Bass Trapping in Separate Room - Connected to Main Listening Room - AVS Forum
Forum Jump: 
Reply
 
Thread Tools
post #1 of 38 Old 05-20-2013, 03:32 PM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Alright, I finally got REW and I have found some interesting things...I have also just gotten a second sub with a third one on the way.
I have 2" panels at first reflections and a few others here and there as shown on the picture. I also have about 5-6 panels doing nothing specific, while playing with REW I put 4 in the rear corner as shown in the picture and it made a difference on the waterfall but I want to be more intentional.
So I want to re-locate all my subwoofers. Basically the third is a Dayton 15" I am waiting for my Flat Pack enclosure to arrive so I can finish it. For now I have:
Klipsch RW12d 12" Ported
Atlantic Technology 372PBM 15" Sealed
I need to figure out a good way to sub-crawl or use REW to tell me where to place subs..have yet to find a specific post with a how-to on speaker placement using measuring equipment.

As you can see, I have a LOT of volume in this open space. One of my problems is I do not have a ton of corner space in the listening room for traps. I can move the bookshelf where the current makeshift stack is and see what that does, though as I go to each corner, I find the front left corner has the loudest bass. I ALSO find that one of the corners in the Dining room that is open to living room has a lot of bass. I suppose in theory I could just put the subs in the three corners of the main room...I am not sure.

Main question- Can I do Bass Trapping in a "separate" room from where the system is...i.e. in the Dining room that is open by a 12' opening to the living.

Considering bass, I can find high spots and low spots in all the rooms connected to living room, so I assume I am basically pressurizing most the house.
So can I trap in another room? Which corner in this massive and not-square room is technically the best likely candidate. Could I theoretically put a subwoofer in the other room? It would be beneficial to not have to take up more space in the living room....

Thanks for the input. REW is awesome! I can't wait to get striving for a great room!
If you want pics of the room for real I am happy to provide if it will help.
shaneb0422 is offline  
Sponsored Links
Advertisement
 
post #2 of 38 Old 05-21-2013, 11:29 AM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 134
Bass traps help the most when placed in the room the speakers and subwoofer are in. However, in your case with large openings you might get some benefit from traps in a connected room. The real answer to this and all of your other questions is simple: Yes, REW will help you find the best placements, but you'll need to do a lot of experimenting, measuring after each small change.

Also, a large room like that needs a lot more than just five or six 2x4 foot bass traps.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #3 of 38 Old 05-21-2013, 11:42 AM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,118
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Liked: 46

Here's my room, from near the LP with nothing but the sub's internal boost/cut filter. The room is 22' long, so it can't support that resonance below 20Hz... clear indication of a scondary resonance. In my case, it's a 5' doorway in a wall with no corners (furniture), opposite a brick fireplace. The tail in the mid 20's is the lowest normal mode, and the house 2nd harmonic.

Do this in your room and let's see what you get. This is called a "spectrogram" in REW. If you've done a waterfall, you're very close; same data. Key bits are:
- measure loud, so you get 50-60dB above your noise floor
- choose the color axis carefully, so a -40dB decay is easy to see.
- turn on contour lines as well as color
- Include the 10-20Hz octave, so you catch room interactions.

One criteria for a good listening room is about 0.3sec for a 40dB decay. I've scaled the chart so there's 40dB between min/max contour lines. My room meets that criteria quite uniformly down to 50-60Hz, when -40dB decay extends to 0.5sec. I'm not sorried about the infrasonic decay from the rest of the house, even if you are.

The important point to note is that I've added no acoustic treatment to the room. This is not surprising if you look at data for typical residential rooms.

Since you've treated your room, the first question you should have asked is "what's my room like" right now. The current state of a room is immaterial until a problem is identified. The solution may be to add something, or to take something present away.

I will wager you see room interactions that are likely far worse than mine. Long tails in the bass representing contributions from adjoining space coming from both foyer and dining rooms.

Since you have multiple subwoofers, the first thing I'd suggest is finding the worst resonance frequencies, and then locating the subwoofers to minimize energy injection into that mode. Measure with your largest sub in the left front corner and you should excite everything. Whichever frequencies have the longest resonances are those we want to avoid if possible. (Not everything's possible).

For example
- corners excite all room modes, thus a good place for initial measurement
- mid-wall placement only excites even harmonics along that wall
- 1/3 wall placement excites fundmental and 2nd harmonic evenly, but really drives the 3rd harmonic, OK if that frequency is well above the 80Hz sub crossover.

