"Orchid XP v3" <voi### [at] devnull> wrote in message 
news:46dee812$1@news.povray.org...
>>>> Interesting, how do they do that?
>>>
>>> You think *I* know?
>>
>> It used to be that more efficient speakers in general had more unwanted 
>> resonances and lumps in their frequency responses: IOW poorer fidelity. 
>> I don't particularly know why but that's how it was.  Obviously the 
>> designers would have overcome that if they could have, but some chose low 
>> efficiency in return for better sound quality.  I don't know how well 
>> they are doing now with that trade-off, it's been some years since I last 
>> read any reviews.
>
> That sounds about right.

Actually now I think of it, I remember a very common example of two 
different speaker designs that speaker manufacturers often choose tradeoffs 
with:  Infinite Baffle, vs. Tuned Port.

Theoretically, an Infinite Baffle speaker is simply a driver mounted in a 
wall (or baffle) that extends to infinity in all directions of its plane. 
No sound energy that radiates backwards from the driver (and is inverted) 
can get around the baffle where it would interfere with the 
forward-travelling sound wave.  In practice however, an IB speaker is a 
driver in a sealed box with a limited internal volume.

Good points of IB are smooth frequency curve, linear or slow-changing phase 
over frequency, good damping, low colouration -- in general high-quality 
sound with good 3-D imaging on the virtual sound stage.  Bad points are bass 
response starts to tail off slowly at a relatively high frequency due to the 
limited cabinet volume and can really lack guts on low notes like the bottom 
E1 of a bass guitar (~41 Hz).

Tuned Port speakers, on the other hand, have a vent in the cabinet (often in 
the front).  Its entire purpose is to extend the bass response of the 
speaker below the frequency limit usually imposed by the cabinet's internal 
air volume.  The port connects to the internal cavity by a tube of a length 
calculated to tune to a chosen bass frequency half-waavelength.  At that 
frequency, the wave at the port entrance (ultimately coming from the back of 
the driver) is in reinforcement phase with the wave from the front of the 
driver, extending the speaker's freq. range.

Good points of TP are deeper extension of bass response for a cabinet size 
and relatively flat(tish) bass response below 100Hz down to the tuned freq.

Bad points are the low-frequency response can actually have a peak at the 
tuned frequency, then it will plummet off a cliff just below it, the phase 
of the bass tends to change dramatically with frequency, the speaker has a 
lumpy impedance graph - presenting a very low impedance* to the amp at the 
tuned frequency and high-impedance at nearby frequencies (more difficult 
load for an amplifier to drive).  If not carefully designed, TP can 
over-emphasise sound near the tuned freq., causing the effect known as 
"one-note bass" or "boom box".  The port's resonance has inertia and stores 
energy which the driver takes time to overcome, it can continue transmitting 
for several cycles after the amplifier has stopped the signal, which means a 
TP speaker's extended bass response comes at the cost of "mushing up" the 
sound (time-smearing).

Just an example, y'know.  :-)

* [impedance could be the opposite way to my memory, but point is, it's 
still lumpy]

>>>> Hard to see how you could deliberately make the system less efficient 
>>>> without just plonking a huge 50W resistor in series (which would 
>>>> totally screw up the quality of the sound).
>>>
>>> And why would that be?
>>
>> The answers lie in the way passive networks of electronic components work 
>> and in speaker mechanics.
>> [...]
>> So if you plonk a great big resistor in series with all that, the amp 
>> can't damp unwanted speaker motion, the crossover detunes, the frequency 
>> response goes lumpy, the sound goes muddy, and you think "bleccch!"  :-)
>
> I'm sure that would be the case.
>
> Now, what if that resistance was part of the design right from the 
> beginning?

Possibly...  But I think it would prevent the amplifier from sinking the 
back-EMF current from the speaker.  The amplifier's output stage should have 
an apparent impedance (Z) as close to zero as possible, but instead its Z 
would be the resistor's value, allowing a back-voltage and thus impacting 
sound quality.  I don't think there'd be a way to design around that problem 
in the speaker alone.

> By the way... The documentation for my mum's amplifier claims that it 
> contains special circuitry to cancel out the electric signals generated by 
> the speakers themselves. (I have no idea whether this is special or 
> whether it's something all modern amps do and they just wrote about it to 
> make themselves sound cleaver...)

"We have carefully designed into our mower, a special feature to cut grass!"

Every power amp does it, with negative feedback taken from the output stage. 
Any voltage that is not equal to the amp's instantaneous output drive is fed 
back, differenced, inverted, amplified and output again, cancelling the 
error.  That's also how amplifiers get to look like zero impedance or short 
circuit to error signals appearing at the output transistor stage.

