GM-416-8B MLTL Corner Cabinet

[srivenkat]

Greets!


Bummer about your family. Hope your mom's getting [a lot] better medical care than me and at least stable enough for ya'll to be able to somewhat enjoy this beginning of the holiday season.


Anyway, this project has moved far afield from the original and either I forgot stuff in my design considerations/trade-offs or I guess chose to selectively ignore them to minimize the acoustic trade-offs since I want a ~all encompassing tutorial to point to in the future.


The vents were to be on the lower front sides like Billfort's and for the dual driver/511 combo I chose to put the horn in the cab since it would be too far away from the woofers with the desired XO [point] and recessed ~like the M19's, which has been already worked out for us by Heathkit [Altec?] many decades ago.


Not much tech info per se, but I did calculate it close enough way back when using the sales brochure and peering through the grillcloth of one, though couldn't find it it in the relatively few notes I still have available and can't recall ATM if I actually built one, but these should suffice:

http://www.heathkit-museum.com/hifi/hvmhh-1-c.shtml

https://www.google.com/search?q=heathkit+legato&rlz=1C1AVNG_enUS675US675& espv=2&biw=1044&bih=514&tbm=isch&tbo=u&source=univ &sa=X&ved=0ahUKEwismeSD063QAhUCOSYKHRM0BHMQsAQIIQ& dpr=1.1

http://i40.tinypic.com/2vvkilh.jpg

https://s-media-cache-ak0.pinimg.com/236x/7b/82/f4/7b82f49c59a0ecb3539c6ce3c7abf2ac.jpg

If a top mounted horn is used, then the woofers ideally need to be at the extreme top as the Lp is too close for good summation, though the woofer's output will theoretically sound audibly different in an A/B comparison to the Legato variant.


More to come as time permits.........and hope ya'll have an enjoyable, filling, profitable [if applicable] holiday weekend if I don't make it back before then.


GM

GM,

Thanks for the details. I was under the impression that single woofer configuration will have the horn in the cab but the dual will have it on top of the cab. For both, I can have the horn (511 and 811) inside the cab.
For 811B horn (total height - 8-5/8") - you have "horn down - 4.75"
So, I guess for 511B (total height - 10-5/8") - I should add 2" down based on its height. This requires woofers offset to go relatively 2" down?

For Port - you have given the details....
"Vent = [1] 5" dia. x panel thickness [0.75" assumed]/side for ~25 Hz Fs or can both be on one side horizontally.
Recommend using a removable baffle to try up to [1] 9" dia. vent hole/side for more typical Altec tuning or just start big and add smaller hole discs till it sounds right."

Thanks and have a great holiday weekend.

-Sri

- - - Updated - - -

Sri, thanks for the kind words of encouragement. My 84 year old mother-in-law is in a drug induced coma and a ventilator, but she needs to be weaned off of it and start breathing on her own. It is still touch and go and she is developing congestive heart failure which is fluid surrounding the heart.

Anyway, it appears that pine hand railing comes in 1.5" diameter and the 4x4 ply plates will have that same size hole drilled in them so the railing is the full inside box height and the plates slide over it and will act like a large gusset and increase the gluing surface area from 1.75 to 16 sq in plus the .75" depth.

I envision using 2x2's cut diagonally into 1.5x1.5 triangles to also give a large gluing surface area and I would screw the removable panels to them with 1.5" #12 screws @4"O.C. and I suppose a highly contrasting screw hole plug could look acceptable (like cherry plugs on a light birch finish) and in that case, you could go back to the original drawing with just the areas for the speaker(s) and ports doubled up.

I still don't know where to place the ports and I don't know what affect having a stepped thickness near the ports will have on their function. If you could router a step into the port board outer diameter, you could leave that area just a single thickness and just change out different circles with various diameter ports.

Let me do some more drawing.

James

James,
Very sorry to hear about the mom's situation. Hope things get better for you and your family.

-Sri

[VolvoHeretic]

Thanks for the support guys, here is the latest. I moved the ports to the utmost bottom and left/right, should I pick 7th harmonic points or what? If the baffle is step routed .375"x.75" you can have several port baffles mirror routed, cut 10 or so different diameter port holes and interchange those to come up with the ultimate port dimensions and even do A/B testing.

I want to make the front baffle two piece - one for the horn and the second for the main woofer and port. These could be separated with a piece of speaker/port matching brass looking 1/4 bar stock. I will evenly space and dimension the exposed baffle screws which need to be drilled with a good recessed pilot hole drill bit with the correct plug, chamfer, and pilot hole all-in-one step unit. If (and I hope)(maybe insist if GM's and my names is published on the blueprints) a brass look is used for all metal parts (speaker cloth cover rings) including the exposed screws for the horn are used, brass plugs could also be used to cover the screws if not actual exposed brass screws. (I love brass/gold )

Sri, the plywood can be nailed together as you assemble the box with a brad nailer using finish pin nails. I can't remember what length would be best, but 2.5" comes to mind. I would start at the front and work your way to the rear corner, making adjustments as you go. After every thing is glued and pinned together I would also use cinch straps to suck everything up snug. MAKE SURE TO KEEP EVERYTHING SQUARE, PLUMB, AND LEVEL!!!!

Since the base and cap panels will be free cut, mark everything out on your plywood top and bottom panels using a mechanical .5mm pencil using hard hb lead for the finished outside dimensions, cut those panels an 1/8" oversize beyond the front panel on the rear panel sides and after the vertical sides are fit, glued, nailed up, and dried, use a trim router bit to trim up the base and cap to match the actual sides wherever they eventually wind up (actual resulting fit is not that important, but final fit is crucial to the finished product(it is what it is). In other words, try to follow the outside dimension numbers, try to make sure the outside miters touch first and if need be narrow the miter angels to make sure the outside of the miters are the first parts touching. This will be a living, breathing contraption.

