[sdiy] Dynamics and speakers, was:Advice

[phillip m gallo]

Harry,

.... besides all those altec drivers are needed for "articulation"
devices.

regards,
p


-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of harrybissell
Sent: Tuesday, February 03, 2004 6:26 PM
To: Thomas Dunker
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Dynamics and speakers, was:Advice


And a good ramble it is... otoh the old Altec A-7s (Voice of the
Theatre) didn't
fit too well in the VW Beetle   :^P

Horns are efficient, and do a wonderful job of impedance matching the
driver to the
medium (air).   But they are too big and very few people have the room
for them.

In speakers (imho) bigger is almost always better... to the limit of
bigness you can

afford to live with....

H^) harry  (whose EV Eliminators - the original ones... have been on
semi permanent loan these past twenty years)

Thomas Dunker wrote:

> On Tue, 3 Feb 2004, Richard Wentk wrote:
>
> > The real point of compression is that given the limitations of most 
> > speakers, there's no point trying to accurately reproduce the peaks 
> > anyway. Studio monitors can reproduce peaks accurately (more or 
> > less) but nothing else in the world can, so that headroom is 
> > effectively wasted.
>
>  Hey, couldn't resist commenting on this since the reproduction of 
> uh..."life-like" dynamics has been my quest as a DIY audio nut for the

> past 10 years I have spent a great deal of time trying to figure out 
> what it is the audio industry actually wants us to believe. Some of 
> the most able speaker technology in terms of dynamics (or dynamic 
> linearity to be more precise) just happens to be the oldest, and in 
> domestic hi-fi terms also the "most obsolete" - namely horn speakers. 
> Wherever horns are used in the pro audio industry today (SR rigs, 
> stadiums, movie theatres etc.) it's precisely because they have vastly

> better dynamic linearity (distortion vs. output SPL) than most 
> alternatives. Horns are also used a lot specifically for other primary

> reasons, like dispersion control, but they got me interested because 
> of the dynamic potential.
>
>  Anyway, the sad story goes something like this: Ever since the direct

> radiator speaker came about (circa 1928, by Rice and Kellogg in the US

> who beat P.G.A.H. Voigt to the patent office - Voigt also had working 
> prototypes at the time), an ongoing trend has conspired to effectively

> remove "lifelike dynamics" from most people's criteria for "high 
> fidelity" reproduction. The first theater sound systems had speakers 
> with something like 50% efficiency (modern hi-fi speakers have 
> something typically around 0.1% efficiency, which probably explains 
> the fact that efficiency is represented by a decibel figure at 1 watt 
> input, yielding a more impressive number) and were powered with 
> sub-10W triode amps. This would fill an entire movie theater with 
> sound of unprecedented fidelity for the time (1930s).
>
>  Movie sound was developed into the forefront of audio technology 
> during the 1930s, and advanced to give birth to multi-track studio 
> recording techniques and fantastic analog reproduction systems by the 
> end of the thirties. This is exemplified by the Fantasound system 
> developed for Walt Disney's picture Fantasia by Hollywood sound 
> engineers like Howard Tremaine, along with speakers and amps by RCA 
> and Altec, and the three-track optical stereo soundtrack developed by 
> Bell Labs. This optical sound track utilized a proprietary system 
> called TOGAD (tone operated gain-adjusting device) which formed the 
> basis of what must have been one of the very first "companding" 
> schemes for recording. Separate gain control voltages for each of the 
> three main channels were modulated onto different frequency carriers 
> that were mixed and recorded as a separate track that ran along the 
> three audio channels. These four tracks were recorded onto a dedicated

> 35 mm film that was syncronized with the picture film. During 
> playback, the gain control voltages were recovered from the TOGAD 
> track and fed to VCAs (!) in conjunction with the playback preamps.
>
>  Believe it or not, but this optical recording system enabled the 
> Fantasia score to be recorded and reproduced with about 90dB of 
> dynamic range!
>
> THAT'S ANALOG RECORDING STATE OF THE ART IN THE YEAR 1940
>
>  During the Fantasia recording sessions, multitrack recording 
> technology as we know it was invented, except they mixed it down to 
> three discrete channels (left, center, right). Orchestral "sound 
> effects" were also worked into the mix and triggered by the TOGAD 
> system to be played by various speakers placed around the theater, so 
> even surround sound is a
> 60+ years old technology.
>
>  The speaker technology used reflected the demands of the 
> recording/reproducing chain. The specs were insane for the time, 
> something like 120dB peak in the rear of the theater, with 6dB of 
> headroom. Huge, balanced class A triode amps powered bass horns and HF

> horns. A few theaters were equipped with insanely expensive Fantasound

> systems, but there was also a portable system complete with diesel 
> generators, projectors, cables and everything.
>
> Read more here:
>
> http://www.widescreenmuseum.com/sound/Fantasound1.htm
>
> (I got a lot of first hand dope on Fantasound by one of the aging 
> engineers who worked on the system in the 1940s, a guy named Jack 
> Strayer)
>
>  OK, this is megalomaniac triode-age movie theater HI-FI madness, but 
> demonstrates how we should probably be a little careful using phrases 
> like "the state of the art" today, realizing that the actual state of 
> the art TODAY is very far from reaching into most people's experience 
> with reproduced audio.
>
>  And that's because of how amplifiers and speakers have developed 
> since the days of triodes and horns. Triodes were replaced by 
> pentodes, making amp power cheaper, causing some idiot to think hey, 
> what do we need this kind of speaker efficiency for, and along come 
> smaller, less efficient speakers. Pentodes were eventually replaced by

