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

[hifitown]

I have a pair of Goodmans Twin Axiom 10s and am considering using pine or Douglas Fir for the enclosures.

20+ years ago I was researching enclosures and found quite a few designs from the 1930's that sure appeared to be resonant. So does the Telefunken OB enclosure. I did not save them and now they don't come up in a search. I had a pair of Auris speakers from Hans Kortenbach, RIP, that were resonant. The front baffle was Sitka Spruce. The cabinet shape was named Rondo came up when I searched back then. Havenite efud made a pair with Betsy drivers.

6moons.com - industry features: Will the original please stand up?

http://www.auditorium23.de/Speakers/SoloVox_AW.pdf

A cabinet patent from 1954 mentions resonance.

Cool post thanks. Resonance is a big deal for sure. Surely takes us further down the rabbit hole of what to do in cabinet design.

I think it's fair to say that most of these cabinets,( so long as they are not sealed boxes intended to be dead ie AR1/AR3...and all others since)... depend on techniques that accentuate low frequencies in a semi resonant manner. That's why it's very important to use wood that is hard, has a nice tonality, and that it's it's not too dark or dead etc.

Going overboard on rigidity, thickness or "deadness" may actually reduce the enjoyment factor of many bass reflex, some ported and most certainly open baffle designs.

We may have had some of those Tele OB cabs in our heydey of that in the 90s.. I would agree – – the Germans were thinking of res on the thin plywood there a little bit, maybe not allot. Interestingly enough, Auditorium23 must've picked up the name from the Hammond Solovox cabinet of the (early 50s? maybe?) ... it was a potentially resonate design (on purpose).. and a very simple open baffle "Tone" cabinet. Very streamline 1940s for a 8 or 10" as I recall. Our exporter used to have a bit of luck with those in Japan. I am not sure if they were ever practically used. The A_23 build is much more complex for sure.

In the Summer/Fall of 1989~till 1991 or so, Walt setup a wood shop, and added a carpenter to payroll.... He made jigs and built a few of his 1st gen Airwave cabinets for the Western Electric 755. I think it was going to be an export product to Japan, but I don't recall. We all liked it. Walt's was not totally happy with the non-vented (but surely leaky Altec 618, and or others spec'd to fulfill Western's very vague CuFt recommendation in the 1940s Literature. By the late 1980s, calls came in almost daily on how best to construct enclosures for the newfound interest in the magical WE 8"incher..so he saw the need.

The Altec 618 universal slant cabinet is often copied in 3/4" Birch ply.. Potential builders take note, as the originals were made from 1/2" or so, ridiculously thin, ridiculously hard pine plywood with very little bracing. The cabinet is extremely resonant, a bit boomy to me. It still sounds great in most settings if off the floor...... perhaps thanks to the material.. I'm guessing Walt drew some inspiration from the good sound of this cabinet and intended to improve upon it's good qualities.

I still have a lot of the hardwood sides, which serve as structure and bracing... (in exotic species like Purple Heart, and other very hard woods) to build these cabinets and the design – – rigid in places, and not in others... Here's One of the Yellow prototype cabinets we've loaned out to a few friends over the years. The front body of the cabinet is made out of bent 16th inch acoustic plywood.... sounds nice and looks beautiful...and it was allot of work (would be easier now).... And for the next 25 years he recommended open baffle for the 755A... Because he really liked the efficiency and clarity that OB gives so well...and gives almost anyone an easier route for less expense.

American instruments Airwave cabinet, circa 1989 for 755A

 

[FloriduhBoy]

I don't know what the Germans/ Europeans intended regarding resonance with thin wall cabinets, but the older cabinets do appear to resonate like a musical instrument. Drivers in that era were pretty efficient and driven by low-power tube amps. Things changed when high power SS amps became the norm.

 

[Felice]

I would like to add; My Westrex 828 cabinets from the - estimated late forties early fifties were not painted. There are no traces of glue. But you can see the rusty screws wonderfully. When empty, the cabinet can almost be lifted with one hand.
Is painting an issue? Applied thickly or thinly or not at all?
Felice

 

[RPMac]

I would like to add; My Westrex 828 cabinets from the - estimated late forties early fifties were not painted. There are no traces of glue. But you can see the rusty screws wonderfully. When empty, the cabinet can almost be lifted with one hand.
Is painting an issue? Applied thickly or thinly or not at all?
Felice

Another option would be tung oil. Give some life and shine to the wood, but won’t hide the “character/age”.


I love old wood. I have some ruff cut boards that the tree was probably over 100 years old before it was cut 100 years ago.

