AudioKinesis writes:
>In reply, I'd like to point out that, with the same 4 to 16 ohm impedance difference described here, the power that a transistor amp puts out varies by 6 dB, because it is putting out constant voltage rather than constant wattage. Why does the audio world accept this without a blink, and yet think there's a problem when a tube amp exhibits less variance in power output into the same load??
Those of us with a little technical knowledge accept and expect it because at lower frequencies dynamic loudspeaker driver output is proportional to voltage.
Individual drivers together with their enclosures form spring-mass systems where oscillating movements at frequencies approaching system resonance take less energy for a given excursion and therefore less power since that distance is traversed in a fixed time interval like the five milliseconds for a half wave of a 100Hz tone.
Even order acoustic cross-over networks with their drivers in-phase (or to be pedantic a multiple of 180 degrees out of phase with the polarity of one driver flipped for odd multiples) have an efficiency peak at the cross-over point due to mutual coupling which is 3dB assuming the two drivers have matching efficiency.
To apply audiophile pseudo-science dictating simpler is better you want to go with this flow (implying negligible output impedances like the .01 - .02 Ohms of many transistor amplifiers) instead of adding electrical circuits and their errors to mash things together.
This is completely orthogonal to the maximum output an amplifier may deliver where some technologies (output transformer equipped amplifiers with taps optimized for various load impedances and some digital amplifiers) allow more similar limits regardless of load impedance.
I'm also ignoring that you can design an amplifier with output current proportional to the input signal and combine it with an appropriate cross-over network to yield better performance because audio output is no longer reduced by voice coil heating (which increases resistance and therefore decreases current flow with a constant voltage source) and affected by inductance changes as the voice coil moves through its range (this causes IM and harmonic distortion) since such combinations are uncommon and would be a hard sell to the audiophile market that could no longer make arbitrary amplifier and speaker swaps. DSP cross-overs with current/voltage programs and relays to switch amplifier configuration would make a fun Burning Amp presentation.
> Back to the original question, what's with 4 ohm speakers if they're harder to drive, well in general they can play louder with a solid state amp, and most people have solid state amps, so they get more sound per dollar with 4 ohm speakers (quantity outsells quality).
Quantity becomes quality when it avoids clipping.
When I play a nice jazz recording at a less than live but realistic sounding 85dB average SPL with 20dB peaks that can be pushing 108dB 1 meter from a speaker.
With 86dB / 2.83V / 1 meter speakers having a 4 Ohm bass compliment I'm just going to miss clipping an amplifier built to meet a 100W into 8 Ohm FTC rating (they measure with sine waves that have a 3dB crest factor).
Keeping the same efficiency but increasing impedance to 8 Ohms takes a 200W amplifier.
This fits well with the desire for single box speakers especially where last octave extension is desired (example - the Revel Salon 2). Keep the size, loose the bottom octave or move it to a sub-woofer, and you could have another 9dB of efficiency for a 92dB sensitive/efficient 8 Ohm speaker.
The two approaches work for different market segments and I'm aware that yours is the latter.
>In reply, I'd like to point out that, with the same 4 to 16 ohm impedance difference described here, the power that a transistor amp puts out varies by 6 dB, because it is putting out constant voltage rather than constant wattage. Why does the audio world accept this without a blink, and yet think there's a problem when a tube amp exhibits less variance in power output into the same load??
Those of us with a little technical knowledge accept and expect it because at lower frequencies dynamic loudspeaker driver output is proportional to voltage.
Individual drivers together with their enclosures form spring-mass systems where oscillating movements at frequencies approaching system resonance take less energy for a given excursion and therefore less power since that distance is traversed in a fixed time interval like the five milliseconds for a half wave of a 100Hz tone.
Even order acoustic cross-over networks with their drivers in-phase (or to be pedantic a multiple of 180 degrees out of phase with the polarity of one driver flipped for odd multiples) have an efficiency peak at the cross-over point due to mutual coupling which is 3dB assuming the two drivers have matching efficiency.
To apply audiophile pseudo-science dictating simpler is better you want to go with this flow (implying negligible output impedances like the .01 - .02 Ohms of many transistor amplifiers) instead of adding electrical circuits and their errors to mash things together.
This is completely orthogonal to the maximum output an amplifier may deliver where some technologies (output transformer equipped amplifiers with taps optimized for various load impedances and some digital amplifiers) allow more similar limits regardless of load impedance.
I'm also ignoring that you can design an amplifier with output current proportional to the input signal and combine it with an appropriate cross-over network to yield better performance because audio output is no longer reduced by voice coil heating (which increases resistance and therefore decreases current flow with a constant voltage source) and affected by inductance changes as the voice coil moves through its range (this causes IM and harmonic distortion) since such combinations are uncommon and would be a hard sell to the audiophile market that could no longer make arbitrary amplifier and speaker swaps. DSP cross-overs with current/voltage programs and relays to switch amplifier configuration would make a fun Burning Amp presentation.
> Back to the original question, what's with 4 ohm speakers if they're harder to drive, well in general they can play louder with a solid state amp, and most people have solid state amps, so they get more sound per dollar with 4 ohm speakers (quantity outsells quality).
Quantity becomes quality when it avoids clipping.
When I play a nice jazz recording at a less than live but realistic sounding 85dB average SPL with 20dB peaks that can be pushing 108dB 1 meter from a speaker.
With 86dB / 2.83V / 1 meter speakers having a 4 Ohm bass compliment I'm just going to miss clipping an amplifier built to meet a 100W into 8 Ohm FTC rating (they measure with sine waves that have a 3dB crest factor).
Keeping the same efficiency but increasing impedance to 8 Ohms takes a 200W amplifier.
This fits well with the desire for single box speakers especially where last octave extension is desired (example - the Revel Salon 2). Keep the size, loose the bottom octave or move it to a sub-woofer, and you could have another 9dB of efficiency for a 92dB sensitive/efficient 8 Ohm speaker.
The two approaches work for different market segments and I'm aware that yours is the latter.
