T48 stack

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jakkle21
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T48 stack

#1 Post by jakkle21 »

I am starting a build tread for the 4 T48s I plan to build.
This is my original post viewtopic.php?t=26326.
Can I get some help on plywood terminology? I just called the local specialty wood place, and asked for 1/2" plywood made of either for or spruce and they said they didn't have anything like what I was asking for. Their website says they carry hard and soft plywoods of various grades.
Hardwood Plywood
Alder, Ash White PL/SL, Birch Natural, Red Birch, Read Oak Rotary, Walnut, Clear Pine, Genuine Mahogany PL/SL, CVG Doug Fir, Aspen, Cedar Aromatic, White Maple, Knotty Pine PL/SL, Cherry PL/SL, Red Oak PL/SL, White Oak PL/SL, Hickory.
Specialty & Imported Plywood
Baltic Birch (Prefinished & Unfinished), Homasote, Maple, Cherry, Melapi, White Luan, Poplar Bending Board, Red Oak, Birch & Wiggle Board
Softwood Plywood
BBX, Boat Ply, CDX, CCX-PTS, & Marine Ply
So I'm pretty sure I just didn't ask for the right thing. I know they have good Baltic Birch, but I wanted to go with one of the lighter woods.

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Bill Fitzmaurice
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Re: T48 stack

#2 Post by Bill Fitzmaurice »

Fir and spruce are softwoods.

9830Lark
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Re: T48 stack

#3 Post by 9830Lark »

https://www.toolcrowd.com/how-much-does-plywood-weigh/

According to this, you'll drop from ~48 lbs to 40 lbs for a 4' x 8' x 1/2" sheet BB vs softwood. I thought Bill's recommendation for Baltic Birch is due to the integrity (lack of voids and the uniqueness of the layering). IMHO, not worth the risk/hassle to save a few pounds.

jakkle21
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Re: T48 stack

#4 Post by jakkle21 »

Thank you for replies
I was assuming I would use Baltic until I saw the softwoods listed in the plans and then I read that they have good acoustics. I'm not trying to cut corners. I want to use whatever will be better. If the extra weight is worth it, I'm fine with that.
If I'm not sacrificing anything by using a quality softwood, I will just go into the shop on a slower day and talk to them in person.

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Bill Fitzmaurice
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Re: T48 stack

#5 Post by Bill Fitzmaurice »

Softwoods are OK if they are at least 5 ply. Most 1/2" softwoods are only 4 ply.

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fender3x
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Re: T48 stack

#6 Post by fender3x »

There is some weight savings using a softwood plywood. The website I found suggest that a 4'x8' sheet of 1/2" BB should weigh about 7 lbs more than a sheet of pine/spruce plywood.

https://theplywood.com/weight/

I used high quality radiata pine plywood on my DR-250, mostly because I could not get BB at any local lumberyards. It worked fine on the DR, but I just took a look at my T-39 plans, and it said that softwood ply is only a an acceptable substitute if your driver complement is less than 500W. If 500W or higher, the plans recommend BB for strength.

At lumberyards where I live I can find most of the types of plywood that you have listed. Through hard experience I have found that they are ALL to be avoided except BB and pine plywood with at least 5 plies. The others generally have super thin veneers of the hardwoods they are named after--including the birch plywood, uless it says baltic birch and the top an bottom plies are roughly the same thickness as the rest of the plies. Same with the pine. All five plies should be about the same thickness.
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

Grant Bunter
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Re: T48 stack

#7 Post by Grant Bunter »

Every one of Bill's designs I have has been built with Radiata Pine ply. In older plans that was referred to Arauco.
None have failed.

Clear pine should have no branch nodules in it and will be softwood, + the other choices Bill has mentioned.

What is most important is your ply has:
At least 5 plies, all of equal thickness, and no thin outer "face" ply on either side.
What is most important after that is you use PL Premium adhesive...

Weight is a premium that may need to be taken into account.
I couldn't run my business by myself with DR250's built with BB. I couldn't lift them into position. Well more the dual CD loaded ones on top of the melded array ones, but you get my drift.
I couldn't dead lift my T39's to stack in the truck by myself if made with BB.

No one who has seen my rig has ever said it doesn't sound good, or is structurally insufficient because of what it's made from.
In fact, no one ever asked.

