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

I'll gladly suffer through sensory deprivation to play with Axioms all day.

I'd like to stick my head in an anechoic chamber. Just my head. To hear my neurons firing. It would be, as Jim Morrison called it, a "bright midnight".

So, I'm still trying to get my head around this chart, Di, and widening the sweet spot

First, let’s figure out what Di really means … because my understanding and my intuition don’t seem to align.
If I understand it correctly the directivity index is the difference between these two curves (I think Di actually uses the on-axis response as the reference instead of the window but the window works). As they approach each other this index gets smaller … and at zero I think you supposedly have a perfect omni-directional speaker. Intuitively, I find that hard to to believe … the LFR is a perfect example … as a dipole, even if you could control all the drives perfectly, you are radiating along a single axis. As one approaches 90 degrees off axis you’re gonna loose the highs as they are more directional. Now you can make that up in the sound power curve by cranking the rear firing highs so they average out the sound power curve but that’s not going to make your speaker omni-directional …

Now my next question … the sweet spot ...
I sort of understand if one ignores the delay coming off the rear and side walls the rear levels will boost the missing frequencies. I can also see that the way pressures add works for you to fill in evenly. I'm kind of guessing that getting the rear firing speaker to put in the energy to fill in the spectrum as if it were omni directional may give you the frequency intensities you need to correctly fill the missing info to widen the sweet spot. But what about the delay


P.S.
I'm assuming, guessing, the sound power curve in the plot is sound power converted to dbSPL at the listening windows mic distance.

You can automate the sound power measurement... the magic words are Arduino and openbuilds (or equivalent)

DI is the difference between On-axis or the Listening Window and the Sound Power. Some manufacturers use On-axis and others use the Listening Window. I am assuming Axiom uses the Listening Window because that is what they publish. Recognize however that it's up to each designer to interpret the results as they see fit. So Axiom may use the On-axis curve to tailor the DSP filters in order to make the Listening Window "better".

"Omni-directional" is only in the context of the curves I describe in my poem above. Don't interpret "omni-directional" to mean you can sit directly in between the plane of the speakers, or behind them, and experience Nirvana. You have to be somewhere between the speakers and at a distance where the direct and reflected sounds can be heard (diffuse sound field) which may be 12 feet or more away depending on the room and the distance between the speakers. On this point, Ian has said measurements are taken circumferentially. I think this is well-beyond the SAE spinorama standard which includes the angles in my poem. It's just another example of Axiom wanting to characterize their speaker system as much as possible so they can eke out every last bit of performance.

The DSP compensates for the delay between front and rear drivers.

The Sound Power is indeed the SPL in dB at 1 meter away. I don't know how far the mic actually is.

Thought sound power is in watts and independent of pressure or distance from the object. Although related to both ... if you know one you can get the other.

I skipped your poem but I’ll have another look

Omni directional, ideally, is to radiate evenly in all directions. If I had a perfect one I’d expect to hear the same response curve no matter where I stood. A really good one would sound great no matter where I stood. A lousy one would sound equally lousy no matter where I stood. BTW I know you know I know you know ...but to be clear we are talking mono here.

Sound power can be converted to sound pressure as you say. I think though sound power is a convenient yet incorrect term because it is sound pressure that is directly measured and not sound power. But it's really tomatoes, tomatos, potatoes, potatos.

Axiom certainly didn't say they're ideal omni-directional radiators like a pulsing sphere. Just wait though. Ian will make them more ideal by putting drivers on the top, bottom and sides...LOL!

They're omni-directional to the extent they need to be in order to satisfy the spinorama.

I had a chat with Andrew yesterday about the sub-out. We think this is a good idea. We can also add a switch to the DSP that would allow you to set the High Pass crossover for the LFR to match the subwoofer. It would be for use with at least two subwoofers (right and left) as there is one DSP per channel.

Ah yes, the perfect 360-degree sound radiator. We are a still a long way off from that. I wonder how you would mount it in the room? The response curves of this device would all be identical and would need to have a similar downward tilt like we see in the LFR curves. As to how it would actually perform, all I can say is I would love to be in that blind listen test!

For the purpose of loudspeaker measurements, the Sound Power is in dB SPL. We run the measurements with the mic located two meters from the loudspeaker and then use 2 watts to bring us back to 1 watt/1 meter. The response curves that make up the resulting Listening Window and Sound Power all have their own unique characteristics but with similar trends. In the case of an omnidirectional the 90 will have the maximum downward tilt. In a conventional front firing the 90 will tend to look like the Sound Power. Technically an LFR is a Bipole design but the linearity of the front and rear off-axis responses make it operate more like an omnidirectional.

Thanks Ian.

Just curious, why does the Listening Window need a downward tilt in the first place ? I am starting to suspect that one of the reasons I keep gravitating to the bookshelf speakers is that they tend to have a flat-ish LW while the larger speakers tend to have more of a downward tilt.