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Old 08-04-2014, 06:47 PM - Thread Starter
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Audio Geek - SI HT 18" D4 subwoofers

I purchased four Stereo Integrity HT 18" D4 subwoofers several months ago (when at the time that it seemed that they were going out of production). Originally, I was going to just get two but I ended up buying four since I was afraid that I wouldn't be able to get another two in the future. Nevertheless, I've been busy with life (I've got two young kids), and I keep vacillating between different ideas on what to build. So, I'd appreciate any help with getting this project started and finished.

These will be going into my living room/dining room which is about 14' x 24' x 8'. The TV is situated along the short wall. Facing the TV, the front right leads to a hallway as well as the entryway. The back right opens into the kitchen. So, there's a lot of open space. I currently have a Hsu Research VTF-15H sitting in the front left corner.

My plans were to build two subs up front, and then two subs in the back to even out room modes.

I purchased a Behringer iNUKE NU3000DSP amp. This should be good for the first two subs. I'll build the first two subs and then go from there.

So, my questions:

Sealed or ported? I'm thinking that with the amount of space to fill, it seems that ported is necessary.

Two Ikea Lack side tables serve as speaker stands for my Fusion-12 Tempest speakers. I'm planning on replacing these two tables with the subwoofers. The rightmost side table juts into the hallway a tad right now so I can't go much wider than the current tables (21-5/8" wide). How narrow can I build a subwoofer cabinet for the 18" speakers? I see the diysoundgroup.com's 4 cu ft flat packs are 20" wide so I figure that should be doable.

The current height of the side tables is perfect to put the Tempest's waveguide at ear height. Sitting on top of the subwoofer, I'd flip the speakers over so that the woofer would be above the waveguide. It'll probably look really imposing, though.

Would a DBA (double bass array) work with just two speakers up front and two in the back?

Does it make sense to face the speakers toward the wall?

I was thinking along the lines of a Mini Marty Sub but it's too wide. How would a narrower sub (~21.5") affect the plans (I'm assuming the port will need to be longer)? I'll be aiming for a 17 Hz tuning.

Thanks, all.

I'll have more questions as I progress ...
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Old 08-04-2014, 06:47 PM - Thread Starter
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Old 08-04-2014, 07:21 PM
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Ported with two up front and two near field. Nearfield subs are just awesome for tactile and for feeling bass at -5 to -15 dbs. Four subs like this will have good room response.

I would much rather have two Nearfield and a slight dip or null then super flat and no Nearfield. Great thing you can move two subs around and where you like it.

I would make two large ported up front to hit 15 hz and two smaller 2' cube for Nearfield.

That's what I would do.
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Old 08-05-2014, 09:43 AM - Thread Starter
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Are you saying 2' sealed or ported? So the two sets of subs would be covering different frequency ranges? For behind the couch, I could make bigger subs, but they would have to be shallow (18").
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Old 08-05-2014, 01:17 PM
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Quote:
Originally Posted by Audio Geek View Post
Are you saying 2' sealed or ported? So the two sets of subs would be covering different frequency ranges? For behind the couch, I could make bigger subs, but they would have to be shallow (18").
All ported. Can do shallow. Something like 18 by 28 by 28.
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Old 08-07-2014, 03:52 PM - Thread Starter
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Thinking some more about the subs in front ... if I make them downfiring, I can replace the Ikea Lack TV unit and keep it low profile. The height (13-3/4") is perfect for my TV right now (Mitsubishi WD-73738) and can't change. I can go as wide as 102". I'm thinking two subs of 51" wide each.

What's the ideal height off the floor for a downfiring sub? Seems other implementations have been 3". I have a wood floor.

According to Parts Express Subwoofer Qualification Formulae For Downfiring Configurations, Percentage of Sag = 981,000 / (Xmax * (2 * Pi * Fs)²).

