That's interesting, but like many of these LF passive absorbers they are only effective over a narrow band and hard to tune. Some kind of active feedback seems more flexible. Another thing is that they all appear to use a sealed box, how well would that work with an open baffle system?
@Whatever gives sufficient heat for a given pressure I suppose. Don't forget that the cone area is small compared to the walls ..
..corners may play a part in each room mode but not necessarily a big one.
I would expect it to be the reverse of how well the open baffle works as a speaker in this respect?
Would not an open baffel have the same preasure on both sides of the baffle below say 90 Hz (4 meter wavelength). So the speakermembrane will not move?
The passive load is to broaden the working freq area to about an octave. Seems an active load works over 2 octaves.
For modest SPLs guess one could experiment with old discarded speaker project and 1 watt resistors.
(Agree that an speaker and resistor is hardly an active system other that volts and currents are involved🙂. I referrred to the first paper as active system)
The passive load is to broaden the working freq area to about an octave. Seems an active load works over 2 octaves.
For modest SPLs guess one could experiment with old discarded speaker project and 1 watt resistors.
(Agree that an speaker and resistor is hardly an active system other that volts and currents are involved🙂. I referrred to the first paper as active system)
This one?
I was wondering how a sealed absorber would work with a dipole since it doesn't pressurise the room in the same way as a monopole
Sorry, I misunderstood, thinking of an dipole absorber.....
The paper is adressing noise in general. No idea if an diple noise source gives different results. I would be a little suprised, though
The paper is adressing noise in general. No idea if an diple noise source gives different results. I would be a little suprised, though
Guys, I think I struck gold: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.905.8842&rep=rep1&type=pdf
"This study has shown that series RLC network used as shunt for electroacoustic absorbers are good candidates for varying the acoustic properties of the resonator without the need of active devices. This is an interesting result that could pave the way to very cheap and stable semi-active sound absorbers devices, with broadband absorption capabilities."
I am rusty on math and I am wondering what R,L,C values would be good candidates to start with. R could be 5 ohm, what about L and C?
Found something, at least about C value, 500uF --> Control of Resonant Acoustic Sound Fields by Electrical Shunting of a Loudspeaker (PDF Download Available)
"To the knowledge of the authors, a passive capacitor and resistor offers the best possible performance commensurate with simplicity and cost"
"This study has shown that series RLC network used as shunt for electroacoustic absorbers are good candidates for varying the acoustic properties of the resonator without the need of active devices. This is an interesting result that could pave the way to very cheap and stable semi-active sound absorbers devices, with broadband absorption capabilities."
I am rusty on math and I am wondering what R,L,C values would be good candidates to start with. R could be 5 ohm, what about L and C?
Found something, at least about C value, 500uF --> Control of Resonant Acoustic Sound Fields by Electrical Shunting of a Loudspeaker (PDF Download Available)
"To the knowledge of the authors, a passive capacitor and resistor offers the best possible performance commensurate with simplicity and cost"
Last edited:
Sorry for the R/L/C question, I found those values in the 1st place:
Series RLC
I 1.5 Ω 15 mH 177 μF
J 1.5 Ω 8.3 mH 406 μF
K 1.0 Ω 5.5 mH 550 μF
Tomorrow I will start other tests (already found by ear that short-circuit was best compared with 50, 33 or 4.7 ohms).
I'm looking forward to see if an R-C or R-L-C circuit is more effective than simple short-circuit (I am using a pair of AE Evo1 bookshelfs, with closed ports, put in a corner and have played same track; it was pretty effective to compare open circuit, short circuit and some R values).
Series RLC
I 1.5 Ω 15 mH 177 μF
J 1.5 Ω 8.3 mH 406 μF
K 1.0 Ω 5.5 mH 550 μF
Tomorrow I will start other tests (already found by ear that short-circuit was best compared with 50, 33 or 4.7 ohms).
I'm looking forward to see if an R-C or R-L-C circuit is more effective than simple short-circuit (I am using a pair of AE Evo1 bookshelfs, with closed ports, put in a corner and have played same track; it was pretty effective to compare open circuit, short circuit and some R values).
Last edited:
Just finished reading the first paper, it looks interesting, carry on the good work with your experiment, I look forward to hearing how you get on. I shall tackle the second paper a bit later.......
An open baffle still produces sound, so as this absorber, sound already in the room could move the cone. Have I missed the point? Not sure how efficient it would be.
I may be way off, but it looks like the impedance/phase should be as flat as possible in the damping region.
So maybe REW impedance analyser can be used to find real world RLC values.
I may be way off!
Good luck with experimenting!
So maybe REW impedance analyser can be used to find real world RLC values.
I may be way off!
Good luck with experimenting!
Possibly not. That got me wondering though, does a conventional absorber have to be effectively sealed to work?
It has "nearly the" same pressure on both sides and its displacement will diminish as the frequency goes down reaching zero at DC.
A shorted dipole would be a terrible LF absorber. A closed box would be better at LFs and a dipole better at HFs. Neither will actually be very good since the area is so small. It takes the area of a wall to be really effective at LFs.
Couldn't this be effectively multiplied by making it active?
Can I ask do you damp your walls because it seems the most fundamentally appropriate and straight to the source fix, or just because it is the most effective, or was it meant only to help make the job of multiple subs less critical?
Of course active is likely to be much better, but that all depends on what kind of scheme one uses for the active. A single mic at the loudspeaker will be less effective than more mics further out into the room, but this later technique would not be very feasible.
I damp the walls because it is the most effective. If you look at realistic values of absorption for very low frequency signal you will see that they become astonishingly small. It takes a whole wall to be effective.
Smoothing the natural response of a room with absorption at LFs does make the use of multiple subs less necessary.
I damp the walls because it is the most effective. If you look at realistic values of absorption for very low frequency signal you will see that they become astonishingly small. It takes a whole wall to be effective.
Smoothing the natural response of a room with absorption at LFs does make the use of multiple subs less necessary.
I did a "with and without" test with a 2x8inch decomissioned subwoofer as electroacoustic absorber with drivers in series and short circuited. The room has 75 cubic meters and some acoustic treatment (2 big Hofa basstraps). The absorber under test was placed into an up corner and the change in the bass was easily observed by ear. The measurement also confirmed this (green is with absorber, red is without).
I found at Moser some 8mH/2ohm inductances and 330uF non-polarised capacitors to test an RLC shunt, but still looking to source them localy because shipping is pretty expensive.
I found at Moser some 8mH/2ohm inductances and 330uF non-polarised capacitors to test an RLC shunt, but still looking to source them localy because shipping is pretty expensive.
Attachments
Last edited:
That's a very impressive result, hard to see how it could be improved upon. Have you any idea of the resonant frequency of the speakers you used? Were they both together in one top corner of the room? BTW you can make a bipolar capacitor out of two polarised ones back to back of twice the value.
What are your subjective impressions of the sound quality of the bass?
What are your subjective impressions of the sound quality of the bass?
This is not what I would expect to see.
It looks like the data was taken with HolmImpulse. Could the raw data be posted? Was the window identical in both cases?
It looks like the data was taken with HolmImpulse. Could the raw data be posted? Was the window identical in both cases?
- Status
- Not open for further replies.