Suggestions on room treatment

[Rantenti]

Hello all,

I have been using the Neumann KH-80s in this room (floor plan attached) for a while. The speakers sound good using DSP, and I do not have noise problems. However, I am hoping to treat the room to bring improvements to two problems:

1. The bass coming from the speakers is right (concerning amount) and tight but some low frequencies boom in the room.

2. the phantom image is very slightly left of centre, which is stubborn even with small changes in speaker placement/ toe-in. Perhaps it is related to the two shelves of different height above the desk as well as the asymmetry of the room where there more wall on the left of the left speaker.

I am not allowed to dismantle any shelves. I could place a few sound absorbent panels/ diffuser panels behind the speakers and on the wall behind my seat, and change new curtains. Problem is, I cannot install diffuser panels on my left or right side because on my left are curtains and on my right is a book cabinet and a open door.

Any suggestions or experience to deal with these limitations will be very welcome. Thanks!

 

[ernestcarl]

You said re-arrangement of shelves was not possible. Still, I think it would be better if you can swap the shelves and table (with monitors) the other/opposite way around. A certain degree of symmetry between the hard boundaries is important. The room is also too small for any properly sized diffusors to fit in. Absorptive treatment are usually advised for very small rooms and not the former.

Take individual measurements of the left and right channel at the MLP. See where the measurements differ — e.g. frequency response, early reflections and decay spectrum. Try minimizing gross correctable deviations with per channel EQ. Adjust volume between left and right channels in small increments using mono vocal tracks or pink noise i.e. perceived subjective balance is important as well.

 

[abdo123]

The boundary behind the speakers is the most problematic, i would probably cover all of that up with GIK acoustics Impression Series (4 or 6 inches thickness only).

 

[FeddyLost]

First, i'd try to
relocate some books to convert any bookshelf available into some kind of diffuser with random position
and
remove doors from bookshelf behind you and keep them in corner behind an opened door.
It's fast, cost nothing and maybe will help to some degree with boominess and specular reflections.
But most probably phantom imaging symmetry will not be improved without symmetry of massive boundaries.
I'd swap working zone 180 degrees (table below and bookshelf is on top of picture) if that possible.

 

[Rantenti]

Thanks for all your suggestions. The desk and bookcases were built into the wall so they are not movable, but indeed I can place absorbers on the wall behind the speakers and remove the doors of the bookcase behind my seat.

That bookcase is full of books and will make a good absorber-diffuser. However, it is only 1.2m high. Should I place some absorber panels on top of the bookcase to a height of about 1.7m so that sound from the speakers don't hit the bare wall directly? I can not nail the panels to the wall and simply stand the panels on the flat top of the bookcase at a slight angle so that they lean against the bare wall and not fall over.

Thanks!

 

[abdo123]

Thanks for all your suggestions. The desk and bookcases were built into the wall so they are not movable, but indeed I can place absorbers on the wall behind the speakers and remove the doors of the bookcase behind my seat.

That bookcase is full of books and will make a good absorber-diffuser. However, it is only 1.2m high. Should I place some absorber panels on top of the bookcase to a height of about 1.7m so that sound from the speakers don't hit the bare wall directly? I can not nail the panels to the wall and simply stand the panels on the flat top of the bookcase at a slight angle so that they lean against the bare wall and not fall over.

Thanks!

the boundary the farthest away from the speaker is the least important in my opinion. you're doing a positive thing by having 1/3 of the length of the room being the 'listening area' pushing the back wall very far behind you.

focus on the (front) wall behind the speakers and then the side walls and ceiling.

Look at it this way, the quicker (the less distance it takes for) for a particular reflection to arrive to your head the

1) louder they are
2) more likely your brain will register them as direct sound rather than echo.

both of these things pollute the direct sound of the speaker.

 

[Rantenti]

You said re-arrangement of shelves was not possible. Still, I think it would be better if you can swap the shelves and table (with monitors) the other/opposite way around. A certain degree of symmetry between the hard boundaries is important. The room is also too small for any properly sized diffusors to fit in. Absorptive treatment are usually advised for very small rooms and not the former.

Take individual measurements of the left and right channel at the MLP. See where the measurements differ — e.g. frequency response, early reflections and decay spectrum. Try minimizing gross correctable deviations with per channel EQ. Adjust volume between left and right channels in small increments using mono vocal tracks or pink noise i.e. perceived subjective balance is important as well.

Thanks, can you kindly recommend a tool which is cost-effective and simple enough for the measurement? I would appreciate it if some basic reading could be recommended as a primer so that I can learn to do the measurement and how to act on the results in the EQ settings.

Thanks!

