Axiom Home Page Forums General Discussion Home Theater Starting to oggle new gear

Yes, Audyssey is correct.

There is no table or lookup conversion because audyssey is correcting for phase. Each subwoofer will have it's own internal latency due to the onboard amplification\dsp and the mass of the driver. On top of this, where you put the subwoofer in the room in relation to the main R\L speakers will affect the phase offset too. Ideally subwoofers should be equidistant to your main speakers or symmetrical if you have 2. This is so that the phase of the subwoofer can be corrected to properly track both R\L channels.

Advancing the subwoofer (adding distance) shifts the phase positive in rotation. Retarding the subwoofer (subtracting distance) shifts the phase negative in rotation. Each shift is relative to the mains, that would be the reference signal.



Borrowed from Wikipedia. It is showing the phase of 2 waveforms and relative shift. This shift can be expressed in degrees or time if it is a fixed frequency. To find the time length of a frequency divide 1000 by the frequency wanted. You will get the time of duration of the wave in ms.

80hz is 1000/80= 12.5ms per cycle. So to shift a 1/2 cycle you need to move 6.25ms or 7.087ft.

To measure phase you need a relative difference between 2 signals. The transfer function tool in audio tools lets you accomplish this with a built in sweep generator and pink noise. Or you can let Audyssey or Dirac do it for you.

The trouble is when you have multiple subs. It is best to phase align the subs to eachother first, then let the algorithm match them to your mains as one sub signal. Pretty cool when it works. Super tight and efficient output. High startle factor.

All you need to do a frequency check is pink noise and the two included modules RTA and FFT plots. Pink noise can come on a CD or there are tracks on spotify for this. If you have a cable to route from the device there is a built in generator as well included.

Here is one on spotify for everyone to use.

Pink Noise -10Db ref
https://open.spotify.com/track/7apGZoUjP97d6UPDdMMc2e?si=f481a3c14a334581

Pink noise will give you a good impression of standing wave behavior in your room and general frequency response.

Sweeps or chirps will be a more accurate impression of how actual source material will sound in your room.

Most TV content does not have sustained frequencies that excite standing waves, but it is useful and important when listening to music or movie soundtracks to know where your problem frequencies are.

Please note: A microphone is only measuring one point in space. Even a binaural setup is not a great representation of what we hear. You need to take multiple measurements or move the mic around to get a better impression. It is really easy to fake a great room repsonse measurement and post to a forum. Lots of differences in moving just a few inches, so keep that in mind.

Yes, that module is great! Able to catch multiple measurements and compare and average graphs. I used that module to measure the M5HP and used the different graph panes for angles off the tweeter axis. Great tool.

One note on AudioTools ... Andrew also offers AudioToolsMax which comes with all the modules + any future ones. At the time I bought it, he was running a sale ... $200.

Might sound like a lot but I justified it as an inexpensive alternative to buying specialized equipment for the bench.

Thanks for the confirmation. I'm only getting back to the adjustments this afternoon. I ran a 6 position test late last night. The app worked quite smooth so i'm in the minority i guess compared to others who've posted negative reports on the app.

That makes sense YET, someone doing it themselves manually would still have set the sub at 11 foot distance. There should be some explanation on this in the manual.

Interestingly, my older EP350 has a Phase switch on it. I could try flipping it to 180 degrees from 0 just to see what Audyssey does, but perhaps later as i have much more important tweaking to try first.

There is a plan to add a second sub. I've always noted that the sub-sounds are weighted to the left side of the room where the sub is located. Likely boundary reinforcement but with that second sub i expect the smoothness often observed with the addition should come about.
That is the plan and hope.

This is why i think the standalone LARSA app might be better for determining the room response. I had thought about just using pink noise with the RTA but since the LARSA is the same cost as the base Audiotools, which one would i likely use more?
I can only think of the one use which is testing the room response under different conditions (wall treatments, new speakers, speaker movements, etc.). Convince me otherwise that Audiotools is still the better way to go over LARSA or would it matter?
I think i prefer the idea of the frequency sweep using individual tones via the chirps.

The graphs from the first Audyssey run last night, taken from the Audyssey app and after i corrected the midrange adjustment (turned off) and corrected their idea to roll off the upper end past 4 kHz for some reason.
The surrounds and centre channel were setup as 'small' and different crossovers of 80Hz and 60Hz respectively (by the app).

Have you been keeping detailed notes of curves vs listening impressions?

I haven't done any listening yet. Was just setting things up.
I need some quiet time at home. That hasn't happened yet. Probably next week during the day. Then i'll have a chance to get that other app as well.
The first time i tried to do the sound tests, someone was playing with the dog on the main floor banging things around so i had to start over. The the furnace kicked on, had to shut that off and start over, then the wine cellar AC turned on....