Bass issues in my new writing room...

[noisyneil]

THE ISSUE

I've got a pair of Neumann KH 120 A speakers, which are meant to be pretty flat down to 50Hz, but, predictably, there are issues with the bottom end. The oddest of these is that, when they're on the desk shelf (sitting on IsoAcoustics stands), the bass drops off in a straight line from 100Hz. Pushing the desk right up to the window improves things slightly, and putting the speakers on stands is better still.

I'm using IK Multimedia ARC to try to mitigate some of the dips and peaks, and the result is workable for the time-being, but to get any kind of solid centre image and bass response, I've had to pull my listening position quite far from the speakers, which leaves me feeling a bit disconnected.

THE ROOM

Here's a 3D model of the room to scale.

Here's a photo of the room.
Here's one from behind the speakers, looking the other way.

Room Dimensions:

Width: 330cm
Height: Main: 250cm, Kitchen: 213cm
Length: Window to kitchen units: 645cm, unit recess: 55cm

Facing the window, the left and rear walls are plasterboard, the right wall is brick and the floor and ceiling are both concrete. The five panels are 11cm thick Melatech.

REW MEASUREMENTS:

Here's a photo to give you an idea of the speaker and measurement mic configuration for the tests below.

Download Measurement Files


SOLUTIONS?

The room's usability is most important to me, so my ideal scenario would be to get the speaker stands just behind the desk. This would give me back about 50cm of floorspace and mean I'm not listening quite so far away.

Perhaps your discerning eye has spotted something in those REW graphs I could remedy with some kind of additional treatment. However, I'm aware that this can sometimes be a game of "hit and hope", trying various treatment strategies until the problem is corrected. That could get expensive.

GIK has recommended Tri-Traps in the corners behind the speakers and free-standing traps behind the speakers themselves. Will this make much of a difference? From what I've read, you need serious volume of absorption to make impact issues in the low end.

I described all this to a friend of mine who'd been in a similar position and said I should get a sub, so I've been hovering my finger over a KH 750 buy button for the past few days. This particular sub has the added advantage of DSP phase and frequency response correction (of the entire setup), so it seems like it might help fill in the low-end gaps as well as improve the performance of the existing two-way speakers.

If you've read this far, I'm already very grateful for your time, and if you have any suggestions or comments on any of the above, I'd be even more so.

[RichardT]

I don’t know melatech but it looks to be a lightweight foam. It won’t be doing anything to tame the lower frequency behaviour in your room. It might be helping with first reflection points to some extent.

The GIK recommendation seems quite sensible. You can always get more trapping later. It’s very good value for money in improving your room’s sound quality.

I don’t think you’ll find mineral wool trapping to be hit and miss - in my experience, getting more gets you a better sound. Obviously there is a limit to how far you can take this, but the GIK recommendation is nowhere near it!

If you implemented the GIK suggestions and replaced your melatech with similarly-scaled mineral wool absorbers then you would probably be heading towards a quite well-controlled room.

Personally I wouldn’t buy a sub while you have such serious room issues. Get the room in better shape first.

When you have trapping in place, you will be able to experiment with different speaker / desk positions. At the moment you will be getting a lot of reflections off the desk if I read the angles right

[noisyneil]

Thanks for the reply. You're right, Melatech doesn't do much
for the sub-200Hz area. I suppose I was wondering whether GIK's solution of two corner traps and two boundary traps will actually make a meaningful difference.

The existing foam panels on the walls and ceiling could be refilled with mineral wool. Perhaps that should be my first order of business? If so, can you recommend a product and density? Rockwool, presumably?

Thanks again!

[Hugh Robjohns]

GIK has recommended Tri-Traps in the corners behind the speakers and free-standing traps behind the speakers themselves. Will this make much of a difference?

Acoustic problems respond best to acoustic solutions, so Gik are right... installing decent bass trapping will make a substantial improvement. But you are also right that you'll need a fair amount of trapping, ideally in the corners. Specially tuned traps may take up less space than broadband bass traps, but need to be designed for the specific room.

I described all this to a friend of mine who'd been in a similar position and said I should get a sub, so I've been hovering my finger over a KH 750 buy button for the past few days.

