Ported VS. Sealed enclosure

Discussion in 'ICE -In Car Entertainment' started by appleyard, Mar 1, 2005.

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  1. appleyard

    appleyard Senior Member
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    ok since most of you will argue about what enclosure is the best out there lets have a discussion on it. Any opinions are welcome but pls give facts over fiction.

    i copied an articles about it. Read and share your view:


    Ported systems are all around good performers, and most commercial home speakers use some type of ported enclosure. Automotive subwoofer manufacturers also like the ported enclosure, and most design drivers for this type of installation. The tuned port in these systems increases efficiency by nearly 3 dB in an optimum enclosure, and the roll-off frequency can be much lower, often by as much as 1/3 - 1 octave below a sealed enclosure. Think of the extra 3 dB as equal to the output you would get using twice the amplifier power on the driver. Add several ported drivers together and you can achieve impressive SPL's indeed! Because of the ports damping characteristics on the driver above Fb, distortion levels are also lowered because driver excursion is less. So, with nothing more than a properly designed optimum vented enclosure, you have very efficient bass reproduction with several advantages over an optimum sealed enclosure.

    So, why in the world would anyone waste the time designing and building a sealed enclosure? Like anything, there are compromises in all designs, and ported systems are no exception. A very clear advantage for a sealed enclosure is simplicity - you can get good performance with nearly any driver with an EBP of less than 90 in a simple sealed box. Enclosure volume is not critical with these designs, and a volume change of +/- 10 - 20% will not adversely affect the sound. Ported boxes must be fairly precise in volume and tuning. Consider also the fact that sealed boxes have very gentle roll-off characteristics after F3 at -12 dB/octave. Because ported system cut-off is a steep -24 dB/octave, often lower bass can be realized with a sealed design even if the ported F3 is lower. (Note: attenuation slopes after cutoffs are almost never exactly these values, and may be steeper or more gentle depending on alignments).

    On the downside, a sealed driver reaches maximum excursion at resonance, which adds considerably to the distortion produced at high output levels. A ported system receives maximum damping at resonance, with minimal driver excursion. The port "takes over" at Fb, and the driver hardly moves at all. This minimizes low frequency distortion, but ported systems progressively lose damping from the enclosure the lower you go below Fb, which amounts to a loss of control for the driver at very low frequencies. This is definitely a factor to consider if you are planning on building a ported system much smaller than optimum, as the tuning frequency may approach 50+ Hz, a frequency generally considered quite usable by most listeners. Subsonic filters can help with this unloading experienced with some ported systems.

    While a ported enclosure is damped by the port at resonance, the sealed enclosure is wholly dependent upon the air trapped behind it in the enclosure. Once placed in the enclosure, the Fs turns into Fc, or the box/driver resonant frequency. The air in the box acts as a restoring force upon the driver cone, with a larger Vb usually meaning the driver can respond to lower frequencies (to a point).



    so what do you think? B)
     
  2. Yong_5290

    Yong_5290 Senior Member
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    wah...tis 1 need sq sifu 2 xplain y they choose sealed...

    me not hiding bhind of ppl ok....coz 4 me...of coz i'll go 4 ported...

    1st...i like to char kei...techno....
    2nd...wat i wan is loud..SPL....but thumping bass...tight n solid...
    3rd...so if i wan SPL...sure i need ported enclosure 2 get those xtra 3dB spl..
    4th...of coz i like those bandpass design...hehee...very nice :P
     
  3. kenlimfornication

    kenlimfornication Senior Member
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    are there any pics of sealed and ported enclosures?
     
  4. Yong_5290

    Yong_5290 Senior Member
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    erm..sealed enclosure...no hole on the enclosure

    ported...the other way round...got hole
     
  5. mattrig

    mattrig Senior Member
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    thanx for the info appleyard.looking at home hi-fi system the speaker c/w ported box but why for ice(sq) most ppl go enclosed type?i think ported also can play sq.may becoz everybody going for bass up front.for me tonality is my priority coz i'm not into any competition :P .let hear from other sifu.....this is newbie opinion only :ph34r:
     
  6. normality78

    normality78 Senior Member
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    someone PM me before to ask abt this question.

    So bro, this is what u r looking for. hope u will find ur answer here
     
  7. appleyard

    appleyard Senior Member
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    more on what i found.

    Sealed
    - Easy to design and build

    - Very forgiving of errors in design and construction

    - High power handling but one of the least efficient enclosure designs.

