need help with sub EQ

[bikehikefish]

After reading posts extolling the virtues of parametric equalization to improve subwoofer performance, I purchased the Stryke Bass Zone CD and used a Radio Shack analog meter to measure the spl from 20 hz to 160 hz. You can see the results below. The third column is the spl with the meter correction values added in.

Can one of you bass experts help me analyze this data? To my eye, it looks pretty bad. A huge spike at 40 hz and then it drops off fast below 36 hz. The sub is a Paradigm PS-1000 which I thought should be giving loud sound down into the mid 20's.

The sub is located on the front wall between the TV and the right front speaker. I tried moving it next the right wall, and the results were worse.
Do I have this setup wrong, or do these stats look normal for an un-equalized sub. Would the parametric equalizer help?

FREQ RAW SPL SPL (comp)
20 50 57.5
22 56 62.5
25 58 63.0
28 61 65.0
32 69 72.0
36 76 78.5
40 85 87.5
45 80 82.0
50 77 78.5
56 80 81.5
63 72 73.5
71 70 71.5
80 74 75.5
89 75 76.5
100 74 76.0
111 65 66.0
125 67 67.5
142.5 64 64.5
160 70 69.5

[agtpunx40]

yea, my results aren't any better
(w/ rat shack SPL after corrections corrections)
25hz - +7db
28hz - +7db
31.5hz - +1db
36hz - -3.5db
40hz - +1db
45hz - -3db
50hz - -3db
56hz - -1.5db
63hz - -2.5db
71hz - -5.5db
80hz - +6.5hz
I want to get a parametric eq, but I was thinking that my next audio purchase, once I get the money, will probably be a yamaha rxv1400 with the built in parametric eq. Still not sure though, what do you guys think, especially since these are all over the place, I thought a BFD might work much better since I'd have more bands for just the sub. On the other hand, if I could just take care of those huge bums and nulls at the top and bottom, it'd sound 10x better. Luckly I graduate in the spring so I can get out of these concrete walls that they won't let me do anything with because of fire codes.

[piece-it pete]

This post sure would have gotten some serious responses at the old forum (sigh).

I've got nasty humps, with the worst being +11 db at 79hz. I haven't bought a BFD yet but believe it's the only thing that really works - the guys here talk sense! I'm getting my sub crossovers/amps in order then buying one. For $110 it sounds like one of the real bargains in audio. I'll find out soon (mid-spring, hopefully).

Everything you ever needed to know about BFDs':

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

I found specs online for yours at Paradigm that says 22hz @ -3. So your in-room response is interesting.

Perhaps Dick Hertz or Richard Greene and a ton more will bless you with their presence:) . Run "Behringer Feedback Destroyer" through the search & read the joy!

Pete

[Woochifer]

Your numbers don't look all that far off from a typical in-room response. If the low end reinforcement is your main concern, then you should put the sub into the corner. That will probably bump up the low end numbers considerably, but it might also cause some other spikes in your frequency response. Having the subwoofer in the middle of the front wall probably is probably not the best place if the deep bass is what you're looking for.

From the looks of things, a parametric equalizer would help your system by bumping down that large peak you have at 40 Hz. A peak that large could cause your bass to sound overly boomy and bloated. Taking that large peak down will make the overall bass sound tighter and better balanced. And it will also allow you to adjust the overall level bass higher because you no longer have that one frequency peak distorting your wideband SPL measurement. If you want to do further fine tuning to even out the frequency response even more, a parametric equalizer gives you the option to do that.

But, for starters, I would try a corner placement on the subwoofer and do another measurement.

[bikehikefish]

Placing the sub in the corner improved the sound (to my ears at least). It did increase the low end by a few dbs, but oddly enough, between 60 and 70 hz there was a 10 db drop.

What I found really interesting was that the 10 db drop was in a small ( about 3ft by 3ft) area at the listening position. If I measured a little forward, back, or to either side, there was a big jump in volume. I noticed this same behavior with certain frequency test tones; other frequencies seemed to be more consistant throughout the room.

I change the phase by 180 and much of the 10 db dip was eliminated, but the bass seemed more "muddy". The phase change also caused the level between 80 -90 hz to increase. Would that contribute to a muddy sound?

These last couple days of playing with the test tone cd and the spl meter have been enlightening. How does someone tune the bass where it is more consistant throughout the room? I feel as though the only good place to listen is one spot, and I had better not lean back or forward.

