How big? Solid stone or brick etc?
Any mediation work such as bass traps or drapes ?
All have a bearing as usually the room effects dominate.
My wife is tolerant but draws a line at 18 inch subs in the lounge room, she thinks even 15s take up too much real estate
Any mediation work such as bass traps or drapes ?
All have a bearing as usually the room effects dominate.
My wife is tolerant but draws a line at 18 inch subs in the lounge room, she thinks even 15s take up too much real estate
You should ask what kind of sub has been used in this room and proven to be too weak. Most "HIFI-people" can not imagine what two 18" drivers do in a small room. They do not realize that effiency rises with cone diameter, so the same amp power is much louder than with a small sub.
Also the 4 Ohm /8 Ohm thing in practice is much less dramatic than they expect.
Under living room conditions a single, well designed 15" should work quite well, even for extreme loud music reproduction.
Also the 4 Ohm /8 Ohm thing in practice is much less dramatic than they expect.
Under living room conditions a single, well designed 15" should work quite well, even for extreme loud music reproduction.
My wife loves filthy techno rumbles..... But then again, she is a right dirty bitch (eyeroll)
Okay, I have much to reply to here..... I do not know how to multi-quote on this forum, I would like to touch base with everyone who has posted.
I suppose I will begin by replying in chronological order, oldest first.
@ GM in Post # 11 upthread ^^^^^^^
Excuse my ugly post but I have to quote some of your remarks like so ----->
"Vas/1.44 tuned to Fs"
"Note too that Vb = Vas/1.44"
"This optimum volume does not depend upon the size of the speaker nor its resonant frequency per se but rather on the ratio of enclosure air stiffness
to the speaker cone suspension stiffness. This optimum ratio is 1.44"
I went over this a number of times, looking and scratching and pondering the evils of the world.
Next, I inputted my own Vas (201.1 litres), and this number, divided by 1.44 gave me an insanely small box (140 litres), that just didn't check out.
I modelled many small boxes against the Faital Pro 18XL1600-C drivers in WinISD, including a bunch where I just lobbed the driver into a small box
simulation and drove the box tuning frequency off the scale to see what would happen.
The Frequency Response SPL graphs had insane peaks but all the bass just wasn't there.... Missing.... Gone, and nothing I could do would bring it back.
Hmmm !!
I modelled quite a few small enclosures at 50... 60.... 70.... 80Hz..... This created an awesome SPL on a full range speaker with a Fs of 39
and it beat the total crap out of my Faital Pro monster woofers (over 3 times the monitors power) everywhere above 45=50Hz.
Great on the tops..... Absolutely useless for the subs.
(eyeroll)
But then I noticed something..... If I divide my Vas (201.1 litres) into my box volume (290 litres), which is effectively the force of the air "thrown
off the cone" against the volume of air already in the enclosure (we'll call this "the brake")....
I get a magic result of 1.444803
WOAH !! That couldn't bee a coincidence..... This is good, no.....?
Okay, that'll do for now...... And just for the benefit of the forum, I am going to drop this below.....
Okay, I have much to reply to here..... I do not know how to multi-quote on this forum, I would like to touch base with everyone who has posted.
I suppose I will begin by replying in chronological order, oldest first.
@ GM in Post # 11 upthread ^^^^^^^
Excuse my ugly post but I have to quote some of your remarks like so ----->
"Vas/1.44 tuned to Fs"
"Note too that Vb = Vas/1.44"
"This optimum volume does not depend upon the size of the speaker nor its resonant frequency per se but rather on the ratio of enclosure air stiffness
to the speaker cone suspension stiffness. This optimum ratio is 1.44"
I went over this a number of times, looking and scratching and pondering the evils of the world.
Next, I inputted my own Vas (201.1 litres), and this number, divided by 1.44 gave me an insanely small box (140 litres), that just didn't check out.
I modelled many small boxes against the Faital Pro 18XL1600-C drivers in WinISD, including a bunch where I just lobbed the driver into a small box
simulation and drove the box tuning frequency off the scale to see what would happen.
The Frequency Response SPL graphs had insane peaks but all the bass just wasn't there.... Missing.... Gone, and nothing I could do would bring it back.
Hmmm !!
I modelled quite a few small enclosures at 50... 60.... 70.... 80Hz..... This created an awesome SPL on a full range speaker with a Fs of 39
and it beat the total crap out of my Faital Pro monster woofers (over 3 times the monitors power) everywhere above 45=50Hz.
