# Trying to improve acoustics



## Paverne (Jul 8, 2013)

Hi guys, hopefully there will be an attachment below this....


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## Paverne (Jul 8, 2013)

OK, sorry about the hiccup, something went wrong with my post... anyway, let's move along....

Hi guys, I'm pretty new in here, interested in home theatre, music, DIY, and looking to improve my LF. When I posted in the new members section it was suggested I drop a post in here to find out if my improvements may come, at least in part, from modifications to my room acoustics.

My system is a set of Wharfdale Pacific Evo speakers and an Onkyo TX NR801 receiver. I live in a small rented apartment. When I moved into this apartment I found I had to place some acoustic treatment (just from gut feel, I know little about this, though I am technical and have done some DIY) to tame the mid/upper mid (my guess!) due to my room arrangement. (see attached on previous post)

I was happy enough with no sub, but recently thought I'd give it a go using an old pair of Kef Concertos that were my first set of speakers. I put both B139 drivers in isobaric in the one Concerto enclosure (about 50 litres) and tunes with a port that no protrudes about 300 mm out from the enclosure (too long to fit inside) have bought a cheap plate amp to drive this. While the plate amp is supposed to be flat, I have seen tests online which show it has a 3 dB hump in the mid bass region. I suspect my speaker also has a similar hump, as I think my port may still be a little short (it's what I had). Anyway, the system definitely sounds muddy on music and even muddy for theatre, though more dramatic that no sub!! I'm sure my placement is a big part of the problem as the speaker is in a corner as well.

So thinking EQ and "love to know what is really going on" I've ordered a miniDSP and test mic, and have downloaded REW.

I'm going to post this now and add more in 10 minutes time


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## Paverne (Jul 8, 2013)

Ohh, when I say I'm technical, I'm not "in depth" or "theoretical" when it comes to speakers like a lot of you guys, technical is my profession, but not acoustics or speakers, I only have a vague idea about that stuff... though very interested!

So very interested to hear opinions and recommendations....

So to add some info to the sketch above:-

The key thing to understand is that the main speakers, TV and sub are all sitting under a stairway leading to the upstairs bedrooms - so the sit in a triangular hole in effect - the triangular hole is about 1 foot high on the left and 8 ft high on the right, and 3 ft deep.

The main speakers are where they are because that's pretty much the only place they can go. The left speaker cannot go further left due to the lack of height further to the left. I did have the speakers further forward (not in the hole) and wider, but they have been put in the hole to create more living space (read "yoga"). It will be possible to swap the room about after Christmas but that does have the disadvantage of putting me on the hole, and I've been avoiding that.

So with what I've got here, I was forced on first pass) to put the sub where it is as the length of the port wouldn't allow me to aim it forwards. It's close to the corner because that lets me crawl around behind the furniture to play with connections (I only just re-arranged this with new furniture to get the whole thing back a bit and changed from 42" to 60" TV). Looking again, the speaker could be re-orientated to aim to the front IF I put it on a small stand of sorts and put it upside down (driver at the top). I could move if further from the corner, though it will be aiming closer to the left wall (well, the sloping staircase), or, if aimed towards the front more directly into the back of the TV panel. I could also lay the speaker on it's back and fire upwards. The speaker is not something that can be seen..... well, it has 300 mm of pipe sticking out the front and a back-to-front speaker as well... and it all looks the 43 years old that it is.....

Re the sub itself - long term I could build a different (more appropriate?) enclosure, though there is limited space in there (but not really a height issue if I was to use height to get the cubic). There is enough space to the left of the left main speaker to put a 250 litre oddly angled enclosure to house the two forward firing drivers in normal parallel, though it would be a box than only worked (shape-wise) in that one location.

Re acoustic treatment - for the sub - I have no idea, I have pretty much open slather in that hole, though mention of acoustic treatment anywhere else prompted looks of very much "what planet are you from again?" heh, the existing treatment (behind sofa and beside right main) pre-dates my partner's arrival.... Anyway there is one corner where I could sneak in a bass trap (I've got that term looking through this forum) but it's only one corner (the bottom left on the plan, above the computer). I could certainly put one in the hole with the sub... but would this soak up the direct field?

My gut says it would be nice to have something on the ceiling, but as previously mentioned, I'm renting, and can't think of a way to attach it in a way that won't cause problems with that....

I could increase the thickness of the material behind the sofa. This is not full height, and I don't think it could be since it's on a frame and not attached to the wall.

