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post #11 of 191 Old 08-23-08, 12:52 PM
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Re: REW Noob

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My MBM xo has been "out" during all my first testing and that's what all the previous graphs show. I just switched it to "in" and
hehe, now we're getting somewhere.........

So, you have a small peak at 50Hz to deal with and you now know that you need a bit of work at the crossover where the mid bass module starts.......

Can you reposition your main sub to ameliorate the 50Hz peak?

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post #12 of 191 Old 08-23-08, 12:58 PM Thread Starter
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Re: REW Noob

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hehe, now we're getting somewhere.........

So, you have a small peak at 50Hz to deal with and you now know that you need a bit of work at the crossover where the mid bass module starts.......

Can you reposition your main sub to ameliorate the 50Hz peak?

brucek
Unfortunately due to WAF, I cannot move my main sub for now. Can you elaborate a little more on your thoughts about the crossover for the mid bass? Do you think it should be raised to 100Hz?

Next week, I am going to try and switch the main sub and MBM around and see what readings I get.
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post #13 of 191 Old 08-23-08, 01:07 PM
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Re: REW Noob

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Do you think it should be raised to 100Hz?
Nope, you just need to adjust the phase control on one or both of the main sub and mid bass sub, while being careful that an adjustment of phase to the mid bass sub (assuming it has one) does not deteriorate the crossover smoothness between the mid sub and Main speakers. At that point you can also change the receiver sub distance setting so that the main sub and mid sub phase will move in concert against the main speakers.

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I am going to try and switch the main sub and MBM around and see what readings I get
I thought the theory was that the mid unit was to be placed near the listening position.

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post #14 of 191 Old 08-23-08, 01:14 PM Thread Starter
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Re: REW Noob

Ok, they are both set to 180.

In theory yes, the MBM is suppose to be nearfield, but can be moved next to the mains. It is usually done in pairs though.

Looking at the new graph, it looks more like the manual one I plotted. I still don't understand why the 16Hz and 80Hz readings are so different.
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post #15 of 191 Old 08-23-08, 01:22 PM
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Re: REW Noob

REW is far more accurate representation of the response than continuous test tones are...

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post #16 of 191 Old 08-23-08, 01:28 PM Thread Starter
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Re: REW Noob

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Nope, you just need to adjust the phase control on one or both of the main sub and mid bass sub, while being careful that an adjustment of phase to the mid bass sub (assuming it has one) does not deteriorate the crossover smoothness between the mid sub and Main speakers. At that point you can also change the receiver sub distance setting so that the main sub and mid sub phase will move in concert against the main speakers.
What am I looking for that shows a smooth crossover between the mid and mains? Am I correct in understanding that my current graph does not show a smooth crossover?
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post #17 of 191 Old 08-23-08, 01:55 PM
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Re: REW Noob

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What am I looking for that shows a smooth crossover between the mid and mains?
Well, the mid bass module certainly adds another complication to the mix (whether necessary or not, is another question), but it is no different than a single sub and mains with respect to getting a smooth transition at the crossover.

If you look at the pic below, it shows a typical sub and mains with an 80Hz crossover and the resultant mix is a perfect smooth transition as shown. The mains and sub are both 6dB down at the crossover and they add to a flat line.

That's all there is to it, in a perfect world.

Some people like a bit more bass and add a house curve, but the theory is the same.

REW Noob-crossover-flat-resultant-combined-80.jpg

An MBM is no different, except now you have three signals to integrate.

The pic below shows the main sub and then in red, the MBM sub. Add in the mains and you get the idea.

You want them to all add to a straight line..... good luck....

Name:  MBM.jpg
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Size:  25.0 KB

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post #18 of 191 Old 08-23-08, 02:02 PM Thread Starter
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Re: REW Noob

brucek for your help!

Here are a couple graphs. The phase is (MBM setting, main sub setting). Let me know your thoughs.

Graph 1 - MBM XO Out (180,180) Phase
Graph 2 - MBM XO In (180,180) Phase
Graph 3 - MBM XO In (0,180) Phase
Graph 4 - MBM XO In (0,0) Phase
Graph 5 - MBM XO In (180,0) Phase
Attached Thumbnails
REW Noob-mbm-xo-out-180-180-phase.jpg  

REW Noob-mbm-xo-180-180-phase.jpg  

REW Noob-mbm-xo-0-180-phase.jpg  

REW Noob-mbm-xo-0-0-phase.jpg  

REW Noob-mbm-xo-180-0-phase.jpg  

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post #19 of 191 Old 08-23-08, 02:18 PM
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Re: REW Noob

You can see that graph 3 and graph 5 are the best (and quite close).

You still have a dip, but I wouldn't decide on which setting to use (between graph 3 and 5) until I added the mains to see which setting married with the mains the best.

You've still got that pesky peak at 50Hz, that likely won't go away without equalization or movement of the main sub.

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post #20 of 191 Old 08-23-08, 02:37 PM Thread Starter
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Re: REW Noob

Ok... here we go!

Graph 1 - MBM XO Out (180,180) Mains On
Graph 2 - MBM XO Out (0,180) Mains On
Graph 3 - MBM XO Out (0,0) Mains On
Graph 4 - MBM XO Out (180,0) Mains On
Attached Thumbnails
REW Noob-mbm-xo-out-180-180-mains-.jpg  

REW Noob-mbm-xo-out-0-180-mains-.jpg  

REW Noob-mbm-xo-out-0-0-mains-.jpg  

REW Noob-mbm-xo-out-180-0-mains-.jpg  

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