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post #1 of 78 Old 10-19-2013, 04:23 PM - Thread Starter
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Hello all,

This is kind of a continuation from my recent post in the Martysub thread. There a pair of Martysubs (SI HT18D4) was the plan, powered by an inuke 3000DSP. However, looking at my living room where these will go, I'm not so sure it's the best route due to placement limitations. I would have to place them lengthwise to either side of the TV, butted to the walls and am not so sure this would be optimal.

Here is a picture of the space. (with my two helpers)

Note the AV rack can move and the small table and air filter will go away.

And a dimensioned layout. Note the adjoining open spaces (sunroom, hallway and kitchen)
LivingRoomLayout2.pdf 24k .pdf file

So, my goal is for sub 20Hz extension and smoothing of room modes for home theater only. I like the ported models for the added efficiency. I've considered 24" dia x 6ft sonotubes, but cannot fit them and have low WAF.

My budget is about $1k for drivers, amp, dsp, wood, glue, finishing and miscellaneous hardware. I have access to some hand tools (skill saw, router, planer, etc..) so that shouldn't affect the budget.

Other items I've looked at (mostly by reading threads here)
SI HT18D4 <- seems the best bang for buck driver out there for HT use
inuke 3000 <- Again, kw/$ ratio is good, DSP option while sufficient, is a little limited. Will probably go amp only and minidsp
minidsp <- I like this and am not worried about interconnects. I have a background in industrial controls and can do the interconnects
minidisp umik-1 <- Have it for before and after as well as eq-ing work
REW <- still need to download and learn
My bookshelves are highpassed at 80Hz and the bass management is engaged.

Having said all of that, I'm looking for some ideas and to sort out a direction on improving the movie audio experience.
Maybe 2 18" LLTs are overkill and I should be looking at 15" sealed?
Maybe I should look at downfiring to remove any directionality from the output?
Maybe putting both subs on the TV wall isn't optimal?

In the end, this thread will include my build pics and I'll pull together a summary of the rationale that comes out of the discussion.

Thanks in advance!
-Paul
Attached Files
File Type: pdf LivingRoomLayout2.pdf (23.5 KB, 10 views)

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post #2 of 78 Old 10-19-2013, 04:28 PM - Thread Starter
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post #3 of 78 Old 10-19-2013, 04:29 PM - Thread Starter
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post #4 of 78 Old 10-19-2013, 04:34 PM
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Paul, I think that two of the SI-18's in some large low tunes enclosures would be great! I would not consider a sealed 15" as that would not even come close to the spl and extension of a ported 18" driver(s). The iNuke3000 would be a great amp, and is exactly what I am using to power my Marty Subs. As far as placement, you really need to experiment and try several locations.
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post #5 of 78 Old 10-19-2013, 04:37 PM - Thread Starter
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Originally Posted by Martycool007 View Post

Paul, I think that two of the SI-18's in some large low tunes enclosures would be great! I would not consider a sealed 15" as that would not even come close to the spl and extension of a ported 18" driver(s). The iNuke3000 would be a great amp, and is exactly what I am using to power my Marty Subs. As far as placement, you really need to experiment and try several locations.
For the

Good point about the placement. I have a 12" Ported, 23Hz tune, 150W sub in the corner at the moment. That came after a few subwoofer crawls and is the best of 4 positions along the TV wall.

I can fit two MartySubs on either side of the TV, but am worried about them touching the walls.

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post #6 of 78 Old 10-20-2013, 03:05 AM
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Why would you worry about them touching the walls? I don't think that would be a problem if the rear of the enclosures are touching the walls because they are front ported.
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post #7 of 78 Old 10-20-2013, 05:47 AM - Thread Starter
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Why would you worry about them touching the walls? I don't think that would be a problem if the rear of the enclosures are touching the walls because they are front ported.

Maybe I worry because I read too many internet forums? smile.gif

Truthfully, I've seen alot of advice about placement 1/4 wavelength off of the boundary and the criticality of subwoofer placement. along with that, they can only go in one place as shown.



