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Discussion Starter #1 (Edited)
The Periscope Subwoofer B&C 21DS115

I recently sold my (2) HT18 sealed subwoofers along with the iNuke 3000 DSP amp. I also sold my (4) 1260w in sealed boxes that were in my living room. I also removed the htib subwoofer from my bedroom. Why? Because I decided I wanted to better contain and focus my hobby. (I may have been nudged by my wife to consolidate, so what..).

I took the money from the subs I sold and picked up a couple of new B&C 21DS115-4 (inspired by @eng-399 awesome subs) to pair with my recently rebuilt Fusion8's. All of it will go behind a used 120" AT screen from @brian6751, a gorgeous silver ticket 120" and images will be provided by my Optoma GT1080 Darbee short throw projector.

For each box, I have 20" depth (22" but I want the driver to have room to move), 32" width and 96" height. I think I'll limit the height to 48" so I can add two Moaaar subs someday if I wish.

I'm working on a side firing slot design that will be externally tunable for these. Tune range will go from 14hzish to 20hzish.

Each box will end up somewhere in the 11.25 to 12ish cuft after driver and port are subtracted depending on if I go 30" wide or 32". I may keep it to 30" so I can upgrade to wider mains someday.

Pics and progress to follow..

Edit: I'm dropping the "tunable" part of this sub because...i'm lazy.

Edit: adding finished pics. I ended up building the subs, the center console/stand, speaker stands all from the 4 sheets of plywood I used for the sub build. The inwalls behind everything are the original monoprice setup that surrounded a 60" sharp LCD TV. I've left them in place as a reminder...

 

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Discussion Starter #2 (Edited)
Edit: scrapping the tunable part of this but retaining the side firing g design.

Externally tunable side firing slot bass reflex design.

48"T x 32"w x 20" deep. Double baffle. 3" tall slot port that runs up the side and fire out of the side. This keeps to the same design principals @eng-399 employed so as to not shake the screen. You remove tuning "plates" to raise the tune or keep them all in to get the lowest tune. After designing it this way it occurred to me that maybe fine tuning by 1hz is not that useful. I need to verify the effective port length with testing and measurements. My understanding is you add half the height of the port past the internal port inlet so that your actual tune matches winisd. Thus the actual port length is less.
 

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Sounds like an awesome project. I will be following your progress! I was also inspired by the great eng-399 sub system. Can’t wait to see how these drivers work for you.


Sent from my iPhone using Tapatalk
 

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I'm soooooo excited for you! These subs in person is something to see.... there big! can't wait to see the box with multiple tunes and that's not by plugging one of the ports. Everyone will see soon
 

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Discussion Starter #7
How will you power these?
I have a iNuke 3000 DSP from the 1260w subs (better known as the sausage subs) that I didn't sell so right now I think I'm going to get another 3000 DSP and sun one amp bridged per sub. Or I guess I could sell the amp I have and just get a 6000DSP. Problem with the 6k is I'd have to deal on with the "power on thump" as I'd plan to use a smart power strips to turn it on. The third option is to look at another amp altogether as I do have an unbalanced minidsp in the arsenal as well. Not sure what that option should/could be yet. I think a clone would likely be more power than needed. I'll post more design stuff later like my SketchUp model and WinISD screenshots.
 

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Discussion Starter #8
I'm soooooo excited for you! These subs in person is something to see.... there big! can't wait to see the box with multiple tunes and that's not by plugging one of the ports. Everyone will see soon
Yeah they are definitely really nice up close. The quality is definitely there. The basket reminds me of the Lexus f-sport rims. Heck these are actually bigger than f-spot rims! I need to find some time to break them in free air and take some T/S measurements.
 

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are you planning to make the port exit ever larger as you remove panels or are you going to move the panels up and block off the extra port length?

if the former, I wonder whether that sort of rapid expansion at the mouth would have any negative effects. You might be able to approximate that in hornresp by modelling the port as a horn though the segments it has may not be enough to adequately model that sort of expansion.
 

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I assume you have to prevent "tune boards" from rattling. how will you do that?
 

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Discussion Starter #11
are you planning to make the port exit ever larger as you remove panels or are you going to move the panels up and block off the extra port length?

if the former, I wonder whether that sort of rapid expansion at the mouth would have any negative effects. You might be able to approximate that in hornresp by modelling the port as a horn though the segments it has may not be enough to adequately model that sort of expansion.
It would get larger as boards are removed.
 

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Discussion Starter #12
I assume you have to prevent "tune boards" from rattling. how will you do that?
If I don't get lazy and build it as designed, I think I would do tongue and groove between the planks and also on the sides. Open to ideas.
 

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It would get larger as boards are removed.
it's hard to tell from the diagram exactly but the current model looks like it already expands from a 3" x 15" port into a mouth of 6" x 15", is that right? If so, is that intentional?

