Estive a ler um artigo interessante de um designer de amplificadores que defende que o melhor som possível implica muita potencia disponível:
Challenges in Faithful Reproduction of Musical Peaks
A Power Amplifier Designer's Perspective
Article by Simon Thacher, Ph.D. Of Spectron Audio
http://www.enjoythemusic.com/magazin...708/index.html
To reproduce realistically a peak loudness of 109dB using the speaker with a sensitivity of 88dB to 89dB located 12 feet from the listening chair, the amplifier must produce about 400 watts peak power. To reproduce realistic peaks of a rock band, the amplifier must produce 4000 watts of peak power
.
These projections are accurate only if the speaker in question has purely resistive impedance. However, loudspeaker loads comprise complex impedances with both resistive and reactive (capacitive and inductive) components. Such impedance can be depicted as a vector with its magnitude (modulus) and angle (phase), and both vary with frequency. In general, the voltage and current waveforms, in complex impedance load, are out of phase with each other and therefore, to characterize accurately a speaker's load impedance, both modulus versus frequency and phase versus frequency plots must be known. Frequently, the phase angle is much more crucial to the speaker load than the modulus alone. Their peaks and dips, as a rule, do not coincide with each other. Because of those disparities, the resulting actual load can be very severe at frequencies that would not be intuitively obvious from looking at the separate plots.
To deal with this phenomenon, Keith Howard (2) introduced the figure of merit he has labeled Equivalent Peak Dissipation Resistance (EPDR). This is, simply, the resistive load that would give rise to the same peak power device dissipation as the speaker itself. Using EPDR as a figure of merit, the speakers can be compared directly with each other. It is an excellent idea, and John Atkinson of Stereophile has supported its use (3). However, speaker manufacturers are not utilizing it, and amplifier manufacturers are not demanding it.
Using the
B&W 805 speaker, with 87.5dB/W/m sensitivity, and the
powerful Music Fidelity amplifier, Howard did a number of measurements of produced peak SPL from a few recorded classical pieces. He found that peak SPL can be as high as 120dB at 10 feet from the speakers.
The measured peak power at this peak was 3.4 kW. While this output is extremely difficult to achieve we still should remember that B&W 805 is only a bookshelf speaker (albeit an excellent one) and the comparison with more difficult-to-drive speakers would be most instructive. For example,
the estimate for B&W 803D for the same recordings is that its peak power requirement would be as high as 7 kW. Many speakers have even more reactive loads making truly enormous demands of the amplifier power delivery.
Power Supplies: Peak Voltage
While perhaps a very few amplifiers can deliver such a peak power, that does not mean that they can reproduce an undistorted musical event. Headroom is the more accurate measure of the amplifier's ability to reproduce large transients.
Power Supplies: Peak Current
When a musical note is played at the frequencies where the impedance dips, the current demands skyrocket. When this happens with amplifiers that lack large output current capability, the amplifier "current clips." Those transients will be both attenuated and quite distorted, and as a rule high frequency and bass performance will be degraded.
Duration Of The Peaks
Some 16 years ago, NAD investigated maximum power output versus duration capability before clipping; they found that musical signals demand hundreds of milliseconds of power burst for accurate reproduction of musical peaks
Output Stage: Heat Handling Capability
However, if output devices can't handle these instantaneous high-power conditions they will be pushed beyond the safe operating area and without protection circuitry they will fail. On the other hand, if the amplifier's protection is activated, its output will be clipped. This is even though the speaker's voltage and current demands may be within its power supply capability. Therefore, the heat dissipating capability of the amplifier output stage is paramount in the delivery of required peak voltage and current, frequently over the periods of hundreds of milliseconds
Output Stage: Thermal and Other Distortions
Rising temperature of the output devices will also cause thermal distortions, which add to the harmonic distortions caused by clipping. These distortions are particularly harmful at low frequencies, where output devices can heat and cool during a single cycle.
Undistorted Musical Peak: Should We Care?
The exploration of the origin of "listener fatigue" is extremely interesting, at least, for this writer. We believe that when our subconscious mind detects a small unnatural trace of distortion in reproduced acoustic music (which is not recognized yet as a very low level irritant by the analytical part of our brain) it activates a subtle alarm. This forces the listener into the tense or alert mode. Indirectly supporting this hypothesis is the common description we hear from Spectron users who utilize the two powerful monoblock amplifiers (7 kW peak power, each): "how relaxing" is my listening now.
Re: Quanta potencia é necessária para umas determinadas colunas (mais cabos)
Orpheus escreveu
Nem precisam, trazem para casa e experimentam.
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