# Perceived volume level and bass traps



## thewire (Jun 28, 2007)

I understand that by placing bass traps in a room changes the perceived level of bass because these improve a null, but what exactly does this mean by a preceived level? Does this mean that the bass has not in fact increased in level and that we simply think we hear more? If the level of the bass decreases in amplitude does this have the same effect in what we think we hear? This difference is not always able to be measured and/or heard?


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## bpape (Sep 14, 2006)

No - it can really increase due to a lack of cancellations. It's just a matter of getting it more the same level in more places in the room. 

Bryan


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## chadci (Feb 13, 2008)

I recently started installing reflection panels and my first bass trap. All diy. I had the system calibrated before and yesterday after the kids were off for school I decided to recalibrate. On a few channels I had to raise the level a few db's, but, on some I had to lower them a few. Everything changes.. for the better.

I have not installed a sub just yet( recently moved, IB sub goes in the ceiling..) so I am running my mains as large. Before the room treatments, the bass response was boomy and, maybe muddy. When I put the treatments in the room, it cleaned up, quite a bit actually. Now it's very smooth and a bass guitar has different notes unlike before the treatments... at the same time, that boomy-ness added to the preceived amount of bass in the room, it's not thumpy like it was. I'm ok with that. I would rather have smooth, clean sound that muddy boomy sound... that's just me.


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## thewire (Jun 28, 2007)

I tried placing some insulation in the back of the room to see what difference this made on the volume of low frequencies. This improved the tightness of very low frequencies but none of which were very audible. Removing it from my corners significantly reduced the overall uniformness of bass in the various front row seats however, and midbass became punchy and less defined. I measured an explosion in WOTW a scene in the basement of a home with an explosion. When I measured before my meter read one reading at 110dB while they run to another room to escape. I added the insulation back to the corners and measured again and it read 3 different readings at 106dB, 107dB, and 108dB. I guess that one might percieve a higher level of bass because it becomes less distorted.

I will be adding alot of Quiet Batt to the front of my room above my tile ceiling in the coming weeks. I expect this will make some difference, because in my own opinion, there is also a very great amount of lower 20Hz - 30Hz info inside the ceiling in the front of my room which is 2" steel, and a layer of concrete which looks about 9", or 6" thick, then covered with paint above in the garage. When I stick my head up there while listening to the opening to Star Wars 3 there is an increadable amount of boominess up there, but not in the back of the room where subwoofers are not located.

If I am adding this 5 1/2 quiet batt directly above my subwoofers is the SPL level going to go down if I am placing them in an area that sounds boomy? If my SPL level goes down anymore my subwoofer pink noise will be bellow 75dB, and I am not able to raise the level on them at this time.

Does boomy area = cancellation? Then treating cancellation = more SPL?


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## bpape (Sep 14, 2006)

Boomy bass means buildup and long decay times. 

Remember that when you measure broadband SPL, you're getting an AVERAGE level from all frequencies. So, you may be getting more of some but less of others when you smooth things out. It's just not an absolute thing.

Bryan


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## thewire (Jun 28, 2007)

I think this is the same seat measured. Treating the back wall (blue) versus treating the left and right upper corners (red, older measurement) each seemed to have their advantages. If I remember correctly adding absorption to the ceiling simply does similar more to what the blue looks like. I'm not sure so I will have to wait and see what happens then.

Disclaimer: No crossover & SPL level was calibrated same for each.


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## fredk (May 14, 2008)

From what I understand, the location of the treatment would effect which room modes you are absorbing the most. So, placing absorbers on the back wall would have much more effect on modes relating to the length of the room than those relating to the width or height.

Adding absorbtion to the ceiling would effect those modes related to height more. I also wonder how much effect absorbtion in the ceiling at the front of the room would have on measurements or sound quality at the back of the room.


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## thewire (Jun 28, 2007)

I ended up with better results placing the Quiet Batt in the front 1/3 of the ceiling. I still plan on treating the back wall however. Here are before (red) and after (blue) waterfall graphs and some comparrison graphs with equalization using a FBQ2496. I moved some other insulation to the left and right sides of the room and in a few other areas. I could not have improved things by moving insulation prior. I had some comments by a viewer in the back row things were improved. I tried playing the scene in The Matrix Reloaded where the keymaker says "every alarm triggers the bomb" loud rumble - Other person says "did he say bomb?". The room did not have the usual vibrating sensation followed by a flutter. There were no rattles also which was nice. We watched Iron Man and that sounded great, which got the expressed thought of improvement. They are trained to listen for sounds in their proffession so I trust their judgement.

