Subwoofer Materials and Technology (1 Viewer)

[Shawn Solar]

Hello,

I'm in the final stages of completing a research project for my EE course. I am in the misdt of comparing old subwoofer driver materials to those of today. I was just trying to find the most common materials that used to be used. Like what was used for the cone and magnets and anything else that technology has improved. I'm also looking at more sources for design protocol 30yesrs ago compared with today. How much is done by machine vs by hand. Anybody?

Any info or links would really help

 

[StephenHa]

machine to hand built comparos are depending on brand and price level (many high end companies still do hand assembly)

 

[Shawn Solar]

Thanks steve,

I'm trying to keep brand names out of it and focus more on generalization. I suspect that a lot of it is still hand made I just don't how much of the design process this accounts for as compared to 30yrs ago. I Had even a hard time pin pointing when subwoofers really broke into the consumer market. In fact, I had to go back to the first speaker and try to work my way though various manufacturers to try and find the point when the various enclosure designs were first invented. I found a few websites with some info but I basically looked at a few of the older speaker companies like JBL and acoustic research.

I still have to look at newer Technology like adire's XBL^2 and Servo drive to name a few. that along with underhung and overhung designs used. If I have time I might touch on advancements in Suspension technology. Does anyone know which underhung and overhung type coils were used first?

 

[Tim Hoover]

I imagine Kyle at Acoustic Visions and Tom at SVS would probably help with some info, if you can catch them in a spare moment!

 

[Shawn Solar]

Hopefully they'll see "subwoofer" and chime in.

 

[Brian Bunge]

Shawn,

I imagine if you email Dan Wiggins of Adire Audio he can give you more information than you could possibly use.

 

[Mark Seaton]

Hi Shawn,

I would second Brian's suggestion to try and e-mail Dan Wiggins, as he has a great deal of insight into many different ends of driver manufacturing and design, along with some interesting current resources and experience.

While at Purdue I had used a few personal speaker design projects as segments of lab projects for my EE courses. The trick often is to narrow things down rather than trying to cover everything. You learn more, and you find that once you start to account for real world conditions and material limitations there is much more engineering involved than just the theoretical ideal.

So far as materials used in subwoofer design, I would point out that while many like to focus on cone materials, this accounts for a relatively small percentage of subwoofer improvements. Where materials make a huge difference is with magnet density, metalworking tolerances and certainly adhesive and insulating improvements. In many cases what we see today as very high power handling speakers are similar to older designs yet the enamel on the voice coil wire, the adhesives holding the wire to the former, and even the adhesives holding the various parts together can now withstand much higher operating temperatures. We also see cases where heat conductive phase plugs or even metal cones and formers work to better dissipate heat.

This was of course did not occur randomly, but rather evolved with the availability of high power, solid state amplifiers. Conventional loudspeakers are on average ~1% efficient. This means the majority of input power turns into heat, making thermal capacity a real problem when we started increasing available amplifier power by a factor of 2 to 10. With more power we saw justification of higher excursions at low frequencies which we could now usefully produce in realistic packages.

There is certainly plenty to write and study...

 

[Shawn Solar]

Thanks Mark,Brian,

I will now have to rework my paper a little bit. Its actually a bonus and I am not required to do it but, I want to more or less educate some of the people in my course. 90% are under 20yrs old and into car subwoofers and don't have a clue about the physics behind how the subwoofer works. There are also little resources within the college about subwoofers and crossovers and anything speaker related. Even the teachers aren't real sure though most of them are very intellegent electrical and electronic technicians and engineers. I may join the IEEE and also try to make some changes in the school

The thermal limits of a subwoofer is really the driving force in the advancement of "getting louder deeper bass" in other words. well that and the motor stucture. What about the suspension, xmax and surround? Mr. Wiggins expect an email. Mark you too

 

[Shawn Solar]

Anybody else? I'm probably finalize the report tonight. That is not to say it is a done deal. I may add to it over time as I learn a bit more. For now, It looks like this:
Bass 101
What is a Subwoofer?
History of the Subdriver
Advancements in Technology
Design process advancements

Each has a few sub headings (no pun intended) Under it but thats the just of it. I hope the history is correct as You more or less have to look at patents to decide what came out when. Even then enclosure designs are really not patented and circle from each manufacturer in each time period.

 

[ChrisBee]

You might want to look as far back as domestic exponential horns. The first true subwoofers. Though of massive proportions to achieve a low roll off point.

One of the first subwoofer designs published in a magazine was a folded horn design called the Basset (or something similar) This used four drivers or 2 x B139s.

I built a 7 feet high x 18" diameter bass Tricolumn (another folded horn design usually of much smaller dimensions) probably in the early 70's.

The idea was always to try and drag the high resonant frequency of the speaker cone down to a lower level by loading it with a horn. Most drivers were paper with corrugated surrounds of the same meterial or of cambric in those days. Only later did the sealed box (called an infinite baffle at the time) provide drivers with roll surrounds and very low resonant frequencies. The closed box forced up the frequency so the driver was made that way to compensate for this disadvanatage.

There was an interesting design in a DIY magazine article for a subwoofer with four polystyrene panels forming the sides of the enclosure. I got as far as making the panels and rubber surrounds but couldn't afford the driver at the time. I suppose it was a form of reflex driven ABR. (Auxilliary Bass Radiator)

ChrisBee

 

[Shawn Solar]

Cool,

Ya it seems that most designs were either sealed or horn loaded up to about the 80's. Of course there were bass reflex but I didn't get the feeling they were popular. cerwin Vega even had a servo-controlled sub in the 1970's. One thing to note was that a lot of the prototyping and R&D were done by the same handful of people. Mind you they seem to circle from one manufacturer to another.

 

[ChrisBee]

There were occasional articles in the mags on large, corner-built house-brick reflex enclosures. With a 15" driver I suppose they might have reached 20Hz. Whether this is a true subwoofer in the modern sense is a different matter. The problem was often the crossover. Building a very low frequency passive crossover required truly massive components to avoid series resistance in the induction coils.

Don't forget the resistive tapered labyrinths. I believe I read of an 11Hz standing wave in a closed room during one mag review of the big full range (IMF?) speakers. I don't suppose anybody thought of offering the labyrinth section as a seperate item and calling it a subwoofer though. :b

I have always thought of the development of the roll-surround suspension driver being the true turning point in deep bass reproduction for the average bass enthusiast. Once the "floppy" driver was available. Putting the rest of the technology together was then possible (and inevitable).

ChrisBee

 

[Shawn Solar]

Any idea on how much travel the average driver had. I mean in the 70's compared to today. I can't imagine they had a lot of travel. Then again loud bass came from huge enclosures and today I find more and more manufacturers stuffing huge subs in small boxes. It seems that some of the design goals have changed over the years. Probably a little from the business practices of today but mostly from the influence of home theatre in the last decade is my guess. Every one wants a sub but a general conscensous wants it small, to play deep and loud with high effeciency Whats scary is might actually cheat the laws of physiscs