Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 25 - AVS Forum
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post #721 of 10744 Old 01-28-2013, 01:21 PM
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Yes - experiment with the sub distance while measuring the effect. The sub 'distance' is really a delay, so changing the delay changes the phase relationship between the mains and the sub. There may be a delay setting that provides a better integration of the subs + mains. In fact I can't recall anyone who has tried it who didn't find an improvement, except Jeff (pepar). It made a substantial difference for me.  This is one of Audyssey's weaknesses which we can overcome with independent measuring - Audyssey measures the speakers separately, and the sub(s) separately but never measures the combined result of the mains plus subs together.
Good point. Here is a recent article on wrote on this topic, together with a bunch of measurements on improvements you can get by optimizing the subwoofer and crossover parameters: http://www.madronadigital.com/Library/Computer%20Optimization%20of%20Acoustics.html. Per my conclusion in the paper, you really want computer automation for this as the combinations when you include multiple subs and seating position become sky high. Sans that, if you have a ton of time on your hands smile.gif, you can accomplish some of it manually.

Here is a quick graph from the paper to give you a sense of how much better you can do:

JBL-Synthesis-Main-to-Subwoofer-Optimizer-room4.png

There are many other actual before/after measurements in the paper.

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post #722 of 10744 Old 01-28-2013, 01:32 PM
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What exactly do you mean by experimenting with the sub/mains phase adjustment?  Is this just modifying the distance setting for the sub in Audyssey or do you also mean experimenting with the LCR's?  Audyssey calculated the distance of the sub to approx. 18' 6" while the actual distance is somewhere between 13'-14'.  I know this isn't atypical for Audyssey so I didn't give it much thought but in a different room with the same sub, my DHC-80.3 pretty much pegged the sub distance to the physical distance.  

 

Yes - experiment with the sub distance while measuring the effect. The sub 'distance' is really a delay, so changing the delay changes the phase relationship between the mains and the sub. There may be a delay setting that provides a better integration of the subs + mains. In fact I can't recall anyone who has tried it who didn't find an improvement, except Jeff (pepar). It made a substantial difference for me.  This is one of Audyssey's weaknesses which we can overcome with independent measuring - Audyssey measures the speakers separately, and the sub(s) separately but never measures the combined result of the mains plus subs together.

 

Thanks Keith!  I'm assuming I would start with larger offsets in both directions to see if there's a benefit in one or the other direction (not sure what I would do if both resulted in an improvement if that's even possible?) and then start to narrow up my increments working back towards the distance/delay that Audyssey set originally?  Is it correct to assume that I would want to try and find the optimal point that is closest to the delay that Audyssey set or might I find something better with a larger offset from this value?

 

Given the measurements I provided (18' 6" in Audyssey and let's say 13' 6" actual), what do you think would be reasonable starting points around the Audyssey value (e.g. 14' and 22')?  I'm assuming the only threshold at play here is not to go lower than the actual physical distance measurement?

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post #723 of 10744 Old 01-28-2013, 02:11 PM
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Given the measurements I provided (18' 6" in Audyssey and let's say 13' 6" actual), what do you think would be reasonable starting points around the Audyssey value (e.g. 14' and 22')?  I'm assuming the only threshold at play here is not to go lower than the actual physical distance measurement?

As a point of reference, I ended up with a smaller distance for both of my sub channels, but not a very large amount. 1.4 ft and 1ft for the two channels, respectively.

Just pick a starting vale, say 14', and measure. Then try 13', and measure. If 13' is worse, go the other direction, say 15', and measure. By trial and error, you will find a value for the distance that produces the smoothest result. It may be a significant improvement, or a subtle improvement. Everyone's case is a different one. The process is tedious, but can yield good results.
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post #724 of 10744 Old 01-28-2013, 08:29 PM
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I was wondering if you played around at all with generating waterfalls as this is completely new for me and I'm just getting my arms around understanding FR curves?  I have been reading a ton lately though and I'm beginning to understand the significance of the time domain.

 

Here are some waterfalls:

 

Left, no Audyssey

 

 

Right, No Audyssey

 

 

 

Left, with Audyssey

 

 

Right, with Audyssey

 

 

All exhibit problematic ringing in the 30-50Hz range.

 

ETC for left channel with Audyssey

 

 

ETC for right channel with Audyssey

 

 

The first three reflection points (common to both graphs) are:

 

 

Just taking a guess, the second reflection (18.7 ft) could be caused by the back wall (blue line).  The third reflection (24.6 ft) could be caused by the signal from the left speaker bouncing off the right wall (red line).  The first reflection (9.8 ft) could be the ceiling.  The reflections are pretty serious, down only -5dB to -7dB.  Recall, the general objective is to have all reflections below the -20dB level.  To determine for sure what is causing the reflections, you need to conduct the "string test" (familiar with that?).

 

If I am correct, this would suggest a requirement for full-band acoustic treatments on the side walls at the first reflection points (always a must), and the same type of treatments for the back wall (always a problem area).  BTW, since WAF is an issue in your listening room, these products are reasonably priced and, if ordered in a neutral color, might pass the WAF test.

 

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post #725 of 10744 Old 01-28-2013, 10:11 PM
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Originally Posted by AustinJerry View Post

Here are some waterfalls:

Left, no Audyssey




Right, No Audyssey





Left, with Audyssey




Right, with Audyssey




All exhibit problematic ringing in the 30-50Hz range.

ETC for left channel with Audyssey




ETC for right channel with Audyssey




The first three reflection points (common to both graphs) are:




Just taking a guess, the second reflection (18.7 ft) could be caused by the back wall (blue line).  The third reflection (24.6 ft) could be caused by the signal from the left speaker bouncing off the right wall (red line).  The first reflection (9.8 ft) could be the ceiling.  The reflections are pretty serious, down only -5dB to -7dB.  Recall, the general objective is to have all reflections below the -20dB level.  To determine for sure what is causing the reflections, you need to conduct the "string test" (familiar with that?).

If I am correct, this would suggest a requirement for full-band acoustic treatments on the side walls at the first reflection points (always a must), and the same type of treatments for the back wall (always a problem area).  BTW, since WAF is an issue in your listening room, these products are reasonably priced and, if ordered in a neutral color, might pass the WAF test.



does anyone know if psychoacoustic considerations are important when considering addressing first reflections generated from speakers placed from the opposite side wall that create the reflections at the LP? In other words left speaker reflecting off right side wall to LP. I thought I read somewhere that getting a first reflection in the opposite side does not have the same implications for sound quality. BTW great thread for AVS!

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post #726 of 10744 Old 01-29-2013, 03:51 AM - Thread Starter
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I was wondering if you played around at all with generating waterfalls as this is completely new for me and I'm just getting my arms around understanding FR curves?  I have been reading a ton lately though and I'm beginning to understand the significance of the time domain.

Here are some waterfalls:

Left, no Audyssey




Right, No Audyssey





Left, with Audyssey




Right, with Audyssey




All exhibit problematic ringing in the 30-50Hz range.