Great on the tops..... Absolutely useless for the subs.
(eyeroll)
But then I noticed something..... If I divide my Vas (201.1 litres) into my box volume (290 litres), which is effectively the force of the air "thrown
off the cone" against the volume of air already in the enclosure (we'll call this "the brake")....
I get a magic result of 1.444803
WOAH !! That couldn't bee a coincidence..... This is good, no.....?
Okay, that'll do for now...... And just for the benefit of the forum, I am going to drop this below.....
Last edited:
Double post.....
DESIGNING A DUCTED-PORT ENCLOSURE
James F. Novak,
Senior Engineer,
Jensen Mfg. Div.,
The Muter Company,
The author has researched this subject thoroughly. The following material is reprinted with his permission.
Reprinted in part from January, 1966, issue of Electronics World
Optimum Enclosure Size
"A careful study of bass-reflex operation from a theoretical standpoint reveals a complexity far greater than the extremely simple
construction would indicate. A number of generally unknown facts come to light concerning low-frequency extension and optimum
transient response.
"l. A bass-refiex enclosure can be too large. After a certain maximum volume is reached, further volume increases result in 'boomy"
bass rather than an appreciable extension of low-frequency response. This is particularly true when a speaker with a small magnet is used.
It is best to use a completely closed cabinet in this case.
"2. A bass-refiex enclosure can also be too small. A common assumption is that the enclosure can be made much smaller by using
a duct behind the port. While the use of a duct allows one to tune the enclosure to very low frequencies when volumes are small,
it is the ratio of enclosure air stiffness to speaker stiffness that determines the low-frequency cut-off.
As the enclosure volume is made smaller, the enclosure stiffness increases and so does the cut-off-frequency.
This will remain true regardless of how the enclosure is tuned.
A false "boomy" bass will generally result and the enclosure may as well be left closed. In some cases a better sounding
bass will result if the back of the speaker enclosure is removed.
"A nagging question in the design stage of any enclosure of this type is "How large shall it be?" It was pointed out earlier that the
enclosure can be too large or too small for proper bass-reflex action.
This implies that an optimum volume exists and indeed it does.
This optimum volume does not depend upon the size of the speaker nor its resonant frequency per se but rather on the ratio of enclosure
air stiffness to the speaker cone suspension stiffness.
This optimum ratio is 1.44 or, looking at it another way, the speaker resonant frequency in the enclosure before porting should be 1.56 times the
free-air resonance of the speaker. This size enclosure, when properly tuned, yields at the same time the most extended low-frequency
response and a transient response with subjectively unnoticeable hangover, assuming sufficient damping exists.
Compared to the entirely closed cabinet, the half-power point (3 db down) occurs at 0.7 times the closed cabinet speaker resonance for an extension
of one-half octave.
Only one condition of cabinet tuning and damping will result in optimum transient response, i.e., "freedom from hangover or boom".
Because a speaker in a bass-reflex forms a closely coupled system of two tuned circuits, the system will tend to decay with two frequencies.
The achievement of optimum transient response demands that the system decay with one frequency and with a specified time constant.
In order to make the system decay in one frequency, the enclosure volume and port combination must be tuned to the free-air resonance of the speaker.
A specified decay can be achieved by adding acoustic resistance, in the form of damping material, to
the enclosure. The proper amount of damping material can be determined
by means of a test method described later.
BASS REFLEX DEFINED
From : How to Build Speaker Enclosures
Alexis Badmaieff and Don Davis (1966)
The phase-inversion enclosure allows the back radiation to be usefully added to the output of the front radiation. This improves
the low-frequency response of the system. The mechanics of this process may be described as follows: The entrapped air volume
of the enclosure is used as an extension of the cone to move a volume of entrapped air in a port or opening
APPROXIMATELY EQUAL TO THE AREA OF THE AIR DISPLACED BY THE FRONT OF THE CONE
The air volume in the enclosure acts as a "spring" coupling the back of the cone to the "cone" of air entrapped in the port area.
This "spring" has the effect of delaying the transfer of the cone movement to the volume of entrapped air in the port area.
This time delay brings the two radiations (from the cone and from the port) from an out-of-phase, or opposed, condition into an in-phase
condition at the necessary low frequency.
