since several years ago... i've been in search of a speaker that could reproduce the intensity of a strings assemble (cellos, violins, pianos...) with flutes, trumpets, baritones and the like.
but most notibly, organs.
however, still have the capability of reproducing modern movie soundtracks with ease at high decibals.
Now i understand that most speakers have difficulty in doing this (especially with most loudspeakers in the 3000-8000 range being directed to hometheater and general music reproduction)
I've been modeling some cabinets and doing some calculated measurements with winisd. Seems as though the larger the cabinet, the smaller the port can be. Makes sense right? in order to reproduce a given frequency, the soundwave has to travel a certain distance before exiting the port. (top of my head correct me if i'm wrong pls...)
so with a smaller box, you would need a longer port for a given hz.
ok, so onto my question. I'm trying to design a port/cabinet combo that will give me an above average gain in the hz that the port/tube is tuned at, however i dont want any "boom" in the reproduction. will having an absurdly long port create this? if not, is there a limit to how long the port can be?
what i'm trying to create, is an exceptionaly musical cabinet/port/driver combo but still have a high tuned gain.
assume that the box volume is equal to the port volume, and you'll the idea of what i'm trying to achieve. The would be true for all drivers in the cabinet excluding those allready tuned by the driver manufacter (tweeter, some midranges. however, i would like to tune those myself where possible).
if this doesn't make any sense to any of you, pls let me know. Looking around the net at the more knowledgable group of entusiast/diy'ers, seems as though you guys would know best and hoping the combined knowledge of the few who might understand this would be able to help out with an experienced answer.
thanks in advance.
wish me luck in the woodshop.
but most notibly, organs.
however, still have the capability of reproducing modern movie soundtracks with ease at high decibals.
Now i understand that most speakers have difficulty in doing this (especially with most loudspeakers in the 3000-8000 range being directed to hometheater and general music reproduction)
I've been modeling some cabinets and doing some calculated measurements with winisd. Seems as though the larger the cabinet, the smaller the port can be. Makes sense right? in order to reproduce a given frequency, the soundwave has to travel a certain distance before exiting the port. (top of my head correct me if i'm wrong pls...)
so with a smaller box, you would need a longer port for a given hz.
ok, so onto my question. I'm trying to design a port/cabinet combo that will give me an above average gain in the hz that the port/tube is tuned at, however i dont want any "boom" in the reproduction. will having an absurdly long port create this? if not, is there a limit to how long the port can be?
what i'm trying to create, is an exceptionaly musical cabinet/port/driver combo but still have a high tuned gain.
assume that the box volume is equal to the port volume, and you'll the idea of what i'm trying to achieve. The would be true for all drivers in the cabinet excluding those allready tuned by the driver manufacter (tweeter, some midranges. however, i would like to tune those myself where possible).
if this doesn't make any sense to any of you, pls let me know. Looking around the net at the more knowledgable group of entusiast/diy'ers, seems as though you guys would know best and hoping the combined knowledge of the few who might understand this would be able to help out with an experienced answer.
thanks in advance.
wish me luck in the woodshop.
Hi, the port is shorter with a bigger box because you have more air in the box so the airmass in the port need to be smaller to tune at the same frequency. Why? I don't know exactly, but it's not because the soundwave has to travel a certain distance before exiting the port. If it was like that, port placement would be crucial, but in a vented enclosure, you can place the port anywhere.
You want to use a small box with a very long port. You must be careful with 1st port resonance frequency. If you use WinISD Pro, you'll see the 1st port resonance frequency in the "Vents" tab. For example, a 50 liters box tuned to 16.4 Hz (most of the time, the lower organ note) need a 68 inches long port if it's 4 inches in diameter. That port will resonate at 100 Hz, if your crossover is at 80 Hz, that resonance will not be attenuated enough and will mess up the sound a bit.