It's a common suggestion, but when the room is inherently lumpy at the bottom end, putting in more LF energy usually makes things worse rather than better. The subwoofer dsp will only replicate what you're already doing with your Arc system.

...it seems like it might help fill in the low-end gaps...

Another common misunderstanding. The 'gaps' (and peaks) are caused by the LF sound waves from the speakers reflecting within the room and combining with the direct sound. Where the direct and reflected sounds are phase shifted around 180 degrees you get a big dip. And the amount of phase shift depends on the room dimensions and signal frequency.

Putting in even more LF energy still creates the same dips and peaks in the room, while people outside the room wonder whats making the building shake.

The solution is bass trapping which stops (or reduces) the reflections inside the room. No (or reduced) reflections mean no (or reduced) peaks and dips.

In your situation I'd find a project studio acoustician to design an appropriate room treatment design for your specific room -- the different wall constructions and windows all affect the required solutions. For example, DACS offer this service although there are many others. A good designer costs, but its far more cost-effective than buying exotic subwoofer and buying random generic acoustic panels.

[RichardT]

Thanks for the reply. You're right, Melatech doesn't do much
for the sub-200Hz area. I suppose I was wondering whether GIK's solution of two corner traps and two boundary traps will actually make a meaningful difference.

The existing foam panels on the walls and ceiling could be refilled with mineral wool. Perhaps that should be my first order of business? If so, can you recommend a product and density? Rockwool, presumably?

Thanks again!

Yes, they will make a difference, but more would be better.

Most people here have used Rockwool RW3 which is 60Kg/m3.

[Hugh Robjohns]

This article describes the acoustic treatment I needed to get a reasonably flat bass response in my own project studio. You'll see how much space I had to devote to bass trapping...

[Nazard]

Last week, I contacted Acoustic GRG - RPG products, and Matthew was very helpful, even though my requirements are quite modest. I got the contact link from Hugh's articles on his own studio: my space in our new house is almost identical in size.

http://www.rpgeurope.com/products/produ ... ducts.html

[noisyneil]

Thankyou all for your replies.

Another common misunderstanding. The 'gaps' (and peaks) are caused by the LF sound waves from the speakers reflecting within the room and combining with the direct sound.

Thanks for the explanation. I do understand that, as it happens, but I didn't adequately communicate what I meant by "fill in the gaps". ARC is able to improve things, but the KH 120 A speakers don't have much oomph in the low end to begin with, so corrective EQ is likely to tax them at the expense of overall headroom. I figured a sub might be able to take on that responsibility more effectively. As this is a writing room and not a mixing room, there's some leniency when it comes to faithfulness of representation, but it would be nice to have a solid low end.

In your situation I'd find a project studio acoustician to design an appropriate room treatment design for your specific room

I contacted Level Acoustic Design, who recently completed work on RAK Studio 4 (RAK is my wife's family business), and they said it would be £1-2k for them to visit the room and make their recommendations, before we even get onto build costs. Does this seem to be par for the course?

Most people here have used Rockwool RW3 which is 60Kg/m3.

This article describes the acoustic treatment I needed to get a reasonably flat bass response in my own project studio. You'll see how much space I had to devote to bass trapping...

I suppose if I refilled my existing panels with Rockwool and added some corner/boundary traps, I'd end up with a fair amount of absorption, at least at one end of the room. Not much I can do at the kitchen end.

Last week, I contacted Acoustic GRG - RPG products, and Matthew was very helpful

Would it be appropriate for you to give me a ballpark all-in cost for a room of that size, based on your experience? You could PM me I suppose.

[Hugh Robjohns]

ARC is able to improve things, but the KH 120 A speakers don't have much oomph in the low end to begin with, so corrective EQ is likely to tax them at the expense of overall headroom. I figured a sub might be able to take on that responsibility more effectively.

A sub would certainly have more headroom but, far more importantly, you can potentially site it more optimally in respect of the room modes...

But fundamentally you still have the same problem: LF reflections interfere with direct sound resulting in partial cancellations and big peaks and dips in the perceived frequency response at the low end.

