Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 360 - AVS | Home Theater Discussions And Reviews
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post #10771 of 13336 Old 07-28-2014, 12:46 PM
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Originally Posted by AustinJerry View Post
It is not obvious from the room mode calculator that the 45Hz dip is associated with any of the room dimensions.
That's strange Jerry because the REW room sim clearly shows the 45hz dip...unless the sub is located in the back 1/4 of the room.
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post #10772 of 13336 Old 07-28-2014, 01:32 PM
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I am not familiar with how the room simulator works. However, the formulas in the room mode calculator are simple mathematics, and are accurate.
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post #10773 of 13336 Old 07-28-2014, 01:36 PM
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Originally Posted by jim19611961 View Post
That is easier said than done. Unfortunately, they dont explain how to graph the results in a comparative and helpful way. Instead, they want you to pay $75 for their analysis
Did you listen to the test signal over headphones? How does it compare to how it sounds when played back on your speakers?

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post #10774 of 13336 Old 07-28-2014, 03:33 PM
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Quote:
Originally Posted by AustinJerry View Post
I am not familiar with how the room simulator works. However, the formulas in the room mode calculator are simple mathematics, and are accurate.
the room mode calculator just tells you where the modes are, the rew room sim solves for modes and the listening position (and delays etc dialled into each source).

As far as I can see, placing the MLP and the sub at the same distances from each wall (at 1/3 the length) produces that dip at 45Hz. I'm not entirely sure why.

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It doesn't look a great room for 1 sub tbh, how big is the listening area? do you have multiple rows of seats? for a single seating position, sitting at 1/5 the distance from the rear wall and a sub in the corner looks about as good as you can expect.

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post #10775 of 13336 Old 07-28-2014, 03:57 PM
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OK, let's see if he tries that, and what the measurements show. It will be interesting to see how accurate the room simulator is. It should work reasonably well in a rectangular sealed listening room. I have an open floor plan, and such simulators are of no use whatsoever, unfortunately.
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post #10776 of 13336 Old 07-29-2014, 12:03 AM
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Originally Posted by HDgaming42 View Post
I was shocked running REW with my new sub (empty room) to find a nasty nasty null. I've moved both my MLP and sub around to a number of positions and could use some guidance. My room's dimensions aren't THAT far off a recommended ratio--or so I thought.
Well... room dimensions ratio... My understanding...

A room (enclosed space) is going to have nodes - frequencies that produce standing waves due to reflections. A Cube is usually quoted as the worst, same nodes in all directions, so they reinforce each other. I suppose a sphere would be the ultimate bad room.


The recommended room dimension ratios don't eliminate nodes, but, the nodes for end to end, side to side, floor to ceiling, and the angular reflections, occur at a range of frequencies, not falling on top of each other, not reinforcing each other.

I suppose if the room is bumpy enough it looks smoother, as opposed to one with a few totally black holes in the response.

Close your eyes and see if what you HEAR is as bad as what you think you see when you MEASURE, and go from there.

Musical intruments are not one frequency, they have harmonics and overtones. The ear/brain is adept at filling in the gaps.

I have a big hole at 55hz, and never guessed until I measured it. Didn't notice anything wrong. Now chasing it. That's the hobby.

If you want no nodes, you need an anechoic chamber.

I see the science boys have created the blackest material yet, almost no reflectivity/emission for light. Maybe somebody is working on the same for sound.

https://en.wikipedia.org/wiki/Room_modes

I'll be back later...


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post #10777 of 13336 Old 07-29-2014, 01:35 AM
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I see the science boys have created the blackest material yet, almost no reflectivity/emission for light. Maybe somebody is working on the same for sound.
Already exists, it's called DBA:
Double Bass Array (DBA) - The modern bass concept!

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post #10778 of 13336 Old 07-29-2014, 09:14 AM
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Originally Posted by RayDunzl View Post
Close your eyes and see if what you HEAR is as bad as what you think you see when you MEASURE, and go from there.

Musical intruments are not one frequency, they have harmonics and overtones. The ear/brain is adept at filling in the gaps.
Sadly this is one of the things that drew me to measuring my room. One of my favourite songs features successive piano chords descending the scale (Spoon--Beast and Dragon Adored). Playing it in that room made me want to weep. Some chords simply disappear. Others play too loudly. To hear them butchered like that in direct succession was like a knife to the heart after a $1000 subwoofer purchase!

If I have to fill 90% of this room with Rockwool, or teach myself how to build Helmholtz resonators / Metal Panel Absorbers I'll do it. This was to be my room of solace, and sadly listening to my Grados sounds better...

