OB W-frame build

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aceinc

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OB W-frame build
« on: 12 Feb 2017, 12:26 am »
I am just into building the GR-Research OB W-Frame subs.

I have a question regarding two measurements;

16.30" The closest I can come up to in SAE is 16-5/16".

15.55" The closest I come up with on SAE is 15-9/16".

Are these approximations going to affect putting everything together?

Also my assumption is I will need to receive the drivers to get the hole pattern correct for the "bolt holes" and drill the holes before I start putting everything together. Correct?

On the same topic Because I can get to both sides of the drivers, I should be able to user bolts, washers and lock washers instead of "T" nuts, which I seem to screw up at least one on every sub I've built. Is this the best way of mounting the drivers? Or should I fight with T-Nuts, or something else?

How difficult is it to mount these drivers and bolt them into place once this unit is all together? Anything I need to look out for like making sure the bolt pattern doesn't put a bolt in the top & bottom middle?


Captainhemo

Re: OB W-frame build
« Reply #1 on: 12 Feb 2017, 01:47 am »
Here is the mechanical drawing for the woofers, you can get the  bot/screw apcing from that if yo ulike or you  can wait until you have the  woofers
http://gr-research.com/pdf/12in%20mechanical%20drawings.pdf

I've never seen   /  heard of anyone  striping one of the screws into .75"  or 1'   baffles.  . I'm sure you can use  bolts/ washers, nuts,   & locktight if you want but not necessary IMHO.  If you look at peter's last  build thread,  he   uses a cool technique to  harden and then tap the  material to accept machine screws  http://www.audiocircle.com/index.php?topic=139529.0    , can't reacll what page it was .
You can  install  the woofers after assembly..... if you  add an additonal brace  in the  "V" (large unbraced area)of the  "W",  yo uhave to watch where you  postion it to be sure an leave yourself enough room to get the  woofer in

jay
« Last Edit: 12 Feb 2017, 02:59 am by Captainhemo »

mlundy57

Re: OB W-frame build
« Reply #2 on: 12 Feb 2017, 03:16 am »
These drivers do not use T-nuts for mounting. They mount using 8 hex head screws which come with them.

Captainhemo

Re: OB W-frame build
« Reply #3 on: 12 Feb 2017, 03:26 am »
I assumed he was going to change the screws to  bolts/washers/t-nuts ...   .
And be aware,   the screws  ARE in  the box with the woofers,  if you don't see them   reach up under the magnet.  Many of the ones we've received  have had the little screw bag ripped  and that's where the screws migrate to

jay

Danny Richie

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Re: OB W-frame build
« Reply #4 on: 12 Feb 2017, 04:04 am »
Yeah, those hex head screws hold really well. No reason to over complicate things.

aceinc

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Re: OB W-frame build
« Reply #5 on: 12 Feb 2017, 04:36 am »
So the drivers come with hex head "wood screws" do I need to drill pilot holes for these screws?

More importantly what are the SAE dimensions I referenced? My tape measure doesn't have tenths of an inch.

mlundy57

Re: OB W-frame build
« Reply #6 on: 12 Feb 2017, 05:02 am »
My circle jig is graduated in 1/16" increments so I either use the exact dimension specified if it comes out to 1/16" or any multiple of 1/16". If the specified dimension works out to be between two 1/16" increments, I use the 1/16" increment above the specified dimension.

Yes, pilot holes are needed. I use a Vicks bit. This is a centering bit designed for drilling pilot holes for hinges. Personally I wait until i have the drivers in hand. That way I know the holes will line up.

Mike
« Last Edit: 12 Feb 2017, 03:04 pm by mlundy57 »

aceinc

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Re: OB W-frame build
« Reply #7 on: 12 Feb 2017, 04:27 pm »
The drawings for the W-Frame sub do not show dimensions showing the distance from the front edge & rear edge of the cabinet to the baffle. Does it matter? Should they be the same, different, can one part be against the edge?

Because of my plans I would like to put the two pieces of the baffles that attach to the top & bottom of the cabinet as close to the edge of the cabinet as possible like the drawing below

. Is that a problem?

Danny Richie

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Re: OB W-frame build
« Reply #8 on: 12 Feb 2017, 09:20 pm »
No problem on your baffle layout either.

aceinc

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Re: OB W-frame build
« Reply #9 on: 13 Feb 2017, 02:23 am »
OK, I have the wood for the inner cabinet all cut, the woofer holes cut, and dry fitted one of the cabinets.

