Bass reflex port tuning

Bass reflex port tuning. At high sound pressure levels a bass-reflex port produces blowing sounds, especially in the case Aug 4, 2009 · Overview: This is a calculator for designing a L-Slot Vent Bass Reflex Enclosure. Feb 19, 2019 · There are two types of plugs that I’ve seen sent with speakers before. At frequencies near fb, cone excursion shrinks to a minimum. most players don't notice the transient response drop of ported systems and are happy with the extended bass response compared to sealed. cause distortion, noise, and compression. The information is from the book "High Quality Sound Reproduction" by James Moir: Le = A (2150²/f²V - 1/√A) L = Le - 0. Varying the enclosure volume and port tuning allows you the ability to tune the alignment that you want within the limits of the selected driver. And the combined pressure from the port. MJK's MathCAD does this, as does Unibox. If what you're hearing is the result of excessive group delay caused by an aggressive bass alignment, it will clean that up too. By using a ported enclosure (bass reflex), the energy generated by the back side of the loudspeaker cone is put to useful work, by adding it to the radiation generated from the front of the cone. A selection of Bass Reflex Ports / Tubes. Last Aug 26, 2009 · The good thing about using port tubes is that it is easy to change the tuning and choose what you like. . I used an AC ammeter (Fluke multimeter), and used a frequency generator to find where current was maximum. 732, hence the default value set in the port length calculator. If we assume a . How is the difference in a port location significant? 1. 2cm square. It is common to assume that k = 0. Shop for speaker port tubes for your next vented box design. Using the software program, I entered ia higher box tuning frequency of 37Hz which allowed me to use a 16 inch port of the same diameter. Oct 5, 2023 · Port tuning simply means adjusting the size and length of a speaker’s port, and venting ensures smooth airflow inside the speaker. 5 cubic feet with a 50hz port tuning. Bass Reflex Port 30mm £3. The main reason many smaller bass-reflex speakers use rear ports is the lack of adequate space to accommodate them on the front baffle. Aug 22, 2023 · A larger port will typically produce a deeper bass, while a smaller port will produce a tighter, more controlled bass. Basically, the patent discusses a new technique to tune a port of a loudspeaker, in this case multiple ports that will be open or selectively closed, in function of an analysis of the frequencies of the signal being played. The formulas used in the calculator create a design that suggests the most maximally flat response in an anechoic environment based on the number of drivers, the thiele small parameters and the allotted dimensions specified in the user’s input fields. Jun 22, 2023 · Before we get into the principles behind subwoofer port tubes, here is a list of some of the best subwoofer port tubes on the market: 1. When the port eigenfrequencies get excited by flow separation and vortex shedding, they are very audible to the human ear, because they are outside the Oct 8, 2019 · Particle velocity contours for ports with 3:1 aspect ratio at port tuning frequency of 40 Hz. One of the problems is accomodating the vent. 732 factor is for one flanged and one free end, you can use 0. π: Mathematical constant, approximately 3. At that point, impedance is minimum, which is indicative of port tuning. A bass reflex system (also known as a ported, vented box or reflex port) is a type of loudspeaker enclosure that uses a port (hole) or vent cut into the cabinet and a section of tubing or pipe affixed to the port. This step requires precision, but the results are worth it. 16 cm H. Learn about the frequency of sound waves by checking out our frequency calculator. Adjustment range: 128-245mm. This means that unless you choose a narrow port your port length will be long. there is plenty of guys more than happy with 12" ported speakers at 55Hz to 60hz. 2007-11-08 4:57 am. Feb 1, 2008 · Yes, the Fostex recommended BR @ 35l is a QB3 alignment. Aug 4, 2009 · This is a calculator for designing a L-Slot Vent Bass Reflex Enclosure. The result was the blue line. there is a second port with a tuning frequency. May 1, 2024 · @Mosquito I have found a note I made many moons ago relating to traditional reflex tuning using a tube or rectangular tunnel. What is a Bass Reflex Speaker Box? A bass reflex speaker box, also known as a ported enclosure, is a type of speaker enclosure that includes a A bass reflex tube is used to amplify sound waves with low frequencies. SVS will provide a port tuning plug for free if you reach out to them, helping you tailor the bass output. RCA bass reflex shelf stereo speakers. Start with the port longer then calculated and measure the impedance. Then Vd >= 1. This could be different for you though since every room & speaker is different. The Yin: At the tuning frequency (“fb”), the port or passive radiator generates 70-80% of the air movement. Much better sound and extended bass. Jul 18, 2014. 