How do you eq your sub? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 43 Old 10-09-2003, 05:13 PM - Thread Starter
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After reading many a heated debate over the usefullness of MCACC and YPAO, I've read a lot of opinions stating that sub frequencies need to be eq-ed more than any other. Considering you buy the necessary parametric eq to handle these duties, how do you go about doing it? Is it just a trial and error method, or is there some science to it (minus spending gobs of money on measurement equipment?) Actually, this is right in my $ range I'm willing to spend on this. I've got an attic HT room with slanted ceilings that I think is giving my some boominess in the upper bass regions. Dropping my crossover on the sub helps a lot, but it still needs some help. So does this peq go in-line b/w the sub pre-out and sub input? And you just get some RCA - TRS adapters? And as far as deciding what freqencies to adjust, you just get a CD that's got a bass sweep (I've got DVE) and measure the levels. If the levels are way off (+/-) you compensate through the peq. Do I got it? Thanks a trillion.

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post #2 of 43 Old 10-09-2003, 07:24 PM
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The best explanantion I've found is at the following PC software measurement website called ETF Acoustics.

In the demo room, Part 1 is a discussion about sub placement, room modes, and parametric EQ.

This software is also very useful for measuring and graphing the sub's in room frequency response (so you know the center frequency, the "Q" filter width, and the SPL level cut ).

By the way, you can download the ETF5 software and try it out for free (no saving or printing) and you can use the RS SPL meter as the mic and mic-preamp (it has an RCA output jack) for the LINE-IN on the computer soundcard for the ETF software (no test tone CD needed).

Yes, the Behringer BFD 1100 and BFD 1124 both have 12 stereo or 24 mono parametric filter settings, the Behringer Ultra only has 6 filter settings (IIRC).

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post #3 of 43 Old 10-09-2003, 07:44 PM
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It doesn't have to be expensive. Many people have had great success using a Radio Shack SPL meter (approx $35) and some test tones to analyze their room, and then a Behringer Feedback Destroyer for the EQ. (approx $120)

http://www.behringer.com/02_products...1124P&lang=eng

Search here on AVS and over on HTF for "Behringer" or "BFD". There are quite a few posts on how to do it. Also, look for posts on the topic "room curve" or "house curve" for a bigger picture explanation of what you are trying to accomplish.

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post #4 of 43 Old 10-09-2003, 10:46 PM
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Isn't there another Behringer product that works better? It's an EQ and an RTA. It used to be around $200 and I wanted to get one eventually, but forgot which one it was. You couldn't EQ and RTA at the same time, so you might need 2, but they seemed pretty nice. Maybe someone will chime in who knows what I am talking about.

There are no stupid questions, but there are a LOT of inquisitive idiots. Me being one of them at times.

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post #5 of 43 Old 10-10-2003, 05:57 AM
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The only other one I am familiar with people using is the DSP1100P

http://www.behringer.com/02_products...1100P&lang=eng

... and the DSP1124P posted above is the successor to that product. The DSP1100P is discontinued, but there is always one for sale on ebay.

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post #6 of 43 Old 10-10-2003, 06:41 AM
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This may be the advanced product you are thinking about from Behringer, the UltraCurve.


http://www.musiciansfriend.com/srs7/...p?q=ultracurve
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post #7 of 43 Old 10-10-2003, 09:04 AM
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If you go the poor man's route, discrete test tones, and an SPL meter will work fine. The trick is to use tones that provide stable readings on the SPL meter.

I have an Audiocontrol Bijou that has 1/6th octave sliders from 20 to 80 Hz for the sub. The tones I have best results with are from a Bass Mekanix CD. They have tones in 1/2 hertz increments from 20 to 99 hertz.

While I have the RS SPL meter, I find that the Infinity RABOS meter gives me better results with the Bass Mekanix tones.

YMMV.

BGL

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post #8 of 43 Old 10-10-2003, 10:19 AM - Thread Starter
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Cool, I was always wondering what that BFD stood for. I'd go to Behringer's web site and look for a model number with an acronym of "BFD." LOL

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post #9 of 43 Old 10-14-2003, 10:56 AM
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Stumbled across this while looking for something else. Kind of an "everything you ever wanted to know about BFD'ing but were afraid to ask" site.

http://www.snapbug.ws/bfd.htm

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post #10 of 43 Old 10-14-2003, 05:26 PM - Thread Starter
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Quote:
Stumbled across this while looking for something else. Kind of an "everything you ever wanted to know about BFD'ing but were afraid to ask" site.
That's the most perfectest of perfects link. Thanx.

