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post #121 of 143 Old 10-09-2013, 04:52 PM - Thread Starter
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This is a little off topic for the thread, but I'm curious about baffle walls and controlled directivity speakers. If the speakers need to be toed in so much, is it even possible to get the advantages of a full baffle wall?


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post #122 of 143 Old 10-10-2013, 07:04 PM
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scott, great question and yes, just make the baffle/wall at an angle!


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post #123 of 143 Old 10-28-2013, 07:50 PM - Thread Starter
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Well, that front wall reflection is certainly an issue. It shows up with both the subs and the LR in the same spot at about 100Hz, which based on a calculator I saw in another thread matches up with the placement. I'm looking into some treatment for it, but it's not a huge concern for me right now. Overall everything looks good enough for me taking into account that I may not be in this space in 6 months.

Mains alone


Subs + mains


Another thing that surprised me was how well the response matched the room simulator in REW. It's actually a pretty cool tool, and it's neat to see that it can actually translate to a real environment to a certain extent. It's not perfect obviously, but it resembles the actual measurements more than I expected.



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post #124 of 143 Old 10-28-2013, 11:52 PM
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Could try rotating subs sideways or backwards with drivers facing wall. That way the sub and speaker drivers are different distances off front wall. Could also play around with a bit higher crossover based on results. Might be worth a shot. smile.gif
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post #125 of 143 Old 10-29-2013, 07:01 AM
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I'm not sure what bass mgmt. scheme is employed, but the sub's response looks good, really good actually. . . If they're low passed around 80hz, and within 3.5' feet or so, they should be fine.

The mains on the other hand appear to be encountering significant SBIR. I'd back them as tightly up against the front wall as you can. If the front radiating surface is within 18" or so of the boundary, that should help smooth the ~180hz downward region. I'd opt for the dense of glass fiber panels, ideally 705, or if you had 703 that'd work too. But in my experience, this is one culprit of the issue; destructive quarter wave interactions. That said, you may be encountering similar issues from the boundary behind the LP, if you're seated close to the wall behind you.

I'd like to see a combined response (subs+mains), in the manner in which you'll use them (bass managed, etc).

The sub response looks very workable IMO. Just knock down the excessive energy in the low 50's, and you're way ahead of where most find themselves.

---

fwiw, different topic ... in such lack of symmetry room scenarios, such as this (right up against right wall, rear wall), you may examine the possibility of rotating the entire operation about 45degrees. Placing the display and focal point in the corner, this removes the L-R asymmetry, and re-directs sidewall energy behind you (studio technique). Just consider it, it may not even be an option and that's cool. Your existing set-up is very clean, very nice. I'm looking at the overall approach from above, .. thinking about what improvements are possible imaging wise, which subjectively would pay off wonderfully over time, if it was better.

Just suggesting to think about it. Nice system, and the room, and it's interaction is of huge significance to the experience.

Best of luck

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post #126 of 143 Old 10-29-2013, 08:10 AM - Thread Starter
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Oops, it looks like I uploaded the wrong plot for the subs. That one is actually the subs + the mains, not just the subs on their own. The measurement of the mains (and the subs by themselves which I'll post when I get home) both include the 100Hz crossover from the AVR. I've measured 80Hz xover as well, and it looks almost identical, so I just left it at 100Hz for now since localization isn't an issue with the subs right under the mains.

I'm actually not using any bass management other than the AVR xover right now, but I'm hoping to pick up an inuke3000dsp in the next couple months to play around with it.

Thanks for all the info and the suggesstions! I'm going to try moving the mains closer to the wall (although with the toe-in it'll only be a few more inches than it is already), and then the next step is to look into some fiberglass. There's an SPI in the area, but it's a bit of a hike.

Another question: the subs are already as close to the wall as they can get at that angle, so if I move the mains back, there will be a decent amount of surface right in front of them from the top of the sub (8-10 in) will that matter as far as causing unwanted reflections? Or will the space be too small compared to the wavelengths that will reach it to make a difference?


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post #127 of 143 Old 10-30-2013, 05:34 AM
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I personally wouldn't want the subs to be right in the first sound wave path, and yes it will most definitely cause a reflection, but in reality you might not ever notice an audible difference.
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post #128 of 143 Old 11-08-2013, 11:19 AM - Thread Starter
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Well I did some experimenting with placement, and while it was informative, I don't think I'll be changing much until I can get some absorption for behind the LR.

I tried turning the subs around so the drivers are facing the wall, which made a big difference with my dip around 100Hz. It moved it up slightly, and made it more shallow. I also moved the LR back as far as possible, and changed the crossover to 80Hz. The net effect of this was that the jagged region from 100Hz to 200Hz was evened out slightly.

