an article about sub - box's
02-26-2002, 05:03 PM
#1
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an article about sub - box's
i (and i am kackarot) typed up something you guys would prolly want
heres the link
http://www.altimas.net/forum/showthr...threadid=25471
heres the link
http://www.altimas.net/forum/showthr...threadid=25471
02-26-2002, 05:04 PM
#2
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Join Date: Feb 2002
Location: AUSTIN BABY
Posts: 692
heres the article
Before you try to build you own box, you have to ask, "what makes a woofer woof..." Today's woofers come in many sizes and shapes, from a 4-inch bookshelf speaker woofer to a 72-inch outdoor concert system woofer. For mobile audio purposes, woofers tend to vary from 6 to 18 inches in diameter. Because woofer are designed for low frequencies, ofter those below the threshold of human hearing, they operate more like air pumps than air vibrators, such as typical speakers. Woofers must move air to produce low frequencies and there must be a means to push this air.
If you were to compare an automotive engine piston to a woofer, you can readily see that a piston outside of an engine cannot produce much energy. Not until the piston is installed in the cylinder sleeve does it become useful. The same holds true for low frequency speakers. If they're not installed in, or used with, some sort of baffle or enclosure, they're not as effective. The four most common enclosure types are listed below.
* Acoustic Suspension (sealed)
* Bass Reflex (ported)
* Infinite Baffle
* Bandpass
Acoustic Suspension
This type of enclosure is characterized by a sealed design with an internal volume of less than 1/3 of its VAS specification. This means that when a box is used with a volume of three times or less than that of the speaker's complicance (VAS), the system exhibits characteristics of an acoustic suspension system. The benefits of an acoustic suspension enclosure are traits such as good transient response and ease of enclosure construction. The low frequency response of this type of enclosure will be excellent with a roll off rate of about 12 dB per octave. This allows for deep extension of bass even below that of the theoretical cutoff frequency. Furthermore, when these types of enclosures are used in the automotive environment, they will benefit from acoustic coupling, otherwise referred to as Cabin Gain. Cabin Gain simply means the loading up of low frequencies in a vehicles interior.
Mind Your Q's
When designing and building sealed enclosures, there are a few variables that can be changed to modify a woffer's response. The first is box size. In a sealed enclosure, the air trapped inside the enclosure acts as a spring to the woffer. This, in turn, causes a rise in the woofer's primary resonant frequency and an increase in the response. By adding damping materials such as fiberglass, Dacon or wool, the box's Q can be lowered. This is a form of trickery in that, by adding these materials, the box will effectively increase in internal volume size to the woofer.
Confused? By adding these materials your're slowing down the rear acoustic wave of the woofer. This is achieved partially by changing the pneumatic apring action of the enclosure's air from adiabatic to isothermic. What this means is that the fibers absorb the energy coming from the back of the driver and then later release it in the form of heat. As the energy is absorbed, it's slowed down. With a slower speed of sound comes shorter wavelengths, which have the effect of making the enclosure seem larger (Don't you just love engineering?).
Don't overdo it on the filling. As the saying goes, too much of a good thing is too much of a good thing. As a rule of thumb, start with 1.5 pounds of damping material per cubic foot of enclosure. Be sure to leave enough breathing area behind the woofer so as not to restrict air motion directly behind the woofer. One method of keeping material away from the woofer is to staple a sheet of mesh material across the inside of the enclosure. By experimenting with different amounts of material, different responses can be measured.
Specification Spectacles
A speakers Q will be listed as the Qtc-specification on the woofers spec sheet. Here are some common Qtc specs and what you can expect from the woofer ahead of time.
Qtc = .5
Extremely tight bass. Low perceived level of bass. Not thought of as an efficient design as too much energy is dampened. A smooth response in upper bass frequencies makes this an excellent mid-bass woofer with good transient response.
Qtc = .7
Good tight bass response. A compromise between very tight and very strong bass. A common target for pudiophile home spaker designs.
Qtc = 1.0
Strong perceived bass output. Good target for certain autosound applications. Some transient response is compromised for oare bass output. Since the transient overshoot is much too high, this design is best suited for subwoofer applications only.
