Speaker advancements in the past 30 yrs.

Factual Questions
1

Has something been discovered or invented in the last 30 years or so that has enabled mankind to get excellent, rich audio output from tiny, plastic speakers?

When I was growing up in the '70s and '80s the finer points of one’s stereo set-up were discussed and debated among teens and twenty-somethings like the Talmud. I, personally, never got too involved in such matters myself, but I did absorb a couple of the larger principles of component selection. One of them was that you could never, ever get good sound from a dinky speaker. The laws of physics said it could not be done. You needed lead-dense cabinet walls and big air.

Is this still true? It seems like little plastic speakers are everywhere, and no one I know is complaining. What happened, did someone repeal those laws of physics?

2

Two different audiophile ways of looking at this:

  1. Nah. People just stopped complaining. Most never realize better is possible (the iPod effect).

  2. Improved cabinet design can make any driver sound better. We are more familiar with materials and designs and can do the design on computers, simulating the results, so even cheap speakers can sound pretty good.

The truth, as always, includes some of both. Consumers still equate lots of bass with high quality audio and, to be honest, lossy compression techniques like in the iPod and MP3 files mean that you probably don’t really want to hear those files in all their glory, though I just put together a couple of multi-thousand-dollar systems with receivers that have iPod inputs. Maybe the owners will just crank the bass.

All that said, well-designed and built 30-year-old speakers can still sound great. The technology has been more finetuned than advanced.

3

There have been some innovations in small speaker enclosures - Bose’s folded horn, Tivoli porting their table radio cabinets to get more low end out of those little speakers, B&W have done some intersting things with it’s bookshelf enclosures.

Probably the biggest thing to come down the pike is the affordable sub/satellite combo that you see in a lot of budget home theaters. Sure, subs have existed for a long time, but only in the last 10 or so years have they become a standard element in Joe Blow’s $200 sound system.

Ribbon tweeters and Electrostatic speakers have come down from the stratosphere somewhat. There’s been an advancement in cone and surround materials, especially in car stereos. That’s all I can think of off the top of my head.

A lot of this stuff has existed at the high end for years, but now it’s trickled down.

4

I beleive that digital signal processing has allowed them to “enhance and trick” the speakers into doing things that anlog signals could never do. Also, the use of rare earth magnets has greatly influanced speaker design by allowing for smaller drivers. Many bass boxes now have finely tuned ports that accentuate the lower level bass response, this is simple physics but is only doable within a certain range.

Cone size is still the most important and best way to get premium level sound. The vast majority of people don’t really know enough (or care enough) about hi fidelity sound to make a differance in the market place. Good enough sound is acceptable to over 90 percent of the population. This drives audiophiles nuts. :smack:

5

One of the big changes is that of fully active crossovers.

Typical passive speakers have crossover units made up from a network of inductors(coils of wire on formers) along with capacitors and perhaps some resistors.

They divide the signal into bands and direct these signals to the speaker elements that can cope with a particular range of frequencies.

The problem is that with passive crossover networks, you cannot get an ideal filtering effect, so that there is always a compromise, IIRC the best you can do is around 6dB per octave, and it means that you end up with a small amount of the wrong frequency signal reaching the wrong speaker element, they also use up power but in a frequency dependant manner.

Things have moved on greatly, signals are transmitted through cables or through optical links from the master unit, which does not have a power amplifier in it.

The digital stream is sent to the speaker, where it is seperated into high medium and low frequency bitstreams, each of which is converted to an analogue signal, which is amplified and is directed to the relevant speaker element.
The digital filtering allows very precise control over which band of frequencies is sent to which speaker element.

In addition to all this, the power supplies in many of these speakers are switch mode units, similar to the type in your computer, which allows for a far smaller unit, which has better current regulation, and increases the dynamic range.

This describes a fully active crossover, and is being employed by Meridian, Bang & Olufsen, Thomason among others.

Another advantage of the active crossover is that you can acoustically monitor the room and change the equalisation though the active network to compensate for any shortcomings.