We're on an express elevator to hell...goin' down! -- Pfc. Hudson
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post #11 of 43 Old 10-14-2003, 08:00 PM - Thread Starter
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By the way, does using the TRS to RCA adapters degrade the signal in any way, at least noticably?

We're on an express elevator to hell...goin' down! -- Pfc. Hudson
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post #12 of 43 Old 10-16-2003, 10:42 PM
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The Best EQ is the least EQ
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post #13 of 43 Old 10-17-2003, 12:02 AM
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^^^ A very true statement.
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post #14 of 43 Old 10-18-2003, 06:32 AM
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Well folks,
I have the DSP1124P, the trusted Radio Shack SPL meter, and am now ready to equalize the subs. Questions: what is my target?
I have attempted to get a flat curve from 20 to 120, but in my room it sounded very poor. Can you guys recommend a starting point?
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post #15 of 43 Old 10-18-2003, 10:07 AM
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Shumi, If you were using the Rat Shack meter, did you at least compensate for the C-weighting curve? A few websites have suggested correction values.

It should be noted to all that the RS meter has been confirmed to have a non-flat response apart from the C-weighting curve and can be significantly off at some frequencies. The errors generally are not a problem when calibrating levels with pink noise, but when looking at specific frequencies this can be an issue. I have found some very good quality mics for about $80 recently, and there is also the Mity Mic. Combine this with a software RTA or spectrum analyzer and you are worlds beyond what you can do with the Rat Shack meter.

It is very true that equalization of a subwoofer can be a tricky thing indeed. The biggest issue is knowing what you can fix and more importantly what you can't. Your best approach is to think of your EQ as the doctor. Your measurements tell you that certain frequencies hurt (big peaks/modes) and the doctor tells you "Don't do that!" (in this case by reducing the level of the offending frequency. You can also do some contouring of the response, as well as tayloring of the response to allow for more headroom or more extension when you have some additional output available(admittedly a rare thing without multiple subs).

Hope this helps some.

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post #16 of 43 Old 10-18-2003, 03:13 PM
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even when c-weighted you need to use the appropriate correction values found here:

http://www.danmarx.org/audioinnovation/rsmeter.html

The Rat Shack meter works well, but is less sensitive to lower frequencies. If you EQ flat using the meter without the correction values, you will have an extremely boomy bass.
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post #17 of 43 Old 10-18-2003, 04:42 PM
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Guys, thanks for pointing out the correction factors...but I think I am ahead on that. I am using the Granite bass CD which allows me to test from 16 to 100 Hz in steps of one. So I have taken the correction factors published for a few frequencies and fitted a smooth curve that allows me to compensate at any frequency, assuming no discontinuity...it is a sixth order polynomial but the fit is almost perfect (R^2~.995). The issue I have is that I do not really know what I should strive for...Is it safe to assume that the total SPL curve (curve of equalized subs+ curve of main speakers) should be as flat as possible? That means that the sub curve needs to be sloped in order to compensate for the gradual contribution of the main speakers from low to high frequencies?
Is this right?
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post #18 of 43 Old 10-19-2003, 02:16 PM
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Can someone tell me where to get the Bass Mekanix CD? Google didn't turn up anything.

Thanks

Noah
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post #19 of 43 Old 10-19-2003, 04:11 PM
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post #20 of 43 Old 10-20-2003, 12:19 AM
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BGLeduc,

Thanks! Do you know which one of the three has ther very low freq in .5 Hz increments? They all list test tracks.

Thanks again.

Noah
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post #21 of 43 Old 10-27-2003, 11:10 AM
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Shumi,

If you can post some 1/6-octave readings, taken with both mains and subs on, I’ll recommend some filter settings. It will also be helpful to know what size your room is (cubic ft.).

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post #22 of 43 Old 10-28-2003, 03:12 PM
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Wayne,

If your offer is open to others, I've posted my frequency response readings below. I purchased a BFD a couple weeks ago and so far have been mostly playing around with subwoofer position to try to find the optimum spot in my room. Unfortunately, it appears there is no optimum spot but the response below is the best I can get.

