144:
resonances. Since the backwave is already in opposite polarity with the front wave, this inversion brings the two emissions in phase (although the vent emission is lagging by one wave period) and therefore they reinforce each other. This has the useful purpose of producing higher output (for any given driver excursion compared to a closed box) or, conversely, a similar output with a smaller excursion (which means less driver distortion). The penalty incurred for this reinforcement is time smearing: in essence the vent resonance augments main driver output by imposing a "resonant tail" on it. For frequencies above the natural resonance of the driver, the reflex alignment has no influence. For frequencies below the vent resonance, polarity inversion is not accomplished, and backwave cancellation occurs. Furthermore, the driver behaves as though suspended in free air, as box air springiness is absent.
195:. Acoustically, they behave largely the same around their tuning frequency as a port, as they also act as a Helmholtz resonator excited by the rear side of the bass driver's diaphragm. Passive radiators can be tuned independent of their dimensions by adding or removing mass from the diaphragm of the passive radiator. This makes them useful for smaller enclosures with the same box tuning where an equivalently tuned port would be impractical. They also sidestep the midrange pipe resonances that can be an issue on ported enclosures in full range systems. However, to be effective, they require a much greater surface area on the cabinet exterior than a port. They are also considerably more expensive than a port tube, as they are effectively a speaker driver minus its voice coil and motor magnet.
220:) that allowed designers to produce useful, predictable responses. Keele extended the design options by presenting a new set of 6th-order vented-box loudspeaker system alignments. All of these results made it possible for speaker manufacturers to design bass reflex loudspeakers to match various sizes of enclosures, and to match enclosures to given speakers with great predictability. Due to the physical electromechanical constraints, it is not possible to have a small speaker in a small enclosure producing extended bass response at high efficiencies (i.e., requiring only a low-powered amplifier). It is possible to have two of these attributes, but not all; this has been termed Hofmann's Iron Law after J. Anton Hofmann of
334:
rest of the pass-band of the loudspeaker system. This behaviour can add a "booming" one-note quality to the reproduction of the bass frequencies. Although some may consider that this is due to the port resonance imposing its characteristics to the note being played, it is simply the result of a non-maximally flat frequency response function. If such a peak in the bass response of a bass reflex enclosure coincides with one of the resonant modes of the room, a not unusual occurrence, the effects will be further exacerbated. In general, the lower in frequency a port is tuned, the less objectionable these problems are likely to be.
311:). Due to the latter, a flat steady-state bass response does not occur at the same time as the rest of the sonic output at higher frequencies in the operating region. Instead, it starts later (lags) and the lag increases, accumulating over time as a longish resonant "tail" arriving behind the main "body" of the acoustic signal. As a result of their electrodynamic characteristics, ported enclosures, which are well approximated as 4th-order high-pass filter systems, generally result in poorer transient response at low frequencies than do closed-box loudspeaker systems, which are 2nd-order high-pass filter systems.
159:), manufacturers often consider the advantages of porting (increased bass response, lower bass response, improved efficiency) to outweigh the disadvantages (port noise, resonance problems). The design is popular among consumers and manufacturers (speakers cabinets can be smaller and lighter, for more or less equivalent performance) but the increase in bass output requires close matching of driver, the enclosure, and port. Poorly matched reflex designs can have unfortunate characteristics or drawbacks, sometimes making them unsuitable for settings requiring high accuracy and neutrality of sound, e.g.
283:
128:, depends upon the effective length and cross sectional area of the duct, the internal volume of the enclosure, and the speed of sound in air. In the early years of ported speakers, speaker designers had to do extensive experimentation to determine the ideal diameter of the port and length of the port tube or pipe; however, more recently, there are numerous tables and computer programs that calculate, for a given size of cabinet, how large the port should be and how long the tube should be. Even with these programs, however, some experimentation with
315:
much less power than in an equivalently-sized sealed enclosure. For this reason, high-powered systems using a bass reflex design are often protected by a high-pass filter that removes signals below the vent tuning frequency. Unfortunately, electrical filtering adds further frequency-dependent group delay. Even if such filtering can be adjusted not to remove musical content, it may interfere with sonic information connected with the size and ambiance of the recording location or venue, information that often exists in the low bass spectrum.
