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Multi-Way Conventional loudspeakers with crossovers

Alec Model 19 Custom Built-In Cabinet Plans
Alec Model 19 Custom Built-In Cabinet Plans
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Old 25th July 2019, 07:58 AM   #11
GM is offline GM  United States
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I tried helping on several sites including GPA before the buyout/reconstruction and while I helped some, the basic structure of FB is no place for any serious effort nor long term storage for reference, so basically avoid it like the plague.

Re the room, pretty much what I feared, got a ~same divided room situation locally, though his is a large separates horn system, so some flexibility.

Regardless, the 'heart'/'magic' of the M19 is its XO combined with driver spacing and offset, so need to adhere to the factory spacing dims as close as practical.

Ideally, the width/height of the horn recess should be the same with replica foam inserts, though IIRC these are no longer available, so either DIY something close or line with 1" acoustic fiberglass insulation same as the early M19, Valencia 846B and 878B Santiago.

The closed off horn box should be ~stuffed with blocks of rafter fiberglass insulation or better still, open it up like the M19 for some extra net volume [Vb] and just damped like it.

The Woofer box appears long enough to justify centering the vent at L [i.d.]*0.848, so up near the top or a shelf vent at the very top or either located out of sight on the top [each will have minor tuning differences].

Then there's the room modes to consider and while we can assume where the modes theoretically are, we don't know how lossy the floor or ceiling is, so short of mapping it they may be offset one way or the other.

Know any roofing, foundation details?

GM
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Old 25th July 2019, 01:35 PM   #12
Aeroaudio is offline Aeroaudio  United States
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Thank you for the input GM. Attached is a Rev A drawing showing the port center relocated to 0.848 X the box inside height dimension. Any thoughts on port configuration? Round versus rectangular, single versus dual, etc?

The spacing between the horn and the woofer is currently slightly smaller than on the 19. But if it is critical I can match the 19 spacing. I changed it to better match the grill openings, but most of the time the doors with the grills will be open.

I have enough volume to meet the GPA recommended 8.8 ft. for the 416 woofer without adding the volume around the horn. Plus people have commented that it is beneficial to keep the volumes between the horn and the woofer separate. Personally I want to keep the volume for the horn separate to allow me to re-position the angle without affecting the sealing of the cabinet.

Regarding construction of the room. The floor is pier and beam construction. Floor joists are 2 x 12 on 12 centers. The terrazzo floor is 8 thick concrete and quartz stones. The flat roof ceiling is also 2 x 12s, but on 18 centers. It is also a flat roof, so the space between the ceiling and the roof is stuffed with fiberglass installation. The surface of the ceiling is not conventional American drywall but is what is called here plasterboard. Which is both thicker and smoother. FYI, the walls are not plaster but are double row brick construction. The left wall however is covered with a tapestry like material floor to ceiling.
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Old 26th July 2019, 07:39 AM   #13
GM is offline GM  United States
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You're welcome!

Round is most efficient, ergo shortest due to lowest friction losses. That said, the full width shelf vent is physically shortest due to having three walls to 'finish' it [biggest end correction]. Square where its area = round area and rectangular up to a ~1: 1.273 ratio where the short side is the pipe's circumference/4 and the the long side is the diameter of the pipe are acoustically close enough to it.

I normally recommend round since it's best and so many folks can easily cut it out quickly plus easiest to test different tunings, though use rectangular when just a predetermined material thickness reflex slot and only bother with shelf vents when it needs to be unacceptably long.

Altec seems to have spent considerable time determining the cab/drivers/XO 'system', but not having researched it nor reading anything other that marketing hype, all I can say is YMMV, though tilting larger horns perched on top out in the open can audibly impact summed polar response. Not an exact example, but from this you can imagine how tilting the horn will shift pattern: Linkwitz-Riley Crossovers: A Primer

Based on factory drawings, component volumes, the M19 is ~15,789.6875"^3 gross, less ~890.688"^3 = ~14,899"^3 = ~ 8.62106 ft^3 net, so GPA's 8.8 ft^3 gross is a little small, but not audibly so and maybe uses more accurate component volumes.

