelling it out.  Now where's my e-mail from Herb!

Quote:

Originally Posted by sdurani 


Or turn your's 90 degrees.

Sigh, if only I had that choice, Sanjay.  One side of the length wall consists of a brick fireplace flanked by a window and a glass french door.  The other side is really only a half-wall opening out to the entryway of my home.  Obviously not a dedicated home theater, but I make do with what I have.