As to your questions, you can absorb bass energy anywhere it's present. You want to find the highest pressure areas, then use a pressure-based absorption device, not a velocity-based device such as your current panels. These traps like corners because corners concentrate pressure, but they work elsewhere in the room. Same with subwoofers, but both want to be placed for optimum results, not maximum results.

The other thing I'll recommend is measuring in multiple places. This looks like a single-sweet-spot layout, and even the width of your elbows will result in massive response changes. Thankfully we have two ears!

So convert some waterfalls, or post them if you prefer that display. Based on the data, there may be some specific approaches indicated... guided by the result they produce.

Have fun,
frank
fbov is offline  
post #4 of 38 Old 05-22-2013, 10:20 AM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
This has been incredibly helpful guys.
I understand I need more bass trapping, I was using those panels in the corner just to see what happened with the measurements..
I will try your ideas this weekend and post results. Just so I understand wholly, I will follow this process.
I have a total of 11 2" panels and initially purchased them for first reflections and to help with whatever else I thought I may need them for after learning to measure.
1. Place first sub in corner and measure
2. In places with most energy try placing second and third subwoofers (I have noticed, the location where I say Dayton sub is a very loud place when standing there. I imagine that could be a high energy location). Measure response with subwoofers in these high energy locations
3. If response not flattened by this, do I leave subs in these locations (corners or midwall or wherever) and bass trap other available corners? I.e., will subwoofers likely end up in three highest energy corners or locations?

Thanks guys! I will post graphs ASAP.
shaneb0422 is offline  
post #5 of 38 Old 05-22-2013, 12:43 PM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,118
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Liked: 46
I agree with #1.

#2 you would do the opposite; add subwoofage where it's lacking. You want to fill in holes, and this may be the best way in a very complex room.

#3 is tough without data.

Remember the process: analyse the problem first, generate potential solutions next based on that analysis, then implement and measure to confirm the result. Until the analysis is done, how do you know what to do?

Have fun,
Frank
fbov is offline  
post #6 of 38 Old 05-22-2013, 12:54 PM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 134
Quote:
Originally Posted by fbov View Post

Until the analysis is done, how do you know what to do?

Exactly. And only by measuring can you see what is helping or hurting.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #7 of 38 Old 05-22-2013, 03:31 PM
FOH
AVS Special Member
 
FOH's Avatar
 
Join Date: Apr 2010
Location: Midwest
Posts: 4,749
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
Liked: 213
Frank, Ethan ... +1

All too often individuals don't confirm with measurements. Yeah, there's the typical "low hanging fruit" acoustically*, but adequate measurement systems are affordably available, and a vast array of tutorials exist to help anyone interested. Until one measures, you're really flying blind.


*there's also many counter-intuitive elements in acoustics eek.gif

------------------------------------
Flat, Deep, Clean, Linear, and Loud
------------------------------------
Active 16.8kw, 7.3 system
(3)Seaton Cat12C up front, (4)QSC K8 sides/rears
(2)Seaton SubM-HP, (4)18" IB
FOH is offline  
post #8 of 38 Old 05-23-2013, 12:28 PM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:
Originally Posted by fbov View Post

Remember the process: analyse the problem first, generate potential solutions next based on that analysis, then implement and measure to confirm the result. Until the analysis is done, how do you know what to do?

Quote:
Originally Posted by Ethan Winer View Post

Exactly. And only by measuring can you see what is helping or hurting.

--Ethan

Quote:
Originally Posted by FOH View Post

Frank, Ethan ... +1

All too often individuals don't confirm with measurements. Yeah, there's the typical "low hanging fruit" acoustically*, but adequate measurement systems are affordably available, and a vast array of tutorials exist to help anyone interested. Until one measures, you're really flying blind.


*there's also many counter-intuitive elements in acoustics eek.gif

Exactly what I'm shootin' for! Thanks guys.
shaneb0422 is offline  
post #9 of 38 Old 05-24-2013, 07:40 PM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Alright! After worn out fingertips and a sore back, not to mention at least 100 measurements. I think I have my two subs placed! Hopefully I won't have trouble with the third. I did learn that my new sub I am building as a table may not be a great idea frown.gif.
Klipsch ended up about half way between corner and next to TV and the AT went from next to couch to opposite wall where I was going to end up with the new sub.
It took putting the AT over there to get the 70hz null to go away...
Also I took my mic around in SPL mode with the receiver playing constant tone and noticed even in the back corner of dining room i was getting 4db louder in that corner than at listening position. I was also surprised to see how much making very very slight adjustments made in the graphs. I just wish the listening position could be as good as the couch spot!
Also, I noticed before I started, Audyssey made a good bit of difference, though I forgot to measure with it or re-run it before I rolled up the measuring gear. Do you recommend Audyssey, or using the manual EQ (Onkyo NR709).

