Plywood 1930s till Now -- rethinking the love of Baltic Birch (vintage or new)

[Salectric]

@mrgoodsound
In your photos I noticed the horizontal cleats or braces attached to each side of the cabinet with the field coil driver. With my previous OB cabinets I experimented with similar horizontal boards and found they had a significant effect on the sound. In my case I used maple 1x2 pieces screwed into the plywood sides. The first pair were intended merely to support a plywood divider board stretching from side to side. After listening to that for a while, I concluded I liked the sound better without the shelf but with the side cleats left in place. That led to my trying additional maple cleats at other locations on each side, but ultimately I concluded a single board on each side sounded best. What was curious to me was that the additional boards had such an impact at all. You can hardly feel the sides of the OB cabinets vibrating when music is playing yet there are clearly resonances in the plywood that are being damped or shifted in some way by the cleats on the side walls.

 

[FloriduhBoy]

It's not like I haven't heard this type of gear. I have and at length.
My question was more philosophical, I suppose.

I seem to be doing more lower-level listening and this approach works for me. It's an experiment.

 

[mrgoodsound]

@mrgoodsound
In your photos I noticed the horizontal cleats or braces attached to each side of the cabinet with the field coil driver. With my previous OB cabinets I experimented with similar horizontal boards and found they had a significant effect on the sound. In my case I used maple 1x2 pieces screwed into the plywood sides. The first pair were intended merely to support a plywood divider board stretching from side to side. After listening to that for a while, I concluded I liked the sound better without the shelf but with the side cleats left in place. That led to my trying additional maple cleats at other locations on each side, but ultimately I concluded a single board on each side sounded best. What was curious to me was that the additional boards had such an impact at all. You can hardly feel the sides of the OB cabinets vibrating when music is playing yet there are clearly resonances in the plywood that are being damped or shifted in some way by the cleats on the side walls.

Yes, there are all sorts of small details like that in the design.

There also was healthy discussion about the actual mounting of the speakers to the frame. Some preferred screwing them directly to the front baffle. Others advised the use of an intermediary panel with felt washers (closest to the 1930s radio design) which would further reduce the influence of side wall vibration, and potentially create an acoustic short circuit with the front of the case. Some also advocated for not attaching the speaker to the case at all and simply propping it up on a wooden or metal pedestal and 'parking' it in front of the baffle!

I am sure all approaches are valid and it depends on the cabinet materials, drivers, room, and taste.

 

[Salectric]

Here’s a question that’s more on topic. Since everything (literally) in a speaker cabinet or touching it seems to affect the sound quality, what about veneer on the exterior? Or paint for that matter? Does anyone have experience, good or bad, with the before and after sound once veneer or paint is applied?

 

[Roscoe65]

These guys are making 614 and 612 cabinets out of 12mm BB. I don’t know the driver they are using, but it looks like an Eminence Beta 12 CX. Subtracting driver weight, their 12mm 614 cabinet weighs in at 32 lbs. For comparison, the plywood Altec 614 (24.75 x 18.75 x 14.25) weighs in at 39 lbs and the Altec particleboard 614 (24 x 20.5 x 15.25) weighs 35 lbs. I find it interesting that the smaller Altec plywood box weighs more than the larger Altec particle board box. I recall Joe Roberts indicating the particleboard used was of varying density. If the published weights are to be believed, the particleboard enclosure must be considerably less dense than MDF.

The two plywood cabinets are the same size. The cabinet with 12mm (1/2”) plywood weighs 32 lbs while the Altec plywood 614 weighs 39 lbs. If I simply scale the plywood thickness with weight, I would expect the construction to be of 5/8” plywood.

EDIT: I found both WE and Altec engineering specifications that require plywood thickness of not less than 3/4”.

 

[FloriduhBoy]

Here’s a question that’s more on topic. Since everything (literally) in a speaker cabinet or touching it seems to affect the sound quality, what about veneer on the exterior? Or paint for that matter? Does anyone have experience, good or bad, with the before and after sound once veneer or paint is applied?

