Therefore, there would be many cases where MDF with high vibration damping has been used recently. However, I think that such a design concept itself has made it difficult to reproduce the sound with rich musicality, that is, “Real-Sound” that I have pursued or long looked for.
Certainly, the design concept of the Altec Corona, which Alan-san and Paula-san considered to be good and have enjoyed over the past few years, is completely different from that of recent years.
First of all, the material of the speaker box is made of plywood by “Douglas fir” which easily resonates, furthermore, the area of the baffle board is large and the internal reinforcement, also the use of sound absorbing material seems almost requisite minimum.
Inside the vintage Altec 832A Corona loudspeakers.
Isn't it really designed to sound the box as well? Certainly, I think that the material selection and such structures were based on a design concept far from the recent designing of speaker cabinets. For my personal taste, I far prefer a speaker box that sounds beautiful and isn't too robust of a structure, made from this near-natural material.
Now, I would like to talk about my very personal experiences from the perspective of this woodworking material and sound quality. It's been around 15 years ago, but in my final career at Pioneer, I was given the chance and actually developed a speaker on my own.
In the early summer 2006, Pioneer's US branch opened a fashionable retail store at South Coast Plaza in Costa Mesa, CA. As one of the highlight products sold only at this directly managed store, I was in charge of developing audio-video equipment that looked like high-grade furniture in combination with Pioneer's 60-inch plasma TV, which had highly evaluated picture quality at that time.
The planning of this product was also based on the idea of only a few members, including myself, and also a good collaboration with the gifted person in charge of the managing this shop.
I naturally struggled to design the speaker for the first time, which was built into the furniture. However, what was useful here was the various kinds of experiences about woodworking and a lot of wooden materials in Semarang, Indonesia, as well as technical information on musical instruments obtained from the engineers of Yamaha and Roland.
Furthermore, in my personal hobby area, I had enjoyed the self-made speaker system by Altec 414A, Onken 500MT driver, 5000T Esprit tweeter for a long time, so I had some knowledges of LC network.
Well, first of all, from a preliminary experiment, I adopted the relatively strong Pioneer 12-inch subwoofer unit for the woofer. This was because the rich and the enveloping low frequencies of this 12-inch woofer never appeared in two 8-inch woofers with almost the same diaphragm area.
As the material for the speaker box, I dared to use “laminated solid panels” made of European or German spruce imported from Austria. Compared to ordinary plywood, this board is made from much thicker board than each of the usual laminated boards (more HERE).
I was fascinated by the thickness of each piece, because I thought that it would be possible to fully demonstrate the goodness or beauty of spruce sound.
You might have known well, spruce has long been used in the soundboards of many acoustic instruments, for example, violin, guitar and piano.
In short, I considered the speaker to be an instrument as well. But, of course, the more experienced speaker designers are, the less likely they would be to make such a bold and radical attempt.
I’d like you to think about it, is there any speaker unit or driver in the world, all ages and countries that has the right physical characteristics?
Compared to other electronic devices such as amplifiers, the size and the shape of the uneven peaks and valleys of frequency characteristics and impedance characteristics would be even pessimistic. For example, single-cone and double-cone speaker units designed to cover the full range always have to compromise on how to balance the low and high frequencies, and the high frequencies could be somehow maintained by the divided vibration of diaphragm. This divided vibration can be said to be a mass of undesirable 3rd distortion, and of course the time axis could be shaken by its complicated phase fluctuation.
Given that, this would be a natural result that we can't expect so-called coherent reproduction. Of course, since this colors the overtones, there were cases where the glossiness was evaluated and liked, and I know that there have been still many fans who like this. But this could be one of the signs to the fact that a speaker driver would be more like a musical instrument than a converter that accurately converts electrical energy into mechanical energy.
Well, even the 2-way or 3-way speaker system has various contradictions. For example, an LC network that divides the current at a certain frequency, but the inductor itself would be a mass of contradictions. A pure inductor cannot exist because any inductor, with or without a core, consists of a coil of copper wire or copper foil, and there is always a resistance component in it. It can be said that this resistance component wastes the useless current and the voltage drop here will slow the rise of the diaphragm. In particular, the inductor for low frequency division inevitably has a large inductance and also unignorably resistance factor.
Therefore, in some cases, an inductor with iron core, which has a smaller resistance, may be preferable to an air core coil in terms of sound quality. And, regarding the relationship between the wire diameter of the coil and the sound quality, if the copper wire is thick, the resistance value of the coil can be made smaller, but it may be related to the current value that flows, from the point of view of skin effect, it is hard to say that the thicker wire would be well-balanced in sound quality.
Even just considering the above few examples, speaker development and design requires how to overcome too many contradictions compared to the designing of amplifiers, which manages voltage or current amplification with pure electrical energy.
I don't think it can be overcome simply by the technical level of the designer. Of course, the musical background and the innate sense of the designer would be also an extremely important factor, and it is just a craftsmanship that requires deep experiences.
So, I hope you understand what I mean by saying that a speaker is an instrument.
Well, please allow me to repeat it a little, among the various approaches, I first sought the richness of the low frequencies and so I selected a 12-inch woofer, which would be rare in recent years, and a special plywood made of spruce for the box including baffles.
