lincolntc690 10+ year member
CarAudio.com Elite
Sealed - 2nd Order Acoustic Suspension
Basic Theory
Widely popularized by Acoustic Research back in the 50’s. The driver is mounted in a completely sealed, airtight enclosure, generally with the front of the driver facing outward but is not restricted to this method only. The system is designed to achieve a desired Q factor which controls the response characteristics of the driver/enclosure combination and usually ranging between 0.5 and 1.5. The total system Q (also known as Qtc) is dependent upon: volume of enclosure, T/S parameters of driver and internal treatment compounds including insulation, stuffing or wall-deadening materials. Best suited for drivers with an EBP of 50.0 or lower and drivers with Qts values above 0.40 but is not restricted to these exact alignments. Cutoff rate is about 12 dB/octave below f3, however higher system Q's result is a somewhat sharper roll-off while lower system Q's result in a slightly more shallow roll-off varying by about +/- 2 dB. Better damping and better transients is achieved by shooting for a lower system Q which can be accomplished by either making the enclosure larger or by adding stuffing/damping material such as polyfill, Dacron, fiberglass, acoustic foam, or any other suitable type of fill material. Box stuffing will also affect f3 by either raising it or lowering it depending upon the type and amount of stuffing used.
Advantages
Sealed enclosures are the simplest of all designs. They are easy to model with speaker software and it's easy to achieve predicted results. Box size and shape are generally the least complex. Great for both beginning and advanced DIY’ers. The exact response characteristics which are desired can be achieved by simply designing for a particular Qtc. You can alter its performance by varying the size of the enclosure and the amount of stuffing material used. Qtc ranges from 0.5 to 1.5 while 0.7 is generally considered ideal however some drivers may perform better (i.e., sound better) with Qtc values less than 0.7, especially where the driver dictates a smaller-than-optimal box at Qtc=0.7.. Slowest of all cutoff rates below fB of 12 db/octave. This results in much quicker group delay responses ranging from 1ms – 10 ms. Fast, quick, natural, smooth, tight, accurate, controlled and warm are some common terms that audiophiles use to describe sealed enclosures. Transient response is the best of all enclosure types. The excursion of the driver increases as the frequency applied decreases until fB is reached after which the driver excursion begins to decrease once again. There's no need for subsonic filtering due to the enclosure’s natural tendency to inhibit extremely low frequencies. This results in less bottoming out of drivers at subsonic frequencies. However as the enclosure size gets larger, more Xmax is required for any given input power. More extended low frequency response than vented enclosures given the same f3 for both. Phase shift is minimal within its normal operating frequency range.
Disadvantages
Very low frequency output is minimal. The f3 also know as (3dB down poin) is usually fairly high, above 30 Hz in most applications. Less power efficiency by about –3 dB as compared with vented enclosures. Lower over SPL capabilities. There's a strong need for drivers with a very large Xmax in order to ensure safe operation at least down to fB, especially if the box is designed for Qtc values
Best Applications
Best suited where a completely uncompromised sound quality is desired. Best for classical music and most rock and pop type music. Most widely used in car stereo systems where cabin gain can make up for its lack of low end
Ported - 4th Order Vented
Basic Theory
Also known as bass-reflex or ported. The driver is mounted into an enclosure which houses a large opening, port, vent or slot that extends into the cabinet a specified length. The length and size of this vent are extremely critical to the proper function of this enclosure. The port and driver contribute together to provide the desired response characteristic. The driver is generally mounted with the front facing outwards, but is not restricted to this method only. The vent which extends into the cabinet tunes the enclosure to a specific frequency (known as fB) thereby acting as a high pass filter on the driver. Driver excursion is at its minimum at fB where the vent then takes over and does most of the work. Cut-off rate below fB is 24 dB/octave but can be varied up or down 5-6 dB depending upon the exact tuning frequency and volume of the enclosure. There are various types of alignments that all fit into the ported 4th order category. Some common types are QB3, EBS, SBB4 and SC4. By varying the enclosure size and the tuning frequency, it is possible to achieve a variety of distinct low frequency performances from a single driver. The vent acts by damping the load produced by the driver above fB causing it to behave somewhat as if it were in a sealed enclosure. Best suited for drivers with an EBP near 100.0 or higher and Qts
Advantages Extended low frequency response. 3 dB down points (f3) are capable of being near or even below 20 Hz. Increased power handling above fB due to reduced driver excursion at and while nearing fB. More efficient system. Generally 3dB increased output over sealed enclosures due to the combined output of driver and port. More overall SPL capabilities. Deep, powerful, full, loud, inspiring, incredible, and earth shattering are common terms associated with vented enclosures.