If you go too extreme with long ports, you might end up with a Transmission Line box I guess. Correct me if I'm wrong on that. Maybe it can limit how long the port can be, because you won't have any gain over a sealed box when you go too far I guess. The airflow might be restricted.
I also want to add that a big box with a short port is not boomy if you design it correctly. Because the box is big, you can also use more port area, so longer ports, since you can have longer ports easily in a big box.
You want to use a small box with a very long port. You must be careful with 1st port resonance frequency. If you use WinISD Pro, you'll see the 1st port resonance frequency in the "Vents" tab. For example, a 50 liters box tuned to 16.4 Hz (most of the time, the lower organ note) need a 68 inches long port if it's 4 inches in diameter. That port will resonate at 100 Hz, if your crossover is at 80 Hz, that resonance will not be attenuated enough and will mess up the sound a bit.
If you go too extreme with long ports, you might end up with a Transmission Line box I guess. Correct me if I'm wrong on that. Maybe it can limit how long the port can be, because you won't have any gain over a sealed box when you go too far I guess. The airflow might be restricted.
I also want to add that a big box with a short port is not boomy if you design it correctly. Because the box is big, you can also use more port area, so longer ports, since you can have longer ports easily in a big box.
thanks for the help.
your right about the soundwave not having to travel a certain distance... i think its something to do with air moving in and out of the cabinet. like blowing into a beer bottle.
i didn't know, however, that ports them selves had a resonant frequency... i just downloaded winisd pro (had the beta without a vent mach) and well see what frequencies i can pull. cause the port i have here is the most complicated to build.
i'm hoping i dont have to croos my front speakers over though. so far, the lowest dip is at 32hz -3.5 db.
my 3 ports are 72 cms long at 6 cms wide in a 100 liter box. 3x8 inch woofers. i'll read up a bit more and model a bit more
and some more and some more....
and then build it to see how it performs.
then... onto the midbass to get rid of that dreaded "dead" feel to cellos!
your right about the soundwave not having to travel a certain distance... i think its something to do with air moving in and out of the cabinet. like blowing into a beer bottle.
i didn't know, however, that ports them selves had a resonant frequency... i just downloaded winisd pro (had the beta without a vent mach) and well see what frequencies i can pull. cause the port i have here is the most complicated to build.
i'm hoping i dont have to croos my front speakers over though. so far, the lowest dip is at 32hz -3.5 db.
my 3 ports are 72 cms long at 6 cms wide in a 100 liter box. 3x8 inch woofers. i'll read up a bit more and model a bit more
and some more and some more....
and then build it to see how it performs.
then... onto the midbass to get rid of that dreaded "dead" feel to cellos!
yeah i was thinking about this... because the drivers i'm using are the dayton audio ref series for this system and the drivers dont seem to have much in the way of xmax.
so... was thinking either three times 10 inches. the originall design i had for these was a 160 liter box with 8cm diameter wide ports. basically the same idea but in a double bass reflex with a port in the main chamber as opposed to all three in the bottom. (or rear)
with this (if i can remember correctly) i was getting much better numbers with two tunable regions. so one at 16hz and the other where the woofer dips. howover... 10 is probably the biggest i want to go as "more material, heavier woofer"
so with a 10 inch woofer. i'd have to change the design of the top cabinet and incorperate another 6 inch or figure something out for midbass.
and that just gets even more expensive.
keep in mind though.. the two subs that will be accompanying these will be two times double 12inch subwoofers built into an isobarik design.
quick and musical but has the displacement to achieve good spl as low hz.
again we'll see. i'm hoping to build a few of these if the triple 8's turn out. if they do i'll sell those and build another along with the tens and go with the top/center cabinet. and cross compare them.
but yeah. so far so good on acad and winisd.
