Can someone explain digital speakers

[mark1101]

I am wondering about the digital outputs on my HT system and PC soundcard. They show digital outputs going to speakers in the manual. Is this really a digital input to a speaker amp? Is there anything different about the speakers themselves or are they the same with on board DAC?"

Thanks

[Guest BobG]

Same with onboard D to A converter and amp(s)

[mark1101]

Thought so, thanks Bob. Just like high definition "ready".

[sfogg]

Mark,

One other thing that can be different about digital speakers is them may not have conventional crossovers in them. The crossover functions may be performed using DSP then on to D/As and the amps. Meridians digital speakers do this.

I believe there are also starting to be digital speakers which use DSP for crossovers then it goes directly to digital amps. Tacts speakers I believe are built like this.

Shawn

[KiNNi C P]

the best example of today's digital speakers are the speakers made by Meridian, i think the model number is something like DP8000, i think i am wrong, but check out their website.

anyways, digital speakers arent really possible since only analog signals can power a driver.

[sfogg]

"anyways, digital speakers arent really possible since only analog signals can power a driver."

That isn't really correct. Digital amps drive can driver speakers using things like pulse width modulation.

See:

http://www.crownaudio.com/amp_htm/amp_info/bca.htm

for example.

Shawn

[DMF]

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That isn't really correct. Digital amps drive can driver speakers using things like pulse width modulation.

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Color me "skeptical".

Actually, with PWM you may be feeding the signal as digital, but you'd be using the tranducer as a mechanical DAC. You still need a non-zero derivative to get an audible output.

[FirebirdTN]

If you look closely at PWM, the amplifiers themselves are pure "switches", making it a digital amp, however the filtering following the PWM amplifiers filters out the switching frequency, thereby effectivly converting the signal back to analog to drive the speakers.

In that very link that someone provided above, look down at almost the bottom of the page at the diagram of the "output" signal.

-Alan

[DrWho]

what is termed a "digital amplifier" is actually a class D switching amplifier (they just switch really freaken fast)...

here's an article if you wanna read about it:

http://www.prosoundweb.com/lsi/next/next.php

and here's a snippet for those as lazy as me:

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One unfortunate confusion has entered our vocabulary, however. Because switching amplifiers use on-off operation, they superficially resemble binary logic circuitry, and are frequently called digital amplifiers. This is quite misleading, as the switching amplifier is still very much an analog system, with all the usual problems of analog error correction.

and some more of my own clarification:

digital amplifiers are still fed an analog signal (and output an analog signal as well)

[KiNNi C P]

haha, i knew someone was going to comment on what i said

good info though, however what i need to said has already been said by the above posters

[dougdrake]

I believe Dogg makes some digital speakers, available from a white van near you!

[sfogg]

"digital amplifiers are still fed an analog signal (and output an analog signal as well)"

There are a few digital amps that don't have analog inputs. I think most of the models from Tact can have direct digital inputs as do a few of the models from Spectron. A few receivers are using digital amplifiers as well and keep the signal digital into the amps. The Harman/Kardon DPR1001 does this for example.

Shawn

[FirebirdTN]

I didn't want to say anything because I wasn't 100% positive, but if class D isn't a digital amp, what *IS* then?

I have seen some amp designs like you mentioned that convert the incoming digital from PCM?!? (I think that is correct) to PWM to "direct drive" the PWM amplifier.

In this case, the input signal coming from the source device can be digital, and stay digital, although going thru a conversion from one type of digital to another, and finally only becoming analog to drive the speakers post PWM filter. In this setup, its still a class "D" amp, however the ONLY time the signal ever becomes analog is basically at the speaker terminals.

-Alan

[DrWho]

For the "digital" amps that have digital inputs, there is still a D/A conversion being performed before the signal is amplified. you'll note that in the following pic, the input signal (as well as the output) is drawn as a waveform:

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I didn't want to say anything because I wasn't 100% positive, but if class D isn't a digital amp, what *IS* then?

no amp is a "digital" amp (at least as far as i know)

[sfogg]

"For the "digital" amps that have digital inputs, there is still a D/A conversion being performed before the signal is amplified."

Read the Tact literature or the Spectron literature. They convert from PCM to PWM directly.. not going to analog first. The amps that have analog inputs covert the analog input to digital for the PWM.

For example:

http://www.tactaudio.com/M2150/Features.html

Also notice the output from the transistors of the digital amps. It is binary... either on or off. It is the filters later on that filters it down to an analog waveform.

Shawn