204:
299:
response of a conventional B4 vented box alignment, while (b) represents the step response of a B2 closed-box alignment with Q = 0.7071. The transient response of a vented-box loudspeaker can be improved by choosing a QB3 alignment similar to (c), which results in a more well damped transient response than that produced by the B4 alignment. However, a C4 vented-box alignment similar to (e) results in a less well damped transient response.
183:
104:
338:
high air speeds. Enclosures with a rear-facing port mask these effects to some extent, but they cannot be placed directly against a wall without causing audible problems. They require some free space around the port so they can perform as intended. Some manufacturers incorporate a floor-facing port within the speaker stand or base, offering predictable and repeatable port performance within the design constraints.
249:
136:
319:
274:
261:
properly, can extend the frequency response of the driver/enclosure combination to below the range the driver would reproduce in a similarly sized sealed box. The enclosure resonance has a secondary benefit in that it limits cone movement in a band of frequencies centered around the tuning frequency, reducing distortion in that frequency range. Ported cabinet systems are cheaper than a
236:
32:
337:
Ports often are placed on the front baffle, and may thus allow transmission of unwanted midrange frequencies reflected from within the box into the listening environment. If it is undersized, a port may also generate "wind noise" or "chuffing" sounds, due to the turbulence around the port openings at
314:
Another trade-off for this augmentation is that, at frequencies below the vent tuning frequency, the port unloads the cone and allows it to move with very large displacements. This means the speaker can be driven past its safe mechanical operating limits at frequencies below the tuning frequency with
260:
Novak concluded that a bass reflex enclosure can have greater acoustic output for a given amount of distortion, lower total harmonic intermodulation, and transient distortion than a completely closed-box of similar size. Such a resonant system augments the bass response of the driver and, if designed
190:
Passive radiators are similar in operation to ported bass reflex systems, and both methods are used for the same reason: to extend the system's low frequency response. A passive radiator is the use of one or more additional cones (diaphragms) in a cabinet instead of ports. These passive diaphragms do
123:
cut into the cabinet, generally consisting of a pipe or duct (typically circular or rectangular cross section). The air mass in this opening resonates with the "springiness" of the air inside the enclosure in exactly the same fashion as the air in a bottle resonates when a current of air is directed
306:
resonances: one from the driver and the boxed air, and another from the boxed air and the port. At the vent tuning frequency, the output from the port is the primary source of sound output, as the displacement of the woofer is at a minimum. This comprises a more complex, higher-order system than an
298:
response, resulting in longer decay times associated with the bass notes. Some example step responses for various high-pass filter functions are shown in the relevant figure, where each filter has an identical −3 dB cut-off frequency of 50 Hz. In that figure, (a) represents the step
333:
Whether or not the effects of these in a properly designed system are audible remains a matter of debate. A poorly designed bass reflex system, generally one whose vent is incorrectly tuned too high or too low in frequency, tends to produce excessive output at the tuning frequency relative to the
143:
If this vent air mass/box air springiness resonance is so chosen as to lie lower in frequency than the natural resonance frequency of the bass driver, an interesting phenomenon happens: the backwave of the bass driver sound emission is inverted in polarity for the frequency range between the two
346:
Port compression is a reduction in port effectiveness as sound pressure levels increase. As a ported system plays louder, the efficiency of the port reduces, and distortion emitted by the port increases. This can be reduced by port design, but not totally eliminated. Asymmetrical loading of the
63:
that uses a port (hole) or vent cut into the cabinet and a section of tubing or pipe affixed to the port. This port enables the sound from the rear side of the diaphragm to increase the efficiency of the system at low frequencies as compared to a typical sealed- or closed-box loudspeaker or an
277:
Step responses of various high-pass filter functions, each with a −3 dB cut-off frequency equal to 50 Hz. The step response of a standard B4 vented-box low-frequency alignment is depicted in (a), while that of a standard B2 (Q = 0.7071) closed-box low-frequency alignment is depicted in
211:
The effect of the various speaker parameters, enclosure sizes and port (and duct) dimensions on the performance of bass reflex systems was not well understood until the early 1960s. Subsequently, pioneering analyses by A.N. Thiele, J.E. Benson and
374:
speaker cabinets, which have to reproduce low-frequency sounds down to 41 Hz or below, are often built with ports or vents, which are typically on the front of the cabinet (though they are also placed on the rear). Even some expensive
167:
in monitoring facilities, recording studios etc. However it is possible to design a bass reflex system that mostly overcomes these drawbacks; and quality bass reflex designs are commonly found in demanding environments across the world.