Throwing more power at it doesn't stop the cancellations. The ONLY real solution is to prevent (or at least radically reduce) LF reflections.

While you may gain some improvement by installing a sub — mostly through the ability to place it optimally which might reduce some cancellations — the extra LF going into the room will also generate massively more LF leakage outside the room.... and that's often a bigger problem.

I contacted Level Acoustic Design, who recently completed work on RAK Studio 4 (RAK is my wife's family business), and they said it would be £1-2k for them to visit the room and make their recommendations, before we even get onto build costs. Does this seem to be par for the course?

That feels on the high side to me....but much depends on what they are quoting for. What quality of outcome are they guaranteeing? I'd look around and get more quotes. If you're prepared to do the install yourself I'd expect the consultation and recommendation to be much less than £1k.

Most acoustic product manufactures have a bureau design service too... but few actually make workable bass traps, sadly!

[jaminem]

Hhhmmmm, ok to be honest I think you're buggered....
The places you'd want to concentrate you bass trapping are in the corners and in the Tri corners, and Id want a load on the back wall, but you've got floor to ceiling kitchen there so I suspect the low freq's are hitting the kitchen and bouncing back and as Hugh says mixing with the output from the monitors.

At the other end you've got patio doors, which are:
a: very reflective
b: letting in light so you wont want to cover them in bass traps to stop the sound bouncing back at you.

Id definitely follow GIK's advice and put Tri taps in the corners but that's only gonna do so much. It also looks like the Kitchen ceiling is lower than the where you desk is, could you treat that bit ? that may help a little too, and maybe a big thick ceiling cloud potentially angled may also help.
You may get some improvement by moving the desk into the room, but thats gonna eat space which you say you don't want and to be fair with that sofa n there probably isnt practical

Probably not what you want to hear but for you I reckon headphones are the best choice. I fear you could spend a load of cash on treatment, it not do that much and you're still disappointed...

I suppose the other choice is turn the desk 90 degrees so you can get some traps behind the desk and behind you, but that's gonna mash your stereo image unless its centrally placed, which will also eat space.

[Wonks]

Bass traps don’t have to go in corners, but they are far more effective there. You’d probably need almost twice the amount to get the same effect if they went against a wall.

[James Perrett]

One thought - could you hang a heavy curtain in front of the kitchen area which you can pull across when you need to do some critical listening? This would certainly help reduce higher frequency reflections.

The other place you could put bass traps is at the wall/ceiling corners along the side of the room. I would have thought that there is also scope for trapping in the corners next to the patio doors.

[jaminem]

Bass traps don’t have to go in corners, but they are far more effective there. You’d probably need almost twice the amount to get the same effect if they went against a wall.

He's already got them there...

[noisyneil]

Firstly thankyou so much for the kind replies!

I think you're buggered....

I appreciate the honesty! You seem to have understood why this is causing me nothing but anxiety at the moment!

It also looks like the Kitchen ceiling is lower than the where you desk is, could you treat that bit?

Would this be smart?

I reckon headphones are the best choice.

Unfortunately, not really an option for cowrites.

could you hang a heavy curtain in front of the kitchen

I did think of doing that, but the HF reflections aren't bothersome in the least. It's still an option, but the bass issue is pretty fundamental (no pun intended) when trying to create a certain energy in a writing session.

scope for trapping in the corners next to the patio doors

Absolutely. This is where I would pop a couple of Tri-Traps. This room has to be ergonomically functional, first and foremost, so I'm slightly limited as to how much more treatment I can add and where it can go, but corner traps are fairly inobtrusive. Replacing the melamine in the existing panels with Rockwool might also be an improvement, as might freestanding boundary traps behind the speakers, although I'd prefer not to block the light.

He's already got them there...

Not yet, actually! All I have so far is those five Melatech panels.

I'm getting a headache...

[Hugh Robjohns]

The oddest of these is that, when they're on the desk shelf (sitting on IsoAcoustics stands), the bass drops off in a straight line from 100Hz. Pushing the desk right up to the window improves things slightly, and putting the speakers on stands is better still.

Just had a chance to take a proper look at your graphs.

