Maelstrom 2xPR18 preBuild questions

4838 Views 27 Replies 8 Participants Last post by SturmMD, Apr 12, 2009

SturmMD

Discussion Starter · Feb 7, 2009

Hi everyone,
I've been lurking for several months now and will be building a subwoofer soon. I'm hoping to have some questions answered as I'm currently in the prebuild stage - gathering materials and trying to find spare time.
My goal is to build a 25" cube out of 3/4" MDF with double thick front and side baffles. It's a larger and more complicated project than other speakers I have build in the past and will require a good amount of planning since I will either have to rent or borrow a table saw and router. I would also like to finish it faster than my last project which took more than 6 months

Here are my questions so far.
1. What size hurricane nuts should I use 10-32 or 1/4-20
2. What type of screws should I use for the drivers. I prefer the black allen head machine screws but there are a couple different head types. The holes in the driver frame are pretty large so will I need washers?
3. What is the reason for the tape? around the edge of the driver and baffle cutouts I see in pictures of build threads.
4. Should I use glue as well as screws to attach the outer part of the double-thick baffles, and what type/preparations (ex. sanding).

I'm sure I'll have some more questions. Hopefully this will speed my build instead of like last time when I spent a lot of time looking at the pieces and thinking of what to do next

1 - 20 of 28 Posts

cinema mad

· #2 · Feb 8, 2009

Hi SturmMD,
have A look at my Maelstrom X + 2x PR18 (8.6Qf) sub twins DIY thread for all the info on Tnuts Hex head bolts and so on in the Member DIY subwoofer DataBase or the Exodus audio forum in hear http://www.hometheatershack.com/forums/exodus-audio/14515-maelstrom-x-2x-pr18-passives-build.html...

Cheers...

SturmMD

Discussion Starter · #3 · Feb 8, 2009

Thanks for the link. I remember reading it before but now that I'm building a box I noticed more of the details. It looks like your 5mm hex screws are equivalent to #10-32 and you did have to use washers. What's the reason for the yellow/green tape around the driver edge?

Other than that it looks like my questions so far are answered. I'll update if I have more before I start.

cinema mad

· #4 · Feb 9, 2009

Yes I used 10mm "od" Flat washers 2 per bolt placed underneath the rubber gasket Direct on the 8x Speaker chassis mounting holes....

Cheers....

cinema mad

· #5 · Feb 9, 2009

When I first ordered my Maelstrom X's & PR18's There were no PR18 passives in Australia at the time. So I Built the first box and ran A single Maelstrom X untill the passives shipped A few weeks latter then I cut the two holes in the side baffels to install the 2 passives...

So The Reason For the Green Scotch 3M tape was so I did'nt chip or mark the outer baffel Edge when installing the Maelstrom and pulling it out A couple of times...

Cheers....

cinema mad

· #6 · Feb 9, 2009

Here's A shot of the Mael X + 2x PR18" Twins in my set up to help give you some motivation.

As you can see I still have'nt removed the Green 3M tape :bigsmile:, After I finnish my room Treatments I will give them A spray :T...

Cheers....

See less See more

SturmMD

Discussion Starter · #7 · Feb 10, 2009

I've put together some more concrete plans for my build. I still have to buy the MDF and arrange for the cutting so I'm looking for comments and suggestions. I'll start a build thread when the time comes

It's a 25" external cube made of 3/4" MDF with double-thick front and side-baffles. My calculations put it at about 6.4 ft^3 after accounting for the braces and drivers. The following figures show the side, front, and top sides of the box.

There is a brace along the back since top, bottom and back panels are only 3/4" thick. Also there are two braces, side-to-side, to strengthen the top and bottom.

I'm also toying with the idea of putting some brackets on the back of the box and hanging an EP2500 vertically on them. Any ideas on this?

The cutsheet plans assuming 4'x8' (49"x97") MDF panels

Amazingly, in this layout, 50% of all the cuts can be made with the table saw set to 23.5".

Using excel I made sure that the driver and PR frames had enough clearance between them. For this layout the PRs have to be offset 1" towards the back of the box from being centered (internally).

