I'm wanting to build a couple of duel 18 bass reflex subs but can't for the life figure out how to tune the box I'm not even sure where to begin. How do read the T&S specs and how do they depict the port size? Or do I just use software and go from there? Im also using this project to learn and have fun with so any help is appreciated.
How to tune subwoofer box
- Thread starter Eddie Ybarra
- Start date
Unless you're very into maths and circuit theory, I would go straight to the more common software to get a feel for what's going on first.
WinISD is the one I'm most familiar with, and it's not too hard to get your head around.
The helpfile has a good explanation of how to enter data for new drivers if the default library doesn't happen to include ones you're interested in.
Bear in mind that there is still a degree of interpretation required, for example different driver manufacturers use different ways of calculating theings like maximum useable excursion, some more conservative than others.
Also, none of the free/off the shelf software takes account of non linearities that tend to come in as you push the volume higher, so treat all max SPL predictions with a grain of salt., and assume you need to use bigger ports.
Also, depending on how you build the cab it's easy to find that your port tuning comes out lower than predicted - particularly if the port is built in along a cabinet wall or corner - that's because the continuation of the cabinet wall past the end of the "port" makes it behave as if its longer than actually built. Some trial & error may be required to get it right.
HTH,
David.
WinISD is the one I'm most familiar with, and it's not too hard to get your head around.
The helpfile has a good explanation of how to enter data for new drivers if the default library doesn't happen to include ones you're interested in.
Bear in mind that there is still a degree of interpretation required, for example different driver manufacturers use different ways of calculating theings like maximum useable excursion, some more conservative than others.
Also, none of the free/off the shelf software takes account of non linearities that tend to come in as you push the volume higher, so treat all max SPL predictions with a grain of salt., and assume you need to use bigger ports.
Also, depending on how you build the cab it's easy to find that your port tuning comes out lower than predicted - particularly if the port is built in along a cabinet wall or corner - that's because the continuation of the cabinet wall past the end of the "port" makes it behave as if its longer than actually built. Some trial & error may be required to get it right.
HTH,
David.
I would highly suggest using an already developed plan. There are a lot of box plans with drivers already selected and tested. Some of the more advanced guys can come up with cabinets from scratch with good results but it you are just starting off I would think it would be more than helpful to have build drawings. There is usually some well thought out bracing in a lot of sub designs.
hey
As said, using the software that is available like WinISD is a huge bonus and saves a lot of complex maths, its the best place to start.
For a basic reflex box, there can be two approaches depending on what you want to achieve.
Firstly, if you already have an idea of the driver you would like to use, you can enter its specifications into the software and start to play with different sizes of boxes and port tuning etc to give you the response you would like. The 2 main things you're looking to adjust are the volume of air in the box (bigger boxes will go lower, but will give you a little more group delay and make it easier to over-excurse the driver) and the port tuning, which will control at what low frequency you get your boost of response at the bottom end before the response falls away.
Alternatively, rather than starting with the driver you can approach if from the other side if you want. If you already have an idea of what the final box is that you'd like to aim for (maybe a particular size or shape to make it transportable, or fits under a stage, or any other requirement) you can enter that into the software first, and then try a selection of different drivers in it to see what results you get and what suits your design.
In reality, it'll probably be a mixture of both, having a rough idea of what you're looking for, trying a few different drivers, making adjustments to sizes and port shapes and tunings, till it all comes together in a design you're happy with.
in term of the driver specs, it takes a long time and lots of experience to know what you're looking for and what will suit a particular design, but there are some common threads to spot. Drivers with a low natural resonance frequency (fs) such as big beefy drivers like the BMS 18n862, will be easier to make play super low frequencies down towards 30Hz or below, and will probably have a slightly looser motor system (qts, higher number is looser) and a longer a X-max (how far they can move forward and back) to match and really push air. They'll work well in big reflex boxes to push out low frequencies, however will probably be a little less sensitive and need some decent grunt in their amp too.
Drivers with a slightly higher resonance and a stronger motor system (lower qts) wont go to the same super lows as the others, but will sound a bit tighter and punchier, and can usually be made into more compact boxes that are a bit easier to transport. They'll also (by dint of their own slightly higher sensitivity as well as the more compact box) be a bit more sensitive and give you a touch more volume watt for watt.
Then there are other drivers with especially strong magnets and motor systems which can work in a well designed ported box, but shine inside some of the more complex designs like horns etc.
For live music, a strong response to 40hz or just below is often fine and this allows you to keep the box a little more compact, most decent 18" drivers and even many good 15" drivers will work for this. If you're planning to use it with a lot of synthesizers or electronic/dance music with extra-low frequencies, using the more high spec drivers and pushing down towards 30hz will make a big difference.
Once you know the port area/length, volume of air that's required in the cab, and the driver, it's then time to take these and work out how to actually make that into a speaker cabinet.
As said, its always a good idea to make the ports as big as possible within the box, and also add plenty of bracing on all sides (though remember these things subtract from the air volume inside the cabinet, so the cab then has to be made bigger by the same volume to keep the air volume the same).
A wooden shelf port or corner ports are great for doubling up as bracing to the cabinet walls, but it can be hard to judge exactly how long to make them. The software will tell you a length, but if they're against a sidewall this makes the port seem a little longer and they need to be shortened slightly to balance that out. You'll probably need a prototype made to nail this before your final production cabs.
Plastic tube ports dont have the same advantage of bracing the sidewalls, but they're advantage is you can change them without having to build the whole box again from scratch, so you can make them a touch longer than needed initially and then gradually cut them down slightly as you measure the response or impedance of the cab, eventually getting them to the right size for your tuning.
