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post #1 of 63 Old 02-13-2013, 03:34 PM - Thread Starter
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I originally started this thread just to get some feedback on MY measurements - I'm very glad to see that it may be continuing on indeffinitely helping others with REW! It's great to see Amir and GIK helping out us less educated with this sometimes hard to understand information. Thanks guys!


Here are some guidelines for posting graphs:

The preferred axis for ALL subwoofer graphs is:

VERTICAL = 45dB-105dB
HORIZONTAL = 25Hz-120Hz.
NO SMOOTHING


The preferred axis for full range graphs is:

VERTICAL = 45dB-105dB
HORIZONTAL = 25Hz-25,000Hz.
1/24th SMOOTHING

For subwoofer Waterfall graphs:

- Time range should initially be set to 300ms, never more than 600ms
- Lower limit should be set just above the noise floor in your room, typically around 45-50db - anything below this is useless background noise


>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

I posted this in the REW/USB/HDMI Setup thread, but it moves so fast, I think it's getting lost. I thought re-posting in it's own thread might get me a better response. Thanks in advance for any insight!

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

OK, I got some good measurements last night after pushing subs around my room for about and hour and a half. rolleyes.gif I've got 3 subs - 2 new, 1 older that is mismatched - and the placement combinations are seemingly endless! Anyway, I think I've got the bass response as good as it's gonna get without treatment (in the plans).

These measurements were taken with my UMM-6 and legacy audio connections (PC audio out to AVR). I've still got a small ground loop hum at 60hz that I need to hunt down and kill though.

Here's my graphs:

Subs + L/R, Audyssey OFF:



Subs + L/R, Audyssey ON:



Subs + L/R, Audyssey ON/OFF overlayed:



Subs + L/R, Audyssey OFF, full range sweep:



Subs + L/R, Audyssey ON, full range sweep:



Subs + L/R, Audyssey ON/OFF, full range sweep, overlayed:



Subs + L/R Waterfall, Audyssey OFF:



Subs + L/R Waterfall, Audyssey ON:



Drawing of my room with current sub placement:



MDAT file:

Alan P2.zip 1751k .zip file

The sub response to me looks really good with Audyssey off, but after it's turned on there is some weirdness going on above the crossover point (80hz). Audyssey did however flatten it out nicely between 30-60hz.

On the full range sweeps, Audyssey created a big dip between 90-170hz. This is the "meat" of the mid-bass, correct?

Waterfalls are set to 600ms to get the last of the decay - looks not too bad to me, but what do I know.

After I took these measurements, I had a listen to some demo material I'm familiar with (Audyssey on) and the (for lack of a better word) "richness" was lacking - bass was almost non-existent. Checking the speaker levels in my AVR with the SPL meter in REW showed them to be quite a bit under 75db. Some were off by just a couple db, but the subs were down a good 10-11db. This has been my experience every time I run Audyssey on this system in my room though, so no surprise there.

I wrote down the speaker levels set by Audyssey, then adjusted the FL/FR and subs to as close to 75db (per REW's SPL meter) as I could. WOW! The sound really got "rich" after this - much more bass and mid-bass. I know, I'm gonna go to Audyssey Hell for this, but whatever it takes to make me smile I guess. Listening to the same demo material again did most certainly bring a smile to my face. I stayed up way too late enjoying the audio goodness!

I have not taken measurements after adjusting the speaker levels, but plan on doing that tonight.

Too anyone reading this, I can't stress enough the importance of experimenting with sub placement - especially if you have multiple and/or mis-matched subs. The inter-reaction between them is key to getting good sound. I'm stunned by how just moving one sub from the front to the back of the room made a world of difference. I also gain matched (thanks Craig!) these subs for the first time last night (was always level matching before) and I think this may have greatly contributed to the results I'm getting.

Thanks to you guys for all your helpful input!
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post #2 of 63 Old 02-13-2013, 04:37 PM
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When you say you have showing Sub+L/R are you driving the subs plus both Left and Right speakers? If so, let's do away with that. Please post just the subs, then just Left and then sub+Left.

On using your ears instead of trusting Audyssey, that is absolutely what you must do! Audyssey targets a flat response for bass which is against every bit of research we have. The result is exactly as you describe: you will perceive less bass than you think you should be hearing. The right fix is a sloping down response but the poor man's version is what you have done with is to adjust the subs total.