 

[Roscoe65]

Do we know what type of paint was used on the early gray cabinets?

 

[prime minister]

I don't know what the Germans/ Europeans intended regarding resonance with thin wall cabinets, but the older cabinets do appear to resonate like a musical instrument. Drivers in that era were pretty efficient and driven by low-power tube amps. Things changed when high power SS amps became the norm.

This is what concerns me some about this approach. Rather then creating a reasonably neutral sounding reproducer of the recorded music, wouldn't we be designing a Musical instrument that dramatically effects the sound of the recording? It seems counter to what the commonly understood goals of "high fidelity" equipment seem to be.

All that being said, I've got no issue with someone liking the sound it produces. Whatever floats your boat.

 

[FloriduhBoy]

This is what concerns me some about this approach. Rather then creating a reasonably neutral sounding reproducer of the recorded music, wouldn't we be designing a Musical instrument that dramatically effects the sound of the recording? It seems counter to what the commonly understood goals of "high fidelity" equipment seem to be.

All that being said, I've got no issue with someone liking the sound it produces. Whatever floats your boat.

These were designs from days gone by when low-power tube amps and efficient speakers were the norm. I have a NOS pair of these coming. I found/ stumbled upon the Philips recommended enclosure size and will give them a try. They are the 7 ohm version 97/98db, large Alnico magnets, and a max of ten watts. Bing or Belefonte, acoustic jazz, etc. sound beguiling. Electronica and Metal need not apply.

John's Radio Web, mijn verzameling historische radio's

www.hupse.eu

With today's drivers and high-power amps, an inert box is required.

 

[mrgoodsound]

This is what concerns me some about this approach. Rather then creating a reasonably neutral sounding reproducer of the recorded music, wouldn't we be designing a Musical instrument that dramatically effects the sound of the recording? It seems counter to what the commonly understood goals of "high fidelity" equipment seem to be.

All that being said, I've got no issue with someone liking the sound it produces. Whatever floats your boat.

I prefer to think of it as resonating in tune with the recording, whereas the stiff cabinet does not want to keep time with the music and something is lost, if that makes any sense. It is difficult for me to listen to speakers in inert or non-resonate cabinets without becoming bored or fatigued quickly. The most fun I can have with such systems are when they involve horns, but then I become fatigued for other reasons.

In Russian forums, the topic of open-backed and thin-walled cabinets with proportions similar to American radios from the golden era of the 1930s is discussed. Many enthusiasts built systems from old radio speakers using this principle with good results.

Personally I am conducting my own experiments along similar lines. I visited my cabinet builder yesterday who built the boxes below based on my drawings. I asked him to use the thinnest pine he had with minimal bracing. When I told him they were for speakers he looked at me funny.

The grills on the sides are to break up standing waves from internal reflections. The grill on the front acts as a diffuser for a paper cone speaker. There will be no back wall, or if there is it will be highly lossy (thin and full of holes). I dropped off some special primer and varnish and hope to get the final product in a few weeks.

 

[Salectric]

I prefer to think of it as resonating in tune with the recording, whereas the stiff cabinet does not want to keep time with the music and something is lost, if that makes any sense. It is difficult for me to listen to speakers in inert or non-resonate cabinets without becoming bored or fatigued quickly. The most fun I can have with such systems are when they involve horns, but then I become fatigued for other reasons.

In Russian forums, the topic of open-backed and thin-walled cabinets with proportions similar to American radios from the golden era of the 1930s is discussed. Many enthusiasts built systems from old radio speakers using this principle with good results.

Personally I am conducting my own experiments along similar lines. I visited my cabinet builder yesterday who built the boxes below based on my drawings. I asked him to use the thinnest pine he had with minimal bracing. When I told him they were for speakers he looked at me funny.

The grills on the sides are to break up standing waves from internal reflections. The grill on the front acts as a diffuser for a paper cone speaker. There will be no back wall, or if there is it will be highly lossy (thin and full of holes). I dropped off some special primer and varnish and hope to get the final product in a few weeks.

View attachment 49276

Interesting to say the least! Of course your post raises some questions:

Will you be using a full-range driver on the front?

What are the grill/diffusor strips near the floor on the side?

What thickness plywood did the builder use?

 

[prime minister]

These were designs from days gone by when low-power tube amps and efficient speakers were the norm. I have a NOS pair of these coming. I found/ stumbled upon the Philips recommended enclosure size and will give them a try. They are the 7 ohm version 97/98db, large Alnico magnets, and a max of ten watts. Bing or Belefonte, acoustic jazz, etc. sound beguiling. Electronica and Metal need not apply.

