The Loudspeaker - Some things never change

Since the 1960's samarium-cobalt and neodynium iron magnets are new, and can sustain much higher permanent magnetic fields across the speaker coils.

A serious long-throw speaker would use a synchronous linear motor and elaborate drive electronics to sustain a constant driving force over the whole length of the throw, but I haven't seen any evidence that anybody has spent that kind of money.

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Bill Sloman, Sydney

Well, pots are now digital. Resistors have gotten a *lot* smaller (my standard size is now 0402). Switches (as in the click-click type) are extinct. ;-)

They've changed, too. Rare-earth magnets are commonplace and as you note, materials have changed quite a bit.

I believe they're called "actuators". Might work for earthquake simulators. ;-)

You must have missed the electrostatic speakers of... maybe the 80's? I think the bass was their weakness, but I don't really recall... it may have simply been the price. They were large and needed high voltage if I recall.

In high school (I'm about the same age as you) I built a flame speaker for a science fair project. I didn't understand loading and tried boosting the volume by using a higher output tap on the transformer. It didn't do anything while the class was there. Once they left I realized what I had changed and got it to work again, but I don't know if anyone believed me.

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Rick

I've been playing around with electronics since I was in my teens, which was in the 1960s. Some electronic components have drastically changed, while others have always been about the same. The main components were once vacuum tubes, then transistors, and now most are ICs. Capacitors, while similar, have actually changed quite a lot. The old electrolytic "Cans" are now small, but they normally handle much smaller voltages. I guess resistors have never really changed all that much, nor have switches, potentiometers, and so on.

But I'm posting this regarding Loudspeakers, or just Speakers as they are normally called now a days. Over all these years, they have changed very little. Sure, some now have plastic cones instead of paper, but the design is the same. And horn speakers (tweeters) are almost identical too.

All these years in electronics, and Speakers still amaze me. While they obviously work, and work well, it's still amazing how much sound can come out of a piece of moving paper. Even more amazing is how long that paper lasts considering all the movement and flexing it encounters. Recently I was in a bar and the music was very loud. They have huge speakers and a powerful amp, and there are no grills over the speakers. They had the music extra loud that night, and I watched those large 15" woofer cones being 'abused'. Yet they just kept on working, moving in an out at least an inch with every beat. (I believe their amp is 500W per channel RMS, and it drives two cabinets on each channel, with two

15" woofers and a horn in each cabinet).

At the same time, I know that not too long ago, they had to replace a few of those speakers because some customer turned up the volume too much and blew them. (Which is why the moved the amp, so only the bartender can change the volume now).

Anyhow, after all the changes we have seen in electronics over the years, Speakers still remain the same. I guess some things just dont need to be improved, unlike many other things, particularly noticable in computers. Then again, sometimes I think the older computers were better, which is why I am posting this messsage using my preferred operating system, Windows98.

Anyhow, I cant see any real way to change speakers, nor can I see any other way to make them. They work well, and I guess that is all we need!

One final comment. Back in the late 60's or early 70's, I recall going to a long gone company called "Olson Electronics". They sold a device that was a magnet assembly that was supposed to be screwed to a wall, and would turn that wall into a speaker. I wanted to try one of them, but money was tight and I never did buy one. Apparently they never worked as well as they were advertised, or we would see them in use now. I have never seen one of them since Olson went out of business!

Electrostatic speakers go back as far as the '50s. The lack of bass is solved by building huge panels. Jansens were 4-5' tall, IIRC. High voltage, yes, at least 5kV. Hybrids worked better, though.

For a bass speaker, the only interesting parameter is the amount of air volume a speaker is capable of moving (surface area x throw). For a specific SPL at a specific frequency, you really need to increase the speaker surface area or the cone throw to get the correct audio volume.

Anyway. I am still astonished, how good some mobile phone speakers are (of course at low absolute SPL).

(primarily answer to sci.electronics.design )

Actually loudspeakers have changed.

Nowadays loudspeaker life sucks...

Today the suspension are normally made of foam rubber - and that rot (disintegrate) after 10-20 years:

Speaker Buying Tips - The Dreaded FOAM ROT - YouTube:

Re-foam your old speakers:

"... Actually you wouldn't tell, but this is an ordinary situation for a 20 years old woofer, indeed the edges (made of foam or rubber), after many years crumble. ..."

Why so complacent about "Foam Rot" ?:

Quote: "... Over the years I've lost three sets of speakers to foam rot. Everyone on the forums here seems to consider this to be normal wear and tear, like tread on a tire. Although new surrounds are available, it sounds like a delicate and difficult fix. I am skeptical about the transparency of such a fix. Will the speaker really sound the same afterwards? Surely the speaker manufactures can find materials that last longer than 10 years My vintage Jensens are still going strong after 60 years, so it can be done! ... Foam rots beacuse of ozone and general oxidation. The material is connected producer of ozone albeit a very small amount, it is enough to cause rot. As Spartanmanor stated, it is easy to fix so not a big deal really.

Foam is used bacause the designer wants a specific compliance on the driver - it was their choice for a reason!!! ... Absolutely it's our friend. Just a couple weeks ago I brought home a pair of infinity kappas for the price of a fast food meal. These speakers had foam rot but they retailed for $900 in the 90's. Foam rot is great stuff. ..."

January 28, 2012, Fixing Old Speakers ? The Common Woofer Foam Rot Problem:

Replace dry rotted speaker surrounds with cloth replacements:

"... This Instructable will show you how you can replace these by making your own surrounds out of scrap cloth, thus enabling you to renew sometimes expensive speakers and have a fantastic stereo for next to nothing. ... The best cloth to use would be a synthetic blend, tightly woven, and smooth.I've used all sorts of cloth, including canvas. ... This was perfect! I used a nylon 30% cotton 70% blend fabric and sealed the fabric with really watered down wood glue mixture for the last step (no spray paint laying around) and now my old speakers are working very nicely...and it didn't cost me a dime! ..."