The next step is to buy the kits. Once I have a driver I can finish drilling the pilot holes and start assembly.

My additions to the standard design will be to add a second layer of 3/4" MDF to the top, bottom and sides. These pieces will extend 3/4" past the front & back, allowing for a frame to hold a grill cloth.

The inner cabinet will be screwed and glued. I am thinking of using the 45 degree pieces I cut off the baffles to brace where the baffles meet the top & bottom if the drivers will allow it.

mlundy57

Re: OB W-frame build
« Reply #10 on: 13 Feb 2017, 04:33 am »
Pictures?  Build threads need pictures ...

aceinc

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Re: OB W-frame build
« Reply #11 on: 13 Feb 2017, 04:55 am »
Soon... Right now all I have is a pile of cut wood.

bdp24

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Re: OB W-frame build
« Reply #12 on: 13 Feb 2017, 06:47 am »
OK, I have the wood for the inner cabinet all cut, the woofer holes cut, and dry fitted one of the cabinets.

The next step is to buy the kits. Once I have a driver I can finish drilling the pilot holes and start assembly.

My additions to the standard design will be to add a second layer of 3/4" MDF to the top, bottom and sides. These pieces will extend 3/4" past the front & back, allowing for a frame to hold a grill cloth.

The inner cabinet will be screwed and glued. I am thinking of using the 45 degree pieces I cut off the baffles to brace where the baffles meet the top & bottom if the drivers will allow it.

The place you want to install a brace is in the middle (top to bottom) of the two side panels , at their front edges (at the left hand side in your diagram). That will tie the two panels together at their least supported area, greatly reducing their ability to flex and resonate. A single length of dowel or block of wood will leave enough clearance for the two woofers to pass by on their way to being mounted on their baffles.

Captainhemo

Re: OB W-frame build
« Reply #13 on: 13 Feb 2017, 05:13 pm »
this  is crude but....
if this is your  "w" , yo want a cross brace   where the arrow is
                        ^
                        |
As  mentioned,  it will run from side panel to side panel
Just be sure you leave enough room to get the lowerwoofer in  and not interfere with the  back of the upper woofer
jay

                 

aceinc

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Re: OB W-frame build
« Reply #14 on: 13 Feb 2017, 05:37 pm »
Does the crude image below look like what y'all are talking about?




mlundy57

Re: OB W-frame build
« Reply #15 on: 13 Feb 2017, 05:39 pm »
Does the crude image below look like what y'all are talking about?




Yep, that's it.

Mike

bdp24

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Re: OB W-frame build
« Reply #16 on: 13 Feb 2017, 07:54 pm »
Does the crude image below look like what y'all are talking about?




As Mike just said, that's the spot. You can even run the brace from the front edge of the side panels towards the back of the cavity, where the two baffles meet, for more bracing. But you must then insure that there is still enough clearance to be able to get the woofers passed the brace and onto the baffles. Either way, a brace eliminates the one advantage the H-frame has over the W---structural stiffness.

On the other hand, some people claim, as Danny has mentioned a few times, that the W affords a benefit of it's own over the H, that of a slight reduction is harmonic distortion. It has to do with the opposing force-cancellation created by the arrangement of the woofers on the 90 degree baffle relationship. Over my head, technically! It's a very small advantage, nothing too important to sound quality as far as I know.

aceinc

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Re: OB W-frame build
« Reply #17 on: 13 Feb 2017, 10:02 pm »
By doubling all four walls to 1-1/2" of MDF should offer a fair amount of rigidity and mass to the enclosure.

If one wanted to be pedantic about structure at the expense of increasing the height by 3/4" and some additional complexity, one could put a shelf through the center front to back. The drivers would need to move towards the top & bottom for clearance as well.


bdp24

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Re: OB W-frame build
« Reply #18 on: 14 Feb 2017, 06:15 am »
That's an interesting idea Ace. I wonder if the full "shelf" brace would create a cavity resonance in each resulting chamber in the front of the W-frame. What's say, Danny?

aceinc

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Re: OB W-frame build
« Reply #19 on: 14 Feb 2017, 01:02 pm »
I'm sure Danny will have a better grip on the effects, but in my mind the size of each cavity would be small enough to have a resonant frequency above the range of the drivers.