Hi kevzep;
Will you explain the screen shot in post 147 a bit? I have not used SMAART and am trying to understand exactly what I'm seeing. In the top half of the screen is the yellow trace the sub run from the bottom up to about 200hz and the blue the 4410's from the top down to about 60? Can you manipulate the receive delay to unwrap the phase or is that the preferred display?
On the lower half of the screen what is shown in the 200 Hz and down range? Coherant summation? Why are the traces at about zero above that? It's not the noise floor I suppose as the traces and scale go negative as well? Is that just a set reference level?
Are these tests sampled with the mic at a boundary?
Thank you in advance,
Barry.
Sorry for the slow reply, this part of the forum is tucked away and I only come in here every few days.....
Welcome to AK, best forum on the internet........:thmbsp:
Okay, one thing to realize about particularly this older version of Smaart, is that it works best outdoors, or in large arenas, using it in a lounge like I am can be a bit misleading if you dont know what you are looking for, because of the confined space creating early reflections, and some of the information which shows up isnt as accurate as the newer version 7 (will be getting a copy soon).....particularly in the coherency department......
But, if you use it all the time like I do, then you know what to believe and what not to believe......
The setup is this, Smaart is looking at two signals, one is a reference signal, which is directly from the source (pink noise generator), and then the microphone, which is positioned in this case at the listening position.....
Smaart looks at both signals, the dry signal, and the signal being picked up by the microphone, the response is the result of a comparison of the two signals so we can see what is actually coming from the system, rather than looking at all the sound being picked up by the mic including reflections and background noise, we use the transfer function to tune the system, we are not interested in what the room is doing when we tune the system, if we try to tune the system with the RTA, we could be looking at room nodes or nulls and trying to compensate these by compromising the performance of the system......after we have the system optimized, we can then look at the performance of the system with regards to the room, but in the case say of looking at the phase relationship of the subs in the system, we dont want the room screwing up the readings.....
The object here was to make sure the sub was showing a compatible phase correlation to the low end of the 4410A's.....(moot now, because I have my JBL L5's back in service, so I went through the whole process again)
What you are seeing in the top window, is indeed the phase trace of the SB-115 sub. (I think that picture might have been before I moved the crossover point down). In this case you can see the 0 degrees is in the middle and it goes to 180 degrees either side, so of course as the frequency goes higher the phase shifts, this is a typical trend for a driver of this size producing these frequencies....
When you see a wrap, its showing 360 degrees phase shift....it wraps and continues on from the opposite side of the display....
You can change the display to unwrap the trace, but we use this as the default display, this is more useful for what we are doing and less likely to give the "wrong impression"......
So this trace is whats active currently.........I have the 4410A's off at this point.....
The blue trace is the 4410A phase trace which I captured as a snapshot. The reason I am looking at this, is to see how the sub phase trace on its own, lines up with the lower range of the 4410A. As you can see, in the area of its active response it lines up, especially at the crossover point, so its all good....If it doesnt line up, I would have to use some delay to effectively push the sub into a position where it is lined up......
Some care is needed because it is easy to apply too much delay and think you have it lined up, but in actual fact, you have it lined up a whole wavelength behind where it should be.......you can tell by the amount of wraps, which will basically double over the same frequency range as the captured trace....
On the lower window, the yellow trace is the frequency response on the SB-115 sub, and the blue trace is the captured frequency response of the 4410A.
When I turn the 4410A on I can then see how the response is affected at the crossover point.....
When both speakers are going at the same time it becomes all too obvious if you have got your alignment wrong.....or right for that matter.....
So you see why we dont want the room to interfere with the readings......
The red trace, is the coherency trace, this is supposed to tell us if what we are seeing is actually coming from the system, or whether it is a reflection of some other interference......
The coherency in this version of smaart is a bit rudimentary and cant always be taken at face value......
For example, it says there is something weird happening at 250hz, but I know from experience using this version, and my ears, that its just an anomaly in the coherency calculation within smaart....could have been a random reflection off the wall behind the mic, although in this case unlikely..
The level is at zero when the two signals are at the same level, I have turned the sub up a bit from the trace I took of the 4410A because of the lack of sensitivity to the low frequencies, the readings tend to be more accurate and defined for the low frequencies with the system producing a bit more SPL.......
The microphone was sitting pretty much where I took the photo from....
The B&K4007, very important to use a good mic, I think these are upwards of $2500US.....but if you want high accuracy......
I hope it all makes sense Barry, and again welcome to Audio Karma!!!