Hi guys I am very confused, I have read that the reason speakers need an enclosure is to prevent the low frequency waves coming from the front to interact with the low frequency waves(opposite phase) coming from the back and cancelling out.
Also that the quarter wavelength of the desired low frequency we would like to hit, must be smaller than one of the faces of the baffle.
The problem is that I made an experiment today and placed speakers (tang band 4" and a tang band 3" w3-1878) directly into the middle of a RW45 Rockwool pack (1200mm x 600mm x 400 mm).
The were no enhancement in bass, the only "sound" is one which is produced when all the holes behind the speakers are closed. You know, the boxy sound.
If that theory was really good, I believe all the low frequency waves coming from behind the speaker would be absorbed by this huge amount or rockwool, and that the waves coming from the front of the speaker would not be cancelled out.
But the sound was the same, no bass enhancement.
I think I must have done or understood something wrong and I would love to have some help.
Could anyone please explain why when a speaker plays on its own(without any enclosure) it produces low level of bass (sounds like a big roll off) ?
Many many thanks!
Also that the quarter wavelength of the desired low frequency we would like to hit, must be smaller than one of the faces of the baffle.
The problem is that I made an experiment today and placed speakers (tang band 4" and a tang band 3" w3-1878) directly into the middle of a RW45 Rockwool pack (1200mm x 600mm x 400 mm).
The were no enhancement in bass, the only "sound" is one which is produced when all the holes behind the speakers are closed. You know, the boxy sound.
If that theory was really good, I believe all the low frequency waves coming from behind the speaker would be absorbed by this huge amount or rockwool, and that the waves coming from the front of the speaker would not be cancelled out.
But the sound was the same, no bass enhancement.
I think I must have done or understood something wrong and I would love to have some help.
Could anyone please explain why when a speaker plays on its own(without any enclosure) it produces low level of bass (sounds like a big roll off) ?
Many many thanks!
Bass enhancement in an enclosure comes from resonance either as a Helmholz resonator or as quarter wave / transmission line or a horn - all these methods require an output port. A sealed enclosure has no bass enhancement, it has very clean bass but is limited by the fs of the driver. This is similar to an open baffle. The bass you get will look very much like the manufacturers freq response curve. Any bass enhancement or 'gain' in bass comes from resonant amplification in an aero acoustic device.
You require something rigid to prevent the front wave and back wave from reaching one another. Damping material does little to absorb the lower frequency waves that are being cancelled when combined. Try a piece of wood and it will all become clear. 
Damping material really only has value above what we think of as 'bass'. It helps prevent standing waves inside the cabinet and attenuates the 'midrange' frequencies that you don't want exiting the port.
Best not to use the 'enhancement' term here. It's got X answering a different question.
Damping material really only has value above what we think of as 'bass'. It helps prevent standing waves inside the cabinet and attenuates the 'midrange' frequencies that you don't want exiting the port.
Best not to use the 'enhancement' term here. It's got X answering a different question.
Yes, Cal is right. In your case with a rock wool baffle you are getting worse than no bass enhancement but bass cancellation a negative gain effect. You can use even a sheet of cardboard or maybe foam core for the baffle to isolate the front and back waves. You won't get enhancement or gain but at least it won't be bass cancellation or loss.
for the baffle to isolate the front and back waves. You won't get enhancement or gain but at least it won't be bass cancellation or loss.The problem is that what I hear doesn't come close to the frequency response graph of the manufacturer, in the sense that it seems to roll off way sooner (higher low mids). But 800Hz and more it is very representative of the graph.
I actually don't want bass enhancement but want it to sound like it it on the manufacturer's frequency graph.
Dipole will give a figure 8 polar pattern within the suitable pass band. Above the pass band they'll have a "ridged" polar response and below the pass band (bass) they'll have little to no output. The pass band is determined by the baffle width, which is typically very narrow or even baffleless in order to widen the pass band as much as possible. Are you listening directly on axis when you're experimenting? A microphone will help you understand what's happening here.
Can you explain more clearly what the problem is? The multiway forum may offer better explanations. Not many here do the open baffle thing. I'd love to give it a try someday, but I don't know much more about it than what I just typed.
Can you explain more clearly what the problem is? The multiway forum may offer better explanations. Not many here do the open baffle thing. I'd love to give it a try someday, but I don't know much more about it than what I just typed.
I was indeed listening directly on axis
The problem is that people explain the lack of bass is due to low frequencies from the back interfering with frequencies coming from the front as they are out of phase.
But in my experiment where I placed the speaker in a big rockwool pack, which at this thickness and size have a huge absorption coefficient, and the result was as I explained in the original post.
Hi Bob, thank you for your insight, but Rockwool is used in studios to absorb low frequency resonances isn't it(and they are using relatively thinner panels), why wouldn't it work behind a speaker for example ?
Rather than try to conduct a tutorial here, I suggest that you look into the coefficient of absorption of various materials. Start with http://www.bobgolds.com/AbsorptionCoefficients.htm
There is nothing with regards the RW45
But the coefficient of absorption of 3" of RW3 to be 0.34 and the coefficient of absorption of 3" of RW5 to be 0.40 at 125Hz ... The RW45 should be in between, and now I didn't use 3" but actually 15" of this material(the whole packet)... which should take the coefficient of absorption to be more than 1, if I am not mistaken.
Why didn't it work ?
Correct me if i'm wrong :S
As I said I actually had a 120cm x 40cm x 60 cm packet of rockwool
Would you suggest other more absorbant materials please ? I would love to experiment
You only have an inch or so of rockwool between the front and back of the driver. The air is just moving back and forth around the driver. No pressure builds up so you get poor response.
It's already been said but - go and cut a hole in some board and listen again and everything will become clear.
It's already been said but - go and cut a hole in some board and listen again and everything will become clear.
I guess you made a hole for the driver on the front rockwool sheet and stacked the other sheets behind. That probably means you left a very small volume behind the driver and Fs went to moon. For a couple of years I have been playing with rockwool baffles (not enclosures) with mixed success and I just don't believe 2+ inches thick rockwool will be that transparent below 500 Hz. Of course one cannot expect to hit buch below 200 Hz or so...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.