REW Noob

[weverb]

I am trying to start using REW. Can you please help point me in the right direction on measurments. This is the graph I am getting. What am I missing?

[brucek]

What am I missing?

You're taking a measurement of your loopback cable to test your soundcard cal file, and have the SPL meter calibration file loaded. It should not be loaded when you do this test, as the result will be a perfect inversion of the SPL meter cal file....

brucek

[weverb]

Thanks for the help. Just had the loop back connected backwards. I feel like a .... Here are the plots. The first is just subs and the second is with the mains on.

[brucek]

Change your graph axis to the standard of:

Vertical = 45dB-105dB
Horizontal = 15Hz-200hz.

Anyway, it doesn't look like the first graph is a sub only through the receiver, with the crossover set, and mains disconnected (in fact, both graphs look identical). The usual starting point is to do the sub only and position it for the best response. Then add the mains and get the best crossover response.

brucek

[weverb]

Sorry for the graphs. This should be correct. I turned of my external amp for the first so my mains would not receive anything. Do I have to go into the receiver and tell it there are no main speakers?

[brucek]

I turned of my external amp for the first so my mains would not receive anything. Do I have to go into the receiver and tell it there are no main speakers?

Well, I think you can see that the "sub only" graph is simply not tracking the standard target crossover.

You simply need to turn off the mains. But, you certainly have to have the mains set at small in your receiver and the crossover set at the normal crossover you use (i.e. 80Hz).

BTW, set the measurement level at 75dBSPL. You're a bit high.

brucek

[weverb]

brucek

Thanks for your help. The speakers are currently set to small and the crossover is set to 80Hz. When I manual get a reading playing the test tones on the HSU disk, I get a graph that looks like this (with mains on).

[brucek]

That graph also doesn't really make sense. How can the signal after 80Hz continue to produce ~75dBSPL all the way up to 250Hz. The crossover is suppose to continue to reduce the signal above the crossover frequency.... The signal should act like the target REW shows. This is a bit confusing.

I would suggest to use REW to check out the receivers crossover. Feed the soundcard line-out to the CD or AUX input of the receiver and then feed the receivers sub out signal to the soundcard line-in and do a Check Levels setup and a measure up to 200Hz and see what the graph looks like. It should track the REW ideal target....

brucek

[weverb]

The above graph was with the mains on. That is why it continued to produce 75dB. What gets me is the major dip at 80Hz with REW versus the manual reading of 75dB at 80Hz when playing that specific tone.

I will try your recommendation of testing the crossover. I can say, when I play those different frequencies manually, you can verify that at 80Hz the mains start to play.

[weverb]

Found something interesting. 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....

[brucek]

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?

brucek

[weverb]

brucek wrote:

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.

[brucek]

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.

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.

brucek

[weverb]

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.

[brucek]

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

brucek

[weverb]

brucek wrote:

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?

[brucek]

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.



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....



brucek

[weverb]

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

[brucek]

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.

brucek

[weverb]

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

[weverb]

And more....

Graph 1- MBM XO In (180,180) Mains On
Graph 2 - MBM XO In (0,180) Mains On
Graph 3 - MBM XO In (0,0) Mains On
Graph 4 - MBM XO In (180,0) Mains On

[weverb]

So brucek which do you think looks the best so far? I am thinking Graph #2 (MBM XO Out (0,180) Mains On) in the first group of 4 graphs. I am going to try to reposition the MBM to see if it effects the 80Hz dip.

[brucek]

I'd say graph 1 looks the best.

It's a lot easier to do comparisons by using the REW Measured Tab..........

brucek

[weverb]

Here is a new graph with rotating the MBM 90 degrees (port facing lp) and switching the phase to 0. Mains are on.

[weverb]

Comparison of the two different settings.