Room Acoustics

I've got a nasty dead spot (below 200hz -8db or more) right around my listening position.

If I go and crouch in the corner on either side or somewhere in front of it, all is fine. In fact perfectly balanced which does make me think I might need some EQ also.
I don't really want to use my parametric EQ even though it is very good, as it limits me to using digital playback only and also toslink cables.

So I've decided to treat the problem with bass traps and panels.

I'm just wondering if that will work as if I'm getting the sound I want in the corners of the room where the modes collect, absorbing may not give me any extra bass in my listening position?

I don't really know if the dead spot is because waves are colliding there or because something else is stopping them getting there if that makes sense.

I will be treating the the main two corners behind the speakers with 100 x 30 x 30 bass traps and 50mm panels at various reflection points around the room as well as behind my listening position. Plus some strategically placed bookshelves and storage units of vinyl etc.

I'm hoping for a much improved sound but I'm just wondering if there is anything else I can do to address it?

Room is a weird shape kind of like a plus sign with the speakers in one section of the 'plus' and the listening position at the front of the opposite section.

I did have it sounding better but I moved some stuff around and now can't recreate whatever acoustic effect the 'stuff' was having.

Any advice or suggestions much appreciated.

Cheers,

Chris

I would have thought that the bass null you've got at your listening position will probably stay there regardless of where the speakers are sited, but I see you're using REL T3 subs, so could you use bass traps to reduce the bass in the corners, and then turn the wick up on the subs until you find a level of bass you're happy with? And if you're using two subs you can perhaps experiment with their positioning. Lots of options there.

Just a thought, I'm sure some more intelligent ideas will be along soon :)

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Originally Posted by Opti-cal

I've got a nasty dead spot (below 200hz -8db or more) right around my listening position.

.............

I don't really know if the dead spot is because waves are colliding there or because something else is stopping them getting there if that makes sense.

I will be treating the the main two corners behind the speakers with 100 x 30 x 30 bass traps and 50mm panels at various reflection points around the room as well as behind my listening position. Plus some strategically placed bookshelves and storage units of vinyl etc.

I'm hoping for a much improved sound but I'm just wondering if there is anything else I can do to address it?

Room is a weird shape kind of like a plus sign with the speakers in one section of the 'plus' and the listening position at the front of the opposite section.

I did have it sounding better but I moved some stuff around and now can't recreate whatever acoustic effect the 'stuff' was having.

Any advice or suggestions much appreciated.

Cheers,

Chris

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Hi Chris,

I and a friend of mine have played around in out listening rooms with speaker positions, listening position, and dampening devices to try and get it as good as possible. Based on what you said about your room I would suspect it is reflections converging at your listing position and canceling each other out.

How are you measuring the 200hz dead spot? I use REW(free for Mac or PC) and us a simple USB microphone. After calibrating with the mic at my listening head position I do a sweep measurement form 20 to 20Khz and look at the curve. If the past I then made simple adjustments to speaker positions and so on looking for improvement. I also tried temporary bass traps by placing old blanket in the corners on poles/lampstands and hanging towels off the walls at strategic points. This would be worth trying IMO before splashing out on traps only to find they make little difference. Each time you make a change re-measure and see if its better.

I hope this helps a bit, but perhaps you have already done this. By the way I would turn the subs off to start with and get it right with the mains and then re-introduce the subs and see if they are the issue or not.

Thanks for the replies so far chaps.

I've measured it using my Behringer microphone connected to my DEQ digital EQ. It can boost the frequencies around that area but is also likely boosting the cancelling wave so not a huge improvement, Plus it doesn't really help me out for the vinyl!

The bass traps I've ordered were fairly cheap compared to a lot of them and I already have some strategically placed pillows/duvets around the place. I've had this problem in other rooms and they did the trick perfectly in those instances, this one is a bit harder to shift.

Some bass traps are on the way so will hopefully go some way towards improving things. I did take the subs out of the system and was really appreciating the 'natural' sound but a lot of my music is electronic and I was really missing the bass after a while even though my speakers do easily go into the low 20Hz (my Grand Masters not the Quads which roll off at 45hz) . That gets to the listening position no problem but then with this null there is a noticeable dip in between the mid low and the sub bass frequencies.

I can't move the speakers as I've been there, done that for weeks and where they are sounds 10 x better than any other placement, it is THE spot.

