[sdiy] Dynamics and speakers, was:Advice

[harrybissell]

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