John's Radio Web, mijn verzameling historische radio's

www.hupse.eu

With today's drivers and high-power amps, an inert box is required.

Just so I understand, wouldn't low bass notes even with big drivers/low powered amps still cause noticeable cabinet resonances? Do you give up low bass? Would you not want a speaker that handles all kinds of music well?

 

[prime minister]

I prefer to think of it as resonating in tune with the recording, whereas the stiff cabinet does not want to keep time with the music and something is lost, if that makes any sense. It is difficult for me to listen to speakers in inert or non-resonate cabinets without becoming bored or fatigued quickly. The most fun I can have with such systems are when they involve horns, but then I become fatigued for other reasons.

In Russian forums, the topic of open-backed and thin-walled cabinets with proportions similar to American radios from the golden era of the 1930s is discussed. Many enthusiasts built systems from old radio speakers using this principle with good results.

Personally I am conducting my own experiments along similar lines. I visited my cabinet builder yesterday who built the boxes below based on my drawings. I asked him to use the thinnest pine he had with minimal bracing. When I told him they were for speakers he looked at me funny.

The grills on the sides are to break up standing waves from internal reflections. The grill on the front acts as a diffuser for a paper cone speaker. There will be no back wall, or if there is it will be highly lossy (thin and full of holes). I dropped off some special primer and varnish and hope to get the final product in a few weeks.

View attachment 49276

Again, and there is no judgement at all in what I am saying, it sounds to me like you are making a musical instrument, rather then a loudspeaker, as it is usually understood. Your driver, as it were, is not just the driver, but the combination of the driver and the box.

 

[hifitown]

This is what concerns me some about this approach. Rather then creating a reasonably neutral sounding reproducer of the recorded music, wouldn't we be designing a Musical instrument that dramatically effects the sound of the recording? It seems counter to what the commonly understood goals of "high fidelity" equipment seem to be.

All that being said, I've got no issue with someone liking the sound it produces. Whatever floats your boat.

I completely agree with this sentiment! It's a very tradditional, and logical.... some might say postwar view of audio reproduction in a Normal WAF restricted audio-space.
The problem is, almost no reproducer is going to meet that criteria. On can certainly attempt it... 1000's of watts, active EQ's, DSP's, sand filled CNC framed reinforced Laboratory speaker playing in an anechoic chamber --- maybe you'll get it flat..... (and in then end, those don't sound great either).
You're attempting to go that route with a monitor sized or bookshelf size to speaker – – I don't think it's possible you're just going to get 52 different flavors of the same thing. There are definitely some good speakers this size and so many bad ones.
It's arguable that some of the new attempts at it with aluminum cone speakers are pretty formidable (like the much heralded ELAC Unifi series) – – but I haven't heard any of those that I would call "balanced neutral" or "non fatiguing".

The original AR LST speaker was incredibly flat, non resonant speaker that comes to mind. It took a lot of power to drive it – – but it was very good and just plain eerie sounding. I'm not sure you could live with it indefinitely. The Western Electric 757 was also designed to perform this way... and is a mostly flat sounding speaker (if we are talking vintage).
So you definitely have a point – – you have to be very careful dealing with "boominess" and colorations when you are doing bass reflex, sound panels, labyrinthine or any sort of porting.

The large Cinema systems the really big ones – – did sound pretty darn neutral. (not perfect, but very good). They were big because they had to be sensitive efficient -- the pleasant colorations that they do impart and there are few – – or merely a side effect of the really good performance of that old plywood..

Since the 1930s, it's all been about miniaturization and marketing. If you look at the spiel when the first acoustic suspension speakers came out – – they were very much about laying out the problem with bass reflects and other ported designs. That's true, but they weren't talking much about their very huge problem -- excessive power consumption and far less than perfect frequency response (read Hump!) characteristics.

Well you certainly don't want to go for a jukebox sound – – it is possible to work with resonance – – a good place to start with is nice sounding would like spruce and not necessarily very thick. The results can be absolutely musical and surprisingly accurate.

 

[hifitown]

I prefer to think of it as resonating in tune with the recording, whereas the stiff cabinet does not want to keep time with the music and something is lost, if that makes any sense. It is difficult for me to listen to speakers in inert or non-resonate cabinets without becoming bored or fatigued quickly. The most fun I can have with such systems are when they involve horns, but then I become fatigued for other reasons.

In Russian forums, the topic of open-backed and thin-walled cabinets with proportions similar to American radios from the golden era of the 1930s is discussed. Many enthusiasts built systems from old radio speakers using this principle with good results.