>>>>> Hmm, I think my amplifier (nothing special) is rated at 60 W per 
>>>>> channel. (IIRC, into 8 ohms at 1 kHz.)
>>
>> For listening at home, the real reason for high-powered amps is not to 
>> make louder noise, but for fidelity.
>
> Hmm, isn't that what *I* said several posts ago? ;-)

Sorry, I probably either missed or forgot that you did.  :-)  Anyhow it was 
more that I thought the others were pulling the discussion of amp power 
specs off-course.

>>> (It's like all toasters have a special setting that transforms bread 
>>> into charcole. We don't know why, but they all have it.)
>>
>> <Ahem>  Just because you didn't figure it out, doesn't automatically make 
>> the manufacturers into idiots.  The high setting on toasters is needed to 
>> get even a _little_ colour into *crumpets*.  But, as you apparently 
>> haven't toasted a crumpet before, they obviously don't exist and every 
>> manufacturer out there is stupid for gratuitously making toasters with a 
>> nuclear setting.
>>  :-P
>
> Wait... Surely to toast a crumpet you want a *lower* heat? (Since it's 
> thicker and hence nearer to the heat source - and also you want to cook it 
> slower so it cooks through completely.)

I see what you mean, but a lower heat would dry it out before beginning to 
brown it, and then you'd have a circular paver for your driveway.  :-) 
There's a fair bit of moisture in crumpets, and despite the honeycombing, 
they have a dense and rubbery texture.  It needs to be high heat to brown 
the outside while leaving the inside soft and mmmmm.  :-)  You don't want 
them "cooked through".

>>> (I once tried connecting a line-level output to the phono input. Big 
>>> mistake...)
>>
>> Ow.  :-(
>
> Sounded a bit like a metal guitar. Also made the sound come out on *all* 
> input selections. o_O

That's because it's the same effect as metal guitar:  massive overdrive / 
extreme clipping.

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"Orchid XP v3" <voi### [at] devnull> wrote in message 
news:46deec35$1@news.povray.org...
> Brian Elliott wrote:
>
>> Firstly, the crossover network divides the signal from the amplifier to 
>> the woofer and the tweeter drivers.  It must be tuned to the right 
>> frequency and shape the frequency falloff curves and phase so that the 
>> sound levels from both drivers are balanced without dips or humps or 
>> comb-filtering at the crossover band where both drivers transmit part of 
>> the signal.  It is also supposed to keep the signal phase true between 
>> the two drivers over the frequency range so they operate in a unison 
>> making the sound wavefront from both drivers combine and arrive at your 
>> ear together.  That is fekking difficult to design, because...
>>
>> Crossovers are passive networks of resistors, capacitors and inductors. 
>> Networks behave much more complicatedly than isolated components because 
>> everything interacts with everything else, not just its immediate 
>> neighbours.  Speaker drivers are *also* R-L-C networks, so crossovers 
>> must be designed with that driver's electrical properties being integral 
>> to it.
>>
>> In short, the whole thing is interbalanced, so if one resistor, capacitor 
>> or inductor changes, everything goes out of whack -- crossover frequency, 
>> frequency response, phase response, impedance response, resonances and 
>> ringing -- and the speaker sounds like crap.
>>
>> For predictability, a speaker and its crossover also rely on the 
>> amplifier's output stage being very low impedance. Signal-wise, the 
>> amplifier is near to a short-circuit, regardless of the voltage swings it 
>> generates.  A speaker is a motor and when moving, it generates back-EMF 
>> through its crossover.  It has mechanical inertia and wants to overshoot. 
>> It  also has natural resonances from driver suspension springiness, 
>> cabinet air volume, acoustic transmission line length, tuned acoustic 
>> port, etc.  That colouration is NOT part of the original signal.  If the 
>> amplifier doesn't soak up that energy (absorb the current), to damp the 
>> unwanted motion (overshoot and ringing) it will reflect back into the 
>> network and colour the sound you hear.
>
> I read about this kind of thing in a DSP book. Damn, IIR filters sound so 
> complicated! Fascinating, but... I wouldn't want to design them for a 
> living.

I'm with you on that!  Fascinating, wish I could do it, but AIUI, there's 
hardly a hope of designing it manually.  It's computerised design with an 
element of alchemy, dead cats, satanic verse and other ancient rituals 
thrown in.  Probably a reading of Pam Ayres poetry too!  Might as well find 
the diff. eqns. for a six-body gravitational orbit.