    - Tight bass with excellent transient response, maximum driver excursion at resonant frequency and higher distortion levels.

    - Gentle roll-off after F3 @ -12 dB/octave.

    - Driver retains enclosure damping below Fc.

    - Unless driver is specially designed for a small optimum sealed enclosure, the optimum alignment may require a large box.

    Ported
    - Fairly easy to design and build, may take some time to tune properly.

    - Enclosure must be fairly precise to attain desired performance
    - More efficient than sealed, need less amplifier to get higher SPL's.

    - Good transient response with optimum alignments, minimal driver excursion at resonant frequency and reduced distortion.

    - F3 can be set much lower than a sealed enclosure, but roll-off after F3 is @ -24 dB/octave.

    - Driver loses enclosure damping below Fb, and may lose control with very low frequencies.

    - Unless driver is specially designed for a small optimum ported enclosure, the optimum alignment may require a very large box.
     
  8. appleyard

    appleyard Senior Member
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    TS parameter explained.

    The compliance, Vas, is a measure of the overall stiffness of the cone, surround (the part the attaches to front of the cone), and spider (the part that attaches to the rear of the cone). It is specified as the volume of air having the same compliance as the driver. A small number corresponds to a small volume of air, which is stiffer than a larger volume of air. Thus, compliance and stiffness are inversely proportional. Optimum enclosure volume is proportional to Vas.

    Free-air resonance, Fs, is the resonant frequency of the driver's voice coil impedance with the driver suspended in free air (no enclosure). The -3 dB frequency (F3) of an enclosure is proportional to Fs.

    The Q, Qts, is a measure of the sharpness of the driver's free-air resonance. It is defined as (Fh-Fl)/Fs, where Fh and Fl are the upper and lower -3 dB points of the driver's voice coil impedance in free air. Optimum enclosure volume is related to Qts but is not directly proportional. It is accurate to say that the volume gets larger as Qts gets larger. Likewise, F3 gets smaller as Qts gets larger, and for the sealed box enclosure, F3 is inversely proportional to Qts.

    The Physical Characteristics of a speaker are:

    Re: The D.C. resistance of the voice coil measured in Ohms.

    Sd: The surface area of the speaker’s cone.

    BL: The magnetic strength of the motor structure.

    Mms: The total moving mass of the speaker including the small amount of air in front of and behind the cone.

    Cms: The stiffness of the driver’s suspension.

    Rms: The losses due to the suspension.

    By understanding the relationship of these physical parameters and how to change them, we may alter the response parameters to fit the desired goal.

    The Thiele/Small Response parameters are:

    Re: The D.C. resistance of the voice coil measured in Ohms.

    Sd: The surface area of the speaker.

    Fs: The resonant frequency of the speaker.

    Qes: The electrical “Q” of the speaker.

    Qms: The mechanical “Q” of the speaker.

    Qts: The total “Q” of the speaker.

    Vas: The volume of air having the same acoustic compliance as the speaker’s suspension.

    Fs This parameter is the free-air resonant frequency of a speaker. Simply stated, it is the point at which the weight of the moving parts of the speaker becomes balanced with the force of the speaker suspension when in motion. If you've ever seen a piece of string start humming uncontrollably in the wind, you have seen the effect of reaching a resonant frequency. It is important to know this information so that you can prevent your enclosure from 'ringing'. With a loudspeaker, the mass of the moving parts, and the stiffness of the suspension (surround and spider) are the key elements that affect the resonant frequency. As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. This is not always the case though, because other parameters affect the ultimate performance as well.

    Re This is the DC resistance of the driver measured with an ohm meter and it is often referred to as the 'DCR'. This measurement will almost always be less than the driver's nominal impedance. Consumers sometimes get concerned the Re is less than the published impedance and fear that amplifiers will be overloaded. Due to the fact that the inductance of a speaker rises with a rise in frequency, it is unlikely that the amplifier will often see the DC resistance as its load.

    Le This is the voice coil inductance measured in millihenries (mH). The industry standard is to measure inductance at 1,000 Hz. As frequencies get higher there will be a rise in impedance above Re. This is because the voice coil is acting as an inductor. Consequently, the impedance of a speaker is not a fixed resistance, but can be represented as a curve that changes as the input frequency changes. Maximum impedance (Zmax) occurs at Fs.


