# Final 4 Filter BFD Equalization of Dual Subwoofer Setup



## bigwoof (Oct 9, 2009)

Hi All,

just wanted to do a quick sanity check of my final filters using a Galaxy CM140 and REW. I have two SVS PC13 Ultra subs on either side of my main speaker setup. The system is used mostly for movies and every now and then for audio.

I first went nuts with REW and created 10-12 filter setups. multiple variants. They did not sound all that great. So I went and read the various howto guides very carefully. Wayne's article on the hard knee house curve was particularly useful. Thanks for writing that Wayne!!

So I setup a proper hard knee house curve (or something close enough). I needed a 9 dB slope. I then adjusted the target level to reduce the number of filters and ended up with just 4 filters. I tested it and it sounded great (both to me and more importantly to everyone else in the house!  )

The top curve is the original. The next is the corrected and the blue line is the target house curve.

1) I measured each sub individually and the curves for both of them looked similar. They just had different perceived volumes which I corrected. Hence, I decided to just equalize them together and use the same filters for both.

2) I've set the crossover at 120Hz as the subs are probably better than the main speakers for everything below 120. is that too high? my understanding is that the region from 80-120 Hz is mostly a dead zone anyway for most movies.

3) Anything else I can do to make this even better?

Thanks,

Raj


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## gperkins_1973 (Aug 25, 2008)

hi there,

I tried a house curve on my diy dual sealed sub and to be honest didn't find it sounded that great. I found creating a similar db slope cut away the mid bass frequencies so things like guns etc didn't have the same impact as a flat curve. 9db is alot of difference between say 20hz and 80hz when playing the same tone. To me its almost like applying a low pass filter and cutting frequencies.

I did read Wayne's thread on house curves and found alot of people very happy with them but to my ears it was not that great. Glad your happy though.

cheers

Graham


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## JohnM (Apr 11, 2006)

It would be useful to see a little further up the frequency range, so a plot that goes to 200Hz would help (we generally aim for 15 to 200Hz span for the sub measurements to make it easy to compare different measurements and see what is happening after the crossover point). Other than that it looks fine, and if it also sounds fine then you are in pretty good shape  

A plot of a main speaker on its own, set to full range, will let you see whether they have useful output below 120Hz - the higher the crossover the more the risk of localising the subs, but with them placed either side of the mains that's not really much of an issue for your setup.


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## bigwoof (Oct 9, 2009)

Hi John,

Thanks for your suggestions. I've attached a wider range graph below.

> A plot of a main speaker on its own, set to full range, will let you see whether they have useful output 
> below 120Hz - the higher the crossover the more the risk of localising the subs, but with them placed 
> either side of the mains that's not really much of an issue for your setup.

This is an interesting idea. I'll dig out the cables and do that later in the week. How would you do this in REW? set the measurement range from 15 to 1000? or higher to say 20,000? The Galaxy CM140 should be okay for full range tests right?

One thing I noticed is that the waterfall plots by REW seem to stop at 110HZ. even though all my measurements are using the default 15-200 Hz range. no idea why (all speakers including the mains with the crossover set to 120Hz are active for all my measurements). I've attached the plots below.


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## JohnM (Apr 11, 2006)

For the speaker measurement you just need to go far enough above the intended crossover point to see what the overall response is looking like, so going up to 1000 would be plenty. The CM140 is OK for full range measurements. The waterfall problem is a bug in REW when the frequency axis is set to linear, if you use the button near the top right of the graph to change the frequency axis to log (as it is for the frequency response measurement) you will see the rest of the waterfall.


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## bigwoof (Oct 9, 2009)

Thanks John! I'll do the measurements later in the week and report back.


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