[srivenkat]

Thanks for the support guys, here is the latest. I moved the ports to the utmost bottom and left/right, should I pick 7th harmonic points or what? If the baffle is step routed .375"x.75" you can have several port baffles mirror routed, cut 10 or so different diameter port holes and interchange those to come up with the ultimate port dimensions and even do A/B testing.

I want to make the front baffle two piece - one for the horn and the second for the main woofer and port. These could be separated with a piece of speaker/port matching brass looking 1/4 bar stock. I will evenly space and dimension the exposed baffle screws which need to be drilled with a good recessed pilot hole drill bit with the correct plug, chamfer, and pilot hole all-in-one step unit. If (and I hope)(maybe insist if GM's and my names is published on the blueprints) a brass look is used for all metal parts (speaker cloth cover rings) including the exposed screws for the horn are used, brass plugs could also be used to cover the screws if not actual exposed brass screws. (I love brass/gold )

Sri, the plywood can be nailed together as you assemble the box with a brad nailer using finish pin nails. I can't remember what length would be best, but 2.5" comes to mind. I would start at the front and work your way to the rear corner, making adjustments as you go. After every thing is glued and pinned together I would also use cinch straps to suck everything up snug.

Since the base and cap panels will be free cut, mark everything out on your plywood top and bottom using a mechanical .5mm pencil using hard hb lead for the finished outside dimensions, cut those panels an 1/8" oversize beyond on the rear sides and after vertical sides are fit, glued, nailed up, and dried, use a trim router bit to trim up the base and cap to match the actual sides wherever they eventually wind up (actual resulting fit is not that important, but final fit is crucial to the finished product. In other words, try to follow the outside dimension numbers, try to make sure the outside miters touch first and if need be narrow the miter angels to make sure the outside of the miters are the first parts touching. This will be a living, breathing contraption.

James,

Amazing drawings, thanks. I think we need to finalize the port position, based on GM, he prefers the port to be on the left and right sides like in Billfort (Billforts Audio Obsession) cabinet.
GM Said in his design notes,
"Vent = [1] 5" dia. x panel thickness [0.75" assumed]/side for ~25 Hz Fs or can both be on one side horizontally.
Recommend using a removable baffle to try up to [1] 9" dia. vent hole/side for more typical Altec tuning or just start big and add smaller hole discs till it sounds right"


Given sides are measured at 6.5" board, not sure whether we can have 9" diameter port. Should we increase the length of this board?

Sorry that you have to keep changing the drawings every time, may be we should finalize the measurements and position to save your time.

Also, for dual woofers, based on GM suggestion - having the 511B horns inside the cabinet, the drivers may require different offset. Not sure.

I think, I can start assembling the cabinet once we know how to handle the port position.

Thank you,
Sri

[VolvoHeretic]

No problem Sri, I am used to satisfying several clients / designers at the same time and I am learning a lot with each change, I always draw what I think the client what's and what I think they need. Our dimensions are the minimums, we can easily increase the perpendicular panels depth, it will just make the box too big, which can easily be shrunk down to size with a simple concrete orb centered in the structure.

[srivenkat]

No problem Sri, I am used to satisfying several clients / designers at the same time and I am learning a lot with each change, I always draw what I think the client what's and what I think they need. Our dimensions are the minimums, we can easily increase the perpendicular panels depth, it will just make the box too big, which can easily be shrunk down to size with a simple concrete orb centered in the structure.

I wish I have the drawing skill to help in this I guess as long as we can manage to maintain the volume we should be ok, am I right? Or, does this take back to 45 degree cab?

Thank you,
Sri

[VolvoHeretic]

We are very close the to the magical 24 cf mark and I don't think that that number is a magical number other than something close is good enough and fine tuning will fix everything (GM?) If everything that I have read is half right, these numbers are a close ball-park and everything is fine tuning (think automotive intake and exhaust pulse tuning where everything is starting and stopping 5,000 per minutes(10,000rpm) and the air velocity is reacting form 0 to plus Mach velocity 5,000 per minute.

[srivenkat]

We are very close the to the magical 24 cf mark and I don't think that that number is a magical number other than something close is good enough and fine tuning will fix everything (GM?) If everything that I have read is half right, these numbers are a close ball-park and everything is fine tuning (think automotive intake and exhaust pulse tuning where everything is starting and stopping 5,000 per minutes(10,000rpm) and the air velocity is reacting form 0 to plus Mach velocity 5,000 per minute.

Sure, I will wait to get your and GM inputs to move further. Hope we can finalize all the details before mid of Dec, last two weeks of Dec will be my vacation and I can spend (all) time on this, if I get done that will be my gift

-Sri

[jocelys1]

Sri, you going with single or double 416 ?

[srivenkat]

Sri, you going with single or double 416 ?

Hello Jocelys1,

GM designed the cabinet for using single or dual woofers (416-8B). I will be starting with single woofer but eventually 'm planning to move to dual woofers. Removable front panel will allow this, 811B horn will be used for single woofer and 511B will be used for dual woofer. Thank you,
Sri

[VolvoHeretic]

After much thinking and attempts at using different polygon shapes, I have come up with a different version of the same 12 sided 30 degree polygon which has the required cubic foot volume and room for 9 inch ports on the sides.