I think I should probably look at deading the room before I get an equalizer. This room has a ceramic tile floor with throw rugs, and no curtains yet.

[Woochifer]

Placing the sub in the corner improved the sound (to my ears at least). It did increase the low end by a few dbs, but oddly enough, between 60 and 70 hz there was a 10 db drop.

What I found really interesting was that the 10 db drop was in a small ( about 3ft by 3ft) area at the listening position. If I measured a little forward, back, or to either side, there was a big jump in volume. I noticed this same behavior with certain frequency test tones; other frequencies seemed to be more consistant throughout the room.

I change the phase by 180 and much of the 10 db dip was eliminated, but the bass seemed more "muddy". The phase change also caused the level between 80 -90 hz to increase. Would that contribute to a muddy sound?

These last couple days of playing with the test tone cd and the spl meter have been enlightening. How does someone tune the bass where it is more consistant throughout the room? I feel as though the only good place to listen is one spot, and I had better not lean back or forward.

I think I should probably look at deading the room before I get an equalizer. This room has a ceramic tile floor with throw rugs, and no curtains yet.

What you're observing is just the oddities associated with low frequencies. Their wave lengths are long enough so that you can have very different bass sounds just by moving a few inches in any direction. In most small to medium sized rooms, the sound waves can interact with one another and create cancellations or severe peaks, depending on where the subwoofer and listening position are. A parametric equalizer is very effective, but only at the listening position. You could still have very different sounding bass a few feet in any direction.

Sounds like you have a very live sounding room. Another solution that you might want to look into would be homemade bass traps. These help to even out the bass response throughout the room, but even after installing these, you still might need to do some equalization, depending on how your room acoustics are.

[bikehikefish]

I found specs online for yours at Paradigm that says 22hz @ -3. So your in-room response is interesting.


I found a review of the PS-1000 in Sound & Vision where they said the bass drops off sharply below 31hz. That is consistant with what I am seeing. Maybe this is an example of marketing specs that are not quite accurate.

[bikehikefish]

Another solution that ou might want to look into would be homemade bass traps. These help to even out the bass response throughout the room, but even after installing these, you still might need to do some equalization, depending on how your room acoustics are.

Thanks for the tips. Bass traps may be my next project. In the past I saw some posts about them, and I spent a little time looking at plans.

If I see BFD going for a reasonable price on ebay, I may get one. Looks like they sell for about $80 used. Seems a little high when a new one costs $120. But that's ebay.

[Richard Greene]

I've been equalizing my DIY subs for over 20 years and wonder how people
can enjoy subwoofers w/o EQ in most rooms.

Bass frequency response using a slow sinewave sweep from 20 to 80Hz. is usually worse than +/-10dB. Using 1/6 octave-spaced sine wave tones tends to smooth the measurements somewhat even then most rooms are worse than +/-8dB.

It's most important to flatten the bass peaks heard at your listening seat.
They can be so loud that they somewhat mask details in the midrange and treble. With action movies the bass peaks make explosions sound louder and that may not bother listeners as much as when certain bass guitar notes sound too loud or a kick drum makes the room "ring".

The PS1000 was the first $500 subwoofer I ever recommended when they first were introduced. Today I like the Adire Audio Rava for $400 that's even better. But neither sub will be strong under 30Hz., especially the 1000 as it rolls off bass at 24dB/octave (sharp roll-off) vs. 12dB/octave for the Rava.

I recommend using C-weighting with no corrections for your Rat Shack
meter. You do not have error corrections for your specific meter, so why use them at all? Also, most of the so-called error corrections are nothing more than deleting the C-weighting -- something that you should not do unless you've developed a custom "house curve" for your room that you like better than C-weighting. C-weighting subtracts some dB from the actual SPL to better match the ear's difficulty hearing low bass frequencies. It works for my ears at the 80dB average SPL I prefer when listening to music.

Looking at your raw C-weighted measurements:
- There's way too much output above 80Hz. for a subwoofer (unless you are measuring the main speakers too). Bass should be down at least 24dB. at 150Hz. if you want a sonically invisible sub, and you should want that.
(Hint: If you can hear male voices through your subwoofer with other speakers turned off, then you have too much output above 80Hz.)
- Your sub has weak response below 30Hz. because of it's bandpass design --I recommend living with that rather than trying to boost it
- You've got a standing-wave-related peak in the 40-45Hz. range that should be reduced with one narrow band of EQ (perhaps 1/6 octave centered somewhere in the 40-45Hz. range
- There are a few frequencies that are weak. I first recommend measuring
each of those frequencies twice -- once with the sound meter microphone located where your left ear would be located, and again with the meter 8" to the right where your right ear would be located . Then average the two measurements. If one ear happens to be in the center of a null (weakest possible bass for certain frequencies where bass reflections off the wall are 180 degrees out of phase with bass still coming from the subwoofer)
then the other ear would be about 8" away from the deepest part of the null ... where the same frequency of bass could easily be 3-6dB louder.