95:, the enclosure volume (and filling if any), and the tube cross-section and length, the efficiency can be substantially improved over the performance of a similarly sized sealed-box enclosure.
232:
work years earlier. The sound pressure produced depends upon the efficiency of the speaker, the mechanical or thermal power handling of the driver, the power input and the size of the driver.
216:
presented the theoretical foundations for the synthesis of bass reflex loudspeaker systems to meet specified low-frequency performance criteria were developed into a series of "alignments" (
347:
driver cone during high level usage can be reduced by placing a baffle at the inside end of the port tube. This baffle can also serve as a stiffening structural element of the enclosure.
265:
speaker with the same performance; whereas a passive radiator system requires one or two "drone cone" speakers, a ported system requires only a hole or port and a length of tubing.
307:
equivalent closed-box loudspeaker enclosure. The interaction between the two resonances results in a system that possesses less damping and increased time delay (increased
124:
across the opening. Another metaphor often used is to think of the air like a spring or rubber band. The frequency at which the box/port system resonates, known as the
20:
391:– a method of loudspeaker cabinet design and utilisation that uses one or more loudspeaker drivers mounted in a sealed box or cabinet.
595:
733:
1011:
404:
705:
Benson, J. E. (1972). "Theory and Design of
Loudspeaker Enclosures, Part 3—Introduction to Synthesis of Vented Systems".
282:
616:
505:
1016:
399:
363:
262:
177:
203:
290:
use ported speakers to improve the bass response and sound performance. Pictured here is a Yamaha DGX-202.
207:
A small
Keesonic Kub speaker. With the front grille removed, the port is visible between the two drivers.
1021:
394:
295:
115:
Unlike closed-box loudspeakers, which are nearly airtight, a bass reflex system has an opening called a
88:
72:
60:
24:
439:
388:
287:
186:
Passive radiator enclosure with front mounted passive radiator; back or side mounting is also used.
125:
147:
When speakers are designed for home use or for high-volume live performance settings (e.g., with
729:
326:
989:
877:
483:
447:
213:
182:
946:
927:
587:
192:
443:
103:
323:
229:
164:
160:
148:
248:
1005:
253:
221:
91:) or rear face of the enclosure. Depending on the exact relationship between driver
371:
217:
107:
Two-inch port tube installed in the top of a Polk S10 speaker cabinet as part of a
92:
36:
135:
87:. The port generally consists of one or more tubes or pipes mounted in the front (
994:. Preprint 10311, AES 147th Convention, October 16–19. Audio Engineering Society.
899:
965:
933:. Preprint 3999, AES 98th Convention, February 25–28. Audio Engineering Society.
826:
801:
776:
751:
682:
657:
539:
359:
318:
308:
273:
225:
19:
882:
865:
487:
302:
In order to achieve their bass output, ported loudspeaker enclosures stagger
952:. Preprint 4748, AES 104th Convention, May 16–19. Audio Engineering Society.
