4x15" Datyon Ultimax Build Questions... - AVS Forum
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post #1 of 11 Old 04-14-2013, 06:17 PM - Thread Starter
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I tried a few questions in the premade subs land. In order to be happy...well, it wasn't going to happen with my budget. Thing is, I have about 8000 cubes to pressurize. As I said in my previous thread, I don't need it to be loud (I'll take 105 dB at the prime listening spot)...i just need it "reasonably" flat down to 20 Hz or so. So, after much nashing of teeth and starting to dig into this sub-forum, I'm at a fork in the road. Framing construction is going to begin on finishing our basement in maybe 1 month (plumbing done, HVAC started). Therefore some items (like cabinetry) need to be ordered "sooner" than later and will affect my future options.

I've attached a PDF to explain what happened and where I am.

The first page reflects my better half's idea of how the media wall should look. The inspiration came from the image in the lower right. Originally we were going to put a sub in the lower left and right cabinets. However, those would have only be 12" and only 2 of them. Simple math said "ruh roh shaggy". Also, putting the plate amps in an enclosed space seemed liked a really bad idea. So then I thought about building 4x15" cabinets and putting them below the screen. While this may work, it definitely takes away a lot of storage (even though it would probalby be the least work for me).

The second page has an alternate idea. What if we brought the screen out 14" or so and put sealed subs behind it. There is where I don't know. The idea would be put to 4x 15" Dayton Ultimax in 4 (website says 3...but WinISD says 6 ish) cubic foot sealed boxes. This allows for 12" deep box with a 1.5" baffle and a surface mounted speaker. Width and height would be adjusted as needed.. The boxes would be mound to the wall and the baffle attached to the box once mounted.

Is this idea even sane? This thought came as a mutation of JapanDave's infinite baffle setup.


Visio-theater_wall_14apr2013.pdf 1904k .pdf file

----
Note: pages 3 & 4 give a bit more detail..but not update yet to reflect what i'm questioning here.
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File Type: pdf Visio-theater_wall_14apr2013.pdf (1.86 MB, 39 views)

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post #2 of 11 Old 04-14-2013, 06:29 PM
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Not sure if option 2 is even an option. The air pressure wave from four 15" Ultimax's at very low frequencies seems as though it would cause the Acoustically Transparent screen to move with the sound wave.


Dan
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post #3 of 11 Old 04-14-2013, 06:42 PM - Thread Starter
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Quote:
Originally Posted by stereomandan View Post

Not sure if option 2 is even an option. The air pressure wave from four 15" Ultimax's at very low frequencies seems as though it would cause the Acoustically Transparent screen to move with the sound wave.


Dan

Source? Quite a few threads in here go against that. More to the point it is ported air that usually causes movement, not the speakers themselves. In my case, these would be sealed and thus the actual base "waves" should pass through the screen no problem. Am I confused?

example --> http://www.avsforum.com/t/1340594/subwoofer-behind-at-screen

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post #4 of 11 Old 04-14-2013, 08:13 PM
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Quote:
Originally Posted by Trepidati0n View Post

Source? Quite a few threads in here go against that. More to the point it is ported air that usually causes movement, not the speakers themselves. In my case, these would be sealed and thus the actual base "waves" should pass through the screen no problem. Am I confused?

example --> http://www.avsforum.com/t/1340594/subwoofer-behind-at-screen

Exactly why I said "Not sure" in my original post. From the thread you linked, it looks as though folks have been able to do this with no problem. So therefore, more power to ya.

Dan
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post #5 of 11 Old 04-14-2013, 09:06 PM - Thread Starter
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Quote:
Originally Posted by stereomandan View Post

Exactly why I said "Not sure" in my original post. From the thread you linked, it looks as though folks have been able to do this with no problem. So therefore, more power to ya.

Dan

Nope..its cool. I'm just incredibly nervous at this point. Many $1000's are about to go out the door and opportunities are quickly disappearing. If I miss something obvious...ugh. Why I look to people, like yourself, here who have been through the gauntlet.

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post #6 of 11 Old 04-14-2013, 09:42 PM
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Quote:
Originally Posted by stereomandan View Post

Not sure if option 2 is even an option. The air pressure wave from four 15" Ultimax's at very low frequencies seems as though it would cause the Acoustically Transparent screen to move with the sound wave.


Dan

Lol! No way, dude.

How many people with AT screens just leaves them flapping in the wind like silk drapes? Mine and every other AT screen on Earth is tensioned in one way or another. The screen will never be affected in such a way from even the most ridiculous system behind it.


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post #7 of 11 Old 04-15-2013, 05:58 AM
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Quote:
Originally Posted by stereomandan View Post

Not sure if option 2 is even an option. The air pressure wave from four 15" Ultimax's at very low frequencies seems as though it would cause the Acoustically Transparent screen to move with the sound wave.


Dan

Like others have stated, not a problem for driver energy. However I wouldn't want any ports within 6" of my screen but the discussion was about sealed anyways.