You guys have any other ideas or tips for me to smooth it out some...or you think I should wait until the third sub is in and do this again then look at it.
Here is before:


After:


Before Spectro:


After Spectro:


And....couch seat (not where I ever sit).
shaneb0422 is offline  
post #10 of 38 Old 05-25-2013, 07:25 AM
FOH
AVS Special Member
 
FOH's Avatar
 
Join Date: Apr 2010
Location: Midwest
Posts: 4,749
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
Liked: 213
Well, it looks like you need to sit on the couch!

------------------------------------
Flat, Deep, Clean, Linear, and Loud
------------------------------------
Active 16.8kw, 7.3 system
(3)Seaton Cat12C up front, (4)QSC K8 sides/rears
(2)Seaton SubM-HP, (4)18" IB
FOH is offline  
post #11 of 38 Old 05-26-2013, 02:07 PM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
So I have 5 oc703 or 705 panels I can cannibalize for bass trapping. Is this desirable or is a super chunk better?
Ethan in your video where you show the difference of diffusion and trapping in a room (can't remember the name) you had a few very thick panels in the corners and it made a difference. I could even straddle the corner if needed. Is that a good place to start with like 6" thick pieces or 8". I could add a few more panels to the mix if needed.
Looks like 50hz is the nasty area in my room. But I have trouble understanding how room modes based on placement acts. Still trying to wrap my brain around it.
shaneb0422 is offline  
post #12 of 38 Old 05-27-2013, 11:31 AM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 134
Panels 4 to 6 inches thick do a great job, and that's a better use of a fixed amount of material. Chunk traps use three times more material, but absorb only a little more bass than 4-6 inch thick panels.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #13 of 38 Old 05-27-2013, 12:53 PM
FOH
AVS Special Member
 
FOH's Avatar
 
Join Date: Apr 2010
Location: Midwest
Posts: 4,749
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
Liked: 213
Quote:
Originally Posted by shaneb0422 View Post

But I have trouble understanding how room modes based on placement acts. Still trying to wrap my brain around it.

Aside from all Real Traps and Ethan's great pages contain, here's some solid ref material for you;

Here's a simple explanation that may help.

However this is a really good read, covering many of the important aspects.

One more example from Acoustic Frontiers contains mucho goodness.

Maybe the best paper on getting good bass in a room is by Toole.


Hopes this helps, those are tremendous resources.

------------------------------------
Flat, Deep, Clean, Linear, and Loud
------------------------------------
Active 16.8kw, 7.3 system
(3)Seaton Cat12C up front, (4)QSC K8 sides/rears
(2)Seaton SubM-HP, (4)18" IB
FOH is offline  
post #14 of 38 Old 05-27-2013, 03:55 PM
AVS Special Member
 
kiwi2's Avatar
 
Join Date: Nov 2010
Location: New Zealand
Posts: 1,630
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked: 144
Quote:
Originally Posted by shaneb0422 View Post

Alright! After worn out fingertips and a sore back, not to mention at least 100 measurements. I think I have my two subs placed! You guys have any other ideas or tips for me to smooth it out some...or you think I should wait until the third sub is in and do this again then look at it.

Just keep experimenting and see what gives you a flatter response. I also once had a room where I left two doors open behind the listening position into my bedroom and spare bedroom for sound waves to defuse and dissipate themselves in, rather than reflecting back. It helped a lot to give a flatter response and the difference was very audible with a tighter and less smeared sound.

Of course also experimenting with placement of speakers, subs, listening position. Also experiment with port plugs on subs and speakers to see what the differences it makes. Then of course AVR bass management settings on top of that. i.e different crossover points, crossover slopes if adjustable, sub distance, sub phase etc.

And don't worry too much about spectro or waterfall measurements because sorting out the frequency response will also make those other measurements look better as well. They are all actually one of the same thing. A large peak in the frequency response will be overloading the room with too much energy at that frequency and will cause long slow decay times.

i.e.. here I have overlaid your before frequency response on top of your before spectro.