 

[Bob-23]

the phantom image is very slightly left of centre,

I'd take into consideration that your left ear might be slightly better than the right one - changing the balance settings can cure it, in that case.

 

[Rantenti]

I'd take into consideration that your left ear might be slightly better than the right one - changing the balance settings can cure it, in that case.

That's possible. Perhaps I'll get an audiometry some day to find out.

Just played some pink noise and pure tones on each speaker separately, I hear each channel as loud as the other. When I play a pure tone in mono on speakers together, the image is slightly diffuse and not so pinpoint but it is quite centred. When I play mono piano works, sound is also quite centre (but a little diffuse, so it's hard to delineate the border of the image to decide whether it is actually very slightly to the left.

It is when I listen to singing in stereo, then I tend to notice the main body of the solo singer slightly to the left. I guess singers are not always placed that way on every CD.

I hope treating the front wall behind the speakers can give me a clearer image as well as maybe move the singer back to the centre. Hope it's not my ears that's malfunctioning. I'll crosscheck my perceived imaging with headphones, which should take away the room influences.

Thanks.

 

[ernestcarl]

Thanks, can you kindly recommend a tool which is cost-effective and simple enough for the measurement? I would appreciate it if some basic reading could be recommended as a primer so that I can learn to do the measurement and how to act on the results in the EQ settings.

Thanks!

UMIK-1 and Room EQ Wizard (REW) should be cost-effective -- there's also the Neumann MA 1 which saves you time, but you are limited in in terms of not having the ability to manually cross-examine the impulse responses.

Check the REW online help documentation, and this general guide as well: REW 101 HTS (simplified setup guide written by AustinJerry)

A recent thread briefly shows some identified reflection examples visible in different graphs and how to look at the evenness of the decay spectrum in a room: an attempt to understand spectral content from an etc.

Julian Krause shows you how to quickly take measurements and apply EQ:

I've only used Equalizer APO once or twice so can't give advice, but there may be tutorials in other threads on the forum if you do a search. Also, try to look at moving microphone measurements / method (MMM) and frequency dependent windowing (FDW) discussions scattered in the forum. Some people may think those aren't necessary, but I think those two esp. are very powerful "filtering" tools which are easier to use than may seem at first glance.

 

[Rantenti]

Just checked with headphones. I hear the female singers also very slightly to the left of centre. Probably my left ear hear higher frequencies better.

I placed some miscellaneous foam and sponges at home behind the speakers and the imaging became immediately cleaner. That wall must be properly treated!

Will look at the measurement tool and also buy some proper acoustic panels for the front wall.

Anyone can suggest their favourite acoustic absorber panels? The thinner (that still works for lower frequencies) the better, since my room is really small. Thank you everyone!

 

[ernestcarl]

Yeah, as @abdo123 mentioned the uneven boundary behind the speakers needs attention. Besides possibly adding absorbers to fill the gap/space, gradually pull the speakers forward (after level matching) until the L-R stereo imaging becomes more balanced to your ears.

*Thicker is better when it comes to bass absorption, but you will still be adding some space between the panel and the wall so you might be able to get by with a 2- to 4-inch thick panel just fine.

 

[ernestcarl]

Just played some pink noise and pure tones on each speaker separately, I hear each channel as loud as the other.

I use band-limited calibration pink noise 500Hz -2kHz. This is what I do for my multi-channel 7.1 system and I can pretty much get the tonal balance by-ear very close to what I get with individual channel swept sine measurements using REW. I expect Neumann speakers to be identical anyways so there is likely little need to adjust anything in terms of L-R volume balance -- it's more about the voices being centered perceptually which may need to be minutely, manually adjusted due to uneven reflections causing a slight skewing of the imaging.

 

[abdo123]

The thinner (that still works for lower frequencies) the better, since my room is really small.

Unfortunately these things haven't been invented yet. The music industry haven't been making enough money lately to push for the development of meta-material that can do what you're asking

Basotect is very good in terms of mass / sound absorption ratio but not much better than other materials with regards to thickness.

the GIK Accoustics Impression Series are the best that you can purchase for the money, but they're not cheap either though.

Most speakers are only forward firing from ~2KHz and upwards, these frequencies are easy to absorb and diffuse, even the furniture in a busy small room should be able deal with it. In fact most busy rooms don't need absorption in that region as long as the speakers are neutral. Pushing the back wall away from the speakers like your 1/3 room length configuration should further alleviate problems in that frequency range.

However 2KHz and below Speakers are Omni-Directional radiating the ceiling, front wall and side walls greatly with sound. To effectively treat for frequencies from 150Hz to 2KHz for a back wall you need porous material with thickness equal to 1/4 of the wavelength of the frequency you're trying to absorb. That means to FULLY absorb a 200Hz frequency the material has to be 50cm / 20 inches thick!