Novak repeats himself here ----->
"In order to make the system decay in one frequency, the enclosure volume and port combination must be tuned to the free-air resonance of the speaker.
A specified decay can be achieved by adding acoustic resistance, in the form of damping material, to
the enclosure. The proper amount of damping material can be determined
by means of a test method described later."
Laters !!!
DESIGNING A DUCTED-PORT ENCLOSURE
James F. Novak,
Senior Engineer,
Jensen Mfg. Div.,
The Muter Company,
The author has researched this subject thoroughly. The following material is reprinted with his permission.
Reprinted in part from January, 1966, issue of Electronics World
Optimum Enclosure Size
"A careful study of bass-reflex operation from a theoretical standpoint reveals a complexity far greater than the extremely simple
construction would indicate. A number of generally unknown facts come to light concerning low-frequency extension and optimum
transient response.
"l. A bass-refiex enclosure can be too large. After a certain maximum volume is reached, further volume increases result in 'boomy"
bass rather than an appreciable extension of low-frequency response. This is particularly true when a speaker with a small magnet is used.
It is best to use a completely closed cabinet in this case.
"2. A bass-refiex enclosure can also be too small. A common assumption is that the enclosure can be made much smaller by using
a duct behind the port. While the use of a duct allows one to tune the enclosure to very low frequencies when volumes are small,
it is the ratio of enclosure air stiffness to speaker stiffness that determines the low-frequency cut-off.
As the enclosure volume is made smaller, the enclosure stiffness increases and so does the cut-off-frequency.
This will remain true regardless of how the enclosure is tuned.
A false "boomy" bass will generally result and the enclosure may as well be left closed. In some cases a better sounding
bass will result if the back of the speaker enclosure is removed.
"A nagging question in the design stage of any enclosure of this type is "How large shall it be?" It was pointed out earlier that the
enclosure can be too large or too small for proper bass-reflex action.
This implies that an optimum volume exists and indeed it does.
This optimum volume does not depend upon the size of the speaker nor its resonant frequency per se but rather on the ratio of enclosure
air stiffness to the speaker cone suspension stiffness.
This optimum ratio is 1.44 or, looking at it another way, the speaker resonant frequency in the enclosure before porting should be 1.56 times the
free-air resonance of the speaker. This size enclosure, when properly tuned, yields at the same time the most extended low-frequency
response and a transient response with subjectively unnoticeable hangover, assuming sufficient damping exists.
Compared to the entirely closed cabinet, the half-power point (3 db down) occurs at 0.7 times the closed cabinet speaker resonance for an extension
of one-half octave.
Only one condition of cabinet tuning and damping will result in optimum transient response, i.e., "freedom from hangover or boom".
Because a speaker in a bass-reflex forms a closely coupled system of two tuned circuits, the system will tend to decay with two frequencies.
The achievement of optimum transient response demands that the system decay with one frequency and with a specified time constant.
In order to make the system decay in one frequency, the enclosure volume and port combination must be tuned to the free-air resonance of the speaker.
A specified decay can be achieved by adding acoustic resistance, in the form of damping material, to
the enclosure. The proper amount of damping material can be determined
by means of a test method described later.
BASS REFLEX DEFINED
From : How to Build Speaker Enclosures
Alexis Badmaieff and Don Davis (1966)
The phase-inversion enclosure allows the back radiation to be usefully added to the output of the front radiation. This improves
the low-frequency response of the system. The mechanics of this process may be described as follows: The entrapped air volume
of the enclosure is used as an extension of the cone to move a volume of entrapped air in a port or opening
APPROXIMATELY EQUAL TO THE AREA OF THE AIR DISPLACED BY THE FRONT OF THE CONE
The air volume in the enclosure acts as a "spring" coupling the back of the cone to the "cone" of air entrapped in the port area.
This "spring" has the effect of delaying the transfer of the cone movement to the volume of entrapped air in the port area.
This time delay brings the two radiations (from the cone and from the port) from an out-of-phase, or opposed, condition into an in-phase
condition at the necessary low frequency.
Novak repeats himself here ----->
"In order to make the system decay in one frequency, the enclosure volume and port combination must be tuned to the free-air resonance of the speaker.
A specified decay can be achieved by adding acoustic resistance, in the form of damping material, to
the enclosure. The proper amount of damping material can be determined
by means of a test method described later."