The room is a very complex arrangement (to my thinking) as it has different heights and angles (the stairs) though they might all be a good thing. I'm thinking of doing the room prediction in REW, but should I consider the whole area to be one room, or just the living part? There must be reflections of the half wall between kitchen and living, so I'm thinking it's some complex mix of big space plus the smaller space? When I clap in the living room I feel that the latest echo comes from the kitchen/dining side, though it's not a long echo as you might expect with no carpet or harder furniture (the sofa would be a bass trap I suspect)

Anyway, I'm very interested to hear any suggestions.


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## bpape (Sep 14, 2006)

If something must be 'in the hole' then the way you have it now is fine. Ideally, both you and the setup would come farther forward. Speakers are giving a big resonance now that needs to be tamed with bass control and thicker absorption as much as you can back in there.

Seating location is bad for bass build up and will never allow a proper surround field to develop when the ears are essentially equal with or behind the surrounds (slightly). Hard to have a rear channel that's in front of you.

Bryan


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## Paverne (Jul 8, 2013)

Thanks Bryan. Sort of like trying to put a dress on a sow then....... :-(

Pretty much stuck with this arrangement, only way to move the seating position forward is to temporarily pull the seat forward, which I will try at some point.

My next step (to my thinking) is to sort out the sub itself - I should have the mic and miniDSP today, but have a bit of a learning curve with the measurement and EQ yet. Check (and tweak if I can) port tuning, amp response - plan to do all that outside.

Once I have that as good as I can get it I'll measure it in the room - as it currently is, and take it from there.

I have a few places where I can add absorption, as per the sketch below:










I assume the absorption at B (in the sketch) is a given (based on your comments in other threads). This could be floor to about 5' 6" (I'm not sure if I can stabilise something higher without screwing into the wall)

The absorption in A is what you are suggesting for my "hole". I can make this from floor to about 4' high and be largely invisible, or go all the way to the underside of the stairs if it will make a difference???

The other options are do-able, but I'm interested to hear your opinion based on your experiance on whether they are likely to be worthwhile:

C - the window is unused (blind always closed) and can be filled with material
D - a corner absorber could go here from about 3' from the ground to as high as the ceiling
E - could be a panel from about 4' high (top of the desk arrangement) to say 7' high
F - this panel could be floor to about 5' 6"

Thanks for your help!


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## bpape (Sep 14, 2006)

Treatment position looks good. For the rear wall, I wouldn't overdo the area but concentrate on the area behind the couch and make that as thick as possible.

Bryan


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## Paverne (Jul 8, 2013)

OK, thanks Bryan, microphone arrives today, have a bit of work to do in discovering the ins and outs of measurement, I suspect I'll post again in a couple of weeks


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## musicguy (Nov 28, 2012)

Using this gentlemen set up as an example. What formula would you use to set the couch from the wall. Real Traps says 38% from the front or rear wall would be the starting point to "Not be in a void". Im my own living room i have a void at 40-50 hertz. Or would it be best to move the speakers more into the room or both. I understand every room has it starting points but guide lines for the best compromise.

muicguy


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## Paverne (Jul 8, 2013)

OK, so I've done some measurements... looking pretty ugly!!

First is a comparison of the right speaker with full spectrum with and without the 20 mm foam on the right hand wall (the speaker is right up against this wall)










Now both main speakers full spectrum, and my new 43 Hz friend :-(










The receiver's crossover and perhaps a bit too much gain in the "sub"









The "sub" response out in the garden (roll-off towards 200 Hz is plate amp LPF)









Combination of mains and "sub"









Combination of mains and "sub" with some EQ (not spending much time with this until more absorption is in place)








Waterfall of the above








Had a play around with room simulator, which picks the 43 Hz issue as the front/walls. Seems like nothing I tried in the simulator makes for a happy world for me, If I fix one problem with absorption another one pops up, though the front/back absorption should tame things quite a lot within the band-pass of the sub.

Have been looking around in the hardware shop for materials for these panels...


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## Paverne (Jul 8, 2013)

I tried a seating position 1 metre on front of my lounge seating position, and got the following result. This is the non-equalised response, and before I did a slight re-tune of the "sub" (port was tuned a bit low). I was surprised - the new position seems to be worse! 