This is very problematic indeed, so studios are usually built with two walls, one rigid outer wall that blocks the outside, and then one 'fake' wall inside the outer wall that is basically made of porous insulation material.

Ofcourse many of us don't have that option so we end up with just covering as much of the walls as we can with as thick as porous material as we can. A 'diffraction plate' on top reflects frequencies higher than 2KHz and makes sure they're not absorbed too much.

If any of this seemed 'too much' feel free to ask any questions to clear it up.

 

[FeddyLost]

Should I place some absorber panels on top of the bookcase to a height of about 1.7m so that sound from the speakers don't hit the bare wall directly?

It will not hurt definitely.

I can not nail the panels to the wall and simply stand the panels on the flat top of the bookcase at a slight angle so that they lean against the bare wall and not fall over.

If you will use multilayer absorber/diffuser with diffusing layer, it may be an option, but i'd keed absorbers vertically to have distance between porous layer and real wall.
For example, GIK Demi Evolution PolyFusor looks like it will stand nice by itself. You can add some improvised support/spacing from the back.
Or you can use solutions thick as your bookshelf ... but it will be very expensive and barely optimal.

Also, you can check possibility of fitting something like Gik Demi Tri-Trap Corner Bass Traps in corners behind your speakers.

 

[Rantenti]

It will not hurt definitely.

If you will use multilayer absorber/diffuser with diffusing layer, it may be an option, but i'd keed absorbers vertically to have distance between porous layer and real wall.
For example, GIK Demi Evolution PolyFusor looks like it will stand nice by itself. You can add some improvised support/spacing from the back.
Or you can use solutions thick as your bookshelf ... but it will be very expensive and barely optimal.

Also, you can check possibility of fitting something like Gik Demi Tri-Trap Corner Bass Traps in corners behind your speakers.

Do you mean there needs to be space between absorber panels and the wall (even for foam types of panels) while bass traps are to be stuck into the corners without space? Thanks.

 

[FeddyLost]

there needs to be space between absorber panels and the wall (even for foam types of panels) while bass traps are to be stuck into the corners without space

Let's see at this Polyfusor for example. It's depth is 155 mm while typical bookshelf is 250 mm and more. If you will fit it into your room design with some airgap, you may have some "free" additional absorption of lower frequencies, though not much.
It's designed for direct hanging on the wall, but i think it will work well free standing also. Maybe it's even mentioned in user manual, need to check.
And tri-corner bass trap is already huge and optimized for corners, so just use it as intended.

 

[Rantenti]

For a quick trial before I buy the more expensive acoustic panels, I placed some cheap 2-inch thick acoustic foam panels covering the wall behind the speakers. The sound became very dull while the bass didn't boom much anymore. I guess it's because the treble is also sucked out by the panels.

Should I remedy it with the KH80's DSP like adjusting room resonant time (I guess the speakers will then lengthen the decay time) and pushing up the treble? or is the cheap foam material the problem? Thanks.

 

[ernestcarl]

For a quick trial before I buy the more expensive acoustic panels, I placed some cheap 2-inch thick acoustic foam panels covering the wall behind the speakers. The sound became very dull while the bass didn't boom much anymore. I guess it's because the treble is also sucked out by the panels.

Should I remedy it with the KH80's DSP like adjusting room resonant time (I guess the speakers will then lengthen the decay time) and pushing up the treble? or is the cheap foam material the problem? Thanks.

2-inch thick foam panels are too thin to have any effect in the bass at all. Are you sure it is not because of a change in speaker/listener position? As to the dulling, likely, yes. It can take a while to habituate to an environment that has less HF reflections. Although, ideally, absorption should be broadband or specific to the problem areas measured in your room response.

 

[FeddyLost]

The sound became very dull while the bass didn't boom much anymore. I guess it's because the treble is also sucked out by the panels.

Actually, without measurements at listening point I'd not call resulting sound "dull" because most probably it became more "correct".
If we talk about hi-mids and HF, they are very directional (radiated only forward), so foam panels absorbed only excessive energy of sound that was reflected. If you are listened this system without foam for some time in this room with a lot of reflecting surfaces, you might get used to this.
If you can't re-calibrate (i.e. make sound correct according to measurements) your speakers, and have no idea how exactly this affected the sound, I'd recommend you to listen for few sessions in such setup paying some attention to hi-mids and HF.
If you still will find this performance not satisfying and dull (not more clear, defined and comfortable), then you might add something like decorative steam heating radiator cover with medium size openinigs over foam. It will reflect some of mid-highs and return treble energy to your LP.