at least when it comes to home use this topic has certainly been discussed plenty all over the internet but i keep coming back to it because anytime i have to design a multi-way system there is always temptation to use something other than 80 hz to cross to the sub and i have to remind myself why it is 80 hz
and for me personally the reasons aren't what is being cited by others. for me it comes down to 2 factors:
1 - 80 hz is the highest frequency that is safely outside of the range of human voice
2 - 80 hz is the highest frequency where you can be certain any prosound subwoofer driver ( and by that i mean the big boys like the 21" Eminence ) can reach this frequency cleanly.
you can't really go higher than 80 hz for that reason even though LFE ( Low Frequency Effects ) channel goes to 120 hz but remember it is "LFE" channel it is not "sub" channel. your processor can send LFE to the mains on other hand they will never mix human voice into the LFE even if the male speaker's voice reaches well below 120 hz.
the purpose of LFE channel isn't to separate frequencies ( your system already has crossover for that ) but to separate content. voice goes into main channels. explosions go into LFE. this allows you to run the LFE channel hot ( which you're supposed to do ) and have properly loud explosions without muddying up speech.
a 80 hz crossover would allow you to do something like that as well but it has to be 80 hz and not 120 hz because it's just a frequency division network and not a guy in the studio that has more power over what goes into which channel. they can get away with 120 hz for LFE but we have to stick to 80 hz for XO at least as a general rule of thumb / best practices / starting point.
and as for why not go lower than 80 hz it's because you can't use main channels to control room standing wave modes. those begin from about 250 hz and down so ideally you would run distributed subs up to 250 hz to control the standing waves except you can't for reasons mentioned. rather you will need to use room treatments that are effective down to 80 hz ( which is a bit of a stretch but doable ) and distributed subs take care of the modes below that.
now for prosound you are facing different tradeoffs. and i know there are people here who know more than me about prosound so please correct me if i am wrong. but in prosound room standing waves are less of a concern and rather the issue is that speakers are usually flown over the crowd so you try to keep their weight down. on other hand subs can sometime be placed on the ground which allows the use of bigger, heavier subs and also gives you the 6db bass gain from the ground plane boundary versus a speaker suspended in free space up in the air.
but because you don't want to deafen the people who will be next to the ground sub stack you want to keep crossover frequency low because people can tolerate loud SPL better when frequencies are lower.
prosound arrays are usually made long to fit as many tweeters as possible because there is often not enough HF reaching the crowd for a number of reasons which means that there will be often a surplus of woofers and with the mutual coupling of the woofers at low frequencies even smaller ones like 10" will usually be able to reach 60 hz which then can be the crossover point to the ground stack subs.
again, i know it's not that simple and prosound guys should correct me on this.
but i think it is interesting just how bad prosound subwoofer drivers are above 80 hz considering their stellar efficiency. for example look at this distortion chart from the following link:
https://audioxpress.com/article/Test-Bench-Eighteen-Sound-18TLW3000-18-Dual-Voice-Coil-Woofer
distortion is lowest at around 60 hz, then doubles by 150 hz ... and this test is in FREE AIR which disadvantages lower frequencies
so this sub is perfectly optimized for its intended frequency range. the rise in distortion at lowest frequencies is unavoidable due to high excursions but the bump around 150-200 hz could have been designed out ... but there was no reason to as this driver will never see those frequencies.
for this particular driver the XO could be stretched to maybe 100 hz, and with some other drivers maybe to 120 hz but i still find it fascinating how true subwoofers like this exhibit this mess right above intended crossover frequency while woofers of similar size do not. to us lay men a paper cone is a paper cone but clearly there is more to it than that. subwoofer, woofer, midrange and full range cones appear to behave differently and it's not about the diameter of the cone. or it may be down to suspension or something else, but the effect is clearly seen in basically all subwoofers Vance Dickason has tested even though he doesn't talk about this.
on a side note this is also why i believe in multi-way designs. drivers can be better optimized for a target frequency range. even though you can certainly build a full-range 2-way i like to keep subwoofer, woofer and midrange separate for this reason.
and for me personally the reasons aren't what is being cited by others. for me it comes down to 2 factors:
1 - 80 hz is the highest frequency that is safely outside of the range of human voice
2 - 80 hz is the highest frequency where you can be certain any prosound subwoofer driver ( and by that i mean the big boys like the 21" Eminence ) can reach this frequency cleanly.
you can't really go higher than 80 hz for that reason even though LFE ( Low Frequency Effects ) channel goes to 120 hz but remember it is "LFE" channel it is not "sub" channel. your processor can send LFE to the mains on other hand they will never mix human voice into the LFE even if the male speaker's voice reaches well below 120 hz.
the purpose of LFE channel isn't to separate frequencies ( your system already has crossover for that ) but to separate content. voice goes into main channels. explosions go into LFE. this allows you to run the LFE channel hot ( which you're supposed to do ) and have properly loud explosions without muddying up speech.