Getting a frequency response that is smoother and more even will also result in decay times that are more even through the frequency response as well.
kiwi2 is offline  
post #15 of 38 Old 05-27-2013, 06:07 PM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Thanks for the links. I read a white paper on Harmon's site a few days ago and lots of it went over my head. I think it's the fact that my room is anything but square that makes the measuring stuff fly over my head. Calculating modes seems a bit impossible.
I am curious if three subs is better than two. Most people only talk about jumping to four.
shaneb0422 is offline  
post #16 of 38 Old 05-28-2013, 10:44 AM
FOH
AVS Special Member
 
FOH's Avatar
 
Join Date: Apr 2010
Location: Midwest
Posts: 4,749
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
Liked: 213
Quote:
Originally Posted by shaneb0422 View Post

Thanks for the links. I read a white paper on Harmon's site a few days ago and lots of it went over my head. I think it's the fact that my room is anything but square that makes the measuring stuff fly over my head.

It does take a little time for all to sink in, however,... before you know it it'll all make sense.


Quote:
Originally Posted by shaneb0422 View Post

Calculating modes seems a bit impossible.

Calculating is mere speculation. Until you actually get in there and measure, all the variables won't be accounted for. The boundary impedances (lossy, movement, etc) can impact calculations, as does the room's furnishings, etc. This is why measuring rules,...it accounts for the real-world variables. It's quite easy really, with free software like Room EQ Wizard, and products like OmniMic are so simple,...minutes after you open the box you're measuring! No kidding.

Quote:
Originally Posted by shaneb0422 View Post

I am curious if three subs is better than two. Most people only talk about jumping to four.

In my opinion, three subs is perhaps the real sweet-spot, with regard to FR smoothing, etc. Two is dramatically better than one, similarly, three is better than two and much more flexible, but moving to four or more, primarily helps with headroom capability, etc. Many discuss four (or even numbers in general) due to symmetry with amplification channels.


Good luck

------------------------------------
Flat, Deep, Clean, Linear, and Loud
------------------------------------
Active 16.8kw, 7.3 system
(3)Seaton Cat12C up front, (4)QSC K8 sides/rears
(2)Seaton SubM-HP, (4)18" IB
FOH is offline  
post #17 of 38 Old 05-28-2013, 03:01 PM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,118
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Liked: 46
A couple things...

Plot a wider dB range; your noise floor is lower than 66dB I trust! Use the same data, just change axis limits so you can look at the time required for a 40dB decay. One aspect of this analysis is looking for peaks, another, looking at overall absorption, measured as T40.

47Hz has a half-wavelength of 12 feet, so your big peak is the room side-side resonance. If the kitchen/dining area you've not dimensioned is also about 12' wide, it would reinforce the peak and provide somewhere to store the energy for the tail. It would be useful to find where the 47Hz is strongest. A location in the adjacent space would allow you to absorb some of that energy without a big change to the room's higher frequency response.

The path you describe (OC703-based devices) will add both LF absorption and add broadband absorption at higher frequencies. Can't say for sure without T40 data, but I suspect you want to repurpose current absorbers rather than add devices, so your higher frequency decay is less affected.

Have fun,
Frank
fbov is offline  
post #18 of 38 Old 05-28-2013, 05:33 PM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
The kitchen is nearly the same width. Interesting info on the 47hz!!!
I re-scaled the graph, hope I understood what you were looking at. I definitely now realize it lasts much longer than I thought...1.5 seconds??? If I am reading right. The waterfall also shows under 30hz takes over 1.5 seconds! I can't even set the limit high enough!

SO- I have always noticed the wall that I moved the second sub to (across from couch) is bass heavy. The reason I ended up with second sub there after measuring is that it smoothed out the 70hz dip. However, I am guessing, based on your 47hz info that it is also reinforcing that frequency. The places I didn't try the second sub is in another "room" or in the back of the living room towards the bookshelf. I have an inclination that the wall I moved it to is one place where I need bass trapping. Again, I will take measurements in several locations to find where 50hz is peaked the most and if I understand correctly. I will take some panels and put them there. Even if it is in a different room. The other side of that 6" deep hollow drywall is a refrigerator that I could easily place panels on top of - angled on ceiling/wall or behind standing up..it appears that could tame the 50hz rather than putting on the living room side which would suck up high frequencies in the listening room.

