Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 22 - AVS Forum | Home Theater Discussions And Reviews
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post #631 of 15547 Old 01-26-2013, 02:22 AM - Thread Starter
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Quote:
Originally Posted by mogorf View Post

Quote:
Originally Posted by sdrucker View Post

Because we can't carry a tune?biggrin.gif

(Running as quick as possible away from the office keyboard - sorry, couldn't resist)

Guys, was my reasoning so bad?

"Though the topic may seem OT, but I think we can relate it to REW if we'd like to have a clear picture of what is happening with our systems. I'm sure severe hum can easily throw off the measurements if untreated."

If so, it was bad. tongue.gif

I personally think addressing noise/hum is very important as it could and does easily skew measurements and the whole point of the measurements is to make our systems better. If we don't first take care of getting the absolute lowest noise floor both electrically and acoustically, then we have already limited the results we'll be able to expect.

Plus it's pretty easy.

But the real reason is because I just made a novel of a post and did it when I should be sleeping and I'd hate to have to delete it lol. biggrin.gif

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post #632 of 15547 Old 01-26-2013, 02:25 AM - Thread Starter
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Quote:
Originally Posted by sdrucker View Post

Quote:
Originally Posted by mogorf View Post

Guys, was my reasoning so bad?

"Though the topic may seem OT, but I think we can relate it to REW if we'd like to have a clear picture of what is happening with our systems. I'm sure severe hum can easily throw off the measurements if untreated."

If so, it was bad. tongue.gif

There actually is minor relevance: if there's a hum produced by a laptop connected to an electrical power source that's being picked up by the mic, it might also represent a problem for someone conducting REW measurements on a desktop PC. Hence Keith's advice to measure REW ONLY with a laptop running on battery. While AFAIK most if not all of us are running laptops for measurements, it's conceivable that a future REW user (and thread participant) might be using a desktop with an HDMI out that doesn't have battery power, and be measuring effects that are artifacts of connecting to a wired electical source. But it's still a sidebar issue.

Great point, Stuart.

I am one of those users. I have a dedicated HTPC and always have my test rig hooked up as I'm measuring "something" just about every day so it's extremely important to isolate and fix any noise/hum issues.

I think it's important to start from the ground up and it doesn't get lower than the noise floor. Okay, bad attempt at a joke, but a clever person could find one in there somewhere. wink.gif

--J

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post #633 of 15547 Old 01-26-2013, 02:46 AM - Thread Starter
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Originally Posted by batpig View Post

Slightly out of scope for this thread, so feel free to redirect me to a link that explains it if we want to avoid wandering off too far.... but I trust you guys to give me a clear and concise (yet thorough!) answer:

I was thinking about this stuff and I realized that I do have a Radio Shack digital SPL meter just sitting around, so as we wait for the USB mic stuff to get settled I was thinking it might be worth getting started with that as a measurement device so I can get up and running and learning REW basics. My understanding is that an SPL meter can be used as the REW mic, with the caveat that it's not very helpful at high frequencies and a correction table is required.

What kind of cabling or gear is required to use REW with a RS SPL meter? Can I just plug it into my laptop's mic input, or is this a situation that will require a external duplex USB sound card? And/or a phantom power supply?

And what are the pros/cons of this approach? Is the RS SPL meter accurate enough for assessing sub performance, room acoustics, crossover splices, etc. if you have the correction table loaded?

Hi BP,

You can absolutely use the RS meter for measurements. Surprisingly, it is pretty darn accurate and is great for relative measurements. It's best to only trust the results from about 20hz to about 3khz though. From 3khz to 7khz it's "ok" but not great and it's pretty useless above 7khz or so.

It gets a bad rap for some reason, but I started with one, have tested several, and they honestly aren't bad and a great, easy, and inexpensive way to get started.

You do NOT need a pre-amp.

However, you should use a Line Input on your computer/sound card and not a Mic input because the RS meter is powered and the mic input will cause too much boost/noise since it's used for non-powered (IE: Audyssey mic) inputs.

All you have to do is plug the RCA cable into the meter and on the other end get an RCA to 1/8" (3.5mm) mono adapter to plug into your computer.

That's it as far as input goes. The output cabling doesn't change and you can still use analog or HDMI.

I wouldn't trust the calibration files that are floating around though.

You'll be able to do everything with the RS meter that you can do with any other calibrated or uncalibrated mic, but I wouldn't make tough (read: expensive) decisions based on the readings on anything other than a calibrated mic from CSL.

It's perfect for relative measurements and will get you in the ballpark for absolute measurements up to around 3khz, so go for it!

--J

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post #634 of 15547 Old 01-26-2013, 02:51 AM - Thread Starter
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Quote:
Originally Posted by LastButNotLeast View Post

Quote:
Originally Posted by batpig View Post

What kind of cabling or gear is required to use REW with a RS SPL meter? Can I just plug it into my laptop's mic input, or is this a situation that will require a external duplex USB sound card? And/or a phantom power supply?


And what are the pros/cons of this approach? Is the RS SPL meter accurate enough for assessing sub performance, room acoustics, crossover splices, etc. if you have the correction table loaded?
It is. It's what I use. I bought a MobilePre (http://www.musiciansfriend.com/pro-audio/m-audio-mobilepre-mk-ii), used/open box. Follow the directions in the original REW thread on HTS for cabling.
Since it would cost as much as the USB mic, is more of a PITA, and isn't as accurate, I suggest you just get the new mic. You'll still use the SPL meter for dB calibration.
Michael

Hi Michael,

You DO NOT use a pre amp when using a Radio Shack SPL Meter. Without going into detail, I'm surprised you were able to get this to even work reliably and without all kinds of issues. wink.gif

The RS meter should be plugged directly into the computer's sound card. No additional hardware is required or recommended.

As far as output, you can still use analog/headphone out or go with HDMI if you wish, but the RS meter should be plugged directly into a "Line In" connection on your computer's sound card.

--J

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post #635 of 15547 Old 01-26-2013, 03:45 AM - Thread Starter
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Originally Posted by AustinJerry View Post

WARNING:  READ BEFORE CONDUCTING A 100DB MEASUREMENT!

Jason recommended a 60dB range on the vertical waterfall axis.  With a noise floor at 40dB, this means the REW sweep must be configured to run at 100dB.  To do this, I simply re-ran the REW mic calibration, adhusting the AVR master volume upwards until it registered 100dB on the SPL.  The final AVR MV level was +5! I then ran a 15-20,000Hz measurement sweep.  THIS WAS EXCEPTIONALLY LOUD.  Seriously, I was very concerned that I had damaged my speakers.  Jason, I think you should have provided some advance warning that measuring at such a level posed a risk of damaging equipment.  I would have been devastated if my expensive speakers had been harmed.

So, I backed the MV off to +0 (Reference), and ran a measurement at 95dB.  This was still very loud, but I was able to take measurements.  Here are the results:

Audyssey off:




Audysssey on:




Note that I have 60dB range on the vertical scale, and 15-300Hz on the horizontal scale, as per our agreement.  Note also that the time interval is maxed out at 1.5 seconds.  Either the waterfalls show that my room is a total piece of crap, or I am still missing something, because these graphs look significantly worse than the ones I posted earlier.

What confuses me is that the room and equipment haven't changed.  Just several different waterfall measurements and representations, and my room goes from good to bad.  confused.gif

Hi Jerry,

First of all, you're right... I need to learn not to assume and am still getting used to giving advice on public forums where I am not in direct control or at least have knowledge of what my advice might lead to in the real world. Point taken, I apologize, and I'm glad you didn't hurt your speakers or your ears.

While it isn't necessarily imperative you take all measurements at 100db, it truly is important to get 60db above your noise floor if you want truly accurate and absolute measurements.

My recommendation is not for everyone to take all measurements starting at 100db, even if it came across that way before. (Who knows, I might have even specifically said to do that in my haste without further explanation and if I did, for that I also apologize.)

This is yet another reason why it is so very important to start with the absolute quietest noise floor possible.

I realize not everyone is going to tear down and start over with true isolation and room inside a room construction nor is everyone going to feel comfortable taking 100% of their measurements at 60db above whatever their noise floor is.

There are some very good reasons for doing this, though.

Once you "think" you're finished with speaker/listener placement, treatments, etc, and you want to see how you did and what your absolute measurements are (assuming you have a properly calibrated at 90 degree mic) THEN you must measure 60db above your noise floor to be able to trust the measurements.

Even then you'll always want to take two or three measurements in EACH mic position, moving the mic several times just as you did when running Audyssey, and you want to do this with Audyssey on and off, too.

You'll quickly fill up the 30 maximum measurement slots in REW this way, with each session, but it's the only way to get trustworthy measurements.

