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Dealing with subwoofer Nulls

Hi @auxinput,

You wrote:

... I have a question on the Bag End. Have you actually used the Bag End E-Traps? I have a pretty good room and do not have any major bass ringing. However, I do have a huge hole around 80hz where bass just falls out (this is a room node where I’m sitting). The Double-Bass Array (DBA) configuration that is popular in Germany would probably solve my problem, but it is just not practical for me to do in my room. I have looked at general broadband absorption, Helmholtz resonators, membrane panels from GIK, etc. I tried a pair of GIK full Soffit bass traps, but I didn’t like them -- they seemed to suck all the life/excitement out of the room. I am curious about the flex-range limiter panel on their monster bass traps and the tuned membrane. I haven’t yet looked into spending money on this problem (maybe next year). My initial thoughts were to try the flex-range-limiter option. However, this Bag End E-Trap looks really effective. There is one review where the user was able to restore a big dip in the bass area. Other feedback indicates the Bag End cannot restore big dips - it can only reduce bass peaks/ringing. Do you have any experience with this? ...

You actaully can make nulls manageable with a bass trap or active devices. I do not have personal experience with the Bag End.

I will say that I think your problem with the bass traps was your EQ didn’t go far enough. :) Usually users try to go for flat, when they should go for a declining response, about 1-1.5 dB per octave.

Before going with a second sub, have you tried inverting the sub and your chair? :) Here are the steps I recommend:

1. Put the bass traps back in
2. Place the sub where you listen, then use a measurement microphone to scout possible locations. Wherever the sub’s output is most full and even is the best place to put the sub.
3. EQ the sub so that it has a dropping response from 16-20 Hz. Approximately 1-2 dB/octave will be your ideal.

Best,


Erik
erik_squires
9 responses Add your response
erik_squires OP
15,647 posts
 
By the way, WITH and only with bass traps it becomes possible to effectively, but not completely, deal with nulls and ringing modes with a single subwoofer and EQ.

I find this the neatest (as in least messy) and most cost effective solution. However those with lots of money and space may go with 2 or 4 subwoofers to do the same. That's fine too, but it's out of my budget.

Those purists who insist that all EQ is bad haven't heard how magnificent it can be done.

Best,


Erik
erik_squires OP
15,647 posts
 
Grrr. I meant when you EQ, find your lowest reasonable output. Somewhere around 16 - 30Hz. Take that as your starting point, then EQ between that point and the upper limits of the sub's output. For me that would be 16 Hz to 120 Hz.

The tilt is up to you, but I find flat TOO flat. Somewhere around 1 to 2 db/Octave gives me the best movie and music sound possible.
erik_squires OP
15,647 posts
 
Grrr. I cannot type cogently I guess.

By tilting I mean tilting down. So an example target curve:

16 Hz - 90 dB
32 Hz - 88 dB
64 Hz - 86 dB
erik_squires OP
15,647 posts
 
And finally, now that the coffee has cut in, I would consider active room cancellors my last option. In order of my personal preference:

  1. Sub + Bass Traps + EQ
  2. Dual or Quad subs + Bass Traps + EQ
  3. Dual Subs + EQ
  4. Single Sub + EQ
  5. Active room canceller (i.e. Bag End)
The Bag End type of solution is last because A - It's another device that has to be placed properly and powered on. Why not have a second sub instead? and B - Limited in benefits to a couple of room modes. Bass traps and EQ are much broader based.

Best,

Erik
auxinput
2,920 posts
 

Thanks for the response.  I have two subs that I have built myself.  They are extremely large - they are 20" wide, 25" high and 30" deep.  They weigh about 190 lbs each and are spiked.  It is a vented design with a 12" woofer.

It is a massive effort just to move them around the room.  That being said, I have experimented with different sub placements and trying to figure out the best position by using your initial steps.  I have RoomEQWizard with a really nice corrected measurement mic.  In all situations, the best results were having the two subs in the front corners and firing forward.  If I had known better, I would have made these subs really tall and shallow because the overall frequency response became better as I pushed the subs closer to the front wall.  The room is 11 feet wide, 17 feet long, 9 feet high.  Room is completely sealed (no joining rooms via hallway, etc.).

Those soffit bass traps are long gone - sent back to GIK a couple years ago.

The response of the subs in deep bass is excellent.  I pretty much have flat response down to 20Hz (really!!) and I can feel my clothes move on the low bass notes (it is definitely moving air!).

I understand the use of EQ in a system when done properly.  I have worked with Dirac Live in my room and did not like the results at all.  Even when I limited Dirac to under 150Hz, it still caused problems and bass impact wasn't the same.  In my situation, I have a big dip (bass null) around 80 Hz which definitely reduces some of the impact of bass on certain music/movies.  I don't think applying a +10/12 DB increase at the 80Hz area via an EQ is the right answer here.  It is definitely a room node where I sit, so the possible options are the GIK flex-range-limiter bass trap or membrane bass trap.  Or this Bag End E-Trap.  Since you don't have any direct experience with it, I guess I'll just have to think about what direction I would go in next year.  The GIK FRL and membrane traps are definitely cheaper, but they only absorb energy.  The don't actively work on cancelling the bass frequencies by doing an inverted pressure wave (which could work better in sucking out the room nodes that cause those bass nulls/dips).

auxinput
2,920 posts
 
Oh, I also built an adjustable Helmholtz resonator.  It had a very minor effect on the bass and I didn't see the benefit in my situation.  The Helmholtz cabinet also cause a lot of blair/harshness in the upper mids highs (probably due to high frequency refraction off the corners of the cabinet).
auxinput
2,920 posts
 
When I was moving subs around, I tried all different combinations.  Subs in the middle of the room, subs 1/3 way into the room, subs next to my sitting position, subs in opposing diagonal corners, subs firing upwards, subs firing backwards, subs in the back of the room.  They still were best in the front corners firing forward.
geoffkait's avatar
geoffkait
23,365 posts
 
 
auxinput
Oh, I also built an adjustable Helmholtz resonator. It had a very minor effect on the bass and I didn't see the benefit in my situation. The Helmholtz cabinet also cause a lot of blair/harshness in the upper mids highs (probably due to high frequency refraction off the corners of the cabinet).

I built a Helmholtz resonator to address a standing wave of about 70 Hz in one corner of the room. The Helmholtz resonator was about 15 feet long. It was a folded S shape resonator, about 8" diameter with medium size nozzle on one end, the other end sealed. White PVC pipe, straight sections and elbows. Purple PVC sealant and PVC cement. Worked great.

erik_squires OP
15,647 posts
 
Hi everyone,

I'm not sure if it's clear, but the key to bass traps is that they work in combination with EQ. Not either or.

Also, I'm not sure if you meant to say it this way or not but it sounds like you placed your subs symmetrically. They probably benefit most from being assymetrically placed. Assuming one of them is near ideal, but you still suffer the 80 Hz null, try the idea of putting the second one in the listening location, and try to find the place where it produces the most fill at 80 Hz. It may be that it works best next to or behind your listening location even. :)

Best,

Erik
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