I will move around and see where I get the biggest 50hz output and the worst dip right before the 50hz and treat it. Would it stand to say that it's possible since the couch seat is so flat that putting a sub in that location might offer a better experience? I hate to move the couch but I'm about to be living alone and I don't care.
As for the T40...I posted the RT60 graph, I am unsure where the T40 is or how to read the RT60 graph...it is weirdly short.


shaneb0422 is offline  
post #19 of 38 Old 05-29-2013, 04:40 PM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,118
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Liked: 46
The one danger of a plotting a 60dB range is that you may be plotting the noise floor, not real resonances. Forced air ventilation is notorious for infrasonic junk, which looks a lot like what you show, or this could be real energy storage.

Regardless, you've got "green" level SPLs showing for an awfully long time in the 10-30Hz range, as you note, so there's real resonance present. You may want to look at one sub at a time, and perhaps move the mic around to see where each one's modes are located, what subwoofer locations excite which resonances. I am aware this quickly turns into data overload, so I'm hoping it's also a bit of fun.

I'm glad to see you get the point about re-purposing absorbers so you don't add where it's not needed. The bigger problem is that resistive absorbers are not very effective at low bass frequencies unless you "filter" the sound energy they see. That's the idea behind a "true" bass trap that only absorbs bass.

One approach is the diaphragmatic absorber. A resistive absorber is placed behind a membrane of some sort that only vibrates at low frequencies, reflecting energy at higher frequencies. The combination of an sealed air cavity and resistive absorber in that cavity serve to absorb a high fraction of the energy in the membrane. This is what I'd consider for the 20Hz region, as they are effective over an octave or two.

For the 48Hz issue, I'd suggest a tuned absorber placed at a point of high 48Hz SPL. That's the one strong, audible resonance you've got, and it's fairly narrow, making a tuned absorber very effective.

The trick to both of these approaches is the need to fine tune after you're done installing it. The diaphragamatic absorber is sensitive to the membrane mass, so adding mass will drive it lower in frequency. The tuned absorber is a Helmholtz cavity, like a bass reflex speaker enclosure, and you'd tune it the same way; port length (fine adjust) and port diameter (coarse adjust).

If you're interested, here's a great read for anyone interested in making their own devices. Page 201-205 is diaphragams, and page 220 shows a Helmholtz used in a case like your 48Hz resonance. He could be talking about you!
http://andrealbino.wikispaces.com/file/view/Master+Handbook+of+Acoustics+-+5th+Edition+-+F.+Alton+Everest,+Ken+C.+Pohlmann.pdf

Lots to digest in this link... lots to digest.

Have fun,
Frank
fbov is offline  
post #20 of 38 Old 05-29-2013, 06:02 PM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
So if I create a "box" around 6" of 703 (3 panels) with reflective material around it that would be my lower bass trap? Find a place with the nastiest -30hz resonance and put there? If I understand correctly, I could use a fairly tight weave material and make a 6" panel that is spaced off the wall and it would achieve this correct? Even if below the material I wrapped some sort of plastic around first?
And it's easy to repurpose. Except for 4 panels at first reflections. The other 7 just lean against whatever random wall I happen to get in my head might help haha.
And for the hemholtz. My understanding is small with that but I Think I get the basics. I will go read that paper now and report back. (When you said pg 200. I knew I was in for it)
Edit: BOOK. I think I will jump around a bit haha.
shaneb0422 is offline  
post #21 of 38 Old 05-30-2013, 04:35 PM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,118
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Liked: 46
Let's back up a bit... what makes an acoustic device effective?

For resistive absorbers like OC703 panels (in an acoustically transparent "bag" let's say), peak effectiveness occurs at peak air velocity.

For diaphragamatic and Helmholtz absorbers, peak effectivness occurs at peak air pressure.

These two are opposites when dealing with room modes. Where pressure is maximized, there's no air motion, and vis versa; when the air can move, no pressure builds up. Walls are always pressure maxima. Mid room is a velocity maxima for all odd modes, as even modes have a pressure max mid-room.

So as an example, if you were to fill the doorway between living and dining with a 2" layer of 703, you'd kill the interaction between the rooms. The doorway is a velocity max, so the resistive 703 works very well. Ironically, you'd do very little to the 48Hz peak, because the doorway is a pressure maximum, just like the wall it parallels, because it's 12' from doorway to a wall in both directions that makes it an even harmonic for the full width living/dining rooms.

Make sense?

Now, add in that pressure-sensitive absorbers must be sealed, save for design requirements (ports, or slat/perf panel absorbers, and you can see that just putting plastic over it won't do all that you want.

And I've got to run... more later.