85 CF net internal volume, 40 Hz tune needs a 4. The 73 Hz tuning will result in a depressed mid and low bass, but would work well if the cab were on the small side (say 3/4 cf). 695cubic feet) a slot that is 8 inches x 2 inches x 1. Three different test signals are recorded at different levels for all ports in the test box. Jan 6, 2024 · Bass reflex is the best for lower frequencies due to the influence of the port or ports. 5"/19cm. These are an excellent item for fine tuning speaker cabinets & allowing you to achieve a tailored bass response. 59 cm W x 10. When the port eigenfrequencies get excited by flow separation and vortex shedding, they are very audible to the human ear, because they are outside the Jan 10, 2024 · A ported box or vented or bass reflex box is a sub-box that uses a vent (a hole) cut into the cabinet connected to tubing or pipe attached to the port. The port in the enclosure inverts the phase of this energy, so it is in phase with the energy from the front of the diaphragm. My calculations put the box at about 68 litres and the port tuning at about 36 Hz. When placed inside a speaker enclosure in combination with the traditional speaker, the bass reflex assembly produces sound by pushing air generated by the main speaker through a port or vent into the listening area. Jul 18, 2014 · Visit site. It changes the speaker's bass alignment that's all. is the lowest point in the impedance (between the two humps). Parts Express stocks a variety of shapes and sizes, including adjustable length and flared ports. However, at high drive levels, the air inside the port can become turbulent and. enclosure box volume (V b) tuning frequency (f b) end correction factor (k) unitless. To keep tuning at 34. $6. (Reno, NV), filed in 2013, and awarded in April 2017. com/courses. 8cm). The volume of air in the speaker cabinet and in the openings form an oscillating system. Bass Reflex Port 25mm £2. Dayton MX15-22 Drivers (wired in series; 4ohm) Behringer NX3000 Amplifier (Bridged; each) MiniDSP HD 2x4. Here is the formula we use: ( (14630000* (D/2)* (D/2))/ ( (Fb*Fb*Vb*1728)- (1463* (D/2)))) Please compare your answers with other programs that include other allowances such as tapered ports Jun 29, 2023 · A bass reflex speaker combines a tube, port, or vent with a traditional speaker driver to produce the desired sound reproduction. I break down the port tuning formula and show you how to use May 24, 2012 · To be accurate, you should measure the impedance and see and listing ! The tuning depends on what is in the box This is what I did. AmmoTenna PSP3 3-Inch Port Kit, Black, 1 Count package dimensions :33. Conclusion In conclusion, a bass reflex calculator is an invaluable tool for designing speaker systems with optimized bass performance. This reduces the overall port output. Passive Radiators vs Bass Reflex Speakers . 3 Hz. Sep 5, 2017 · A box tuned to 34. When it comes to bass reflex with DSP, here's what I'd do: - Pick the tuning frequency according to the desired low-frequency cutoff. The box/port combination presents a stiff load to the driver. Let’s consider a scenario: You’re designing a speaker system for a small room with limited space. Nov 8, 2007 · Joined 2002. 5 Hz gives us an approx port size of 6. Above the port tuning Oct 23, 2023 · A larger port will result in a lower tuning frequency and a more extended bass response, while a smaller port will increase the tuning frequency, providing tighter and more focused bass. So the combined electrical/mechanical sound pressure of the speaker. Im guessing the one of the lengths or widths of your room to be 10 or 11 feet. Strategic adjustments to these parameters can effectively shift the resonant frequency and, in turn, alter your speaker's low-frequency response. Space Requirements. Cross section area (SV ): 34. IMO, 39 Hz would decrease the excursion limited power handling in the midbass - where you really need it. The port, also known as a vent or a bass reflex port, is a hole or duct in the enclosure that allows air to move in and out, enhancing the bass response of the speaker system. Open cell foam plugs allow some air to continue flowing through the port but not at the same level as being completely unblocked. 1. 