Questions about my subs response.

**Jerm357** · **02-04-07, 10:54 PM**

Sorry if this is in the wrong place because its not a REW graph Im posting (I had to do a manual one because I dont have a laptop) Anyways I just finished measuring my subs response and I would like to know what you guys think of it. It was done with the sub calibrated with Avia to match the mains, the main volume at -25 and using the test tones by JMAC 0 dB 256 kbps MP3 from Realm of excursion and measured at the listening position. My sub is a RL-p 15 in a 8.5cf ported enclosure tuned to 17hz. Now these measurements have not been EQed but Im planing on getting a BFD soon to try to level it out but what I would like to know is how bad am I? Will this be tameable with a BFD? Does this look like a normal response for a small room (11.5' x 11' x 8') and an unEQed sub tuned to 17hz? Oh yea I used a digital radio shack spl and added the correction values of....

10Hz +20.5
12.5Hz +16.5
16Hz +11.5
20Hz +7.5
25Hz +5
31.5Hz +3
40Hz +2.5
50Hz +1.5
63Hz +1.5
80Hz +1.5
100Hz +2

Any feedback from you guys would be a big help.
Thanks, Jeremy

**brucek** · **02-05-07, 10:04 AM**

Jeremy,

There are some problems here with your graph. You have plotted values that are spaced 5Hz apart that aren't consistent with a logarithmic graph. Each octave measurement must be equal distance apart. So the distance from 10Hz to 20Hz must be the same as 20hz to 40Hz etc. When you do manual plotting, there is a way around this requirement. Simply measure at octave spacings (or multiples of octaves) and then plot these value on a linear graph (which is much easier). So if you measured at 1/6th octaves (for example), you would test at ~20Hz, 22Hz, 25Hz, 28Hz, 31.5Hz, 40Hz, etc. Then plot these values on a linear axis and everything will be good.

Another problem is that your meter calibration file is an old one that was kicking around the internet and isn't that accurate.

Also, the vertical axis of your graph exaggerates the response. You should reduce the scale to from 45dB to 105dB.

I would suggest using our premade manual method excel spreadsheets on our download page. The calibration files are also there, but they're also built into the spreadsheets. Choose the spreadsheet that matches your meter......... Also on this page are the sinewave files to download and burn to a CD for testing.

Downloads here

brucek

**Jerm357** · **02-05-07, 07:08 PM**

Ok I got REW working on my desktop, made a rca to 3.5mm wire for the Spl and figured out the soundcard and REW setup ( only took about 2hours I just couldent figure out how to get the "line in" to read the SPl). Now all is good, Ive been practicing on my PC speakers and been getting good measurements and feel confident that tomarrow I will do the same when I move this desktop upstairs and do the real system. Should'ent be too hard, all I need is the tower,keybord and mouse since Ill be using my tv (Sony xs955 HDMI to DVI). I actually move this PC around alot since about every mounth I take it to the garage and use the air compresser to blow out all the dust ( It builds up fast because of all the fans). Now all I need to do is figure out how to post the REW graphs?

**brucek** · **02-05-07, 10:15 PM**

POSTING GRAPHS sticky..

**Jerm357** · **02-06-07, 05:49 PM**

Ok just finished my REW graphs. It looks pretty close to the manual one. So how bad of shape am in. Will I be able to fix this responce with a BFD? Does it look like its my room thats sucking out my low end or my hardware some where down the line? This graph was taken with the sub 5dB hotter than the mains by Avia (I have the receiver set with the sub 5dBhot at -10 on the sub out, which is what I used if it matters.)

**brucek** · **02-06-07, 05:59 PM**

Best to post your graphs with a vertical axis from 45dB to 105dB and a horizontal axis from 15Hz to 200Hz. It's a standard we use here and it make it easier to compare.

You simply have peaks at 45Hz and 75Hz that require equalization.............

brucek

**Jerm357** · **02-13-07, 06:35 PM**

Im waiting on my BFD to get here but Ive been working on my EQ plain. What do you think of just cutting every thing down till its about flat with my 20hz dB mark? Heres some graphs. Am I on the right track? Does this look like the right plain to go about my problem? My filters are

Freq Gain BW/60
46hz -7 12
76.6 -7 8
51.95 -8 29
31.5 -2 4

**Wayne A. Pflughaupt** · **02-13-07, 08:04 PM**

Quote:

Im waiting on my BFD to get here but Ive been working on my EQ plain. What do you think of just cutting every thing down till its about flat with my 20hz dB mark? Heres some graphs.

Looks like it will work just fine.

Regards,
Wayne

**Blaser** · **02-14-07, 06:22 AM**

Quote:

Wayne A. Pflughaupt wrote:

Looks like it will work just fine.

Regards,
Wayne

Correct I think as long as you still have amp headroom. I had a similar problem but my case was worse as I needed to have a steep house curve....and I had problems of headroom, hope this will not be your case!

**brucek** · **02-14-07, 07:38 AM**

Quote:

and I had problems of headroom

I don't really feel this is a headroom problem.

Jerm357 is intending to lower the signal level feeding his sub (mostly in the 30Hz to 90Hz range). The concern is that he has suitable gain available in his subamp to amplify the lowered signal without intoducing too much noise. I would think he will have no problem, given the filters he shows.

brucek

edit: actually, if I think about it a bit more. If Jerm357 already had his sub volume control turned up quite high to begin with, such that he was just below clipping using his present input signal, and then fed it a signal where he didn't modify the 20Hz area (for example), but cut the 30Hz to 90Hz area, so he had to dial his sub higher, the 20Hz signal would now clip. So, I guess both gain and headroom could be a problem.....