Max brought up some very good points and tips too, and got to it a few days before me. Sorry again for being so slow. tongue.gif

You can start out at 75-80db and then move up in 5db increments, not only to at least 60db above your noise floor, but until you start seeing compression, which will simply look like measurements that don't show 5db louder when you did indeed turn the volume up 5db (frequency response graph for this one). Once that happens, the measurement directly under it is the loudest your system can comfortably play without compression/distortion/who knows what else.

If you can't get to 105db (115db for subs) then you need to move your speakers closer, get new amps, new speakers, or simply not listen so loud.

Once you measure, again do this in 5db increments, and find the maximum clean level you can play, subtract this from your noise floor (most rooms in the US will be somewhere around 40-45db if not treated) and that is your dynamic range. It WILL be a far cry from those extraordinary Dynamic Range specs on all your awesome gear, which is one good reason why you shouldn't base your decisions on which gear to purchase based on this figure, THD, etc, as ALL modern gear (and most older gear) is going to outperform what you can get in room anyway. That's why I always "listen" to gear, in my room if possible, before deciding what to buy and only based unseen/unheard purchasing decisions based on features I want as I know my room is the limiting factor for ANYTHING I could buy.

It is important to know the dynamic range of your room though and it is important to get your room as isolated from outside noise as possible. For certain types of music, IE: Classical, that can go from very quiet to very loud and back to very quiet again in a second, and do this over and over, it is critical you have the largest dynamic range possible or you'll surely miss a lot of what is on the recording.

This is yet another reason why people always fiddle with the remote turning things up and down. I can ASSURE you that if you have the volume set to a reasonable level and ever have to "turn it up" to hear what he/she said, your room is too noisy. wink.gif

Moving on, besides knowing how your equipment performs and the dynamic range of your room, it's also important to measure loud because it will show any resonances you have. These could be coming from your speakers themselves, light fixtures, items in your room, even your acoustic panels! You don't want to hear these buzzes/rattles when your watching/listening to content and this is the only way to surely excite them and be able to fix them.

Don't worry about the graphs you posted. Something is obviously wrong. When changing the volume, you always need to recalibrate REW, especially the SPL. It's always a good idea to click the "calibrate" button in the REW preferences and just run through the steps, also doing the same thing with the SPL meter in REW just to be sure all the levels are set right. Once you recalibrate everything and have made sure there are no noises/buzzes/rattles in your room when your taking measurements, start back around 80db, moving up 5db at a time, taking 2 or 3 readings without moving the mic at all in between them, and look at the waterfalls. Once you find where these funky graphs start showing, post them again, and I'll have a look. We'll figure this out. I'm SURE this isn't indicative of what's truly going on in your room, since I'm pretty familiar with your actual room.

So for folks reading this, yes, it's important to measure 60db above your noise floor for absolute measurements.

However, always wear ear protection and get there in 5db increments, and of course don't ever measure above the limits of your system.

For every day measurements though, not for ones you're posting here, when you've just tried this or that, something small, and just want to see if it had an effect on your FR or Waterfall, or possibly when you're trying to find a point of reflection with the ETC, it is not necessary to measure this loud and somewhere around 85db is fine.

I personally only measure that loud when I feel I've done the best I can do setting up a room/system with what I have to work with that day and the time I have, to show the absolute and accurate results of my efforts.

REW does have noise filtering built in and you won't "necessarily" start seeing nothing but noise starting exactly where your noise floor begins.

For instance, Jerry, I believe your noise floor was measured at 57db, right? (I'd recalibrate the SPL meter, make sure everything is as quiet as possible, do it late at night when it's quiet outside too, and verify that - it seems like a very high noise floor and 57db is actually pretty bad. I don't trust that measurement.) If you look at your waterfall graphs, you're not going to see nothing but noise starting right at 57db.

This is another good reason to use a very long sweep, too. Always set your measurement sweep length to 1 pass, but a MINIMUM of 512k and preferably 1mb for the most accurate measurement sweeps to get rid of the most noise.

TIP: A good way to see the limits of REW's noise filtering is to look at a Waterfall somewhere in the range of 500hz up to 10khz and then click the "Limits" button, clicking the "bottom" limit down, down, and down some more, until you start seeing "mountains" appear out of nowhere. In the range of 500hz to 10khz or so, we know these aren't actual modes or modal issues, so it's certainly noise.

Next, wherever your noise starts to appear in the graphs, set your permanent "bottom" limit a few DB above this and you'll know you aren't looking at your noise floor, but you are seeing how long it takes for each actual mode to decay TO the noise floor, as actually measured by REW and its noise filtering algorythms. This way you don't have to rely on an actual SPL measurement which can be flawed, especially if just a few frequencies are loud while the rest is much quiter.

Finally, use 60db above that level as your actual measuring level when you wish to make absolute/accurate measurements. You'll likely find that most of the time, in most situations, you won't have to measure much above 90db or so, especially if you have a reasonably quiet room and don't live in Midtown Manhattan. wink.gif

Hope this clears some things up for some folks.

Keith/Jerry, I believe the info/tips in both this post and the one about noise/hum should be added to "A" document sooner or later, whether it be a FAQ or "other" document as this is some important info, especially since it concerns possible damage to speakers and humans. wink.gif Just a note so hopefully you guys can bookmark these posts for later compilation.

Thanks,

--J
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post #636 of 15547 Old 01-26-2013, 04:12 AM - Thread Starter
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Originally Posted by beezar View Post

Wow, just found this thread; looks like I have a lot of reading to do!

Anyway, I was doing a sub crawl using the mic and took some REW measurements today. However, that was before I found this thread. So my measurements don't fit the standard (eg: waterfall graphs are only up to 75dB, and only measured 10-120Hz).

But I'll post them anyway. I understand of course that these graphs may not tell me anything because I didn't measure it properly, but with a newborn, the ability to do measurements (especially up to 100db) would be very infrequent!






Some other info:
- Graphs are with Audyssey OFF
- The noise floor is indeed ~40dB in that room, so I didn't make the waterfall plots go below 40dB
- I did the sweeps with all speakers and subwoofer combined (not like what was recommended, at least for the frequency response in this thread)
- Crossover to the sub is 80Hz
- One sub, SVS PB-12 Plus

Questions:
1) Which of the three would be the best placement for the sub? (with the caveat that I didn't generate the graphs completely properly)

Without a doubt, based on the information given, the "blue" one is the best. It has the lowest extension with the most output in the FR and in the waterfall it shows the shortest decay plus the problems that do exist are high enough up in frequency to easily be fixed by room treatments and/or EQ. It appears as though you already have some treatment in this room. wink.gif Either that, or it's a great room to begin with with natural treatments (furnishings/placement/etc) that really help the response. I can't tell what problems are hiding below 40db since I don't have 60db worth of data to look at though, but I suspect it isn't awful.

2) How do you generate an ETC graph? Not sure if it was posted earlier, as I've only had time to read the first 5 pages of the thread, but any links to a post containing the info would be appreciated. Or the info itself...

Assuming you've saved your measurements and not just these screen grabs (ALWAYS save your measurements) simply open the measurement file and click the Impulse tab in REW. Then click the box at the bottom that says ETC. Follow the guidelines in post 2 of this thread on how to set the parameters for the ETC. Once you've done that, post the ETC and I'll analyze it for you. This will also give you the opportunity to reset the limits on your Waterfall's. Also, be sure to ALWAYS take full range measurements from 0hz to 20000hz since we can view the areas we want. It's imperative you have full range measurements for accurate ETC charts.

3) The SVS PB-12 Plus has parametric EQ--is it better to try to nullify peaks/troughs in the frequency response curves first using parametric EQ before Audyssey, or try to do it after Audyssey on what could not be corrected adequately?

The short answer is, Yes! Always do this first, before Audyssey. I strongly recommend using this PEQ only to CUT frequencies and not boost as boosting in the sub will trick Audyssey into thinking it has more headroom than it does and it will further boost the same frequency which can damage your sub. The built-in PEQ is a great tool if used properly to cut down the first Axial mode, for instance, or just the biggest peaks. Play around with this, taking measurements in between each new setting on the sub, before running Audyssey so you know for certain what the actual starting point is.

4) Does decay matter much for the frequencies below 20Hz, considering they are mostly inaudible? I would imagine that "muddying" of the frequencies which are felt rather than heard don't really matter.

A lot of my answers are absolutes. This one is an opinion. Take it for what it's worth. wink.gif IMHO it matters to an extent, but it sure it difficult to do anything about it.

It matters because ringing is ringing and it sure can dominate, at any frequency. It also matters to measure it and view it, because the harmonics of that first mode are also going to show up in higher frequencies and you want to know where it begins. IE: Fix the first mode and the rest disappear too! Killing two (or ten) birds with one stone, so to speak.