355:
235:
156:
152:
129:
108:
84:
76:
513:
U.S. Patent No. 1,869,178, Application Aug. 15 1930, Patented July 26, 1932
470:
900:"Loudspeaker Port Design for Optimal Performance and Listening Experience"
471:"Performance of enclosures for low-resonance high-compliance loudspeakers"
367:
991:
Loudspeaker Port Design for
Optimal Performance and Listening Experience
866:"Reconstructing atmospheres: Ambient sound in film and media production"
897:
Bezzola, Andri; Devantier, Allan; McMullin, Elisabeth (October 2019).
451:
294:
Compared to closed-box loudspeakers, bass reflex cabinets have poorer
80:
562:
426:
31:
827:"A New Set of Sixth-Order Vented-Box Loudspeaker System Alignments"
376:
317:
281:
247:
234:
202:
181:
134:
102:
75:
type. The design approach enhances the reproduction of the lowest
30:
18:
988:
Bezzola, Andri; Devantier, Allan; McMullin, Elisabeth (2019).
752:"Vented-Box Loudspeaker Systems–Part 2: Large-Signal Analysis"
540:"Vented-Box Loudspeaker Systems–Part 1: Small-Signal Analysis"
132:
is still necessary to determine if the enclosure sounds good.
16:
Type of loudspeaker enclosure with improved bass performance
638:
Proceedings of the
Institution of Radio Engineers Australia
191:
not have a magnet or voice coil and are not connected to a
963:
Salvatti, Alex; Devantier, Allan; Button, Doug J. (2002).
427:"Acoustic Interaction in Vented Loudspeaker Enclosures"
636:
Thiele, A. N. (1961). "Loudspeakers in Vented Boxes".
802:"Vented-Box Loudspeaker Systems–Part 4: Appendices"
563:"The Subwoofer DIY Page - Passive Radiator Systems"
964:
945:
926:
898:
825:
800:
777:"Vented-Box Loudspeaker Systems–Part 3: Synthesis"
775:
750:
681:
656:
538:
469:
425:
256:powered computer speaker with a bass reflex port.
432:The Journal of the Acoustical Society of America
966:"Maximizing Performance from Loudspeaker Ports"
532:
530:
528:
8:
499:
497:
726:Theory and Design of Loudspeaker Enclosures
463:
461:
71:is the distinctive feature of this popular
881:
971:Journal of the Audio Engineering Society
832:Journal of the Audio Engineering Society
807:Journal of the Audio Engineering Society
782:Journal of the Audio Engineering Society
757:Journal of the Audio Engineering Society
688:Journal of the Audio Engineering Society
663:Journal of the Audio Engineering Society
545:Journal of the Audio Engineering Society
379:speakers have carefully designed ports.
272:
929:The Nonlinear Behaviour of Reflex Ports
416:
218:sets of the relevant speaker parameters
683:"Loudspeakers in Vented Boxes: Part 2"
658:"Loudspeakers in Vented Boxes: Part 1"
366:are often fitted with ports or vents.
7:
948:Nonlinearities in Loudspeaker Ports
864:Chattopadhyay, Budhaditya (2017).
14:
907:(Paper Number 10311, Open Access)
586:McGowan, Paul (April 30, 2013).
172:Comparison with passive radiator
139:A small JVC speaker with a port.
598:from the original on 2016-11-27
1:
851:Sound for film and television
728:. Synergetic Audio Concepts.
617:"Passive Radiator Technology"
405:Transmission line loudspeaker
111:project. This port is flared.
870:Communication and the Public
364:sound reinforcement systems
1038:
853:. Boston, MA: Focal Press.
506:"Sound Translating Device"
329:, each cabinet has a port.
178:Passive radiator (speaker)
175:
64:infinite baffle mounting.
27:schematic (cross-section).
944:Vanderkooy, John (1998).
824:Keele, D. B. Jr. (1975).
476:IRE Transactions on Audio
883:10.1177/2057047317742171
488:10.1109/TAU.1959.1166180
47:system (also known as a
763:(July/August): 438–444.
707:A.W.A. Technical Review
1012:Loudspeaker technology
925:Backman, Juha (1995).
724:Benson, J. E. (1993).