So, plugging in the numbers:

Percentage of Sag = 981,000 / (22.5mm * (2 * Pi * 17 Hz)²) = 3.82

Since it's less than 5%, it should be OK.
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Old 08-09-2014, 12:34 PM - Thread Starter
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My current front stage:


Replace side tables with subs (40" high)? It might look too imposing as this is in our living room. Hm.
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Old 08-09-2014, 12:36 PM
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Quote:
Originally Posted by Audio Geek View Post
My current front stage:


Replace side tables with subs (40" high)? It might look too imposing as this is in our living room. Hm.
Living room is Home theater room That's what I tell my wife
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Old 08-09-2014, 12:53 PM
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Sorry. Replied to wrong thread. Darn mobile site strikes again.

But while I'm here. Although replacing those tables with subs would look good. It's probably not the best locations for them. You could make two little amp racks or some sort of shelving to use under the mains.

Last edited by Samps; 08-09-2014 at 02:39 PM.
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Old 08-10-2014, 09:19 PM - Thread Starter
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Samps, where would you suggest for the sub locations?

I know the ideal locations for the subs would be at the 1/4 and 3/4 points along the wall, but using the locations of the tables should be at least enough to cut down the room modes. The components would move to the corner where the current subwoofer is (in the corner).

Last edited by Audio Geek; 08-10-2014 at 09:32 PM.
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Old 08-10-2014, 09:38 PM - Thread Starter
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Quote:
Originally Posted by chalugadp View Post
Living room is Home theater room That's what I tell my wife
Yup, no need to convince me or my wife (she hasn't complained). I've got full 7.1, with the rears behind the dining table.
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Old 08-10-2014, 10:45 PM
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I see now that you will be using 4 18s. I'm not really the best person to advise you on something like that. But two commonly suggested methods for 4subs is midpoints of each wall or all four corners. I think the double bass array would only work correctly if you raised the subs to the midpoint of height in your room.

I don't think you can make a short enough box for a down firing si18 and still keep a tempest low enough. Remember the si18 needs 4-5 inches under it to move plus the depth of the driver, clearance behind the magnet and the thickness of the wood. All that together probably puts the waveguide too high on the tempest.
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Old 08-10-2014, 11:13 PM - Thread Starter
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I'm aware of those methods, but those won't work with my room as one corner is the entryway and another leads into the kitchen. And for the center of the walls, the TV overlaps the center.

Yeah, I'll probably not do downfiring. Doing the calculations, the clearance required eats up valuable volume.

Seems I'll have to build a taller box to compensate for a narrower box, in which case, the Tempests will need to be flipped over.

Thanks for your input.
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Old 08-11-2014, 01:31 PM - Thread Starter
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Actually measured the height the subs would need to be if I flipped the Tempests over to keep the waveguide at the same height. The subs would need to be 36" high. Now that I have two dimensions (21.5" x 36"), I will need to figure out the depth. I suppose I could go as deep as 30" (if I pull forward the TV). That would give an external volume of 13.44 cu ft. That's bigger than a Marty cube (8 cu ft) but smaller than the full/mini Marty (16.67 cu ft).

Been playing around with WinISD and it's beginning to make sense to me. How high should the slot ports be? 2"? What if I did triangular ports? What would be a good tuning? Trying to decide these things.

What happens with the second set of subs? Would it be problematic integrating two sets of subs with different tunings (since the rear subs doesn't have the same constraints on the size).

Last edited by Audio Geek; 08-11-2014 at 01:34 PM.
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Old 08-16-2014, 09:15 AM - Thread Starter
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Was using WinISD Pro 0.50a7. Seeing others' screenshots that looked very different from mine, I realized that there's a newer version out there(0.7.0.900). Wasn't on the Linear Team page for WinISD. Found it via Google. The download is linked from the WinISD Facebook page.