See less See more

4

DaveC

· #8 · Feb 10, 2009

Nice desisign.I'll bet your glad you did enough advance work to discover that the PRs needed to be offset:whew:
Only 1 minor suggestion, when you install your bracing offsewt it from center so you have varying sized panels. This will spread cabinet resonances and help avoid a large single frequency ring.

SturmMD

Discussion Starter · #9 · Feb 10, 2009

DaveC said:
Nice desisign.I'll bet your glad you did enough advance work to discover that the PRs needed to be offset:whew:

Yeah, without the offset it's too close to call until it's actually built. Although, rotation of the PRs might have allowed the spokes of the frame to not hit.

DaveC said:
Only 1 minor suggestion, when you install your bracing offsewt it from center so you have varying sized panels. This will spread cabinet resonances and help avoid a large single frequency ring.

Thanks for the tip, that's a good idea. I'll offset the back brace.

If I do add brackets the mount the EP2500 vertically on the back I'll add some more localized bracing on the back to give it more thickness in those areas.

Mike P.

· #10 · Feb 11, 2009

Nice design. What PR's are you using and what will the tuning frequency be?

SturmMD

Discussion Starter · #11 · Feb 11, 2009

Mike P. said:
Nice design. What PR's are you using and what will the tuning frequency be?

CSS PR18 2100g; Tunes to 16.5Hz

Mike P.

· #12 · Feb 11, 2009

Have you modeled your design?

SturmMD

Discussion Starter · #13 · Feb 11, 2009

Yes, here it is. I will be building a 4th order SSF set to 13hz. I might make it adjustable so that it is set lower until it detects a peak (in content under 20hz) above some number of watts then it will increase for some amount of time.

See less See more

Mike P.

· #14 · Feb 11, 2009

Looks good. Those are the same results I'm getting in WinISD.

vongerv

· #15 · Feb 12, 2009

Building a SSF. That is something I would be interested in. Could you elaborate on that, maybe direct me to some good info?

SturmMD

Discussion Starter · #16 · Feb 12, 2009

vongerv said:
Building a SSF. That is something I would be interested in. Could you elaborate on that, maybe direct me to some good info?

microchip.com has a free program called FilterLab that can calculate the component values for op-amp based butterworth filters of higher orders.

vongerv

· #17 · Feb 12, 2009

SturmMD said:
microchip.com has a free program called FilterLab that can calculate the component values for op-amp based butterworth filters of higher orders.

Thanks! That will keep me occupied for a while.

SturmMD

Discussion Starter · #18 · Feb 20, 2009

another question

I have come across another question.
I'm planning to put a significant amount of polyfill in this box. It is 6.4ft^3 so I was planning to put about 5lbs in it.

How will it stay in place and not interfere with the PR's? Does it stay put or will I end up having to make something to hold it to the walls. I have also seen people mention some really cheap pillows from walmart can be used as fill, maybe I can combine this with normal polyfill and use the pillows to hold it in place.

jongaro

· #19 · Feb 20, 2009

I'm using 1/4-20 hex head bolts without washers and t-nuts. My local supply house had excellent quality t-nuts and if you do drop down to 10-32's, you can get them in a fine thread along with a fine thread t-nut (in black if you like). you will need to use washers. I'm opting to not use the gasket kevin includes because it makes it too difficult to access the nuts and mine are all black and will therefore be hard to view. my allen bolts have a button head on them which is why I don't need washers.

on my build, I'm using BB plywood. it saves on weight and is stronger than mdf.

talking with Kevin regarding fill, he didn't think it made much of a difference, but it sounds like it can't hurt. i believe the poly fill at 16oz=1 cu ft.

Kevin Haskins

· #20 · Feb 21, 2009

Re: another question

SturmMD said:
I have come across another question.
I'm planning to put a significant amount of polyfill in this box. It is 6.4ft^3 so I was planning to put about 5lbs in it.

How will it stay in place and not interfere with the PR's? Does it stay put or will I end up having to make something to hold it to the walls. I have also seen people mention some really cheap pillows from walmart can be used as fill, maybe I can combine this with normal polyfill and use the pillows to hold it in place.

Unless you overfill it, you won't have a problem. It holds it's shape to an extent and the basket helps keep it from pressing against the cone. You just need to make sure there is clearance around the mass bolt and washers.

Kevin Haskins
Exodus Audio

1 - 20 of 28 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.