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Subwoofer measurement question (1 Viewer)

Darren_T

Second Unit
Joined
Oct 1, 2001
Messages
494
Hi Guys,

I've never been real particular about my sub and never measured it's response before, just calibrated it and called it good. Well I just completed a new AV15 Power Cube and took some measurements using the radio shack db meter C weighted and my Bass Mechanik CD test tones.

The results were less than satisfying. Here they are... rounded to the nearest db. I didn't expect it to be flat but I didn't expect the HUGE variance. Any ideas? Just my room? I have a parametric EQ on my amp (PE 500w) but that will only take care of a part of this.

Hz-db
20, 85
21, 87
22, 91
23, 94
24, 96
25, 97
26, 99
27, 99
28, 99
29, 99
30, 101
31, 103
32, 105
33, 107
34, 108
35, 108
36, 108
37, 108
38, 108
39, 107
40-48, 106
49, 105
50, 104
51, 100
52, 102
53, 101
54, 99
55-57, 98
58, 99
59, 100
60-63, 101
 

RodN

Stunt Coordinator
Joined
May 9, 2004
Messages
58
Did you make the relevant callibration adjustments to these figures? It can have huge effect on how the figures look.

Other than that it looks like your sub has a 35Hz bass boost, or you have a room hump (usual) and a 55Hz dip (also fairly usual). Compared to some the variance is not that huge.

Dunno what your amp can equalise but a Behringer BFD will remove them.
 

Wayne Ernst

Effects Supervisor
Joined
Feb 24, 2002
Messages
2,588
Darren,

I've found the Bass Mekanik CDs to be less than desireable when testing out a new sub. I actually have a couple of those CDs sitting on my shelves collecting dust.

However, here's a link to some sine waves that lots of us have used. You might consider grabbing these tones and re-running some of the tests.

Sine Waves

Also, as Rob suggested, some of the issues being detected could be room related.
 

Darren_T

Second Unit
Joined
Oct 1, 2001
Messages
494
Thanks for the info guys. I was wondering if the Bass Mekanik CD was part of the problem. I do realize the room would create some of this. I was mostly concerned with the huge dip below 25hz.



I adjusted the EQ (only has one filter that can be set)and added full boost at 20hz and tapered it off a bit and did improve the 20hz - 30hz numbers bringing them up a bit. I have thought about using a BFD but have never used one... while I've built several subs I have never tried to flatten the response.

I'll download the Sine Waves and give it another run and see if I can improve the numbers. They aren't nearly as bad now that I've set the EQ but I'd still like to flatten the response a bit more if possible.

Thanks.
 

Lee Carbray

Second Unit
Joined
Oct 23, 2002
Messages
308
I wish I had a response like that.

Like Rod said add in the corrections and the low end will not be as low as you think. Use the exel tool from the Snapbug site here. It will add the corrections for you. What do you have it coressed over at? Unless you are at 40Hz you should measure the responce up to at least 100Hz or more.
 

Darren_T

Second Unit
Joined
Oct 1, 2001
Messages
494


Well, I tend to over-do stuff :) Now that I adjusted the EQ the 20 - 25hz range is up in the 95 - 98 db range. Much better than before. I'll re-measure tonight with the new tones and probably call it good.

I'm hoping with the better test tones it will measure even better but I suppose it could measure worse depending on how accurate or inaccurate my first test was.

I'll post my results tonight when I get home from work.
 

ThomasW

Senior HTF Member
Joined
Nov 6, 1999
Messages
2,282
With the sub's tuning you should have even more output in the low 20's, this is a function of room gain. Check room placement, move the sub if possible
 

Darren_T

Second Unit
Joined
Oct 1, 2001
Messages
494


Unfortunately it is our family room and the sub is in it's final resting place.... can't move it anywhere so I have to live with the current placement. :frowning:
 

Darren_T

Second Unit
Joined
Oct 1, 2001
Messages
494
Ok, I messed around with the single filter EQ on my plate amp and after trying several filters in different places I ended up boosting the 20hz with a rather narrow span. Here are the results corrected. Can't be compared to the previous numbers as I used less gain for this test:

16 - 62
18 - 82
20 - 82
22 - 86
25 - 91
28 - 92
31.5 - 94
36 - 98
40 - 96
45 - 97
50 - 93
56 - 90
63 - 90
71 - 86
80 - 90.5
89 - 88.5
100 - 88.5
111 - 84
125 - 77
142.5 - 69.5
160 - 74

Not too bad for minimal EQ. I'm pretty happy with the results. I tried flattening the hump that starts around 36Hz instead of boosting 20Hz but I wasn't happy with the results, seemed lifeless and was still lacking below 25Hz. Boosting 20Hz seemed to be the most pleasing to me.
 

John E Janowitz

Second Unit
Joined
Oct 30, 2000
Messages
445
Darren,

what are your room dimensions? You can find your 3 primary room modes easily by taking 565 divided by the dimensions. So say your room is 20ft x 15ft x 8ft ceiling.

565/20 = 28.25hz
565/15 = 37.67Hz
565/8 = 70.625hz

Those would be your primary axial room modes. You also have tangential(-3dB) and oblique(-6dB) room modes. If you want to find all the room modes in your system, this is a good javascript room mode calculator:

http://www.mcsquared.com/modecalc.htm

It gets to be a pain to take into account all room modes. Ideally when you design the size of a room it's best to try to dimension so that you have an even modal distribution.

John
 

Darren_T

Second Unit
Joined
Oct 1, 2001
Messages
494
Tough to say the dimensions as the room opens up to the rest of the house... basically 2/3 of one wall is wide open. How should I account for that?

The room itself is 16' X 20' with a vaulted ceiling from 8' to 12' in the center. This is the first time I've tried to really get my subwoofer setup "right". I've had several different setups but thought it was time to have a little "fun" and see about calibraiting further.
 

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