Interesting Room Acoustics Video

[MartinC]

It is not 'almost impossible' to treat room modes, but it does involve installing a large number of bass traps, such as GIK Tri-Traps or similar. 

This does depend on the frequency of the room mode as well of course. Tri-traps would do virtually nothing for a mode at around 40 Hz for example, no matter how many were installed.

 

[rdale]

You need to understand the relationship between pressure and velocity , foam traps are just not very effective in low velocity areas, membrane traps ( which I use here) do work but because sound propagates everywhere you need panels everywhere.

EQ is far more effective, subs in a ‘sink source’ arrangement are my next experiment.

Keith

GIK Tri-Traps use rock wool, and they have an optional 'range limiter' membrane. And they do work - do you think GIK don't understand that you need to put them at room boundaries and corners for maximum effect?

 

[PuritéAudio]

Room boundaries are where foam/rock wool traps will be at their least effective, remember you need a quarter wave length, that is a lot of foam.

To see just how effective your traps are simply measure before and after, without moving the microphone.

Just looking at your speakers specs -3dB at 45Hz you may not need to worry too much about bass trapping.

Keith

 

[rdale]

Room boundaries are where foam/rock wool traps will be at their least effective, remember you need a quarter wave length, that is a lot of foam.

To see just how effective your traps are simply measure before and after, without moving the microphone.

Just looking at your speakers specs -3dB at 45Hz you may not need to worry too much about bass trapping.

Keith

You're the only person I've ever come across who thinks the bass traps are least effective in room boundaries and corners. You don't need a quarter wave length of foam - the rock wool Tri-Traps with range limiters are effective down to about 50 Hz.

I do measure my room before and after adding extra bass traps. When I added an extra bass trap to my Klipsch RP600M based system in a small to medium sized room, I posted the results in the 'Tech Corner' section of this site as ' and you commented on them. I was actually surprised that adding a single bass trap and moving it around could have a measurable effect, but it did.

The speakers I have in a much larger room, that I have posted pictures of in this thread, are a pair of KEF LS50 wireless with a pair of KEF R400b sub woofers. They go down to 20 Hz and are flat to 60 Hz, but have a bump between 60-90 Hz because I have room modes at 57, 70 and 87 Hz currently I am expecting three more GIK Tri-Traps with range limiters at ceiling level to have some effect on those room modes.

 

[Jules_S]

How close is your listening position to the rear wall? My understanding is that this is critical with a view to whether absorption or diffusion may be more appropriate.

As I suspect I mentioned earlier, you can buy or make free-standing acoustic panels (in studios referred to as 'gobos') to place in front of patio doors. I've made one. Visually they obviously rather change the view, and reduce the amount of light that comes in though!

My ears are between 90cm and 1m from the rear wall (depending how I sit). Further back than that and I get into a bit of a null, and further back again the rear wall reinforcement starts. If I lean too much further forward, the lower frequencies feel like they're taking prominence again, although not as much as the boundary reinforcement. So it's all about the best compromise. 

Panels in front of the patios? Not. A. Chance.   To be honest that's not just a decision controlled by my other half, I don't think I'd be happy with it either. Shame no-one makes a retractable panel that could be folded or rolled up (hmm..... a market opening?). Short of that, I guess it's about making the best of things however I can.

 

[MartinC]

Panels in front of the patios? Not. A. Chance.   To be honest that's not just a decision controlled by my other half, I don't think I'd be happy with it either. Shame no-one makes a retractable panel that could be folded or rolled up (hmm..... a market opening?). Short of that, I guess it's about making the best of things however I can.

In case this isn't obvious, the point of free-standing acoustic panels is that they can be moved in and out of position as wanted, although this would be a faff frankly and I leave mine in place. The best that can be done is to have them on wheels.

It sounds like you sit way too close to the back wall for a diffuser to be a good idea to me, based on the video I posted and other things I've read. A proper absorber wold be the thing to go for as an upgrade over your rug, which will only be effective at the highest frequencies. The frequency range over which any panel you buy would have an effect over will depend on the material it's made from, it's thickness and any air gap between it and the rear wall. An air gap equal to the thickness of the panel is generally recommended as the best option to optimise its performance.