    Q Parameters Qms, Qes, and Qts are measurements related to the control of a transducer's suspension when it reaches the resonant frequency (Fs). The suspension must prevent any lateral motion that might allow the voice coil and pole to touch (this would destroy the loudspeaker). The suspension must also act like a shock absorber. Qms is a measurement of the control coming from the speaker's mechanical suspension system (the surround and spider). View these components like springs. Qes is a measurement of the control coming from the speaker's electrical suspension system (the voice coil and magnet). Opposing forces from the mechanical and electrical suspensions act to absorb shock. Qts is called the 'Total Q' of the driver and is derived from an equation where Qes is multiplied by Qms and the result is divided by the sum of the same.
    As a general guideline, Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and 0.7 indicates suitability for a sealed enclosure. Qts of 0.7 or above indicates suitability for free-air or infinite baffle applications. However, there are exceptions! The Eminence Kilomax 18 has a Qts of 0.56. This suggests a sealed enclosure, but in reality it works extremely well in a ported enclosure. Please consider all the parameters when selecting loudspeakers. If you are in any doubt, contact your Eminence representative for technical assistance.

    Vas/Cms Vas represents the volume of air that when compressed to one cubic meter exerts the same force as the compliance (Cms) of the suspension in a particular speaker. Vas is one of the trickiest parameters to measure because air pressure changes relative to humidity and temperature — a precisely controlled lab environment is essential. Cms is measured in meters per Newton. Cms is the force exerted by the mechanical suspension of the speaker. It is simply a measurement of its stiffness. Considering stiffness (Cms), in conjunction with the Q parameters gives rise to the kind of subjective decisions made by car manufacturers when tuning cars between comfort to carry the president and precision to go racing. Think of the peaks and valleys of audio signals like a road surface then consider that the ideal speaker suspension is like car suspension that can traverse the rockiest terrain with race-car precision and sensitivity at the speed of a fighter plane. It’s quite a challenge because focusing on any one discipline tends to have a detrimental effect on the others.

    Vd This parameter is the Peak Diaphragm Displacement Volume — in other words the volume of air the cone will move. It is calculated by doubling Xmax (Voice Coil Overhang of the driver) then multiplying the result by Sd (Surface area of the cone). Vd is noted in cc. The highest Vd figure is desirable for a sub-bass transducer.

    BL Expressed in Tesla meters, this is a measurement of the motor strength of a speaker. Think of this as how good a weightlifter the transducer is. A measured mass is applied to the cone forcing it back while the current required for the motor to force the mass back is measured. The formula is mass in grams divided by the current in amperes. A high BL figure indicates a very strong transducer that moves the cone with authority!

    Mms This parameter is the combination of the weight of the cone assembly plus the ‘driver radiation mass load’. The weight of the cone assembly is easy: it’s just the sum of the weight of the cone assembly components. The driver radiation mass load is the confusing part. In simple terminology, it is the weight of the air (the amount calculated in Vd) that the cone will have to push.

    Rms This parameter represents the mechanical resistance of a driver’s suspension losses. It is a measurement of the absorption qualities of the speaker suspension and is stated in N*sec/m.

    EBP This measurement is calculated by dividing Fs by Qes. The EBP figure is used in many enclosure design formulas to determine if a speaker is more suitable for a closed or vented design. An EBP close to 100 usually indicates a speaker that is best suited for a vented enclosure. On the contrary, an EBP closer to 50 usually indicates a speaker best suited for a closed box design. This is merely a starting point. Many well-designed systems have violated this rule of thumb! Qts should also be considered.

    Xmax/Xmech Short for Maximum Linear Excursion. Speaker output becomes non-linear when the voice coil begins to leave the magnetic gap. Although suspensions can create non-linearity in output, the point at which the number of turns in the gap (see BL) begins to decrease is when distortion starts to increase. Eminence has historically been very conservative with this measurement and indicated only the voice coil overhang (Xmax: Voice coil height minus top plate thickness, divided by 2). Xmech is expressed by Eminence as the lowest of four potential failure condition measurements times 2: Spider crashing on top plate; Voice coil bottoming on back plate; Voice coil coming out of gap above core; Physical limitation of cone. Take the lowest of these measurements then multiply it by two. This gives a distance that describes the maximum mechanical movement of the cone.

