How do you record a subwoofer in Smaart? Well, recording a
full range speaker was easy. We just hit play on the measurement over here and
then we use the delay tracker. No problem. But with a subwoofer we can't usually
use the delay tracker in the same way and I want to talk to you about why and
then what you can do about it instead so first let me show you my setup over here
so I've got this PR X sub woofer and I've got my microphone here super close
to the ground it's only like maybe a couple of inches off the ground I'm
doing a ground plane measurement and I'm very close to the subwoofer so I can try
and get you know really good signal-to-noise ratio and here's I'm
going to do I'm going to reset the delay here I'm gonna hit play on the
measurement and then I'll go ahead and turn on the signal generator so this is
what this looks like with no delay now let's talk about why we often have
trouble using the delay locator when it comes to the subwoofer so the first
problem is that as you can see here in the impulse response the signal level of
the sub for the analyzer is much lower there's just much much much less
information here than when we had a full-range speaker the other problem is
that just the time it takes for sound to get out of the subwoofer just because of
its physical construction there could be anywhere from zero to thirty two
milliseconds of delay before sound even gets out of there another reason why the
delay locator is not the best tool for using with subwoofers the sound of the
subwoofer that you hear in the room at most points when you stand in the room
is not actually direct sound from the sub right it's a combination of all of
the reflections in the room so your delay locator is oftentimes going to try
and grab onto one of those reflections which is potentially louder than the
direct from the subwoofers so that the lay
locator may seem to be working but really it's grabbing onto a reflection
that's not the real direct sound and that's not the signal that we want for
that for our measurement so let's talk about some ways that we can get around
this now the first step is just to try the delay locator if we try the delay
locator and it seems to be giving us good data then we can move forward so
let's try that I'll just click this guy here and now look at these numbers
they're all dancing around this doesn't seem to be very helpful I see that I'm
struggling here a little bit so let me turn off automatic delay tracking and
just click find okay so this says eighteen point three three and you'll
see that every time I click this it's going to be a slightly different number
but I'm super closed here my microphone is really close I should have great
signal-to-noise ratio even with that it still it looks like it's anywhere
between 17 milliseconds and 26 so it doesn't exactly know right all right
let's try 18 point six milliseconds so far we've got pretty good coherence
maybe if I stop talking it'll get even better and we do have a flat trace here
around the area that I want to be looking at so in this case this is
probably fine out in the field though once I get you
know a hundred feet from that subwoofer and I have all the reflections from the
room going on this technique might not work so I think one of the quickest ways
to figure this out is that if we set this back to zero if we can see the wrap
arounds if we've got at least enough information here that we can see where
the trace starts and where we want it to be flat let's say around 100 Hertz then
we can count those wrap arounds which in this case would be one almost two
complete wrap arounds and then we can just multiply that by the period of the
frequency we want so 100 Hertz has a period of 10 milliseconds right so
one wrap around would be 10 milliseconds another wrap around would be 20
milliseconds so I could try putting 20 milliseconds into my delay here and that
works pretty well now I've got a flat trace here that that makes this a little
bit easier to read and that's what this is all about right just getting quick
data that's easier for me to make decisions with take action with right
what is another way we could do this well I could also get to this number
pretty quick just by guessing right I don't mean guessing I mean just like
turn out the delay until the face starts to flatten out and this is going to take
a long time but if I just started putting in numbers like 2 4 6 we can see
the phase start to flatten out until eventually I get to a place where I say
oh ok now I can read this coherence is pretty good great so that's how you
measure the subwoofer and smart and in the next video I'm going to show you how
to measure a subwoofer INSAT live sound design