ETC for left channel with Audyssey




ETC for right channel with Audyssey




The first three reflection points (common to both graphs) are:




Just taking a guess, the second reflection (18.7 ft) could be caused by the back wall (blue line).  The third reflection (24.6 ft) could be caused by the signal from the left speaker bouncing off the right wall (red line).  The first reflection (9.8 ft) could be the ceiling.  The reflections are pretty serious, down only -5dB to -7dB.  Recall, the general objective is to have all reflections below the -20dB level.  To determine for sure what is causing the reflections, you need to conduct the "string test" (familiar with that?).

If I am correct, this would suggest a requirement for full-band acoustic treatments on the side walls at the first reflection points (always a must), and the same type of treatments for the back wall (always a problem area).  BTW, since WAF is an issue in your listening room, these products are reasonably priced and, if ordered in a neutral color, might pass the WAF test.



Hey Jerry and jkasanic,

You've offered some very good advice here.

I need to clarify a few things and praise you once again.

First, thank you so much for creating and displaying these graphs the way you did. They are at the proper scale and most importantly, they are large enough to see without having to zoom in my whole browser window and/or download the picture and manipulate it manually to be able to read the numbers.

I would appreciate it so very much if everyone posting graphs would use Jerry's examples here as all but one little thing is absolutely perfect. The right scale, the right amount of data, smoothing, and size is all perfect! I just don't have the time to manually download things (especially as I assume shortly there will be a lot more posts to analyze) and rescale them.

However, on the FR graphs you are using a 10db scale and that really makes things look a lot better than they are and makes it a lot more difficult for me to see. Plus, I may forget that it's not the normal 5db I'm used to looking at. wink.gif You have it set to show in 5db vertical increments on the waterfall and etc but 10db on the FR and we need consistency.

Now, with that being said, I just read about 1000 posts in 20 different threads and it's 6:30 A.M. here, so bare with me, but I'm not so sure about what you've stated re the ETC measurements... Don't recall seeing enough data in the last few posts (maybe in another post a few pages back??) for you to come up with some things, so I want to take a moment to explain exactly what he should be looking at and how to calculate to find what's causing the specular reflections.

We see the first reflection at about .5ms which is almost certainly from the speaker cabinet itself. Depending on how the mic is mounted/placed it could even be from that, but I suspect diffraction effects or the speaker grill, depending on how it's designed (take more measurements without the grills), etc. This does need to be addressed, however.

Second, we see a very high gain specular reflection way too early at around 3ms. The way to figure where this is coming from is to multiply 1.13 times 3ms in this case. (Always multiply the timing of the reflection by 1.13) and ADD that to the "actual" distance between the mic and the acoustic center of the speaker. If the speaker uses a D'Appolito array then you can use the tweeter. That's how long the path of this reflection is traveling in total. You can then mark on a tape measure or cut a string to this length (adding a few inches at each end to be able to tie the string, but making sure the marks on the string are at the exact added distance to the actual distance between mic and speaker in the end) and pull the string taut in ALL directions until you find all the surfaces the string touches. Then, one by one, add an absorber or large piece of insulation to that area and remeasure until the reflection is at least -20db in gain.

Do this for all reflections out to about 20ms.

In a lot of conversations we hear that either all reflections are bad or in some alternative points of view we hear they are helpful and needed.

My philosophy (based on acoustical models that have been around for decades and folks much smarter and with much more experience than me all but unanimously agreeing) is that "high gain" and "early" reflections aren't good and in fact will cause smearing and not give you some of the main psycho acoustic benefits we are striving for in our small acoustical spaces, such as making them sound like larger rooms!

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.

This is difficult to achieve and if you go around filling the room with tons of absorption it could be almost impossible.

There can be too much of a good thing. So, test each spot (mirrors and the "mirror trick" are USELESS for this very reason) relating to the spike in the ETC and ONLY place absorption where it is absolutely necessary to tame that spike.

There are other methods that don't require any use of absorption in the specular region such as reflection/deflection/diffusion but those are a bit more advanced topics we'll touch on later.

As far as the frequency response, it is true you have a null/room mode at 40hz. Due to the wavelength (very long) at this frequency, moving "just a little" to the left/right isn't going to do anything and will just make other things worse. Symmetry is very important.

If you had two subs though, we could effectively cancel this null through placement.

Invest in another sub. smile.gif

If you cannot do that, then through placement of the sub and tweaking of the phase (distance controls, measure in one foot increments starting 5-6' below what Audyssey found and going to 5-6' above) you will still be able (most likely) to smooth things out a bit more.

Make sure to do all this with Audyssey OFF.

As for the waterfalls, it looks like unfortunately Audyssey made things worse in the very low frequencies. Luckily, in the range from 20-300hz (some noise is showing and you might want to raise the bottom limit to 42 or 43db just to make it easier to see the "truth") you don't have a lot of problems that will be extremely difficult to fix. The biggest one is of course between 30-40hz and regular velocity based (pink fluffy) absorption isn't going to work well at that frequency, so placement, phase, and EQ are the best bet for that one unless you don't mind spending some money and getting some pressure based tuned traps for 30-40hz.

Audyssey, by taming the peak at 30hz helped cut down the ringing a bit, but it's still too much and you need bass traps for the rest. 40hz was made worse by it boosting the null in trying to fix it. This is where another sub and/or placement could help a ton.

The ETC's for the L and R channels (you did measure only one at a time, right? Test sweep tones coming only from the L channel for the measurement marked L, right?) are very similar. This is a good thing. The example I gave for the first reflection (diffraction most likely) and the second one at 3ms applies to all the others that are peaking above -20db as well. Just multiply 1.13 by the ms of the reflection and add it to the physical distance between mic/speaker then pull a string taut in all directions, placing insulation/absorption at each spot one at a time, measuring in between, until you tame the peak. You have to do this for all seating positions that you care about and you have to do this separately for the L and R channels though, ok?

So... You have some work to do. I can't wait to see some results! wink.gif

I'm sure I've missed a few things and hope I haven't confused you but we now have a dialog going so feel free to ask more specific questions and I'll be more than happy to help you.

Hope this helps,

--J
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post #727 of 10744 Old 01-29-2013, 04:04 AM - Thread Starter
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Here are some waterfalls:

Left, no Audyssey




Right, No Audyssey





Left, with Audyssey




Right, with Audyssey




All exhibit problematic ringing in the 30-50Hz range.

ETC for left channel with Audyssey




ETC for right channel with Audyssey




The first three reflection points (common to both graphs) are:




Just taking a guess, the second reflection (18.7 ft) could be caused by the back wall (blue line).  The third reflection (24.6 ft) could be caused by the signal from the left speaker bouncing off the right wall (red line).  The first reflection (9.8 ft) could be the ceiling.  The reflections are pretty serious, down only -5dB to -7dB.  Recall, the general objective is to have all reflections below the -20dB level.  To determine for sure what is causing the reflections, you need to conduct the "string test" (familiar with that?).

If I am correct, this would suggest a requirement for full-band acoustic treatments on the side walls at the first reflection points (always a must), and the same type of treatments for the back wall (always a problem area).  BTW, since WAF is an issue in your listening room, these products are reasonably priced and, if ordered in a neutral color, might pass the WAF test.



does anyone know if psychoacoustic considerations are important when considering addressing first reflections generated from speakers placed from the opposite side wall that create the reflections at the LP? In other words left speaker reflecting off right side wall to LP. I thought I read somewhere that getting a first reflection in the opposite side does not have the same implications for sound quality. BTW great thread for AVS!