Think about how you want to lift and transport it and where sensible places might be for handles, and if you want wheels would they be on a removable board or permanently attached to the back. Top hats for pole mounting your top speakers can be added in, and maybe feet on the bottom with matching groves on the top so that speakers can be stacked together.
Of course, a great thing to do is work back through the archive of posts on here and read about some of the other builds, you'll pick up lots of good information and tips on designing and constructing.
K
As said, using the software that is available like WinISD is a huge bonus and saves a lot of complex maths, its the best place to start.
For a basic reflex box, there can be two approaches depending on what you want to achieve.
Firstly, if you already have an idea of the driver you would like to use, you can enter its specifications into the software and start to play with different sizes of boxes and port tuning etc to give you the response you would like. The 2 main things you're looking to adjust are the volume of air in the box (bigger boxes will go lower, but will give you a little more group delay and make it easier to over-excurse the driver) and the port tuning, which will control at what low frequency you get your boost of response at the bottom end before the response falls away.
Alternatively, rather than starting with the driver you can approach if from the other side if you want. If you already have an idea of what the final box is that you'd like to aim for (maybe a particular size or shape to make it transportable, or fits under a stage, or any other requirement) you can enter that into the software first, and then try a selection of different drivers in it to see what results you get and what suits your design.
In reality, it'll probably be a mixture of both, having a rough idea of what you're looking for, trying a few different drivers, making adjustments to sizes and port shapes and tunings, till it all comes together in a design you're happy with.
in term of the driver specs, it takes a long time and lots of experience to know what you're looking for and what will suit a particular design, but there are some common threads to spot. Drivers with a low natural resonance frequency (fs) such as big beefy drivers like the BMS 18n862, will be easier to make play super low frequencies down towards 30Hz or below, and will probably have a slightly looser motor system (qts, higher number is looser) and a longer a X-max (how far they can move forward and back) to match and really push air. They'll work well in big reflex boxes to push out low frequencies, however will probably be a little less sensitive and need some decent grunt in their amp too.
Drivers with a slightly higher resonance and a stronger motor system (lower qts) wont go to the same super lows as the others, but will sound a bit tighter and punchier, and can usually be made into more compact boxes that are a bit easier to transport. They'll also (by dint of their own slightly higher sensitivity as well as the more compact box) be a bit more sensitive and give you a touch more volume watt for watt.
Then there are other drivers with especially strong magnets and motor systems which can work in a well designed ported box, but shine inside some of the more complex designs like horns etc.
For live music, a strong response to 40hz or just below is often fine and this allows you to keep the box a little more compact, most decent 18" drivers and even many good 15" drivers will work for this. If you're planning to use it with a lot of synthesizers or electronic/dance music with extra-low frequencies, using the more high spec drivers and pushing down towards 30hz will make a big difference.
Once you know the port area/length, volume of air that's required in the cab, and the driver, it's then time to take these and work out how to actually make that into a speaker cabinet.
As said, its always a good idea to make the ports as big as possible within the box, and also add plenty of bracing on all sides (though remember these things subtract from the air volume inside the cabinet, so the cab then has to be made bigger by the same volume to keep the air volume the same).
A wooden shelf port or corner ports are great for doubling up as bracing to the cabinet walls, but it can be hard to judge exactly how long to make them. The software will tell you a length, but if they're against a sidewall this makes the port seem a little longer and they need to be shortened slightly to balance that out. You'll probably need a prototype made to nail this before your final production cabs.
Plastic tube ports dont have the same advantage of bracing the sidewalls, but they're advantage is you can change them without having to build the whole box again from scratch, so you can make them a touch longer than needed initially and then gradually cut them down slightly as you measure the response or impedance of the cab, eventually getting them to the right size for your tuning.
Think about how you want to lift and transport it and where sensible places might be for handles, and if you want wheels would they be on a removable board or permanently attached to the back. Top hats for pole mounting your top speakers can be added in, and maybe feet on the bottom with matching groves on the top so that speakers can be stacked together.
Of course, a great thing to do is work back through the archive of posts on here and read about some of the other builds, you'll pick up lots of good information and tips on designing and constructing.
K
Thanks for the replies so far,how do I go about measuring response and impedance, what tools do i need?
for measuring impedance, its possible to make up a fairly simple circuit and use the outputs and inputs from a sound card and software such as Room EQ Wizard. While it works, a more plug and play solution can be found either here...
http://www.daytonaudio.com/index.php/dats-dayton-audio-test-system.html
or here...
http://www.woofertester.com/wt2product.htm
These give very accurate results, and can help both before you design and build your cabinet to measure and get exact t/s parameters for your woofer and afterwards to check that your port length and area is giving you the correct tuning frequency.
For measuring the response of your speaker, you will need a measurement microphone, a sound card/interface to plug the mic into your computer, and software.
The more you can spend on a measurement mic the more accurate it will generally be, but for your first time I wouldn't go crazy much better to get something serviceable and cost effective, and worry about a more expensive one if this becomes something you regularly do in the future.
For the software, Room EQ Wizard, HolmImpulse or ARTA are free and again will give you basic results and let you make some measurements, though investing in one of the dual channel FFT systems such as Smaart, Systune etc will give you very accurate results and let you check phase and line different parts of the speaker up at their crossover points etc.
However what will be even more important is your measurement environment and set up. Much better to do this outside in plenty of space if possible to eliminate room reflections from the measurement.
Kev
A very simple trick if you want to find exursion maximum and minima is to put the sub on it's back, pour a small sample of sawdust on the driver and use a variable sine generator to sweep up and down watching the excursion in real-time.