4 posts were merged into an existing topic: Differential Drive vs Tetracoil vs Split Winding
post a sample design you have in mind including drivers, crossover points, horn or waveguide used and cabinet dimensions / tuning and i will tell you whether it seems sensible or whether it seems like you won’t get the level of performance that will match the cost of the components.
one benefit of designing your system around the concept of subwoofers is you can add more subs later.
you don’t need to nail your sub-bass on day one. you get your top box perfect above 80 hz and you can add more subs when amplifier prices come down.
it’s honestly a no brainer. you will never get perfect bass without subs so why even try. on other hand with subs you don’t need to get it right.
once i switched from full range speakers to sub+sat i never looked back. it is frankly inconceivable for me to go back to full range speakers.
only somebody who doesn’t care about bass should even consider full-range speakers. but if you watch movies or play video games or listen to electronic music you should care.
getting down to 80 hz flawlessly should be the goal. don’t worry about anything below 80 hz - that job is for subs.
just in case i haven’t mentioned it before optimum room placement for bass is also different than for mains.
subs optimally are spread throughout the room.
you can start with two subs - one under each main speaker acting as a stand.
but later upgrade your system by putting two more in the opposing room corners.
and then adding more at wall mid-points.
and so on.
all this will be much easier if you start out your design with the standard 80 hz crossover point in mind.
If you design a speaker for 80Hz on up should the impedance peak be at 80Hz? Or is it more a function of what box size works best for a woofer? You can put something like a B&C sub in a really small enclosure and optimize efficiency for 80Hz on up from that woofer, but it means using basically the smallest enclosure physically possible for the sub. What happens when you use too small an enclosure even if the alignment is still <0.7 Qtc?
download HornResp and learn how to use it.
it’s hard to use but free.
people mainly use it to design horns and transmission lines but it also does all the basic box types.
what is great about it versus other free programs is it can calculate things like impedance and efficiency versus frequency in addition to things like excursion versus frequency etc.
there are tutorials online on how to use it.
it is truly horrible to use because it is like 30 years old program but it’s still being updated - it’s just that the basic interface is still the same as 30 years ago. he just keeps fixing bugs and adding features.
but the upside is it is by far the most fully featured free speaker design program that i know of.
once you spend enough time building boxes in it you will understand pretty much every aspect of speaker design. you will see why speakers are designed a certain way.
when you simulate two boxes and one of them is 5% efficient while another is 2% efficient you won’t need to ask me which one is better unless you enjoy buying big amps just to heat your room …
you seem to be asking about a sealed enclosure and while you could certainly get away with a sealed enclosure in this application in practice satellites / tops in PA / prosound are still vented / bass reflex.
but let’s assume it is sealed simply to answer your question, even though i do not recommend going sealed here as vented would have lower distortion and compression.
anyway for a sealed above 80hz yes you can take a small subwoofer and stuff it into a tiny box … in which case you would have all of the downsides of subwoofer driver ( heavy cone, high inductance ) without any of the benefits ( high bass output ).
unless there is some reason why you want a small enclosure it would be wiser to ask how can we take advantage of a large enclosure to maximize efficiency and minimize distortion ?
the answer is of course by using a driver with larger cone area as well as lighter voice coil with less inductance. such drivers need bigger boxes but sound cleaner.
by using a port you further decrease cone movement keeping the VC more centered in the gap for lower distortion plus the exchange of air through the port reduces temperatures in the cabinet.
although you could go sealed a very efficient driver in a sealed alignment will begin to roll off above 100 hz …
as i said there aren’t ANY prosound or PA tops / satellites that are sealed that i know of. doesn’t mean it can’t be done but it’s just not ideal.
that 8" midrange bucket i keep pushing is sealed - but the spec sheet states its lower cutoff is 400 hz, even though it actually has a resonance frequency lower than that. but due to low QES / QTS it simply begins to roll off as high as about 1 khz.
any efficient driver will begin to roll off high up. sure you can find a sub that can be flat to 20 hz in a sealed box but that sub will be very inefficient.
in fact FS/QTS is known as “efficiency bandwidth product” … this is basically the frequency at which the driver begins to roll off. in other words the higher the driver begins to roll off the more efficient it is.
so for example a driver with 30 hz FS and 0.2 QTS would have a 30/0.2 = 150 EBP and that would be a good prosound woofer.