Just explaining the issues around that dip, it is due to the fact that Audyssey never measures the subs plus your mains. It blindly EQs each and leaves it to chance that the cross over area sums up to unity gain (i.e. flat response). In reality the response of the room distorts the crossover response where both the subs and mains have peaks and valleys in that area which randomly combine and create poor response. I wrote a recent article on this. Here is some graphs from there demonstrating the problem. This is the sample response from the center channel:

center-channel-frequency-response.png

The faint dashed straight gray line is what you want to have. The solid bright green line is what we have instead (post equalization). As you see, the tail of that response as frequencies get lower and lower is not a straight line as it should be. It has a bump instead. That variation gets combined with similar one from the sub creating a sum response that can have holes in it like yours does.

The system I talk about in that paper automatically does what you are trying to do. Namely, it measures the combined output of the sub with each of the mains and optimizes their response. Here is a good before and after:

JBL-Synthesis-Main-to-Subwoofer-Optimizer-room2.png

We see that this system also started with something similar to yours: a dip in the crossover region in the pre-optimization graph above. Then through trying countless variations it managed to fill that in. It is a long shot that you can do that manually across multiple seats but let's see the independent data and then we can see what is possible.

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post #3 of 63 Old 02-13-2013, 04:53 PM - Thread Starter
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Thanks for all the info Amir, good stuff.

I'll try to do those measurements tonight, but in the meantime, how does my response look as a whole? Good, bad, horrible?? To my untrained eye, I think it's looking pretty good for an untreated/un-EQed room.
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post #4 of 63 Old 02-13-2013, 05:05 PM
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I can't quite comment yet since you have three speakers running at once. BTW, are the (low frequency) graphs above with smoothing? If not, then the low frequency response was actually pretty good. Visually the version without Audyssey seems better. Did you do an AB and if so, found Audyssey version to sound better?

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post #5 of 63 Old 02-13-2013, 05:12 PM
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Quote:
Originally Posted by Alan P View Post


Too anyone reading this, I can't stress enough the importance of experimenting with sub placement - especially if you have multiple and/or mis-matched subs. The inter-reaction between them is key to getting good sound. I'm stunned by how just moving one sub from the front to the back of the room made a world of difference.

No doubt.

I got a UMM-6 mic recently and got to play around with it last weekend. Well I had a great time placing my 2 subs all over the room hunting for the best response. Ultimately, I ended up with good response (compared to what I began with), considering my room is in need of treatment, and because the MLP is against a wall.

Your response looks pretty good... I don't think you'll have to work too hard to tame the peaks and valleys.

 


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post #6 of 63 Old 02-14-2013, 09:22 AM - Thread Starter
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Originally Posted by amirm View Post

When you say you have showing Sub+L/R are you driving the subs plus both Left and Right speakers? If so, let's do away with that. Please post just the subs, then just Left and then sub+Left.
.

Here's those measurements, I did them all with Audyssey off then with it on.

Subs only, Audyssey off:



Subs Only, Audyssey on:



Subs + FL, Audyssey off:



Subs + FL, Audyssey on:



FL only, Audyssey off:



FL only, Audyssey on:

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post #7 of 63 Old 02-14-2013, 10:40 AM
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Quote:
Originally Posted by Alan P View Post

Here's those measurements, I did them all with Audyssey off then with it on.
Thanks Alan. Let me first address the easy part:
Quote:
Subs only, Audyssey off:



Subs Only, Audyssey on:

You have very good subwoofer response. The EQ did what it was supposed to which was to smooth out the ups and downs. The one thing it didn't do which you rightly had done manually was to have more of a bass boost than it has. We want a line that slopes down. Level adjustment of the sub will kind of accomplish that although as you can imagine, it raises all the frequencies rather than sloping it down.
Quote:
FL only, Audyssey off:



FL only, Audyssey on:


Let me focus your attention on 2 Khz. In the Audyssey *ON* case (second graph), we see a dip in there. This was inserted by Audyssey on the mistaken notion that speakers are designed incorrectly and need this help. Of course no well designed speaker will have such a peak as to get corrected by Audyssey. Unfortunately the only fix is to leave Audyssey off. Unless you get the Pro version of Audyssey, you can't override this. I am more worried about this than diagnosing the the low frequency one that we are discussing. That is a broad trough that starts at 1 Khz and ends around 3.5 Khz. In such broad changes, our ability to hear the anomaly a lot easier it because so many frequencies hit it. Studies show that we can hear changes as low as 0.5 dB! If I eyeball your graph, the lowest point is at 76 dB and the highest peaks at either end around 85 dB for a whopping 9 dB of difference!

Turn off your subs and just play the mains and listen to *one* channel of your mains. Then turn Audyssey on and off and see if you like what is happening to mid frequencies. It is super important to perform listening tests like this. It will teach you what the effects of these response variations are.