OK, so the eigenmodes will in theory shift up a bit from the floor and across from the brick wall, then if you ever measure them in room it might help explain peaks/dips not lining up too well.

Got a busy next few days, so will be awhile before seeing how the speakers line up with the major modes unless you or others tackle it, though vent location appears to be the only variable.

GM
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Old 14th August 2019, 01:19 AM   #14
Aeroaudio is offline Aeroaudio  United States
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Default Check Out Rev B to Cabinet Design

Well I am finally back home and have some time to revise the Model 19 cabinet design to incorporate GM's and other DIY member comments. Thank you.

The Rev B changes are as follows;

1) 811B horn has been raised 3.5" to 38.6", Closer to ear height.

2) 416-8B woofer CL distance to horn CL change to match Model 19.

3) Horn and woofer now occupy one cabinet volume, which;
a) Simplifies cabinet construction.
b) Reduces cabinet depth to be less square.
c) Provides more than enough volume for bracing and tuning (1.0 cut).

4) Crossover L-Pad panel rotated 90 deg and moved to below the horn. This will require I fabricate a new panel. But the GPA panel is not as classy as the original Altec panel anyway. I can get some brass panels made at a local trophy shop with the Altec logo silk screened on.

5) Grill support on door now centered across middle of woofer. But doors will be open for serious listening anyway.

No sawdust is on the floor yet. So more comments are welcome. Copy of Rev B drawing attached.
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File Type: pdf Vinewood Cabinet Mod to Model 19s Rev B 081219.pdf (633.8 KB, 11 views)
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Old Yesterday, 12:36 AM   #15
Aeroaudio is offline Aeroaudio  United States
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Default Final Custom Built In Altec Model 19 Cabinets Rev C

Was hoping to get some more thoughts from GM or others on the Rev B version of the cabinet plans I posted last week. But in the absence of any additional comments, they must be perfect. Right?

Well not perfect enough for me at least. So therefore attached is Rev C, what should be the final version. Barring any unexpected discoveries when I cut the front off the old cabinets and see what is back there.

Changes from last time are mostly fine tuning and details.

a) Front and back now 1.50" thick, matching the thickness of the existing cabinet sides and bottom. The 0.75" Baltic Birch isn't that expensive for the little I need.

b) Back of cabinet positioned to reduce excess estimated cabinet volume to 0.3 cubic ft over the optimum 8.80 cubic ft. Enough to provide for tuning and unexpected added bracing. Although with all sides 1.50" thick, I don't expect any added bracing will be required.

c) Details on corner reinforcements and L-pad installation added.

For grins I did a estimate of how much the completed cabinets would weigh if they were designed as stand alone speakers. About 220 LBS each. Good thing I will never need to move them.

Heading out of town again for a week. Will begin ordering all necessary components, hardware and wood when I get back. Any last minute comments or ideas welcome.
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File Type: pdf Vinewood Cabinet Mod to Model 19s Rev C 081819.pdf (641.8 KB, 12 views)
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Old Yesterday, 04:47 AM   #16
GM is offline GM  United States
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What's to check? No dims on rev B. Forgot about the eigenmodes, but the layout is too 'fixed', so it is what it is.

Rev C: I have a 17.25" ctc spacing and an i.d height of 46.1/0.848 = 54.36" based on recommended vent offset.

0.3 ft^3 isn't enough to audibly affect tuning.

GM
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Old Yesterday, 10:49 AM   #17
Aeroaudio is offline Aeroaudio  United States
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Thanks GM. You are correct in that the design of my box is literally boxed in for many parameters.

Thanks for your assistance. Time to start making sawdust.

Other than application of insulation to one opposing side, any specific recommendations on type and thickness to use?
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