5 hertz, try to get the “Port Frequency 1,” “Port Frequency 2,” and “Box Frequency” as close to 41. I'm planning to build reflex port as rectangular version to be part of the enclosure. The ports relieve the pressure in the box and make it easier for the woofers to move. Inputs: vent or port diameter (d v) number of ports or vents (N p) unitless. Typically, bass reflex speakers offer enhanced bass response over closed box designs. of the system. Stuffing the port does not ruin the sound. I'm afraid that 180 degree turns affect tuning. If one wanted to switch to two 2" ports, they would both need to be 11" long. The rear radiated sound waves are used to amplify the bass. You might see something like R e =3. It is a technique used to extend the low-frequency output of audio systems, allowing for a more pronounced and powerful bass sound. The ports have all been designed to tune to the same frequency of 40 Hz inside a test box, which is driven by two 10" subwoofers. Aug 14, 2016 · When you take a look at a speaker’s spreadsheet, you might see both values of resistance and impedance. It has to do with baffle step transition of the loudspeaker, which changes Solving for length of port or vent. Quantity: Qty: 4+. A great patent review with lots of informative details. Mar 18, 2011 · - To lower tuning, make box bigger (with same port area and length) In your situation (variable port length) if the port extends into the box, if you want to know what length yields what tuning make sure that you count the volume displaced by the port as you make it longer. Feel free to change it to fit your needs. This is probably what is causing the boom, because both the port tuning and the room mode coincide together at around 50hz. 75" long 2" diameter port. The 0. Oct 11, 2023 · For those opting for a ported enclosure, fine-tuning the length and diameter of the port is pivotal in shaping the tuning frequency. A passive radiator is a type of loudspeaker with no active driver or voice coil but rather a diaphragm that vibrates in response to changes in air pressure. The ports 'fire' sound out in whichever direction they face - so rear ports need a wall behind them to bounce the sound back to you. advanced DSP processor maintains control over the subwoofer at all drive levels for refined, low-distortion sound. Definition and Function. In a Bass Reflex system, a port or vent is This is why it is critical to not tune a cab too high, and is one of the reasons why a lot of cabs (particularly small ones) struggle with low notes, especially at the bottom of the E and B (and lower) strings (overly high port tuning increases the mid-bass which is the only sort of bass ('fake' bass) that some cabs can do in quantity). Feb 25, 2024 · The Bass Reflex Calculator employs the following formula: Fb = v / (2 * π * √ (Vb * ρ / A)) Here’s what each variable represents: Fb: Tuning frequency of the bass reflex speaker (in Hertz). #2. Thanks to Bjorn for his comments. They also require more accurate tuning to get the desired results and are usually larger than sealed boxes due to the ports. 41D where, Le = effective length of tube or tunnel in inches L = physical length of tube or tunnel in Nov 22, 2010 · Member. #3. 5 hertz too. This type of design, as one may observe by looking at contemporary loudspeaker products, is still widely used today. The term nominal signifies the mean value, because the impedance changes with frequency. The effect Mar 14, 2019 · 2019-03-14 9:55 am. Finally, adjust the end correction factor (k \small k k). 14159. 5mm). Is what gives a ported or Reflex cabinet more bass response than a typical sealed or infinite baffle May 17, 2009 · For tuning the port, I prefer using impedance. The only problem in not measuring is in having faith in the published T/S parameters. 85". The enclosure has a fair amount of polyester fill and two 1-3/4” holes drilled through the 3/4” front baffle. v: Speed of sound in air (approximately 343 meters per second). For a back-firing port, a wall or a corner behind the speaker can be used to maximize the efficiency of the bass-reflex port. May 4, 2022 · Bass response under 100-200Hz on a bass reflex box depends entirely from the tuning (*), and port tuning behaviour depends on the T/S parameters of the driver. 75 inch port to tune this enclosure to the Fb above, it would have to be 22 inches long, which cannot fit inside the enclosure unless I extended it outside. For typical port lengths in bass reflex boxes below 0. The calculator does It's all just port resonance Likewise in a nutshell. 95. Port tuning enhances the speaker’s ability to handle specific frequency ranges, enriching both bass response and frequency response. It will reduce the amount of low bass, which may help if the boominess is caused by room gain. Keep shorting the port until you reach the correct tuning frequency. You haven't indicated what tuning you intended in the first instance when you were designing it as a bass-reflex box. A bass-reflex system is a type of loudspeaker design that uses a port or a vent to improve low-. It showed modeling that demonstrated transient response that was almost as good as a sealed box. When the port eigenfrequencies get excited by flow separation and vortex shedding, they are very audible to the human ear, because they are outside the Outside diameter: 76mm. Passive radiators work in conjunction with active drivers to produce sound. 