While on that topic, also play your subs without the mains. Here, you need to pick something with transients. I like low tone guitar tracks. Optimized subwoofers will play this as real guitar strings. Unoptimized they will sound bloated and boomy. This is by no means the only revealing track but one that I happen to have as a demo track and does a fantastic job here: Chris Jones' "No Sanctuary Here." Here is the Youtube version so you get an idea of what it sounds like:

Note that when you compress music the transients are the first things that suffer and unfortunately guitar strings above will be the victims. So while you can try the Youtube clip but best to get the CD. It is one of the top demo tracks anyway to have to show off your system if you don't already have it smile.gif.

Play it full range as you hear it in the above youtube and then turn off all the mains and it should still sound like real guitar playing sans of course all the highs. Leave Audyssey off initially and listen a few times focusing on the strings. Then turn Audyssey back on. If Audyssey is doing its job right, then the guitar strings become tighter and don't last as long. The technical reason for this is that the peaks that you see in frequency display, have tails in time domain. That is, when a quick sound comes, it doesn't go away when the amp stops driving the speakers. The room stores that energy and lets it out over time. This muddies the notes. By listening to those tails (called "ringing") you can tell if the right peaks were taken out or not. Correct bass is very tight and clean.

Now, to diagnose the integration of subs with mains we need yet again a different graph smile.gif. You correctly used 1/6 octave smoothing to analyze the mains because as frequencies go up, the resolution of our ears (in frequency domain) goes down. So we don't want to have too much measurement accuracy or we will be chasing non problems. But there is an exception to this rule. And that is, if you are going to examine what the mains are doing in the subwoofer region, i.e. below 200-400 Hz, then you want to use the same no-smoothing or little smoothing (1/12 or 1/24). Otherwise, we don't see the ups and downs that may have combined with the sub to produce that trough. Right now I have that for the subs but not for the mains so I can't add them together visually and see why that trough got created.

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post #8 of 63 Old 02-14-2013, 11:35 AM - Thread Starter
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Thanks again for all your help, Amir, it is greatly appreciated to have such knowledgeable folks here on AVS willing to help us "not-so-educated" folks. wink.gif
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You have very good subwoofer response. The EQ did what it was supposed to which was to smooth out the ups and downs. The one thing it didn't do which you rightly had done manually was to have more of a bass boost than it has. We want a line that slopes down. Level adjustment of the sub will kind of accomplish that although as you can imagine, it raises all the frequencies rather than sloping it down.

That's the stuff I wanna hear! It seems to be proven in the awesome bass I'm getting while I'm actually using the system and not taking measurements. cool.gif

My only concern now with my bass response is the excess ringing I'm getting under 30hz. Can anything be done for that with standard bass traps (i.e. NOT the very expensive tuned traps or traps the size of a small car)?
Quote:
Let me focus your attention on 2 Khz. In the Audyssey *ON* case (second graph), we see a dip in there. This was inserted by Audyssey on the mistaken notion that speakers are designed incorrectly and need this help. Of course no well designed speaker will have such a peak as to get corrected by Audyssey. Unfortunately the only fix is to leave Audyssey off. Unless you get the Pro version of Audyssey, you can't override this. I am more worried about this than diagnosing the the low frequency one that we are discussing. That is a broad trough that starts at 1 Khz and ends around 3.5 Khz. In such broad changes, our ability to hear the anomaly a lot easier it because so many frequencies hit it. Studies show that we can hear changes as low as 0.5 dB! If I eyeball your graph, the lowest point is at 76 dB and the highest peaks at either end around 85 dB for a whopping 9 dB of difference!

I kind of see what your talking about in the above graphs, but when I zoom in and overlay the 2, they both look very close to me. Here is the FL ONLY with Audyssey ON and OFF, zoomed to 900hz-3700hz, 1/24 smoothing, overlayed:


Quote:
Turn off your subs and just play the mains and listen to *one* channel of your mains. Then turn Audyssey on and off and see if you like what is happening to mid frequencies. It is super important to perform listening tests like this. It will teach you what the effects of these response variations are.

While on that topic, also play your subs without the mains. Here, you need to pick something with transients. I like low tone guitar tracks. Optimized subwoofers will play this as real guitar strings. Unoptimized they will sound bloated and boomy. This is by no means the only revealing track but one that I happen to have as a demo track and does a fantastic job here: Chris Jones' "No Sanctuary Here." Here is the Youtube version so you get an idea of what it sounds like:

Note that when you compress music the transients are the first things that suffer and unfortunately guitar strings above will be the victims. So while you can try the Youtube clip but best to get the CD. It is one of the top demo tracks anyway to have to show off your system if you don't already have it .