I will be working on the back wall some other time. The false wall idea I had for back there was not approved. 

The percieved level of bass is somewhat different now. The level after equalization is about 71dB and before it is 73dB. Thats no good because I can't turn my other speakers down less than reference, but still sounds nice. Overall I would say I notice more clear highs, midbass does not have near as much thump or impact as it did (maybe I will switch back to 80Hz crossover or this might be caused by eq), and lower bass sounds more controlled and balanced in the room. There is the occassional moving of seats on the right side when seats on the left do not move. I still need to complete a few other things like maybe improving a couple subwoofers I rebuilt, and possibly check for loose tiles with some sine waves, but it's a pretty nice improvement that I can tell. I will check the back row probobly tommorow.

After Quiet Batt 










After Equalization. That is the far left seat. I almost never sit there. 










Worst seat after equalization (far right seat) I don't ever sit there.










Best seat after equalization (far left seat again)










No equalization before and after waterfall graphs.

Right











Right 2










Left










Left 2


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## thewire (Jun 28, 2007)

I did not measure the back row sorry. I went instead to sealing the subwoofers. The difference in the low bass is so great with those that are not well sealed, to those that are sealed partially well is so great I hear a difference swaping out subs to other locations, which is just silly. I will remeasure after I have built four of these pictured bellow using 7/8" thick melamine board, carpet, and silcone sealant. They are replacing the paper cup thin plastic peices on the left. Painting them will take awhile.

I will measure again after this. The subwoofers themselves seemed to be the weaker link now, so best get that out of the way. :yes: Hope it works.


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## thewire (Jun 28, 2007)

It sounds better after I sealed my subwoofers. Very even sound throughout the room, and the couches moved so little iin my first test it was not even that noticable. Then I went onto trying to flatten out the response.

The ringing in the back row was not improved. Since the subwoofers did not measure as flat after adding the Quiet Batt, I tried moving the subs. The flatter the response I got in my moving them (moving them made little difference) made the ringing at 20Hz and 30Hz worse. Much worse as in I can't even look in the window for ringing that long in the back row. In the front row it is around 900ms long. :unbelievable: I'm not getting any closer to figuring out a way to treat the back wall without anyone noticing, and there is huge amount of bass back there. I put my ear near the back wall and it was so loud it hurt my ear. :gah: With the strange looking dip in the frequency I decided to check my subwoofers playing on the RTA. I had to place some carpet between a tile and track lighting to prevent a rattle this scene in Transformers caused back there. I don't understand how they can say it sounds better. Maybe because the front of the room was less flat? :dontknow: Here are measurements and a photo. I give up tonight. I might try the left and right wall midpoints again, at least for checking them. There is no way that until we can move the front row seat to the back (if we ever change the riser for it to fit) will I allow a person to sit with their ear less than a foot away from 2 12" subwoofers. I might also try again moving the subwoofers into the center of the room but that is more anoying than ringing. I will see if I can find something with the way it sounds later. It's pretty loud, and I'm tired from moving subs. In the graphs the red are the measurements before eq, and the green is after.

I would move the subs to the left front corner and the back right corner for smoother decay but I would be able to localize some noises. :blink: If they would only let me treat the back wall it would be fine and I would probobly not use my equalizer again. :hissyfit:

Best decay left?










Worst decay right?



















Back row RTA of a movie playing with 2 averaging. :gulp:



















*My conclusion of what I found:*

My response now looks like the day I put a subwoofer in there with little room treatments, only there is less ringing 30Hz up, and slightly better average response across seating. It sounds much louder. If I were to set my subs at 85dB each (as loud as they can be played) instead of 64dB, I think it would be enough bass for just about anyone. That would be something around a 95 target lol. So with lots of headroom, at least I can appreciate the multiple subs. The room treatments are nice because they tamed the standing waves. There was about a 10dB peak after corner traps at around 10dB, now it is 8.5 dB, and my 60Hz null is nowhere to be found. That's progress. :T Now to just figure out where a back up location might be.  I pointed some track lighting up there so that you may observe the chaos.


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## thewire (Jun 28, 2007)

I moved my traps around for a couple hours last night. I also moved the rear couch. Since it is my couch, I can move it out of the room if I wanted. The downside is they will have to sit on the black couch that turns into a bed in the backrow because there is no room to recline. :devil: I sized the riser for it . :innocent: I moved the seat forward about 3 feet only also there is still good sound there, and plenty of leg room. The couch can go other places, or maybe I will just move it when they are not sitting back there. onder: Here are the changes measured. I will still probobly be trying to make it better. :sneeky:


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