Hi,
We know that when there is a room resonance near the frequency of port tuning frequency of a subwoofer then both the resonances couple resulting in boomy bass.
So, does it mean that if one were to test the same situation with a servo sub of some kind, lets say a current driven servo sub (ACE bass etc) then due to the greater control of the driver at port resonance, the boominess can be reduced atleast at one frequency?
If yes, then will it make an audible difference?
Thanks and Regards,
WonderfulAudio
We know that when there is a room resonance near the frequency of port tuning frequency of a subwoofer then both the resonances couple resulting in boomy bass.
So, does it mean that if one were to test the same situation with a servo sub of some kind, lets say a current driven servo sub (ACE bass etc) then due to the greater control of the driver at port resonance, the boominess can be reduced atleast at one frequency?
If yes, then will it make an audible difference?
Thanks and Regards,
WonderfulAudio
I would say no.
The external room has soo low acoustical impedance compared to the box.Open baffel is tha only way I know of that minimizes reflections in the room by only excite one mode.
No boomines or artefacts from horn, ports etc..
The external room has soo low acoustical impedance compared to the box.Open baffel is tha only way I know of that minimizes reflections in the room by only excite one mode.
No boomines or artefacts from horn, ports etc..
Brilliant question, at least to me. I think "maybe". Any room influence that that influences the MFB servo speaker would have consequences for the behaviour of the cone.
But not all eigentones have power in all parts of the room and so may have no power where the servo speaker is located. But on the other hand, eigentones triggered by the servo speaker would, I suppose, be the kind that would influence the servo speaker.
While I don't understand much of what esl63 posted, the matter of impedance (how the room "plays" the cone) would be a consideration. But here we are talking about amplified systems. Active bass absorption is a "fraternal twin" to MFB, sharing some of the same DNA.
B.
But not all eigentones have power in all parts of the room and so may have no power where the servo speaker is located. But on the other hand, eigentones triggered by the servo speaker would, I suppose, be the kind that would influence the servo speaker.
While I don't understand much of what esl63 posted, the matter of impedance (how the room "plays" the cone) would be a consideration. But here we are talking about amplified systems. Active bass absorption is a "fraternal twin" to MFB, sharing some of the same DNA.
B.
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I'm not quite sure what you are asking so I will answer it in two ways:
Q: Does exchanging my "sub X" for a servo sub reduce room resonances overall?
A: No. The only improvement (assuming identical frequency response) will be a reduction in distortion.
Q: If I exchange my "sub X" for a servo sub AND place the servo sub in the room such that it is located where a room resonance antinode is located, will this reduce THAT room mode?
A: No. There are at least two reasons why. #1 is that your typical commercial servo sub does not use a microphone to sense driver output. Instead there is a sensing coil, or it senses the current flow to/from the driver. Neither of these are probing what is going on away from the nearfield. Reason #2 is based on the fact that a driver is a VERY poor microphone itself, being less than 1% efficient at converting electrical energy into sound. By reciprocity it is therefore less than 1% efficient at picking up room sounds and converting them into current (e.g. acting as a microphone). Thus the servo circuitry is largely oblivious to any sound pressure acting on the cone. Also, the driver's output dominates by many times the ambient sound pressure in the room (at any point, even in a pressure antinode). This is why a nearfield driver measurement (e.g. done by a loudspeaker builder) is almost exclusively independent of the room. You need to get "away" from the cone to pickup the room with a microhpone, a distance of typically 3x the driver diameter. Since the room mode will be excited by the sub, the sub's own output is masking the room from any sensor used for "servo" action.
Q: Does exchanging my "sub X" for a servo sub reduce room resonances overall?
A: No. The only improvement (assuming identical frequency response) will be a reduction in distortion.
Q: If I exchange my "sub X" for a servo sub AND place the servo sub in the room such that it is located where a room resonance antinode is located, will this reduce THAT room mode?
A: No. There are at least two reasons why. #1 is that your typical commercial servo sub does not use a microphone to sense driver output. Instead there is a sensing coil, or it senses the current flow to/from the driver. Neither of these are probing what is going on away from the nearfield. Reason #2 is based on the fact that a driver is a VERY poor microphone itself, being less than 1% efficient at converting electrical energy into sound. By reciprocity it is therefore less than 1% efficient at picking up room sounds and converting them into current (e.g. acting as a microphone). Thus the servo circuitry is largely oblivious to any sound pressure acting on the cone. Also, the driver's output dominates by many times the ambient sound pressure in the room (at any point, even in a pressure antinode). This is why a nearfield driver measurement (e.g. done by a loudspeaker builder) is almost exclusively independent of the room. You need to get "away" from the cone to pickup the room with a microhpone, a distance of typically 3x the driver diameter. Since the room mode will be excited by the sub, the sub's own output is masking the room from any sensor used for "servo" action.
i think that there is a reason why servo subwoofer is not commonly available from big brands, either not useful (not to say useless) or you can achieve a better result from non servo driver but higher quality
multiple subwoofer and dual-opposed already proven, so let's forget about servo 😀
multiple subwoofer and dual-opposed already proven, so let's forget about servo 😀
Servo amp might typically have a 24 dB loop gain. Seems to work with small distortion and transient errors so why not with echoes?
Again, active bass suppression system is like MFB but, I guess, usually uses a mic. Of course, MFB could sort-of-theoretically use a mic. So in principle, fraternal twins.
Perhaps we could help this arm-chair theorizing by figuring out how to use REW to test. With servo activated, bumps and dips related to eigentones could be moved more than bumps and dips related to speaker output per se. Just my first wild thought for testing. Anybody better test?
B.