Personally I am conducting my own experiments along similar lines. I visited my cabinet builder yesterday who built the boxes below based on my drawings. I asked him to use the thinnest pine he had with minimal bracing. When I told him they were for speakers he looked at me funny.

The grills on the sides are to break up standing waves from internal reflections. The grill on the front acts as a diffuser for a paper cone speaker. There will be no back wall, or if there is it will be highly lossy (thin and full of holes). I dropped off some special primer and varnish and hope to get the final product in a few weeks.

View attachment 49276

Cool! thank's for speaking several point of blasphemy I don't often delve into.

One point here is, that it's not often – – maybe even never said. Cabinets don't add anything to the speaker. They are there for one reason – – to block the rear wave. They add no energy... they shape it, squeeze it, you name it....most of it's not good for sound reproduction, at least on paper....

When you construct a cabinet that resonates at frequencies that are non-boomy and non, shall we say.. parasitic(?) -- the sound can be second to none... all highly subject to the speaker or speaker/driver combo you choose to tackle.

The open baffle is the purest form, (and always recommended) of this, which is also why it has the least coloration. But of course, very few spaces will allow a large enough baffle to equivocate to most small cabinets.

Hope this implementation works out....I expect it will be pretty good when you find the right driver.
Reminds me allot of the early 1930s "tone cabinets"... made by Jensen, and Lyon/Healy, typically the size of a bedroom dresser.
Most of them were open back (or highly lossy)..they used 18" woofers, with a hearty low FS of high 30's... so they did not need much enclosure..
If you could ever get all the field coil parts working...they sounded like the look... glorious & grand, very full range and realistic.
The Art Deco water fall grille is fairly rare... this is the true, original Jensen Imperial. Units to follow, also carried the name, well into the 1960s. The Federal Telegraph Co / Lyon Healy cabinets utilize director vanes (shaped like air vent louvres) -- which did appear to be active for dispersion.

 

[FloriduhBoy]

Just so I understand, wouldn't low bass notes even with big drivers/low powered amps still cause noticeable cabinet resonances? Do you give up low bass? Would you not want a speaker that handles all kinds of music well?

Use a preamp with a subwoofer out and be amazed. After a bad day at work, hit play...immediate chill. It may not be accurate but you will be transported.

 

[prime minister]

Use a preamp with a subwoofer out and be amazed. After a bad day at work, hit play...immediate chill. It may not be accurate but you will be transported.

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

 

[hifitown]

Use a preamp with a subwoofer out and be amazed. After a bad day at work, hit play...immediate chill. It may not be accurate but you will be transported.

I know, I don't disagree with this sentiment. In fact when when we were building purposefully resonant horns in the early 2000s – we did plan on a sub...

The plan was to use a fairly low wattage subwoofer – – a.k.a. a very fancy version of what you used to see in Walmart dubbed "the 2.1 system" (now a thing of the past...TV's are on to line arrays...woohoo).

The system sounded spectacular for mids and highs – – and the sub did well to fill in a very broad spectrum but humpy collection of lows.
But they were lots of upper-mid bass frequencies missing – – and the whole thing was – – I think the term "shuttered"...

It's a well regarded technique in ProSound to deliberately not reproduce problematic frequencies between deep Lows and easier to reproduce mid range and high frequencies.
In fact most modern sound installations they just completely notch out any particular area they don't like....how uncool is that?

In the end we went with a different way to reproduce low frequencies. The horns worked well with bass reflex and also acoustic-resonant boxes. Just like above posters are talking about. Much more realistic sounding and a 100 times more efficient.

Subwoofers can make everything too dull or cloudy – and as you said... not realistic – and while they are totally fun to chill out to for a little while – – eventually at least me – – I get pretty bored with the sound.

Of course modern music – – has subwoofer bass mixed in it with "triggers".
So how could we call it unrealistic?

 

[mrgoodsound]

Interesting to say the least! Of course your post raises some questions:

Will you be using a full-range driver on the front?

What are the grill/diffusor strips near the floor on the side?

What thickness plywood did the builder use?

You can use a variety of driver configurations from just one driver to a driver + tweeter (I will be using the coaxial Isophon PH2132E) to a full three-way. The selection of drivers will depend on the Quality factor Qts, resonant frequency Fs, choice of amplifier topology. A triode amplifier without NFB and a high output impedance will want a lower Qts value to avoid mumbling near the resonant frequency.

The side grills are to provide relief and break up standing waves occurring up and down the side walls of the cabinet. Without them, there will be 'mumbling' near the resonant frequency of the bass driver (or full-range).