C37 lacquer was the rage 20+ years ago. Vaic Valve used it on tubes. I do recall it being used on speaker enclosures too.

C37 Acoustics Dieter Ennemoser - Violin Maker & Acoustic Researcher

 

[je2a3]

I found that my repurposed Altec Madrid boxes sound "more alive" than the 3/4" baltic birch plywood 614 cabinets built by my neighbor in the late 90s. The bottom and back panels were actually particle board. Since the back panels were starting to disintegrate, I replaced them also when I cut new front baffles.


We're running out of storage space because I hate to see vintage Altec cabinets thrown into the dumpster.😉 So here's another goodie, a pair of Altec Coronado cabinets (3/4" plywood except for particle board back panels)! I compensate for the inverted 32 horn orientation by listening on a low slung recliner.😊

 

[Salectric]

I compensate for the inverted 32 horn orientation by listening on a low slung recliner.😊

Or just stand on your head.

 

[Roscoe65]

I wish I had your dumpsters. the NYC metro area has been pretty much picked clean for years. I also don’t think as much altec home stuff made its way to the east coast.

 

[je2a3]

I wish I had your dumpsters. the NYC metro area has been pretty much picked clean for years. I also don’t think as much altec home stuff made its way to the east coast.

I got the Altec Madrid pair at a hamfest (for free) shortly before I moved to Manila in '08. They sat in my aunt's basement until I returned in 2016. I got the Coronado boxes last year. That's a 13 year gap!

 

[FloriduhBoy]

I wish I had your dumpsters. the NYC metro area has been pretty much picked clean for years. I also don’t think as much altec home stuff made its way to the east coast.

Vintage audio on Craig List seemed to be nonexistent in Florida. But, late to the party, as usual, I'm finding interesting stuff on Facebook Marketplace.

 

[Roscoe65]

I accept that every cabinet will vibrate, whether I try to dampen it or not. In a way, every speaker cabinet is a tone cabinet. In the case of an Altec 614 the cabinet has a radiating area about 27 times that of a single 414A driver. It doesn’t take much vibration to add significantly to the musical output. A YouTube video displays a gentleman rapping on a 614 cabinet with his fist and then a rubber mallet. Each surface was far more live than anything I’ve had in my house and each panel resonated at a different frequency. One would imagine that the enclosure would have a number of vibration modes.

In violin and guitar making, birch soundboards are known for a dull sound. By far the most popular material for tone woods is spruce, but pine and other softwoods as well as maple are also used. Traditionally, violin tonewoods were air dried for at least seven years before use. Plywood manufacture uses green wood and dries individual veneers before glueup. The wood is dry and has had some accelerated aging due to the heat press, but is still fresh wood. When you cut the sheet the cut edge will be a little sticky from the resin. Over time (years) this resin loses moisture and polymerizes, essentially turning into a hard varnish internal to the wood. These same resins were among those used in traditional violin varnishes. There are some who are torrifying tonewoods. This anaerobic roasting effectively fast-cures wood, producing the caramelization, drying, shrinkage, and hardening that would naturally take decades or centuries. The valued properties include

Regarding finishes, I would follow the luthier approach as well. In both violins and guitars, a hard finish is desired, since the soundboard would be dampened by a softer, flexible finish. Shellac and lacquer are commonly used for guitars, and violin makers use their own esoteric varnishes, some of which contained ground minerals which added to hardness. A common practice is to really thin down the sealer coat (or the ground coat for violins) to maximize penetration into the wood. As the resin polymerizes, it will harden deeper in the surface of the wood. A really thin shellac coat would deeply penetrate and be a perfect base coat for anything that followed. An oil finish, such as well-thinned boiled linseed oil would penetrate equally well but would take years to build and fully polymerize ( the traditional recipe was to apply the oil once a day for a week, once a month for year, and once a year for life). The surface coat can be the same as the sealer coat. Shellac works really well and is very repairable. It will harden well if you use thin coats (or French Polish) but will still take months to fully cure. Oil finish pretty much means you are stuck with oil, but shellac is compatible with anything. If I were painting them I would go with a lacquer over the sealer coat. I would want to avoid plasticizers.