Musicguy - I've decided I can't move the speakers forward, as they have just been put back to create space in a pretty small living area. I did note that the bass lifted in the new position, and the plots show I've picked up a big 43 Hz boom, very prevalent when I'm just running the mains, which is my usual music setup. The "sub" was a recent addition, and prompted this "tune-up" effort. Problem I now have is the new position has pushed this boom to new heights, and while I can tame it with EQ on the sub, I have no opportunity for EQ on the mains. With the EQ on the sub I added last night the bass is much smoother sounding when the amp is in stereo mode and thus putting HPF on mains and running the sub, BUT, when I do this (run through the receiver's DSP) I do lose a bit of sparkle - enough to hear quite easily. So I'm hoping the absorption tames that boom....


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## bpape (Sep 14, 2006)

Likely not. 43 is pretty low and would require some VERY thick absorption and in the correct place (TBD). Can you not run the sub when listening to music?

Bryan


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## Paverne (Jul 8, 2013)

My previous experience with my clumsy sub attempts and I guess other people's not so great implementations was that the bass end of music was not as good with the sub. But now that I've got levels and the rough EQ I find the bass end of music is better with the sub than with the un-equalized boomy mains. But I am losing something in the rest of the spectrum through the receiver's DSP - the response ripples (over 400 Hz) are a little different with and without the DSP, and there is a one or two dB drop off in the top end. I can recover that with the receivers treble control, though amazingly, the treble control seems to lift everything from 200 Hz up.

I am finding myself listening to music with the subs rather than without though - the improvement is the bass is a bigger positive than the loss of sparkle, though I'd like to find a way of keeping it all. I will try running an analog stereo output from the music source through the miniDSP and see whether it produces a better result.


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## bpape (Sep 14, 2006)

You should be able to override the EQ if you want so you can keep the bottom end gains and disable whatever it's doing in the top end.

Bryan


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## Paverne (Jul 8, 2013)

Did some SPL measurements @43 Hz around the room just for my education. The attached pic shows roughly what I have - red is high level, green lowest level various shades of yellow and orange are in between.. more red - more hot.









Also re-visited the room prediction in REW. Previously I had treated the room as being just the lounge room part... with a suspicion the whole room may come into play somehow. What I was seeing in my measurements was more complex than the prediction, and some (major) things I was measuring were definitely not in the prediction. It sort of dawned on me that 43 Hz wasn't going to care too much about the half wall in the space so I entered the entire room into REW's prediction and now see something more complex - much closer to what I measure.

The main thing I see is that the predicted front-to-back mode at 40 Hz is complemented by a side-to-side mode at 42 Hz, so no surprise then that I have my 43 Hz friend.

Given your "not likely" and "VERY thick absorption" comments Bryan, and the discovery above, some further on-line reading (things that might work at 43 Hz), and a look around the room to see what is possible.... I've come to the full realisation that I'm doomed to rely on the EQ do tame it, but will add what I can front and back (building 4" rockwool @ 6 lb/sq ft). Hopefully that will help a couple of nulls I have a bit higher up the bass spectrum.

Thanks for your help guys, I'll post the results when I've added the absorption - probably a couple of weeks...


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## bpape (Sep 14, 2006)

Yes - you need to account for the entire room. In fact, you'll have issues with the modes of all the smaller spaces and then the combinations of spaces too. That said, remember that just because a mode exists in a room, you may or may not hear it pending where you sit. 

Bryan


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## Paverne (Jul 8, 2013)

Finished the first 4 panels a bit over a week ago, these are the panels at A and B on my post on 15-July, that is 2 x 1.2 sq metres of panels behind the listener and 2 x 1.1 sq metres of panel in front of listener (behind speakers, in the "hole"). Panels are 2 x 100 mm thick 3 kg/m rockwool compressed into about 150 mm. This was supposed to be 100 mm but they are bulging somewhat, I added some mesh to try and control the front bulge but not much effect, if I built them again I'd add something stiffer to control the bulge. Anyway, the panels contain 200 mm of 3 kg/m rockwool, the rear panels are only about an inch off the plaster board wall.

Based on the untrained ear:

Replacing the 20 mm foam panels with the above rockwool panel made the back wall disappear, it is a little weird, but better. Initial listening was impressive, and may have been more so as I suspect the temporary (casual) placement of the other two panels may have been a more useful placement that their final spot. The temporary position was in the "dining" area - to the right of the listener and probably absorbing a bit of the energy going in to and out of the "dining and kitchen" area (about half the volume of the space). The initial impression was that the focus was more on the speakers and the boomyness of the main speakers (this is listening to music from only the mains) was more controlled,

Then I moved the panels into their proper position behind the speakers - for some reason (too hard to pin down) it was less impressive, though I'm sure the change must have been subtle. The panels at the front sit on floor level (1.1 metres high at top) and the rear are 700 mm up from the floor (1.8 metres at the top).

