power response/off-axis response?

[Lindahl]

Maybe I'm wrong, but it seems to me that people use power response as a synonym for off-axis response. Power response is a very confusing term to me... how and why does power mean the same thing as off-axis in this context? I would have thought that power response would be how a speaker's frequency response changes as it's given more power (which doesn't seem possible... is it?).

[Tommythecat]

Power response in this sense is describing the total power radiated from the diaphram - so we look at the on-axis response and the off-axis response.

[cjd]

It's far broader than simply "off-axis" - it's a generalized combined on/off-axis response curve. Off-axis usually requires a known degree of deviation from on-axis: maybe 15 degrees, maybe 30 degrees...

[Lindahl]

Ok, now the term finally makes sense. Thanks!

[Tommythecat]

Well cjd, you could say your definition is "broader", but I dont limit the off-axis response to any 1 angle. I typically look at the uniformity of the on axis, 15deg, 30deg, 45deg, 60deg. Someone may attempt to say that power response means one thing when in general it refers to the entire power radiated. What i meant by "off axis" was just "not on axis".

[cjd]

Yeah, but do you look at 11.430481 degrees?

It wasn't an issue of limiting off-axis you look at, it's an issue of how the term is used.

If I say "off-axis response was good" the question usually comes up "at what angle?" That is all.

[Tommythecat]

They should be asking "at what angles"

[Dennis H]

Build an imaginary sphere with the speaker at its center. Measure the SPL at equally spaced points all over the sphere and average all the measurements. That's power response.

[Mark Seaton]

To further beat the definition to a pulp, I would first agree that many tend to use the term interchangeably. If we take a closer look at what is really implied and meant in with either, I might describe the on/off axis response characteristics and power response to be two different subsets and representations of the same data; that data being the way the speaker radiates sound in different directions at different frequencies.

While not always implied or meant, I would suggest that referencing on/off axis is more specifically looking at frequency response uniformity over some radiation angle that usually corresponds to a listening area and maybe first reflections. The concept of power response is a bit more global in looking at the full sphere of sound radiated from a speaker at different frequencies. In common home listening environments this relates to what sort of energy balance will be combined with the acoustics of the listening space. In spaces of moderate to small dimensions (not auditoriums), the subjective spectral balance comes from a combination of direct and reverbertant sound. The power response speaks more directly to the spectral balance of the reverberant energy.