These cabinets he would not make them quite as thin as I wanted The side walls are real pine, 20mm. The front baffle is maple ply, 1/2"

Just so I understand, wouldn't low bass notes even with big drivers/low powered amps still cause noticeable cabinet resonances? Do you give up low bass? Would you not want a speaker that handles all kinds of music well?

It depends a bit on your definition of low bass. I listen to a lot of rock music and other modern music and absolutely want a speaker that handles all kinds of music well. I am currently using my 1960s Isophon drivers in an open-backed box that is smaller than the one I showed in the photos and I do not feel a deficiency in bass output. The only issue is excitations near the resonant frequency of the Isophon woofer which causes 'mumbling' in the lows. This is because their current box was not designed to be used without an open back, but rather a cheaply made bass reflex by the Canadian Isophon distributor Noresco in the 60s. As soon as I got the speakers I removed the back panel and the sound improved in every dimension, except for the low frequency mumbling.

For this project I decided to keep the cabinet proportions more or less the same and just scale them up and add resonance relief in the form of side grills to combat the 'mumbling' issue. If everything goes well I will expand the design to be even larger (floor standing) and add a dedicated 15" woofer, in which case there will be no qualms about output to 20Hz. The cabinets in the photos will still go on stands, raised about as much as Altec Valencia's would be off the floor.

I have had a few people over to listen to the current iteration of the speakers and they were all surprised by the prodigious bass output of the oval Isophon woofer, in an open box, with a 2 watt Philips amp!

 

[Salectric]

You can use a variety of driver configurations from just one driver to a driver + tweeter (I will be using the coaxial Isophon PH2132E) to a full three-way. The selection of drivers will depend on the Quality factor Qts, resonant frequency Fs, choice of amplifier topology. A triode amplifier without NFB and a high output impedance will want a lower Qts value to avoid mumbling near the resonant frequency.

The side grills are to provide relief and break up standing waves occurring up and down the side walls of the cabinet. Without them, there will be 'mumbling' near the resonant frequency of the bass driver (or full-range).

These cabinets he would not make them quite as thin as I wanted The side walls are real pine, 20mm. The front baffle is maple ply, 1/2"



It depends a bit on your definition of low bass. I listen to a lot of rock music and other modern music and absolutely want a speaker that handles all kinds of music well. I am currently using my 1960s Isophon drivers in an open-backed box that is smaller than the one I showed in the photos and I do not feel a deficiency in bass output. The only issue is excitations near the resonant frequency of the Isophon woofer which causes 'mumbling' in the lows. This is because their current box was not designed to be used without an open back, but rather a cheaply made bass reflex by the Canadian Isophon distributor Noresco in the 60s. As soon as I got the speakers I removed the back panel and the sound improved in every dimension, except for the low frequency mumbling.

For this project I decided to keep the cabinet proportions more or less the same and just scale them up and add resonance relief in the form of side grills to combat the 'mumbling' issue. If everything goes well I will expand the design to be even larger (floor standing) and add a dedicated 15" woofer, in which case there will be no qualms about output to 20Hz. The cabinets in the photos will still go on stands, raised about as much as Altec Valencia's would be off the floor.

I have had a few people over to listen to the current iteration of the speakers and they were all surprised by the prodigious bass output of the oval Isophon woofer, in an open box, with a 2 watt Philips amp!

I am still stuck on the side grill. Is it just a grill on the exterior or does it cover holes or vents in the side? If the latter, does the hole in the side wall reduce the low frequency reinforcement of the open baffle?
And is there a grill on each side or just one?

Lastly are there any details of the cabinet design online?

 

[mrgoodsound]

I am still stuck on the side grill. Is it just a grill on the exterior or does it cover holes or vents in the side? If the latter, does the hole in the side wall reduce the low frequency reinforcement of the open baffle?
And is there a grill on each side or just one?

Lastly are there any details of the cabinet design online?

There is a rectangular hole cut in the side wall and the grill sits on top of that. Both sides. You could get the same results cutting the slots directly into the sidewall, but I preferred the aesthetics of having the cover. You don't really lose lows (completely ditching the side walls would do that), only reduce the build-up of parasitic resonances.

All the details are in Russian forums, scattered across different threads by different authors. The original design can be credited to Anatoly Likhnitsky, or rather his father, who built a similar case modelled after an American radio console from the 1930s (black and white photo below); and Sergey Shabad, who was a friend of Likhnitsky and prepared diagrams based on the proportions of that homemade cabinet. I share some relevant photos below, but not wanting to hijack this topic I will open a new topic once my cabinets are done with more details.

 

[Salectric]

Very cool! Thanks for the info and photos. I will keep an eye out for your thread dealing with the new cabinets.