Unless your listening room is sized for hobbits, the first axial mode (the strongest) is going to be pretty low. You need to see where this is, as it's the basis for all (okay, most) of your other problems, but you won't be able to fix it with velocity based absorption (IE: Bass traps made with any type of fuzzy stuff/insulation) rather to fix these types of problems, so low in frequency, you'll need pressure based traps like Helmholtz resonators or other types of "tuned" traps. These aren't easy to make and are very expensive to buy, so you may or may not be able to do much/anything about it. That's why this isn't an absolute. IE: Why worry about things you cannot fix? I guess the only answer is that "I" want to know everything and set my goals/aspire to fix ALL problems, so it's important to get accurate and complete measurements.

You'll have to decide for yourself what the limits of your measuring are, and the goals you set for treatment.


5) How do you make REW play a sweep at a higher dB level to average around 100Hz across the frequency response to generate a proper waterfall graph?

I assume you mean 100db?? If so, you can use the Master Volume control on your AVR/Pre-Pro, the sweep level in REW, or a combination. Make sure to read the caveats of doing this in my last few posts. If this isn't what you were asking, try again, as I have to admit, I don't fully understand this question. wink.gif

Sorry for the delayed response. Better late than never, right? tongue.gif

Please see my answers above, bolded, in between your questions.

Hope this helps,

--J

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post #637 of 15547 Old 01-26-2013, 05:00 AM
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Jason said:
"Finally, use 60db above that level as your actual measuring level when you wish to make absolute/accurate measurements. You'll likely find that most of the time, in most situations, you won't have to measure much above 90db or so, especially if you have a reasonably quiet room and don't live in Midtown Manhattan. wink.gif "

Not sure if this meets the 40-45 db 'typical US home' noise floor, but we live on the 20ish floor of a hi-rise building in downtown Chicago, two blocks from Lake Shore Drive, and about four blocks from a major hospital. It's 6:45 AM and sitting on our sofa in our living room/HT, I hear wind tunnel effects from outside that sound like muted engine roar, and an occasional ambulance (as well as the occasional bus or truck). And we have neighbors...

Short of moving and/or aiming for 100+ db test tone measurements as an ideal for capturing optimal dynamic range (and NOT measuring the weekend of the Air and Water Show LOL), I may well be limited to 85-90 db measurement and a noise floor closer to what Jerry observed (mid 50s), hence a 30-40 db dynamic range over the noise floor in practical terms.

Before I do system measurements with the USB mic coming (hopefully, if PE is correct) next week, I may well post the waterfall with the 'sounds of silence' for commentary.

Audio Gear: Trinnov Altitude 16/24, NAD M27 amp, Crown XLS 1502 stereo amps (2)
Display: Panasonic VT50, Lumagen Radiance Mini
Misc.: Oppo 103, Apple TV, JRiver ID NUC
Speakers: PSB Imagine T2, Center, and X2T Surrounds; Atlantic Tech 44-DA heights (4), HSU ULS-15 subs (2)
More gear to follow as I get going with the Altitude...
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post #638 of 15547 Old 01-26-2013, 05:58 AM - Thread Starter
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Quote:
Originally Posted by Nyal Mellor View Post

Quote:
Originally Posted by djbluemax1 View Post

Since this topic has already popped up, I figured I'd comment.

As far as the time range for waterfalls, there are 2 approaches:
1) as Jerry states, increase the decay time setting till you can see the majority of the peaks fall to the noise floor (set at 40db or your individually measured noise floor). This is great for folks curious to see what their room is doing and can help ID modal ringing.

2) set the decay range to 300ms as the goal is to have everything above ~40Hz decay in under 300ms (or by about 200-250ms in ideal conditions).

It's not only important to have the frequencies decay by a certain time, it's also important that the frequency range decays at similar rates over the entire range.

For example, if the octave from 60-120Hz decays much slower than 30-60Hz and 120+Hz, that octave will dominate what is heard. It will also mask/blur everything else.

Because it's harder to damp/absorb bass frequencies than mids and highs, the type and amount of absorption used to control the bass may inadvertently absorb too much of the higher octaves, resulting in drastically shorter high frequency decay rates, which will produce tight bass, but a 'dead' sounding room.

How much treatment is good and how much is too much is something we'll get to later I'm sure, but to get back to the specific issue, if it takes more than 600ms for the bass to decay into your noise floor, you seriously need bass traps anyway, and showing a waterfall to 1000ms is unnecessary, except to show just HOW badly bass traps are needed.

BTW, when folks begin producing waterfalls, they'll see just how powerful XT32 is for reigning in bass ringing, but of course, the better the situation prior to running Audyssey, the easier it is for Audyssey to do its thing and the better the outcome.


Max

I believe some of those targets you quoted are from the white paper I co-authored with Jeff Hedback. There is a ton of pretty detailed discussion about each measurement and relevant targets. You guys should read it, if you haven't already. There's a whole bunch of targets defined in there for things like frequency response, time decay, ETC and so on.

Maybe people missed it (or ignored it) earlier on. To whet your appetite here's the summary page:



And here's the decay target graph:



Please note those targets were for two channel. Am happy to brainstorm with you nice people what the modifications for HT might look like. At a high level they would involve bringing in the bass response frequency response targets quite a bit, decay, ETC, mid/high frequency response and likely T60 targets would remain as is.

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.

I actually did read the paper shortly after you published it, but didn't give it too much thought as at the time it didn't concern me or affect anything I was personally involved in and I'm definitely not one to criticize just to stir up trouble.

If you will kindly read the first page (second post) of this thread, you'll see that I started this thread to help people set goals and work towards achieving them regarding the acoustics of their listening rooms.

I've offered my time and participation in this thread to give back to this community for all the invaluable information and knowledge I've received from this forum and forums like it over the last several years.

I know what it's like to spend a lot of time reading, learning, and then through further research and way down the line find out I was given so much misinformation that I have to try and unlearn and then start all over relearning things the right way and I want to try to teach people the "right" way from the beginning.

The problem is, "right" isn't necessarily fully defined unless your goal includes an acoustical model in which you are trying to achieve.

The first main post of this thread states just how critical it is to set this goal as otherwise, what exactly are we working towards?

Once one has chosen an acoustical model, there are absolute guidelines that are in place to assure certification spelled out in great detail as to what each of the parameters your white paper has mentioned above should actually be, and quite frankly a lot of what you state is simply not supported by these models.

I understand that most people reading this thread and planning on taking measurements and applying treatment to their rooms aren't going to have them LEDE certified for instance, but I strongly believe you must set a goal and have specific ideals to work towards if you ever hope to accomplish anything close to what you set out to do.

In the second post of this thread, I recommended, and for those reading this, am recommending again, that you all read this fine document that details each of the most popular room models from which to choose then pick one to model your own room after. http://www.eetimes.com/design/audio-design/4015907/Acoustics-and-Psychoacoustics-Applied--Part-1-Listening-room-design

Another great article comparing the different acoustical models is from RPG and it goes into even more detail yet is very well written and easy to understand. http://www.rpginc.com/docs%5CTechnology%5CPresentations%5CStudio%20Design%20From%20Mono2Surround.pdf

The point is that this thread is geared towards learning what the different acoustical models are, picking one (setting that as the ultimate goal) then working towards achieving it, starting with learning how to use REW and progressing through all the different graphs and functions of REW, what they mean, how to interpret them, and what to actually "DO" about whatever problems your room has so you can achieve your initial goal.

We're obviously in the very beginning of this process with most here not even having their mic's yet and very few folks are comfortable using REW past very basic measurements and I'm sure it will be quite some time before we get into intricate details on exactly what some of these parameters are and how they'll end up in most folks rooms.

With all that being said and understood, I have to say I believe your white paper can very easily confuse people and deter them from following the proper steps already set in place to participate in this thread.

I suppose what I mean by that is that your white paper is simply arbitrary targets that don't adhere to any standard, especially any standard for an actual and proven room model which people have built and use either to record or for critical listening.

If there were no standards then this would be fine.

Since the whole purpose of this thread is for folks to pick an existing and well proven standard acoustical model, most of which I assume will work towards LEDE/RFZ or NE standards, what exactly do you hope to accomplish here by posting "your" targets?

I mean no disrespect at all and welcome you to continue participating in this thread as I know the knowledge you have was not easily attained nor did it happen overnight. I also know you have surrounded yourself with folks whom I deeply respect and admire, so you're not all bad... wink.gif But I have to say, I do discourage folks from selecting these arbitrary numbers/targets you've set, at least until you can explain exactly what you're trying to accomplish with them.