I also think that Bang & Olufsen also go somewhat further than this, by using final drive amplifiers that are class D bias - effectively digital, which enables things to be even more compact, but this means that the speaker elements have to be constructed with this kind of drving amplifier in mind.

http://www.hometheaterhifi.com/volume_9_4/feature-article-active-speakers-12-2002.html

http://sound.westhost.com/biamp-vs-passive.htm

The other big change I can think of is the acoustic lens, which is a way of ensuring that the sound coming from the speaker goes straight to the listener and that ceiling and ground reflections are minimised, its effectively creating a horizontal beam of sound

http://www.bang-olufsen.com/web2/competences/competences.asp?section=competences&sub=sd&page=sD

It makes these speakers very predictable, every pair can be made within very much tighter limits than can passives.

These speakers are around £10k a pair, but they kick out 2500 Watts apiece, and even the audiophile publications seem to be highly impressed.

I’d expect that others will latch on to the technology.

6

I know what you mean, but some of those iron-bound rules were more folklore than physics. When I first started looking at speakers, there were two basic kinds, bass reflex and acoustic suspension. In the bass reflex kind, the cabinet was not airtight; sound waves and actual puffs of air from the back of the speaker came out a port in the front. You could put your hand in front of the port and feel the air. Acoustic suspension meant the box was airtight, and the captured air acted as a spring for the cones.

Bose shrank the bass reflex style by making the back air go through a tuned, folded labyrinth instead of a cavernous box.

I once had a pair of experimental speakers that were big, but about as heavy as a cheap cooler. Each one had a flat polyplanar speaker (about 6 x 10 inches) glued into a hole in a pressed-foam box, roughly a cube 2 feet to a side. To look at them, you’d think they’d make toy music, rinky-tink and fuzzy. No, they delivered crisp, clear tones and muscular bass. Without something heavy on top, they would move around on a hard floor. I put a plywood disc and a tablecloth on each one. I would amaze guests by asking them to find the speakers; they’d track down the sound and tell me it was impossible. Those white foam boxes can’t sound that way.

With the digital age, the old 15 inch woofers gave way to smaller cones that delivered sharp, crystalline notes. Fuzzy won’t do anymore, even if it thumps your ribcage.

I have seen the new sets; 6 or 7 dinky speakers and one footstool sized rumbler. So far, I’m not impressed. The ones I’ve heard, though, were kinda low-to-middle market stuff, so there may be better teensy satellite speakers out there.

Right now, I have a pair of Boston Acoustics A400s, and they’re due for a rebuild. I wish I had my old uglies to stand in during the repair.

7

Well, Newt Gingrich says he may run for President in '08, but otherwise it seems like a pretty dead-end job…

::D&R::

8

The beauty of music is in the ear of the listener. Whatever suits your ear.
With all the trashy sounding music, the masses wouldn’t pay the cost of decent sound reproducers of any kind.

9

Passive crossovers aren’t limited to 6 db per octave (a first-order filter, 6db for each order). Some cheap speakers use those, but 2nd, 3rd & 4th-order filters are most common in hi-fi speakers. Analog active crossovers usually use the same types of filters as passive ones, but a passive crossovers will have to be bigger, especially in the bass, so an active subwoofer crossover is a lot easier and the passive ones do tend to be just 6db/octave. What’s new are some digital crossovers with extremely steep slopes, sometimes 100db/octave or more.

The behavior of bass systems has been understood since Thiele and Small came up with their equations in the 1970s. I don’t know when their use became widespread, but they made good ported designs easy, instead of hit-and-miss as before. Ported speakers are most common now, and they do go a bit lower and louder than a similar sealed speaker.

In the bass there’s a tradeoff (“Hoffman’s Iron Law”) between efficiency, bass extension (depth) and the compactness of the cabinet. Amplifiers have gotten cheaper, so some designs trade off efficiency in order to get deep bass out of a smaller box. Some compact subwoofers now take it pretty far with small boxes and huge amplifiers.

Bang & Olufsen didn’t invent the acoustic lens. Here are a few from a 1957 JBl catalog:

Here’s how it works. Whenever you don’t know the answer, guess that Bell Labs invented it in the 30’s or 40’s.

The main problem with smaller satellite setups is that the satellites can’t go low enough, so the sub has to go too high and you can hear where it is. For it to really work you have to have a decent bookshelf speaker for a satellite.

A good, solid cabinet is as vital as ever and is the first thing to go in a cheap speaker, but some older speakers had big cabinets without enough bracing.