5 cubic feet with a JBL 2204H driver installed. In addition, the bass reflex port design can allow a speaker to reach much lower frequencies, outside of what the speaker driver was designed for. Acoustic Resistive Elements for Ported Transducer Enclosure. The tuning freq. Engineering drawing: Large adjustable telescopic reflex port. May 6, 2019 · Bass-reflex delivers better bottom end. In Stock. Jul 22, 2020 · You can also change it to somewhere in between. 2 cubic feet. Patent Number: US20170188135A1. 1cm x 4. 732 \small k=0. If you want to understand how the driver and port interact, you need to use a model that shows driver, port and combined outputs. Last edited: 2021-05-12 7:00 pm. If you want to reopen this May 31, 2023 · The patent describes a single chamber, single tuned, bass reflex enclosure system, using a more advanced, single Helmholtz tuned bass reflex design, with a port that is folded and extended. #1. The downside to ports is that at lower Aug 10, 2020 · The higher impedance peak continued to reduce in amplitude and increase in frequency with addition holes in the enclosure. This time a length correction is included. 5 Hz with a 3" port, the length needs to be 5. 274 cm L x 21. That is for Length, Diameter in mm and Length>50mm, Vb in liters and Fb in Hz. MathCad includes this impedance so depending on the geometry of your cabinet the actual tuning frequency might be a little lower than you would expect. 2″ vent => 4″ or 5″ speaker (6″ max) Tuning Ports Tuff 50mm Bass Reflex Port Tube 100mm 75mm with grille Triangular Corner 63mm 110mm 45mm Monacor Tube Skip to main COOKIES: Our website uses cookies in order to provide a better online experience, this is essential for use of the shopping basket, and to login to our website. the driver is in a box of finite size and the air inside the box acts as a spring. The length of this port is critical as it directly affects the tuning frequency and the overall performance of the speaker. Another point: searching for the lowest F3 is almost always not the best tuning. Injection moulded plastic - many of these are made exclusively for us. Jan 8, 2024 · Randy, treating it as a bass-reflex for a moment, you are meant to tune the port to a particular frequency - which as Allen said is the resonance frequency of the air in the port. Cabinet 1 DATS V3 Impedance Sweep to verify port tuning frequency: Cabinet 2 DATS V3 Impedance Sweep to verify port tuning frequency: Near field measurement of the Dec 22, 2011 · I have calculated reflex tuning with winisd beta and tuning results in way too long reflex port to fit inside the enclosure. This hole or port is used to increase the efficiency of the system at low frequencies by channeling sound from the rear of the speaker diaphragm so that the box can be tuned properly. The ports push air out when the woofers move back and suck air in when the woofers move forwards. I got drinking straws, taped a whole load together and cut them so they were about 5 inches long, popped them into the bass ports making sure they were a tight fit and Apr 9, 2012 · May 22, 2006. - Set the cabinet size such that you can get to Xmax above the port tuning frequency when maximum power input occurs (whether that's amplifier or driver limitations). Re is the DC resistance of the voice coil and Z is the nominal impedance. Calculations and measurements are presented for a number ofport ge-ometries. In terms of rear ported speaker placement, I’ve found that a maximum of 4 feet is the point where a speaker can still benefit from room gain but 1 1/2 to 2 feet from the wall often gives a good quality of audio. Jan 6, 2024 · Rear speakers have a port on the rare panel. Oct 25, 2023 · James Croft (Croft Acoustical) reviews a very curious patent from Amazon Technologies, Inc. Dec 3, 2020 · A bass-reflex enclosure includes a vent or port between the cabinet and the ambient environment. Get your hands on a Woofer Tester 3 (or similar testing software). This is the frequency at which the speaker is most efficient and produces the best sound quality. 7 inches according to the first equation. Jul 3, 2022 · Is port placement important? If so, where exactly do we place it?DIY Audio courses: https://audiojudgement. frequency performance. With that info, you can model changes to the port or PRs. Bass Reflex, also known as a ported or vented enclosure, is a design feature that enhances the bass response of speakers and subwoofers. Fixed and adjustable bass ports. Based on those physical constraints, it is best to have a port area of a set minimum radius: A bass reflex speaker should be matched in size with its port. Part# 260-329. 