If each board is about 6" then the cross sectional area at the mouth will get big (relative to the port) very quickly. I don't know what effect, if any, this will have. The safe option would be to add some sort of extra piece to block off the extra port length. On the other hand, do you think you'll ever change the tune?
 

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Not only do you need to make sure they don't vibrate, which will be no small task considering a subwoofers sole purpose in life is to create vibrations. But you also need to make sure all of those seams are 100% airtight. I applaud your creativity, but I think you'd be wise to pick a tune and be happy. Or come up with an easier path to multiple tunes.

Maybe that whole side of the box could be swapped out instead of little slugs? Gasket seal on the port rails and screw on the outside port panel? A big round port made with a sonotube could be easier. They are cheap in small sizes at Home Depot. Then you could just swap out the tube in different lengths.
 

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If I don't get lazy and build it as designed, I think I would do tongue and groove between the planks and also on the sides. Open to ideas.
Sounds fine, but I feel like you need to clamp them with some force at least.
I'd maybe do something like on this pic...
https://img.usaudiomart.com/uploads/large/1268241-grado-ra1-headphone-amp-battery-powered-excellent-condition.jpg
Would use those metal thingies I have no name for that you put in wood to hold the screws and just screw the boards on with some big head bolt screws. :D
 

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Discussion Starter #16
it's hard to tell from the diagram exactly but the current model looks like it already expands from a 3" x 15" port into a mouth of 6" x 15", is that right? If so, is that intentional?

If each board is about 6" then the cross sectional area at the mouth will get big (relative to the port) very quickly. I don't know what effect, if any, this will have. The safe option would be to add some sort of extra piece to block off the extra port length. On the other hand, do you think you'll ever change the tune?
Im not sure I follow you. I'll provide more detail. It is a 3" tall port the whole way and is the same width the whole way. The length is adjusted by removing the planks. I traced out the port length and labeled them. The planks are 6" tall and each plank corresponds approximately to the tune label next to it.

This is the SketchUp model if you want to check it out. https://www.dropbox.com/s/dnuxfcvalhe3gw5/11.5cuft Externally Tunable Subwoofer 15-20hz.skp?dl=0
 

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Discussion Starter #17
Not only do you need to make sure they don't vibrate, which will be no small task considering a subwoofers sole purpose in life is to create vibrations. But you also need to make sure all of those seams are 100% airtight. I applaud your creativity, but I think you'd be wise to pick a tune and be happy. Or come up with an easier path to multiple tunes.

Maybe that whole side of the box could be swapped out instead of little slugs? Gasket seal on the port rails and screw on the outside port panel? A big round port made with a sonotube could be easier. They are cheap in small sizes at Home Depot. Then you could just swap out the tube in different lengths.
Thanks, you may be right in that I should just pick a tune. I'm actually just thinking to shoot for 16hz and call it a day. This would only require a single port brace down the middle and I'd have a 17" effective port width instead of 15.5".
 

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I visualized something similar when I was designing my subs because of my indecision on tune, but eventually abandoned the idea to keep it simple. This design seems like a relatively simple solution, however.

Is this mostly just to be able to experiment when you first build them, and then settle on a tune and keep it there? If so, maybe you should use gasket tape while experimenting, but then once you settle on your tune actually glue the panels in place.
 

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Im not sure I follow you. I'll provide more detail. It is a 3" tall port the whole way and is the same width the whole way. The length is adjusted by removing the planks. I traced out the port length and labeled them. The planks are 6" tall and each plank corresponds approximately to the tune label next to it.

This is the SketchUp model if you want to check it out. https://www.dropbox.com/s/dnuxfcvalhe3gw5/11.5cuft Externally Tunable Subwoofer 15-20hz.skp?dl=0
what I mean is that the mouth of each port is 15" wide and 6" tall so has a cross sectional area of 90 inch^2 whereas the cross sectional area of the port itself is 3" tall and 15" wide so has a CSA of 45inch^2, i.e. the port is expanding from 45 to 90 over the length of that opening. Perhaps this might illustrate

This is the volume of the port as it expands so the base is the main bit of your port (3x15) and the face is the mouth (in this example 12x15 because I was drawing it with 1 extra plank removed), the arc is the centerline of this area so is the "length" of this bit of the path. The lines radiating out are the slices of this volume to split it into segments for hornresp and the length of these lines would give you the cross sectional area for each segment as it expands from the 3" at the entrance to the 6 (or 12 or 18 or whatever) at the mouth.



I think you could then model it in hornresp something like



and if you did then hornresp would complain that the expansion rate is too fast so the model may be inaccurate. If you accept that warning and proceed then it doesn't look like there is any issue however I have no idea whether there would be an issue in reality (i.e. what might lurk behind that warning). I thought it worth pointing it out as the possible issue though.
 

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