They most definitely are!

In fact, it's the biggest reason why we want to tame high energy early reflections.

When you have high gain early specular reflections it will smear the sound.

If you go and get rid of ALL the reflections though, your room will sound dry or dead and lifeless. In fact, getting rid of (or taming all reflections down past -20db) all the reflections would make your room effectively anechoic and I can assure you that you don't want that.

There has to be a happy medium. You definitely want symmetry in your room and your measurements and you want a combination of an effectively anechoic "period" of time terminated by around 20-25ms (a range of 12ms to 25ms is fine depending on how much of the effect you want, how big the room is, and how much time/effort/money you're willing to spend) with a strong reflection about 12db in gain relative to the 0db starting point at 0ms is the goal followed by steadily decaying diffuse reflections past that.

That will cause a psychoacoustic effect that makes your room seem spacious and much larger than it is plus your system will then sound very clear.

Just as in the modal frequencies you don't want long decaying frequencies as the bass will sound "muddy" in the specular region (above modal, which is what ETC measures) you don't want to muddy up the sound with sparse high gain early reflections

As you may continue to research and learn there are some detractors from this approach and the most famous one is Floyd Toole.

However, both for production and reproduction in critical listening rooms it is pretty widely accepted that the methods I'm teaching here, which lean towards (approaches) a LEDE room (which, folks, does NOT mean live end dead end) will make your room sonically, well.... sound! wink.gif

There are several different approaches to designing rooms. I can't say definitively that there is a "wrong" way or a "right" way but I can say what I'm teaching here is proven and a lot of the principals for the different listening models are the same regarding similar decay times throughout the audible range, symmetry, not making the room too dead by using too much velocity based absorption (insulation) and having a relatively flat frequency response.

It seems as though the main differences in room models all comes down to reflections, whether they should exist, where they should exist, at what relative level, etc.

A lot will depend on your individual tastes, your room, your equipment, and your goals, but I honestly cannot see anyone going "wrong" with what we're trying to accomplish here.

I hope this helps and feel free to ask some more specific questions which I'll answer to the best of my ability.

Thanks,

--J

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post #728 of 10744 Old 01-29-2013, 04:20 AM - Thread Starter
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Here is what we would like to see for your room (multiple subs, no smoothing, Audyssey on).  We'll get there!



If only.smile.gif Not in my room. Short of stacking subs from floor to ceiling, (I've thought about it biggrin.gif)I will never not have a dip (null) at about 90hz from the ceiling bounce. And I have 4 identical subs placed to optimize the room response. We may want to think about using a sample that is this ruler flat as I would suggest that this graph might set unrealistic expectations. It might work in a few rooms, but not all, regardless of the number of subs.

This measurement looks great! There is no doubt about that.

I think it's always best to reach for the stars. The higher you set your goals (within reason, of course) and the more you work on your room, the more you will "approach" your goals and the better the results.

With that being said, if you look at the graph on a vertical scale in 5db increments it won't look as good.

If you look at it with Audyssey off and always totally unsmoothed, it won't look as good.

Plus, remember, the FR is but one measurement and in the modal region, what is far more important is to have even decay rates that don't vary too much from the specular region (higher frequencies).

We can only tell that from a waterfall.

With that being said, I think a more realistic target should be +/- 3db. Any time I set up a system/room that's what I strive for. In different rooms, with different equipment, and different budgets (read smaller) this isn't always possible, but most of us that are reading this thread have time to devote to this and it is our hobby/passion so I absolutely believe in keeping the goals set high, but attainable.

With enough EQ and on the proper scale almost any FR can be made to "appear" totally flat, but the real test is to see the waterfall and look at the decay times and any potential ringing.

I'd much rather have a FR that is +/- 5db for instance, yet overall even decay rates that are similar to the higher frequencies than a room that appears to be totally flat but has awful ringing. It's all in how you look at things and whether or not you want pretty graphs or a great sounding room.

I prefer both! biggrin.gif

BTW, you can absolutely get rid of the effects of that null, at least in one position, pretty easily by simply raising a subwoofer off the ground.

I had to do the same thing for a null in my own room and decided to put one sub centered on the back wall on top of the riser and now you don't even see evidence of the null in the MLP. It required no further EQ or trapping of any kind as the riser is a bass trap in itself and the sub is now 15" off the ground!

Placement is key. You have some very capable subs, my friend. I've seen your room and your equipment and you should be proud.

Before EQ'ing that 90hz null away (or trying) with your new toy coming soon, I'd seriously consider trying to raise a sub off the ground, first.

--J

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post #729 of 10744 Old 01-29-2013, 04:25 AM - Thread Starter
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Ok, I got my new cable and can confirm that when using my laptop and REW to generate the test tones, my AVR is only outputting to the center + sub in PLIIx mode and in stereo with my Y adapter cable it's outputting to the L/R + sub.  Suffice it to say I think I had a blonde moment on why my previous setup was not outputting correctly.  I was expecting to be able to output the mono signal to the L and R channels independently without disconnecting the cable at the AVR.

Is there any interest in seeing a comparison between OM and the latest beta of REW using the OM Mic and .omm calibration file?  If so, any particular measurement as I have everything setup at the moment?

EDIT:  @AJ, I think maybe the differences I was seeing between the guide and my REW screens is just a software revision difference.  I was able to match everything up once I got the test tones sorted.  Here's a screen grab of my preferences:



Looking at your setup screen, I'm confused. Isn't the OmniMic a USB mic, and shouldn't it be configured with ASIO? I don't know, I'm just asking.

Just to make sure everything is working OK, why don't you take a sweep measurement 20-20kHz, and post the results with 1/6 smoothing.

Remember, ASIO is ONLY for HDMI connections.

Otherwise, use Java and there is no need for ASIO.

The USB mic is the INPUT device. ASIO has to do with the OUTPUT device and is only if you use HDMI.

Using USB and HDMI is not exclusive. You can use a USB Mic (with Java drivers) and still hook up the output the old way. If doing this, you also don't need an external sound card because you won't be using full-duplex so there is still nothing to buy but the mic itself.

I know this may be cleared up for you two by now already, but I just want to make certain everyone else (and future readers) understand this.

Thanks,

--J

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post #730 of 10744 Old 01-29-2013, 04:30 AM - Thread Starter
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Ok. After many tries it now recognized my Omnimic and HDMI output. Must now experiment. Unquote

Quote: You may not need another mic then Theresa - the ver 2 of OM has a cal file that REW can use. Unquote

Thank you, that is good news.

You (in particular) might want to consider a UMM-6 mic from CSL as it comes with calibration files for more than just one mic orientation.

I strongly agree with this for you, Theresa. wink.gif

Just remember, if for now you'll be using the Omnimic for testing and to become familiar with REW, that's perfectly fine, but if you are going to use the CAL file, you need to point your mic at 0 degrees, straight towards your center channel speaker from your MLP. Do NOT point it up towards the ceiling with the CAL file loaded as it was only created for 0 degrees.

If you end up becoming a convert and you want absolute measurements instead of just relative measurements and also want some nice equipment to use with testing your custom built speakers, I STRONGLY recommend the UMM-6 mic.