Last edited by Audio Geek; 08-16-2014 at 09:22 AM.
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Old 08-16-2014, 10:17 AM - Thread Starter
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Doing the calculations, using 3/4" MDF, I'll have (21.5 - 1.5) * (36 - 1.5) * (30 - 1.5) / 12^3 = 11.38 cu ft... which doesn't include the space taken up by bracing or ports. I'll assume bracing and ports will take up another cu ft or so, so I'll model for 10 cu ft.
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Old 08-16-2014, 10:22 AM - Thread Starter
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Here's a screenshot of my WinISD modeling of the SI18.

http://www.avsforum.com/forum/attach...hmentid=214985
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Last edited by Audio Geek; 08-16-2014 at 10:27 AM.
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Old 08-18-2014, 05:42 PM - Thread Starter
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Just saw the MartySub FAQ (thanks, chalugadp). The Mini Marty and full Marty use 3" high slot ports. To maintain the same port size area (assuming my sub is 21.5" wide), my subs will need to be 3.64" high (67.5 in^2 / 18.5 in = 3.64 in). Is there a reason for this port height? Or can/should I keep the port height at 3" high?

Also, I saw that the Mini Marty is tuned to 18 Hz rather than 17 Hz so perhaps I'll do that.

Last edited by Audio Geek; 08-18-2014 at 05:53 PM.
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Old 08-18-2014, 06:48 PM - Thread Starter
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I found this site:

http://www.carstereo.com/help/Articles.cfm?id=31

Plugging in the numbers for the SI18 sub (23.5 Xmax/17 Hz), I get a minimum of 61.28 in^2.

Divide by 18.5 (width of cab - rails), I get 3.31". I'll use 3.5" (to make measuring easier).

Punching in all the numbers, I get 44.49" for vent length.

How are others figuring out the port size?

I'm figuring this out as I'm going along, so please enlighten me if there's something that I'm overlooking, or doing wrong, or doing the hard way.

Thanks.
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Old 08-18-2014, 08:02 PM
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I am probably not the guy to answer your questions but I will give it a go and if others find my assumption incorrect, then I hope they correct them.
I take it that you plan on a cab 18.5 inches wide so with the port length of 44.49 length you will need a cab length of 48.65, assuming you are using .75 wood. 44.49 is measured in the center of port with your 3.5" added along the back with another .75 for back panel.
If you are keeping the 18.5 width, then your length will be 48.65. I have not modeled this in winisd so I am taking your word on the numbers and that the rear port velocity and cone excursion are all within there limits at max wattage.
Hope that helps. Good luck

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Old 08-18-2014, 08:20 PM - Thread Starter
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Thanks for taking a shot at it. The cab width will be 21.5" so I subtract 4 * 0.75 for the sides and two rails. The cab will be 30" deep.
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Old 08-18-2014, 08:33 PM
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That 3.5 inch height for a port seems to tall. What is the first port resonance at? If I remember correctly it should be above 160 or so.

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Old 08-23-2014, 12:14 AM - Thread Starter
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When I put the numbers into WinISD, it tells me the port (3.5" x 18.5") should be 44.43" long with an 18 Hz tuning. The port resonance is 152.6Hz. This is different than the results I got from the website. Hm.

Last edited by Audio Geek; 08-23-2014 at 12:18 AM.
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Old 08-23-2014, 12:25 AM
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the website is probably making a correction for it being a slot port. making the port a little shorter than what winisd suggests will get you closer to your target tuning freq. don't sweat it too much though. if you are within a hz or so, you'll never know the difference.

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Old 08-23-2014, 12:42 AM - Thread Starter
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Thanks for chiming in, LTD02. For 17 Hz tuning, WinISD gave 50.62". Anyhow, how is the port size determined? Am I on the right track?
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Old 08-29-2014, 08:11 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post
the website is probably making a correction for it being a slot port. making the port a little shorter than what winisd suggests will get you closer to your target tuning freq. don't sweat it too much though. if you are within a hz or so, you'll never know the difference.
Should I be concerned about the low port resonance? I think the target is above 200 Hz (about an octave above 80 Hz).
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Old 08-29-2014, 08:47 PM
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I don't know how to answer that one. For home theater 140hz seems fine. I also wonder if the bend affects the resonance somehow. This was something NeoDan discussed a LONG time ago -- many of his very long ported designs (which had multiple bends) didn't suffer from port resonances nearly as much as the standard models would imply.


with a 4th order 80hz low pass and some cab stuffing...
above 160hz and you are fine.
above 140hz is what I'd call borderline.
less than that would have to be called experimental.