I can move my listening position forward a foot or so and that does improve frequency response a lot it's just I lose a fair amount of soundstage.... Although I think I'll sacrifice that for the missing frequencies at the moment.

Hoping the acoustic treatment gets me there! I'm also making quite a few wall panels myself from 5 to 8cm thick foam. I know this won't do much for the bass but should improve higher frequencies.

Foam is pretty useless for wall panels. You need something like this. https://www.insulation4less.co.uk/pr...iABEgK8tPD_BwE

Make sure you use the 100mm thickness as anything thinner will not have much effect. It is easy to work but make sure to use gloves and a mask.

Geoff

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Originally Posted by Opti-cal

Thanks for the replies so far chaps.

I've measured it using my Behringer microphone connected to my DEQ digital EQ. It can boost the frequencies around that area but is also likely boosting the cancelling wave so not a huge improvement, Plus it doesn't really help me out for the vinyl!

The bass traps I've ordered were fairly cheap compared to a lot of them and I already have some strategically placed pillows/duvets around the place. I've had this problem in other rooms and they did the trick perfectly in those instances, this one is a bit harder to shift.

Some bass traps are on the way so will hopefully go some way towards improving things. I did take the subs out of the system and was really appreciating the 'natural' sound but a lot of my music is electronic and I was really missing the bass after a while even though my speakers do easily go into the low 20Hz (my Grand Masters not the Quads which roll off at 45hz) . That gets to the listening position no problem but then with this null there is a noticeable dip in between the mid low and the sub bass frequencies.

I can't move the speakers as I've been there, done that for weeks and where they are sounds 10 x better than any other placement, it is THE spot.

I can move my listening position forward a foot or so and that does improve frequency response a lot it's just I lose a fair amount of soundstage.... Although I think I'll sacrifice that for the missing frequencies at the moment.

Hoping the acoustic treatment gets me there! I'm also making quite a few wall panels myself from 5 to 8cm thick foam. I know this won't do much for the bass but should improve higher frequencies.

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Quote:

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Originally Posted by Opti-cal

I've got a nasty dead spot (below 200hz -8db or more) right around my listening position.

If I go and crouch in the corner on either side or somewhere in front of it, all is fine. In fact perfectly balanced which does make me think I might need some EQ also.
I don't really want to use my parametric EQ even though it is very good, as it limits me to using digital playback only and also toslink cables.

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have you not considered using an analogue to digital convertor on your analogue sources? Then you could use the parametric eq for them too.

My advice would be to ring REL. Those guys have seen it all and will give great advice about how to optimise their subs.

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Originally Posted by Sherwood

Foam is pretty useless for wall panels. You need something like this. https://www.insulation4less.co.uk/pr...iABEgK8tPD_BwE

Make sure you use the 100mm thickness as anything thinner will not have much effect. It is easy to work but make sure to use gloves and a mask.

Geoff

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Hi Geoff, thanks for the advice and the link. To be fair the wall panels are mostly to deal with reflections and tame the echo as indeed its very hard to absorb any bass with anything as thin as the foam I'm using. They are actually acoustic tiles (so meant for the job) but yes the rockwool would do a better job. Unfortunately it might just be a little too invasive for the other half. I can at least make the smaller panels look a bit like wall art. A huge beefy rectangle of that is difficult to justify . . . but it has got me thinking.

Cheers

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Originally Posted by Macca

have you not considered using an analogue to digital convertor on your analogue sources? Then you could use the parametric eq for them too.

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I did try a 'cheap' one but didn't like what it did to the sound. I'm sure there are better ones out there but my preference and instinct is to deal with the issues passively (if that's the right term?). As in with materials and passive absorbtion/diffusion rather than major EQing. However if it doesn't work I could always try the Dirac route and just bite the bullet and go for 'proper' room correction. My Behringer is good but I know the Dirac stuff is end game.

Cheers

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Originally Posted by bumpy

My advice would be to ring REL. Those guys have seen it all and will give great advice about how to optimise their subs.

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Great suggestion and in fact without even speaking to them I have made some progress, outlined below.

So after some experimentation with sub placement and crossover/volume tweaking (of the subs), things have improved.

My system is setup so I use one output feeding my power amp to the main speakers and another feeding a small Class D amp which independently gives signal to the subs. This setup keeps the sub cabling separate from the main speaker cabling which in my opinion makes a very positive difference. It means I can set the volume on the 'sub' amp and the amps themselves to really dial in the crossover effect from the subs. Turning up the volume on the subs obviously increases the db's but keeps a fairly linear frequency increase (as you would expect). Now increasing the volume on amp feeding the subs (past a certain point anyway) also increases the db's but also seems to add some bass texture and depth. I've wound back the volume on the subs and increased it on the amp and things have definitely improved.