 

[Jules_S]

Unfortunately the shape and layout of the room prevent the seating being too much further away from the wall. Also I didn't care for the way the sound altered as I moved further into the room to be honest, as I said it started to sound a bit "obvious", like the bass had had an argument with the rest of the sound. The cohesion of the performance broke down and became too analytical.

I think I'm just going to have some fun playing around with things and see what happens. After all, that's what it's all about, right? Trying things out, mucking about... no-ones going to come to any harm (although I might go deaf at the volume level...) Either it will sound better and I'll keep the change, or not, and I'll put things back. Simples! 

 

[MartinC]

Unfortunately the shape and layout of the room prevent the seating being too much further away from the wall. Also I didn't care for the way the sound altered as I moved further into the room to be honest, as I said it started to sound a bit "obvious", like the bass had had an argument with the rest of the sound. The cohesion of the performance broke down and became too analytical.

I wasn't suggesting you should sit further from the back wall, just that, as is true for most domestic listening rooms, diffusion is likely not a good option on the rear wall.

You've already done far more than most manage by not having your listening position right up against the rear wall. My own listening position is about 1.3 m from the rear wall, which I've chosen on a similar basis to yourself.

 

[Jules_S]

Ah, right, sorry I misunderstood. I thought you meant that the position should be even further into the room. That might have to wait for the longed-for future when I can have a dedicated room for this stuff, and I can put whatever I damn well want on the walls and ceiling!

One thing I've become very aware of while experimenting with room positioning so far is the effect of the sofa itself. We have a knackered old leather thing (yeah, thanks for ruining that, dog!) and it's quite high-backed. It's very obvious how the sound alters when I lean forward so my head is away from the back. It massively improves the focus of the imaging, at the expense of a perception of a narrowing of the stage over which the performers do their thing. It also seems to result in a reduction in what I would describe as "bloom", a sort-of emphasis in the lower-midrange that drops away when leant forward.

We have a new sofa on order that has adjustable headrests, so I can drop it down to make it effectively open behind my head, or raised for support. I shall be interested to see how much of a difference that makes in the "low" position, reducing the immediate reflections behind my head.

Noted your comments on diffusion for the rear wall. Is that just because of the proximity? 

 

[rdale]

Ah, right, sorry I misunderstood. I thought you meant that the position should be even further into the room. That might have to wait for the longed-for future when I can have a dedicated room for this stuff, and I can put whatever I damn well want on the walls and ceiling!

One thing I've become very aware of while experimenting with room positioning so far is the effect of the sofa itself. We have a knackered old leather thing (yeah, thanks for ruining that, dog!) and it's quite high-backed. It's very obvious how the sound alters when I lean forward so my head is away from the back. It massively improves the focus of the imaging, at the expense of a perception of a narrowing of the stage over which the performers do their thing. It also seems to result in a reduction in what I would describe as "bloom", a sort-of emphasis in the lower-midrange that drops away when leant forward.

We have a new sofa on order that has adjustable headrests, so I can drop it down to make it effectively open behind my head, or raised for support. I shall be interested to see how much of a difference that makes in the "low" position, reducing the immediate reflections behind my head.

Noted your comments on diffusion for the rear wall. Is that just because of the proximity? 

It will be interesting to hear if the new settee has different absorption properties - I'm not sure how raising or lowering the headrests would change the sound but it should be fun to try out. I am very keen on diffuser panels, but as Martin points out you do need to be a certain distance from them such as at least 1.5 - 2 metres away.  I don't agree the diffusion is not likely to be a good option for typical UK living rooms, as long as you are far enough away.

I think diffusion is most effective at the front centre, but both you and Martin have TVs there. Maybe a projection TV system is better where you could have a motorized projection screen coming down when you wanted to watch TV or a film would be better as in my opinion something highly reflective like a TV screen directly behind the speakers is going to help the stereo imaging.