Have fun,
Frnak
fbov is offline  
post #22 of 38 Old 05-30-2013, 09:39 PM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Oh man.
I have mixed feelings about you. I can tell your helping me. By your forcing me to fish rather than giving me a meal. Making me learn rather than telling me what to do.
I don't actually have mixed feelings. I'm über thankful.
I get it for the frequency in question 47hz. Bing that it is 12 ft wide. The door way is always going to be a pressure max or velocity max because it is always 12ft from boundaries no matter what.
I will draw up the the dining kitchen area. But I can tell you it is not a flat 12'. There is a fireplace that separates the two and it may be 13'. Bt I'm guessing a foot either side of 12 is the zone from 45-50hz where my peak is?
Reading the Book now. Going to come up with a plan and we can see if I have learned anything yet Haha.

I for the below 30hz is where I was referring to a think 703 panel wrapped in reflective material. I am reading about a diaphragmatic for the 47hz as you suggested. However for the 30hz. I imaging I need to do some more measuring to verify the best location given a 6" panel wrapped 3" off wall is the proper absorption.

Thanks again


Edit: a few light bulbs went off. So I need to calculate the volume of a diaphragmatic absorber needed and build a box according-hang it on the wall separating the living room and kitchen. Either side of it. (After making sure that is worst offending location.
Ill figure out how to calculate. My only question on that is-what "position" on the wall and how big. Could I make a deep short box or am I better off with a shallow tall box and spans floor to ceiling or corner ceiling wall/floor wall? From the book, I can't tell that it makes a difference. I read on another site (acoustic fields) that the diaphragmatic will absorb everything above the designed resonant frequencies. Is this true even though the book shows wood being used for the face of it.
Or would you recommend copying their approach in the book with a helmhotz. I don't grasp the construction of those as well as the diaphragmatic but sure could figure it out.

I hope that's right!!
shaneb0422 is offline  
post #23 of 38 Old 05-31-2013, 06:41 AM
AVS Special Member
 
localhost127's Avatar
 
Join Date: May 2009
Posts: 2,286
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 40
Quote:
Originally Posted by fbov View Post

So as an example, if you were to fill the doorway between living and dining with a 2" layer of 703, you'd kill the interaction between the rooms.

really?
localhost127 is offline  
post #24 of 38 Old 05-31-2013, 08:37 AM
AVS Special Member
 
jim19611961's Avatar
 
Join Date: Mar 2011
Location: Texas
Posts: 1,406
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 134 Post(s)
Liked: 88
Quote:
Originally Posted by Ethan Winer View Post

Panels 4 to 6 inches thick do a great job, and that's a better use of a fixed amount of material. Chunk traps use three times more material, but absorb only a little more bass than 4-6 inch thick panels.

--Ethan

Depends on the frequency in question.

My Room
My Music
Rega - Apollo, Rega - DAC, Goldpoint Passive, (2) Classe CA-100 bridged power amps (350w)
Jenzen Next
jim19611961 is offline  
post #25 of 38 Old 05-31-2013, 12:53 PM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 134
Quote:
Originally Posted by jim19611961 View Post

Depends on the frequency in question.

I don't think so. When I measured that, spreading a fixed amount of absorption around a room did a better job than using fewer thicker absorbers. Even at the lowest frequencies. Have you ever actually measured a room both ways?

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #26 of 38 Old 05-31-2013, 02:59 PM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,118
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Liked: 46
Quote:
Originally Posted by shaneb0422 View Post

Oh man.
I have mixed feelings about you. ...
You're not the first... I'm no expert in this field, just another hobbyist, so I prefer if folks learn for themselves, so they own the design they create, because they understand why it's made the way it is.
Quote:
...I am reading about a diaphragmatic for the 47hz as you suggested. However for the 30hz. I imaging I need to do some more measuring to verify the best location given a 6" panel wrapped 3" off wall is the proper absorption. ...
I was suggesting that a Helmholtz absorber would be better at 48Hz given there's a resonant tail that's quite narrow. A Helmholtz absorber is a bass reflex (ported) speaker with no driver, just the resonant cavity. Everest's construction example looks like a sonotube sub, because it is... without the driver. I've used Everest's forumula to develop a few designs, with an emphasis on tunability so you can hit the right frequency, regardless the deviations of construction from the theory behind the design.
The result of my calculations, oddly enough, looks like this for a 2 cu ft. cavity, tuned to ~50Hz. (that's why the length "l" (red curve) and end correction curves are centerd on 50Hz) A 2 cu ft cube is a volume that's ~15.5" on a side, so with 3/4" MDF walls, a 17" cube externally. Alternately, an 18" diameter sonotube, 18" long is about 2 cu ft as well. Both would just fit a 10" port.

