Why no 16+ ohm speakers?

[yepimonfire]

One of the major limitations regarding power with both amplifiers and speakers is heat. A majority of this is entirely related to current, and this is one of the reasons many amps have difficulty handling lower impedance loads. If we take a standard 100w @8 ohms amplifier, we get about 28v rms and 3.5A. The reason so many amplifiers fail to deliver 100w continuously into 5/7/9/11 channels is entirely due to current limitations, not voltage, since solid state amps are constant voltage sources.

If we built a 16 ohm speaker, and instead paired it with a 40v rms amp, we could still get 100w, but only using 2.5A. With 7ch, an 8 ohm setup would require 24.5A continuous, with 16 ohm speakers, only 17.5A.

This concept is somewhat similar to 70v distributed audio systems, such as a PA in a store, multiple low impedance loudspeakers would place a massive amount of stress on an amplifier and require large cabling to prevent heat buildup, whereas higher voltage and less current does not. Why can’t this be applied to regular audio?

Am I missing some important detail as to why this wouldn’t work?

 

[rojo]

One of the major limitations regarding power with both amplifiers and speakers is heat. A majority of this is entirely related to current, and this is one of the reasons many amps have difficulty handling lower impedance loads. If we take a standard 100w @8 ohms amplifier, we get about 28v rms and 3.5A. The reason so many amplifiers fail to deliver 100w continuously into 5/7/9/11 channels is entirely due to current limitations, not voltage, since solid state amps are constant voltage sources.

If we built a 16 ohm speaker, and instead paired it with a 40v rms amp, we could still get 100w, but only using 2.5A. With 7ch, an 8 ohm setup would require 24.5A continuous, with 16 ohm speakers, only 17.5A.

This concept is somewhat similar to 70v distributed audio systems, such as a PA in a store, multiple low impedance loudspeakers would place a massive amount of stress on an amplifier and require large cabling to prevent heat buildup, whereas higher voltage and less current does not. Why can’t this be applied to regular audio?

Am I missing some important detail as to why this wouldn’t work?

How would 100w translate to SPL on a 16Ω speaker, versus 8Ω? I suspect the 16Ω speaker would have lower sensitivity, and you'd need twice the wattage to match the same SPL anyway. It's ultimately a wash.

 

[TLS Guy]

How would 100w translate to SPL on a 16Ω speaker, versus 8Ω? I suspect the 16Ω speaker would have lower sensitivity, and you'd need twice the wattage to match the same SPL anyway. It's ultimately a wash.

No, it would be half the sensitivity of an 8 ohm speaker at 2.83 volts 1 meter, but under 1 watt one meter the sensitivity is the same for 4, 8 and 16 ohm speakers. If the speaker all had the same 1 watt 1 meter rating they would all take the same power for the same spl.

To get back to Yep's assertion that solid state devices are current but not voltage limited is untrue.
The output devices are voltage limited because you start to get sudden voltage leaking through the semiconductor material, which punches holes through it. Then you start getting pops through the speakers, and then breakdown of the device and shorting out of the output devices.

Tubes on the other hand are much more current than voltage limited which is why back in the tube era there were so many 16 ohm speakers. In fact that was pretty much the universal impedance.

As solid state amps became prevalent then speaker impedance had to drop to the 4 to 8 ohm range to limit voltage and output device damage. Either way you are in trouble, as heating effect can be equally expressed as the square of the current X resistance, or the square of the voltage/the resistance. So either way you are up against the square of the current or voltage in terms of device damage.

 

[highfigh]

One of the major limitations regarding power with both amplifiers and speakers is heat. A majority of this is entirely related to current, and this is one of the reasons many amps have difficulty handling lower impedance loads. If we take a standard 100w @8 ohms amplifier, we get about 28v rms and 3.5A. The reason so many amplifiers fail to deliver 100w continuously into 5/7/9/11 channels is entirely due to current limitations, not voltage, since solid state amps are constant voltage sources.

If we built a 16 ohm speaker, and instead paired it with a 40v rms amp, we could still get 100w, but only using 2.5A. With 7ch, an 8 ohm setup would require 24.5A continuous, with 16 ohm speakers, only 17.5A.

This concept is somewhat similar to 70v distributed audio systems, such as a PA in a store, multiple low impedance loudspeakers would place a massive amount of stress on an amplifier and require large cabling to prevent heat buildup, whereas higher voltage and less current does not. Why can’t this be applied to regular audio?

Am I missing some important detail as to why this wouldn’t work?

Tube amps use output transformers (most of the time) to match the amplifier's high output impedance and the speaker's low nominal impedance. Solid state amplifiers have extremely low output impedance. Some (not a large number) of musical instrument amplifiers had the speakers wired parallel to provide a 2 Ohm load- this works just fine, as long as the correct output transformer is used.

70V (and others used for those systems which are called 'constant voltage systems') use transformers to determine the output at each speaker, so the amplifier isn't seeing the speaker impedance in the same way as it would if the speakers and amplifier were wired directly. The higher voltage also allows thinner wire to be used on long runs, which means the project cost can be lower than when the distance causes the wire gauge to be an issue. Most 70V (or 25V, 50V or 100V) systems aren't known for great sound quality, but that doesn't mean they can't sound good- it just costs more for better transformers. It's also necessary to set the speaker output taps on the transformers at a level that will allow the amp to maintain headroom and this is where some installations run into trouble- if the system is driven hard and the taps are at the limit of the amplifier's output, the amp's output section can overheat, just like an amp without transformers.

 

[Johnny2Bad]

The short answer is that Solid State amps deliver the most power into lower impedances. So you have two markets (loudspeaker manufacturers and Power Amplifier manufacturers) who work in congruence to encourage low impedance speakers (relative to 8 ohms).

Back when transformer-coupled amplifiers were the norm (tube amps, mostly, but also the McIntosh patent Solid State amps) 16 ohm speakers were more common, as when a transformer tap is closely matched to the speaker impedance, power is identical (so 4, 8, or 16 ohm power output would be the same).

One advantage of a 16 ohm speaker is the resulting amplifier Damping Factor is 4x that of a 4 ohm speaker load (plus cable and crossover impedance, so the net DF is actually closer between the two than 4x, but it is still greater).

Solid State amplifiers that have both the Power Supply reserve capacity and Power Transistors capable of delivering the required current (usually accomplished by increasing the transistor count and required heat sinks) have no problem delivering power into 2 or even 1 ohm loads. Because those three factors are the Nos 1, 2, and 3* most expensive parts of any amplifier, they are also the parts most often compromised in order to meet a price point.

* Plus a fourth incidental cost, shipping due to weight.