 

[MartinC]

The differences noted from leaning forwards and back could either be due to the presence of the sofa back, or the change of where your head is in relation to the room (a room mode effect) or a combination. I'm about to replace my sofa but I am deliberately avoiding anything with a high back for acoustic reasons, but I don't have any personal experience with a high back sofa to comment on.

but as Martin points out you do need to be a certain distance from them such as at least 1.5 - 2 metres away.  I don't agree the diffusion is not likely to be a good option for typical UK living rooms, as long as you are far enough away.

I think we just have a different idea of what a typically sized UK room may be  . The room you have most of your panels in I would consider to be huge!

I think diffusion is most effective at the front centre, but both you and Martin have TVs there. Maybe a projection TV system is better where you could have a motorized projection screen coming down when you wanted to watch TV or a film would be better as in my opinion something highly reflective like a TV screen directly behind the speakers is going to help the stereo imaging.

I'll be honest I'm sceptical how useful diffusion on the front wall (where TVs go) actually is, given the way standardly designed speakers predominantly radiate higher frequencies in the forward direction. The front wall tends to be about the last boundary on which acoustic treatments are suggested for this reason. I did try putting a panel immediately in front of my TV once just out of interest and from memory there was virtually no measurable difference at the listening position. I've just had a quick look and can't find the actual data to share though I'm afraid. I really don't think having a TV where I do is any significant compromise at all though, and anyway it's not going anywhere  . Well, until it's replaced with a larger TV anyway!

 

[Nopiano]

Perhaps you need a Listening Chair?

https://www.stoneaudio.co.uk/?product=gamut+lobster+chair

 

[rdale]

The differences noted from leaning forwards and back could either be due to the presence of the sofa back, or the change of where your head is in relation to the room (a room mode effect) or a combination. I'm about to replace my sofa but I am deliberately avoiding anything with a high back for acoustic reasons, but I don't have any personal experience with a high back sofa to comment on.

I think we just have a different idea of what a typically sized UK room may be  . The room you have most of your panels in I would consider to be huge!

I'll be honest I'm sceptical how useful diffusion on the front wall (where TVs go) actually is, given the way standardly designed speakers predominantly radiate higher frequencies in the forward direction. The front wall tends to be about the last boundary on which acoustic treatments are suggested for this reason. I did try putting a panel immediately in front of my TV once just out of interest and from memory there was virtually no measurable difference at the listening position. I've just had a quick look and can't find the actual data to share though I'm afraid. I really don't think having a TV where I do is any significant compromise at all though, and anyway it's not going anywhere  . Well, until it's replaced with a larger TV anyway!

My living room is Spain where I am now is much smaller than my UK one and I have two Vicoustic Multifuser DC2 panels at the front and rear, along with a GIK Gotham 2d quadratic diffuser at the front as well. It does look more like a man cave that the bigger flat though and I'm not sure I would be able to get that past a non-HiFi partner if I had one.

If you often search for acoustic treatment porn on PInterest like I do, you will find there are an awful lot of high end HiFi systems which have 2d diffusers at the front. I'm not sure if you could measure the effect with REW, but it is very clearly audible. Having said that, I still would have expected putting an absorber panel in front of the TV to have had some sort of audible effect. Maybe it is the kind of thing you have to listen to for a week and then remove to really gauge whether it had an effect.

 

[MartinC]

Maybe it is the kind of thing you have to listen to for a week and then remove to really gauge whether it had an effect.

I didn't listen at all as I just made a quick measurement out of curiosity in the middle of a set of other measurements. I'd have needed to move the microphone to listen to anything and I didn't want to change the setup. I also wasn't too bothered as there was zero chance of a panel staying there  .

If there is an audible difference then there definitely would be a measurable difference via REW, but as soon as you see there is a difference you can't fully judge the effect without listening. The difficulty of course then arises from it being a sighted test. One reason I've actually just had panels up for a while but not done a proper A/B was to try to get a true feel for them.