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This is truely fascinating stuff. I can't believe there isn't more talk about this than there is! Here's some amazing results using a SBA: http://www.gearslutz.com/board/bass-...ts-inside.html
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post #10779 of 13336 Old 07-29-2014, 09:33 AM
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Originally Posted by HDgaming42 View Post

This is truely fascinating stuff. I can't believe there isn't more talk about this than there is! Here's some amazing results using a SBA: http://www.gearslutz.com/board/bass-...ts-inside.html
There is not more talk about partly cause few have seen the thread or know of the concept. But secondly, perhaps more importantly, results just as great can be achieved through other, more conventional means. Extensive bass trapping.

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(1/24th oct smoothing)

This is mine. But at least half a dozen other posters here have gotten similar results, also through conventional means.

Mostly, folks with uneven bass don't provide enough bass trapping in their room. As ive seen posted several times, I have never seen a room with too much bass trapping.

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post #10780 of 13336 Old 07-29-2014, 09:37 AM
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results just as great can be achieved through other, more conventional means.
I beg to differ. DBA approaches free-field conditions. Passive absorption becomes unpractical when trying to achieve same results.
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post #10781 of 13336 Old 07-29-2014, 09:54 AM
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i beg to differ. Dba approaches free-field conditions. Passive absorption becomes unpractical when trying to achieve same results.
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The Cyan is mine, the Red is the waterfall from the dba page. I used similar scale and smoothing. I wouldnt say the dba blows me out of the water.

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post #10782 of 13336 Old 07-29-2014, 09:59 AM
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^
Now compare your room to a DBA setup. That's why I've said "unpractical" Especially when one has concrete walls all around. Very common in Europe. Not such much in the US.

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post #10783 of 13336 Old 07-29-2014, 10:08 AM
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^
Now compare your room to a DBA setup. That's why I've said "unpractical" Especially when one has concrete walls all around. Very common in Europe. Not such much in the US.
Are you insinuating my room is unpractical?

True, I wouldn't get the result I am getting in a concrete room.

Even in a concrete room, the room within a room concept would work pretty well I think.

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post #10784 of 13336 Old 07-29-2014, 10:54 AM
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Originally Posted by HDgaming42 View Post

If I have to fill 90% of this room with Rockwool, or teach myself how to build Helmholtz resonators / Metal Panel Absorbers I'll do it. This was to be my room of solace, and sadly listening to my Grados sounds better...
I still think the most impact will be from a second sub. Then additional bass traps. JMO.
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post #10785 of 13336 Old 07-29-2014, 11:08 AM
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I still think the most impact will be from a second sub. Then additional bass traps. JMO.
Agreed.

But lets consider something else. If your mains are full range speakers, and you don't cross them over, and let their bass extend, you now have two more subwoofers in a sense (that is, two more sources producing in the low bass region).

For those with only one sub, it might be worth trying.

This is basically how my system operates. (2) main speakers run full range (no XO), plus (3) subs. So essentially, I have (5) sources in the bass region.

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post #10786 of 13336 Old 07-29-2014, 11:40 AM
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I still think the most impact will be from a second sub. Then additional bass traps. JMO.
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Originally Posted by jim19611961 View Post
Agreed.

But lets consider something else. If your mains are full range speakers, and you don't cross them over, and let their bass extend, you now have two more subwoofers in a sense (that is, two more sources producing in the low bass region).
My main front speakers are actually monitors - Mackie HR624mkII. They're what I use 8hrs a day at work, so I'm used to them. They're powered and pretty flat (which is what I wanted). Although your full-range idea would probably work, I don't think that's in my future.

My sub is an SVS PB-2000. The thing is a monster in a room my size (10' x 16'). Finding a home for two of them that doesn't interfere with a) L, C, R b) corner bass trapping or c) rear wall treatment d) my television might be a challenge.

Would I be safe to assume the flattest response would be to place both subs in the middle of the width of the room, front and back? I think that's what I gathered from the HK paper. Four subs is a non-starter.

I have about 3hrs a week to devote to that room, so I am now 1/4 the way toward building bass traps for the front two corners. Doing Roxul safe n sound superchunks with about a 32" face (freestanding units that can stack). Once I get those in I can roll the sub back in and do another sweep before and after to see what that does.

Next up--I'm guessing--will be to treat the back wall. My back corners have a door on one side, and a cubby for an equipment rack on the other, so no easy way to trap those corners unfortunately.

Thanks for the help / advice thus far!