Are you suggesting a new acoustical model? Are these the targets for this new model? Why do you feel we need a new model/targets? What's wrong with what we have to choose from?

I don't believe the many different acoustical models (which accommodate many different needs and purposes already) need to be changed as they have all worked quite well and are proven and have been around for many years. Do you?

I'm not trying to be rude or harsh, but I just want people to learn the "right" way to begin with. Most of these folks probably have no idea who Don and Carolyn Davis are and don't know of Trevor Cox's work, or Manfred Schroeder, and all the other pioneers in acoustics. They may have heard of Floyd Toole (whom I also admire and respect, but...) who has his own ideas which are very different from the norm on reflections and the ISD for instance. Most of the folks on this thread aren't going to read the text books that we read/have read and aren't in this due to their passion for acoustics and furthering their education.

Most folks (I'm assuming again) are here to learn how to measure their rooms and make them sound better/perform better.

We've done the hard work and have amassed a lot of information over the years but we have to be very careful in how we disseminate it as it is very frustrating to try and unlearn or relearn something, sometimes to the point that one simply gives up or worse yet, doesn't know they have learned "wrong."

So to keep it "right" I am going to specify exactly what I disagree with and I welcome you to let me know why it is you made the recommendations you did in your white paper and what you're trying to accomplish by changing the standards already set in place long ago that have been working quite well for everything from recording/mastering studios to critical listening rooms for several decades now with few updates/changes to the models in which they're based.

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?

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?

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.

The effects of what you've recommended here are much more devastating than those of what you recommended for the ETC.

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.

Nyal, I know reading this probably upsets you and may even come across as preachy or arrogant but I assure you the intent of this reply is nothing more than an attempt to keep everyone on the same page and encourage them to read up on the TRUE - ACTUAL Acoustical Room Models that are proven with specific targets that which rooms have been built to for decades now.

There is no reason to invent the wheel. The information is out there. The acoustical models we have now work. I'm simply trying to condense as much of the information that is already out there as possible and slowly work through each step in this thread so that in the end, or at least months down the road, other folks will have a reliable source to visit and learn correct and proven factual information so they too can hopefully achieve acoustic nirvana.

I actually agree with all the points in your white paper that I didn't specifically call out, and there are more things I agree with than I don't, but some of the things I don't agree with are critical to the acoustical response of a room and quite frankly are too "easy" and I'd bet a lot of people reading this thread are already within most of your specified targets.

Sorry for this novel of a post and sorry if you take offense to this. I've not once written one post in my tenure at AVS that I feel is likely to offend anyone, yet I'm afraid this may be my first, although I honestly assure you that the education and enjoyment of the readers of this thread are all I truly care about and I wish to preserve the integrity of this thread and all of the masters of this industry that paved the way and wrote the true manuals for us to achieve the best listening rooms possible.

I do hope we can talk again under more pleasant circumstances and get to know each other.

Also, as I'm sure regular readers of this thread have figured out, I am a few days behind as I'm launching a new company soon and just don't have the time I wish I had to dedicate to this thread right now, so if you reply, I may be a bit behind on getting back with you but rest assured I will respond.

Thanks,

--J

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post #639 of 15547 Old 01-26-2013, 05:59 AM
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Originally Posted by sdrucker View Post

Jason said:
"Finally, use 60db above that level as your actual measuring level when you wish to make absolute/accurate measurements. You'll likely find that most of the time, in most situations, you won't have to measure much above 90db or so, especially if you have a reasonably quiet room and don't live in Midtown Manhattan. wink.gif "

Not sure if this meets the 40-45 db 'typical US home' noise floor, but we live on the 20ish floor of a hi-rise building in downtown Chicago, two blocks from Lake Shore Drive, and about four blocks from a major hospital. It's 6:45 AM and sitting on our sofa in our living room/HT, I hear wind tunnel effects from outside that sound like muted engine roar, and an occasional ambulance (as well as the occasional bus or truck). And we have neighbors...

Short of moving and/or aiming for 100+ db test tone measurements as an ideal for capturing optimal dynamic range (and NOT measuring the weekend of the Air and Water Show LOL), I may well be limited to 85-90 db measurement and a noise floor closer to what Jerry observed (mid 50s), hence a 30-40 db dynamic range over the noise floor in practical terms.

Before I do system measurements with the USB mic coming (hopefully, if PE is correct) next week, I may well post the waterfall with the 'sounds of silence' for commentary.

 

I live in rural England. There is no sort of industry for miles (other than farming), no major roads for miles, few people, lots of animals and my house is fairly modern with insulation (thermal) in the walls, floors, ceilings etc. You'd maybe expect my noise floor to be incredibly low, but surprisingly it comes in around 40dB during the day, dropping a few dB late at night. 

 

I am a little concerned from reading Jason's posts that unless I measure at 100dB I am not getting the most accurate results, but I can say without question that I echo Jerry's sentiment here and will not be testing at 100dB. I may well use Max's suggestion of increasing in 5dB increments and looking for compression, but even if my speaker can play 100dB without compression (which they ought be able to - M&K S150s) I still wouldn't want to push sine waves through them at that level. So I guess I will be using 85dB, 90 dB at the most, which is only 40-45dB above my noise floor during the day, when my measurements will be taken.

 

Does anyone (Jason?) think this is a problem?  Will my measurements still be accurate enough to be useful?  I certainly don't test at 100dB with my OmniMic and neither does Audyssey measure at anything like that level either. If a much lower level of test signal is good enough for Audyssey, is it not also good enough for REW?  After all, I would never not use Audyssey, so whatever REW does for me, it will always be working along with Audyssey whose measurements have been taken at 75dB - just 35dB above my noise floor.

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post #640 of 15547 Old 01-26-2013, 06:00 AM
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Hi Michael,

You DO NOT use a pre amp when using a Radio Shack SPL Meter. Without going into detail, I'm surprised you were able to get this to even work reliably and without all kinds of issues. wink.gif

The RS meter should be plugged directly into the computer's sound card. No additional hardware is required or recommended.

As far as output, you can still use analog/headphone out or go with HDMI if you wish, but the RS meter should be plugged directly into a "Line In" connection on your computer's sound card.

--J

Computer's soundcard is awful (graph posted earlier). I don't use the phantom voltage, of course.

 

From HTS:

 

"A microphone input (mic-in) on a soundcard is not suitable (many laptops only have mic-in). 

LAPTOP Note:
If your laptop is limited to a mic-in port with no line-in, then you'll require an external USB soundcard. There are basically two flavors of external USB soundcards.

One type contain an internal microphone preamp(s) with phantom power for condenser mics (such as the ECM8000 or EMM-6). The popular manufacturers of these type are Tascam, EM-U, and M-Audio. The connection diagram for these soundcards is shown at the bottom of the page, but be sure to read through this entire article first.

The second type do not contain a microphone preamp, and have analog line-in and line-out only. The interconnects for this type are the same as for an internal PC soundcard.

Read more: REW Cabling and Connection Basics - Home Theater Forum and Systems - HomeTheaterShack.com"

 

Works. Really.


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post #641 of 15547 Old 01-26-2013, 06:06 AM - Thread Starter
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Originally Posted by sdrucker View Post

Jason said:
"Finally, use 60db above that level as your actual measuring level when you wish to make absolute/accurate measurements. You'll likely find that most of the time, in most situations, you won't have to measure much above 90db or so, especially if you have a reasonably quiet room and don't live in Midtown Manhattan. wink.gif "

Not sure if this meets the 40-45 db 'typical US home' noise floor, but we live on the 20ish floor of a hi-rise building in downtown Chicago, two blocks from Lake Shore Drive, and about four blocks from a major hospital. It's 6:45 AM and sitting on our sofa in our living room/HT, I hear wind tunnel effects from outside that sound like muted engine roar, and an occasional ambulance (as well as the occasional bus or truck). And we have neighbors...

Short of moving and/or aiming for 100+ db test tone measurements as an ideal for capturing optimal dynamic range (and NOT measuring the weekend of the Air and Water Show LOL), I may well be limited to 85-90 db measurement and a noise floor closer to what Jerry observed (mid 50s), hence a 30-40 db dynamic range over the noise floor in practical terms.

Before I do system measurements with the USB mic coming (hopefully, if PE is correct) next week, I may well post the waterfall with the 'sounds of silence' for commentary.

Well Stuart,

If you're in Chicago, in a high rise, in a Condo, with thin walls and can't make noise, you're screwed. biggrin.gif

Honestly, you can only do what you can do. If all you can comfortably do is 85-90 then so be it.

It's not like your measurements are going to be invalid.