Laters !!!
Sorry man, we have the last days of 2023, 1966 is 53 years ago. In Europe we have computers today and so called simulation tools. These will tell you exactly what happens when you put woofer "X" into enclosure "Y". There are no more secrets to be found, no magical calcualtion and no rough guessing. Today you don't build speakers by try and error any more.
The best one for you should be WinISD because it is 90% self explaining.
Please read this thread again and answer a few of the questions asked. This is not the usual idiot forum here, most of the members know what they do.
Best is to start with the room you want to use the sub's in and describe what kind of speakers you want to combine with them.
You don't pick a random woofer and somehow make it fit, but define what you need first. Then work your way up from there.
The best one for you should be WinISD because it is 90% self explaining.
Please read this thread again and answer a few of the questions asked. This is not the usual idiot forum here, most of the members know what they do.
Best is to start with the room you want to use the sub's in and describe what kind of speakers you want to combine with them.
You don't pick a random woofer and somehow make it fit, but define what you need first. Then work your way up from there.
Last edited:
Original scientific literature from the guys who concieved and invented this ****.... That's art, but what would you know...... Relying on software.
Your post comes across as ah,very, er, German maybe.
(eyeroll)
These dudes were real scientists..... Not some idiot forum or whatever you say
Anyway, where do you think all the WinISD parameters came from.......?
If you read the thread yourself you might notice I have used it maybe once or twice.
I was hoping to meet people here with fire in their bellies and a raging thirst for knowledge and sharing,
only "most of the members know what they do" you tell me.
Of course there are no more secrets to bee found, you think I don't know this. That's why the paper was published in 1959.
Sorry for a monent there, I thought this was a forum grounded in physics, science and plain logic, maybe I was wrong.
What a waste of a post..... Let's try and save this...... And, please get in the queue the next time.
Your post comes across as ah,very, er, German maybe.
(eyeroll)
These dudes were real scientists..... Not some idiot forum or whatever you say
Anyway, where do you think all the WinISD parameters came from.......?
If you read the thread yourself you might notice I have used it maybe once or twice.
I was hoping to meet people here with fire in their bellies and a raging thirst for knowledge and sharing,
only "most of the members know what they do" you tell me.
Of course there are no more secrets to bee found, you think I don't know this. That's why the paper was published in 1959.
Sorry for a monent there, I thought this was a forum grounded in physics, science and plain logic, maybe I was wrong.
What a waste of a post..... Let's try and save this...... And, please get in the queue the next time.
Re: Vas to enclosure volume ratio
"The difference between Infinite Baffle and acoustic suspension has been traditionally drawn at a Vas/Vb ratio of 3.
Vas/Vb>3 - acoustic suspension
Vas/Vb<3 - Infinite baffle
Because Fc/Fs=Qtc/Qts=sqrt(Vas/Vb+1)
Qtc/Qts>2 - acoustic suspension
Qtc/Qts<2 - infinite baffle
There is another definition for infinite baffle - that the resonance is increased by less than 10% - which is closer to a Vas/Vb ratio of 0.2..."
"The difference between Infinite Baffle and acoustic suspension has been traditionally drawn at a Vas/Vb ratio of 3.
Vas/Vb>3 - acoustic suspension
Vas/Vb<3 - Infinite baffle
Because Fc/Fs=Qtc/Qts=sqrt(Vas/Vb+1)
Qtc/Qts>2 - acoustic suspension
Qtc/Qts<2 - infinite baffle
There is another definition for infinite baffle - that the resonance is increased by less than 10% - which is closer to a Vas/Vb ratio of 0.2..."
I read that magical Vb=Vas/1.44, Fb=Fs formula and I'm wondering how the researchers came to this conclusion with these exact specific numbers. This is especially interesting because Vas and Fs are not fixed parameters (just theoretically), their values are changing with driving levels in the real world.
They write they did "extensive research" and we need to believe this? That's all? Not that I don't want to believe that, I'm just curious.
They write they did "extensive research" and we need to believe this? That's all? Not that I don't want to believe that, I'm just curious.
Last edited:
@Databass
you started a thread about building a subwoofer with some concrete details.
Now it seems you want back to a time where building speakers was an art only few, with high budget for try and error, practiced. Which lead to all kinds of formulas, tricks and secret, often wrong, knowledge.