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post #10787 of 13336 Old 07-29-2014, 11:46 AM
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Have you tried the sub in the rear 1/4 of the room (as REWs room sim showed that to produce the flattest response)??
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post #10788 of 13336 Old 07-29-2014, 12:25 PM
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Have you tried the sub in the rear 1/4 of the room (as REWs room sim showed that to produce the flattest response)??
Not extensively. I'd read that putting your sub behind you isn't really advisable with mains that cross at 80Hz. I know there are conflicted opinions on that. I'm also not sure how accurately REWs room sim fits my room (with a window and cubby for the rack).

I've attached it's prediction of listening position A, and the actual reading. Would you say that prediction is close (I'm not being snarky--I'm genuinely curious).

I've also attached a placement in the back 1/4 that I interpret as much easier to deal with. Is this what you're referring to? A peak at 70dB and 75dB to iron out instead of many nulls?

I should add my ceiling is 88".
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post #10789 of 13336 Old 07-29-2014, 12:36 PM
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I would say that it is recognisably the same response, the sim has exaggerated the size/q of the first peak to null but otherwise it looks good.

In my experience, of room sim vs reality in a cuboid room that has some shallow alcoves, the sim accuracy degrades as the mic approves the non linear areas (ie the alcoves). The usefulness therefore varies with the listening position.
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post #10790 of 13336 Old 07-29-2014, 12:40 PM
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80hz is actually where your crossover should be to eliminate localization....you'll be fine with the sub behind you.

I would say that REWs prediction is pretty spot-on to your in-room measurement. That's why I think it would be spot-on for the predicted response with the sub behind you.

Yes, Audyssey will be able to iron out those peaks much easier than it can try to fill in the huge null(s)....give it a go, you got nothing to lose but time!
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post #10791 of 13336 Old 07-29-2014, 12:43 PM
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Originally Posted by HDgaming42 View Post
Not extensively. I'd read that putting your sub behind you isn't really advisable with mains that cross at 80Hz. I know there are conflicted opinions on that. I'm also not sure how accurately REWs room sim fits my room (with a window and cubby for the rack).

I've attached it's prediction of listening position A, and the actual reading. Would you say that prediction is close (I'm not being snarky--I'm genuinely curious).

I've also attached a placement in the back 1/4 that I interpret as much easier to deal with. Is this what you're referring to? A peak at 70dB and 75dB to iron out instead of many nulls?

I should add my ceiling is 88".
Seems in your room sim capture that your MLP is in the center of the room, I thought it was 5'4" from the back wall...?
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post #10792 of 13336 Old 07-29-2014, 12:58 PM
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I would say that it is recognisably the same response, the sim has exaggerated the size/q of the first peak to null but otherwise it looks good.
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I would say that REWs prediction is pretty spot-on to your in-room measurement. That's why I think it would be spot-on for the predicted response with the sub behind you.
Thanks!

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Seems in your room sim capture that your MLP is in the center of the room, I thought it was 5'4" from the back wall...?
It was. The graph didn't look great (what did you come up with?) so I moved the MLP forward until it looked fairly flat (attached with original MLP).

Maybe I don't have the hang of the REW room sim, but applying both the 2 and 4 sub HK models to this simulator doesn't seem to really get me any closer to flat than 1 sub with placement in the back 1/4. What am I missing? (i've tried inverting the opposing subs)
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post #10793 of 13336 Old 07-29-2014, 01:12 PM
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In respect to our FR and house curve, I thought id post a variation of something id done before.

Red +4
Orange (Dark) +2
Orange (Light) +0
Yellow -2
Green (light) -4

So about 2db per color change.

Always looking for new ways to look at things.

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post #10794 of 13336 Old 07-29-2014, 03:39 PM
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80hz is actually where your crossover should be to eliminate localization....you'll be fine with the sub behind you.
Is this as true for music as for movies?

I see advice like the following posted around the net...

Quote:
Once again, the subwoofer should be located near one of the main speakers with it's driver approximately the same distance from your ears as the bass and midrange drivers in the main speakers, so integration is seamless. The attack of bass notes (pluck of bass guitar string and slap of kick drum hammer are in the mid-range frequencies and do not come from the subwoofer. The transient response will be best if all the drivers involved with a bass note are located the same distance from your ears.
Many people will not notice a difference of up to three milliseconds
(approximately three feet).
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post #10795 of 13336 Old 07-29-2014, 03:42 PM
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Thanks!



It was. The graph didn't look great (what did you come up with?) so I moved the MLP forward until it looked fairly flat (attached with original MLP).