680:Thiele, A. N. (1971).
655:Thiele, A. N. (1971).
504:Thuras, A. L. (1932).
330:
291:
279:
257:
240:
208:
187:
140:
112:
40:
28:
799:Small, R. H. (1973).
788:(September): 549–554.
774:Small, R. H. (1973).
749:Small, R. H. (1973).
588:"Passively radiating"
567:www.diysubwoofers.org
537:Small, R. H. (1973).
395:Loudspeaker enclosure
370:speaker cabinets and
321:
285:
276:
251:
238:
206:
185:
151:speaker cabinets and
138:
106:
61:loudspeaker enclosure
34:
22:
905:147th AES Convention
424:de Boer, E. (1959).
288:electronic keyboards
163:speakers for use by
849:Holman, T. (1997).
813:(October): 635–639.
444:1959ASAJ...31..246D
389:Acoustic suspension
126:Helmholtz resonance
468:Novak, J. (1959).
331:
327:speaker enclosures
292:
280:
258:
241:
209:
188:
141:
113:
41:
29:
1017:Audio engineering
452:10.1121/1.1907703
358:cabinets used in
322:In this stack of
239:Bass reflex vent.
224:'s summary (with
79:generated by the
1029:
996:
995:
985:
979:
978:
968:
960:
954:
953:
951:
941:
935:
934:
932:
922:
916:
915:
913:
912:
902:
894:
888:
887:
885:
861:
855:
854:
846:
840:
839:
829:
821:
815:
814:
804:
796:
790:
789:
779:
771:
765:
764:
754:
746:
740:
739:
721:
715:
714:
702:
696:
695:
694:(June): 471–483.
685:
677:
671:
670:
660:
652:
646:
645:
633:
627:
626:
624:
623:
613:
607:
606:
604:
603:
583:
577:
576:
574:
573:
559:
553:
552:
551:(June): 363–372.
542:
534:
523:
522:
520:
519:
510:
501:
492:
491:
473:
465:
456:
455:
429:
421:
400:Passive radiator
342:Port compression
263:passive radiator
252:A small plastic
214:Richard H. Small
35:RCA bass reflex
1037:
1036:
1032:
1031:
1030:
1028:
1027:
1026:
1002:
1001:
1000:
999:
987:
986:
982:
962:
961:
957:
943:
942:
938:
924:
923:
919:
910:
908:
896:
895:
891:
863:
862:
858:
848:
847:
843:
823:
822:
818:
798:
797:
793:
773:
772:
768:
748:
747:
743:
736:
723:
722:
718:
704:
703:
699:
679:
678:
674:
669:(May): 382–392.
654:
653:
649:
635:
634:
630:
621:
619:
615:
614:
610:
601:
599:
585:
584:
580:
571:
569:
561:
560:
556:
536:
535:
526:
517:
515:
508:
503:
502:
495:
467:
466:
459:
423:
422:
418:
413:
385:
353:
344:
271:
246:
201:
193:power amplifier
180:
174:
165:audio engineers
101:
59:) is a type of
17:
12:
11:
5:
1035:
1033:
1025:
1024:
1019:
1014:
1004:
1003:
998:
997:
980:
955:
936:
917:
889:
876:(4): 352–364.
856:
841:
816:
791:
766:
741:
734:
716:
697:
672:
647:
628:
608:
578:
554:
524:
493:
457:
438:(2): 246–247.
415:
414:
412:
409:
408:
407:
402:
397:
392:
384:
381:
352:
349:
343:
340:
324:bass amplifier
270:
267:
245:
242:
230:Edgar Villchur
200:
197:
176:Main article:
173:
170:
161:studio monitor
149:bass amplifier
100:
97:
15:
13:
10:
9:
6:
4:
3:
2:
1034:
1023:
1020:
1018:
1015:
1013:
1010:
1009:
1007:
993:
992:
984:
981:
977:(1/2): 19–45.