Today there are no alternative ways to calculate a subwoofer you can discuss any more. It is physics and not "belly feeling" that get's perfect results and avoids waste of time and money.
No one needs "burning desire for fire in their bellies and a raging thirst for knowledge and sharing" if the system is known to the last detail.
If you want the best subwoofer for your situation, even if you find it boring, this is no highly emotional process, but pure sience.
Simulations are compareable to a hack saw. You know how it works, what it does and it is no advantage to know how it manages to make the blade go up and down.
So read about TS parameter as long as you like, but for a result you will use a simulation, not a new magic world formula.
Sorry if you are disapointed now.
If you consider it "German" to look at a technical problem without emotions, you may be surprised that today this is not limited to this single, small country, but a world wide standard for successful engineering. Even in this forum.
you started a thread about building a subwoofer with some concrete details.
Now it seems you want back to a time where building speakers was an art only few, with high budget for try and error, practiced. Which lead to all kinds of formulas, tricks and secret, often wrong, knowledge.
Today there are no alternative ways to calculate a subwoofer you can discuss any more. It is physics and not "belly feeling" that get's perfect results and avoids waste of time and money.
No one needs "burning desire for fire in their bellies and a raging thirst for knowledge and sharing" if the system is known to the last detail.
If you want the best subwoofer for your situation, even if you find it boring, this is no highly emotional process, but pure sience.
Simulations are compareable to a hack saw. You know how it works, what it does and it is no advantage to know how it manages to make the blade go up and down.
So read about TS parameter as long as you like, but for a result you will use a simulation, not a new magic world formula.
Sorry if you are disapointed now.
If you consider it "German" to look at a technical problem without emotions, you may be surprised that today this is not limited to this single, small country, but a world wide standard for successful engineering. Even in this forum.
The theoretically best bassreflex response (trade-off between box size, extension, efficiency and impulse response?) comes from the SBB4 alignment. To get this alignment with a driver with a Qts = 0.393, the Vas/Vb needs to be the famous 1.44 and Fb=Fs. Okay, but what about if the driver Qts differs from 0.393, like 0.28 for example? According to vented box calculators, to get the SBB4 alignment with a lower Qts driver, the Vas/Vb ratio must be higher, so they not produce the SBB4 response with a Vas/VB=1.44. What's more important, the Vas/Vb=1.44 or the SBB4 response? What is the SBB4 alignment anyway? Or is all this irrelevant if we can EQ/shape the response to the alignment we want and/or the listening room dominates the low-frequency responses anyway?
Sorry if off-topic, but this just came to my mind!
Sorry if off-topic, but this just came to my mind!
Last edited:
As mentioned in 2023, we have power amplifiers with >200V rails, DSP and advanced modeling capabilities.
These are not a crutch for a bad design, however. We do not need to concern ourselves with getting the absolute maximum voltage sensitivity and efficiency like in the early days of audio where amplifiers were but just a few watts.
These are not a crutch for a bad design, however. We do not need to concern ourselves with getting the absolute maximum voltage sensitivity and efficiency like in the early days of audio where amplifiers were but just a few watts.
Thank you everyone for your replies.
Re : T/S alignments
When I began this speaker thing not so long ago, I remember reading somewhere just to model in WinISD using
BB4/SBB4 Super BoomBox because it was as good as any and seeing as I was planning on designing a subwoofer
the whole "Super BoomBox" thing sounded appropriate enough so I went with that.
I inputted the Faital Pro driver I am going to use in this project into WinISD and ran 5 simulations,
using all the options in the "Vented Box" menu.
QB3 Quasi-Butterworth, BB4/SBB4 (Super BoomBox), C4/SC4 (Sub) Chebyshev, EBS3 Extended Bass Shelf -3dB and
EBS6 Extended Bass Shelf -6dB
Every simulation was identical, except the "Vented Box" T/S alignments , and every project was set to
"292 litre enclosure tuned to 32 Hz, 2 6" ports and 900watts of input signal".
Every graph curve was exactly the same and I noticed the box sizes of each project wanted to default to their own volume sizes
when a new project was open in the WinISD calculator.
For some weird reason, in BB4/SBB4 Superboom Box mode, my WinISD wants a box size of 102 litres for this driver.
Attached below is a screenshot showing the two transfer Fucntion Magnitude curves, one for the 102 litre enclosure that was sugested
by the WinISD software, and the other for the 292 litre.