Play it full range as you hear it in the above youtube and then turn off all the mains and it should still sound like real guitar playing sans of course all the highs. Leave Audyssey off initially and listen a few times focusing on the strings. Then turn Audyssey back on. If Audyssey is doing its job right, then the guitar strings become tighter and don't last as long. The technical reason for this is that the peaks that you see in frequency display, have tails in time domain. That is, when a quick sound comes, it doesn't go away when the amp stops driving the speakers. The room stores that energy and lets it out over time. This muddies the notes. By listening to those tails (called "ringing") you can tell if the right peaks were taken out or not. Correct bass is very tight and clean.

Great tips for listening tests, thanks! I really don't think running with Audyssey off is going to be a realistic option for me, the wife and I really enjoy the effects of Dynamic EQ (on movies, music and just TV) and I would really hate to give that up. If I can get the system to sound better with Audyssey off (I'm definitely going to try) I may just turn it off for critical music listening only.
Quote:
Now, to diagnose the integration of subs with mains we need yet again a different graph . You correctly used 1/6 octave smoothing to analyze the mains because as frequencies go up, the resolution of our ears (in frequency domain) goes down. So we don't want to have too much measurement accuracy or we will be chasing non problems. But there is an exception to this rule. And that is, if you are going to examine what the mains are doing in the subwoofer region, i.e. below 200-400 Hz, then you want to use the same no-smoothing or little smoothing (1/12 or 1/24). Otherwise, we don't see the ups and downs that may have combined with the sub to produce that trough. Right now I have that for the subs but not for the mains so I can't add them together visually and see why that trough got created.

Here are overlayed graphs from 15hz-400hz, first is FL overlayed with subs, Audyssey off, no smoothing:



FL overlayed with subs, Audyssey on:

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post #9 of 63 Old 02-14-2013, 12:23 PM
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Originally Posted by Alan P View Post

Thanks again for all your help, Amir, it is greatly appreciated to have such knowledgeable folks here on AVS willing to help us "not-so-educated" folks. wink.gif
My pleasure. But just to be clear, this is like the old bear joke: "how fast do you need to run to get away from a bear? Faster than the guy with you." biggrin.gif There is so much to learn about acoustics that it really is a never ending process.
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My only concern now with my bass response is the excess ringing I'm getting under 30hz. Can anything be done for that with standard bass traps (i.e. NOT the very expensive tuned traps or traps the size of a small car)?
I would not worry at all about < 30 Hz. Your first room mode is probably higher than this so there is nothing to correct there. Music tends to have little content there and what there is in movies is LFE effects so who is to say what is right? smile.gif Also, there are a lot of issues involved in how one examines ringing there. It is very easy to use REW incorrectly there. I have written a missive on this (click on the first link in this search and you can read all you ever wanted about the science: https://www.google.com/search?q=site%3Awhatsbestforum.com+Acoustic+Measurements%3A+Understanding+Time+and+Frequency&rlz=1C1SNNT_enUS374US375&oq=site%3Awhatsbestforum.com+Acoustic+Measurements%3A+Understanding+Time+and+Frequency&aqs=chrome.0.57j58.7563&sourceid=chrome&ie=UTF-8). So for now, let's put that aside and we can revisit later.
Quote:
I kind of see what your talking about in the above graphs, but when I zoom in and overlay the 2, they both look very close to me. Here is the FL ONLY with Audyssey ON and OFF, zoomed to 900hz-3700hz, 1/24 smoothing, overlayed:

Ah, the perils of visually matching graphs smile.gif. Thanks for doing that. You are right that it is less of a difference than what I thought was there when I was trying to compare the two graphs separately. But the point remains: we do not want a dip there. The reason you see it even without Audyssey is an issue of speaker design. Let me expand briefly.

When you listen to a speaker (at frequency > 200 to 400 Hz) you hear the direct sound and then reflections that bounce around your room and then combine with the direct sound. Sound coming out of a speaker driver get directional if the wavelength of it gets smaller than the size of the driver. Ideally before that gets too extreme, the crossover hands off the sound to next smaller driver and we maintain our level of "directivity" (how directional the sound is). Alas, there are many speakers that don't do this. Classic example is an 8 inch woofer and a 1 inch tweeter. The woofer plays much higher frequencies before the sound can be handled to the little tweeter. If you measure such a speaker in an anechoic chamber, all would seem well because you are only measuring the direct sound. Now, if you shift the microphone to the side in that chamber, you see that the frequency response has a droop in the middle frequencies where the woofer got directional and was not sending equal energy to the sides.

Same thing happens in your room. The sound bounces off the side wall and then combines with the direct sound. If the side sound has a trough in it, then the combined measurement as shown by REW will have the same. Unfortunately this is quite audible and a problem you want to avoid. You have such a drop in your non-EQ measurement. Audyssey just makes it worse because it took out the one bump that was kind of in the middle of it and pushed the corner on the right 1 or 2 dBs.