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post #731 of 10744 Old 01-29-2013, 04:35 AM - Thread Starter
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A sweep of the center channel using Omnimic:


The dips between 90-100Hz and 300-400Hz probably need room treatment to manage them. The 90-100Hz dip looks like a crossover problem but it's not, it stays there regardless how the crossover is set.

Is this unsmoothed?

Is this with or without the subs, too?

What is the crossover set to for this measurement?

The good news is, if this is without sub, where the problems exist, they are easy to fix with inexpensive velocity based absorption. You are a perfect candidate for some SuperChunk style corner traps made from inexpensive R30 insulation and for under $100 and about an hour for each of the 4 corners in your room (yes, there are actually 12 corners, but you have to start somewhere...) I bet these particular problems would be all but gone.

Is this with or without Audyssey?

Could you import the impulse in REW and then generate some graphs from that or at least post the mdat file?? It'd make it a whole lot easier for me to read and offer suggestions, if you're looking for any. wink.gif

--J

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post #732 of 10744 Old 01-29-2013, 04:38 AM - Thread Starter
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WOOT!  Just got an email from Herb - my UMM-6 has been despatched. US Mail - usually takes at least a week...

I can't believe this!!! Ahhhhhhhhh! I was one of the first to find out about this, started the thread, but due to timing don't think I made it in this batch because I haven't received any info!

You all are gonna have your mics before me! mad.gif

Oh well, such is life I suppose.

Wonder if that Mini DSP is still available from Audioguy?? Is it?

I obviously have a calibrated setup but in order to troubleshoot and be on the same page as everyone else I do want to own both of these mics.

If anyone would like to trade places in line, lol, let me know. wink.gif

--J

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Just remember, if for now you'll be using the Omnimic for testing and to become familiar with REW, that's perfectly fine, but if you are going to use the CAL file, you need to point your mic at 0 degrees, straight towards your center channel speaker from your MLP. Do NOT point it up towards the ceiling with the CAL file loaded as it was only created for 0 degrees.

If you end up becoming a convert and you want absolute measurements instead of just relative measurements and also want some nice equipment to use with testing your custom built speakers, I STRONGLY recommend the UMM-6 mic.

--J

Hi Jason,

I gave a description for a workaround in Post #391 on how to maually modify the cal file (txt extention) to convert it from on-axis to grazing incidence.

Care to comment on it? Thanks in advance.
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Here is the response on HTS from John to my question I posted earlier today.

'You don't need to match input and output when using a USB mic. Do the tests with the test signal at about 75 dB at the listening/measuring position.'

So if you have the USB mic you don't have to level match the IN/OUT, which is good since I would have blown something if I had to get that to match biggrin.gif

Now I have to wait for another quiet moment in the house to try again.

So I guess Jerry for your guide, the matching piece does not seem to apply for the USB mic, unless I am misunderstanding John at HTS.

I guess J do you concur?

The truth is, I don't yet have a USB mic! tongue.gif I'm waiting just like everyone else.

However, John would know! He's the author of REW! So I'd go with whatever he says. wink.gif

Sorry I wasn't much help here. I honestly would've tried to calibrate it/set the in/out levels like I have done with every other mic I've ever used if not for reading this post and have to admit I don't fully understand the implications of "not" doing this with a USB mic, but until I get one in hand I just can't test it or figure it out.

I'd love a bit more explanation myself on the matter. Would love to know the "why" behind this and what, if anything, it changes/alters by not doing this with the USB mics and why it is not necessary and whether or not it is not only unnecessary but also suggested against doing it or doesn't matter either way??

John, are you there? wink.gif

--J

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I agree with Keith.  I probably will never understand half of the audio theory that I see on this site, as well as others like HomeTheaterShack.  I have always hoped for contributions from thread participants who have the patience to develop general recommendations that I can apply to my modest listening room.  It is in this spirit that I authored the simplistic REW guide in this thread--it is certainly not a very advanced guide, but it should provide assistance to the casual REW user who just wants to get things working.

Yep - that is me to a T also, Jerry. I want to get the best I can get in my room, but there is a limit on what I am prepared to try to learn. There is just NFW I am going to read a dozen text books, but I am more than prepared to learn from the  experience of other members and also from the distilled experience of the true experts like J, Nyal etc.

I love you, Keith. wink.gif

Let's revisit this NFW statement regarding reading some books a year from now...Maybe 6 months even, lol!

I'll teach you everything I know if you wish, but if you are truly passionate or become passionate about this, especially once you realize that you're not going to be able to go much further in gear purchases due to the quality of gear you already have and especially once you realize truly just how much of a role the room (by hearing the differences for yourself, in your own room, not just understanding on an intellectual level) plays in your ultimate enjoyment with your system, I can absolutely see both you and Jerry deciding to really get into this, just as I did several years ago and start reading the texts for yourself and learning at your own pace.

We'll see.

--J

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post #736 of 10744 Old 01-29-2013, 04:56 AM - Thread Starter
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However, I want to state it one more time.  The purpose of this thread is to simplify REW by using USB mics and HDMI connections.  There are a number of other possible ways to configure REW, including the "legacy" way that I have been using for several years, but we cannot develop procedures for every flavor in this thread.  
+1. We have our hands full with that alone. Of course, as you say, there is nothing to stop anyone posting their REW graphs for comment and analysis later, once we are all up and running, regardless of whatever REW setup method they employ.

While I started the thread with the initial intent of catering to those users who wanted a setup approaching plug-n-play for the input side without needing a whole lot of other equipment and to explore the new opportunities in REW to use HDMI for output, the real goal is of course analyzing and improving our rooms and soon, that's the direction in which I expect most of the discussions to head.

With that being said, as long as we're not offering tech support for all kinds of setup questions not related to the USB mics and/or HDMI output (the reason being there are already tons of threads for this over several different forums covering this ad nauseam) so we can keep the thread focused as much as possible on improving our listening environments and overall experience, I welcome all the graphs users of the "old way" wish to post and will offer all the help I can to all users no matter the physical connection, assuming that part is already done.

Hope this clears up my intent at least. However, it's everyone's thread and you may proceed how you see fit, of course.

--J

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Here is what we would like to see for your room (multiple subs, no smoothing, Audyssey on).  We'll get there!



If only.smile.gif Not in my room. Short of stacking subs from floor to ceiling, (I've thought about it biggrin.gif )I will never not have a dip (null) at about 90hz from the ceiling bounce. And I have 4 identical subs placed to optimize the room response. We may want to think about using a sample that is this ruler flat as I would suggest that this graph might set unrealistic expectations. It might work in a few rooms, but not all, regardless of the number of subs.

While a ruler flat response is nice to aim for, it isn't really necessary. What matters is what can actually be heard and AIUI there is much evidence to suggest that 'flat' to +/- 3dB will give you more or less the same audible experience as perfectly flat.

Here's mine for example - it doesn't look nearly as good as Jerry's, but it probably sounds very similar in real life. I think we can obsess too much wink.gif




I do believe goals should be set.

I think the goal should be +/- 5db without EQ and +/- 3db with EQ. Unsmoothed, of course. This pertains to the bass frequencies only.