So, without going through a modal or FEA analysis, this room will has simensions corresponding to half wavelengths at 58Hz, 39Hz, 37Hz, 26Hz and 21Hz. I guess I'm afraid of a big suckout near the MLP.

Now if my hypothetical suckout can be attenuated by AudysseyXT or Eq-ing (planning on doing both).

Lastly, I do have a long enginnering background and tend to get hung up on details. Indeed it's the physics of audio and frequency response I find interesting.

Thanks
-Paul

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post #8 of 78 Old 10-20-2013, 06:37 AM
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hi paul. those drivers and amp are a nice combo. quite a bit of performance for the money.

like many, you have a bit of an oddball room and that make predicting your in room response challenging. your really just going to have to do some experimenting with placement and find what works best.

the half-wavelength points are where the room will resonate, so you will get peaks. 1/4 distances or 5/4 distances are more likely to cause cancellations based on reflections. since your couch is near a wall, it is most likely peaks that you will have to eq down.

another forum member is building a marty inspired sub that has a different form factor but should perform the same. his will be 24 x 30 x 36, but will not use recessed driver mounting. not sure if that might give you a little more flexibility or not. if you have some other shape in mind, we could work out that too. it really just depends on how good you are with cutting wood, as limiting cutting while maximizing performance was the idea behind the original marty sub.

nice big tv in there so adding in some big bass will really make that an exciting room!

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post #9 of 78 Old 10-20-2013, 12:24 PM - Thread Starter
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Is that the Annihilator sub thread? I'll tune back into that.

Another placement possibility below. Any rule of thumb against having a weird opposed corner type arrangement? Of course I'll try it when built, also more options will help in the what to build decision process.


I did play with WinISD and am moving away from any 15" or sealed idea. (the posters above helped too)

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post #10 of 78 Old 10-21-2013, 05:30 AM
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This quarter-wavelength placement thing...

How can you determine the quarter-wavelength differences when every single frequency has different wavelengths? *scratches head* lol

If one is stacking subs, should the drivers/ports be located at quarter / half / three-quarters the height of the room??
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post #11 of 78 Old 10-21-2013, 05:36 AM
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"Is that the Annihilator sub thread? I'll tune back into that."

that is another one. i was referring to a different one. it seems that there are countless medium-large ported cabs tuned to around 17hz popping up all over the place.

here is another one, but I didn't have anything to do with this one:

http://www.avsforum.com/t/1493647/the-plasmad-pocket-sub

here is even another option:

http://www.avsforum.com/t/1494029/limited-space-for-new-sub-build#post_23815113

its really up to you to just imagine what you want and we can probably figure out a way to do it. :-)

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post #12 of 78 Old 10-21-2013, 05:41 AM
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"How can you determine the quarter-wavelength differences when every single frequency has different wavelengths? *scratches head* lol"

there are two topics at work and that may be the source of the confusion.

the first is where does a cancellation occur for a speaker near a wall. measure distance to wall. 3.5 ft for example. multiply by 4. 14 feet. divide into 1130ft/s. 81hz will be where you will get a cancellation.

http://www.peavey.com/support/technotes/soundsystems/boundarycancellation.cfm

second topic is room modes. if room is 12 feet wide, side to side room modes can mostly be cancelled out by putting subs at 1/4 distance in from walls. 12 feet / 4 = 3 feet. so place subs 3 feet in from wall.

http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/multsubs.pdf

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post #13 of 78 Old 10-22-2013, 11:48 AM
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"How can you determine the quarter-wavelength differences when every single frequency has different wavelengths? *scratches head* lol"

there are two topics at work and that may be the source of the confusion.

the first is where does a cancellation occur for a speaker near a wall. measure distance to wall. 3.5 ft for example. multiply by 4. 14 feet. divide into 1130ft/s. 81hz will be where you will get a cancellation.