The temptation is to put absorbers on the first reflection points. Alas, you can't take out all the reflections that way and studies show that we rather hear the bad side reflections than no side reflections. At the risk of having you throw a rock at me smile.gif, I have to say that the fix to such high frequency problems is a speaker that doesn't have directivity problems like above. While some EQ systems attempt to correct this issue, in general in falls in the class of not being correctable. Simply because the EQ is ahead of the speaker so it impacts both the direct and indirect sounds.
Quote:
Here are overlayed graphs from 15hz-400hz, first is FL overlayed with subs, Audyssey off, no smoothing:



FL overlayed with subs, Audyssey on:

That's interesting. Looks like it is not a problem of the amplitudes combining to create that trough so this leaves there "phase." Try changing the sub distance iteratively and make a few measurements and let's see if it makes an impact there. For this monitor the combined mains and Sub. And leave Audyssey on since that is the situation we are trying to optimize.

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post #10 of 63 Old 02-14-2013, 01:08 PM - Thread Starter
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Also, there are a lot of issues involved in how one examines ringing there. It is very easy to use REW incorrectly there. I have written a missive on this (click on the first link in this search and you can read all you ever wanted about the science: https://www.google.com/search?q=site%3Awhatsbestforum.com+Acoustic+Measurements%3A+Understanding+Time+and+Frequency&rlz=1C1SNNT_enUS374US375&oq=site%3Awhatsbestforum.com+Acoustic+Measurements%3A+Understanding+Time+and+Frequency&aqs=chrome.0.57j58.7563&sourceid=chrome&ie=UTF-8). So for now, let's put that aside and we can revisit later.

So, I read your very informative post you linked to and so I created a waterfall of my LF + Subs with your settings and I got this:



I have no idea if this means anything, but thought it would be worth including. smile.gif
Quote:
That's interesting. Looks like it is not a problem of the amplitudes combining to create that trough so this leaves there "phase." Try changing the sub distance iteratively and make a few measurements and let's see if it makes an impact there. For this monitor the combined mains and Sub. And leave Audyssey on since that is the situation we are trying to optimize.

I suspect my FL/R speakers - most of the time (but not all) when I run Audyssey I'll get a phase error, but since I've checked and re-checked the wiring to the speakers I just skip it. I think I need to open up my speakers and make sure everything is wired correctly on the inside.

I tried last night messing with the sub distance (I went up and down the entire scale in 1' increments, then .1' increments closer to the original distance), and the Audyssey set distance of 10.2' remained the best setting. I was , however, only monitoring the subs and Audyssey was off. I will try again with the FL/R in the mix and with Audyssey on.
Quote:
At the risk of having you throw a rock at me , I have to say that the fix to such high frequency problems is a speaker that doesn't have directivity problems like above.

Basically, I need new speakers. That's kind of what I thought.

My current (and for the last 20 years) speakers are Klipschorns. I'm assuming you're familiar with them, and being "corner-horns" I've come to realize just recently (from reading here and the Klipsch forums) that they are not really the best choice for home theater. I've never been dissatisfied with their overall sound, although in my particular room they are lacking in bass response. It's only since I've started this latest round of HT upgrades (new receiver, new subs) that I'm realizing the K-Horns probably aren't right for me since I'm now a 80/20 HT/music kinda guy.

Recently I've considered selling them and getting more conventional tower speakers to replace them with (I've looked pretty hard at Aperion, Ascend Acoustics and the Klipsch Reference Series). This may very well be the next step in my journey to audio nirvana. biggrin.gif

Thanks again!
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post #11 of 63 Old 02-14-2013, 06:37 PM
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Quote:
Originally Posted by Alan P View Post

My current (and for the last 20 years) speakers are Klipschorns. I'm assuming you're familiar with them, and being "corner-horns" I've come to realize just recently (from reading here and the Klipsch forums) that they are not really the best choice for home theater. I've never been dissatisfied with their overall sound, although in my particular room they are lacking in bass response. It's only since I've started this latest round of HT upgrades (new receiver, new subs) that I'm realizing the K-Horns probably aren't right for me since I'm now a 80/20 HT/music kinda guy.

Recently I've considered selling them and getting more conventional tower speakers to replace them with (I've looked pretty hard at Aperion, Ascend Acoustics and the Klipsch Reference Series). This may very well be the next step in my journey to audio nirvana. biggrin.gif

Thanks again!
So great to see someone open minded. Usually when I suggest someone get a new speaker instead of hoping and praying for acoustic treatments to mend the same, we no longer stay friends smile.gif.