so... was thinking either three times 10 inches. the originall design i had for these was a 160 liter box with 8cm diameter wide ports. basically the same idea but in a double bass reflex with a port in the main chamber as opposed to all three in the bottom. (or rear)
with this (if i can remember correctly) i was getting much better numbers with two tunable regions. so one at 16hz and the other where the woofer dips. howover... 10 is probably the biggest i want to go as "more material, heavier woofer"
so with a 10 inch woofer. i'd have to change the design of the top cabinet and incorperate another 6 inch or figure something out for midbass.
and that just gets even more expensive.
keep in mind though.. the two subs that will be accompanying these will be two times double 12inch subwoofers built into an isobarik design.
quick and musical but has the displacement to achieve good spl as low hz.
again we'll see. i'm hoping to build a few of these if the triple 8's turn out. if they do i'll sell those and build another along with the tens and go with the top/center cabinet. and cross compare them.
but yeah. so far so good on acad and winisd.
Here's the basics
Ported enclosures are helmholtz resonators. An air mass(the port) and a spring(the air inside the enclosure not including the port). They resonante the same as a mechanical mass and spring.
If you make the spring tighter(smaller internal volume) you need to make the mass heavier(longer port). Making the port of larger cross section also increases the "tightness" of the airspring, hence a longer port is needed.
I always wondered if a TL could be modeled as a ported enclosure but I dont really think its possible... There is no airspring in the TL it's simply a 1/4 wavelength pipe.
The port itself has resonances like a 1/4 wavelength pipe. Bends I believe will attenuate these somewhat.
Ported enclosures are helmholtz resonators. An air mass(the port) and a spring(the air inside the enclosure not including the port). They resonante the same as a mechanical mass and spring.
If you make the spring tighter(smaller internal volume) you need to make the mass heavier(longer port). Making the port of larger cross section also increases the "tightness" of the airspring, hence a longer port is needed.
I always wondered if a TL could be modeled as a ported enclosure but I dont really think its possible... There is no airspring in the TL it's simply a 1/4 wavelength pipe.
The port itself has resonances like a 1/4 wavelength pipe. Bends I believe will attenuate these somewhat.
it wont be a tl. it'll be closely resembling a dbr box.
i'm currently looking for a programs that could model how a sound wave reacts with soundwave.
the port... will work like a "flute" in that in itself will produce a hz. just like a dbr but in a smaller tighter setting with the main box being tuned as a normal dbr with a single large port.
two "vortex" type spiraling ports will feed a parralelogram type chamber (where i need the wave modeler to see what happens when the sound wave comes into the chamger) and what i can do with another port from there.
i dont even know if this is possible but i'm wiling to try.
i figure i would need to tune that chamber according to the tune of the main chamber because we'll... it'll be feeding this secondary chamber.
it'll be almost exactly as the fostex type box but with a slight (but huge difference in tune) difference.
just curious really... if anybody has done something similar. the fostex type box is the closest thing to this and can't find anythign else.
i'm currently looking for a programs that could model how a sound wave reacts with soundwave.
the port... will work like a "flute" in that in itself will produce a hz. just like a dbr but in a smaller tighter setting with the main box being tuned as a normal dbr with a single large port.
two "vortex" type spiraling ports will feed a parralelogram type chamber (where i need the wave modeler to see what happens when the sound wave comes into the chamger) and what i can do with another port from there.
i dont even know if this is possible but i'm wiling to try.
i figure i would need to tune that chamber according to the tune of the main chamber because we'll... it'll be feeding this secondary chamber.
it'll be almost exactly as the fostex type box but with a slight (but huge difference in tune) difference.
just curious really... if anybody has done something similar. the fostex type box is the closest thing to this and can't find anythign else.
never thought of that actually ( and i did mechanical engineering in school)
if you could find a modeler where you can either change the properties of the material being casted (to exact specifics of air) or just select the combonation in relative parts or airs composition...
you'd be set.
but yeah, these programs cost 1200+ canadian.
we'd need something that could calculate the inflow of air also. cause in a cabinet, you have different pressures at any given moment (due to the sound "wave")
a flow gen (that i know of) doesn't calculate both ways, just the positive.
if you could find a modeler where you can either change the properties of the material being casted (to exact specifics of air) or just select the combonation in relative parts or airs composition...
you'd be set.
but yeah, these programs cost 1200+ canadian.
we'd need something that could calculate the inflow of air also. cause in a cabinet, you have different pressures at any given moment (due to the sound "wave")
a flow gen (that i know of) doesn't calculate both ways, just the positive.
re ports
The most optimum coupling between the driver and the Helmholtz resonator causes a peak, i.e. the best coupling is the boom box.