3m/s) so you will have port noises on high volume. The port starts to resonate about 15 to 30 Hz above and below the tuning or Fb. C. Like passive radiators, they use a resonant cavity to achieve a deeper, more powerful bass sound. The 7cm diameter 21cm long vent will have an air velocity arround 19. It’s a clever design feature to get better bass performance from smaller speakers. However, bass reflex speakers use a port to do this rather than a Jan 22, 2024 · Definition of Bass Reflex. FAQs May 12, 2021 · 2021-05-12 6:57 pm. As a result, tuning frequency is kinda fixed from the beginning, and only the port diameter remains the variable. Bass-reflex ports are used to enhance the bass reproduction of loud-speakers. 2010-11-22 8:22 pm. the box has a port that has a tuning frequency. 89 inches long for 70Hz tuning (or 20. These technical tweaks are essential for great sound quality. The calculator…Continue reading → Qty: 1-3. • Mass of air in port and compliance of air in enclosure form a resonator • Bass reflex (vented) can be abstracted to a 2-Mass-Spring-Damper System • Excursion of the diaphragm is reduced compared to a sealed box with same SPL • Nonlinear distortions are reduced Displacement (mm) To calculate the port length of a round port, enter the diameter of the port (D), the box volume (Vb) in cubic feet, and the desired tuning frequency (Fb). I read on somebody's DIY site about the advantages of (I hope I remember this correctly) tuning the port below resonance to get a response that was more along the lines of a sealed box than a ported alignment. Figured I would verify this using REW and a UMIK-1, held the mic flush with the port and ran a measurement between 20-200Hz. 00. For anyone doubting that this is a 6th order enclosure, count along with me: the driver is placed on a baffle. Aug 4, 2009 · So if the “1/4 Wave Tuning Point” is 41. You can lay these curves over each other on the same graph. 44" (163. country of origin :China. A. Ok this may sound weird but having read a few posts about how drinking straws can be used as bungs for bass ports I decided to try this on my RX1's. lightweight, long-throw 10" woofer for enhanced sensitivity and high-output levels. Jul 30, 2020 · Few realize how much more sound output is possible from a DSP Assisted Reflex design. Plus or minus 1-2 hertz is acceptable. I have been thinking of building reflex port as labyrinth into the enclosure. The Aug 3, 2021 · Your vent is probally +/-5cm (2") to get that tuning to 42Hz with a 9cm long vent, but that will increase the air velocity way to high (38. Note that Vd should be entered in cubic meters, as stated below the equation. Your problem would not be related to low frequency extension, anyway*. However, bass reflex enclosures can become noisy at higher volumes. 4 ohms (resistance) and Z=4 ohms (impedance). Bass reflex speakers, also known as ported speakers, are a type of speaker that uses a port or vent to enhance low-frequency response. AKA if the shortest port makes the box 4 cubes at 38 hz, a longer port Aug 10, 2020 · The tuned vent enclosure trades the tight damped bass of a sealed enclosure for extended bass frequency response. The port is in the bottom part of the baffle. Here are some recommendations on minimum vent size compared to speaker size : 1″ vent => 4″ speaker. 732*Dia. If you download WinISD, take these 2 drivers that are already in the database and model them both in 3. The Sep 28, 2005 · Tuning bass reflex port . For example, in the case of the last bass-reflex Nov 18, 2004 · The boxes are about 900 mm (3ft) high and the two drivers are above each other with the tweeter in the middle, one in the upper part of the baffle the other in about the centre of the baffle. The problem is that if I use a 2. By inputting the enclosure volume, port area, and diaphragm area into the Bass-Reflex Calculator, you can calculate the ideal tuning frequency tailored to that specific environment. At the lower Fb both ports work together and so the total port area is the sum of the two port areas. By reducing the port diameter from 3. 125" to 3" and keeping the length same tunes the box to approx 33. 