In addition to this moving them out into the room an inch, things have tightened up as well as gotten louder.

To be fair I'm very happy with the sound as it has hit that immersive sweetspot. Bass is now much fuller and comes from different places in the room (it is an L&R stereo sub setup) without being particularly boomy. I'm hoping with the addition of the new bass traps and some more acoustic tweaking I'll be closer to where I want to be.

I either need to cover (so I can't see it) or rip the volume knob off the amp feeding the subs as its in the absolute optimum position. Same with the subs to be fair. I remember when I set them up before that I would have to add or remove a couple of notches of volume depending on source material. No longer, it sounds well integrated on everything I tried.

Don't really notice the subs now, except when you turn them off. It's amazing how they seems to release the main speakers which seems to get a huge benefit in all frequencies when the subs are setup correctly it seems.

I'll continue some more experimentation tonight and when my traps/panels are complete.

Cheers

Hi Chris,

Yup bass, its a problem all rooms have with some being worse than others. You are experiencing a partial null. The long bass waves thunder around the room combining constructively and destructively causing peaks and nulls. You're sitting in one of the nulls and no amount of EQ will help. You can throw lots of power at it but it just cancels itself with the same power. We are talking low frequency bass power here so you are sapping the amps power and driving it into clipping.

I would totally disregard the advice to convert your precious analogue signal to digital, play with an equaliser in the digital domain and then re-convert it to analogue again.

Way cheaper would be to consider adding an additional sub or two to the ones you have, achieving a distributed bass array. Much can be read on this. Try Floyd Toole an Earl Geddes. It really works and these additional subs can be smaller, less expensive units. If possible try and borrow 2 subs from mates and experiment with placement.

Bass traps I find essential but I'm talking proper size units that can actually absorb down to bass frequencies. All to often I see silly little scraps of foam.

@Sherwood posted a link to the correct stuff. Something approaching the coefficients of absorption of Owens Corning 703 will work. These things are large but can also be installed high up against the wall/ceiling corners. Mine measure 900mm across the face. They, in addition to broad- band absorbers at first reflection points made a huge difference. Combining this with a DBA would be jaw-droppingly transformative.

I include a pic of my attempt at a decent bass trap. I have one in each front corner and CSD plots show I need about 25% more but what I'm getting now is so good I may leave things as they are.

https://i.imgur.com/zdB5zKW.jpg

Ha, awesome traps in the making there Charles.

Seems I need to stop hoping a dip into acoustic treatment will sort my issues and just throw caution to the wind and do it 'properly'.

They are going to look great as I'm sure they will integrate into the room. As my room has odd dimensions it won't look too strange to have something similar. 900mm across, that's big. As you say though seems they have to be significant to do anything like what I'm after.

Thanks for the advice, I'm going to get constructing when time allows as unfortunately (or fortunately as the current situation stands) I'm still at work full time. These things require some commitment though so I will carve out some time to do it as I think my system deserves it!

Cheers,

Chris

From sailor;
"Yup bass, its a problem all rooms have with some being worse than others."

Funnily enough, and my friends agree with me, we have not been able to pinpoint ant bass problems or unevenness in my current listening room. There was a track played today of the golden oldies half hour with an octave run down on the bass, and it was the most even I have ever heard it, it's just happened that way.

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Originally Posted by sailor

https://i.imgur.com/zdB5zKW.jpg

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Hi Sailor,

Please excuse dumb questions (I have no experience of room treatment), but I am impressed with your practical skills :)

When you say that you need 25% more, is that 2 or 3 more slabs in your enclosures? How do you measure to come to this figure?
Will you then cover with speaker cloth?
Do you do the same in all corners of the room or are corners nearest to the speakers the most effective/in need of treatment?

The OP problem of bass "nulling" at certain points in room (I would think also reinforcement if room is long enough?): wouldn't that be sorted by just having one subwoofer for both left and right channels, as I seem to remember reading years ago that below a certain frequency (can't remember which now) bass becomes non directional to our hearing?
I seem to remember a hifi reviewer (Graham Holliman or similar?) saying with "infra bass" that you could just put your sub behind the sofa.

Never used so many question marks before :)