  :-)

> -- 
> http://blog.orphi.me.uk/

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>> Should be noted: It's an *ancient* laptop!
> 
> Heh. I though more of an ancient (and broken) Linux distro.

SuSE 10.2...

>> (Now *my* laptop seems to do all this in hardware, not software. Doesn't
>> matter what software is running, the fan turns on and off now and then...)
> 
> Which is wise choice.

Indeed. I had assumed that *all* laptops work this way. (Surely to be 
any other way is at the very least a fire hazard?)

-- 
http://blog.orphi.me.uk/

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M_a_r_c wrote:

> And what about e-paper?

Hey, I read something about that in Chemistry In Britan...

...12 years ago.

Now, I suppose in product development terms, 12 years isn't very long. 
But I don't expect this technology to entire the mainstream in my own 
lifetime...

-- 
http://blog.orphi.me.uk/

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>> I read about this kind of thing in a DSP book. Damn, IIR filters sound 
>> so complicated! Fascinating, but... I wouldn't want to design them for 
>> a living.
> 
> I'm with you on that!  Fascinating, wish I could do it, but AIUI, 
> there's hardly a hope of designing it manually.

I always wondered why the hell you would put a coin of wire inside a 
circuit. I mean, sure, if you put power through it, you can use it to 
pick up metal objects. But why would you have such a thing inside a machine?

Ah, but wait. When you turn the power off, the magnetic field collapses. 
And what do we know about coils of wire inside a changing magnetic field?

I *so* didn't see that one comming... People are way smarted then me. :-/

Still, the stuff about the Laplace transform was cool. Very hard to 
comprehend, but cool...

> It's computerised 
> design with an element of alchemy, dead cats, satanic verse and other 
> ancient rituals thrown in.  Probably a reading of Pam Ayres poetry too!  
> Might as well find the diff. eqns. for a six-body gravitational orbit.

Oh, the *equations* are easy enough. Now try *solving* them... ;-)

-- 
http://blog.orphi.me.uk/

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Orchid XP v3 wrote:
> 
> SuSE 10.2...

Ah, the latest out there.

> Indeed. I had assumed that *all* laptops work this way. (Surely to be
> any other way is at the very least a fire hazard?)
> 

Not everything in this world work with sense... Unfortunately.

-- 
Eero "Aero" Ahonen
   http://www.zbxt.net
      aer### [at] removethiszbxtnetinvalid

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> Now, I suppose in product development terms, 12 years isn't very long. 
> But I don't expect this technology to entire the mainstream in my own 
> lifetime...

I wonder what people were saying about LCD 20 years ago...

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Orchid XP v3 wrote:
> Indeed. I had assumed that *all* laptops work this way. 

But you can override it in software. So if you override it incorrectly, 
you have a problem.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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scott wrote:
>> Now, I suppose in product development terms, 12 years isn't very long. 
>> But I don't expect this technology to entire the mainstream in my own 
>> lifetime...
> 
> I wonder what people were saying about LCD 20 years ago...

But LCD hasn't changed how a screen is used, it's just made it a bit 
more efficient and a bit smaller (and, arguably, a bit crapper, 
certainly in the low end of the TV market). E-paper requires a whole new 
product and a whole new set of habits from the consumer. This will take 
a little longer. I don't expect to see e-paper widely used anytime soon, 
and only maybe within my lifetime.

Post a reply to this message

>> I wonder what people were saying about LCD 20 years ago...
>
> But LCD hasn't changed how a screen is used, it's just made it a bit more 
> efficient and a bit smaller (and, arguably, a bit crapper, certainly in 
> the low end of the TV market).  E-paper requires a whole new product

You mean like how LCD has popped up in cars, phones, portable navigation 
devices and games consoles etc - none of which had any sort of graphic 
display before LCD.

> and a whole new set of habits from the consumer. This will take a little 
> longer. I don't expect to see e-paper widely used anytime soon, and only 
> maybe within my lifetime.

As I already said, ePaper is already used in supermarkets, it will only be a 
matter of years (not decades) before it becomes more cost-efficient than a 
lot of existing paper-and-ink based things.

Sure, it's not going to replace a real book or a newspaper for a long time 
(perhaps never), but there are plenty of other markets that ePaper will take 
over relatively soon.

Another example is the odometer in cars - the OEMs are already asking for a 
zero-power display for this so that it is always visible.  Expect to see 
ePaper based odometers within 10 years in cars, and cars have one of the 
longest product development cycles.

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