Maybe I don't have the hang of the REW room sim, but applying both the 2 and 4 sub HK models to this simulator doesn't seem to really get me any closer to flat than 1 sub with placement in the back 1/4. What am I missing? (i've tried inverting the opposing subs)
I just crammed the sub into one or the other back corner and left your MLP at 5'4"...seemed to get the best response in the corner without moving the MLP. If you're willing to move the MLP, that changes things a bit.

When I ran the room sim the response was flatter than the one you show above but not as flat as the one with the MLP in the center of the room. I found that to get a decent response, the sub needed to be at least 2.5' behind the MLP, but it looks like the flattest response is with the MLP dead center in the room....which is usually not good.

You're just gonna have to experiment a bit (with the real thing) I think.

Adding more subs won't necessarily get you flatter, but it will make the response flat over a wider area (less seat-to-seat variance).
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post #10796 of 13336 Old 07-29-2014, 03:44 PM
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Is this as true for music as for movies?

I see advice like the following posted around the net...
That only applies if you have no way to delay your sub signal....you do. It's the sub distance setting in your AVR.
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post #10797 of 13336 Old 07-29-2014, 04:00 PM
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I just crammed the sub into one or the other back corner and left your MLP at 5'4"...seemed to get the best response in the corner without moving the MLP. If you're willing to move the MLP, that changes things a bit.

When I ran the room sim the response was flatter than the one you show above but not as flat as the one with the MLP in the center of the room. I found that to get a decent response, the sub needed to be at least 2.5' behind the MLP, but it looks like the flattest response is with the MLP dead center in the room....which is usually not good.

You're just gonna have to experiment a bit (with the real thing) I think.

Adding more subs won't necessarily get you flatter, but it will make the response flat over a wider area (less seat-to-seat variance).
It's all up for grabs right now--nothing's in stone. When I get the bass traps done I'll do some more testing, including the sub behind the MLP, and with the MLP being *shudder* center of the room. I'm curious if the prediction will ring true.

I'm selfish in that if I can get a great MLP while sacrificing accuracy for other seats (for people who frankly couldn't care) and save money in the process-sign me up.

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That only applies if you have no way to delay your sub signal....you do. It's the sub distance setting in your AVR.
Ahh. Wasn't aware of that. Thanks.
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post #10798 of 13336 Old 07-29-2014, 04:13 PM
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Originally Posted by HDgaming42 View Post
I'm selfish in that if I can get a great MLP while sacrificing accuracy for other seats (for people who frankly couldn't care) and save money in the process-sign me up.
Agreed...my wife couldn't care less.
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post #10799 of 13336 Old 07-29-2014, 04:17 PM
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Quote:
Originally Posted by Alan P View Post
That only applies if you have no way to delay your sub signal....you do. It's the sub distance setting in your AVR.
Quote:
Originally Posted by HDgaming42 View Post
Ahh. Wasn't aware of that. Thanks.
Since you were unaware, there's something else you need to be aware of; after you run Audyssey (you have Audyssey, right?), don't be alarmed if the sub distance in your AVR is (significantly or slightly) different than the actual, physical distance. This is perfectly normal, expected even.
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post #10800 of 13336 Old 07-29-2014, 05:38 PM
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Originally Posted by HDgaming42 View Post
Is this as true for music as for movies?

I see advice like the following posted around the net..

Once again, the subwoofer should be located near one of the main speakers with it's driver approximately the same distance from your ears as the bass and midrange drivers in the main speakers, so integration is seamless. The attack of bass notes (pluck of bass guitar string and slap of kick drum hammer are in the mid-range frequencies and do not come from the subwoofer. The transient response will be best if all the drivers involved with a bass note are located the same distance from your ears.
Many people will not notice a difference of up to three milliseconds
(approximately three feet).
.
I agree with this quote if ALL the following are true:

1) Your main speakers are satellites (i.e. depend on the subs for extension)
2) Where the mains happen to be provides a relatively smooth bass response for the subs.
3) The satellite to sub integration is good.

It also depends on not only the XO frequency, but the slope of the XO filter.
example 1) a 80hz XO with a 2nd order XO(12db/octave). You may still have significant sub energy above 100hz and into those frequencies where directionality is a concern.
example 2) a 40hz XO with a 4th order XO(24db/octave). In this case, there will be no significant energy from the subs at frequencies where directionality is concerned.

If your somewhere in-between, you might try to find a track with some drum rolls that pan across the soundstage and see if the imagery suffers dependent on sub location.

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Last edited by jim19611961; 07-29-2014 at 05:41 PM.
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