Poplar is very light. It may be handy to know it's there as a bending ply for other builds (eg DR series, Otop lites etc). Check is it is only bending ply, or not, as it will suffice for most of the horn path build. It will take noticeable knocks easily, so I wouldn't use it for the exterior of the cab though...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

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Bill Fitzmaurice
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Re: T48 stack

#8 Post by Bill Fitzmaurice »

Poplar is very good, with lots of plies and minimum weight. But it's not easy to find. Where bending is concerned that's also a matter of plies, you only want three. There are plywoods made for bending, they have the grain on the same axis with all the plies, but in the thicknesses we use they're not necessary.

Bruce Weldy
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Re: T48 stack

#9 Post by Bruce Weldy »

For what it's worth, I'll chime in here. One factor that hasn't been mentioned yet is workability. Baltic Birch is flat. It stays flat. It is the absolutly the best plywood you'll ever work with.

Since you are building 4 T48s, that means a lot of large panels. The larger the panel, the more likely it is to warp. Baltic Birch won't warp. Your boxes will be square and you won't be fighting wavy panels.

If you put wheels on 'em (and you should), a few extra pounds is unnoticeable. And you will love working with the stuff.

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

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Bill Fitzmaurice
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Re: T48 stack

#10 Post by Bill Fitzmaurice »

Warp is also a matter of the number of plies. Even lauan won't warp, if it's nine ply. If you can't get nine ply half inch just follow the techniques shown in the plans and you'll be OK. I devised those techniques to account for that fact that most plywood does warp. It takes time to make and use guide boards and jigs, so you might be inclined to try and get by without them. Let's put it this way: I've been building speakers since 1968. I won't try to build one without using guide boards and jigs.

ACUA
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Re: T48 stack

#11 Post by ACUA »

https://www.lowes.com/pd/15-32-CAT-PS1- ... 1000105359

I have always bought this for my BFM speakers. In my area HomeDepot rarely carries 5ply wood. Lowes has always carried 5ply. Current price in my area is $27.15 for a 4x8ft sheet. This wood is crude with knots and blemishes all over, un-sanded, usually has forming makes. I have never had a sheet not bow or warp. As a result, I have spent half of my build times just dealing with the warpage. Once I have wrestled the cabinets into shape, I am personally pretty happy with the results, but it doubles my build times. :wall: I intend to keep using this cheap wood for my future builds, call me stubborn or cheap or both! If you can afford to work with a quality Baltic Birch plywood you will surely have less headache during the build and will end up with a better product in the end. :clap:

Good luck with your builds, there are a bunch of smart people around here that will help you out along the way! I doubt you will find a better group when it comes to DIY pro sound!
Advanced Concepts Underground Audio

jakkle21
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Re: T48 stack

#12 Post by jakkle21 »

Thank you for all the great info. This is exactly what I was looking for. I talked with my roommate about the wood supplier, and his exact word were "they aren't interested in selling you wood, they are etuerebto full you order". He said every time he has asked them for something, they said they don't have it but when he goes and looks he can almost always find what he's looking for.

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fender3x
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Re: T48 stack

#13 Post by fender3x »

I have not had luck at big box stores for lumber. I understand that there are Lowe's that sell arauco (radiata pine plywood) in some places, but not where I live. For half inch I found a supplier with a specialty lumber yard. They don't have BB, but they have radiata pine at abut $70 a sheet. I have only found BB at a wholesaler who does not sell the general public. I got them to sell me a couple of sheets of 1/4" BB because I was there talking to them, and someone generous of spirit took pity on me. I am using them as carefully as I can, and treating them like gold.

Calling around I got a lot of false alarms that turned out to be "birch" without the "Baltic".... In other words, thin veneer on top and bottom. You have to look really carefully. I once got some that fooled me because the veneer was so close to the same color as the ply under it. Took some digging to find something acceptable.
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

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Bryan Cox
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Re: T48 stack

#14 Post by Bryan Cox »

Now that I have a supplier for BB that's all I use. It makes a world of difference. In the past, though, I've used ACX and ABX to good success. But I did have to fight the warp. The only way I was able to alleviate this (a little) was if I cut and installed one piece at a time. I still fought warp but not as badly.

Now I batch cut everything in one session and then assemble later. Can't do that with big box stuff.
Otop 12 x 4 (Delta Pro 12-450a) 2x melded, 2x straight
Titan 39 x 4 (3012LF) 20" wide

ACUA
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Re: T48 stack

#15 Post by ACUA »

Jakkle21, I sent you a private message on this forum, feel free to reach out to me if you like.
Advanced Concepts Underground Audio

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