Prev: day shot to hell
Next: Ping Bil Slowman; The global warming hoax reveiled
From: Vladimir Vassilevsky on 23 Nov 2009 21:34


Spehro Pefhany wrote:


> Notwithstanding the PMPO type of lies, I have seen serious audio work
> (new patents and technology etc.) being done to maximize the music or
> vocal performance from a fixed amount of power input.

Simply put, audio signal has Gaussian distribution of amplitude.
Providing ~12dB backoff for peaks, for the same max. output swing, the
average audio power is going to be somewhat 1/8 of the undistorted
sinusoidal RMS power. So, there is little advantage in sustaining high
power at sinusoid, however the amp should be able to handle peak
loads. This allows for saving $$$, especially as audio market is VERY
sensitive to cost. The consideration applies to linear amps and Class D
as well, because the efficiency of Class D is not so good at low power.

There are, however, quite many folks who like to drive amps deep into
clipping and all that matters is loudness. If the amp is overheating, it
turns down the party. The amps for those folks are rated in watts per
dollar, and they should sustain full swing square wave operation. This
is entire special area and the design approach is different.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
From: Vladimir Vassilevsky on 23 Nov 2009 21:42


Joel Koltner wrote:

> "Rich Grise" <richgrise(a)example.net> wrote in message
> news:pan.2009.11.24.00.00.22.409954(a)example.net...
>
>>"Fantastic" as in "a fantasy?"
>
>
> Yep. They say 100W "peak power" output, which of course means nothing at all.
>
> It's the same hyperbole many companies release today... they may well have
> some improvement that make their amplifiers a bit better (notice that nowhere
> to they talk about something as simple as the power *efficiency* of their
> designs), but they have to come up with all sorts of hype to get anyone to pay
> attention... or so they think.

"Power efficiency" is politically correct way of saying "saving on the
heat sink metal".

> The whole "use a low voltage except when you start getting peaks at which
> point you switch on a boost converter and have it track the peaks" is
> well-known (and pretty obvious to anyone "skilled in the art") technique for
> high-power RF amplifiers; I have to imagine the audio guys have known about
> such things for decades too.

Audio is very sensitive to cost; lots of different things could be done,
however the art is about getting it cheap and simple while keeping
reasonable performance.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
From: Dave Platt on 23 Nov 2009 21:50
In article <6JWdnb-qjZhj2JbWnZ2dnUVZ_gudnZ2d(a)giganews.com>,
Vladimir Vassilevsky <nospam(a)nowhere.com> wrote:

>> Notwithstanding the PMPO type of lies, I have seen serious audio work
>> (new patents and technology etc.) being done to maximize the music or
>> vocal performance from a fixed amount of power input.
>
>Simply put, audio signal has Gaussian distribution of amplitude.
>Providing ~12dB backoff for peaks, for the same max. output swing, the
>average audio power is going to be somewhat 1/8 of the undistorted
>sinusoidal RMS power.

Unfortunately (for my ears, at least) the width of the distribution
has been narrowing quite a lot over the past couple of decades. A
great many commercial CDs being released these days have very little
dynamic range - their peak-to-average ratio has been squashed down
into a paper-thin wafer. It seems to be that the "race to be loudest"
(on average) has won out over any sort of dynamic range or
expressiveness.

It's even worse if you're listening to music on the radio... most
stations take the already-squashed material, and squash it down even
further.

Audio amps designed to play this sort of music will have to deal with
a regime in which they just won't see significant changes in
output power level over time, unless somebody actually grabs the
volume control knob and twists it.

--
Dave Platt <dplatt(a)radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
From: JosephKK on 28 Nov 2009 12:56
On Sat, 21 Nov 2009 12:17:49 GMT, Jan Panteltje
<pNaonStpealmtje(a)yahoo.com> wrote:

>On a sunny day (Sat, 21 Nov 2009 09:56:56 -0000) it happened "TTman"
><someone.pc(a)ntlworld.com> wrote in <PPONm.21138$2E.3148(a)newsfe20.ams2>:
>
>>100Watts, runs from a 1.5V battery . Yes, that's correct ! So that would be
>>a 500AHr. single nicad then, with a 2C charger.
>>Its true !
>>http://www.audiumsemi.com/
>>
>>
>
>Links to:
> http://www.audiumsemi.com/news002.php
>100 W *peak* power output.
>That would be 100 mW normal RMS?

Pretty much. For those old enough it seems a lot like the return of
PMPO. And the other amplifier appears to be class A instead of class
D.
From: JosephKK on 28 Nov 2009 12:59
On Sat, 21 Nov 2009 08:10:42 -0800, dplatt(a)radagast.org (Dave Platt)
wrote:

>
>>>100Watts, runs from a 1.5V battery . Yes, that's correct ! So that would be
>>>a 500AHr. single nicad then, with a 2C charger.
>>>Its true !
>>>http://www.audiumsemi.com/
>
>>Links to:
>> http://www.audiumsemi.com/news002.php
>>100 W *peak* power output.
>>That would be 100 mW normal RMS?
>
>Something like that, I suspect. The footnote on their October 9th
>news article says:
>
>[1] Normal listening level is defined as 73dBC sound pressure level
> (SPL) at a distance of 1 metre, with a speaker sensitivity of 89dBC/W
> at 1 metre.
>
>Quiet background music, from relatively efficient speakers located
>only a few feet from you. -16 dBW, or only 25 milliwatts of audio
>delivered to the speakers.
>
>Let's see... "up to 10 months on a set of four C batteries, playing
>for up to three hours per day." That's 300 days, 900 operating hours,
>45 watt-hours (assuming 100% efficiency), or 15 amp-hours at 1.5 volts.
>
>According to The Great Dubious Reference (WikiPedia) alkaline C
>batteries have a nominal capacity of 8530 mAh. Four of them in
>parallel would have about 35 amp-hours of energy, which is
>quite a bit more than the 15 amp-hours which would need to be
>delivered to the speakers. Required "battery in to audio out"
>electrical efficiency would be around 40%.
>
>So, it seems to me that their claims don't necessarily violate the
>laws of physics... assuming high efficiency in the amp, the sound
>level and speaker sensitivity that they assert, and the "up to 10
>months" and "up to three hours per day" boundaries. They don't seem
>to specify frequency response, distortion, or noise levels.
>
>They'd need a *very* different power supply arrangement in order for
>the "100 watt" number they quote to be even slightly relevant and
>believable.
>
>Seems as if it may be an interesting niche product.

The target audience may be people who are dissatisfied with how loud
their mp3 players get.
First  |  Prev  | 
Pages: 1 2 3 4 5 6
Prev: day shot to hell
Next: Ping Bil Slowman; The global warming hoax reveiled