a 80 hz crossover would allow you to do something like that as well but it has to be 80 hz and not 120 hz because it's just a frequency division network and not a guy in the studio that has more power over what goes into which channel. they can get away with 120 hz for LFE but we have to stick to 80 hz for XO at least as a general rule of thumb / best practices / starting point.
and as for why not go lower than 80 hz it's because you can't use main channels to control room standing wave modes. those begin from about 250 hz and down so ideally you would run distributed subs up to 250 hz to control the standing waves except you can't for reasons mentioned. rather you will need to use room treatments that are effective down to 80 hz ( which is a bit of a stretch but doable ) and distributed subs take care of the modes below that.
now for prosound you are facing different tradeoffs. and i know there are people here who know more than me about prosound so please correct me if i am wrong. but in prosound room standing waves are less of a concern and rather the issue is that speakers are usually flown over the crowd so you try to keep their weight down. on other hand subs can sometime be placed on the ground which allows the use of bigger, heavier subs and also gives you the 6db bass gain from the ground plane boundary versus a speaker suspended in free space up in the air.
but because you don't want to deafen the people who will be next to the ground sub stack you want to keep crossover frequency low because people can tolerate loud SPL better when frequencies are lower.
prosound arrays are usually made long to fit as many tweeters as possible because there is often not enough HF reaching the crowd for a number of reasons which means that there will be often a surplus of woofers and with the mutual coupling of the woofers at low frequencies even smaller ones like 10" will usually be able to reach 60 hz which then can be the crossover point to the ground stack subs.
again, i know it's not that simple and prosound guys should correct me on this.
but i think it is interesting just how bad prosound subwoofer drivers are above 80 hz considering their stellar efficiency. for example look at this distortion chart from the following link:
https://audioxpress.com/article/Test-Bench-Eighteen-Sound-18TLW3000-18-Dual-Voice-Coil-Woofer
distortion is lowest at around 60 hz, then doubles by 150 hz ... and this test is in FREE AIR which disadvantages lower frequencies
so this sub is perfectly optimized for its intended frequency range. the rise in distortion at lowest frequencies is unavoidable due to high excursions but the bump around 150-200 hz could have been designed out ... but there was no reason to as this driver will never see those frequencies.
for this particular driver the XO could be stretched to maybe 100 hz, and with some other drivers maybe to 120 hz but i still find it fascinating how true subwoofers like this exhibit this mess right above intended crossover frequency while woofers of similar size do not. to us lay men a paper cone is a paper cone but clearly there is more to it than that. subwoofer, woofer, midrange and full range cones appear to behave differently and it's not about the diameter of the cone. or it may be down to suspension or something else, but the effect is clearly seen in basically all subwoofers Vance Dickason has tested even though he doesn't talk about this.
on a side note this is also why i believe in multi-way designs. drivers can be better optimized for a target frequency range. even though you can certainly build a full-range 2-way i like to keep subwoofer, woofer and midrange separate for this reason.
nothing to do with the human voice, is more about the goals and design of the system
depending on the design and tuning like BR, TH , BP6, BP8
you will have certain bandwidth on the passband, some designs are wider than others , all have their pros and cons
so depending on your goals you need to accept some tradeoffs
do not forget the Hoffman's Iron Law, you cant break physics laws ( i mean even if you try lol )
so....
lets say you design a BP8 to hit as low as 20hz ,the upper limit will be around 60hz,the passband on Bandpass subs are more narrower than bass reflex just to make some comparison, so you need to cross your tops at 60hz, or get a suplemental bass cabinet that will take from 60hz to 100 hz also called KICK BINS, from there you can cross the Mids at 100hz to 2k and from 2khz the HF driver....just to say some ball park XO points
that is a 4 way system.... you have 4 XO points, most of the time people use 3 way systems for easier deployment ( less power amp channels nedded ) , using a bass cabinet that goes up to 100 or 120hz and goes to 40hz on the low side.. for like PA ( outdoor band music... DJ.. etc ) you dont need that low extension that and HT sub can reach....
and depending on your target SPL for your gig, you need to calculate how many cabinets you need
can be point source, those do not splay well and are designed only for one per side as the HF lens are normally 90 ,100 or 120 degrees wide
if you need more SPL for bigger crowds you need boxes that can play nice splayed like danley SH46, that have a 40 degree wide horizontal HF lens, you can splay 3 of em for 120 degree coverage
and if you need more, them you need to switch to the hanging format linear boxes....
there are many tools , and is good to use the right tool for the job.
personally im doing 2 way system
im crossing my bass cabinets at 120hz , from 120 and up i use active 12" 2 way tops cabs....
but it all depends on your needs and wants , your design goals and your budget
i wish to have 8 linear boxes per side hanging and 12 subs on the center
All driven by LAKE or XILICA FIR enabled processors
and powesoft ,labb gruppen or dynacord amplifiers...
but
1... i dont need em as my gigs are for 50 - 100 people max...
2.... i dont have the means to acquire and move such a system
Best. 😎
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