They just won't be "absolutely" accurate. You'll still get a VERY GOOD idea of what's truly happening in your room if you can measure at 90db though, I promise.

Also, remember, if you're in the middle of changing things around, moving MLP/Speakers, adding/moving treatments, etc, and are simply measuring in between each change to see what effect it had, measuring around 75-80db is just fine.

This goes for everybody, no matter what their noise floor is or how loud they can measure. I measure at 85db regularly even though I have a 35db noise floor as right now I'm testing some changes I made recently.

When I test the effects of new diffusors and reflectors I'm designing I do the same thing. When I design a new bass trap and test it though, you better believe I'm measuring with a full 60db to work with, though.

It just depends on what you're doing and what the measurements are going to be used for/how accurate you need them to be.

I hope people are not absolutely shocked when they see the difference between RS meters, Audyssey Mics and their new $100 calibrated mics because unless something is actually physically wrong with the mics, there honestly shouldn't be a "huge" difference over most of the frequency band.

What you're getting with the calibrated mic is peace of mind. You know for a fact it's accurate. That's worth $100 to me! biggrin.gif

Same thing with measuring louder... More accurate but not going to be totally different than measuring at more reasonable levels, however, much more important in the bass/modal range.

Hope this helps,

--J

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post #642 of 15547 Old 01-26-2013, 06:08 AM
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For instance, Jerry, I believe your noise floor was measured at 57db, right? (I'd recalibrate the SPL meter, make sure everything is as quiet as possible, do it late at night when it's quiet outside too, and verify that - it seems like a very high noise floor and 57db is actually pretty bad. I don't trust that measurement.) If you look at your waterfall graphs, you're not going to see nothing but noise starting right at 57db.

 

 

Jason, I don't know where you got the idea that my noise floor is 57dB.  eek.gif  I live in a single-family home in a very quiet neighborhood, am single, and have no pets.  My room is fairly well treated as well.  When I am working with REW, I make sure the HVAC, refrigerator, etc. are turned off.  My noise floor is right at 40dB.

 

I have always wondered what is contributing to the 40dB level, and how I might get it even lower.

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post #643 of 15547 Old 01-26-2013, 06:13 AM
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You've got hum at 60 Hz JChin!! LOL (And repeats itself at 120 Hz, first harmonic, while the one at 200 Hz puzzles me, coz it should be 180 Hz, right??!! Although there is something at 180 Hz which gives me more puzzles.). Look at those fellows that don't decay as time elapses on you waterfall graph. cool.gif On a second note, this questions how accurate the frecuency scale of REW is. Any thoughs welcome.

Q, is it aubible at the MLP? Witout a source you may turn up the MV to 0 dB and listen carefully. If you don't hear the hum at MLP it's all ok. At this frequency our ears are less sensitive to sounds at such low levels as can be seen on the "equal loudness curves". Worry not.

Meantime, in case the 60 Hz mains hum shows its harmonics your sub may be affected by harmonic distortion. Let's try to investigate this case together. Anyone?

To continue beating a dead horse, it may not be hum after all! From Jerry's (wonderful) guide discussing waterfalls:

 

"The remaining resonances are at 36Hz (41.5dB), 58Hz (also 41.5dB), and 66Hz (41dB). The 36Hz resonance coincides with the primary mode of the listening room length (16.3 feet), and the 58Hz resonance coincides with the secondary mode of the listening room width (19.5 feet)."

So perhaps there's no hum at all, and the room is just 20 feet deep.

Hmm.

 


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post #644 of 15547 Old 01-26-2013, 06:15 AM
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I hope people are not absolutely shocked when they see the difference between RS meters, Audyssey Mics and their new $100 calibrated mics because unless something is actually physically wrong with the mics, there honestly shouldn't be a "huge" difference over most of the frequency band.

 

 

I have compared the response curves of my RS SPL to curves measured using my CSL EMM-6 mic, and as you say, the curves are quite similar, especially when measuring frequencies below 1-2kHz.

 

BTW, I asked this question earlier, but received no response.  My EMM-6 comes with "narrow band response" calibration files, and with "one third octave band response" calibration files.  Which should I be using, and what is the difference betweem the two? 

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post #645 of 15547 Old 01-26-2013, 06:17 AM - Thread Starter
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Originally Posted by kbarnes701 View Post

Quote:
Originally Posted by sdrucker View Post

Jason said:

"Finally, use 60db above that level as your actual measuring level when you wish to make absolute/accurate measurements. You'll likely find that most of the time, in most situations, you won't have to measure much above 90db or so, especially if you have a reasonably quiet room and don't live in Midtown Manhattan. wink.gif "


Not sure if this meets the 40-45 db 'typical US home' noise floor, but we live on the 20ish floor of a hi-rise building in downtown Chicago, two blocks from Lake Shore Drive, and about four blocks from a major hospital. It's 6:45 AM and sitting on our sofa in our living room/HT, I hear wind tunnel effects from outside that sound like muted engine roar, and an occasional ambulance (as well as the occasional bus or truck). And we have neighbors...


Short of moving and/or aiming for 100+ db test tone measurements as an ideal for capturing optimal dynamic range (and NOT measuring the weekend of the Air and Water Show LOL), I may well be limited to 85-90 db measurement and a noise floor closer to what Jerry observed (mid 50s), hence a 30-40 db dynamic range over the noise floor in practical terms.


Before I do system measurements with the USB mic coming (hopefully, if PE is correct) next week, I may well post the waterfall with the 'sounds of silence' for commentary.

I live in rural England. There is no sort of industry for miles (other than farming), no major roads for miles, few people, lots of animals and my house is fairly modern with insulation (thermal) in the walls, floors, ceilings etc. You'd maybe expect my noise floor to be incredibly low, but surprisingly it comes in around 40dB during the day, dropping a few dB late at night. 

I am a little concerned from reading Jason's posts that unless I measure at 100dB I am not getting the most accurate results, but I can say without question that I echo Jerry's sentiment here and will not be testing at 100dB. I may well use Max's suggestion of increasing in 5dB increments and looking for compression, but even if my speaker can play 100dB without compression (which they ought be able to - M&K S150s) I still wouldn't want to push sine waves through them at that level. So I guess I will be using 85dB, 90 dB at the most, which is only 40-45dB above my noise floor during the day, when my measurements will be taken.

Does anyone (Jason?) think this is a problem?  Will my measurements still be accurate enough to be useful?  I certainly don't test at 100dB with my OmniMic and neither does Audyssey measure at anything like that level either. If a much lower level of test signal is good enough for Audyssey, is it not also good enough for REW?  After all, I would never not use Audyssey, so whatever REW does for me, it will always be working along with Audyssey whose measurements have been taken at 75dB - just 35dB above my noise floor.

Hi Keith,

I promise you that most of your measurements, most of the time, are going to be perfectly fine at 90db or even 85db. (Wouldn't go lower than that though)

You should absolutely verify the limits of your system to calculate your dynamic range as I stated in a previous post (which Max beat me to; again wink.gif ) and when you have made a major change or feel you're "done" with treatments, at the end of class, (and maybe for mid-terms too) when you're ready to put this thread away forever, that's when you need to measure at 100db (in your case, since your noise floor is actually 40db) but in between, which is most of the time, when you just want to compare one measurement to another to see what effect that last change you made had, measuring at a reasonable level such as 85db is more than adequate!

Don't even think twice about this again. I promise you it's fine.

I actually stated exactly this in one of my previous posts, but it was buried in one of my novel posts since I had so much to cover and catch up on while I was sick with the Flu frown.gif

Since you're so great at writing and putting things together, maybe you can pull this part (as it's sure to be on a lot of people's minds) and also the tip I gave about using REW noise filters to your advantage and checking the actual noise floor as shown in a waterfall graph by looking at higher non-modal frequencies, and maybe put a new post together in your words which are much more eloquent (and shorter) than mine. wink.gif I know there are some good tips and some gems in there but I also know I use way too many words to get my points across and things get buried. I need to work on that, but if everyone will bare with me, I promise you I'll eventually get better, but I doubt I'll ever be able to write like you and Jerry.

Don't you love how every time I answer one of your posts I volunteer you for more work? biggrin.gif

--J

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While it isn't necessarily imperative you take all measurements at 100db, it truly is important to get 60db above your noise floor if you want truly accurate and absolute measurements.
I would strongly advise people not to attempt measurements 60dB above the background noise level in their environments. Measuring at high levels risks damage to equipment, hearing and relations with your neighbours and pushes equipment out of its linear range, increasing distortion and degrading measurement quality.

