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Discussion Starter #1
For those that may want to read it, round one is here.

Sketchup of Room:

Recap:
The main area of my apartment is 20x20 with the kitchen set in the middle of one wall. The 'outside' walls, ceiling and floor are poured concrete, the kitchen walls are probably plaster on metal lathe. Initially I looked at my space as 20x11 (main livingroom) with extensions.

At the main seating positions, I saw a nasty peak at 52Hz and nulls at 42Hz and 76Hz. I build one set of traps 4'x2'x6" and noted significant improvement at 42Hz and a narrowing of the 76Hz null.

It was not until near the end of round one that I realized I was basically dealing with a square concrete room. The monster peak at 52Hz made sense as this matched with axial and tangential modes of 20'. This made me curious to know what a wider set of measurements would show, hence round 2.

So, here is a set of measurements taken at the points in the room where you see circles. The one at the very front of the room behind the display and the one in the dining area are not in this set.


Just look at the consistancy of the peak at 52.5Hz through all but one of the measurements.

This leads me to one question. Given that this peak seems to be consistant over the entire main listening area, and given that it is addative (a peak), does this make it an ideal candidate for the dreaded equalization?

In an odd twist of fate, the best measurement came from the dining area where 22-40Hz is almost flat. That explains why music sounds so good when I am sitting at the table for dinner. :bigsmile:
 

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That isn't brought up to often so let me see what I can recall. Some things that come to my mind are:

Difussers (front of the room?) and a dead front wall.

Ceiling Helmholtz Resonators (lots of boxes aimed at a target frequency)

Thick panels hung envenly around the room or maybe some tube trapping would be better.

Changing the height of the floor. (sloped)

Adding splayed walls.

I realize some of these are all somewhat impractical but it's the best I can think of. :huh:
 

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To answer your question - yes. It's consistent so it will be effective for all seats - AND - it's purely in the subwoofer range so it's not impacting sound quality in the mains.

All of that said, ignore ANY measurement that is not where a seat is - it's totally irrelevant. Also, make sure you measure where the ear will be height wise.

Bryan
 

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Discussion Starter #4
Thanks Bryan. It looks like my next acoustic investment should be a Feedback Destroyer. It should clean up a large part of the boomieness I hear.
 

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Just understand that EQ will only deal with the frequency response aspect. It won't help any to deal with excessive decay times and ringing in the room - nor will it deal with nulls in response. Treatments will. Usually the best option is to do things in the following order:

- placement
- treatment
- EQ

Bryan
 

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Discussion Starter #6
Yup, I understand. No amount of treatment is going to remove that peak. Placement just seems to move the peak in frequency. Surprisingly, ringing is not as bad as I would have expected.

The plan is to eqaulize that peak to see what it gets me, and then continue on with treatments. I still need to work on the upper end as well.
 

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Most likely, since the peak is pretty much everwhere in the room, it's either:

- height related

OR

- boundary response issue due to sub placement

Bryan
 

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Discussion Starter #8
?

Given that a mode calculator gives axial and tangential modes at 56Hz for a room of 20' I would have thought this peak more likely relates to that length/width. Particularly since in reality my system is in a square room.

I would have thought that the 71-76Hz null I see around the room is related to height. Again, it matches with a predicted mode at 71Hz.

Edit: It probably at least has a boundry component as the only two places I can put it at the moment are in a corner or along the one wall. If I remember I will move the sub out from the wall and do some measurements just to see what happens.

Either way, it matters not. It needs fixing. :)
 

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If it was purely the combination of axial and tangential, it would change or disappear in different places in the room which vary with length. Your measurements indicate that it doesn't - except for one trace that just has it reduced in intensity (likely a null overlaying it).

You're right though, it needs fixing.

Bryan
 

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Discussion Starter #10
Good point. I was expecting the null to dissapear or shift as I moved to the narrow part of the room. This acoustics stuff is an odd beast.
 

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Discussion Starter #11
Woohoooo! Picked up a used BFD 1100 today. Now all I need is some cables and I can make those REW graphs do all kinds of funky things. :bigsmile: ;)
 

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Discussion Starter #12
WOHOOOOOOO!!!!

It worked! Exactly the way REW predicted! Exactly!

Well, colour me impressed. I defined the filters in REW based on my last set of extensive measurements. I used the auto-generate tools in REW on my main seating position. REW gives me a set of numbers to enter into the DSP1100. I added a filter for the worst peak at 56.2 Hz.

I then did the calibration stuff with REW and did two measurements: one with the filter, one without. It took a 14db cut to pull that peak down so I do not know what effect that will have on the overall quality of sound.


I then loaded the filters I had created on the without filters graph to compare the actual result to that predicted by the filter and I'll be if it didn't exactly match the predicted filter result. Talk about dead simple.