28/ea. Jan 5, 2024 · Example of Bass-Reflex Calculator. Product Type :SPEAKERS. Thread starter beamnet; Start date 2005-09-28 2:03 pm; Status This old topic is closed. Tuning bass reflex port. Use the “Port Front Width,” “Port Rear Width,” and “Port Exit Width” fields to fine tune the frequencies towards a closer match. Aug 4, 2009 · This is a calculator for designing a Dual Chambered Tri-Tuned Bass Reflex Enclosure. If this goes for TLs, it's a likely explanation for bass reflex designs as well and should explain the discrepancy between calculated and actual vent length. Mar 2, 2024 · A: Tuning frequency determines the point at which the speaker and port resonance align, affecting the bass response of the speaker system. This article was Jul 5, 2018 · While speaker size and power handling is a given, port diameter and tuning frequency is at your discretion. Ports allow bass energy to exit from the internal speaker chamber to increase bass response, and depending on size and Feb 22, 2010 · Firstly, high-Qts drivers suited for aperiodic (lossy) enclosures would not be used in a bass reflex enclosure, so I would not worry about getting the tuning "right". The resonance frequency of a bass reflex speaker should extend the frequency limit. We have 3D printed 9 different port profiles and tested them in our anechoic chamber. there is a second enclosure. The port acts as a Helmholtz resonator which extends the bass response. Oct 3, 2015 · Also, need a good estimate of net internal volume. 3cm x 5. Flange diameter: 96mm. However, when you open up a port air velocity calculator, you mainly checking to see the velocity for different port diameters. 4 days ago · Input the tuning frequency (F \small F F). The active driver, usually a woofer, has sound by moving a diaphragm in and out. The location of the resonator has to be considered with regard to the layout of the listening room. Oct 6, 2020 · Ported (also known as bass reflex) speakers are designed to enhance the bass response of a loudspeaker through a series of calculations involving cabinet volume, cabinet filling and woofer response, among other variables. Dec 15, 2022 · Bass Reflex, 20hz Port Tuning Frequency. If it is, your room as a resonant point of around 50hz. Hope this helps. Aug 4, 2009 · Overview: This is a calculator for designing an On-Axis Bass Reflex Enclosure. austin,tx. However, the quality can begin to suffer when the bass roll-off starts at 24dB/octave. 34 cm^3 = 34e-6 m^3. The Eminence Beta15 (or 15A, same thing), and the Eminence Legend CB15 (or 158, same thing). So keeping the port length the same should not cause any major issues. 732 k = 0. 85 if both ends are flanged. bass-reflex (ported) cabinet design. Various sizes available. However, at higher output levels, the bass-reflex port nonlin-earities, specifically the unsteady separation of the acoustic flow, can lead to blowing sounds and acoustic losses. Jun 15, 2022 · Length=2350*Dia^2/ (Vb*Fb^2)-0. Although bass reflex enclosures offer enhanced bass performance, they may have some trade-offs to consider. May 16, 2024 · D is the port diameter in centimeters ; F b is the tuning frequency in hertz ; To calculate the box volume, tuning frequency, or port diameter, use the formula above and solve for the missing variable. 5 m, 𝑓𝑝1 is larger than 343 Hz, which is several octaves higher than typical port tuning frequencies in loudspeakers. Another important aspect of bass reflex technology is the tuning frequency. Phone helpline: 01702 523999 or contact us. Jul 19, 2011 · But as a suggestin I could start with trying 70Hz tuning freq in a 48L box that I can use also for trying lower tuning frequencies? That would mean, if I get it right, for a box of 48L (1. Our 50mm port is great for the classic Spendor BC1. 98/ea. 0. The first is an open cell foam plug and the second is a closed cell foam or rubber plug. Front ported speakers have a port on the front baffle near the drivers. 3. Nov 12, 2022 · Rear Ported Speaker Placement. Sometimes ports used near the floor or near a wall or corner of a room may perform differently. Damping Q factor - Wikipedia For fun look at these links: For perspective and more fun. htmlMusic Credits:"Werq" Kevin MacLeod Jan 13, 2021 · I'm trying to confirm that my bass reflex port length is correct, I was going for 38Hz using a 2" port with an external flare, and the length is roughly 7. In other words, the acoustic suspension will have a much better response somewhere down the line than the bass reflex. [1] [2] This port enables the sound from the rear side of the diaphragm to increase the Port tuning is part art and part science, in this video I do what no other YouTube video does. so finding a speaker with low fs and simple tuning to fs creates a more punch and response. Net Internal Volume 8. Sep 7, 2016 · The B&W CM6 bass-reflex port has a dimpled surface Bass-reflex technology: resonator placement. Just stuff a sock in the port. 5m/s which is within reasonable limits. But the key role of bass reflex speaker design (bass ports) is the bigger bottom end they deliver. Try 45l. Here is another tool to calculate the minimum port diameter: Flare-it - Free Speaker Design Software. Although the construction of bass-reflex enclosures is fairly simple, their design is not simple, and requires proper tuning. This past Friday I took out a base-reflex enclosure, about 1. 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