After listening to the system for a while (TV and music) the main issue (ignoring bass which had to be re-equalised) was of thin vocals - I seem to have some issues 200 - 500 Hz from one speaker or other (and particularly the centre which I haven't measured).

The following sweeps to the listener position are for the mains only, one at a time. What I hadn't noticed before was the lump at 150 Hz on the right hand speaker (sits very much against a wall and 600 mm out from the back wall) that is maybe worse with the panels than without. There is a slight improvement of the 40 Hz.


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## Paverne (Jul 8, 2013)

With both main speakers driven the bass looks like this:-








I had trouble matching levels between this and earlier measurements - think I'm doing something wrong with REW as it seemed I had to drive the speakers harder to get the same level on the plot, and looking at the distortion plot confirmed that they were being driven harder (something like 6 dB). So level matching for this plot is a bit of an approximation..

The waterfall shows overall slight improvement everywhere except 40 Hz which appears a bit worse, so again I suspect something to do with different output levels required from the speakers to provide the same level at mic or in REW....


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## Paverne (Jul 8, 2013)

So in trying to arrive at a EQ I had a lot of trouble with the unsymmetrical response of the main fronts - the right speaker against the wall had such a lump in the 120-180 Hz area that was outside of control of my EQ (sub EQ only) and somewhat dictated the direction I went in. Looking at the response from each front speaker with the 80 Hz crossover switched in (eliminating much of the left speaker's 40 Hz problem) the left appeared to want 4 dB more bass and the right needed 10 dB less at 150 Hz. 

I ended up going to 150 Hz crossover to try and tame the lump as much as I could. I'm not sure what the downside of this is. Even with that crossover setting the 150 Hz lump still clouds the overall result.

Right and left responses with a few crossover options:

















And the current overall response with my "sub" after EQ. Because of the high level at 120-180 Hz I was somewhat forced to ramp up everything below it (thinking the "house curve" concept was something I'd like). I did try the house curve starting at 80 Hz (leaving a 5 dB hole at 80-100) but it didn't sound good. The current response sounds good generally though I think it would be better if everything from 180 down was 3 dB less. Sounds like a bass control is needed  though the Onkyo bass control seems to hinge from about 30 kHz!!! winding down the bass even effects 20 kHz a bit (something I really didn't expect) So doesn't help me. Playing with the sub EQ ( a MiniDSP) even with the 150 Hz crossover doesn't have much effect on the lump.

Note that the level around 200 Hz on the plot below is a bit of a hole, but the overall bass level at 180 Hz is about 3 dB or so above the average level above 200 Hz, so the overall sound is a little bass heavy for me.









The original intention here was to attempt the re-introduction of my cobbled up "sub", and I have mixed feelings with the result. 

Adding the sub has been generally successful - I have deeper smoother bass, I little heavy with bass heavy R&B but not crazy. Sounds much improved for HT. Level wise no problems for music at the levels I listen at (small room) and generally good for HT though I have found one movie (Looper) that has a club scene that pushes the sub into non-linear excursion at my loud listening level (not that loud, but about the max that other listeners and the neighbor are good with). Heh, putting this into perspective with other systems on this forum, I have a "sub" in isobaric with a cone area about equivalent to a 10" driver, a linear excursion of 6 mm p-p, and effective driving power of 150 W (actually 2 x 150, but isobaric) and with the EQ I've probably only got a quarter of that on average. Anyway, it is 95% enough for my situation. I'll look at upgrading in the future, just to get a bit of headroom if nothing else, and maybe a little more level at 20 Hz.

But I've found all my problems in the process... it's been an interesting but a little frustrating process to date. I've gained, but become aware of a few issues - issues that probably need considerable expense to rectify. Limitations of the room size and layout, limitations of the receiver (don't think there is any way to add EQ to all channels), limitations of the speakers (I suspect they contribute a little to the thin vocal) (top end roll-off doesn't bother me as I can't hear much over 12 kHz these days :-()

I did have plans to add more absorption, but I'm not sure now. My biggest problems now are thinish vocal and the 120-180 lump from the right speaker, and while acoustics may be a contributor to both, I suspect my room size/shape and inflexible speaker/listener position situation are the main issue (I think you pointed that out at the beginning Bryan ), and adding treatment may not help.


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