Qtc = 1.5 and greater
Very boomy bass output. An inexperienced listener may think this type of response has a lot of bass. This type of bass is a good target for those listeners who want to vibrate mini-truck camper shells
Bass Reflex (ported)
A bass reflex enclosure is a design in which a tube or port is implemented to utilize some of the internal box energy and to channel it out to enhance the direct radiator's output. This idea dates back to the '30's. Over the years, however, many improved methods have been derived by creating various port dimensions. Today we're able to utilize a type of forecasting method created by Neville Thiele and Richard Small (T-S). Thiele and Small published a series of formulas to help us forecast the speaker/enclosure relationship and estimate its output performance before the enclosure is built. Needless to say, this saves a lot of time and money.
A bass reflex enclosure is generally much larger in size then any other design. Unlike a sealed enclosure, which takes much more power to operate, bass relex enclosures are much more efficient in design. The drawbacks first being size and second being lack of producing tight bass rlative to that of a sealed design.
A well-designed bass reflex enclosure can produce twice as much perceived bass output as a sealed enclosure, given the same type of driver and power.
Even with today's advanced computer programs it's difficult to predict exactly how an enclosure will perform in your particular vehicle. Be prepared to play with various lenghts and diameters of ports when attempting this application.
Bandpass
Bandpass enclosures (sometimes called 7th or 6th order enclosures), have been around for some time now - documentation dates back to the '50's. In this application, the woofer is entirely enclosed with either a singled sealed chamber and a front ported champer, or a dual-ported design. This is a unique design in that the woofer does not directly radiate into the listening environment. Instead, it passes through one, or more, ports. Because of this, the output and overall tune of the enclosure can be greatly tailored.
If you're not trying to create really deep or precise bass, but rather are focused on achieving maximum output, bandpass designs are a novel way to achieve your goals.
Bandpass enclosures are notorious for destroying woofers due to the speakers sensitivity to design flaws. Unfortunately, these design flaws rarely show themselves until its too late.
Infinite Baffle
This is without a doubt the simplest type of enclosure. And it's not really an enclosure at all. The aim here is to isolate the front and rear outputs of the woofer by utilizing the rear deck of a car or a truck bed/cab. For car owners this may be a more viable method of installing woofers. However, dont expect nearly the performance of a sealed or ported enclosure in its reproduction of its bass.
sources
Soundstream technologies
heavyweight boxing manual
If you were to compare an automotive engine piston to a woofer, you can readily see that a piston outside of an engine cannot produce much energy. Not until the piston is installed in the cylinder sleeve does it become useful. The same holds true for low frequency speakers. If they're not installed in, or used with, some sort of baffle or enclosure, they're not as effective. The four most common enclosure types are listed below.
* Acoustic Suspension (sealed)
* Bass Reflex (ported)
* Infinite Baffle
* Bandpass
Acoustic Suspension
This type of enclosure is characterized by a sealed design with an internal volume of less than 1/3 of its VAS specification. This means that when a box is used with a volume of three times or less than that of the speaker's complicance (VAS), the system exhibits characteristics of an acoustic suspension system. The benefits of an acoustic suspension enclosure are traits such as good transient response and ease of enclosure construction. The low frequency response of this type of enclosure will be excellent with a roll off rate of about 12 dB per octave. This allows for deep extension of bass even below that of the theoretical cutoff frequency. Furthermore, when these types of enclosures are used in the automotive environment, they will benefit from acoustic coupling, otherwise referred to as Cabin Gain. Cabin Gain simply means the loading up of low frequencies in a vehicles interior.
Mind Your Q's
When designing and building sealed enclosures, there are a few variables that can be changed to modify a woffer's response. The first is box size. In a sealed enclosure, the air trapped inside the enclosure acts as a spring to the woffer. This, in turn, causes a rise in the woofer's primary resonant frequency and an increase in the response. By adding damping materials such as fiberglass, Dacon or wool, the box's Q can be lowered. This is a form of trickery in that, by adding these materials, the box will effectively increase in internal volume size to the woofer.
Confused? By adding these materials your're slowing down the rear acoustic wave of the woofer. This is achieved partially by changing the pneumatic apring action of the enclosure's air from adiabatic to isothermic. What this means is that the fibers absorb the energy coming from the back of the driver and then later release it in the form of heat. As the energy is absorbed, it's slowed down. With a slower speed of sound comes shorter wavelengths, which have the effect of making the enclosure seem larger (Don't you just love engineering?).
Don't overdo it on the filling. As the saying goes, too much of a good thing is too much of a good thing. As a rule of thumb, start with 1.5 pounds of damping material per cubic foot of enclosure. Be sure to leave enough breathing area behind the woofer so as not to restrict air motion directly behind the woofer. One method of keeping material away from the woofer is to staple a sheet of mesh material across the inside of the enclosure. By experimenting with different amounts of material, different responses can be measured.
