# Correcting Subwoofer Response: Many precise filters vs. Few wide filters?



## chargedmr2 (Mar 4, 2012)

Hello,

I'm pretty new to this topic and would like to learn more. I can't seem to find a certain answer to the best approach for EQing a single subwoofer. Currently I'm in the market for an EQ and was strongly considering a Rane PE17 or Symetrix 551e since they have the ability to apply filters down to 10Hz. Both of these units have five filters that could be used for the sub frequencies.

Obviously this would depend on the room, but generally speaking, is five filters too few for correcting the in-room response?

I was under the impression that using the fewest filters needed for a flat response was a good approach. But then I read more and see that some (including the author of REW) suggest that many precisely placed filters is the best approach. I also read this in the references section of the Rane website. 

Now I worry that the EQ's that I am considering will not have enough filters to address all of the nuances of the room resonances.

Please help.:huh:


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## Wayne A. Pflughaupt (Apr 13, 2006)

AFAIK, the folks who prefer lots of filters are going after the best-looking waterfall graph. However, I’ve yet to see someone show that this resulted in an audible improvement in sound quality vs. a more traditional approach. Perhaps this is because at the end of the day, an equalizer can’t improve ringing (low frequency decay times) beyond what the room naturally exhibits (see more on that here.) On the other hand, we have seen a number of people here who initially "overequalized" their subs and then re-calibrated response with fewer filters, and claimed it sounded better afterwards.

As to whether or not five filters will be enough for your sub, that depends on which approach you want to use. If you want to equalize for the “best” waterfall, then five filters probably won’t be enough. If you want to go with the traditional approach, five filters will probably be enough. I say “probably” in both instances because it’s impossible to make an accurate prediction without seeing your frequency response graph.

Regards, 
Wayne


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## chargedmr2 (Mar 4, 2012)

Thanks for the response Wayne. I think I'll probably try out the Rane unit to start and if it doesn't work, I can always sell it and go with another option. I've had some help with ideas about filters for my frequency response on another forum, and it seemed that somewhere between 3 to 5 filters would be sufficient for the traditional approach, based on projections from REW.

Here is my response with both mains running and crossed to the sub at 80Hz. This is also the best usable location that I have for the sub (WAF). Sorry that I didn't get the rules correct for posting frequency response charts! I can create a new one if needed:


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## AudiocRaver (Jun 6, 2012)

What you are hoping for is a clear consensus of opinion. Good luck. I think the closest you will get is something like "simpler is better, but sometimes it gets more complex out of necessity."

Check out Wayne P.'s article. Note also that the REW tutorials by author John M., along with the way EQ filters are generated by REW, start out by attacking room modes directly, and sometimes a high q values, a very sound approach, so if that gives a few more filters, they are probably needed.


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## chargedmr2 (Mar 4, 2012)

Consensus does seem to be that elusive characteristic of audio discussions. 

Well I hope that the Rane unit will at least be a reasonable approach, or do you guys think I should just go with the BFD (1124p) instead? I really wanted to address the response below 20Hz for HT use, but for music this obviously isn't as big of a deal.


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## tonyvdb (Sep 5, 2007)

Just remember the lower the frequency the longer the wavelength and less impact multiple filters will have any meaningful audible impact. One filter with a somewhat wide Q at 20Hz would be enough to bring that up


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## Erin H (Aug 26, 2009)

Wayne A. Pflughaupt said:


> AFAIK, the folks who prefer lots of filters are going after the best-looking waterfall graph. However, I’ve yet to see someone show that this resulted in an audible improvement in sound quality vs. a more traditional approach.
> Regards,
> Wayne



I completely understand what you're saying, however, I think there's _some _clash here. Typically when someone wants "proof" it is requested in the form of objective data. Obviously just taking someone's word for it isn't enough. In the case of the EQ-by-decay method, how are you to quantify 'audible improvement'? Measurements of a controlled subjective test (done in such a way it can be used as objective data). Measurements are used to tell you where to focus. If the end user has reported success then is it true success or confirmation bias? I do believe I've found some AES papers regarding room correction targeting modal response via EQ with subjective feedback as the data set (though, some were focused on mechanical _and _electrical correction) but I cannot remember what they were.

I will say in my car... where the Schroeder frequency is nearly twice what a standard home media room is, the use of Parametric EQ has helped immensely with clearing up higher midbass/lower midrange issues and I've gotten a lot of great feedback from others specifically noting the clarity of the low frequency response. This would constitute blind listening though no A/B/X testing. With standard graphic EQ I couldn't do much to these problem areas without altering the tonality to the degree it was a negative impact overall. I either had to cut so much it adversely impacted tone or dealt with the modal issues as they were. With user defined Q and center frequency capability, I've been able to mitigate that side effect. It's still a process, though, and I don't recommend just fully trusting data blindly. A good bit of time was spent by myself doing A/B comparisons to make sure I was heading down the right path. 


- Erin


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