You might be interested in watching this video. It is a set of slides (no audio) of a presentation on double blind tests of speakers including a Klipsch. Skip to around 2:15 as the first part of the presentation is unrelated to this topic:



While the report does not name the specific speakers, they are ordered in the same way they are shown on the intro slide. I.e. Klipsch is speaker "C." As you see, it finishes third out of four. Follow on slides explain how measurements back that. Namely, one needs to have smooth on axis (direct) and off axis (indirect) sound of the speaker. If you want to read a much lengthy discussion with the author of that test, Dr. Olive, click on the first link in this Google search: https://www.google.com/search?q=site%3Awhatsbestforum.com+Some+More+Evidence+that+Kids+(American+and+Japanese)+Prefer+Good+Sound&rlz=1C1SNNT_enUS374US375&oq=site%3Awhatsbestforum.com+Some+More+Evidence+that+Kids+(American+and+Japanese)+Prefer+Good+Sound&aqs=chrome.0.57j58.4893&sourceid=chrome&ie=UTF-8

Now you know more than most people on your block about what makes a good speaker and what it means in acoustic measurement sense smile.gif.

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post #12 of 63 Old 02-15-2013, 09:56 AM
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Alan, can you post the RT60 measurements? All you have to do is click the RT60 button in REW and only select Topt. That will tell us if you have enough general absorption in the room or not (I.e. is your room overall too reflective or "live").

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post #13 of 63 Old 02-15-2013, 10:06 AM - Thread Starter
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Here it is, I have no idea what this means, but I assume you're gonna tell me. wink.gif

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post #14 of 63 Old 02-15-2013, 04:25 PM
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Originally Posted by Alan P View Post

Here it is, I have no idea what this means, but I assume you're gonna tell me. wink.gif
You are a good "straight man" to me smile.gif. Yes, that was the intention to get us to the next area of acoustics. First was low frequency optimization. This one relates to what happens to *late* reflections once the bounce around the room for a while. Here, we want some of it but not too much. If we have too much, it can interfere with such things as speech intelligibility. Speech has a cadence of about 4 Hz. So if once the reflections in the room linger past 0.25 seconds they can start to impinge on our ability to understand them. On the other hand, we like to have a sense of space and reflections give us that. Based on these high level requirements, we have a range of desirable values of about 0.2 to .5 seconds. The smaller the number, the "deader" or "dryer" the room. The higher the number, the more "live" it is.
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The graph shows the computed reverberation time for a few selected frequencies. I personally only look at 500 Hz but others look at the shape of the graph. Eyeballing the reverbration time at 500 Hz we get around .32 seconds which is within the acceptable range per above. Since it is on the low side, it indicates the room has fair bit of absorption already. Is that the case?

FYI an empty room tends to have reverberation times above 1.5 seconds and hence the reason it is hard to understand speech there. On the other hand, a well furnished room (with carpet and curtains) tends to be close to 0.4 seconds which per above rule is actually what we want it to be. In other words, typically furnished (living) rooms can be fine from point of view of overall reverberation. Here is a nice graph from Dr. Toole's book that shows what happens incrementally as we add furnishings to the room and below it, a large scale survey of (Canadian) homes and their average reverberation times:

i-jjWhnJp-XL.png

On the other hand, when building a dedicated theater, it is an empty box and therefore will have too many (late) reflections which should be tames with acoustic products. Here is an example measurement I made from a room with a carpet and a few chairs:

i-nt9ktvZ-L.png

We see that it is clearly "too live" given its 500 Hz of around 0.9 seconds.

I started this post with explaining that this is about *late* reflections in the room. This is very different situation than the *early* or *strong* reflections which occur when the sound immediately comes out of the speaker bounces from immediate surfaces. We will get to that later but for now, note that this post is about late reflections and hence, you can absorb their effects by putting furnishings/acoustics products where you like.

BTW, you may read elsewhere that "small rooms" which includes just about all of our home listening spaces do not have a "diffused sound field" and hence reverberation time calculations are not correct for them. That is true in the absolute. However, for the purposes of roughly determining how reflective a room is, the calculation is actually fine. It is a bit like the gas gauge in your car. It doesn't quite tell you how many miles you can drive but you can easily determine if you are full, half full or empty. Same here with the RT60 measurements above. To wit, the study in the top portion of the graph confirms that the measure changes correctly as we add furnishings (or acoustic treatments thereof) to the room.

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post #15 of 63 Old 02-15-2013, 04:28 PM
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BTW, I have asked Nyal to join me in answering questions on this topic. He is one of the few acousticians I have met who are aware of the latest research and understanding in acoustics (as opposed to just old school 1970s ideas that were devoid of much of psychoacosutics we know today).