The room is a large room with a tall cathedral ceiling open to a bunch of other spaces (far from acoustically ideal). The room itself is ~7000 cubic feet, the total volume including the adjacent open spaces is ~10000 cubic feet. Sub is an SVS PB2+

Corrected RS meter readings:
Frequency dB
15.8 65
16.8 63.5
17.8 63.5
18.8 66
20.0 71.5
21.1 76.9
22.4 81.8
23.7 84.6
25.1 85.0
26.6 83.6
28.2 82.6
29.9 83.5
31.6 82.8
33.5 80.85
35.5 82.65
37.6 88.55
39.8 88.3
42.2 86.4
44.7 82.9
47.3 84.65
50.1 85
53.1 81.7
56.2 87.1
59.6 88.1
63.1 87.3
66.8 75.7
70.8 77
75.0 84.3
79.4 77.1
84.0 80.1
89.1 85.75
94.4 81.5
100 80.8
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post #23 of 43 Old 10-29-2003, 04:56 AM
 
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I've just bought a subwoofer (SVS 20-39 PC Plus) and wondering if a parametric equalizer that has a microphone and built-in test tones, with the ability to self-eq is out. I would rather the unit corrects itself automatically- connect everything up then press a button and it does everything for you- outputting various frequency test tones, then adjusting peaks/troughs and then checks again and so on - instead of manually messing around with a spl meter, excel correction values, a laptop with sound test tones etc.

Any plans a more advanced unit is being planned?

Thanks
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post #24 of 43 Old 10-29-2003, 09:29 AM - Thread Starter
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Sometimes I would agree with you fatbottom, but other times I just don't think the whole HT experience is the same unless you get your hands dirty with the nitty gritty aspects of setting everything up. Ya know? That way you can appreciate it more. I know this is a hard sentiment to come by nowadays in the U.S. (just like there will be a huge line for the escalator but the stairs will be empty) but it does feel good to put in the work sometimes.

We're on an express elevator to hell...goin' down! -- Pfc. Hudson
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post #25 of 43 Old 10-29-2003, 10:35 AM
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Kevin,

If you’re going to use the BFD, you don’t have to worry about looking for an “optimal location†- if you’re referring to “best response, that is. The equalizer will give us the “best response,†so look for the spot with the lowest extension and highest gain. With a room that big you need all the “free†gain you can get, so I suggest trying a corner, one that has the longest uninterrupted wall length in both directions.

Response may look worse than what you’ve already posted, but don’t worry about that. Just because one location shows the “smoothest†response – that is, the least deviation between the high and low points - that doesn’t mean it will be the easiest curve to equalize.

For instance, the response you’ve posted is problematic because some of the peaks and valleys are asymmetrical. The peak at 59Hz, for instance: one side is steeper than the other. An asymmetrical peak or valley will always require two or more filters to correct.

By comparison, most symmetrical problems can be addressed with a single filter, because EQ filters are also symmetrical. So naturally, the easiest response curves to equalize have symmetrical peaks and valleys - even if the difference high and low points are greater.

Also, it’s best to take readings with the main L/R speakers and subs combined.

That said, if you want me to go ahead and work with the numbers you’ve posted, I’ll do that.

Regards,
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post #26 of 43 Old 10-29-2003, 12:13 PM
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Thanks for the reply, Wayne! When I said "best response" what I was really looking for was a lack of nulls, since I know a BFD won't fix those. In this position there are dips at 69 and 80 Hz, but if I move the sub 6" or so those dips get worse by ~20 dB. Another location had a bit smoother top end, but had a huge null at 40 Hz and tailed off pretty badly below 50 Hz in general. The third location that is available (space-wise) in my room is next to a hallway and the overall volume drops 6-7 dB in that location, so I ruled it out without taking measurements of the frequency response.

Unfortunately, there is no true "corner" in my room with long walls in which to place the sub. The sub is currently placed with the ports facing a 23' long wall, but the wall to the right of the sub is only ~12" longer than the sub itself. (Side note: I designed the house myself, so I have no one but myself to blame for poor sonic quality of the room. Unfortunately, I knew little about home theater and especially subwoofers at the time - everything I'd read to that point said that subwoofer sound was non-directional so placement didn't matter.)

As far as the measurements - I took those with the front L/R speakers turned off. It seemed like since the BFD was only eq'ing the sub input that I should only measure the sub response. I realize that some of the material the subwoofer plays is crossed over from front speakers, so above/near this point the main speaker frequency response and the crossover slope will come into play. However, some of the sound also comes from the center & surrounds, which have their own FR and crossover points. Some also comes from the LFE channel, which is unaffected by these things.

If you think it's best to use the from L/R speakers, I'll re-take the measurements tonight. I used test tones that I had burned onto a CD - are those recorded in stereo or just in mono? If the latter, how do you get them to be in stereo?
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post #27 of 43 Old 10-29-2003, 07:00 PM
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Kevin,

Quote:
When I said "best response" what I was really looking for was a lack of nulls, since I know a BFD won't fix those.
True, but not all under-represented areas are actually nulls. Some are phase-related, or simply the natural response of the driver/enclosure combination. Those can be addressed with equalization.