I also did a quick check to see how the filters would affect the other measured positions, and for the most part, I think it will improve sound in almost every measured position.

I'm off to listen to a Balrog have a dissagreement with Gandalf to see what the difference is with the filter on and off.
 

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Discussion Starter #13
It has been an interesting evening. I added 3 more filters tonight and did some listeining. The filters were at 23, 29 and 34 Hz. I wanted to see what impact a broad range of filters together would have.

For music, the difference was very, very subtle, and only for stuff with low low bass. Listening very carefully to several tracks from ELP's debut album, I could hear a slight difference in the kick drum; like someone toned it down a little. The same could be said for some pipe organ stuff. I don't think it was super low though.

One interesting thing, with the EQ on, I think I noticed the hole at 40-45 Hz a little more as the organ notes moved through that range, you could feel the notes weekening and strengthening again.

Most of the bass boom is still there. Looking at waterfalls, the shape of the ridge at 56Hz is exactly the same, just reduced.

I put on LOTR the Cave troll and Balrog scenes. Here the difference was more noticable but still subtle. There was a noticable reduction in boom in some scenes and some of the effects were more defined, like those when parts of the bridge collapse.

Looking at the output LEDs on the BFD there is WAY more low frequency output from LFE than music.

So, the EQ did not have nearly as much effect as I had hoped it might, despite dropping the 56Hz, frequency by 14db. Most interesting.
 

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All a matter of frequency response adjustments vs. getting decay times right.

EQ has it's place - but it's the last adjustment to make behind proper positioning of seating, subs, and speakers - and bringing the bass decay time into line

Bryan
 

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Discussion Starter #15
So it seems. I also wonder if some of the boom that I atributed to 56Hz may well be higher than I thought(bass guitar).

We see so much focus on the stuff below 30Hz on these forums, that it is easy to forget that bass extends up much higher than that.

I am beginning to see a patern where any given change is quite subtle, but [hopefully] the sum of multiple changes will be strikingly different.

I believe that I had one corner position where the 40-45Hz hole was eliminated, but the 56Hz peak was shifted down quite a bit. If that peak is as consistant as the 56Hz one, I can EQ it as well. I was originally worried that I would not be able to effectively treat it with bass traps because it is so low.

After that I will go back to additional bass traps along the front wall.
 

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Discussion Starter #16
As usual it seems to take a few days for things to sink in.

So, if I understand correctly, the boom I am hearing could still be from the 52Hz region. The reduction in ringing from 700 to 500 ms. due to the 14db reduction in volume is not enough for me to perceive any reduciton in boom.

Ah well, onward. My next step is to try the sub in my rear corner where the 42Hz null was eliminated last time I measured. Unfortunately I have no way to do an A/B comparison of the two positions for what I would expect to be a subtle differences.
 

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What most people describe as 'boom' is considerably higher than 25 Hz.

Also, reducing the amplitude of a frequency in relation to the other frequencies has no impact on decay time in and of itself. That doesn't mean that proper treatment can't be both. I just wanted to make sure that you understand that they're not necessarily always going to go together.

Bryan
 

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Discussion Starter #18
When I talk about boom, it is the sound of a specific note or set of notes and how they sound in relation to others close to them in frequency. To me, it has nothing to do with a specific frequency range. The way I would describe it is that, in addition to the difference in sound, I can feel addtional preasure on my ears for certain notes.

It could still be that what i am calling boom matches your description and is coming from higher up. If this is the case, then additional broadband traps should reduce this.

Once I have moved the sub to play with it a bit in the corner, I will get back to additional absorbtion to see what that does for me.

Where do decay times need to be in order to perceive a meaningful reduction in boom?

Also, reducing the amplitude of a frequency in relation to the other frequencies has no impact on decay time in and of itself.
Agreed. I was only commenting that, starting from a lower amplitude, you get to zero (or the 45db floor on the graphs) sooner. In my case that was 45db ~200ms sooner. It looks like a reduction on waterfalls, but is not meaningful in how those frequencies sound. I think this is where the confusion arises that EQ can reduce ringing.
 

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What you're describing as boom sounds to me like modal peaks where 1 or 2 notes are considerably louder than other surrounding tones. Excessive decay times only exacerbate the issue. Having the 20x20 dimensional issue makes the peaks even more intense

I'd like to see the decay time from 100Hz down to be no more than 400ms

Bryan
 

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Discussion Starter #20
I'd like to see the decay time from 100Hz down to be no more than 400ms
The decay time at 52Hz is just over 500ms and for the peaks as 34 and 24 it is above that. Hmmm. So I am close on my largest peak and the one that is in the range of most bass. I think I should take a few measurements with my mains included to see what is happening up around 80-150Hz.
 
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