Axiom Home Page Forums General Discussion What's New At Axiom LFR1100 Active

The red curve is the Listening Window and the blue is the Sound Power. The Listening Window is 0 to +/- 30 degrees horizontally (phi plane) and +/-10 degrees vertically (theta plane). The Sound Power is a weighted mean of a number of curves: Axial Response, Listening Window, and Early Reflections.

I don't think Ian has ever said publicly what the angular resolution of those measurements is. And for all I know, Axiom may extend these curves beyond the nominal angular ranges I've described. The weights for the Sound Power are Axiom secret sauce.

The recipe is right below. You and your whole family can sing it to the tune of "We Three Kings from Orient Are":

We six curves of Axiom are
30 years old we've come so far
every one eighteenth pi rad, an anechoic curve we add
of spinorama data not scalar.

Refrain:

O curves of tone and SPL
curves with similar shape and flare
gentle slope, low Q nope
perfect sound these curves foretell.

Direct sound real flat without any gain
"Axial Response" that is my name
simple content, most important
over all curves I reign.

Repeat refrain

A "Listening Window" nine curves mean am I
0 to +/-30 degrees across, 10 degrees down, 10 degrees high
within a dB, these curves must be
for listeneners to joyously sigh.

Repeat refrain

Image width, stability, timbre to tame
+/-40, 60, 80 across and 50 down and high's the game
most that we hear, bounce from quite near
"Early Reflections" is my aim.

Repeat refrain

A speaker's signature doth we take now
weighted mean of 70 curves is how
downward tilting, no broad wilting
"Sound Power" curve art thou.

Repeat refrain

The "DI" curve is the cash cow
the "Listening Window" from "Sound Power" take away now
closer to zero, it's a hero
listeners will procalaim a big "Wow!"

Repeat refrain

One last curve is for finesse
"Early Reflections" from "Sound Power" we minus
lateral prophylaxis, from far-off axis
"Early Reflections DI" shows polar bias.

Repeat refrain

Low DI with curves smooth and similar
disperse the sound as not to be insular
audio pornography, via sonic holography
sharp images spaced out renders them singular.

Repeat refrain

Axiom's direct radiators sound great when they're played
sound power declining 3dB per decade
if that DI, is a bit high
constant, low DI LFRs can be yours via trade.

I thought that the listening window measurement is the average of 4 off axis measurements 15 Degrees left, right, up, and down from center. I’m sure someone will set me straight if I got that wrong ...

I’m sure it’s done in the anechoic chamber but I’d bet two walls of the chamber need to be covered (at least partially) or you would not be able to measure the Omni directional effect

All the chamber walls are covered with sound-absorbing material which renders the walls acoustically invisible and hence why I said "No walls."

You don't need reflections to measure the omni-directional effect because the effect is "encoded" within the curves. When you place the LFR in a room, the speakers interact with the room and the omni-directional effect within the curves is decoded thanks to your ears-brain system in that room.

The Listening Window is (traditionally) a mean of the curves I described but as I said, Axiom may be extending the angles to more fully characterize the speaker response.

Hmmmm .... We need to know the setup to understand what we are looking at. The curves from the front firing speakers alone or the curves from the front combined with the rear reflections. I’ll bet that the off axis measurement is not going to improve much if only if it’s the front alone. If the curves are synthized from the front and rear being measured separately (I.e. the rear driver needs to face the mic) then it’s not much of a measurement. If it’s a real measurement .... how would you propose to measure it.

It's the curves from the entire speaker. You put the speaker on a turntable and rotate it horizontally and take measurements. You rotate the microphone for vertical angles. The measurements are frequency sweeps across the audible range. You generate 234,389 curves and drink your face off and smoke the good stuff for 20 days straight to make sense of all of them. Then when you do, you go to the DSP and tweak all the filter coefficients, and then go back to the chamber and do it all over again until you have the angelic curves Ian posted.

I’m going to bed ... I think you should reread my post
BTW I do undstand what Ian means when he talk about the spinorama

You want to know how the rear measurements are taken and integrated with the front.

I will see if I can clarify these two measurements. The Listening Window and the Sound Power, or Total Radiated Sound Power, are the two main curves in what has been coined the “Spinorama”. Both these curves are averages of a "family-of-curves”, or amplitude response graphs, measured in an anechoic chamber. The Listening Window will always be an average of a group of curves centred around the on-axis curve. The Sound Power will always be an average of curves taken in all directions around the loudspeaker in an anechoic chamber. Exactly which curves are used, at which degrees of steps, and using which weighting will vary a bit depending on who is doing the measuring and when. This type of research began in earnest in the 1970’s when Dr Floyd Toole began comparing various anechoic measurements to strictly controlled listening tests at the National Research Centre (NRC) in Ottawa, Canada. I was fortunate enough to have been involved in this research at the NRC for eleven years. Over the years we were able to refine the importance of the various measurements taken based on the results from the double-blind listen tests. The magnitude of this research is daunting as you need to verify consistency in the double-blind listen test results across many people and environments. A handful of companies have continued the research since the NRC days, Axiom being one of them. API being another one, which is where Andrew was before Axiom. API, because of the Mirage line, did a lot of research into the nuances of omnidirectional loudspeakers on this research. When Andrew first arrived at Axiom it was really interesting to chat about our various findings since the NRC years. Following this time Version 4 was born.

For a conventional front-firing loudspeaker the Listening Window should be linear across the frequency band and the Sound Power should have a consistent tilt downwards from 0 dB in the low frequency to around -10 dB at 10 kHz when compared to the Listening Window. For an omnidirectional speaker the way to read it is a bit different as now you have the ability in the design phase to bring the Listening Window and Sound Power closer together. In order to maintain a proper spectral balance, you cannot just bring the Sound Power curve up to match the Listening Window, instead both need to move towards each other. By creating the LFR1100 Active we had an incredible amount of control over the five driver sets which allowed us to experiment with making the Listening Window and the Sound Power the same. I think you will love the result!

"By creating the LFR1100 Active we had an incredible amount of control over the five driver sets which allowed us to experiment with making the Listening Window and the Sound Power the same."

This statement is telling us actives alone won't yield a null Directivity Index. We need active LFRs to experience Nirvana.

I'd really like to understand, in terms of soundstage, imaging, etc what the qualitative differences are between passive, active and active LFR.