Room Acoustics

[Opti-cal]

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

[sailor]

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.

[Opti-cal]

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

[Pharos]

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.

[guy]

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