http://www.peavey.com/support/technotes/soundsystems/boundarycancellation.cfm

second topic is room modes. if room is 12 feet wide, side to side room modes can mostly be cancelled out by putting subs at 1/4 distance in from walls. 12 feet / 4 = 3 feet. so place subs 3 feet in from wall.

http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/multsubs.pdf
Thanks for the links, very much appreciated smile.gif

More reading to do! lol

In my room placement discussions are technically moot because I only have one location for sub(s), but it's good to know the background detail as it is applicable elsewhere and helps me understand any issues that may arise smile.gif
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post #14 of 78 Old 10-23-2013, 04:00 AM
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"How can you determine the quarter-wavelength differences when every single frequency has different wavelengths? *scratches head* lol"

there are two topics at work and that may be the source of the confusion.

the first is where does a cancellation occur for a speaker near a wall. measure distance to wall. 3.5 ft for example. multiply by 4. 14 feet. divide into 1130ft/s. 81hz will be where you will get a cancellation.

http://www.peavey.com/support/technotes/soundsystems/boundarycancellation.cfm

second topic is room modes. if room is 12 feet wide, side to side room modes can mostly be cancelled out by putting subs at 1/4 distance in from walls. 12 feet / 4 = 3 feet. so place subs 3 feet in from wall.

http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/multsubs.pdf

So the 1/4 wavelength from the side walls is figured by taking the width of your room and dividing by 4, right? So say your room is 20 feet wide, the 1/4 wavelength place where there will be a room mode is 5 foot from each side wall, right?

Do you use the same method in figuring out where the modes will be length wise? Like say your room is 40 foot long, that would make the 1/4 wave length spot for room modes at 10ft,,right?

Are these room modes either peaks or dips, and how can you know if they are peaks or dips?
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post #15 of 78 Old 10-23-2013, 04:49 AM
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that's correct.

as to whether a mode will be a peak or a dip, it depends where you are in relationship to the modal resonance. it also depends on how many and where the subs are placed in the room.

pretend that this is your room.

if it is 12 feet wide, the first mode (the top picture) will occur at 1/2 wavelength = width of room. in this case, ~47hz. so if you stand next to wall, 47hz will be a peak. if you move to the center of the room, 47hz will be a null.

the middle picture is the second mode and will occur at 1 wavelength = width of room. 94hz. but now, if you stand in the middle of the room or along the wall, in both places, you get a peak and by moving in from the wall 1/4 distance, that is where you will get dips.

it is more complicated than that in reality, but that is the basic idea of the first concept, room modes.

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post #16 of 78 Old 10-23-2013, 05:51 AM
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that's correct.

as to whether a mode will be a peak or a dip, it depends where you are in relationship to the modal resonance. it also depends on how many and where the subs are placed in the room.

pretend that this is your room.

if it is 12 feet wide, the first mode (the top picture) will occur at 1/2 wavelength = width of room. in this case, ~47hz. so if you stand next to wall, 47hz will be a peak. if you move to the center of the room, 47hz will be a null.

the middle picture is the second mode and will occur at 1 wavelength = width of room. 94hz. but now, if you stand in the middle of the room or along the wall, in both places, you get a peak and by moving in from the wall 1/4 distance, that is where you will get dips.

it is more complicated than that in reality, but that is the basic idea of the first concept, room modes.


Thanks for explaining that! Now, just to pick your brain a little more, how did you figure where will be 1/2 wavelength and the 1 wavelength? How do you know that the first mode will occur at 1/2 wavelength and how did you conclude that the second mode will be at 1 full wavelength? Is that going to be the case for every room?
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post #17 of 78 Old 10-23-2013, 06:37 AM
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"Now, just to pick your brain a little more, how did you figure where will be 1/2 wavelength and the 1 wavelength? "

http://www.wikihow.com/Calculate-Wavelength

"How do you know that the first mode will occur at 1/2 wavelength and how did you conclude that the second mode will be at 1 full wavelength? Is that going to be the case for every room?"

yes. in an ideal setting.

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post #18 of 78 Old 10-23-2013, 07:16 AM
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Again, thanks for the explanation! I am a little confused as to how to find the frequency of a given mode, versus how to find the proper placement of your subs in avoidance of placing it in a 1/4 wavelength spot??

For a 20ft wide room, you would take the waves speed, which is 1130ft per second, and divide it by the rooms width, which comes out to 56.5, then to find the 1/4 wavelength spot for placement of the sub, you divide the 56.5 by 4 and that will tell you where the 1/4 wavelength will be, right?
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post #19 of 78 Old 10-23-2013, 09:16 AM
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I am a little confused as to how... to find the proper placement of your subs in avoidance of placing it in a 1/4 wavelength spot??
You can't, as there will always be 1/4 wavelength distances at some frequency to some boundary in the room, and 1/4 wavelength distances from the LP to some boundary in the room. That's why multiple subs must be used, so that where one creates a null another does not. The idea is to create a large number of shallow nulls instead of a small number of deep nulls.

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post #20 of 78 Old 10-23-2013, 09:35 AM
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"You can't, as there will always be 1/4 wavelength distances at some frequency to some boundary in the room..."

bfm, by placing 2 subs at 1/4 distances from the walls, the cancellation that comes from one will be equally offset by the gain that comes from the other. strange, but true.

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post #21 of 78 Old 10-23-2013, 09:50 AM
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bfm, by placing 2 subs at 1/4 distances from the walls, the cancellation that comes from one will be equally offset by the gain that comes from the other. strange, but true.
If you only had one pair of boundaries and played only one frequency and its even order harmonics that would be true. But there are six or more boundaries in a room, and hundreds of frequencies within the sub pass band.

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"If you only had one pair of boundaries and played only one frequency and its even order harmonics that would be true."

no. it kills all the modes between the two boundaries. seriously.

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post #23 of 78 Old 10-23-2013, 07:29 PM
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it kills all the modes between the two boundaries. seriously.
I know. It's moot. You're only considering the effect of two boundaries. Add two more walls and a ceiling and everything changes.

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"...and played only one frequency and its even order harmonics that would be true."

that's not what I was referring to. this stuff about one frequency is and its even harmonics is what I was referring to.

"I know. It's moot. You're only considering the effect of two boundaries. Add two more walls and a ceiling and everything changes."

no it doesn't. it just gets more complicated. the interaction between the two walls (the so-called axial mode) still remains and is the dominant effect. tangential and oblique modes are further down the scale of importance.

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post #25 of 78 Old 10-26-2013, 02:29 PM - Thread Starter
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I have another question, but was unsure about starting a new thread for it....

My wife is considering getting me some speaker kits for christmas, so I'm looking at diysoundgroup for Left, Center and Right speakers. However, I don't really know anything about selecting them.

The idea would be to use the current HTD L2 bookshelves as 7.1 surrounds and sell the center along with the subwoofer.

Any recommendations? The tempests have a lot of good threads, but the center is puzzling for me. I have to lay any center speaker horizontally under the TV. and there is only 15" of clearance there. Would the Fusion-8 Alchemy MTM pair up well with the Tempests?

Also, I'm open to any ideas or recommendations here. Whatever is built will be run off of my Denon AVR-1713.


Oh, and if I should cross post this into Erich's thread, that's no trouble.

Thanks a ton!
-Paul

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post #26 of 78 Old 10-26-2013, 03:17 PM
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Quote:
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I have another question, but was unsure about starting a new thread for it....

My wife is considering getting me some speaker kits for christmas, so I'm looking at diysoundgroup for Left, Center and Right speakers. However, I don't really know anything about selecting them.

The idea would be to use the current HTD L2 bookshelves as 7.1 surrounds and sell the center along with the subwoofer.

