Reducing bass humps with furnishings

Posted by: Mr_Sukebe on 08 October 2002

As a result of buying a subwoofer, I've discovered that my existing system (when the sub is turned off) has an interesting set of bass humps.

The sub came with a frequency test CD and it shows that there is a hump around the 70hz mark and another bigger one around 40hz.
That would certainly explain some of my reactions to certain tracks with low bass played on my system.

So, first thing is, what do you think the cause is:
- Speakers themselves. They are non-ported Linn Kabers, which I got the impression were pretty flat in their reponses
- The electronics. I'm assuming that they are likely to be fairly flat, but maybe not. What about if a deliberate "loudness" effect was built into the CD player I have? (Arcam 7SE and Nait 5)
- Positioning in the room. I have a rectangular box room, no fireplace, concrete floors, cheapo non supporting cardboard walls. The system is along one wall, facing the opposite side, so it looks fairly good. One speaker is approx 60cm away from a sidewall, the other no where near a sidewall. I've tried moving the speakers away from the walls, (upto 100cm away) and it doesn't appear to make much difference).
So I'm assuming it's less likely to be the positioning, and more likely to be the system itself.

The key question is how best to reduce this bloom. Does anyone have any suggestions of furnishings that can "tune out" bass humps?

Failing that, do I throw away the CD player and replace it?
Posted on: 08 October 2002 by gusi
You can buy bass traps from accoustic supply companies. They look a bit like wall skirting and fit in the join between the wall and ceiling or the wall and floor.

I haven't used them myself but they are supposed to be effective. I don't know if they will trap all frequencies or whether you can tune them.

Alternatively you could fire your system down another axis of the room and see if you get different nodes.

Gus
Posted on: 09 October 2002 by Martin Clark
quote:
The sub came with a frequency test CD and it shows that there is a hump around the 70hz mark and another bigger one around 40hz.

It's one of two things and nothing to do with your source or amplification.

The first to try is the crossover control on the subwoofer. The 70Hz peak could be due to overlap between the top of the subwoofer's passband and the bottom end of the speakers.

The second thing is to try again with room position for the speakers and the subwoofer. 40 and 70Hz are very typically fundamental modes in most 'normal' size living rooms - you are getting them to play along with the music, an effect which absolutely swamps any difference between source components.

Be aware you will never eliminate standing waves, but you can minimise the negative effects. Try a trawl with the search engine on this site for ideas - it has beeen done to death. Alternatively try a quick'n'dirty spreadsheet I have posted at acoustica under 'speaker positioning' - it may help you visualise the problem.

Try these things before you start buying bass traps; it will work, and make a bigger improvement than just trying to mop up a mess with random absorption.

M
Posted on: 09 October 2002 by Mr_Sukebe
I tried the acoutica solution, i.e. by moving the Linns to a "better placement point". Didn't seem to make much difference frankly.

What I did think about along the way was the tightness of the Ku-stone and spikes, and checked those. There was an easy 1/4 of a thread for each of the ku-stone bolts (without thread-stripping levels of torque) and the spikes had room for improvement too. Either way, dealt with those and it made a big difference. Certainly makes me wonder about the impact of using mana stands underneath the speakers.

Any thoughts?
Posted on: 09 October 2002 by J.N.
I've had problems, dealing with a bass hump around 50 Hz in my listening room.

Better equipment/supports will help, but if the room is generating the problem, it won't disappear.

I've used RPG acoustic foam panels to good effect further up the frequency range, but even the corner 'bass panels' are ony effective down to 125 Hz.

'Busy' rooms seem to sound best in my experience (lots of absorptive and diffractive items), and older properties, particularly with high ceilings.

The construction of the relatively modern house seems pretty unsubstantial in Hi-Fi terms.

I've arrived at a sound I'm reasonably happy with by placing my SBL's either side of an arch to the dining room, off the listening room.

There's no substitute for humping the speakers around the room (inch by inch, if necessary). There are also computer programs available to work out the best position.

Good luck.
Posted on: 10 October 2002 by Phil Sparks
before you start buying lumps of unsightly foam you can try the 'clutter' approach. As mentioned above 'busy' rooms seem to work better. The best upgrade I made for my HiFi was to buy a big Turkish rug (plus underlay) for the floor. I'm always amazed how much difference small items make - for instance, we did a bit of doecorating recently and the room had noticeably more echo when we took down a couple of smallish pictures from the wall.

Phil