Originally Posted by Heinrich S
I'm a little confused on this one. If I have a speaker and add more woofers in parallel would that increase the sensitivity?
Using the common definition of sensitivity which is SPL for a given applied voltage, the usual answer is yes.
It is possible to misconfigure the additional drivers so that they cancel other than add.
Or it would just mean each driver "sees" less power, less work per woofer?
That requires a series/parallel configuration. A pure parallel configuration reduces the system's efficiency which will then draw more power from the ampliifer for a given voltage.
I assumed that adding drivers to a speaker would increase the sensitivity.
The law of conservation of energy always applies. From a general engineering standpoint there is no actual over-all increase in SPL for a given applied power. However, many secondary effects can take place. One is the reduced impedance causing more power to enter the speaker system from the amplifier for a given output voltage or volume control setting. Adding more drivers in-phase will somewhat narrow the speaker's directivity, which means more SPL on-axis, but less SPL off-axis in most cases.
Depending... depending... depending.
I discussed this with an EE and he said that sensitivity would not go up.
He was probably thinking about the law of the conservation of energy, which is valid in its way even though paralleling speakers usually causes the speaker array to draw more power, become more directional, and create more SPL on axis.
If a single speaker is at 90 db at 1 watt and you add another single at 90 db it would still net 90 db total but the power would be divided.
Not true if the drivers are connected in parallel, radiate into the same space, and you drive them with a typical amplifier that provides a very low-impedance source.
If one speaker driver were an 8 ohm load, then the two drivers in parallel would make up a 4 ohm load which would double the power draw right there. If the two speakers were radiating into the same general space in phase then they would be more directional than one driver which would also provide an additional increase in directionality and might add a dB or more SPL on-axis at the cost of off-axis sensitivity.
Just to further complexify things, the directionality and impedance effects would depend on frequency. The impedance effects would depend on the enclosure and the mounting of the two drivers in the enclosure. The directionality effects would also depend on the room, location in the room and the distance from the listener to the speaker.
Acoustics can make simple seeming questions end up with complex answers.