The lack of LF with the speaker on the shelf is probably because the shelf moves in sympathy with the LF from the speaker. The bass restoration near the wall is the usual boundary effect, and the much better response on stands is because the speaker is being supported much more rigidly in space. These are all normal expectations.

I'm using IK Multimedia ARC to try to mitigate some of the dips and peaks, and the result is workable for the time-being...

I'd say those corrected responses are entirely acceptable. You're within +/-3dB all the way down to 20Hz. What more do you want?

... but to get any kind of solid centre image and bass response, I've had to pull my listening position quite far from the speakers, which leaves me feeling a bit disconnected.

The solidity of the centre image is generally determined by local reflections. In your case, it's probably diffraction from the screen edges and the desk itself — but you're obviously aware of that because of the cushion placement. I'd normally recommend bringing the speakers in closer but given your previous comments, that's not practical. So raising the speakers might help, if the stands allow, as might pushing the big screen further back behind the plane of the speakers. And more effective acoustic damping around the rear and tops of the desk will also help.

...But it's always going to be a compromise, and that's why decent headphones are such a help!

[Hugh Robjohns]

Would this be smart?

It certainly wouldn't do any harm, and it could make a useful improvement without affecting normal daily living in any way.

...the bass issue is pretty fundamental (no pun intended) when trying to create a certain energy in a writing session.

I'm getting the impression that what you really want is not a flat bass response at all (since your ARC plot shows you're already getting that), but that you're really after a more visceral, trouser-flapping bass to give the impression of club-like 'energy'. Sadly, that's not gonna happen with KH120s. Not what they're designed to do.

The KH750 sub would give more LF energy that you can feel, obviously, but it will also lead to disturbed neighbours and, in all probability, a more lumpy bass response.

I'm getting a headache...

In a multi-functional space like yours, there must always be a significant level of compromise. You simply can't install the amount of acoustic treatment needed to achieve pro-studio standards of performance. I suspect you can make it a little better than it currently is with well designed and placed bass trapping, but you'll also need to accept the inherent limitations and find ways to work around them.

[James Perrett]

... but to get any kind of solid centre image and bass response, I've had to pull my listening position quite far from the speakers, which leaves me feeling a bit disconnected.

The solidity of the centre image is generally determined by local reflections. In your case, it's probably diffraction from the screen edges and the desk itself — but you're obviously aware of that because of the cushion placement. I'd normally recommend bringing the speakers in closer but given your previous comments, that's not practical. So raising the speakers might help, if the stands allow, as might pushing the big screen further back behind the plane of the speakers. And more effective acoustic damping around the rear and tops of the desk will also help.

I use monitors in my home setup that are the same size as the OP's and, similarly, I've had problems with the bass disappearing at the listening position but being stronger further back. Quite by accident (I tried putting them on top of some bigger speakers one day) I found that raising them about 400mm above the desk really helped. I would guess that I am no longer hearing the desk reflections.

The bottom of the speakers are just below ear height while the fronts of the speakers are just in front of the screen. This results in a very convincing stereo image which would probably only be bettered if I used a pair of point source speakers.

[noisyneil]

I'd say those corrected responses are entirely acceptable. You're within +/-3dB all the way down to 20Hz. What more do you want?

Fair point, but the issue is that in order to get the bass response to a level that's correctable (i.e. without the ports turning into leaf blowers), the speakers have to be quite far from the listening position. They're currently 1.6m from my head, which means they also have to be quite far apart, and the result is quite far-away feeling. It also means, as you rightly point out, that the screen is in front of the driver plane, so that's not ideal.

you're really after a more visceral, trouser-flapping bass

No, not at all. If you could hear it in here, you'd know what I mean. ARC says it's correcting, sure, but I suspect there are a few variables it doesn't account for and the result doesn't have much natural weight or punch. As soon as you stand up and move a couple of feet back, it's all there, of course, but then you're reheheeally far away.

not gonna happen with KH120s. Not what they're designed to do.

Hence my pondering a sub, but it seems that might create its own issues. I might try and borrow one and see what it does.

disturbed neighbours and, in all probability, a more lumpy bass response.