Specification Spectacles
A speakers Q will be listed as the Qtc-specification on the woofers spec sheet. Here are some common Qtc specs and what you can expect from the woofer ahead of time.
Qtc = .5
Extremely tight bass. Low perceived level of bass. Not thought of as an efficient design as too much energy is dampened. A smooth response in upper bass frequencies makes this an excellent mid-bass woofer with good transient response.
Qtc = .7
Good tight bass response. A compromise between very tight and very strong bass. A common target for pudiophile home spaker designs.
Qtc = 1.0
Strong perceived bass output. Good target for certain autosound applications. Some transient response is compromised for oare bass output. Since the transient overshoot is much too high, this design is best suited for subwoofer applications only.
Qtc = 1.5 and greater
Very boomy bass output. An inexperienced listener may think this type of response has a lot of bass. This type of bass is a good target for those listeners who want to vibrate mini-truck camper shells
Bass Reflex (ported)
A bass reflex enclosure is a design in which a tube or port is implemented to utilize some of the internal box energy and to channel it out to enhance the direct radiator's output. This idea dates back to the '30's. Over the years, however, many improved methods have been derived by creating various port dimensions. Today we're able to utilize a type of forecasting method created by Neville Thiele and Richard Small (T-S). Thiele and Small published a series of formulas to help us forecast the speaker/enclosure relationship and estimate its output performance before the enclosure is built. Needless to say, this saves a lot of time and money.
A bass reflex enclosure is generally much larger in size then any other design. Unlike a sealed enclosure, which takes much more power to operate, bass relex enclosures are much more efficient in design. The drawbacks first being size and second being lack of producing tight bass rlative to that of a sealed design.
A well-designed bass reflex enclosure can produce twice as much perceived bass output as a sealed enclosure, given the same type of driver and power.
Even with today's advanced computer programs it's difficult to predict exactly how an enclosure will perform in your particular vehicle. Be prepared to play with various lenghts and diameters of ports when attempting this application.
Bandpass
Bandpass enclosures (sometimes called 7th or 6th order enclosures), have been around for some time now - documentation dates back to the '50's. In this application, the woofer is entirely enclosed with either a singled sealed chamber and a front ported champer, or a dual-ported design. This is a unique design in that the woofer does not directly radiate into the listening environment. Instead, it passes through one, or more, ports. Because of this, the output and overall tune of the enclosure can be greatly tailored.
If you're not trying to create really deep or precise bass, but rather are focused on achieving maximum output, bandpass designs are a novel way to achieve your goals.
Bandpass enclosures are notorious for destroying woofers due to the speakers sensitivity to design flaws. Unfortunately, these design flaws rarely show themselves until its too late.
Infinite Baffle
This is without a doubt the simplest type of enclosure. And it's not really an enclosure at all. The aim here is to isolate the front and rear outputs of the woofer by utilizing the rear deck of a car or a truck bed/cab. For car owners this may be a more viable method of installing woofers. However, dont expect nearly the performance of a sealed or ported enclosure in its reproduction of its bass.
sources
Soundstream technologies
heavyweight boxing manual
08-19-2002, 12:04 PM
#5
Contributing Member
Join Date: Jul 2002
Location: Queens NY
Posts: 838
i like sound systems... especially when i go to car shows.. man there are some really creative people... .... the best sound systems are located in big suv's in my opinion... damn pimps and their escalades and navigators
09-25-2002, 11:21 AM
#13
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Join Date: Feb 2002
Location: AUSTIN BABY
Posts: 692
Originally posted by m3dia_lab
the w7 is not as bad *** as everyone thinks it is, the mtx 8000 line is louder (spl) than a w7 for almost 1/2 the price....
the w7 is not as bad *** as everyone thinks it is, the mtx 8000 line is louder (spl) than a w7 for almost 1/2 the price....
05-30-2003, 05:55 PM
#14
Registered User
Join Date: May 2003
Location: So-Cal
Posts: 192
well as soon as i can afford it, im plannin on getting a custom box made for my car (show quality) and im thinkin either 4 10's or 3 12's... or maybe a mix... any ideas? will 4 10s even fit? (gotta save some amp room too) maybe 1 12 and 2 10s? ;x SO MANY CHOICES!!! 