Disadvantages
Larger enclosure size. More difficult to accurately achieve predicted results. Misaligned enclosures can result in very poor bass quality. Very accurate T/S parameters of actual driver is required. Although sometimes you can get away with using manufacture’s specifications. Driver unloading or bottoming out below fB is very common. Xmax is reached easily below fB and may cause sever damage the the driver's suspension, voice coil or cone. This usually requires the need to install additional high pass filtering below fB. But is not a always a necessity as long as power levels and frequency content are kept within reason. Transient response is degraded, yielding typical group delay curves as high as 50 ms. Muggy, boomy, sluggish, one-note, slow, and inaccurate are common terms associated with vented enclosures. Port diameter must be large to avoid unwanted port noise, which in turn requires the port to be long for any given Fb, which then drives up the volume of the enclosure, sometimes to undesirably large proportions.
Best Applications Where the deepest and loudest bass is necessary. Where size is not a huge issue but may still be a definite factor. For Home Theater and music. May be best suited for sound reinforcement, theater, live performances, DJ and other situations where lots of loud deep bass is needed and transient response is less critical.
Bandpass - Dual Chamber Vented/Sealed 4th Order
Basic Theory
The front and the rear of the driver are housed in their own separate and distinct enclosures. The front of the driver is in a ported enclosure while the rear of the driver is in a sealed enclosure. The driver may be mounted the other way around however as long as one chamber is sealed while the other is vented. The enclosure is designed as a sealed enclosure but with the addition of an acoustic filter (the port) in series with the front of the driver that acts to limit the driver's bandwidth and therefore increase its SPL capabilities within its bandwidth.
Advantages Very low f3 is possible at the expense of lower efficiency and increased ripple. Extremely high SPL is also possible at the expense of a higher f3 and narrower bandwidth. Less overall driver excursion. More control over cone movement. Bandwidth and efficiency are inversely proportional.
Disadvantages Combined volume of both chambers results in large overall enclosures. Difficult to design properly. Results may vary substantially due to misalignment of both front and rear chambers as well as tuning frequency. Tend to have "one-note" bass, especially if designed or built poorly. In order to achieve a wide useable bandwidth, there must be some amount of mid-band ripple as well as decreased efficiency. Drivers can be easily blown due to high compression factors because of lowered cone motion and thereby exceeding the thermal limits of the driver before exceeding its mechanical limits. Bandwidth and efficiency are inversely proportional.
Best Applications Where the large size of enclosure is of little concern. In cars where the design calls for high SPL where the limited bandwidth which results can be increased due to cabin gain. The cabin gain will help achieve a flatter and wider bandwidth across the desired range while maintaining the increased SPL of the enclosure. Very popular in car applications for this reason.
Basic Theory
Widely popularized by Acoustic Research back in the 50’s. The driver is mounted in a completely sealed, airtight enclosure, generally with the front of the driver facing outward but is not restricted to this method only. The system is designed to achieve a desired Q factor which controls the response characteristics of the driver/enclosure combination and usually ranging between 0.5 and 1.5. The total system Q (also known as Qtc) is dependent upon: volume of enclosure, T/S parameters of driver and internal treatment compounds including insulation, stuffing or wall-deadening materials. Best suited for drivers with an EBP of 50.0 or lower and drivers with Qts values above 0.40 but is not restricted to these exact alignments. Cutoff rate is about 12 dB/octave below f3, however higher system Q's result is a somewhat sharper roll-off while lower system Q's result in a slightly more shallow roll-off varying by about +/- 2 dB. Better damping and better transients is achieved by shooting for a lower system Q which can be accomplished by either making the enclosure larger or by adding stuffing/damping material such as polyfill, Dacron, fiberglass, acoustic foam, or any other suitable type of fill material. Box stuffing will also affect f3 by either raising it or lowering it depending upon the type and amount of stuffing used.
Advantages
Sealed enclosures are the simplest of all designs. They are easy to model with speaker software and it's easy to achieve predicted results. Box size and shape are generally the least complex. Great for both beginning and advanced DIY’ers. The exact response characteristics which are desired can be achieved by simply designing for a particular Qtc. You can alter its performance by varying the size of the enclosure and the amount of stuffing material used. Qtc ranges from 0.5 to 1.5 while 0.7 is generally considered ideal however some drivers may perform better (i.e., sound better) with Qtc values less than 0.7, especially where the driver dictates a smaller-than-optimal box at Qtc=0.7.. Slowest of all cutoff rates below fB of 12 db/octave. This results in much quicker group delay responses ranging from 1ms – 10 ms. Fast, quick, natural, smooth, tight, accurate, controlled and warm are some common terms that audiophiles use to describe sealed enclosures. Transient response is the best of all enclosure types. The excursion of the driver increases as the frequency applied decreases until fB is reached after which the driver excursion begins to decrease once again. There's no need for subsonic filtering due to the enclosure’s natural tendency to inhibit extremely low frequencies. This results in less bottoming out of drivers at subsonic frequencies. However as the enclosure size gets larger, more Xmax is required for any given input power. More extended low frequency response than vented enclosures given the same f3 for both. Phase shift is minimal within its normal operating frequency range.