 

[FalseMetal666]

the traditional recipe was to apply the oil once a day for a week, once a month for year, and once a year for life

Violin making is so cool

 

[FloriduhBoy]

I accept that every cabinet will vibrate, whether I try to dampen it or not. In a way, every speaker cabinet is a tone cabinet. In the case of an Altec 614 the cabinet has a radiating area about 27 times that of a single 414A driver. It doesn’t take much vibration to add significantly to the musical output. A YouTube video displays a gentleman rapping on a 614 cabinet with his fist and then a rubber mallet. Each surface was far more live than anything I’ve had in my house and each panel resonated at a different frequency. One would imagine that the enclosure would have a number of vibration modes.

In violin and guitar making, birch soundboards are known for a dull sound. By far the most popular material for tone woods is spruce, but pine and other softwoods as well as maple are also used. Traditionally, violin tonewoods were air dried for at least seven years before use. Plywood manufacture uses green wood and dries individual veneers before glueup. The wood is dry and has had some accelerated aging due to the heat press, but is still fresh wood. When you cut the sheet the cut edge will be a little sticky from the resin. Over time (years) this resin loses moisture and polymerizes, essentially turning into a hard varnish internal to the wood. These same resins were among those used in traditional violin varnishes. There are some who are torrifying tonewoods. This anaerobic roasting effectively fast-cures wood, producing the caramelization, drying, shrinkage, and hardening that would naturally take decades or centuries. The valued properties include

Regarding finishes, I would follow the luthier approach as well. In both violins and guitars, a hard finish is desired, since the soundboard would be dampened by a softer, flexible finish. Shellac and lacquer are commonly used for guitars, and violin makers use their own esoteric varnishes, some of which contained ground minerals which added to hardness. A common practice is to really thin down the sealer coat (or the ground coat for violins) to maximize penetration into the wood. As the resin polymerizes, it will harden deeper in the surface of the wood. A really thin shellac coat would deeply penetrate and be a perfect base coat for anything that followed. An oil finish, such as well-thinned boiled linseed oil would penetrate equally well but would take years to build and fully polymerize ( the traditional recipe was to apply the oil once a day for a week, once a month for year, and once a year for life). The surface coat can be the same as the sealer coat. Shellac works really well and is very repairable. It will harden well if you use thin coats (or French Polish) but will still take months to fully cure. Oil finish pretty much means you are stuck with oil, but shellac is compatible with anything. If I were painting them I would go with a lacquer over the sealer coat. I would want to avoid plasticizers.

Fleetwood Sound Deville SQ speakers use torrified wood.

Fleetwood Sound Company DeVille SQ loudspeaker

Oswalds Mill Audio's products espouse a sort of steam-punk-meets-modern visual style, but the company's philosophies are straight from hi-fi's '50s and '60s glory days, an era when idler-drive turntables, low-power tube amps, and horn-loaded loudspeakers were the norm. That history and hi-fi's...

www.stereophile.com

 

[Roscoe65]

Fleetwood uses torrified Ash. Gibson and a couple of other guitar makers use terrified tonewoods. Torrification accelerates shrinking and hardening and produces some of the tonal characteristics of age. Not everyone agrees that the tone is the same as naturally aged wood but the resulting product is dry, fully reduced in size, and stable. Fleetwood uses solid Ash in the cabinet, so stability is of importance. Ash is not very popular as a tonewoods except for electric guitar bodies.

 

[FloriduhBoy]

Fleetwood uses torrified Ash. Gibson and a couple of other guitar makers use terrified tonewoods. Torrification accelerates shrinking and hardening and produces some of the tonal characteristics of age. Not everyone agrees that the tone is the same as naturally aged wood but the resulting product is dry, fully reduced in size, and stable. Fleetwood uses solid Ash in the cabinet, so stability is of importance. Ash is not very popular as a tonewoods except for electric guitar bodies.

Stability, not tone, is likely why it was used.

 

[MrEd]

I think my departed friend Bill Collings of Collings Guitars would absolutely cringe over using torrified wood.