I think the standard +/- 3db for the specular region is fine as a goal and with EQ is mostly achievable, but make no mistake, one of my major personal goals for this thread and every system I set up is to achieve these goals as closely as possible WITHOUT EQ.

There are many fine systems both in the production and reproduction world that would be honored to achieve a +/- 3db unsmoothed, un-eq'd room. It's hard to do, in some rooms more than others, but absolutely CAN happen.

I've actually given this a lot of thought well before it just came up in this post.

While the goals need to be attainable they also need to be specific and have reason.

If met, they need to show that considerable attention and effort was made to the system as a whole to attain the goal set forth in the beginning and I think these figures will accomplish all of the above.

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

Yours too, Audioguy.

We can always tweak the goals to individual's tastes, rooms, and budget.

Also, a lot of folks, myself included, set a house curve with a rising bass response similar to what you'd see using Dynamic EQ (I don't have that on my Denon 5805CI but haven't found anything that I consider a true "upgrade" from it other than the Denon AVP which is out of my budget for now) but it's important to start flat to know what you can accomplish and what you have to work with, of course.

There's nothing wrong with adding a little spice or flavor as long as you start with reference or as close as you can get and hopefully we'll all get a little closer with REW's assistance.

--J

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post #738 of 10744 Old 01-29-2013, 05:17 AM - Thread Starter
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Here is what we would like to see for your room (multiple subs, no smoothing, Audyssey on).  We'll get there!



If only.smile.gif Not in my room. Short of stacking subs from floor to ceiling, (I've thought about it biggrin.gif )I will never not have a dip (null) at about 90hz from the ceiling bounce. And I have 4 identical subs placed to optimize the room response. We may want to think about using a sample that is this ruler flat as I would suggest that this graph might set unrealistic expectations. It might work in a few rooms, but not all, regardless of the number of subs.

While a ruler flat response is nice to aim for, it isn't really necessary. What matters is what can actually be heard and AIUI there is much evidence to suggest that 'flat' to +/- 3dB will give you more or less the same audible experience as perfectly flat.

Here's mine for example - it doesn't look nearly as good as Jerry's, but it probably sounds very similar in real life. I think we can obsess too much wink.gif




Guys, thanks for the feedback thus far on my measurements and I look forward to improving my results (hell, I'd take Jerry's curve WITH some smoothing!).  I should have my UMM-6 mic later this week or early next week at the latest.  I will redo the measurements with my avr and mic calibrated in REW as well as perform another sub crawl.  In the meantime, you might recall that I did post some results of a crawl using OM in the Audyssey thread here.

The room dimensions are as follows:

18' 3" long on right side and 17' 1/4" on left x 14' 3" wide x 8' 8" high with two door size openings on the right side of the room for the stairway at bottom right and access to the unfinished portion near the top right).  LCR's are MKSound S150's, mids are Speakercraft AIM Wide Ones and rears are Speakercraft AIM8 Ones.  The subwoofer is an older Infinity SSW-212 300W dual 12" woofers that is right corner loaded behind the false wall.  I just added the LCR's and was planning to upgrade the surrounds and subs as (time and money) permits.  As you can see from the pics below, this is not a dedicated theater space.  MLP is approx. 13' from the false wall.  Also, I can add surround speaker locations if anyone thinks that's relevant (guessing not at this point):








I know it's hard to tell because I only have a full range graph with the OM measurement but would you categorize my results as "consistent" between OM and REW based on these two graphs (full range, 1/24th smoothing applied) of sub only with no Audyssey (and offset added to REW graph to adjust output at 20Hz to be approx. 75 dB to match OM results since mic calibration was not performed during my REW measurements):







I think it's fairly consistent given the fact that 2 setups were involved but I was curious what others might think?  The OM mic is going back today so I'll be a dedicated REW user from this point forward.

While overall they look somewhat consistent, are you absolutely sure they are both smoothed the same?

It appears the OM measurement might be smoothed at 1/24th yet the REW measurement looks unsmoothed.

It could just be me, but I studied both images for a bit and the vertical scale is the same (pretty close) as far as the space/lines in between each 5db increment yet the REW graph shows +/- 5db MORE variation than the OM graph which tends to show they are not to the same scale re smoothing.

Either way, I wouldn't worry about it. I doubt you got the mic in the exact same position, on the same day, and you are using two different systems, etc.

REW is much more powerful and a lot cheaper, so I wouldn't worry about it going forward too much. Just curious re the absolute scale/smoothing between graphs.

--J

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post #739 of 10744 Old 01-29-2013, 05:22 AM - Thread Starter
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While a ruler flat response is nice to aim for, it isn't really necessary. What matters is what can actually be heard and AIUI there is much evidence to suggest that 'flat' to +/- 3dB will give you more or less the same audible experience as perfectly flat.

Here's mine for example - it doesn't look nearly as good as Jerry's, but it probably sounds very similar in real life. I think we can obsess too much wink.gif




Is that 1/12th smoothing, Keith? Pretty darned good if we 'settled' for this in the 15 to 200 Hz range (or should I say 5 Hz with your Submersives LOL)

I'd give almost anything to get to 5hz with a bunch of output, too! The problem is, I have a 4500 cu ft concrete bunker! I have a wonderfully flat response and some of the prettiest charts and graphs I've ever seen, but.... I doubt I'll ever get much output below 20hz as I have no modes to support below that and with concrete floors I'll never get that true slam and feeling in my chest that I crave.

I will say this... For folks like me that either have very large rooms, and/or concrete floors, and/or not enough budget for the awesome subs Keith has, I recently installed a Buttkicker LFE and although I'm still fine-tuning it, there has been a huge smile on my face over the last few weeks.

I've actually installed them for others before but always discounted them and never spent time with them other than initial testing.

They work wonders for folks with my situation and I strongly recommend tactile transducers if you can't get it the "real way" like Keith has.

So jealous of Keith! cool.gif

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post #740 of 10744 Old 01-29-2013, 05:30 AM - Thread Starter
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If only.smile.gif Not in my room. Short of stacking subs from floor to ceiling, (I've thought about it biggrin.gif )I will never not have a dip (null) at about 90hz from the ceiling bounce. And I have 4 identical subs placed to optimize the room response. We may want to think about using a sample that is this ruler flat as I would suggest that this graph might set unrealistic expectations. It might work in a few rooms, but not all, regardless of the number of subs.


I've read that raising a subwoofer up off the floor can address the floor ceiling mode. Apparently rooms are 3-dimensional under current understanding which is why Geddes approach is 3 subs.

I read this somewhere too but I don't recall any method for determining just how high it should be?  Is there a general rule based on the distance from floor to ceiling?  I suppose measuring is the only surefire way to know.

It can be calculated and is different for every room. It has to do with the height of the room, the mode that creates, and when you calculate that, you can figure out the placement.

There is an Excel spreadsheet on the Harman web-site that allows you to input your room dimensions and it will show you, graphically, where your modes are and at what area, both graphically and printed out in specific hz vs ft and inches where the modes are strongest, weakest, and mid-way.

It's pretty neat and a great tool to be able to visualize best placement for speakers/subs and listeners in the room.