There's a good reason I like the spruce material and the Douglas fir used in the vintage Altec speaker boxes.
First of all, I would like you to confirm that both spruce and Douglas fir are woods that are classified as coniferous trees. To put it simply, they are materials that are particularly easy to resonate among a lot of wooden materials, but from a physical point of view, they can be said to be the wooden material with a higher vibration transmission speed.
This vibration transmission speed is said to be expressed as a numerical value obtained by dividing Young's modulus, which is an index of the strength of the material, by the mass of the material. That is, the higher the rigidity of the material and the lighter the material, the higher the transmission speed.
From this point of view, the spruce and Douglas-fir mentioned above have a certain direction, but they have a relatively higher Young's modulus, and on the contrary, they have a lighter mass. As far as I once calculated, its vibration transmission speed is the highest among wooden materials.
Some tropical evergreens have surely high strength and can be submerged in water, but my calculation results show that this transmission rate is far inferior to that of the above conifers. As you know, conifers grow naturally in relatively cold, high altitude areas. That's why these conifers have clear annual rings and are dense, and so the vibration transmission speed in these parts will be high.
On the other hand, the portion sandwiched between the annual rings has a low density and contain tree resin, that is, it is soft and has the effect of appropriately absorbing the vibration. This mysterious balance of nature is probably the qualitative reason why it has been used for the soundboards of various musical instruments since ancient times.
I heard about this, but it is the spruce, which grows naturally in northern Italy, was used for the soundboard of Stradivarius. And also it was said the Little Ice Age, more than three hundred years ago at that time, might have produced good quality spruce with dense annual rings.
Now, I would like to return to the speaker, which was designed to build into the audio-video furniture.
In fact, during this early development stage, I had the valuable opportunity to make the prototype speaker boxes of several different wooden materials, albeit with exactly the same shape and dimension and also the hearing comparison of their sounds.
The materials, which I prepared for the prototype speaker box were the highly versatile particle board, Russian birch plywood with excellent water resistance, an expensive maple single board, and laminated solid panel of spruce.
Even though the built-in speaker unit and the prototype network were exactly the same, the difference in sound depending on the each material was overwhelming, and it could be said that it was amazing result.
What is clear in my memory right now is that only the sound of spruce box was so wonderful in a speaker cabinet. The volume of its sound was rich, the tone more beautiful, and the music far enjoyable.
What I learned from these experiences are that the material of the box has a decisive influence, especially on the mid-low range sound, which is also the most important band of music, and the sound of wooden materials, which have long been considered to have a good sounding and beautiful tone, are uniquely pleasing to the human ear.
From a physical point of view, or the actual measurement results of vibration transmission characteristics using an impulse hammer, this seems to be the result of the higher speed at which the sound rises and the smoothness of the decay waveform.
In any case, the kinetic energy of the diaphragm is received by the baffle plate as its reaction force, but this does not naturally disappear instantly, and the energy is gradually attenuated by the internal loss of the baffle plate. That is, during this period, the baffle plate and also the speaker box will vibrate in some way, and so will generate sound at some minute level.
The sharp hearing of human beings could catch the sound or the noise of these minute vibrations on baffle boards and boxes. Otherwise, the difference in sound quality due to the differences in each material cannot be explained. Vintage speakers like as Altec Corona can be said to have created a very natural and pleasing sound thanks to the high-efficiency units, or the woofers, but also with the help of the comfortable and desirable sound of speaker boxes, which were made of “Douglas fir”.
Now, it should be pointed out that the softwood material was a decisive factor in that vintage Altec woofer's open, comfortable sound quality, with a feeling of bouncy dynamism. It is the cone paper used in the 414A, 803A, 416 series, and 515 series, which was molded from pure softwood pulp that looks pretty normal.
It seems that no surface treatment had been done, and in the hot and humid environment of summer in Tokyo, the sound loses its lightness, probably because it might absorb moisture. However, when the air was clear and the humidity was low, I have felt the original Altec sound, which might be just reminiscent of the pleasant dry breeze of Anaheim, California, where the Altec company used to be located. That cone paper seems more like a breathing creature than an industrial product, which is why it could produce a unique and natural sound that is kind to our hearing.
In the sound quality benefits of such Altec high-efficiency woofers, the most notable one would be the splendid compatibility between the sound and the tone of the horn speakers, I think. Surely, there would be not any sense of discomfort for my hearing.
Anyway, the rise of the mid-low range sound around 400Hz to 800Hz, which is almost the cutoff frequency of the horn speaker, is extremely fast, and so it could not be inferior to the high-speed sound and rich tone emitted from the metal diaphragm of the horn driver.
Of course, that may be due to two major factors, the one would be the lightweight but tough cone paper, which was processed with good quality softwood pulp made of long fiber, and the other would be the powerful magnetic circuit with the valuable Alnico magnet at present. Even so, what a mysterious and strange fact that a diaphragm made of a completely different material produces the same type sound and tone.
Jeff-san might have been feeling just the same way on every listening session in his home, I only suppose (Yes! - Jeff).
Conifers are, of course, are creatures, but the strange relationship between the beautiful and soothing timbres they bring and their physical characteristics, an exquisite balance between strength and softness, or suppleness would be the one of the mysteries that humans can never recreate, and so it’s amazing.