You can tell a true null because it won’t respond at all to equalization. And typically they are very narrow – about 1/6-octave. It’s unusual for two nulls to be as close together as your 69-80Hz problems; I expect at least one of them will respond to equalization.

Quote:
Unfortunately, there is no true "corner" in my room with long walls in which to place the sub. The sub is currently placed with the ports facing a 23' long wall, but the wall to the right of the sub is only ~12" longer than the sub itself.
Pretty impressive, then, that you get good response down to 25Hz at such a “inopportune†location, as it were. Bodes well for the SVS, I expect.

Quote:
As far as the measurements - I took those with the front L/R speakers turned off. It seemed like since the BFD was only eq'ing the sub input that I should only measure the sub response.
True, you’re only equalizing the sub’s response, but phase issues between the sub and mains can affect the sub’s response. Generally these will show up in the readings, and they can be equalized.

Quote:
I used test tones that I had burned onto a CD - are those recorded in stereo or just in mono? If the latter, how do you get them to be in stereo?
They are probably mono, and that’s fine for both the mains and subs.

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post #28 of 43 Old 10-29-2003, 07:33 PM
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Okay, just re-ran the tests a few times with the main speakers on. My DVD player is temporarily in the shop, so I couldn't use Avia to set the sub/main level relative to each other. Instead, I adjusted the sub volume until the below and above crossover volumes (sine waves at 40-45 Hz and 100-250 Hz) were about the same. The curve is a bit different from the one a couple posts up - one of the dips seems to have disappeared, and I lost a little bit of low end volume (looks almost like a reverse house curve). Here are the corrected numbers with front L/R:

Frequency dB
18.8 60.5
20.0 64.8
21.1 69.1
22.4 76.4
23.7 78.2
25.1 79.8
26.6 77.4
28.2 75.4
29.9 76.0
31.6 77.6
33.5 75.55
35.5 79.75
37.6 83.45
39.8 83.9
42.2 82.3
44.7 80.1
47.3 82.35
50.1 82.7
53.1 80.4
56.2 85.4
59.6 85.7
63.1 86.5
66.8 85.3
70.8 85.8
75.0 76.8
79.4 62.5
84.0 76.3
89.1 87.55
94.4 85
100 85.8

FWIW, I took every Hz measurements from 70 to 90 Hz with the results below (uncorrected, but in this range I don't believe it matters):
70 85.5
71 84
72 81.8
73 79.0
74 76.2
75 75.1
76 76.3
77 76.2
78 73.3
79 62.6
80 64.2
81 70.7
82 73.8
83 73.8
84 74.4
85 78.0
86 81.2
87 84.1
88 85.5
89 86.0
90 85.9
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post #29 of 43 Old 10-29-2003, 09:29 PM
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Quote:
Originally posted by speco2003
The Best EQ is the least EQ
IMO, the Best EQ is NO EQ..... ;) Just speaker/driver white papers, then room measurements and refinements in the speaker crossovers (resistors, inductors, capacitors) themselves - what quality speaker builders usually will do (well for production runs for the 1 "cast" model). Also room dimensions, nodes, bass traps etc. where in a good sized room the low end is what mostly seems to get out of hand… And +/-2 to 3dB from 16Hz- over 20kHz. ;)
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post #30 of 43 Old 10-30-2003, 06:54 AM
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Quote:
IMO, the Best EQ is NO EQ
Well, this is certainly dreaming or unawaredness as to what is going on in the room.

Placement is very important and EQ is next in imporatnce to tame room nodes and flatten response.

Last night, my calibrator and I EQ'd my subs using a digital EQ (QSC DSP IV). A mid priced EQ that can help tame the worst room modes.

Now, even though my room was professionally designed and built and completely treated acoustically, parametric EQs were used for all seven channels and the digital EQ for the bass.

THe freq response of the room had peaks and valleys varying by over 20 db!! Peaks, valleys, holes, it sounded terrible prior to EQ. THe 20 hz freq was greatest being almost 20 db over level.

After implementation of all EQ, we came to +/- 2.5 db along the freq. range with a little punch from 16 hz to 25 hz and then a slight roll off to 8 hz. The amp cuts out at 8 hz as you'll see a steep drop.....

Bottom line, any subwoofer of moderate performance should also be purchased with an EQ. Otherwise, you are not getting your money's worth on the sub...

I will be posting the before and after graphs soon!

Goodbye to a great audio and video genius and writer... JOHN GANNON. I enjoyed your friendship, wit and a nice long run we took around Indianapolis at CEDIA years back... and for buying my Runco 980 Ultra years back... you saved my ass! Rest in peace.
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