Loudspeaker System, Method and Apparatus for Absorbing Loudspeaker Acoustic Resonances
A loudspeaker system ( 700 or 800 ) and method for tuning ported loudspeakers and reducing unwanted acoustic resonances provides reduced port noise, eliminates undesired port resonances and improves the accuracy and fidelity of reproduced sound in a loudspeaker system of relatively high efficiency with an enclosure including an Eigen Tone Filter structure (“ETF”) comprising a pipe or set of pipes 720, 820 placed inside a loudspeaker vent to absorb the “open pipe” acoustic resonance of the vent. The open-pipe resonance is unwanted and interferes with the midrange performance of the loudspeaker, when in use, if not corrected.
1 . A method for tuning a loudspeaker system, comprising:
providing a loudspeaker system comprising a loudspeaker enclosure having a port opening and an interior volume, a driver supported by the loudspeaker enclosure, a vent lumen associated with the port opening to provide communication between the interior volume and an environment, and an Eigen Tone Filter (“ETF”) structure comprising a first pipe segment, a second pipe segment substantially coaxially aligned with the first pipe segment, and a circumferential slot or a sidewall gap between the first and second pipe segments and positioned within the vent lumen.
2 . The method of claim 1 , wherein the first and second pipe segments have first and second pipe interior volumes, respectively, and wherein the circumferential slot or sidewall gap provides communication between the vent lumen and the first and second pipe interior volumes.
3 . The method of claim 2 , wherein the first pipe segment has a first segment length, wherein the second pipe segment has a second segment length, wherein the first segment length is approximately one quarter of a wavelength at a first selected ETF port signal notch frequency which is within a band of frequencies comprising an open pipe resonance of the vent lumen.
4 . The method of claim 3 , wherein the second pipe segment length is approximately one quarter of a wavelength at a second selected ETF port signal notch frequency which is within the band of frequencies comprising the open pipe resonance of the vent lumen.
5 . The method of claim 4 , further comprising selecting the first and second segment lengths, wherein said selecting is an iterative process.
6 . The method of claim 5 , wherein said selecting comprises:
plotting stock port data of the loudspeaker system to identify a frequency range having an undesired open pipe resonance energy; and
selecting the first and second segment lengths to reduce or “notch out” the undesired open pipe resonance energy.
7 . The method of claim 6 , further comprising estimating the quarter wavelength frequency to determine an initial frequency tuning estimate.
8 . The method of claim 7 , further comprising
adding foam material in the ETF structure to slow air velocity within the ETF structure.
9 . A loudspeaker system, comprising:
a loudspeaker enclosure having a port opening and an interior volume;
a driver supported by the loudspeaker enclosure;
a vent lumen associated with the port opening to provide communication between the interior volume and an environment; and
an Eigen Tone Filter (“ETF”) structure comprising a first pipe segment, a second pipe segment substantially coaxially aligned with the first pipe segment, and a circumferential slot or a sidewall gap between the first and second pipe segments and positioned within the vent lumen.
10 . The loudspeaker system of claim 9 , wherein the first and second pipe segments have first and second pipe interior volumes, respectively, and wherein the circumferential slot or sidewall gap provides communication between the vent lumen and the first and second pipe interior volumes.
11 . The loudspeaker system of claim 10 , wherein the first pipe segment has a first segment length, wherein the second pipe segment has a second segment length, and wherein the first segment length is approximately one quarter of a wavelength at a first selected ETF port signal notch frequency which is within a band of frequencies comprising an open pipe resonance of the vent lumen.
12 . The loudspeaker system of claim 11 , wherein the second segment length is approximately one quarter of a wavelength at a second selected ETF port signal notch frequency which is within the band of frequencies comprising the open pipe resonance of the vent lumen.
13 . The loudspeaker system of claim 12 , wherein:
the loudspeaker enclosure comprises a front baffle supporting and aiming at least one loudspeaker driver and a bottom baffle supporting the ETF structure;
the vent lumen comprises a cylindrical internal vent lumen having a central vent lumen axis along which the EFT structure is supported; and
the ETF system has a proximal closed end cap and an opposite, distal downwardly projecting end cap nested within a diffuser.
14 . The loudspeaker system of claim 13 , wherein:
the ETF structure has a rounded or “bullet-nose” shaped end cap.
15 . The loudspeaker system of claim 14 , wherein the first and second pipe segments have an axial length that is substantially equal to 150 mm.
16 . The loudspeaker system of claim 14 , wherein the first and second pipe segments have an axial length that is substantially equal to 100 mm.
17 . The loudspeaker system of claim 9 , wherein the ETF structure is substantially coaxially aligned with the vent lumen and has an inside diameter in a range of 25 to 38 mm.
18 . The loudspeaker system of claim 9 , wherein a length of the sidewall gap between the first and second pipe segments is in a range of 1 to 1.25 times a diameter of the first and second pipe segments.
19 . The method of claim 1 , wherein the driver comprises a midrange driver or a midbass driver, and wherein the loudspeaker system further comprises a baffle supporting the midrange driver or midbass driver.
20 . The loudspeaker system of claim 9 , wherein the driver comprises a midrange driver or a midbass driver, and wherein the loudspeaker system further comprises a baffle supporting the midrange driver or midbass driver.