Any recommendations? The tempests have a lot of good threads, but the center is puzzling for me. I have to lay any center speaker horizontally under the TV. and there is only 15" of clearance there. Would the Fusion-8 Alchemy MTM pair up well with the Tempests?

Also, I'm open to any ideas or recommendations here. Whatever is built will be run off of my Denon AVR-1713.


Oh, and if I should cross post this into Erich's thread, that's no trouble.

Thanks a ton!
-Paul

Hey Paul, no specific recommendations, but I think it'd be a great idea to pursue some of the SEOS offerings. Remember, they have a good forum over there too.

In my opinion, I'd employ three identical LCRs across the front .. thus proceed to accommodate that if possible. The center is so vitally important, it carries a huge percentage of the load ... I'd not skip on CC capability or CC implementation if possible. I do however understand logistics of the display and living space do play a role.

If you do go the SEOS route, the value is way high, so you'll very likely be happy once set up and optimized.

Good luck

fwiw, if I had a modest amount of $ for a set up, I'd go easy on the loudspeakers, and dedicate a good bit to the room treatment. It's the single most important component ... the room.

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post #27 of 78 Old 10-27-2013, 04:31 AM
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Thanks for explaining that! Now, just to pick your brain a little more, how did you figure where will be 1/2 wavelength and the 1 wavelength? How do you know that the first mode will occur at 1/2 wavelength and how did you conclude that the second mode will be at 1 full wavelength? Is that going to be the case for every room?

Ok, now that I slept on it, I can see the theory and understand the point you were trying to illustrate with that graph. Thanks!

With regards to subwoofer(s) placement, is it usually ideal to place the subs at 1/4 distances between the side walls, and 1/4 distance from the front & rear wall, and ideally, if possible, also place them at 1/4 distance from the floor & ceiling? I could place my two subs at 1/4 between the side walls, and also 1/4 from the front & rear walls. Is that the best way for me to place them? I guess that one day I could experiment with building subwoofer stands to also get them up & off the floor at 1/4 distances between the floor & ceiling.
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post #28 of 78 Old 10-27-2013, 05:54 AM
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Just stand your Marty sub on end, it will be 4 feet tall.
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post #29 of 78 Old 10-27-2013, 10:00 AM
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Quote:
Originally Posted by RickD1225 View Post

Just stand your Marty sub on end, it will be 4 feet tall.

Yeah! A square sono.. smile.gif Put some feet or a base on it, and now it's a down fireing square sono lol

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post #30 of 78 Old 10-31-2013, 04:20 AM - Thread Starter
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Okay, time for me to start ordering parts. The aim is to build over the week of Thanksgiving.

I am working up a BOM (copied below) for the project and have a few questions.

Going with the iNuke3000DSP, should I get the D4 or D2 SI woofers? I'm sure this has been answered a thousand times, but my search skills this morning seem to be off.

What gauge speaker wire should I get? This will be used to wire up the cabinet and for the runs to the amp. The runs will be about 15 ft unless I do an alternate positioning and do a 100ft run.

What little bits from parts-express am I forgetting?

I keep waffling between MDF/Duratex and oak or birch ply and varnish for finishing. These will be front and center in the living room, so it has to look decent. Any advice?

Fasteners and finishing (other than Duratex if used) will be acquired by the obligatory Home Depot panic runs....

Thanks!
-Paul

Qty Description
4 Ply or MDF 3/4" x 4' x 8'

1 iNuke 3000DSP
2 SI HT 18" D4

1 Duratex 1 gallon

2 260-311 Binding posts
1 260-542 1/2" Gasket Tape
1 Speaker Wire ??ga
4 092-190 Speakon NL4FX Neutrik

Denon 1713 AVR
HTD Level 2 Bookshelf Surrounds and L/R
HTD Level 2 Center
Two MartySubs powered by iNuke3000DSP

Sharp Aquos LC-70LE632U

HTD Level 3 Subwoofer (for sale, currently unused)
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