Diaphragamitic absorbers are better suited to the 20Hz stuff as they can cover an octave or two. Depth is as important as diaphragm density, and you can trade them off as long as the product is constant. The idea is to create a cavity that wants to resonate at the target frequency, then absorb all the energy that enters. If it's not sealed, it will have Helmholtz resonances as well. Construction details...

In all fairness, I'm also using a lot of background knowledge from Floyd Toole's book, Sound Reproduction, loudspeakers and rooms. It's not public domain, so no link to the text, but a lot of the material is covered in Harman's white papers, especially the one at the bottom, Part 3.

IT's helpful to understand how standing waves work, and your comment:
The door way is always going to be a pressure max or velocity max because it is always 12ft from boundaries no matter what
belies a bit of misunderstanding.

Assuming both rooms are 12' wide (for simplicity), and you have a 48Hz resonance, 48Hz is the fundamental in each individual room, but it's the second harmonic in the doorway where walls are 24' apart, and you're in the middle. At 48Hz, the doorway is a pressure max only because the 2nd harmonic has a pressure max in the middle. It supports a 24Hz fundamental that's the root of the room linkage.

Make any sense?
Frank
fbov is offline  
post #27 of 38 Old 06-01-2013, 08:57 PM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:
Originally Posted by fbov View Post

IT's helpful to understand how standing waves work, and your comment:
The door way is always going to be a pressure max or velocity max because it is always 12ft from boundaries no matter what
belies a bit of misunderstanding.

Assuming both rooms are 12' wide (for simplicity), and you have a 48Hz resonance, 48Hz is the fundamental in each individual room, but it's the second harmonic in the doorway where walls are 24' apart, and you're in the middle. At 48Hz, the doorway is a pressure max only because the 2nd harmonic has a pressure max in the middle. It supports a 24Hz fundamental that's the root of the room linkage.

Make any sense?
Frank

I have to be honest...I audibly laughed. "belies a bit of misunderstanding" it's almost like when I open my mouth you know that I have no idea what is going on. Haha.
I think it makes sense. But truthfully that statement was the reasoning going off in my head, which may have been sound, just too elementary to know why it is.
I just watched 30 minutes on youtube about how standing waves work...so my understanding is now a bit more basic I think. The the 47hz is roughly 24 ft long, and the midpoint of that should be a node, which would be high pressure. At 47hz half the wavelength is the same width as the room. So at either side of both rooms, kitchen and living, there will be a pressure max at 47hz given no cancellation. Placing some type of absorption on that mid-wall would be very prudent given the sub is opposite it 12ft away, and would possible also reduce the perceived output of that frequency in the kitchen.

The Helmholtz bits are going somewhat above my head..I understand the concept but application alludes me...so literally placing said 2 ft3 device in a high pressure spot will work? there is no difference in height of placement etc...just in a pressure area and the resonator will suck up said pressure? My assumption with this is placing the mic at varying heights and whatever "height" along the measured area should be the opening of said helmholtz or diaphragmatic.
The diaphragmatic also seems appealing - in that case you would recommend building one designed to resonate at 20hz which will work from 20hz up until waves are reflected off the face of it?

I think I get the Helmholtz resonator thing, so I guess another question with those is, how many "resonators" does one need, in theory, does one just need a single 2ft-ish one or is the decay so bad that it takes multiple resonators or one huge one to counteract the amount of pressure available to suck up.
Also, I have heard that they can have issues when there is more than one source of said frequency, i.e. multiple subs...this was some guy on gearslutz so who knows.
shaneb0422 is offline  
post #28 of 38 Old 06-02-2013, 09:05 AM - Thread Starter
Member
 