Quote:
Originally Posted by Trepidati0n View Post

I tried a few questions in the premade subs land. In order to be happy...well, it wasn't going to happen with my budget. Thing is, I have about 8000 cubes to pressurize. As I said in my previous thread, I don't need it to be loud (I'll take 105 dB at the prime listening spot)...i just need it "reasonably" flat down to 20 Hz or so. So, after much nashing of teeth and starting to dig into this sub-forum, I'm at a fork in the road. Framing construction is going to begin on finishing our basement in maybe 1 month (plumbing done, HVAC started). Therefore some items (like cabinetry) need to be ordered "sooner" than later and will affect my future options.

I've attached a PDF to explain what happened and where I am.

The first page reflects my better half's idea of how the media wall should look. The inspiration came from the image in the lower right. Originally we were going to put a sub in the lower left and right cabinets. However, those would have only be 12" and only 2 of them. Simple math said "ruh roh shaggy". Also, putting the plate amps in an enclosed space seemed liked a really bad idea. So then I thought about building 4x15" cabinets and putting them below the screen. While this may work, it definitely takes away a lot of storage (even though it would probalby be the least work for me).

The second page has an alternate idea. What if we brought the screen out 14" or so and put sealed subs behind it. There is where I don't know. The idea would be put to 4x 15" Dayton Ultimax in 4 (website says 3...but WinISD says 6 ish) cubic foot sealed boxes. This allows for 12" deep box with a 1.5" baffle and a surface mounted speaker. Width and height would be adjusted as needed.. The boxes would be mound to the wall and the baffle attached to the box once mounted.

Is this idea even sane? This thought came as a mutation of JapanDave's infinite baffle setup.


Visio-theater_wall_14apr2013.pdf 1904k .pdf file

----
Note: pages 3 & 4 give a bit more detail..but not update yet to reflect what i'm questioning here.

I don't like the cluster orientation in the center of the wall for modal distribution. You'll likely see a flatter response by reading up on multiple sub placement and avoid modal pressure minimas and maximas.

For a space that large I'd be thinking horns behind the screen. Look at lilmike's stuff hes got a flavor for every budget and performance requirement. There are other horn designers out there too every shape and size.

If not horns then def ported subs you'll need the output IMO.
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post #8 of 11 Old 04-15-2013, 11:05 AM
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Quote:
Originally Posted by Trepidati0n View Post

...I have about 8000 cubes to pressurize. ...I don't need it to be loud (I'll take 105 dB ..."reasonably" flat down to 20 Hz or so. ... I'm at a fork in the road. Framing construction is going to begin on finishing our basement in maybe 1 month ...
There's still time... lucky you included pages 3 and 4

Good bass is a combination of capable drivers in appropriate enclosures driven by massive amps... and a room. Loudspeakers and rooms - never separated in use.

No one's mentioned the room, even though NOW is the right time to address some additional aspects. Finished basements are acoustic nightmares as cinderblock walls effectively prevent energy loss, resulting in high amplitude wave interference issues. You need to add bass absorption, and that's not as simple as hanging a few absorber panels because you have a large space resulting in 1 and perhaps 3 infrasonic modes. Your "8000 cubes" tells me you understand that the entire orange area on page 4 is energized; now understand that the entire area will contain bass modes, some based on the ~50' long direction, some based on the 16.5' theater depth and some based on the ~32' "L" area, and finally some based on ceiling height. In all cases, resonance occurs when
"n/2 x dimension = wavelength for any integer "n," or (565 / dimension).
I use a spreadsheet like this.

Now is the right time because the most effective bass traps are part of a wall, not hung on one. I would suggest diaphragmatic absorbers to populate two walls, one across the ~50' dimension, the other across the ~30' dimiension of the L. I would also suggest a ceiling treatment a la the picture on page 1, but designed for absorption down to 70Hz, assuming 8' ceilings as 565 / 8 = 70.6Hz, the fundmental in that direction.

Take a look at some diapgragmatic absorber diagrams and you'll realize that stud walls already contain most of the required features... lots of information here; flip to page 201 for diaphragmatic absorbers.

Additional room treatment analysis would then wait until you were fully furnished, as it's not as hard to absorb energy above 100Hz., and you may find that room furnishings do most of the work.

I would also find a way to move the seats to the center of the room, near the angle center on page 3; sound is always bad against a wall.

Have fun,
Frank
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post #9 of 11 Old 04-18-2013, 05:51 PM - Thread Starter
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Did a bunch more reading. Good news is I should start and least build 2 cabs soon. Talking with my better half, it is a a more "sensible approach". So, I did some modelling in WinISD..and got something odd. The dayton website says 3 cubic feet with stuffing yields 0.707 QTC. However, WinISD is staying otherwise. QI and QA are set to 10. Did I do something wrong?


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post #10 of 11 Old 04-19-2013, 04:25 AM
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Quote:
Originally Posted by fbov View Post

There's still time... lucky you included pages 3 and 4

Good bass is a combination of capable drivers in appropriate enclosures driven by massive amps... and a room. Loudspeakers and rooms - never separated in use.