There are a class of reflex alignments that use this peak in conjunction with a high pass filter to produce an overall flat responce and these are known as the QB5 class II alignments.
These optimise excursion limited power handling, and are much used in sound reiforcement, the reason being that they allow both the full voice coil and the full excursion capabilty to be used simultaniously, giving a very large amount of sound, the drawback is that the speakers f3 needs to be at least twice the cut off frequency, for the best extension /size/power handling.
Next are the class I alignments, these are generally similar to a B6 alignment described by Don Keele in which you take a standard B4 box, reduce the port tuning by .7, and feed it from a Q=2 filter tuned to the same frequency.
This results in optimum bass extension in a given volume, but the power handling is less and is usually limited by cone excursion, subwoofers of this sort are widely used in such applications as large monitoring systems.
Richard Smalls testing showed that if you keep the air velocity in the vent at not more than 4.5% of the speed of sound no vent noises are heard, in Win Isd if the vent velocity is below 10m/s.,
Low tuning means big vents and if the box is small they are difficult to accomodate, Peerless for instance makes passive radiators for its xxls series because of this.
On the matter of pipes, a pipe is essentially a transmission line that is periodic, it will resonate at frequencies at which the amplitude of the ratio of the forward and reflected wave is unity, a Helmholtz resonator is the acoustic equivalent of a parallel resonant electrical circuit and will resonate at the equivalent parallel resonant frequency, if the inductance is in the form of a pipe this will have pipe resonances.
The most optimum coupling between the driver and the Helmholtz resonator causes a peak, i.e. the best coupling is the boom box.
There are a class of reflex alignments that use this peak in conjunction with a high pass filter to produce an overall flat responce and these are known as the QB5 class II alignments.
These optimise excursion limited power handling, and are much used in sound reiforcement, the reason being that they allow both the full voice coil and the full excursion capabilty to be used simultaniously, giving a very large amount of sound, the drawback is that the speakers f3 needs to be at least twice the cut off frequency, for the best extension /size/power handling.
Next are the class I alignments, these are generally similar to a B6 alignment described by Don Keele in which you take a standard B4 box, reduce the port tuning by .7, and feed it from a Q=2 filter tuned to the same frequency.
This results in optimum bass extension in a given volume, but the power handling is less and is usually limited by cone excursion, subwoofers of this sort are widely used in such applications as large monitoring systems.
Richard Smalls testing showed that if you keep the air velocity in the vent at not more than 4.5% of the speed of sound no vent noises are heard, in Win Isd if the vent velocity is below 10m/s.,
Low tuning means big vents and if the box is small they are difficult to accomodate, Peerless for instance makes passive radiators for its xxls series because of this.
On the matter of pipes, a pipe is essentially a transmission line that is periodic, it will resonate at frequencies at which the amplitude of the ratio of the forward and reflected wave is unity, a Helmholtz resonator is the acoustic equivalent of a parallel resonant electrical circuit and will resonate at the equivalent parallel resonant frequency, if the inductance is in the form of a pipe this will have pipe resonances.
yeah. you just found a complicated way of saying something i allready knew...
my original question and current dilemma was the lenth/size of port and if there were limits to their design application in real life.
as i stated.. i'll be using a relitively small box with a very low tuning... two tunings in fact. one at 16-18 hz- the other at 30-35 i have yet to complete my crossover as that will be a big deciding factor as to exactly what tune it will end up to be.
