How to kill a 100Hz open baffle resonance?

[Katapum]

Hi all,

Last summer I built according Kuei Yang Wang plans (65cmx105cm) an open baffle speakers (215S non bicone and a super tweeter). Since then a notice a HORRIBLE resonance at (around) 100Hz.

How to kill a 100Hz open baffle resonance?

Is it a listen room problem or a placement problem or an open baffle problem?

Any comments or suggestions are very welcome and sorry my English.

Katapum

[Rudolf]

Katapum,
this might well be a room or placement problem. It would be helpful to have some more details about your room and the location of the OB in it:
room size, distance from OB to next walls, position of Supravox on OB.

Rudolf

[Cal Weldon]

Can you take a couple of pics for us? Include the location in the room please.

[Katapum]

Hi,

Supravox placement:
40cm from the top to drive centre;
25cm from one side to drive centre.

Listen room:
3m x 3,5m (with some furniture).

Speakers placement (with some furniture):
50cm to rear wall
20cm to side all.

Katapum

[janneman]

If it is a room problem you would also hear it with 'normal' speakers.....

The open baffle has two effects:

At the frequency where the path length around from front of cone to the back approaches half the sound wavelength you loose output (acoustical short), so you would loose bass pretty quickly. At the sizes you give, the path around is abouth 80cm, right? At 320m/sec sound speed, 80cm takes around 2.5 msec which would be 5 msec for a full wave or 200Hz. So your freq response starts to fall off from around 200Hz downward.

Another effect is that there is no damping whatsoever of the speaker resonant frequency. I suspect that is the problem here, that the driver has enough resonance at 100Hz to overcome the fall-off from 200Hz downwards.

Jan Didden.

[Katapum]

Hi,

Another effect is that there is no damping whatsoever of the speaker resonant frequency. I suspect that is the problem here, that the driver has enough resonance at 100Hz to overcome the fall-off from 200Hz downwards.

Supravox datasheets

Katapum

[Rudolf]

Katapum,

the room seems to be the main culprit IMHO. I believe 3,5m is the length of your room. That leads to room modes at about 50 Hz, 100 Hz, 150 Hz, 200 Hz. 50 Hz is too low to be excited heavily by the Supravox, but wavelength for 100 Hz is very near 3,5 m!

Second culprit could be the distance of the speaker to the rear and side wall. The direct reflection of the dipole backwave from the rear wall will lead to a peak at ~170 Hz, but another reflection off the sidewall could easily drop that to 100 Hz.

Can you arrange your listening position ~85 cm from the front wall? This will give your ears minimal excitation with 100 Hz. Sitting near to the frontwall or to the middle of the room will result in maximal excitation.

Is there any chance to make the diagonal through the room your listening axis? This seems to be the best way to get rid of that nasty 100 Hz without resorting to absorbers and traps.

Rudolf

[Katapum]

Hi,


so is not a speakers problem… now I´m better… I spent a lot of hours to build it.



Katapum

[Rudolf]

so is not a speakers problem… now I´m better… I spent a lot of hours to build it.

This is long-distance diagnosis, so no guarantee for that! But the dimensions of your room are a very strong argument and I never heard anyone complain about those baffles before.

And what about Jannemans question? Did you never hear this 100Hz resonance with conventional speakers in that room?

[Katapum]

Hi,


I moved my listened position 50cm back and everything is better… more balanced sound with less bass and without 100Hz resonance (but I´ll check again with another conventional speakers pair). Thanks to all.


To Rudolf:
I’d to learn more about room modes and dipole reflections. Have any link?


Katapum