Glenn

On a sunny day (Sat, 28 Mar 2015 11:09:11 +0100) it happened Glenn wrote in :

In the old house I had my bass speaker mounted to the floor, the space below the floor makes a great bass resonator (whatever you call it). I usually drive that bass speaker till I can smell the voice coil. The interesting thing is when the chairs start jumping up and down with the music. This guy does one better though:

Mine has rubber, not foam. Rubber is OK.

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RMS watts is fiction.

John Fields

The Quad ESL-63 I belive came out in 1963. Absolutely unparalleled. Distortion lower than some amps, and that is quite a feat in speakers. Little bit bass shy but we know what subwoofers are.

I think some of the older speakers were quite a bit better. The sealed cabi net produces better bass, more well defined and to a gentler rolloff at it' s low point.

they went to ports and passive radiators and it increased the efficiency bu t cost that bottom octave. Sealed systems, you could use an equalizer and s tretch the low end, now the rolloff is too step and even if you had an EQ t hat could doo it, you might run out of amplifier power or the speaker's abi lity to handle it by the time to get anywhere near flat.

Newer speakers don't really get much more SPL per volt, but it allows them to pull less current having a leess drastic impedance curve. This allows th e amps to be build cheaper. In the old days you saw 60 watt per channel amp s with 4 outputs per channel and a massive power transformer to be able to supply the current. Now a 60 watt per channel amp is on a chip.

Many newer amps go into current limiting when driving old speakers. I've ru n across people who actually thought they were shorted. My Boston Acoustics woofers measuered 3.2 ohms DC resistance. You can't drive them properly wi th just any new amp from Bestbuy. Some of them actually go into proteection .

And newer speakers ? I have tried. I have blocked off the ports, replaced p assive radiators with more speakers and EQed it to sound right. Know what h appened ? The cabinet started cracking.

It's an abuse of terminology - I assume what they mean is something like that they're measuring maximum "undistorted" (say like 1% THD) continous sine wave power output across some load using the RMS value of the voltage waveform across the load, rather than the peak value of the wave, or maximum power output for 100 mS, or some other BS figure like that.

It's possible to actually calculate "RMS watts" by squaring V^2/R, taking the mean and then the square root, but I don't know that the result has any physical meaning.

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Actually they could have used anything. The RMS watt thing is technically w rong but it came into its own kinda as a standard. It's like when you inven t a word. Once it is understood it is a word. Like "ain't". Of course "ain' t" ain't a word, it is a contraction for "are not" or "is not" and maybe so mething else now that does not come to mind. But people understand it.

It beats the hell out of some ratings systems. Like those little "200 watt" car stereo boosters with the 4 amp fuse. That I think is PIPILS, Peak Inst antateous Power If Lightning Strikes.

One thing about amps and receivers is you don't get as much extra power as you used to. In the old days it was hard to keep the voltage response absol utely linear as the output approached the power rails. This may have only c aused 2 or 3 % THD at those levels but they rated them lower to get the sub 1 % numbers. People buying an amp would see this 1.8 % THD at 110 watts an d fly away. But if they see 0.08 % at 75 watts, it looks alot better.

Now, the transistors have more gain and it is probbly more linear as well. Therefore the THD curve isn't rising until it really is damnear clipping. S o the power rating and THD are there, but what you don't get in the newer s tuff is what's called "clippping headroom". This differs from dynamic headr oom which refers specifically to short term bursts of power before it drain s the charge off the main filters and makes the rectifiers work again.

There is alot to like about old stereo equipment. The fact that they made i t so good in the first place with technology we consider prehistoric today. Another thing is the value. Almost every improvement to a product makes it cheaper to build. I was just reading somewhere that Marantzes smallest rec eiver in the 1970s, the 2010 rated at ten watts per channel. I have worked on one and I can tell you they are considerably more than that, but the thi ng is they sold for $199 back then which translates to about $1,100 in toda y's dollars.

I simply gotta hear this one.

Also, when and where is RMS Watts nonfiction?

Think about it. RMS volts, yes. RMS amps, sure. "RMS watts" has no meaning.

Perhaps in a (somewhat) parallel universe.

My brain farted again, sorry.

rtion lower than some amps, and that is quite a feat in speakers. Little bi t bass shy but we know what subwoofers are.

One of my ex-colleagues from Cambridge Instruments ended up as a quality co ntrol manager at Quad. He was a full bottle on the weirdness of the electro static speakers. The conducting layer on the moving film has to have a very high resistance - of the order of Gigohms per square - to prevent it disto rting into little peaks - and Quad's scheme for getting that was something complicated involving sulphur (IIRR - I took care not remember proprietary detail).

The EL-63 was a series of rings of electrostatic film, driven by a high-vol tage analog LC delay line. Very weird indeed. Their research manager really knew a lot about transformers.

--
Bill Sloman, Sydney

tortion lower than some amps, and that is quite a feat in speakers. Little bit bass shy but we know what subwoofers are.

control manager at Quad. He was a full bottle on the weirdness of the elect rostatic speakers. The conducting layer on the moving film has to have a ve ry high resistance - of the order of Gigohms per square - to prevent it dis torting into little peaks - and Quad's scheme for getting that was somethin g complicated involving sulphur (IIRR - I took care not remember proprietar y detail).

I remember some old DIY articles that used either rubbing the plastic with graphite on cotton balls or fabric softener

-Lasse

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OK... 

http://en.wikipedia.org/wiki/Root_mean_square 


>Also, when and where is RMS Watts nonfiction? 

Never and nowhere.