    Usable frequency range This is the frequency range for which Eminence feels the transducer will prove useful. Manufacturers use different techniques for determining ‘Usable Frequency Range’. Most methods are recognized as acceptable in the industry, but can arrive at different results. Technically, many loudspeakers are used to produce frequencies in ranges where they would theoretically be of little use. As frequencies increase, the off-axis coverage of a transducer decreases relative to its diameter. At a certain point, the coverage becomes ‘beamy’ or narrow like the beam of a flashlight. Following is a chart that demonstrates at what frequency this phenomenon occurs relative to the size of the transducer. If you’ve ever stood in front of a guitar amplifier or speaker cabinet, then moved slightly to one side or the other and noticed a different sound, you have experienced this phenomenon and are now aware of why it occurs. Clearly, most two-way enclosures ignore the theory and still perform quite well. The same is true for many guitar amplifiers, but it is useful to know at what point you can expect a compromise in coverage.

    Power handling This specification is very important to transducer selection. Obviously, you need to choose a loudspeaker that is capable of handling the input power you are going to provide. By the same token, you can destroy a loudspeaker by using too little power. The ideal situation is to choose a loudspeaker that has the capability of handling more power than you can provide lending some headroom and insurance against thermal failure. To use an automobile as an analogy; you would not buy a car that could only go 55mph if that were the speed you always intended to drive. Generally speaking, the number one contributor to a transducer’s power rating is its ability to release thermal energy. This is affected by several design choices, but most notably voice coil size, magnet size, venting, and the adhesives used in voice coil construction. Larger coil and magnet sizes provide more area for heat to dissipate, while venting allows thermal energy to escape and cooler air to enter the motor structure. Equally important is the ability of the voice coil to handle thermal energy. Eminence is renowned for its use of proprietary adhesives and components that maximize the voice coil’s ability to handle extreme temperatures. Mechanical factors must also be considered when determining power handling. A transducer might be able to handle 1,000W from a thermal perspective, but would fail long before that level was reached from a mechanical issue such as the coil hitting the back plate, the coil coming out of the gap, the cone buckling from too much outward movement, or the spider bottoming on the top plate. The most common cause of such a failure would be asking the speaker to produce more low frequencies than it could mechanically produce at the rated power. Be sure to consider the suggested usable frequency range and the Xmech parameter in conjunction with the power rating to avoid such failures. The Eminence power rating is derived using an EIA 426A noise source and test standard. All tests are conducted for eight hours in a free-air, non-temperature controlled environment. Eminence tests samples from each of three different production runs and each sample must pass a test exceeding the rated power by 50 to 100W. The Eminence peak power rating is double that of our standard RMS rating.


    Happy Reading :)
     
  9. appleyard

    appleyard Senior Member
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    usually ppl prefererred sealed than ported because they thought sealed will give you the most SQ with tighter bass.

    Ported usualy had a bad reputation because manufacturer (accessory shop too) build one ported box and dump any subs in the box and the result is a nightmare. Little they realize that all speakers are different, like human has a personality. So Each sub is speacialized for one box only while will sound good or average in other box.

    A sealed box is a quick solution for SQ which but little they know that sealed box with 0.8 qtc need like 6 cu. ft enclosure. And sealed box need higher power input from the amp becuase the sub may face resistance when moving as a result in air trapped inside the box.
     
  10. mattrig

    mattrig Senior Member
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    appleyard,
    wat du think....can ported box play sq if the box is build according to specs.looks like u need more power from amp to power the enclosed one.i think i want to go for ported coz less power and...less money to spend on amp :D .used to see one car (from xtream car mag) use ported box for his peerless sub (sq set up) :ph34r:
     
  11. xtorm

    xtorm Senior Member
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    hm...........js audio boss told me sealed is stil the best for sqwor........hmm, but i nvr try ported b4 with the same subie.....
     
  12. Yong_5290

    Yong_5290 Senior Member
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    easy...y dun we try 2 mail woofer manufacturer 2 ask them which type of enclosure most suitable 4 SQ
     
  13. km_chew

    km_chew Senior Member
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    How to get those low sound from the sub? sealed or ported?
     
  14. energie

    energie Senior Member
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    How low do you want to go?
     
  15. Bert

    Bert Senior Member
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    I wanna make the car next to me shake when I play a 20hz tone :P
     
  16. Charles

    Charles I brake very late....
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    Bert,
    How bad you want that car next to you shake? :P
     
  17. Bert

    Bert Senior Member
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    hehehe... if got cun chick then we try the 33hz test tone to see. :P
     
  18. km_chew

    km_chew Senior Member
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    what is the hz means?
     
  19. Bert

    Bert Senior Member
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    hz is the frequency which mean how many times second there is a vibration.
     
  20. appleyard

    appleyard Senior Member
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    i always like subs that play low and loud. Its like your car is falling apart.
     
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