 

[Aleixo_Camara]

heres that tapping video mentioned above - this is lajazzaudio



as to the vintage ply photos in page one. boy is that familiar - it was all over gramma's house...may go back and remodel the floor in the back room !

as with everything - materials are not the same as they used to be - transformers/iron/non fda approved chems etc. tubes are not the same, and pulp is not the same so as musicians know modern 'clones' of vintage celestion jensen etc are never the same as the originals...it comes down mostly to old growth trees. yes glues where different too. but those pics of teh old ply made of old growth have a quality easily sensed either by eye or tapping...so yes that old ply and modern 13 ply BB are different beasts....

am in process of sourcing ply for a build and will likely do a mix of baltic birch and either a cheaper 6 ply or maybe even a bit of particle board for a back or bottom....will just go and tap and visualize and let intuiton guide the build


also, towards the bottom of post one page one...did the originator of this thread mispeak/type when he said

..... Latex of course the soft binder which gives the plywood a slight rubbery feel when you pick into it on the edges or in the fill areas.... This type of pine flooring grade plywood that is made for outdoor use is still a choice you can go with – I even recommend this over the much prettier Baltic birch ply if you are after the Classic American sound......


This seems 180 degrees from the other info where he suggests that plywood that is built to take on moisture is the one to avoid (ie exterior ply)....interior ply as seen in those pics he posted is not for wet use.....so I believe he meant to type INTERIOR there and not exterior...unless w'ere missing something as is often for me....anyone?



one last observation regarding the tapping vid....whenever you tone tap and A/B a piece(s) of wood the dimensions obviously need be the same...these two cabs with identical measurements have that variable taken out....also he needs to tap in exactly same spot on each.....at times hes a bit off it seems and other quite close..and yet the tap tone is different for that 'same spot'....i can only surmise that is either because on the inside there is different baffles or filling or something is different. or the joinery on one of the cabs somewhere, has separated a bit compared to the other....this would make one cab's tap tone different from the other.only other explanation is that the two cabs used different wood...not different per say, but the same plywood from different stacks/batches . its either one or both of those variables, or the mic position picked the two cabs up different.....one would think those cabs should tap damn near the same otherwise....we'll never know but still the tones generally themselves are interesting to hear......anyone know what era those cabs are and what altec was using then? ie is he tapping particle board era, plywood era or the era when they used a mix of the two?



one last idea- regardless of what wood ones chooses...the after the fact bracing can then be used to tune your cabs. but only if you first build a 'active' cab...if you start out dense ded mdf. then you cannot lighten it up but you can go from active to less active - to a degree.......this is what i intend to do after basic cab is built and 'tapped'......but while building will have to commit to the joinery decision...so hard to decide

may go with basic lengthwise running rabbets on side/top/bottom joints. and will likely dado/inset and glue in the front baffle vs attaching it with 1x2/screws as altec seemed to do? need to find more pics to see how they did the baffles - probaly depends on the model.. but it seems they tended to leave them a bit 'rickety' and not rigidly integrated with dado/glue....that is a feature im reluctant to copy and so intend to dado/glue but if anyone can talk me out of this in favor of a simple 'screw with 1x2 that are glued to the front interior cabinet sides' approach, please advise



one last problem ! i recall in the altec literature, when specifying cab construction they mention making sure material choice for the sides i believe, needs to account for 'sheer strength'...so i assume a 13 ply rigid BB would suit that...problem is they didnt say whether that was for tone reasons or maybe for more practical rigid/shipping considerations....overall it doesnt seem altec spent alot of time on their cab construction and probably just got lucky to some degree much like jim marshall did with his instrument cabs...a bit of experimentation, look at what material is cheap and available and its off to the races , is my guess as to what happened. so may not want to take too much effort into replicating Altec. other than their dimensions, they probably got down. As many have since seemed to enjoy and not find fault with their basic box design... Which again though is odd. as isnt the basic rule not to use squares and rectangles as speaker boxes? shouldnt at least one of the 4 surfaces be a few degrees angled at least? This is another variable im considering to add. one side angled in maybe 10 degrees rather than a rectangle....