It's a starting point, of course. You will have to measure and it won't be perfect as it assumes true boundries of thick concrete walls for instance, where you may actually have openings, or only one or in some cases two layers of drywall and mass is critical when trying to calculate modes, as is symmetry/rectangle room, but it is always pretty close and I use it a lot.

I'll post the link when I have time to dig it up later unless someone else beats me to it.

If I knew the height of the ceiling and the height of the listener's ears, I could tell you approximately where to place the sub vertically to negate the effects of the null in that position, but would need more detail.

Find that spreadsheet on the Harman web-site and you can see for yourself. I got lucky and in my case only had to raise a sub (it only took 1 and I have 4) 15" off the ground and I already had a 12" riser for the second row in a dedicated theater, but it can be done in any room.

--J

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post #741 of 10744 Old 01-29-2013, 05:48 AM - Thread Starter
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Jerry, I saw your post on specific responses to your questions so even though some of this is repetitive from my previous post, I thought the least I could do is collect all of your questions and answers into one post!  Thanks again for your help!

Now that you mention it, I recall seeing your posts in the Audyssey thread.  Sorry, I monitor too many threads, but I should have remembered.  The advice you received from Roger Dressler is good advice, so I have nothing to add at this time.

I plugged in your dimensions in the Room Mode Calculator:






The primary resonant frequency associated with the width of the room is ~40Hz.  If your MLP is halfway between the left and right walls, this would place you directly in the null associated with 40Hz, which the measurements seem to support.  One way to address this would be to move the MLP to the right or left a bit and re-measure to see if there is an improvement.

The secondary resonant frequency associated with the width is 80Hz, and the secondary for the length is 62Hz, and the primary for the height is 65Hz.  I don't see anything associated with room modes that might be causing the issue at ~75Hz.  You should experiment with the sub/mains phase adjustments.

I think we should wait for Jason's opinion regarding whether bass treatments might be a solution for you.  For example, I have 96 sq ft of bass traps (eight 4x2 velocity traps, half from RealTraps, the other half from GIK).  Even though the treatments are not in a dedicated HT room, I am single and don't have WAF issues to deal with.

I think I covered most of these questions in my previous post, but let me know if I missed anything.

Jerry is on the right track here. What is your ceiling made of? If for instance it's in a basement and is a drop ceiling, you need to measure to the sub floor above as acoustically the ceiling doesn't even exist. That could be an explanation for the discrepancy between the 62hz and 75hz. That's just one example, of course.

For all but your first axial mode you can pretty easily treat the other ones with velocity based absorption.

In looking at the size and layout of your room, you are a perfect candidate for cheap and easy Superchunk style bass traps.

If possible (and it's easiest) I'd simply go buy R30 insulation (15" x 300" x 9.5" thick rolls at Lowe's for $15.87 last time I bought it a month or two ago) and make a soffit style trap in each corner. You could use two or four pieces, hanging from ceiling to floor. I use 4 pieces for a roughly 18x30" trap. This way you don't have to cut a bunch of triangles and support them so they don't compress (you don't want compression - you need it to stay as fluffy as possible) and you'll get good absorption with this type/style all the way down to 40hz.

Depending on your decay times and what it takes to treat your reflections (need you to try and clean up that ETC first) you may want to get some Contac brand self adhesive paper and adhere it directly to the soffit insulation (which will be hanging in a simple frame made up of 1x2's or 2x2's) so you don't over absorb the highs and the trap becomes a true bass trap instead of a huge broadband absorber.

If, though, you don't end up needing a lot of insulation to clean up the ETC and your room is over 300-400ms at an overall/average specular decay rate then you can do without the Contac paper as you'll want to bring those decay rates down a bit.

I've yet to see a room that cannot benefit from absorption in the modal region though. So no matter what, I'd build some inexpensive and easy floor to ceiling bass traps. You have 12 corners in your room, remember. Do the 4 main corners first, measure, and let's go from there.

You can buy them too, if you have more money than time and/or DIY skills, but... Be careful. If you're going to buy products make sure you get products that perform well and have been independently measured.

I recommend GIK Acoustics (at this time - more to come on that later) as they are honest, I've worked with them many times before, they have great performing products, a fast turnaround time, great looks, and quite frankly the cheapest prices, in some cases by far compared to any other company currently on the market today) and specifically the Soffit Trap (still a whole lot cheaper to build yourself though) the Tri-Trap, the 244 bass trap (which I believe should be used as broadband reflection panels to clean up the ETC more so than actual bass traps other than maybe some filler for problems with higher frequencies) and then if you still have problems you need to take care of in the lowest frequencies, they have Pressure based absorption called Scopus Tuned Traps that perform well (you'll need more than a few though) that will take care of your lowest modes and these type are NOT easy to build. It can be done but you need some good skills and a lot of time and patience.

I talk more about this in my previous post, but remember, for your 40hz width mode, if you had two subs, one on each side wall, they would combine to effectively produce 40hz right in the center of the room, which is your current MLP (and the best place for it as moving it just a bit isn't going to make a difference at that frequency) and your null would be gone!

I strongly recommend investing in a second subwoofer or upgrading if possible and buying two new capable subs.

Without knowing your budget (both money and time) and what exactly you hope to accomplish it's a bit difficult to offer any more advice at this time.

Hope this helps,

--J

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post #742 of 10744 Old 01-29-2013, 05:59 AM
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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! :)

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post #743 of 10744 Old 01-29-2013, 06:12 AM
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I agree with Keith.  I probably will never understand half of the audio theory that I see on this site, as well as others like HomeTheaterShack.  I have always hoped for contributions from thread participants who have the patience to develop general recommendations that I can apply to my modest listening room.  It is in this spirit that I authored the simplistic REW guide in this thread--it is certainly not a very advanced guide, but it should provide assistance to the casual REW user who just wants to get things working.

Yep - that is me to a T also, Jerry. I want to get the best I can get in my room, but there is a limit on what I am prepared to try to learn. There is just NFW I am going to read a dozen text books, but I am more than prepared to learn from the  experience of other members and also from the distilled experience of the true experts like J, Nyal etc.

I love you, Keith. wink.gif

Let's revisit this NFW statement regarding reading some books a year from now...Maybe 6 months even, lol!

I'll teach you everything I know if you wish, but if you are truly passionate or become passionate about this, especially once you realize that you're not going to be able to go much further in gear purchases due to the quality of gear you already have and especially once you realize truly just how much of a role the room (by hearing the differences for yourself, in your own room, not just understanding on an intellectual level) plays in your ultimate enjoyment with your system, I can absolutely see both you and Jerry deciding to really get into this, just as I did several years ago and start reading the texts for yourself and learning at your own pace.

We'll see.

--J

 

:)  Part of me hopes you are right and part of me hopes you are wrong. It is much more difficult for me to get up to speed with the text books than it is for some because my background is definitely non-scientific. I graduated from University in foreign languages and have worked all my life as an advertising copywriter (running my own multi-million dollar turnover advertising business at the same time). I am interested in science and try to study it and improve my knowledge, but complex math is very difficult for me to absorb and many of the acoustics books I have glanced at are very math-heavy. So yes, we'll see :)

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post #744 of 10744 Old 01-29-2013, 06:17 AM
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I'd like to see your FR and Waterfall with and without Audyssey, Keith. wink.gif

 

 

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.