Alan, are you OK once we have exhausted your case study that we open to the floor to others who want to share their measurements and seek input from opinionated people like me? biggrin.gif

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Quote:
Originally Posted by amirm View Post

BTW, you may read elsewhere that "small rooms" which includes just about all of our home listening spaces do not have a "diffused sound field" and hence reverberation time calculations are not correct for them. That is true in the absolute. However, for the purposes of roughly determining how reflective a room is, the calculation is actually fine. It is a bit like the gas gauge in your car. It doesn't quite tell you how many miles you can drive but you can easily determine if you are full, half full or empty. .

it's more like averaging the weather across the entire continental US to determine if you need an umbrella in your town at a particular time of day.
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post #17 of 63 Old 02-15-2013, 09:01 PM - Thread Starter
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Quote:
Originally Posted by amirm View Post

Eyeballing the reverbration time at 500 Hz we get around .32 seconds which is within the acceptable range per above.

So....the verdict is....?

From reading your post, it seems to me that my late reflections look pretty darn good, eh?
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Since it is on the low side, it indicates the room has fair bit of absorption already. Is that the case?

The room is not treated at all. Carpeted, big cushy recliners and couch, about 8' of drapes - but the walls of the entire space are covered in pine paneling. Could the paneling be what is keeping my reflections down so well?

Based on this graph, would you say I could benefit from further treatment, or am I good to go?

Thanks again Amir!
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post #18 of 63 Old 02-15-2013, 09:02 PM - Thread Starter
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Quote:
Originally Posted by amirm View Post

BTW, I have asked Nyal to join me in answering questions on this topic. He is one of the few acousticians I have met who are aware of the latest research and understanding in acoustics (as opposed to just old school 1970s ideas that were devoid of much of psychoacosutics we know today).

Alan, are you OK once we have exhausted your case study that we open to the floor to others who want to share their measurements and seek input from opinionated people like me? biggrin.gif

Certainly, the more the merrier I always say! smile.gif
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post #19 of 63 Old 02-15-2013, 09:02 PM - Thread Starter
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Originally Posted by localhost127 View Post

it's more like averaging the weather across the entire continental US to determine if you need an umbrella in your town at a particular time of day.

localhost - I don't get your meaning here, went right over my head apparently. frown.gif
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post #20 of 63 Old 02-15-2013, 09:36 PM
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Quote:
Originally Posted by Alan P View Post

So....the verdict is....?
Means you are in good shape!
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The room is not treated at all. Carpeted, big cushy recliners and couch, about 8' of drapes - but the walls of the entire space are covered in pine paneling. Could the paneling be what is keeping my reflections down so well?

Based on this graph, would you say I could benefit from further treatment, or am I good to go?

Thanks again Amir!
The carpet, recliner, couch and drapes are doing the job. The paneling doesn't help here since it is reflective at higher frequencies.

Since you are on the low side, you should be careful in not adding more absorption.

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post #21 of 63 Old 02-17-2013, 09:05 AM - Thread Starter
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Quote:
Originally Posted by amirm View Post

Since you are on the low side, you should be careful in not adding more absorption.

Well, thanks for that - you just saved me a good chunk o' change! smile.gif

But, a question for you or any others following this thread, I think I could still benefit from some bass trapping and I'll tell you why. Even when I do not have a sub there, my right rear corner seems to just eminate it's own bass, seeming to me that it is building up there. Is this incorrect thinking?
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post #22 of 63 Old 02-17-2013, 10:20 AM
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Originally Posted by Alan P View Post

Well, thanks for that - you just saved me a good chunk o' change! smile.gif
You are welcome.
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But, a question for you or any others following this thread, I think I could still benefit from some bass trapping and I'll tell you why. Even when I do not have a sub there, my right rear corner seems to just eminate it's own bass, seeming to me that it is building up there. Is this incorrect thinking?
It doesn't matter what bass builds up where you don't sit. When you use multiple subs, you get to create an area in the middle of the room that has very good response. The 1/3 perimeter of the room will continue to have room modes and you want to avoid sitting there.

Also, note that what the industry calls "bass trap" isn't! If you use absorption which is the common type of "bass trap" (i.e. insulation material), it works on the principal of where the velocity of sound is the highest. By definition once a sound wave hits the wall, it is not moving at all. You have to step into the room before that happens. Because the wavelength of the sound becomes very large as frequencies go down, you have to go way into the room or use very thick material to have any effectiveness.