**Jerm357** · **02-14-07, 12:46 PM**

With the graph shown I have the gain at only 1/4 (9 oclock) and 0db on the subout, I feel I have a lot of headroom on the amp.
When I play a 20hz sine wave the woofer barly moves. For this reason I feel that more gain would be a good thing but, the problem is when I calabrate the levels with Avia my level (on the amp) must stay very low (below 1/4) to get it to match up at 85db. This is probly because of these high peaks at 45hz and 75hz, Dont you think?

**brucek** · **02-14-07, 12:55 PM**

Quote:

This is probly because of these high peaks at 45hz and 75hz, Dont you think?

Yep.....

**Blaser** · **02-15-07, 03:03 PM**

Quote:

brucek wrote:

edit: actually, if I think about it a bit more. If Jerm357 already had his sub volume control turned up quite high to begin with, such that he was just below clipping using his present input signal, and then fed it a signal where he didn't modify the 20Hz area (for example), but cut the 30Hz to 90Hz area, so he had to dial his sub higher, the 20Hz signal would now clip. So, I guess both gain and headroom could be a problem.....

This is what I mean, and this is by the way what exactly hapenned to me. I tamed a huge Peak from 33 to 37 Hz, which was making my sub sound loud (but one note sound). I did a 15 db cut, and then, the sub was asked to play much more 20 Hz stuff, but it couldn't do it properly

I need better subs!!

Blaser

**Jerm357** · **02-21-07, 12:34 PM**

I think I may have found whats causing my low-end problem. If you look at the picture the stuffing is covering the four cutouts on the brace. When I did this I thought this was a good thing because I could stuff the top chamber of the box and the brace would keep it from falling out,(I did this because I lined the box after it was built and could not reach the top. What a PITA) So I started to think.... well its not restricting air flow to the port but, is it restricting air flow to the top of the box? So I then entered my box design in Winisd and subtracted 2.1cubes from my 8.5cube design and the graph looks pretty close to the REW graphs. So needless to say I removed all the polyfil from the top and even went one futher. I lowered the tune from 17hz to 15.45hz and I can tell an improvement. I only listened at low volume (like -40) to some music for a little while but I could feel more vibrations than I could before at that volume. I also did not hear lower output from lowering the tune which I was worried about and is why I tuned higher when I built it. You can probly measure a (slight) difference in over all output but I dont hear one

Im still waiting for my BFD to get here and waiting to take measurements when it does. Thanks goes to SteveC for putting the stuffing idea in my head and I'll get some measurements posted soon so we can see the difference this has made.

**Jerm357** · **03-03-07, 04:52 PM**

A quick post to up date these graphs since I finally recived my BFD. Heres what I have now using four filters and with the mains off. What do you think? The filters are....

Freq Gain BW/60
46hz -14 18
75.75 -11 12
115 -9 19
178 -8 7

The first one is from 15hz to 200hz and the next is 13hz to 200hz.

**Blaser** · **03-03-07, 05:06 PM**

Looks good.

If your room is big enough, you will probably not need a house curve!

Good results!!

**Jerm357** · **03-04-07, 11:43 PM**

I was reading the thread called "Strange RS SPL meter calibration results" about how Ilkka was calibrating a newer type analog Radio Shack SPL meter and how is was so different from Sonnies correction file. I look at the graph Ilkka made and it looked like it had about the same drop in the low end that my sub's graph has. And since this response is just about the same as sonnies old analog meter file I decided to install it instead of the new digital file that I was using. Heres a pic of my old measurement with the old analog file installed, Now the measurement has not been adjusted by the calibration file yet but you can see the rolloff is about the same. Im going to take some more measurement tomorrow to see what happends, Im almost getting my hopes up that this might be my problem

. What do you guys think of this? Could it be that some of the new digital meters are off like Ilkka's new analog one?

**Jerm357** · **03-05-07, 06:36 PM**

Heres the new sub only measurements with the right calibration file and no EQ and the new 15.45hz port tune. Its 2.5 db hot over 75db with the port grill on and an 80hz crossover. These were taken at the LP with the receivers sub trim at -10 and the amp gain under the 1/4 or 9oclock position and the MV at -25 (I dont have it balanced yet with the mains, was just trying to get measurements) Thank god I dont have the severe problem I thought I did

. The other pic is both with and without the port grill. Yes the sub is air tight SteveC

**Jerm357** · **03-23-07, 06:27 PM**

Ok Ive been playen with the EQ again and was wondering what you guys think of these results.
I changed the settings from this.......

Feq Gain BW
47.50hz -10 13
77.45hz -7 10

To this....
20hz +3 18
25hz +3 6
34.9hz +2 8
45.50hz -7 10
50.65hz -3 8
77.45hz -7 5

Now the first set of EQ settings match with the mains with signal set to where it is and the next set is a little hot but I can ajust it to match. Which one would you use going by the pic and the EQ settings?
The first is with no EQ - the second one is the old and the new EQ - next is the new EQ and the last is before and after EQ (the new eq settings). How bad are these small boosts?

**brucek** · **03-23-07, 07:11 PM**

Quote:

How bad are these small boosts?

They're minor. I think you should quit now, since you have a response as flat as a skating rink, and begin to do some listening.....

You're done.......

brucek

**Jerm357** · **03-23-07, 09:01 PM**

Will do.

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