No one's mentioned the room, even though NOW is the right time to address some additional aspects. Finished basements are acoustic nightmares as cinderblock walls effectively prevent energy loss, resulting in high amplitude wave interference issues. You need to add bass absorption, and that's not as simple as hanging a few absorber panels because you have a large space resulting in 1 and perhaps 3 infrasonic modes. Your "8000 cubes" tells me you understand that the entire orange area on page 4 is energized; now understand that the entire area will contain bass modes, some based on the ~50' long direction, some based on the 16.5' theater depth and some based on the ~32' "L" area, and finally some based on ceiling height. In all cases, resonance occurs when
"n/2 x dimension = wavelength for any integer "n," or (565 / dimension).
I use a spreadsheet like this.

Now is the right time because the most effective bass traps are part of a wall, not hung on one. I would suggest diaphragmatic absorbers to populate two walls, one across the ~50' dimension, the other across the ~30' dimiension of the L. I would also suggest a ceiling treatment a la the picture on page 1, but designed for absorption down to 70Hz, assuming 8' ceilings as 565 / 8 = 70.6Hz, the fundmental in that direction.

Take a look at some diapgragmatic absorber diagrams and you'll realize that stud walls already contain most of the required features... lots of information here; flip to page 201 for diaphragmatic absorbers.

Additional room treatment analysis would then wait until you were fully furnished, as it's not as hard to absorb energy above 100Hz., and you may find that room furnishings do most of the work.

I would also find a way to move the seats to the center of the room, near the angle center on page 3; sound is always bad against a wall.

Have fun,
Frank

Good post Frank! So with regards to that formula that you posted, 565/2 x dimension, what does that tell us? Can you elaborate on that some more? What deminisons do you use to multiply the 565/2 with? The length? The width?
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post #11 of 11 Old 04-19-2013, 07:41 AM
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The speed of sound in air at sea level is about 1130 ft/sec.
Standing waves (between equivalent boundaries) only occur when (dimension = N/2 x wavelength) for any positive integer N.
And, of course, speed C = wavelength x frequency, so (wavelength = c / frequency)

Thus, dimension = N/2 x (c / frequency), and for the lowest frequency, N=1
Dimension = c / (2 x frequency)
which for c = 1130, c/2 = 565,
dimension = 565 / frequency, and frequency = 565 / dimension

Basic standing wave calculations can (and should) be applied to all room dimensions to identify the "normal" modes. Note that "normal" here is a geometric term meaning "perpendicular." Do a search for "Harman room mode calculator" and download the spreadsheet.

What you get looks like this:
Freq. | Adjacent mode spacing
25.7
37.7 | 12.0
51.4 | 13.7
70.6 | 19.3
75.3 | 4.7
77.0 | 1.7
102.7 | 25.7
113.0 | 10.3
128.4 | 15.4
141.3 | 12.8
150.7 | 9.4
154.1 | 3.4
179.8 | 25.7
188.3 | 8.6
205.5 | 17.1

"Freq." is a room mode, and there's a chart to help identify which dimensions are involved. "Adjacent Mode Spacing" is the "distance" in Hz to the next mode. Even spacing is the goal, but since wall placement's involved, it's not always adjsutable. Note that I have an issue at 70-75Hz, due to modes at 70.6, 75.3 and 77.0 - a 3rd harmonic in the longest dimension, 2nd harmonic across the room, and fundamental in the third - ceiling height.

All based on the formula frequency = 565 / dimension for the fundamental.

This is the theory. Practice will vary with the room construction and furnishings as well as dimensions.
- cinderblock walls reflect bass causing worse standing waves below grade than above
- normal above-grade construction using sticks and sheetrock can be very good for bass resonances, mainly due to leakage.
- slab foundations and second stories are like cinderblock walls compared with a basement or attic
- soundproofing reduces leakage, making standing waves worse
- open doorways allow leakage, and modify room resonances, driving them lower
- windows are leaky, making drapes over windows an adjustable broad band-type absorber.

And in your case, complex room geometry (L-shape open space within complex rectangular basement, alcove for screen, dividing walls to other rooms, adjacent room volume, staircase reinforcement of one wall, etc.) makes anything more than very basic calculations of questionable predictive value. However, I hope you see that there are a lot of aspects of your room that will scramble the resonance pattern, and perhaps give you a uniformly dense mode spacing that makes large spaces sound better than small.

But I also suspect that something to absorb some of the fundamental resonances may be in order. It doens't take much to test, and frequencies below 100Hz are far less affected by furnishings than above, so you don't need to test in a finished room. But test data is the only way to characterize the problem so countermeasures are appropriate to the problem.

As to the need for this, read through some of the multi-sub threads and you may notice that folks love to throw subs at room mode issues... issues they could treat and be done if low bass treatment were easy in a finished room - it's not. Thankfully, your room isn't finished!

HAve fun,
Frank
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