Here is a simulation of one with the blue showing a 4 inch absorber and the pink, the same with 4 inches of air gap:

i-z9qfMLf-X2.png

As you see all the way to the left, the frequency is 62 Hz. And the response has already dropped way off even when you dedicate 8 inches (4 inches for the product and 4 inches of air gap behind it). You can add a lot of them to compensate for that but since these have very high absroption at higher frequencies you wind up overdoing it. In your case you don't want to get rid of any more mid to high frequency absorption so it is not advisable to go this way anyway.

There are other classes of absorbers that work the other way, e.g. on maximum pressure principal (the condition at the wall). But they are challenging to DIY and and even buy and deploy. In your case you already have smooth sub response so I don't see much of a need for them.

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post #23 of 63 Old 02-17-2013, 11:27 AM
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^^^ why is it this user never gives due credit to Chris Wealey's Porous Absorber Calculator when he makes references to it - and continues to refer to it as his "simulations"?

http://www.whealy.com/acoustics/Porous.html

Quote:
You can add a lot of them to compensate for that but since these have very high absroption at higher frequencies you wind up overdoing it.

this is called operator error and usually a result of a scenario where the user does not know what they are doing.
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post #24 of 63 Old 02-17-2013, 07:10 PM
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Ok I hope I am posting this in the right place now, I did a bunch of measurements today with and without Audessy, Full Range, Subs Only etc... and I wanted to see what knowledgeable people think of my room response and speaker measurements. Thanks in advance for the help.

Audessy Off


Audessy Flat


Audessy On

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Originally Posted by dstr212 View Post

Ok I hope I am posting this in the right place now, I did a bunch of measurements today with and without Audessy, Full Range, Subs Only etc... and I wanted to see what knowledgeable people think of my room response and speaker measurements. Thanks in advance for the help.
First a quick point, let's not worry about waterfalls for now. I assume the above display is the sub plus one of your mains? If so, and focusing on bass response, that is not too bad. That sharp drop around 70 Hz is probably too narrow to be audible. And the rest is fairly smooth for bass response.

I suspect subjectively the bass sounds weak. Go into your AVR and dial up the bass level gradually and report back if you like higher sub levels better. As I post elsewhere listeners prefer an elevated bass response. "Flat" sounds to us as insufficient bass. Of course if you like it this way, by all means leave it the same. smile.gif

Next can you run the RT60 as I advised Alan above? This will tell us if your room is too bare to sound good in general (read my earlier posts in this thread).

Also, can you please post one of your main front speakers with 1/6 octave smoothing? Again we are just looking for the frequency response ("SPL") graph. No waterfall. This would get rid of all of those sharp variations at higher frequencies (called "comb filtering") and let us see the proverbial forest from the tree. Also set the vertical scale maximum to 100 db. That will let us zoom in some and not have so much unused graph space.

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post #26 of 63 Old 02-18-2013, 07:35 AM
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Great thread and I will continue to follow it. I have a quick question for dstr212. The additional color lines at the bottom of your SPL graph appear to be the calculated room modes overlayed on the graph. Is this a feature of REW?

-Greg
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Great thread and I will continue to follow it. I have a quick question for dstr212. The additional color lines at the bottom of your SPL graph appear to be the calculated room modes overlayed on the graph. Is this a feature of REW?
It is a feature of REW but it is *way* buried in the program and you will never find it on your own! Dstr must be clever to have found it smile.gif.

To get to it, click on the "EQ" button. It opens up a new set of graphs and on the right there are a number of tabs. One of them is "Modal Analysis." Click on that and you see a bunch of boxes where you can put in your room dimensions. Populate those with your room size and you will see them displayed both on that graph and when you exist, on the main graph.

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post #28 of 63 Old 02-18-2013, 10:26 AM
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^Excellent and thanks for sharing this knowledge! This seems like a pretty useful tool.

-Greg
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post #29 of 63 Old 02-18-2013, 12:23 PM
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Quote:
Originally Posted by dstr212 View Post

Ok I hope I am posting this in the right place now, I did a bunch of measurements today with and without Audessy, Full Range, Subs Only etc... and I wanted to see what knowledgeable people think of my room response and speaker measurements. Thanks in advance for the help.

These views make it difficult to see the information clearly. Could you reduce the time to maybe 800ms or so and bring up the bottom volume a good bit, maybe to 35? I usually look at a 50-60dB range with waterfalls.

Alexander Reynolds
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These views make it difficult to see the information clearly. Could you reduce the time to maybe 800ms or so and bring up the bottom volume a good bit, maybe to 35? I usually look at a 50-60dB range with waterfalls.


I adjusted the ranges, I hope I brought the dbs in the correct way, but I was able to reduce the ms time?

Aud On

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