shaneb0422's Avatar
 
Join Date: Jan 2009
Location: DFW, TX
Posts: 96
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Just watched a lot more...understanding velocity vs displacement(pressure) now. AND the fact that against a corner there is a pressure antinode, while a velocity node so helmholtz is taking that pressure and converting it to velocity - i.e. potential energy to kinetic by use of helmholtz or diaphragmatic.
Also making sense that 47-50 or so is the fundamental/first harmonic on the 12ft axis in my room, though interesting that it peaks in the middle of the pressure wave, a node.
Anyway, before I confuse myself...I now understand the relation bewteen pressure and velocity, so way back towards post 1 when I was told to place my second and third subs in "velocity" weak or node areas, I was figuring out placement based on pressure...i.e. what my ears or mic picked up as quietest. Not sure that works.
Also looking at the shape and size of my room, its CRAZY to think I could ever know the math to figure out sound wave dispertion in there...I can take hundreds of measurements and learn by doing, but to be able to say "oh here is a node, cancellation, or anti node" is ridiculous, the axis changes based on area shape is too comlex for me.
I took REW and played with the Room Mode Sim program, making the room the size of all rooms combined without the wall between kitch and living and without the combined...its incredible how awesome the seat near the wall is, I also found a few more spots that I could possibly move my seat to a bit...but no matter subwoofer placement, I always found that there is a gnarly spike in the 40-50hz region and something near 70hz happening. It will be interesting to see if I can get those to flatten out a lot...
Given I have some materials already, I am going to take some resistive panels and mount them off the wall several inches to see what happens, now that I understand we are trying to catch velocity, and at the boundaries those are nodes, I understand why we space off the wall...because ideally we would go in the middle of the room for the first harm, and for other harms we would need to catch at least the 1/4 wavelength.I am also super interested in the other types of absorbers we have talked about...gotta keep learning to figure out how those things work exactly.
shaneb0422 is offline  
post #29 of 38 Old 06-02-2013, 01:38 PM
AVS Special Member
 
localhost127's Avatar
 
Join Date: May 2009
Posts: 2,286
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 40
Quote:
Originally Posted by shaneb0422 View Post

I just watched 30 minutes on youtube about how standing waves work...so my understanding is now a bit more basic I think.

a wavetank simulator is a great way to illustrate behaviors.
http://www.falstad.com/ripple/
Setup = NxN Acoustic Modes
Color Scheme = 2
Check the "3D" box
localhost127 is offline  
post #30 of 38 Old 06-03-2013, 12:36 PM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,118
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 55 Post(s)
Liked: 46
Quote:
Originally Posted by shaneb0422 View Post

...47hz is roughly 24 ft long, and the midpoint of that should be a node, which would be high pressure. At 47hz half the wavelength is the same width as the room. So at either side of both rooms, kitchen and living, there will be a pressure max at 47hz given no cancellation. ...
I find the "node/antinode" nomenclature confusing, as a pressure node is a displacement antinode, and vis versa, so you have to qualify what kind of node you're talking about. Max and min are more familiar concepts.

But you've noticed that the midpoint of a full wavelength looks a lot like the ends... thus the use of half-wavelengths for room mode discussions. This is basis of your room coupling, as some of the 48Hz energy can be stored in the combined rooms as a 2nd harmonic

You've also got the right idea behind the Helmholtz resonator. Placed at a pressure max, the box protects the interior volume from the wave, allowing the port to just absorb energy at the tuning frequency. Pressure outside becomes velocity in the port, which is absorbed by the acoustic absorbant inside the box (like OC703). Placed in a room corner, port down, you treat all directions, but only pull energy at the tuning frequency.

And you see why modeling real spaces is non-trivial. Measurement describes reality, but theory is still helpful in finding which direction to go.

One more thing; air velocity rises quickly as you move away form the wall. In a 12' room, you have over 25% of maximum air velocity only 1' from the wall, and 8" gets you 17.5%, for only 5.5% intrusion into the room space. You don't need to always hit the perfect spot to get real and beneficial effects.

I love the wavetank simulators, but I haven't seen one that quite applies where we're talking - the lowest frequency I can get is 4th harmonic. It is useful for the NxN mode display, and for seeing what happens when the room is much larger than the wavelength. Room modes never go away, they just get so tightly packed we can't hear the dips inbetween. Play long enough and you start to see the regions in the frequency spectrum:
- sub-modal, lower than the lowest mode where room gain is greatest
- room mode dominant, where resonances are spaced so the peaks and dips are audible
- transition, where modal density is getting high enough we can't hear peaks and dips, but wave properties still dominate.
- ray, where wave properties no longer dominate, and we can use striaght lines and Snell's law reflections (as in ETC analyis for first reflections).

BTW, 70Hz is floor-ceiling I bet...

HAve fun,
Frank

This is Everest, p 229, fig 13-6.

HAve ufn,
Frank
fbov is offline  
Reply Audio Theory, Setup, and Chat

Tags
Klipsch Rw 12d 12 Subwoofer Each

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off