Just looking at the frequency response I was impressed, and after demoing a few of my favorite scenes (Hurt Locker opening, and Olympus Has Fallen Washington Monument) I could tell a difference, although a lot of it was the increased vibrations in the room which I guess I should have expected from firing the drivers directly at the wall.

Later I realized that I forgot to check the time domain as well, and now I'm less convinced that turning the subs around was a good idea. The waterfalls are much worse than before, with the decay times increased significantly across the whole bandwidth for the subs. I'll post the measurements I took when I get home, but I'll probably be turning the subs back around.

Edit: plots

Frequency response with subs turned around (ignore that ringing look. It's something weird going on with my measurement setup)


Waterfall with subs turned around


Waterfall with subs facing forward


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post #129 of 143 Old 11-22-2013, 12:01 PM - Thread Starter
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Since the right speaker is in a corner would I have to treat both behind it and to the side to mitigate the SBIR?


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post #130 of 143 Old 11-23-2013, 04:17 AM
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My recommendation would be to start by treating the first reflection point on the side wall, then treating behind the speaker on the front wall. Then measure, adjust, and repeat.
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post #131 of 143 Old 11-23-2013, 06:26 AM - Thread Starter
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I would definitely start with the early reflection points on the side wall if I could, but to the left is open, and to the right is a window that takes up most of the wall. For now I'm just going to try to get back my 100ish Hz.


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post #132 of 143 Old 11-24-2013, 07:06 AM
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What about heavy curtains on the window? While not as good as dedicated absorption treatment, it's still better than nothing.
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post #133 of 143 Old 11-24-2013, 08:50 AM
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I can appreciate your enthusiasm and drive to improve both the measured the overall subjective listening experience.

I mentioned the suggestion below, in a previous post, is this a possibility? Many rooms just don't lend themselves to a slight rotation due to aesthetic concerns, foot traffic, etc. But if possible, if you could slightly shift the entire set-up, creating an angled boundary adjacent left and right to the loudspeakers. This redirection of the sidewall energy allows the recorded event and image recreation to be fully resolved in your brain, quite similar to what the engineering team experienced and much closer to what they want the user to experience.

It's all about the Initial Time Delay Gap, or ITD gap. This is essentially the time difference at the listening position, between arrival of the direct energy, and the first strong reflection. The reason we want a longer ITD gap, is simply to allow you to hear the time domain localization cues that our listening process needs to recreate the image. SBIR, a separate issue, but a potential by product nonetheless, is the smoothing impact in the freq domain.

Quote:
Originally Posted by FOH View Post

fwiw, different topic ... in such lack of symmetry room scenarios, such as this (right up against right wall, rear wall), you may examine the possibility of rotating the entire operation about 45degrees. Placing the display and focal point in the corner, this removes the L-R asymmetry, and re-directs sidewall energy behind you (studio technique). Just consider it, it may not even be an option and that's cool. Your existing set-up is very clean, very nice. I'm looking at the overall approach from above, .. thinking about what improvements are possible imaging wise, which subjectively would pay off wonderfully over time, if it was better.

Just suggesting to think about it. Nice system, and the room, and it's interaction is of huge significance to the experience.

Best of luck

The Left-to-Right symmetry is very important, and quite likely one of the most important elements in the playback experience. Outside of studios and dedicated rooms, it's tough to fully pull off in residences and multi-use rooms. However any efforts directed toward more symmetrical environment will pay off huge, I assure you.

Another by product of a set-up shift, would be the area behind the listening position, expanding it and allowing again for more path distance of the energy...smoothing response/comb filtering etc., and again more imaging detail.

Yeah, one can address the ITD gap with absorption, like the vast majority do (myself included, no choice). But angled walls, or angled set-ups and redirection off lateral energy is the preferred method to create a sufficient gap between the direct energy and the first strong reflected energy. It's preferred because it doesn't filter the reflection like an absorption panel does, and maybe more importantly the precious lateral energy is preserved but added back in later thus creating great spaciousness, immersiveness.

Hope this helps, let me know if you'd like more specifics.


Best of luck.

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post #134 of 143 Old 11-26-2013, 05:36 AM - Thread Starter
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Well, I gave angling the setup a shot, and so far I'm very impressed. I haven't broken out the measurement gear yet, so I can only give subjective impressions right now. The first thing I noticed was that at high levels and high frequencies it never once sounded harsh. Before certain things like glass breaking, etc would make me wince a little, but now everything just sounds very clear. Turning up the volume just sounds like the sound source is getting bigger and closer without getting more harsh. I'm sure this is mostly from getting the listening position away from the wall. However, when calibrating I did notice that it turned my subs up to +1 (from -6 before) on the receiver. It was kind of late when I finished, so I didn't watch a familiar bass scene to check out the bass but I'll do that when I can. The huge increase in level on the receiver has me a bit worried, but when I watched Dredd (on netflix, no Dolby Digital mad.gif) it seemed like there was a decent amount of bass.

I'll post measurements when I get a chance, and report back with my bass impressions later. So far, though, I'm very happy with how this experiment turned out.



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post #135 of 143 Old 11-27-2013, 08:13 AM
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Nice looking setup, Scott. Sadly, I'd never get away with it in my abode, though. I bet that does sound really good.

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post #136 of 143 Old 11-27-2013, 05:31 PM - Thread Starter
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Thanks Bill, I got around to measuring, and it seems to confirm what I heard. I'm glad that I wasn't just caught up in the "new" sound, and it actually measures pretty well (or it does now). Here's what it looks like:

Right + subs


Left + subs


Right + Left (80Hz xover)



After looking at this I realized why the bass seemed so different. It looks like the mains were interfering with each other/the subs pretty heavily, so I decided to raise the crossover to 100Hz and see if that helped the problem.

Right + Left (100Hz xover)



This moved that deep null up a little bit, but more importantly it raised up the region from 30-70Hz (theoretically-- the R+L plots are just REW's addition function with the individual channels. I realize that having the subs active on each of the individual channel measurements would double the apparent contribution from the subs in the REW plot, but for pure comparison I think it's valid).

Here's a comparison of the crossovers:



Finally, here's a look at the waterfall for the new setup:



Vs. the old setup:


Honestly it looks slightly worse waterfall-wise, but it's close enough that I'm not concerned. If I can get some DSP to cut back those really resonant areas that should fix up the time domain as well, correct?


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post #137 of 143 Old 11-27-2013, 06:54 PM
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Quote:
Originally Posted by bwaslo View Post

Nice looking setup, Scott. Sadly, I'd never get away with it in my abode, though. I bet that does sound really good.

Welcome back, Bill!

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post #138 of 143 Old 11-27-2013, 07:14 PM
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+1

hope things are well

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post #139 of 143 Old 11-28-2013, 05:51 AM
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Quote:
Originally Posted by Scott C. View Post

Thanks Bill, I got around to measuring, and it seems to confirm what I heard. I'm glad that I wasn't just caught up in the "new" sound, and it actually measures pretty well (or it does now). Here's what it looks like:

Scott, does your REW measurement use loopback for a timing reference? If not (as occurs when using a USB mic for example), the computed L+R will often be incorrect, as the correct timing relationship from one measurement to the next is not preserved in general without a loopback reference.

If you aren't using a loopback timing reference, this can be fixed by energizing the L and R simultaneously and measuring the result.
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post #140 of 143 Old 11-28-2013, 06:16 AM - Thread Starter
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Quote:
Originally Posted by andyc56 View Post

Scott, does your REW measurement use loopback for a timing reference? If not (as occurs when using a USB mic for example), the computed L+R will often be incorrect, as the correct timing relationship from one measurement to the next is not preserved in general without a loopback reference.

If you aren't using a loopback timing reference, this can be fixed by energizing the L and R simultaneously and measuring the result.

I'm inclined to say no because I didn't do anything special for that. Would that just mean using a loopback in one channel while measuring/outputting to the receiver with the other channel?


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post #141 of 143 Old 11-28-2013, 06:32 AM
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If you're not using a USB mic, but an XLR one, you can connect a cable from the second output channel of the sound device to its second input. Then, on the Preferences dialog, Analysis tab, select loopback as shown in the pic below:



Once you've done that, go back to the Soundcard tab of the Preferences dialog, and configure it something like this (results will be hardware-dependent):



With a USB mic, this technique will not work though.
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post #142 of 143 Old 11-28-2013, 06:38 AM - Thread Starter
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Thanks! I don't currently have the cabling for that, but when I do I'll try it out. For now I guess it's safe to say that I should disregard the summed plots. Just out of curiosity, why would the propagation delay through the sound card change between measurements done minutes apart with nothing changed in the setup?


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post #143 of 143 Old 11-28-2013, 06:58 AM
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Quote:
Originally Posted by Scott C. View Post

Thanks! I don't currently have the cabling for that, but when I do I'll try it out. For now I guess it's safe to say that I should disregard the summed plots. Just out of curiosity, why would the propagation delay through the sound card change between measurements done minutes apart with nothing changed in the setup?

It's probably easier to just use a Y cable to energize the L and R analog inputs simultaneously and just do one measurement of L+R.

When the software computes the impulse response, it's in the form of an array of values. The point t=0 must be determined as a separate step. The default way of doing this is shown in the grayed text on the Analysis tab in the pic above ("set t=0 at IR [impulse response] peak"). But this has the effect of wiping out any actual delay difference between the two measurements (say, due to differing distances).

Edit: For more information, see John M's comments in this thread.
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