Disadvantages
Very low frequency output is minimal. The f3 also know as (3dB down poin) is usually fairly high, above 30 Hz in most applications. Less power efficiency by about –3 dB as compared with vented enclosures. Lower over SPL capabilities. There's a strong need for drivers with a very large Xmax in order to ensure safe operation at least down to fB, especially if the box is designed for Qtc values
Best Applications
Best suited where a completely uncompromised sound quality is desired. Best for classical music and most rock and pop type music. Most widely used in car stereo systems where cabin gain can make up for its lack of low end
Ported - 4th Order Vented
Basic Theory
Also known as bass-reflex or ported. The driver is mounted into an enclosure which houses a large opening, port, vent or slot that extends into the cabinet a specified length. The length and size of this vent are extremely critical to the proper function of this enclosure. The port and driver contribute together to provide the desired response characteristic. The driver is generally mounted with the front facing outwards, but is not restricted to this method only. The vent which extends into the cabinet tunes the enclosure to a specific frequency (known as fB) thereby acting as a high pass filter on the driver. Driver excursion is at its minimum at fB where the vent then takes over and does most of the work. Cut-off rate below fB is 24 dB/octave but can be varied up or down 5-6 dB depending upon the exact tuning frequency and volume of the enclosure. There are various types of alignments that all fit into the ported 4th order category. Some common types are QB3, EBS, SBB4 and SC4. By varying the enclosure size and the tuning frequency, it is possible to achieve a variety of distinct low frequency performances from a single driver. The vent acts by damping the load produced by the driver above fB causing it to behave somewhat as if it were in a sealed enclosure. Best suited for drivers with an EBP near 100.0 or higher and Qts
Advantages Extended low frequency response. 3 dB down points (f3) are capable of being near or even below 20 Hz. Increased power handling above fB due to reduced driver excursion at and while nearing fB. More efficient system. Generally 3dB increased output over sealed enclosures due to the combined output of driver and port. More overall SPL capabilities. Deep, powerful, full, loud, inspiring, incredible, and earth shattering are common terms associated with vented enclosures.
Disadvantages
Larger enclosure size. More difficult to accurately achieve predicted results. Misaligned enclosures can result in very poor bass quality. Very accurate T/S parameters of actual driver is required. Although sometimes you can get away with using manufacture’s specifications. Driver unloading or bottoming out below fB is very common. Xmax is reached easily below fB and may cause sever damage the the driver's suspension, voice coil or cone. This usually requires the need to install additional high pass filtering below fB. But is not a always a necessity as long as power levels and frequency content are kept within reason. Transient response is degraded, yielding typical group delay curves as high as 50 ms. Muggy, boomy, sluggish, one-note, slow, and inaccurate are common terms associated with vented enclosures. Port diameter must be large to avoid unwanted port noise, which in turn requires the port to be long for any given Fb, which then drives up the volume of the enclosure, sometimes to undesirably large proportions.
Best Applications Where the deepest and loudest bass is necessary. Where size is not a huge issue but may still be a definite factor. For Home Theater and music. May be best suited for sound reinforcement, theater, live performances, DJ and other situations where lots of loud deep bass is needed and transient response is less critical.
Bandpass - Dual Chamber Vented/Sealed 4th Order
Basic Theory
The front and the rear of the driver are housed in their own separate and distinct enclosures. The front of the driver is in a ported enclosure while the rear of the driver is in a sealed enclosure. The driver may be mounted the other way around however as long as one chamber is sealed while the other is vented. The enclosure is designed as a sealed enclosure but with the addition of an acoustic filter (the port) in series with the front of the driver that acts to limit the driver's bandwidth and therefore increase its SPL capabilities within its bandwidth.
Advantages Very low f3 is possible at the expense of lower efficiency and increased ripple. Extremely high SPL is also possible at the expense of a higher f3 and narrower bandwidth. Less overall driver excursion. More control over cone movement. Bandwidth and efficiency are inversely proportional.
Disadvantages Combined volume of both chambers results in large overall enclosures. Difficult to design properly. Results may vary substantially due to misalignment of both front and rear chambers as well as tuning frequency. Tend to have "one-note" bass, especially if designed or built poorly. In order to achieve a wide useable bandwidth, there must be some amount of mid-band ripple as well as decreased efficiency. Drivers can be easily blown due to high compression factors because of lowered cone motion and thereby exceeding the thermal limits of the driver before exceeding its mechanical limits. Bandwidth and efficiency are inversely proportional.
Best Applications Where the large size of enclosure is of little concern. In cars where the design calls for high SPL where the limited bandwidth which results can be increased due to cabin gain. The cabin gain will help achieve a flatter and wider bandwidth across the desired range while maintaining the increased SPL of the enclosure. Very popular in car applications for this reason.