> transistors and by the 1970s typical "hi-fi" speaker efficiency had 
> settled somewhere around 87dB/1W/1m - or somewhere below 0.1% relative

> efficiency. (Or 99.9% of input power directly converted into HEAT and 
> other losses, rather than sound).
>
>  Specifying the efficiency in decibels is useful some times. The most 
> inefficient speakers, like LS3/5As, Magnepans and such, are around 
> 85dB/1W/1m. The most efficient speakers (big/horn based systems) can 
> easily be around 105db/1W/1m. Most people don't realize how much a 
> 20dB difference is in terms of amplifier power. If the speaker is 20dB

> LESS efficient, it needs 20dB or A HUNDRED TIMES MORE POWER. Think 
> about it:
>
>  If you drive the 105db speaker with a humble 10W amp, comfortably 
> below the speaker's max power rating, with 115dB peaks, you would - 
> theoretically - have to have a 1000W amp driving the 85 dB speaker to 
> get to the same max SPL or useful dynamic range - EXCEPT the 85dB 
> speaker's voice coils would begin to self destruct at a mere couple 
> hundred watts of input. No matter how much you up the amp power, the 
> bottleneck will be in the speaker's power rating - BECAUSE OF ITS 
> ULTRA LOW EFFICIENCY. It is therefore impossible to entirely 
> compensate for inefficient speakers by increasing amp power as far as 
> dynamics are concerned.
>
>  Next time you see a monster amp driving tiny speakers, don't be 
> impressed, be sad.
>
>  Okay, so speakers can be more or less efficient, but it's not as 
> simple as that. I brought up how 99% or more of the input power is 
> converted into heat loss in the speaker. This has brought us fabulous 
> innovations like high temperature cements and coil former materials 
> allowing the low-efficiency insanity to escalate. An often overlooked 
> fact is that when a piece of copper wire gets HOT its resistance 
> increases. In a speaker it can typically imply that the impedance of 
> the speaker may DOUBLE at "highish" input power, still well below max 
> power rating. Since the industry has also decided that speakers - 
> inherently current controlled devices - MUST ONLY be driven by low 
> output impedance (undistorted
> voltage) amplifiers, another no-brain industry standard - this gives
rise
> to what we call "POWER COMPRESSION", well known in the pro sound
industry,
> but obviously a taboo in the "hi-fi" branch.
>
>  Quantitatively, power compression can very easily amount to something

> like 6dB loss of dynamics, give or take some. This compression will 
> also be subject to unpredictable effects as the copper coils in 
> different drivers will have different thermal time constants. Consider

> passive crossover/filter networks and you have the textbook definition

> of "A MESS". Not even the Q parameters or the actual efficiency of the

> drivers can be constant if the voice coil resistance isn't. A matter 
> of speaker effciency and/or applied power.
>
>  I have spent years reading about all kinds of  distortion effects in 
> speakers and the amp-speaker interface, so it's a little hard for me 
> to get off the soapbox when I'm at it. But, the single most important 
> thing to understand is that the harder a speaker must work (the more 
> the cones move, the more power it tries to get rid of etc.) the more 
> distortion (relative to the input signal) it makes. It's not cool that

> the woofer cones move an inch, it tells you you're probably listening 
> to 20-30% THD and intermodulation distortion and horribly distorted 
> transients too.
>
>  The subjective perception of music dynamics has to do with more than 
> just SPL ratios and dynamic distortion. It also has something to do 
> with the reproduction of transients, which typically has to do not 
> just with amplitude levels, but also with time domain stuff. Like, how

> well are the system resonances damped? A bass reflex speaker is 
> incapable of reproducing transients without some degree of periodic 
> "overshoot", because the whole idea is that the resonance should only 
> be damped to a certain degree so we get a little extra "bass" for 
> cheap out of speakers that are too small. This is another 
> "standardized" type of distortion typical in speakers.
>
>  Summed up, "state of the art" speakers and the amps that drive them 
> are not suited for really big dynamics. Even most studio monitors 
> except maybe Westlakes, UREIs, TADs and nice big old JBLs. Not the 
> undersized stuff they tend to use today.  It should be quite possible 
> - with the right speakers - to hear more of the recorded dynamic range

> than the recording engineer did when listening to the final mix.
>
>  It's not the recording industry's fault that the consumer audio 
> people turn out so much misengineered junk, but it's sad how it's 
> defined lifelike dynamics out of the "hi-fi" world. It's like they try

> to bring it back with amazing new digital media - WHY, IF THE SIGNAL 
> WILL BE COMPRESSED DOWN TO 30-40dB DYNAMIC RANGE ANYWAY. What do we 
> need all this dynamic resolution for then? You *can* get more dynamic 
> range recorded onto 33 1/3 RPM vinyl than is common in most CDs out 
> there.  How cool is it to have 24 bit resolution and 120dB S/N ratio 
> when the recorded signal ends up being compressed to the dynamic range

> of worn cassette tape - or worse. Why are we supposed to get all 
> excited about THAT? What a joke!
>
>  Still, the most dynamically capable speakers can make even the most 
> awfully compressed recordings come alive, I know from experience, that

> only proves how much compression the average speaker ADDS. I had no 
> idea until I could hear it for myself. Never would have happened at 
> the hi-fi store.
>
> Pardon the ramble and off-topicness...
>
> Thomas Dunker
>
> Trondheim, Norway