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While a ruler flat response is nice to aim for, it isn't really necessary. What matters is what can actually be heard and AIUI there is much evidence to suggest that 'flat' to +/- 3dB will give you more or less the same audible experience as perfectly flat.

Here's mine for example - it doesn't look nearly as good as Jerry's, but it probably sounds very similar in real life. I think we can obsess too much wink.gif



Is that 1/12th smoothing, Keith? Pretty darned good if we 'settled' for this in the 15 to 200 Hz range (or should I say 5 Hz with your Submersives LOL)

I'd give almost anything to get to 5hz with a bunch of output, too! The problem is, I have a 4500 cu ft concrete bunker! I have a wonderfully flat response and some of the prettiest charts and graphs I've ever seen, but.... I doubt I'll ever get much output below 20hz as I have no modes to support below that and with concrete floors I'll never get that true slam and feeling in my chest that I crave.

I will say this... For folks like me that either have very large rooms, and/or concrete floors, and/or not enough budget for the awesome subs Keith has, I recently installed a Buttkicker LFE and although I'm still fine-tuning it, there has been a huge smile on my face over the last few weeks.

I've actually installed them for others before but always discounted them and never spent time with them other than initial testing.

They work wonders for folks with my situation and I strongly recommend tactile transducers if you can't get it the "real way" like Keith has.

So jealous of Keith! cool.gif

 

That is very nice of you to say so, J - what worries me is that I seem to have got where I have got by luck rather than judgement. I am hoping to confirm my luck as we progress on this journey, and also to improve on it!  The FR graph looks good, but as you say, and as I have learned, there's more to it than FR and I am especially looking forward to making waterfalls and ETCs once my mic arrives. I think this is where I need the judgement more than the luck ;)

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post #746 of 10744 Old 01-29-2013, 06:26 AM - Thread Starter
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Hi Nyal,

We haven't had the pleasure of meeting or speaking before. Although I don't know you and am not familiar with your work, I know Jeff and his work very well and respect him very much.

I'd love to have further conversations with you since we don't exactly have the largest pool of acousticians and acoustical consultants to pick from when seeking new friends with our common interests.

With that being said and with all due respect, I must humbly disagree with several recommendations your white paper recommends, though.

Hi, I do not want to derail this thread, but I would like to answer some of your specific questions and also provide some more on where we are coming from.

The main thing to bear in mind is that our perspective is that acoustical model are just imperfect representations of reality. Each model is a by product of a particular time in history. As acousticians learn more and have better tools available to them the models change. I do not think you have to design a room based on any one acoustical model.

The white paper represents a 'stake in the ground' by Jeff and I and is a statement of our current knowledge, understanding and real world experience in designing and implementing room acoustic solutions for two channel systems. The targets describe a room that has good spectral balance in the direct and reflected sounds in the midrange/treble and reasonably flat response with low modal ringing in the bass frequencies. Many of the room models do not cover all the aspects of room acoustics that Jeff and I think are important. For example LEDE focuses nearly exclusively on the use of ETC, to the detriment of a lot of other things, and without covering the potential issues in general use of the ETC.

The targets are NOT easy to achieve in the context of a two channel system. I have measured many rooms and none meet the targets in the white paper without effort and acoustic treatment. Like I said earlier I believe that with EQ and subs the low frequency targets can be substantially tightened up for home theater applications. We think that if the targets are met and / or exceeded then your room will not be a detriment your overall reproduction experience. This is based on our real world experience of many hundreds of two channel rooms.

There are many ways to meet the targets without having to be forced into designing to meet a LEDE, NE, or other type of room.

With the above high level overview of our position on acoustic models etc let me just briefly comment on some of your particulars...
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Originally Posted by jevansoh View Post

First, why do you feel the ETC should show "10db reduction by 40ms?" Do you not believe in an ISD Gap? Do you not believe early reflections high in amplitude are destructive? Do you not believe in the termination of the ITG?

LEDE standards are pretty clear that energy should not be above -20db from 0 to "around" 20ms or so to create an effectively anechoic gap which is then strongly terminated to increase the apparent size of the room and so the direct signal has time to form free of clutter. This will reduce muddiness and improve the listening experience with absolutely no argument against doing this from most well respected people in the field. What would the purpose of having a ton of high energy reflections all the way out to 40ms only 10db down be?

- 10dB reduction is to ensure that the precedence effect does not break down and that reflected sounds are not audible as echos. You should read the target as 'AT LEAST' 10dB, not 'JUST' 10dB.
- I do not believe all 'strong early reflections' are destructive. I am in the 'Toole' camp when it comes to that.
- I do not believe in designing LEDE rooms for reproduction so any discussion of ISD is not relevant to me. LEDE was to me a product of a particular age of studio building and the use of particular speakers with poor off axis performance in that era.
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Second, you reference RT60, 30, 20 yet there is absolutely NO REVERB TIME in Small Acoustical Spaces!! I'm SURE you know this. You stated these targets you set were for two-channel and you may amend them for home theater so this paper was obviously not written for concert halls, yet you reference taking RT measurements!

While looking at modal decay times and insuring they are even and contained to the appropriate range for the size of the room and the actual proven acoustical model targeted is necessary you won't find it by looking at the RT60 nor will that measurement help for the mid-hi frequencies either.

You can simply use the ETC and Cumulative Spectral Decay plot to find decay times and setting specific decay targets without taking into consideration the model, the room, etc, in my opinion is far from ideal.

You suggest targeting between .2 and .5 seconds with not much more explanation than that, but that is a HUGE difference. A room that has an overall average decay time of .2 seconds will sound quite dead no matter the size, especially considering you stated this document was created with two channel in mind, whereas with HT you'd at least have the surrounds so .2 wouldn't be so dead and dry, yet .5 in small rooms can be WAY too long. So have you defined specific targets for specific rooms in this new model of yours? What are the "why's" behind these numbers or are they just arbitrary limits you selected?

- Of course I know there is no RT in small rooms.
- The main use of the 'T' measures is to look at how sound is decaying across different frequency bands. It's another way of looking at the spectral balance in the room.
- You are wrong that a room of 0.2s will sound dry. Small rooms with a lot of diffusion can have 0.2s and sound normal.
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Next, you suggest a +/- 10db FR in the low frequencies at 1/24th smoothed! That isn't much of a goal! First, low frequencies should NEVER be smoothed at all. We need to see all the resolution possible here. Second, a 20db swing is worse than most people that have taken 5 minutes to "try" will ever see, especially now that RC software like Audyssey is now so popular. Anybody that would actually be reading your paper or this post is not going to accept a 20db swing in the most important frequency band in the audible spectrum whether 1/24th, 1/48th, or totally unsmoothed, which is the only way the FR should be viewed in this range.

- our intent for the target was a 10dB window rather than +/-10dB. This needs revising. In the context of a two channel WITH NO SUBS OR ROOM CORRECTION this is a hard target to achieve.
- of course low frequencies should be smoothed. We don't hear the unsmoothed frequency response. It's only relevance is to precisely identify the frequency of peaks or dips.
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Originally Posted by jevansoh View Post


As for decay times, should not the target be simply as even throughout the entire audible spectrum as possible with as little deviation as possible?