Measurement software can see well below the acoustic noise floor of your room. The important signal-to-noise (S/N) ratio in measurements is the S/N of the recovered impulse response. To see that, open the Impulse plot with the vertical axis set to dB FS - by default this plot is normalised, which means the peak value is at 0 dB FS, and the noise floor of the impulse response will be apparent when zoomed out so the plot spans a second or so - if the noise floor is at -50 dB FS, for example, the measurement has 50 dB S/N. If the impulse response S/N is below 40 dB or so you may start to see noisier frequency response plots and the floors of waterfalls and spectrograms will start to show more noise, but the measurement still remains useful.

If the S/N of the impulse looks poor and you are using a microphone and preamp or a line input adjust the input gains to keep the signal at a good level, with the peak during a measurement getting to around -10 dB or so (this is shown on REW as the "Headroom" figure when you measure, it should not be too high). USB mics will usually show lower levels as they tend to accommodate wider input ranges, but should still give good impulse response S/N values.

The best way to improve S/N in the measurement is to use a longer sweep, each doubling of sweep length improves S/N about 3 dB. If you are already at the maximum sweep length, try multiple sweeps, though the improvement from each doubling of the number of sweeps is usually not quite as much and some soundcards do not maintain synchronisation between sweeps, causing invalid measurements (evident in multiple peaks at or near 0 dB FS in the impulse response, one per sweep).
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post #647 of 15547 Old 01-26-2013, 06:22 AM
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With that being said and with all due respect, I must humbly disagree with several recommendations your white paper recommends, though.
 

I read, and even understood, your long post, J. I can see where you are coming from and I have nowhere near enough knowledge to take sides on the issues you raise. In fact, everything you say makes perfect sense to me.

 

What I liked about Nyal's 'targets' though was that they were very simply and clearly expressed. I will never be able to follow complicated text books because I don't have enough math and I also don't have the motivation (my one and only acoustics text book is The Master Handbook of Acoustics by F. Alton Everest, which is probably on a par with a kid's first reading primer to you guys). So while I understand what you are saying, it is also equally true that I (and possibly many other virgins here) would really like a simplified set of targets to work to - guidelines if you will rather than absolutes. These targets could be caveated to hell, but they would be useful to me I am sure. I have read about LEDE and RFZ rooms (they are covered in my own and only text book!) but I am not sure either model is what I can achieve in my Hobbit-sized HT. I just want to try to get the best I can out of it and accept inevitable compromises as, well, inevitable (unless I move house and get a better, bigger room). So would it be impossible to suggest a simple list of targets I can aim for, with regard to FR, decay times, ETCs etc? If I had something like that to work with, it would make my REW work so much easier. If I am being too simplistic, please just say so - I am here to learn.

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post #648 of 15547 Old 01-26-2013, 06:25 AM
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^^ Welcome to the thread, John!  Looking forward to hearing more from you.

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post #649 of 15547 Old 01-26-2013, 06:29 AM
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Hi Keith,

I promise you that most of your measurements, most of the time, are going to be perfectly fine at 90db or even 85db. (Wouldn't go lower than that though)

You should absolutely verify the limits of your system to calculate your dynamic range as I stated in a previous post (which Max beat me to; again wink.gif ) and when you have made a major change or feel you're "done" with treatments, at the end of class, (and maybe for mid-terms too) when you're ready to put this thread away forever, that's when you need to measure at 100db (in your case, since your noise floor is actually 40db) but in between, which is most of the time, when you just want to compare one measurement to another to see what effect that last change you made had, measuring at a reasonable level such as 85db is more than adequate!

Don't even think twice about this again. I promise you it's fine.

I actually stated exactly this in one of my previous posts, but it was buried in one of my novel posts since I had so much to cover and catch up on while I was sick with the Flu frown.gif

Since you're so great at writing and putting things together, maybe you can pull this part (as it's sure to be on a lot of people's minds) and also the tip I gave about using REW noise filters to your advantage and checking the actual noise floor as shown in a waterfall graph by looking at higher non-modal frequencies, and maybe put a new post together in your words which are much more eloquent (and shorter) than mine. wink.gif I know there are some good tips and some gems in there but I also know I use way too many words to get my points across and things get buried. I need to work on that, but if everyone will bare with me, I promise you I'll eventually get better, but I doubt I'll ever be able to write like you and Jerry.

Don't you love how every time I answer one of your posts I volunteer you for more work? biggrin.gif

--J

 

:) LOL. I will do all I can to help this thread, J, be assured! I am doing very little right now because I want to wait until the thread really gets started, when we all have our mics. Then we will know the issues that come up repeatedly. I am also wondering whether we even need a FAQ - Jerry's Guide, if expanded (as I believe Jerry intends) may cover all the bases on its own - but we can wait and see how it ll pans out.

 

Thanks for the reassurance about the measuring levels. Sorry to hear you were unwell - hope you're fully recovered now.

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I hope people are not absolutely shocked when they see the difference between RS meters, Audyssey Mics and their new $100 calibrated mics because unless something is actually physically wrong with the mics, there honestly shouldn't be a "huge" difference over most of the frequency band.


 

I have compared the response curves of my RS SPL to curves measured using my CSL EMM-6 mic, and as you say, the curves are quite similar, especially when measuring frequencies below 1-2kHz.

BTW, I asked this question earlier, but received no response.  My EMM-6 comes with "narrow band response" calibration files, and with "one third octave band response" calibration files.  Which should I be using, and what is the difference betweem the two? 

Sorry Jerry, I didn't see that question. I really do try to answer every question I see that hasn't already been answered. I'll just have to look harder. wink.gif Let me know if I've missed anything else.

Narrow band simply means more point of measurement/comparison than 1/3rd. It's just like viewing an unsmoothed vs 1/3rd octave smoothed FR.

You definitely want to use the narrow band files for REW as we'll mostly be viewing at high resolution unsmoothed or maybe 1/48th smoothed for higher frequencies.

If you look at the difference (in the same measurement) between a FR graph that is unsmoothed and 1/3rd smoothed you'll see that the comb filtering in the higher frequencies shapes the 1/3rd graph differently and artifacts can cause the 1/3rd graph to not be as accurate.

The 1/3rd files are used on equipment that doesn't have high resolution. For instance, if you use an actual Real Time Analyzer that maxes out at 1/3rd octave then the most accurate results would be to use the 1/3rd cal file as it takes into consideration the smoothing you're using to provide more accurate data.

If you really want to get anal about it ("I" don't even do this) you could load the narrow band for all unsmoothed down to 1/24th smoothed and load the 1/3rd file for when you're looking at 1/3rd smoothed graphs, but since 1/3rd smoothed graphs are absolutely useless and I won't be recommending we use them AT ALL, I see no point.

It's just that Herb doesn't know who will be using software like REW and who will be using specific hardware solutions with built in RTA's at 1/3rd, so he is thorough enough to provide both.

Hope that clears it up for you,

--J

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

I read, and even understood, your long post, J. I can see where you are coming from and I have nowhere near enough knowledge to take sides on the issues you raise. In fact, everything you say makes perfect sense to me.

 

What I liked about Nyal's 'targets' though was that they were very simply and clearly expressed. I will never be able to follow complicated text books because I don't have enough math and I also don't have the motivation (my one and only acoustics text book is The Master Handbook of Acoustics by F. Alton Everest, which is probably on a par with a kid's first reading primer to you guys). So while I understand what you are saying, it is also equally true that I (and possibly many other virgins here) would really like a simplified set of targets to work to - guidelines if you will rather than absolutes. These targets could be caveated to hell, but they would be useful to me I am sure. I have read about LEDE and RFZ rooms (they are covered in my own and only text book!) but I am not sure either model is what I can achieve in my Hobbit-sized HT. I just want to try to get the best I can out of it and accept inevitable compromises as, well, inevitable (unless I move house and get a better, bigger room). So would it be impossible to suggest a simple list of targets I can aim for, with regard to FR, decay times, ETCs etc? If I had something like that to work with, it would make my REW work so much easier. If I am being too simplistic, please just say so - I am here to learn.

 

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.

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Narrow band simply means more point of measurement/comparison than 1/3rd. It's just like viewing an unsmoothed vs 1/3rd octave smoothed FR.

You definitely want to use the narrow band files for REW as we'll mostly be viewing at high resolution unsmoothed or maybe 1/48th smoothed for higher frequencies.

 

 

Yes, that is the clarification I needed, thanks.  I'll add this information to the REW Guide, since a number of us will be getting mics from CSL with similar calibration files.

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Hi Keith,


I promise you that most of your measurements, most of the time, are going to be perfectly fine at 90db or even 85db. (Wouldn't go lower than that though)


You should absolutely verify the limits of your system to calculate your dynamic range as I stated in a previous post (which Max beat me to; again wink.gif ) and when you have made a major change or feel you're "done" with treatments, at the end of class, (and maybe for mid-terms too) when you're ready to put this thread away forever, that's when you need to measure at 100db (in your case, since your noise floor is actually 40db) but in between, which is most of the time, when you just want to compare one measurement to another to see what effect that last change you made had, measuring at a reasonable level such as 85db is more than adequate!