Addendum :
Datasheet reports the QTS of driver to bee 0.31
I used GM's recommended "New QTS with series resistor" calculator to calculate my QTS in the real world and I get a figure of 0.358
http://www.mh-audio.nl/Calculators/newqts.html
I then tried to follow the "Calculate box size using bass reflex alignments" calculator
http://www.mh-audio.nl/Calculators/BRA.html
on the same website using my newly calculated QTS number.
I ran into difficulty at the alignments table.... My Vas is 201.1, Fs is 32Hz and my port size is 150mm diameter.... 2 of them.
I did not know what to do with the "H", "a", "F3/Fs" and "Peak" numbers so I ran out of steam on that one and didn't revisit again in my research.
Quote from one of GM's posts ----->
"With specs like this [and up to a 0.403 Qts'], the pioneers determined that the optimal box/driver compliance with best transient response [least 'hangover./'boom'], max gain BW is [measured] Vas/1.44 tuned to Fs."
Seems close enough to my "New QTS" of 0.358, I was hoping it would do.
Screenshot graph shown below
Red Line - 102 Litre box vs. Black Line - 292 Litre Box - All other things being equal
Re : T/S alignments
When I began this speaker thing not so long ago, I remember reading somewhere just to model in WinISD using
BB4/SBB4 Super BoomBox because it was as good as any and seeing as I was planning on designing a subwoofer
the whole "Super BoomBox" thing sounded appropriate enough so I went with that.
I inputted the Faital Pro driver I am going to use in this project into WinISD and ran 5 simulations,
using all the options in the "Vented Box" menu.
QB3 Quasi-Butterworth, BB4/SBB4 (Super BoomBox), C4/SC4 (Sub) Chebyshev, EBS3 Extended Bass Shelf -3dB and
EBS6 Extended Bass Shelf -6dB
Every simulation was identical, except the "Vented Box" T/S alignments , and every project was set to
"292 litre enclosure tuned to 32 Hz, 2 6" ports and 900watts of input signal".
Every graph curve was exactly the same and I noticed the box sizes of each project wanted to default to their own volume sizes
when a new project was open in the WinISD calculator.
For some weird reason, in BB4/SBB4 Superboom Box mode, my WinISD wants a box size of 102 litres for this driver.
Attached below is a screenshot showing the two transfer Fucntion Magnitude curves, one for the 102 litre enclosure that was sugested
by the WinISD software, and the other for the 292 litre.
Addendum :
Datasheet reports the QTS of driver to bee 0.31
I used GM's recommended "New QTS with series resistor" calculator to calculate my QTS in the real world and I get a figure of 0.358
http://www.mh-audio.nl/Calculators/newqts.html
I then tried to follow the "Calculate box size using bass reflex alignments" calculator
http://www.mh-audio.nl/Calculators/BRA.html
on the same website using my newly calculated QTS number.
I ran into difficulty at the alignments table.... My Vas is 201.1, Fs is 32Hz and my port size is 150mm diameter.... 2 of them.
I did not know what to do with the "H", "a", "F3/Fs" and "Peak" numbers so I ran out of steam on that one and didn't revisit again in my research.
Quote from one of GM's posts ----->
"With specs like this [and up to a 0.403 Qts'], the pioneers determined that the optimal box/driver compliance with best transient response [least 'hangover./'boom'], max gain BW is [measured] Vas/1.44 tuned to Fs."
Seems close enough to my "New QTS" of 0.358, I was hoping it would do.
Screenshot graph shown below
Red Line - 102 Litre box vs. Black Line - 292 Litre Box - All other things being equal
Last edited:
The question is: if they are EQ-ed to the same response and the amplifier is up to this task, they would sound identical or not?
When a driver moves, it distorts.
Drivers move LESS per a given voltage in BP enclosures compared to BR and Sealed enclosures.
That makes BP's sound better too!
My BP enclosure only needs 1,175 watts to get to 128dB's at 37hz. The 311 liter BR enclosure needs 1,600 watts in the same size enclosure. My 314 liters includes the driver hole volume (Sd x 0.75 inch).
Last edited:
If the solution is that simple, then why so rare this construction in commercial speakers?
Because the enclosure is sensitive to driver parameters. There is more room for variance when it comes to factory tolerances on drivers.