976:
972:
967:
959:
956:
950:
949:
940:
937:
931:
930:
921:
918:
906:
901:
893:
890:
884:
879:
875:
871:
867:
860:
857:
852:
845:
842:
838:(5): 354–360.
837:
833:
828:
820:
817:
812:
808:
803:
795:
792:
787:
783:
778:
770:
767:
762:
758:
753:
745:
742:
737:
735:0-9638929-0-8
731:
727:
720:
717:
713:(4): 369–484.
712:
708:
701:
698:
693:
689:
684:
676:
673:
668:
664:
659:
651:
648:
644:(8): 487–508.
643:
639:
632:
629:
618:
612:
609:
597:
593:
589:
582:
579:
568:
564:
558:
555:
550:
546:
541:
533:
531:
529:
525:
514:
507:
500:
498:
494:
489:
485:
481:
477:
472:
464:
462:
458:
453:
449:
445:
441:
437:
433:
428:
420:
417:
410:
406:
403:
401:
398:
396:
393:
390:
387:
386:
382:
380:
378:
373:
369:
365:
361:
357:
350:
348:
341:
339:
335:
328:
325:
320:
316:
312:
310:
305:
300:
297:
289:
284:
275:
268:
266:
264:
255:
254:Harman Kardon
250:
243:
237:
233:
231:
227:
223:
219:
215:
205:
198:
196:
194:
184:
179:
171:
169:
166:
162:
158:
155:speakers and
154:
150:
145:
137:
133:
131:
127:
122:
118:
110:
105:
98:
96:
94:
90:
86:
82:
78:
74:
70:
65:
62:
58:
54:
50:
46:
38:
33:
26:
21:
1022:Bass (sound)
990:
983:
974:
970:
958:
947:
939:
928:
920:
909:. Retrieved
904:
892:
873:
869:
859:
850:
844:
835:
831:
819:
810:
806:
794:
785:
781:
769:
760:
756:
744:
725:
719:
710:
706:
700:
691:
687:
675:
666:
662:
650:
641:
637:
631:
620:. Retrieved
611:
600:. Retrieved
591:
581:
570:. Retrieved
566:
557:
548:
544:
516:. Retrieved
512:
479:
475:
435:
431:
419:
372:keyboard amp
354:
351:Applications
345:
336:
332:
313:
303:
301:
293:
259:
210:
189:
146:
142:
120:
116:
114:
68:
66:
56:
52:
48:
44:
42:
37:shelf stereo
23:Bass reflex
592:psaudio.com
482:(1): 5–13.
360:home cinema
309:group delay
269:Limitations
226:Henry Kloss
99:Explanation
77:frequencies
69:reflex port
57:reflex port
45:bass reflex
1006:Categories
911:2021-05-15
622:2024-09-19
602:2024-09-19
572:2023-01-02
518:2022-07-02
411:References
244:Advantages
157:subwoofers
130:prototypes
93:parameters
53:vented box
356:Subwoofer
296:transient
153:PA system
109:DIY audio
85:subwoofer
73:enclosure
39:speakers.
25:enclosure
596:Archived
383:See also
368:Bass amp
440:Bibcode
199:History
732:
89:baffle
81:woofer
49:ported
509:(PDF)
377:hi-fi
286:Some
228:) of
730:ISBN
480:AU-7
362:and
278:(b).
121:vent
117:port
878:doi
484:doi
448:doi
304:two
222:KLH
119:or
83:or
55:or
1008::
975:50
973:.
969:.
903:.
872:.
868:.
836:23
834:.
830:.
811:21
809:.
805:.
786:21
784:.
780:.
761:21
759:.
755:.
711:14
709:.
692:19
690:.
686:.
667:19
665:.
661:.
642:22
640:.
594:.
590:.
565:.
549:21
547:.
543:.
527:^
511:.
496:^
478:.
474:.
460:^
446:.
436:31
434:.
430:.
67:A
51:,
43:A
914:.
886:.
880::
874:2
738:.
625:.
605:.
575:.
521:.
490:.
486::
454:.
450::
442::
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