Again, it may not be likely that everyone will be able to get to within 10% of the full spectrum regarding decay times like the BBC demands for its rooms, but if you don't set the goal and understand the importance of ringing and vastly different decay times, especially in the lower frequencies, then your "critical" listening room is going to sound pretty bad.

--J

- the targets for the time decay are relaxed in the ultra low bass for a number of reasons including general lack of musical content <35Hz (remember this is two channel, not HT) and the difficulty of achieving the targeted decay time targets in the low bass.

Hi Nyal,

First I wish to thank you for responding in a civilized manor and without getting defensive.

I've read a lot of text books in my time, I've spent a lot of time on forums, and I've been involved in different aspects of business for awhile now, but no matter how much one reads and learns, experience counts the most in my opinion.

Based on what you stated in the text above, it seems as though I may have less than 10% of your real world experience at this point in my life and career, however, I do believe strongly in continuing education, gaining more experience both for knowledge sake and in that it means my bottom line continues to grow (I have work).

I'm sure over time my ideals may change a bit as I continue to learn and grow and I hope I never become a crotchety old man stuck in his ways.

But for now, I only have the education and experience I've gained so far to go on and have to respectfully continue to disagree with just a few of your ideals regarding the targets for 2-channel audio expressed previously.

I do respect where you're coming from and hope you understand that while I have some different viewpoints on certain aspects of what you believe, I don't know that either of us could say the other is "wrong" as all it boils down to is what make the customer happy.

For this thread I want to introduce folks to standard ways of doing things that aren't challenged by most and even if certain goals aren't totally met by each person, I know that nothing I'm teaching is going to make their rooms sound worse. There will always be room for improvement, but at least I'm doing no harm.

I'm sure through your experience you have found numerous reasons to come up with your own way of doing things and go down your own path, so to speak. At this point though, with my level of experience and knowledge, I simply feel more comfortable in teaching what I've learned and know works and for the most part is widely undisputed.

So I guess what I'm saying is, welcome. There is room for many different theories on what is "right" but the most important thing in my opinion is for one to decide what that path is going to be and follow it. If goals are set and worked towards to achieve them by passionate audiophiles, they will simply learn a lot along the way and enjoy their systems that much more and that enjoyment and knowledge gained will last a lifetime.

I'm glad to learn there is a typo in your document as quite frankly I mainly took issue with two of your points, one being a +/- 10db window is a "goal" and is acceptable, however, now realizing that is supposed to read +/- 5db I wholeheartedly concur. We are on the same page.

Where we remain opposed however is in regards to reflections. I never once stated all reflections are bad. In fact, I believe they are absolutely necessary.

I do believe that high gain early reflections are absolutely detrimental. I believe they cause smearing and muddiness as I've heard it myself. I also believe that nobody likes to listen in rooms approaching anechoic conditions therefore reflections after a certain termination point are necessary and they create the psychoacoustic effect of making the room seem larger than it is. Therefore, reflections become necessary, after a certain point and to a point, just not random uncontrolled reflections.

When creating a room that has a small period (12-25ms depending on the size of the room, budget, goals regarding focus on 2-channel or HT, etc) of low gain early specular reflections around -20db terminated by a high gain (around -12db or more) specular reflection and followed by a diffuse and infinitely decaying rate of further reflection, the direct sound will be heard, clear, no smearing or muddiness, and the room will sound spacious and live.

There are of course many other factors that if are not addressed will cause this effect to collapse, however, and I believe we are in agreement on most of them.

I don't think the goals for 2-channel and HT are all that different. Yes, there are differences, but let's face it, most rooms are multi-purpose including dedicated rooms as most folks (the folks reading this thread at least) don't have a dedicated 2-channel room and a dedicated HT).

I disagree that a room with an average 200ms decay time will not sound very dry, however. Maybe "dead" was a bit harsh, but 200ms sounds quite dry and you can't just fix it by adding a ton of diffusers and diffusers, by nature, also absorb and will reduce that further, plus too many diffusers, if not placed surgically and strategically in the room will cause other problems such as interfering with the early reflections you worked so hard to tame, lobing issues depending on the design, etc. If the diffusers are broadband then the room has to be large enough, too. So just placing a ton of diffusers all around a room with a 200ms decay time is NOT an answer IMHO.

As for the rest, we're pretty much on the same page.

I like to target +/- 5db with no EQ - full band. +/- 3db with EQ - full band.

Depending on the size of the room I like to target between 300-500ms and quite honestly will accept 250ms in smaller harder to control rooms and seldom reach much over 400ms in all but the largest of rooms. The target is always 10% but I'll be the first to admit I've yet to achieve it. 20% is more reasonable and I cannot disagree with your 25% recommendation fully, however, I do believe that should be the absolute limit.

With those targets, it's not necessary to state that the bass can decay slower than the specular region other than to say it is common for the lower frequency range to be the hardest to tame and it will take the most skill, time, and budget to get in line without affecting the specular region negatively. Why create two different targets then also state you need to keep the full band decay time within 25% relative?

So again, we may belong to some of the same clubs, pay membership dues to some of the same places, and have similar ideals with but a few differences, but one thing is sure and that is our experience differs by a great amount with you simply having more of it.

I hope we can speak again and would like to get to know you better.

I hope you can at least see that there is room for my philosophy and yours, and that the important thing for folks trying to learn is that they understand the differences, pick a model (yours, mine, or other) and start working towards it to accomplish true audio nirvana!

I hope our paths will cross again sometime, Nyal.

--J

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post #747 of 10744 Old 01-29-2013, 06:41 AM - Thread Starter
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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! smile.gif

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

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post #748 of 10744 Old 01-29-2013, 06:45 AM - Thread Starter
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I'd like to see your FR and Waterfall with and without Audyssey, Keith. wink.gif


 

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

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Just remember, if for now you'll be using the Omnimic for testing and to become familiar with REW, that's perfectly fine, but if you are going to use the CAL file, you need to point your mic at 0 degrees, straight towards your center channel speaker from your MLP. Do NOT point it up towards the ceiling with the CAL file loaded as it was only created for 0 degrees.

If you end up becoming a convert and you want absolute measurements instead of just relative measurements and also want some nice equipment to use with testing your custom built speakers, I STRONGLY recommend the UMM-6 mic.

--J

 

Yikes, I guess this nullifies my first REW measurements!  I used the OM mic in the upright vertical position (same as I used it with OM) as I thought this was the direction that it was calibrated?!  If it's not then how does OM function well in this orientation?

 

I'll get my UMM-6 mic soon and redo all the measurements including the sub crawl.  In the meantime, I'll remove the link to my .mdat files so others don't spend any time reviewing them.  Sorry to those that already did as I was completely unaware of this caveat.

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Yikes, I guess this nullifies my first REW measurements!  I used the OM mic in the upright vertical position (same as I used it with OM) as I thought this was the direction that it was calibrated?!  If it's not then how does OM function well in this orientation?

I'll get my UMM-6 mic soon and redo all the measurements including the sub crawl.  In the meantime, I'll remove the link to my .mdat files so others don't spend any time reviewing them.  Sorry to those that already did as I was completely unaware of this caveat.

Hi jkasanic,

You don't need to sweat on the case of mic orientation in the bass department. See my post here: Post #391
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