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Old 08-29-2014, 08:53 PM
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"Thanks for chiming in, LTD02. For 17 Hz tuning, WinISD gave 50.62". Anyhow, how is the port size determined? Am I on the right track?"


definitely are on the right track, but technically for a slot port, the port extends a bit out past the end of the actual measured port length because of the end correction factor (see the orginal martysub post for some discussion on this).
Large Ported Dayton HO18's


taking about 10% or so off the winisd number gets you pretty close, so if winisd comes in at 50" and you build it 44", you will be pretty close +/-. the port resonance will also be that of a 44" not the 50", of course.


ideally air speed is kept to about 17 m/s, 34 m/s is borderline, higher is experimental/will chuff (but it may or may not bother you too much). these are rule of thumb guidelines. the best empirical study of port chuffing is collo's work. just search on: collo subwoofer port, and it should all come up.

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Old 08-29-2014, 09:14 PM
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Quote:
Originally Posted by Audio Geek View Post
Thanks for chiming in, LTD02. For 17 Hz tuning, WinISD gave 50.62". Anyhow, how is the port size determined? Am I on the right track?
If I understand things right:


I think you are asking how to determine the needed "port area" from your "port size" questions, the "CROSS AREA" in the vents tab.


You look at the "REAR PORT-AIR VELOCITY" graph in winisd. Keep making the port area/size bigger till you get the velocity low enough.
I keep reading .08 mach or less, differing opinions and seemingly dependent on the smallest dimension of the port.
But less than or about 90 ft/sec or 30 m/s unless the port frequency is less than 20hz then more is allowable, or if you flare the port then higher is ok.
The consequence is that the larger the area, the longer the port is.
Then the longer the port is, the lower the port resonance is.


So....it depends


Hope that is what you were asking, and it helps.
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Old 09-05-2014, 12:23 AM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post
ideally air speed is kept to about 17 m/s, 34 m/s is borderline, higher is experimental/will chuff (but it may or may not bother you too much). these are rule of thumb guidelines. the best empirical study of port chuffing is collo's work. just search on: collo subwoofer port, and it should all come up.
Thanks, LTD02. Good pointer to resources. I did come across the subwoofer-builder site before. I'll reread the info on ports.

Quote:
Originally Posted by More is Better View Post
I think you are asking how to determine the needed "port area" from your "port size" questions, the "CROSS AREA" in the vents tab.

You look at the "REAR PORT-AIR VELOCITY" graph in winisd. Keep making the port area/size bigger till you get the velocity low enough.
I keep reading .08 mach or less, differing opinions and seemingly dependent on the smallest dimension of the port.
But less than or about 90 ft/sec or 30 m/s unless the port frequency is less than 20hz then more is allowable, or if you flare the port then higher is ok.
The consequence is that the larger the area, the longer the port is.
Then the longer the port is, the lower the port resonance is.
Yup, that's what I was asking. Thanks. That's in line with what I've been reading. The problem I have is in WinISD, I see only a peak of 0.582 m/s which is an order of magnitude lower than what I expect.

http://www.avsforum.com/forum/attach...247202&thumb=1

I finally figured it out, though. I needed to set the System Input Power to 600W (was 1W). Now the results are in the ballpark what I expect. Actually, should I be using 1100W (peak) instead?

http://www.avsforum.com/forum/attach...247210&thumb=1
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Last edited by Audio Geek; 09-05-2014 at 12:37 AM.
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