Don't even think twice about this again. I promise you it's fine.


I actually stated exactly this in one of my previous posts, but it was buried in one of my novel posts since I had so much to cover and catch up on while I was sick with the Flu frown.gif


Since you're so great at writing and putting things together, maybe you can pull this part (as it's sure to be on a lot of people's minds) and also the tip I gave about using REW noise filters to your advantage and checking the actual noise floor as shown in a waterfall graph by looking at higher non-modal frequencies, and maybe put a new post together in your words which are much more eloquent (and shorter) than mine. wink.gif I know there are some good tips and some gems in there but I also know I use way too many words to get my points across and things get buried. I need to work on that, but if everyone will bare with me, I promise you I'll eventually get better, but I doubt I'll ever be able to write like you and Jerry.


Don't you love how every time I answer one of your posts I volunteer you for more work? biggrin.gif


--J

smile.gif LOL. I will do all I can to help this thread, J, be assured! I am doing very little right now because I want to wait until the thread really gets started, when we all have our mics. Then we will know the issues that come up repeatedly. I am also wondering whether we even need a FAQ - Jerry's Guide, if expanded (as I believe Jerry intends) may cover all the bases on its own - but we can wait and see how it ll pans out.

Thanks for the reassurance about the measuring levels. Sorry to hear you were unwell - hope you're fully recovered now.

I'm a HUGE baby and PITA when I'm sick and believe me, you all should be very happy I wasn't around in the last few days as I know for sure my family wishes that.

You know, since Jerry has done such a great job and has gone into so much detail I do feel his guide would be a good place for the FAQ's and TIPS.

I must admit, I feel like a lot of the tips I've written and a lot of the information (not all the words in between, but the actual info lol) will be coming up again and again and I do wish you and/or Jerry could/would go through my last several posts and pull out the actual pertinent information (which should be rather obvious to pick out) and if nothing else, copy it to a notepad of some kind for future inclusion in the guide because I just know a lot of this stuff is going to start coming up soon, especially since the mics are on the way. (Funny thing is I don't know if I made it into the first batch of UMM-6's yet!! Plus, as soon as I get one I have to send it off to John for inclusion in REW so I'm not even going to have one of these for awhile lol)

Anyway, thanks for everything, Keith... I most definitely could not get this thread going and keep it going without you and Jerry. I really mean that. With the little time I have and sometimes not being able to get on here for a few days, then being sick recently, I do at least feel between you two everyone is in great hands and you all can hold the fort down until I come back.

I have some exciting things to announce soon which will hopefully be of use to most in this thread and hopefully soon I will have a little more time open up to where I can at least get back on here regularly every evening, at a minimum.

For now though, I must head to the office for even more acoustics fun! wink.gif

See ya,

--J

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Narrow band simply means more point of measurement/comparison than 1/3rd. It's just like viewing an unsmoothed vs 1/3rd octave smoothed FR.


You definitely want to use the narrow band files for REW as we'll mostly be viewing at high resolution unsmoothed or maybe 1/48th smoothed for higher frequencies.


 

Yes, that is the clarification I needed, thanks.  I'll add this information to the REW Guide, since a number of us will be getting mics from CSL with similar calibration files.

Cool beans... I was just talking to Keith and have to admit I do feel there are several nuggets from my latest few posts (especially the long ones) that I feel would be pertinent to the guide.

What is your opinion on a separate faq vs adding some of the tips and other bits o' info to the guide you've already created?

I don't want to intrude or alter what you've set out to create, and I do appreciate all you do very much, but if you have time would you mind going through today's posts and possibly grabbing the tips, tricks, how-to's, etc for possible inclusion into, if not your guide, some type of document? I just put way too much "noise" in between all the good info and I'm afraid not everyone is going to read the long posts... See, I can't even make a simple request without turning it into a novel. wink.gif

Thanks Jerry,

--J

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post #655 of 15547 Old 01-26-2013, 06:50 AM - Thread Starter
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With that being said and with all due respect, I must humbly disagree with several recommendations your white paper recommends, though.

 
I read, and even understood, your long post, J. I can see where you are coming from and I have nowhere near enough knowledge to take sides on the issues you raise. In fact, everything you say makes perfect sense to me.

What I liked about Nyal's 'targets' though was that they were very simply and clearly expressed. I will never be able to follow complicated text books because I don't have enough math and I also don't have the motivation (my one and only acoustics text book is The Master Handbook of Acoustics by F. Alton Everest, which is probably on a par with a kid's first reading primer to you guys). So while I understand what you are saying, it is also equally true that I (and possibly many other virgins here) would really like a simplified set of targets to work to - guidelines if you will rather than absolutes. These targets could be caveated to hell, but they would be useful to me I am sure. I have read about LEDE and RFZ rooms (they are covered in my own and only text book!) but I am not sure either model is what I can achieve in my Hobbit-sized HT. I just want to try to get the best I can out of it and accept inevitable compromises as, well, inevitable (unless I move house and get a better, bigger room). So would it be impossible to suggest a simple list of targets I can aim for, with regard to FR, decay times, ETCs etc? If I had something like that to work with, it would make my REW work so much easier. If I am being too simplistic, please just say so - I am here to learn.

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.

Here's what I can do.

I have a lot of knowledge of the different targets for the different room models and even know which few most here are going to pick to model.

I do not have a lot of time right now nor quite frankly do I have the skill that you guys have in creating documentation.

I can give you the info for a LEDE/RFZ room and for a NE room that Nyal gave for whatever he calls his "model" and if you have the time, patience, and skill (I'm only sure of the last one) to help translate my hard data into the pretty guide/graph then as a team we can finally get this "Correct" information out to the masses so they don't have to read textbooks and study for years like a few of us have.

I STRONGLY suggest reading the seven page article I linked to and downloading RPG's paper that both explain the different room models and targets, though.

I really hope everyone does this and then selects one. It's the absolute first step. If we can't get folks to do this then I don't see how we're going to move past the "how to use REW" which is coming up next, because after that we should all be working on specific goals to accomplish a specific model to get known results that many many people are happy with.

Tell me what you don't understand or what you'd like more of from those two documents so I can get a few opinions and start crafting the beginnings of a more thorough document and compile more information for a simple chart/graph folks can quickly refer to along the way (like Nyal made) to check their rooms against the actual targets.

If you guys can do that and help me help you, I promise to spend the time to compile all relevant information and I know between you two, the end result will be easy to read and very worthwhile.

Thanks a bunch,

--J

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Narrow band simply means more point of measurement/comparison than 1/3rd. It's just like viewing an unsmoothed vs 1/3rd octave smoothed FR.


You definitely want to use the narrow band files for REW as we'll mostly be viewing at high resolution unsmoothed or maybe 1/48th smoothed for higher frequencies.


 

Yes, that is the clarification I needed, thanks.  I'll add this information to the REW Guide, since a number of us will be getting mics from CSL with similar calibration files.

Cool beans... I was just talking to Keith and have to admit I do feel there are several nuggets from my latest few posts (especially the long ones) that I feel would be pertinent to the guide.

What is your opinion on a separate faq vs adding some of the tips and other bits o' info to the guide you've already created?

I don't want to intrude or alter what you've set out to create, and I do appreciate all you do very much, but if you have time would you mind going through today's posts and possibly grabbing the tips, tricks, how-to's, etc for possible inclusion into, if not your guide, some type of document? I just put way too much "noise" in between all the good info and I'm afraid not everyone is going to read the long posts... See, I can't even make a simple request without turning it into a novel. wink.gif

Thanks Jerry,

--J

 

I'll give it a shot somtime this weekend.

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While it isn't necessarily imperative you take all measurements at 100db, it truly is important to get 60db above your noise floor if you want truly accurate and absolute measurements.
I would strongly advise people not to attempt measurements 60dB above the background noise level in their environments. Measuring at high levels risks damage to equipment, hearing and relations with your neighbours and pushes equipment out of its linear range, increasing distortion and degrading measurement quality.

Measurement software can see well below the acoustic noise floor of your room. The important signal-to-noise (S/N) ratio in measurements is the S/N of the recovered impulse response. To see that, open the Impulse plot with the vertical axis set to dB FS - by default this plot is normalised, which means the peak value is at 0 dB FS, and the noise floor of the impulse response will be apparent when zoomed out so the plot spans a second or so - if the noise floor is at -50 dB FS, for example, the measurement has 50 dB S/N. If the impulse response S/N is below 40 dB or so you may start to see noisier frequency response plots and the floors of waterfalls and spectrograms will start to show more noise, but the measurement still remains useful.