I'm lucky in that the neighbour thing isn't really a problem, but the lumps might be. The room doesn't adjoin any other properties apart from one above, and between me and them is about a foot of concrete. I don't tend to listen loud at all either.

there must always be a significant level of compromise... accept the inherent limitations and find ways to work around them.

100%. I'm trying to get to the best case scenario, but I'm under no illusions.

The bottom of the speakers are just below ear height while the fronts of the speakers are just in front of the screen.

Are you angling them down a bit so that the tweeters are pointing at your head? The bottom of my speakers are currently about 13cm above the desk shelf.

[RichardT]

You can have a good room frequency response and yet the if the level of resonance at bass frequencies is too high you will hear mush. Without trapping in your space, you are not hearing the bass as it should be, even in the places where it has punch!

This is why room correction software is quite limited in what it can do - it doesn't actually deal with the biggest problem in domestic acoustics.

Trapping is explicitly designed to help with this. Broadband trapping, like the GIK acoustics traps, is the best thing to start with, possibly supplemented with tuned traps once the basics are in place. Broadband traps absorb frequencies down to 100Hz or so and if they are very thick lower than that. Tuned traps can operate at lower frequencies, but they only work for a range of about an octave around their centre frequency.

I definitely think you're not buggered in that space as long as you're willing and able to install the necessary treatment. If you need to maintain the light from the front windows, you could get some freestanding traps that you can move into position just when you're working at the desk.

My mixing space is essentially a long, narrow underground concrete tunnel which sounded dire, but now sounds pretty good. I've used a lot of trapping behind, beside and above the speakers, even between them, and supplemented that with some broadband trapping towards the rear and some tuned traps at 70Hz. So it can certainly be done.

Just to add - it can be ok for the end of the room away from the speakers to be more 'live' than the end with the speakers.

[Martin Walker]

I use monitors in my home setup that are the same size as the OP's and, similarly, I've had problems with the bass disappearing at the listening position but being stronger further back. Quite by accident (I tried putting them on top of some bigger speakers one day) I found that raising them about 400mm above the desk really helped. I would guess that I am no longer hearing the desk reflections.

Raising the loudspeakers above the desk can certainly improve bass end, but not necessarily connected with the removal of desk reflections (although they may be improved too).

Given the typical dimensions of the home studio, it's fairly common for the loudspeakers to end up positioned halfway between floor and ceiling, where they would be sitting at the null point of the lowest vertical room mode.

Without lots more bass trapping to even out this mode, it might simply be that placing your loudspeakers into a different part of the vertical room mode enables them to flatten out that particular bass dip.

[noisyneil]

Update:

Two pairs of GIK Tri-Traps and one Monster Bass Trap just arrived.

Traps in position.


Here are some new REW measurements.


TL;DR:

1.5m no traps vs traps


1.15m no traps vs traps


As you can see, the new traps make much more of a difference when the speakers are further away, but perhaps this means there's more of a problem for them to fix and I should have them closer to the listening position. Sorry if this is a silly way of thinking about it; I'm new to all this.

Would you say this is a marked improvement or is it a drop in the ocean when it comes to absorbing low end?

Thankyou once again for all your helpful comments.

[RichardT]

Personally speaking, I would judge the effectiveness of the trapping by ear, rather than by measurement - or at least I would treat what it sounds like as more important than how it measures.

How you hear the room is dependent on a complex mix of frequency responses, reflections, resonances, cancellations and non-linear hearing processes and in particular the frequency response graph isn’t a good indication of the quality of the sound you’re going to get.

Because of all that complexity, it’s very important to experiment with positioning of the traps.

Obviously the corner traps have to go in the corners - though you can tune the distance from the walls.

I would be tempted to bring the speakers in and put the monster trap at speaker level, between the speakers and the windows. That way it will help with first reflections from the windows and absorb a high proportion of back-facing sound energy. Of course, that may not be domestically acceptable!

[Wonks]

Just linking to the pictures directly for you.

1.5m:


1.15m

[noisyneil]

help with first reflections from the windows and absorb a high proportion of back-facing sound energy

Tricky to do the way you're describing, but what I could do is get a second Monster Trap and have one behind each speaker. They happen to fit neatly into the window frame. As I only have the one at the moment, here's the left speaker with the monster in both positions: