Acoustics 102 with Anthony Grimani - AVS Forum
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post #1 of 35 Old 10-15-2013, 12:12 PM - Thread Starter
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In Part 2 of this informative discussion, acoustician Anthony Grimani talks about room acoustics in relation to seating and speaker placement, including the best places to put your seats, risers for the second row to maintain good sightlines and possibly provide a bass trap, speaker directivity and its relationship to room acoustics, the best places for the front three speakers, the benefits of multiple, smaller subwoofers over one big sub, the best places for a single sub and multiple subs, answers to chat-room questions, and more.

 

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post #2 of 35 Old 10-15-2013, 02:43 PM
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Scott ? is Anthony a AVS member ?
You have some of the A/V industry's best.
Here's a shout out to Scott, Robert, and Anthony, you guys are the best in what you do.
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post #3 of 35 Old 10-15-2013, 03:05 PM
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I second that! Good stuff

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post #4 of 35 Old 10-15-2013, 05:03 PM
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Wonderful stuff discussed......thanks Scott i have learned a lot.
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post #5 of 35 Old 10-15-2013, 05:20 PM
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Anthony is a awesome guy,.
ScottWilkinson I have issue, your shows need to be another hour long!. Haha maybe you can talk to twit CEO or who ever runs their network smile.gif.

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post #6 of 35 Old 10-15-2013, 06:00 PM
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Scott ? those who have those center speakers with 2 woofers would getting into the inside of the speaker and disconnecting one of the woofers work ?
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post #7 of 35 Old 10-15-2013, 07:07 PM
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Quote:
Originally Posted by DLPProjectorfan View Post

Scott ? those who have those center speakers with 2 woofers would getting into the inside of the speaker and disconnecting one of the woofers work ?


I can see a ton of concern over this. I'm wondering which brands actually have this corrected and why is there so many built like this if its a known problem?


Great episode!!
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post #8 of 35 Old 10-16-2013, 05:10 AM
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This was my first episode and I found it extremely informative and interesting to watch. I have a question though. Looking from the screen wall to the back of my room, the rear wall is split in half for the stairs. When calculating the length of the room (for optimal seat placement, etc), should I use the measurement to the far back wall (27') or the closer 1/2 stair wall (24')?

Thanks!

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post #9 of 35 Old 10-16-2013, 06:42 AM
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Good stuff! This Scott.
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post #10 of 35 Old 10-16-2013, 07:32 AM
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Quote:
Originally Posted by zebracatzebra View Post

This was my first episode and I found it extremely informative and interesting to watch. I have a question though. Looking from the screen wall to the back of my room, the rear wall is split in half for the stairs. When calculating the length of the room (for optimal seat placement, etc), should I use the measurement to the far back wall (27') or the closer 1/2 stair wall (24')?

Thanks!


The example used in the demo was for a specific frequency (or wavelength) for a specific room dimension. This is done because it makes things much easier to understand. In reality, you'll have peaks and troughs at varying frequencies in different locations all around the room. I wouldn't attempt to place your seating based on what you see in this video with regards to subwoofer frequencies. It makes a lot more sense to put seating for best viewing location and then try moving subs around to get the best sound. The best solution for peaks and troughs at subwoofer frequencies is to use multiple subwoofers at varying locations within the room. As a matter of fact, if you don't use multiple subs, there's really no way you can sit anywhere and not be in a trough at some frequencies.
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post #11 of 35 Old 10-16-2013, 09:03 AM
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Using RTA inside REW is your best friend for locating multiple sub-woofers.
You can start with best practices for placement of your subs, or based upon physical constraints of your room layout, you put them in locations along your corners/walls/etc.

Then using RTA can see the effect of each sub as you bring it online and it's modal coupling with the other sub(s) and your room.
http://www.hometheatershack.com/roomeq/wizardhelpv5/help_en-GB/html/spectrum.html#top

Rinse/repeat for multiple seat locations and multiple subs.
Have tape handy to mark each sub location, paper to record good/better/best locations.

After 2-3 hours, you should have them dialed in, put in your favorite demo scene with LFE and enjoy!
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post #12 of 35 Old 10-16-2013, 09:40 AM
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First time I've ever heard that sitting dead center is not appropriate...
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post #13 of 35 Old 10-16-2013, 10:21 AM
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Quote:
Originally Posted by Orbitron View Post

First time I've ever heard that sitting dead center is not appropriate...
Only because it is the location of the greatest frequency response variation (tallest peaks and deepest nulls). If you sit off-centre, the frequency response will be smoother, but the soundstage will appear lopsided.

You can address frequency response variations with subwoofer placement, room treatments and equalization. This will allow you to sit in the middle and have a symmetrical soundstage. By comparison, there's not much you can do to fix a soundstage that appears unbalanced due to sitting off-centre.
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post #14 of 35 Old 10-16-2013, 07:01 PM
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The one question I would have asked if I'd been in the chatroom concerns placement of acoustical panels. Specifically, what does he think of the first-defense tactic of placing an acoustical panel on each side wall a the point of first reflection? I always thought that was the starting point.
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post #15 of 35 Old 10-16-2013, 09:25 PM
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Loved this one Scott!

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post #16 of 35 Old 10-16-2013, 09:50 PM
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Tony is awesome. Back in 2002 he still taught all the acoustics, design, installation, calibration and verification blocks of the THX training...when I attended. It was a longer course back then; all week and part at Skywalker including a class in the Stag Theater and a screening on Friday night (for the employees, but we were invited). It was FOTR.

The training was a firehose in the face for the days that Tony taught, but he has some amazing training aid gadgets that he's built over the years to demonstrate things like axial modes, etc. One demo he did that week was in a large room in the hotel. He put a giant, loud subwoofer in one corner and fed it the frequency that corresponded to the first axial mode in the room. If we stood in the middle of that room, there was silence. Take one large step forward or aft, and it was deafening. This obviously speaks to the subject of Acoustics 102...speaker and seating placement.

Terrific series.
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post #17 of 35 Old 10-16-2013, 11:21 PM
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Quote:
Originally Posted by Utopianemo View Post

The one question I would have asked if I'd been in the chatroom concerns placement of acoustical panels. Specifically, what does he think of the first-defense tactic of placing an acoustical panel on each side wall a the point of first reflection? I always thought that was the starting point.

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post #18 of 35 Old 10-17-2013, 05:40 AM
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Great episode, would love to hear more from him. Thanks Scott for hosting these!

This begs the question: Measuring distance to seating using di-poles in diffuse mode when placed perpendicular to listening positions.
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post #19 of 35 Old 10-17-2013, 08:24 AM
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Quote:
Originally Posted by Orbitron View Post

First time I've ever heard that sitting dead center is not appropriate...

Only at frequencies whose wavelength divides evenly into a room dimension. For example if a room is 20 feet long, a 10 ft long wavelength would have a null in the middle, but a 7 foot wavelength would not. This assume the sound emanates from a wall at a single source.
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post #20 of 35 Old 10-17-2013, 09:13 AM
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003.JPG 2655k .JPG file Understood - the room is 11.5' x 25' built to the acoustic analysis of Chris Huston of Rives Audio. Scott did a show with him some time ago. I sit dead center and it is SWEET.
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post #21 of 35 Old 10-17-2013, 09:38 AM
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This was an excellent, informative and entertaining show! Please consider adding many more Acoustics with Anthony Grimani episodes. I would enjoy and benefit from an entire series.

Thank you for a great AVS Forum radio show
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post #22 of 35 Old 10-17-2013, 11:47 AM
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Quote:
Originally Posted by DLPProjectorfan View Post

Scott ? those who have those center speakers with 2 woofers would getting into the inside of the speaker and disconnecting one of the woofers work ?
Putting a low-pass filter on one of the woofers would work. At low frequencies where they are still acoustically coupled they will both work, then as the frequency rises above the low-pass filter, only one of the woofers will work. You get the best of both worlds.
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post #23 of 35 Old 10-17-2013, 01:01 PM
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Quote:
Originally Posted by Utopianemo View Post

The one question I would have asked if I'd been in the chatroom concerns placement of acoustical panels. Specifically, what does he think of the first-defense tactic of placing an acoustical panel on each side wall a the point of first reflection? I always thought that was the starting point.

If you go to his site he has some installation manuals for the room treatment he sells, I skimmed them the other day and I believe he has a step where you cover the first side reflection.
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post #24 of 35 Old 10-17-2013, 01:50 PM
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They also make Theater Seats that are built for the back row. They are called back row seat that have a riser built into the seats.
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post #25 of 35 Old 10-17-2013, 02:04 PM
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Another note: My Receiver Pioneer SC-27 does have about 5 seating positions that can be programmed into it once the MCACC is ran with the microphone.
When we watch movies I never tell the family that it is set to my seating location where ever that may be heheheh wink wink.
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post #26 of 35 Old 10-17-2013, 09:40 PM
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Quote:
Originally Posted by Orbitron View Post

003.JPG 2655k .JPG file Understood - the room is 11.5' x 25' built to the acoustic analysis of Chris Huston of Rives Audio. Scott did a show with him some time ago. I sit dead center and it is SWEET.
As Grimani mentioned in the podcast, placing a sub (or speaker) at the null of a room mode will minimize the effects of that mode. Your centre speaker is at the midpoint of room width, so it is cancelling all the nulls at that location (your seating location).

Depending on where your L/R speakers are placed, they can cancel some of the peaks at the centre of the room.

Like I said in my previous post, subwoofer and speaker placement can ameliorate some of the modal problems that come with sitting at the midpoint of room width.

However, if you put a subwoofer at one corner, then the centre of room width will be the worst place to sit (tallest peaks, deepest nulls).

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post #27 of 35 Old 10-18-2013, 08:11 AM
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Quote:
Originally Posted by sdurani View Post

As Grimani mentioned in the podcast, placing a sub (or speaker) at the null of a room mode will minimize the effects of that mode. Your centre speaker is at the midpoint of room width, so it is cancelling all the nulls at that location (your seating location).

Depending on where your L/R speakers are placed, they can cancel some of the peaks at the centre of the room.

Like I said in my previous post, subwoofer and speaker placement can ameliorate some of the modal problems that come with sitting at the midpoint of room width.

However, if you put a subwoofer at one corner, then the centre of room width will be the worst place to sit (tallest peaks, deepest nulls).

This has me really thinking. I am going to move my sub off to the other side of my center channel speaker as I looked last night and this is the middle of my room. As shown in my picture. He did mention that the best scenario on a budget if you have two subs is to have one in the center front and one at back of the room.

Can anyone tell me what direction the sub should be firing straignt? Any advantage to point sideways ect. The back of my sub has a phase control with there being two settings. 0 and 180. Currently I have it set at 180 have only one sub. If I add another sub does this phase control need to change on one or the other subs or do they both stay on the same phase setting??? AXIOM EP500.jpg 281k .jpg file
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post #28 of 35 Old 10-18-2013, 09:07 AM
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Thanks Scott for bringing these two 'episodes' on room acoustics to us featuring Anthony Grimani. They were both very informative and I plan to directly implement some of his suggestions as I build out my new media room. Excellent material and presentation. - Rick

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post #29 of 35 Old 10-20-2013, 09:05 AM
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Hi Scott, these Acoustics 101 and 102 episodes have been my favorite! Please have Anthony back soon for an Acoustics 103!! From how he had to rush a bit through his slides, it looks like he had a lot more good information. Thanks!

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post #30 of 35 Old 10-21-2013, 05:38 AM
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Good show indeed, great job to everyone who was involved!

I also have a question regarding my room and speaker/sub placement. The middle of my room width wise, runs into the open entry space on the right hand side when looking at my screen. So I can't put a sub on either side of the room in the middle. If I put one at the front and back of the room in the middle of the space between walls, does that interfere with the center channel in any way? I guess I am not sure how that would work?

I don't have alot of height in my basement so my center stands on he ground and barely fits under the bottom of my projector screen. Could the sub go right next to the center? Could I move them each slightly off center? I guess I am worried about the center speaker being within 2 feet of my two fronts if I place a sub there.

Does anyone have any advice, or know of a guide that may discuss this? Thanks if you can help!
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