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Case: Fixing room acoustics for a F205 system

Questions often asked are:

  • Does a small room - smaller than a typical living room - compromise sound?
  • Can the room be too dead - or does it just get better the more you absorb any reflections and shorten the decay?

While a small room can be challenging simply because there may not be room to place treatment and speakers and equipment, they will actually perform very similar to a some larger room, when treated properly. Even in larger rooms, the reverb from the room is still very small compared to a concert hall, and thus do not contribute in a positive way to create a better sensation of being in a large room. The room-information must come from the recording, and this room sound is best preserved by reproduction in acoustic surroundings where reverb from the room itself is sufficiently low so that this contribution does not drown the room already present in the recording.

Too dead can cause envelopment and rendering of acoustic object to be less full and realistic, and you certainly do not want a colored frequency balance from the room. To achieve this desired flat room response, it is required to add some reflection at higher frequencies - either by mounting reflective surfaces on top of absorption, or leaving surfaces untreated - and this will lead to a room that still has plenty liveliness in its reverb.


Thank you Øyvind for your great advices regarding acoustic treatment in my listening room.

After this post was written, I have performed some more dampening in the room. The corners in the front have been built to include ventilation with "sound silencer".

The remaining space in the corners are filled with acoustic dampening mats from "Mittet".

The room is quite small, and I have always had issues with low frequencies. That was until I applied the acoustic treatment described in this post.

Before the treatment, certain low frequencies was very dominant, and no matter EQ's applied, the result was not good.

I will try to describe the sound after the acoustic treatment:

The first impression is the presense of the instruments and the vocals. It is like they are in the room. This was also a sensation I partly had before treatment also, but in a completely different league.

Even when a "Double Bass" enters the stage, it's position is clearly defined in the soundstage. No matter which of the strings played.

The bass is now very tight and "dry", and more addictive than before the treatment.

I was not aware that it was possible to reproduce sound in this way, espesially not in my little room.

It is so relaxing to listen to music now, because I do not need to listen for possible optimalisations.

I'm very satisfied with the result 🙂



Hello, Bjarte!

I had a quick look at the measurements for this latest addition to your room, and there is a difference in decay in the bass range from around 50hz and up  into the midrange, slightly better, may be audible. If it is audible, the bass should be even more dry and precise, perhaps better impact/tactile as well.

This change did not change the higher frequencies, it did not make the room more dead, at least not from what can bee seen in the measurement.

Excellent descripton of the sound impact of acoustic treatment in a small room. Especially this sense of presence, that you describe, really is something that can not be understood until you experience it, those who still believe it is not necessary to treat a room properly to get good sound really have no idea what this is about.

Decay, as the room is now:

And the RT60 250hz + 2khz:

We see a slight improvement in low frequency decay. In the Decay graph, the frequency response looks different, and that is due to more precise mic placement, and there are also small changes around 50hz which is likely due to the corner absorbers added.

When looking at measurements, we are interested in observations of what is going on in time. The frequency response alone does not provide any useful information. You should always start out with speakers with flat and smooth frequency response - both on and off-axis - which will usually give a neutral and correct tonal balance, and never require eq above around 200hz.

Quote from hemiutut on 26/08/2021, 23:02

Exactly what he has used I do not have all the details on, as I recall it is dacron from a local supplier called Mittet, I can see a measurable difference in low frequency decay, not huge, but it made some improvement.

Quote from hemiutut on 27/08/2021, 19:37

If you look at the picture, you get an idea of the dimensions, the front wall absorption is 20cm thick.

It is not practical to do side wall absorption in this room, and really not necessary for the F205 loudspeaker with its excellent full-range directivity control - very little sound is radiated into the close side wall from the speaker.

Yes, proper acoustics are addictive, and once you experience it there is no way going back to untreated rooms.




Quote from hemiutut on 28/08/2021, 15:15



Thank you, this is good information for everyone who wants to build absorbers.

Dacron is favorable due to its rigid mechanical properties - it does not fall apart - and there are no problems with dust or health issues.

Be aware that dacron must have the right density, just as with other insulation materials, the density can be different for different products.