i didn't, however, know that there was a specific mach at was a port would start to "whistle" at. although... acquiring a flow modeler will help in the end design and will most certainly affect my current design.
i believe i'm in the final stages of my first draft design for my prototype. i will post pics of my acad and hopefully a flow model gif (but i doubt it) asap.
you'll have an idea of what's going on here.
my original question and current dilemma was the lenth/size of port and if there were limits to their design application in real life.
as i stated.. i'll be using a relitively small box with a very low tuning... two tunings in fact. one at 16-18 hz- the other at 30-35 i have yet to complete my crossover as that will be a big deciding factor as to exactly what tune it will end up to be.
i didn't, however, know that there was a specific mach at was a port would start to "whistle" at. although... acquiring a flow modeler will help in the end design and will most certainly affect my current design.
i believe i'm in the final stages of my first draft design for my prototype. i will post pics of my acad and hopefully a flow model gif (but i doubt it) asap.
you'll have an idea of what's going on here.
I'd tested the next:
then next:
even next:
but the best way for port noise minimize was:
it's translucent for some waves material, so it seems like indefinite diametr of ports.
An externally hosted image should be here but it was not working when we last tested it.
then next:
An externally hosted image should be here but it was not working when we last tested it.
even next:
An externally hosted image should be here but it was not working when we last tested it.
but the best way for port noise minimize was:
An externally hosted image should be here but it was not working when we last tested it.
it's translucent for some waves material, so it seems like indefinite diametr of ports.
re ports
The most comprehensive treatment if ports I know about is a paper that appeared in the AES Journal, Vol. 50 No.1/2, Jan/Feb, 2002.
The point that I was attempting to make before is that what you require is a musical subwoofer that goes down to the lowest frequencies. Most of the designs you will see such as shelving alignments, are for home theatre, and are intended to make large low frequency noises that sound somewhat like the sound effects people intended, and they have large amounts of non linear distortion and tend to use ports that are too small.
A subwoofer that will give a genuine 16Hz. note with very little distortion at a level that you can actually hear is another beast entirely, and unless it is very large electronic assistance is almost mandatory, and it depends very significantly upon the amount of room gain you have.
In short first ascertain your room gain by measurement and then design a subwoofer that will give the required output.
Also note that a shelving type reflex box is cheap and easy to do, and it might well satisfy your ears although its objective specs might leave something to be desired.
The most comprehensive treatment if ports I know about is a paper that appeared in the AES Journal, Vol. 50 No.1/2, Jan/Feb, 2002.
The point that I was attempting to make before is that what you require is a musical subwoofer that goes down to the lowest frequencies. Most of the designs you will see such as shelving alignments, are for home theatre, and are intended to make large low frequency noises that sound somewhat like the sound effects people intended, and they have large amounts of non linear distortion and tend to use ports that are too small.
A subwoofer that will give a genuine 16Hz. note with very little distortion at a level that you can actually hear is another beast entirely, and unless it is very large electronic assistance is almost mandatory, and it depends very significantly upon the amount of room gain you have.
In short first ascertain your room gain by measurement and then design a subwoofer that will give the required output.
Also note that a shelving type reflex box is cheap and easy to do, and it might well satisfy your ears although its objective specs might leave something to be desired.
If you're looking for 16hz at a level that you can hear you cant design your subwoofer around your listening environment. The listening environment must be designed to accomedate such intense sound pressure. Otherwise you will just hear the house rattle and shake and vibrate and well you might THINK that its 16hz that you're hearing but you're wrong. The human ear loses its ability to recognize pitch below 20hz anyhow.... 18hz 16hz 10hz they all sound the same, its just the amount of SPL it takes for you to 'hear' it
Electronic assistance is Almost mandatory.... I have an Adire Tumult... If I had 3 good 18" PR's on it then it could pump out a very low(comparably) distortion 16hz tone in less than 5 cubic feet at over 110db Anechoic. No EQ needed
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