The bass you hear is an average of what your two ears hear -- since room nulls are very narrow, it's valuable to measure for both ears and then average the results.

Don't try to EQ a null -- that wastes lots of power and bass speaker stroke (XMAX) ... when all you have to do is move your ears 6" to a few feet to move away from that null. Bass peaks are much broader than nulls -- it's almost impossible to move your chair/ears away from all of them.
That's why smart people invented parametric equalizers.

[bikehikefish]

I've been equalizing my DIY subs for over 20 years and wonder how people
can enjoy subwoofers w/o EQ in most rooms.

Bass frequency response using a slow sinewave sweep from 20 to 80Hz. is usually worse than +/-10dB. Using 1/6 octave-spaced sine wave tones tends to smooth the measurements somewhat even then most rooms are worse than +/-8dB.

It's most important to flatten the bass peaks heard at your listening seat.
They can be so loud that they somewhat mask details in the midrange and treble. With action movies the bass peaks make explosions sound louder and that may not bother listeners as much as when certain bass guitar notes sound too loud or a kick drum makes the room "ring".

The PS1000 was the first $500 subwoofer I ever recommended when they first were introduced. Today I like the Adire Audio Rava for $400 that's even better. But neither sub will be strong under 30Hz., especially the 1000 as it rolls off bass at 24dB/octave (sharp roll-off) vs. 12dB/octave for the Rava.

I recommend using C-weighting with no corrections for your Rat Shack
meter. You do not have error corrections for your specific meter, so why use them at all? Also, most of the so-called error corrections are nothing more than deleting the C-weighting -- something that you should not do unless you've developed a custom "house curve" for your room that you like better than C-weighting. C-weighting subtracts some dB from the actual SPL to better match the ear's difficulty hearing low bass frequencies. It works for my ears at the 80dB average SPL I prefer when listening to music.

Looking at your raw C-weighted measurements:
- There's way too much output above 80Hz. for a subwoofer (unless you are measuring the main speakers too). Bass should be down at least 24dB. at 150Hz. if you want a sonically invisible sub, and you should want that.
(Hint: If you can hear male voices through your subwoofer with other speakers turned off, then you have too much output above 80Hz.)
- Your sub has weak response below 30Hz. because of it's bandpass design --I recommend living with that rather than trying to boost it
- You've got a standing-wave-related peak in the 40-45Hz. range that should be reduced with one narrow band of EQ (perhaps 1/6 octave centered somewhere in the 40-45Hz. range
- There are a few frequencies that are weak. I first recommend measuring
each of those frequencies twice -- once with the sound meter microphone located where your left ear would be located, and again with the meter 8" to the right where your right ear would be located . Then average the two measurements. If one ear happens to be in the center of a null (weakest possible bass for certain frequencies where bass reflections off the wall are 180 degrees out of phase with bass still coming from the subwoofer)
then the other ear would be about 8" away from the deepest part of the null ... where the same frequency of bass could easily be 3-6dB louder.

The bass you hear is an average of what your two ears hear -- since room nulls are very narrow, it's valuable to measure for both ears and then average the results.

Don't try to EQ a null -- that wastes lots of power and bass speaker stroke (XMAX) ... when all you have to do is move your ears 6" to a few feet to move away from that null. Bass peaks are much broader than nulls -- it's almost impossible to move your chair/ears away from all of them.
That's why smart people invented parametric equalizers.

Thanks for looking at my measurements. It's always good to get another viewpoint (especially from people who know what they are doing).

You are right about the sound above 80hz. I measured with my main speakers on. The logic was that I wanted to know the response with the mix of the main and subwoofer; i.e. replicating normal use. There should not be much above 80hz going to the sub, since I have the crossover in the receiver set to 80. I'll disconnect the mains and listen for the male voices to test this.

The advice on the nulls seems sound (bad pun). I'll rearrange the furniture, and po the wife, to try to avoid the null.

I guess the BFD will be on my Christmas list.