a prosound subwoofer should really have QTS closer to 100, so it would be less efficient but able to reach lower.
you basically want EBP as high as possible while still being able to reach as low as you need to.
with a vented alignment you can use a higher EBP driver and still reach lower - that’s why all prosound cabinets are vented.
the main downside is going to be the driver itself. if you constrain yourself to a tiny box you’re not going to be using the best possible driver if you choose the optimal driver for that tiny enclosure.
but one potential other downside is maybe the stresses on the cone might be greater. this might result in more distortion or premature failure.
but that is just speculation. i mean even without any enclosure there will still be stress on the cone from just acceleration anyway. ultimately the forces originate at the motor not at the air spring. so no matter what the air spring looks like for a cone to fail the motor will need to be stronger than the cone. and you can argue that resonance will actually be helping move the cone along rather than having the air spring resist the motor.
i mean if we look at bucket drivers like that 8" Eighteen Sound midrange ( JBL also makes similar ones, as well as RCF and B&C too ) - most of these drivers are operated down to the resonance frequency ( the 18 sound may be an exception as it’s sort of the highest end of the bunch, except the JBL ).
in other words these sealed buckets could have been made larger in volume but nobody bothers to do that because apparently there is no real benefit in doing so.
but again, these bucket midranges have like 200-400 hz lower cutoff. you’re talking 80 hz. at that point you really should be looking at vented.
to have a clean 80 hz crossover you’re probably looking at about 50 to 60 hz tuning for the vented box unless you’re going to do some kind of a brick wall ultra high slope crossover. the thing is brick wall filters are FIR filers and FIR don’t work at lower frequencies ( the memory / computing requirements and latency get too high ).
check what your DSP solution can do in terms of crossover slopes then tune that box accordingly. if the most you can do is 24 db / oct crossover then you wouldn’t want to tune that box right at 80 hz because there would still be significant energy reaching the driver at lower frequencies where the driver would be essentially operating as free air …
but again that also depends on driver mechanical design. if the driver has a very strong and stiff suspension it may be able to handle a bit of energy below tuning frequency. HornResp will help with this as well.
the driver, box, vent and high pass filter all work together as a system … with HornReps you would be able to get a feeling for this …
although i don’t think HornResp models high pass filters ( maybe it does, don’t know ) it isn’t much of a stretch to imagine how such a filter would affect things once you see the graphs HornResp does generate.
if you have an idea of what energy distribution looks like for the type of music you listen to ( i posted those, i can post them again if needed )
and you have HornResp to model excursion ( or any other program that will accurately model it )
and you have the Klippel data that can tell you how much distortion to expect at any given excursion level
and you have the data on distortion audibility versus frequency
and you don’t forget to account for any kind of bass boost you may wish to apply, which is actually standard practice and not a sin as audiophiles would have you believe
then you can design a system that will have essentially inaudible distortion while playing as loud and deep as you like
but it will likely involve some subs 
oftentimes the subwoofer is only slightly larger than the top box / satellite it’s used with.
why ?
because cabinet volume as a resource is shared by all the speakers in the truck. if your top / satellite is tiny but your subs are huge you still need a big truck so you achieved nothing.
so optimally the sub and top / satellite are almost the same size and instead the sub is able to go deeper by using more power at the expense of muddier sound due to larger VC mass and inductance.
the sub will also have larger ports that can move more air at the expense of adding more coloration in the midrange.
what i’m saying is basically the difference between a 15" woofer and a 18" subwoofer have less to do with driver size and maybe even not so much with cabinet size and more to do with tuning of motor, cone and ports.
well … in terms of box VOLUME that 18" sub in an optimal configuration will have significantly larger volume than 15" top, but in terms of cabinet DIMENSIONS it will be a small difference.
because volume is proportional to dimensions CUBED so small changes in dimensions result in larger changes in volume. but also subs tend to be more like a cube which maximizes volume while speakers tend to be more elongated which isn’t as volume efficient.
a good design would use both tops and subs that are as large as possible while still allowing you to move them freely wherever you want to put them. so they must be able to to fit through the doors, elevators, staircases etc. and must be light enough to lift ( handles help )
in practical terms this means tops are probably about 50-80 lbs and subs about 90-130 lbs. if that’s not enough low end you simply use more subs.