If the S/N of the impulse looks poor and you are using a microphone and preamp or a line input adjust the input gains to keep the signal at a good level, with the peak during a measurement getting to around -10 dB or so (this is shown on REW as the "Headroom" figure when you measure, it should not be too high). USB mics will usually show lower levels as they tend to accommodate wider input ranges, but should still give good impulse response S/N values.

The best way to improve S/N in the measurement is to use a longer sweep, each doubling of sweep length improves S/N about 3 dB. If you are already at the maximum sweep length, try multiple sweeps, though the improvement from each doubling of the number of sweeps is usually not quite as much and some soundcards do not maintain synchronisation between sweeps, causing invalid measurements (evident in multiple peaks at or near 0 dB FS in the impulse response, one per sweep).

Hi John,

Great to see you over here!

I hope you'll subscribe and stick with us.

BTW, I plan to send you a UMM-6 mic as soon as the backorder comes in in the next week or two.

Of course, you are right and you were more specific than I was.

Again folks, read my latest posts and see that I do not recommend taking all your measurements at that level and John has given you yet another way to calculate a level to take "regular" measurements at.

Between his example above and my previous example in looking at the noise floor of the higher (non modal) frequencies in the waterfall you should be able to easily find a happy medium that is both loud enough but also doesn't damage your ears or equipment.

I must reiterate though, IMO it "IS" important to measure 60db above the noise floor at least twice. Once to see the limits of your equipment and where compression and distortion start to go into full swing and if ever a time comes when you feel you are truly done tweaking the acoustics of your room.

I'm sorry I wasn't this specific in the beginning and you guys got the idea I recommended taking 100db+ measurements every single time, but at least we got the man himself to join our discussion, right! biggrin.gif

Thanks again John, for all you do.

I'm sure you realize by now, with the latest improvements to REW a lot more people will be using and enjoying your software and I sure hope others remember to kindly donate to the cause as John has put countless hours into making REW free for all of us and asks for nothing in return. REW is quickly becoming (I believe it already has) the most powerful acoustical measuring software available and it does all it does, for free!

--J

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post #658 of 15547 Old 01-26-2013, 07:20 AM - Thread Starter
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With that being said and with all due respect, I must humbly disagree with several recommendations your white paper recommends, though.

 
I read, and even understood, your long post, J. I can see where you are coming from and I have nowhere near enough knowledge to take sides on the issues you raise. In fact, everything you say makes perfect sense to me.

What I liked about Nyal's 'targets' though was that they were very simply and clearly expressed. I will never be able to follow complicated text books because I don't have enough math and I also don't have the motivation (my one and only acoustics text book is The Master Handbook of Acoustics by F. Alton Everest, which is probably on a par with a kid's first reading primer to you guys). So while I understand what you are saying, it is also equally true that I (and possibly many other virgins here) would really like a simplified set of targets to work to - guidelines if you will rather than absolutes. These targets could be caveated to hell, but they would be useful to me I am sure. I have read about LEDE and RFZ rooms (they are covered in my own and only text book!) but I am not sure either model is what I can achieve in my Hobbit-sized HT. I just want to try to get the best I can out of it and accept inevitable compromises as, well, inevitable (unless I move house and get a better, bigger room). So would it be impossible to suggest a simple list of targets I can aim for, with regard to FR, decay times, ETCs etc? If I had something like that to work with, it would make my REW work so much easier. If I am being too simplistic, please just say so - I am here to learn.

Keith,

Your request is simple enough and I think I can accomplish what you want. I won't have the time to make it pretty like Nyal did, but I can and will compile all the raw information and send it to you and/or Jerry to work on because if I post it here, not only will it not be pretty but it will surely also be too wordy. wink.gif

BTW, MHOA is a wonderful book and is the first one I read, too! It is definitely not comparative to a first grade reader. Once you read, then re-read, and start applying some of the things you learned in MHOA you'll find that most other text books are on specific subject matter and are more of expansions on specific chapters in MHOA.

For instance, for anyone interested in making their own acoustical treatment instead of buying it (it's actually great for folks buying, too, as just because you own something doesn't mean you know how to use it/where to place it) I strongly recommend THE BOOK, "Acoustic Absorbers & Diffusers" by D'antonio and Trevor Cox of RPG. These folks "LITERALLY" wrote the book in this case and brought us LEDE, developed QRD Diffusors, and have done so much for us, and a lot of it is just given away in that book... All you have to do is read it.

It just depends on how far you want to take your knowledge, how passionate you are about acoustics, and what you want to do with the knowledge you gain.

I fully understand most people haven't viewed the field of acoustics and psychoacoustics their hobby and passion for several years as I have and most people don't want to read all the posts in this thread let alone textbooks on the subject, so I will try to compile some data and if you and/or Jerry can put it in an easy to read/understand form like Nyal did, all the better.

The info IS there. It's different for each model and there are ranges and there are of course caveats which we can explain in the thread in more detail and as the questions arise, but there is no reason we can't start by getting the criteria for a certified LEDE room out there and even offer some examples and projects along the way, as I personally have both of those. wink.gif

I'll work on this but don't expect it "today."

As for your room, no, with the size of your room, you probably won't be able to get it LEDE Certified, but you'd never try to do that anyway. None of us would since we are critical music listeners and not recording studios. However, there is no reason you cannot "approach" a LEDE room. You won't get a 20ms ISD Gap but with the proper compromises and the proper treatment, as long as you're willing to invest the time to gain the knowledge, you can get very close. A few compromises a room your size will most likely end up with is around a 10ms ISD Gap and a relatively even modal decay rate that is longer in time than the mid-hi range which we'll have to be very careful to not overdeaden but it can be done and in fact HAS been done.

There is a great thread by a member called Lupo, over on Gearslutz (I "think" that's his name - will have to look up the thread when I get back tonight) who lives in Europe, has a very small room, and he has achieved LEDE without a million traps through clever use of reflection and diffusion with a moderate amount of bass trapping. He shows pictures and his ETC's along the way and the result is quite nice! So you can do it, but you'll only get out of it however much you put into it.

Hope this helps, and I'll be back this evening to talk more.

See ya,

--J

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post #659 of 15547 Old 01-26-2013, 07:35 AM - Thread Starter
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Originally Posted by jevansoh View Post

For instance, Jerry, I believe your noise floor was measured at 57db, right? (I'd recalibrate the SPL meter, make sure everything is as quiet as possible, do it late at night when it's quiet outside too, and verify that - it seems like a very high noise floor and 57db is actually pretty bad. I don't trust that measurement.) If you look at your waterfall graphs, you're not going to see nothing but noise starting right at 57db.


 

Jason, I don't know where you got the idea that my noise floor is 57dB.  eek.gif   I live in a single-family home in a very quiet neighborhood, am single, and have no pets.  My room is fairly well treated as well.  When I am working with REW, I make sure the HVAC, refrigerator, etc. are turned off.  My noise floor is right at 40dB.

I have always wondered what is contributing to the 40dB level, and how I might get it even lower.

Sorry Jerry, I thought I saw a measurement of yours showing the SPL reading from REW and it showed 57. I must be thinking of someone or something else.. Was only going from memory, and a bad one at that.

40db is pretty normal for a quiet house.

Even if it sounds dead quiet to you it's reading around 40db because of lower frequencies that have long wavelengths that also travel far and aren't audible at that level.

You won't get it much below that without working on your transmission loss levels and the only way to do that unfortunately is construction. Your situation is very common which is why in fact "most" people's noise floor is right at 40db. I've put a TON of work into my room, everything short of building it all over again, and I've only gotten to 35db so don't feel bad. It's a ton better than the 57db I thought you had! wink.gif

If you truly want to know what you could do to lower it more and improve your dynamic range and get the most out of your listening experience, I'd be happy to discuss it with you, but be forewarned, it's a lot of work and will cost a bit of money, too.

Let me know,

--J

Thanks to EVERYONE that Helps Make These Threads so Awesome!

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post #660 of 15547 Old 01-26-2013, 09:02 AM
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Ok finally have a few minutes to get my first reading.

Following Jerry's instruction guide and when I am trying to calibrate the left speaker and it pushes the signal the first bar is -12db snd then without touching anything the second bar hovers around -57db and when I up the volume to get the two to be 'close' it is extremely loud and on my AV7005 it is pushing zero on my volume on the avr and it is making me nervous and I actually don't think they would match even if I maxed out the volume.

I am obviously doing something wrong. I have the UMIK mic with its calibration file loaded. I have everything set I believe correct, but something is off.

Help!

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