need to calculate the point of no returns 
for how many 18" i will be using in my HT setup
( could be 15" ..not 100% on that yet )
they will occupy most of the front wall
in a "planar wave" type of array
( distributed equally over front wall area )
the room will be of 25' depth
by 20' width
by 8-9' height ( rear half is 8' for seats leveling )
How can we determine how many subs will yield the best $$$ VS performance for this particular setup ?
( please don't suggest other loudspeakers config, my choice is already made on to this one )
rear wave will be evacuated to garage room
( 26' by 26' )
i was planning for 16 individual 18" drivers
could also work with more 15" like the Dayton IB
over at parts express if $$$ and result are worth it
so would like a way to calculate response vs number of drivers and possibility!
thanks for your time!
for how many 18" i will be using in my HT setup
( could be 15" ..not 100% on that yet )
they will occupy most of the front wall
in a "planar wave" type of array
( distributed equally over front wall area )
the room will be of 25' depth
by 20' width
by 8-9' height ( rear half is 8' for seats leveling )
How can we determine how many subs will yield the best $$$ VS performance for this particular setup ?
( please don't suggest other loudspeakers config, my choice is already made on to this one )
rear wave will be evacuated to garage room
( 26' by 26' )
i was planning for 16 individual 18" drivers
could also work with more 15" like the Dayton IB
over at parts express if $$$ and result are worth it
so would like a way to calculate response vs number of drivers and possibility!
thanks for your time!
Nobody knows but you as it depend on your own requirements to start with, I guess if not complete or not known in detail, its difficult to answer but maybe this attempt to answer is adequate to start with:
Why not do most of the investigation works by your self? Make your choices and tell us to see if we can agree upon your driver/amp power demands/opinions of what is good performance for a HT set-up.
See 1(1) or go to: http://www.myhometheater.homestead.com/splcalculator.html
Added a 4 x driver DBA polar simulation for a room of 2.4 x 4 x 6 m where XO frequencies (LP= 12 dB/octave) is marked (black line) ensuring an acute (frontal, horizontal) wide enough initial planar (surge) wave coincident to both ears of any listener placed at the rear half of the room without any lateral velocity gradient occurring than caused by the main speakers (even at higher SPL when distortion often pops out from the subs randomly from the same but differently placed drivers) : 2(2).
b
1(2)
Attachments
woa!
nice answer !!!!
2 things come out of this mainly for me :
1- could you please explain all of this,
as this is seriously more advanced than my very very tiny limited knowledge now!!
2- i do not know exactly what i want/need as a result of this system, what i need right now is formulas or ratios ...stuff like that , that would permit me to determine
and play with different values to see what can be achieved and what would be the best possible compromise to choose on the drivers and number of drivers on this system ( sub bass system )
this system will have to match very efficient floor to ceiling line arrays ( again ..should be very efficient
as they will operate in nearfield and site not very far from the listening positions )
thanks again for your time!
nice answer !!!!
2 things come out of this mainly for me :
1- could you please explain all of this,
as this is seriously more advanced than my very very tiny limited knowledge now!!
2- i do not know exactly what i want/need as a result of this system, what i need right now is formulas or ratios ...stuff like that , that would permit me to determine
and play with different values to see what can be achieved and what would be the best possible compromise to choose on the drivers and number of drivers on this system ( sub bass system )
this system will have to match very efficient floor to ceiling line arrays ( again ..should be very efficient
as they will operate in nearfield and site not very far from the listening positions )
thanks again for your time!
JinMTVT said:
Assuming an 80 Hz 4th order XO, then you ideally want the drivers < 1/4 WL apart at 160 Hz = ~13560"/4/160 = ~21.1875" c-t-c driver and to wall spacing. That's a lot of drivers and if 18"ers are used the wall will look like a giant's wine rack.
In reality though, unless you can damp the modes at the other end of the room this close spacing/large number of drivers will mostly be a waste of time/$$$/effort IMO compared to distributing around the room. Sure will be impressive though, like a large Bessel Array for cinema apps, but with a large, long bass-horn's acoustic efficiency, so I imagine the cones will barely move at 'voice of God' LFs.
why do we need to space the drivers that close?
why the 1/4 WL formula ?
i would like to follow the " DBA" theory
( double bass array )
but minues the double ( rear reversed wave )
what would happen if i'd have only 16 18" drivers on the front wall of 20' by 9' high ?
they would be positionned according to the "mirror" image effect ...
why the 1/4 WL formula ?
i would like to follow the " DBA" theory
( double bass array )
but minues the double
( rear reversed wave )what would happen if i'd have only 16 18" drivers on the front wall of 20' by 9' high ?
they would be positionned according to the "mirror" image effect ...
Because you said you wanted "a "planar wave" type of array
( distributed equally over front wall area )" and to do this requires enough polar overlap between drivers to cover the BW. If you XO lower and/or use a steeper slope, then you can use a wider spacing/fewer drivers. Or you can do it anyway and accept the collapse of the planar wavefront at some lower frequency. Never having built a large one I don't have a clue at what point it might be obviously audible depending on seating location.
( distributed equally over front wall area )" and to do this requires enough polar overlap between drivers to cover the BW. If you XO lower and/or use a steeper slope, then you can use a wider spacing/fewer drivers. Or you can do it anyway and accept the collapse of the planar wavefront at some lower frequency. Never having built a large one I don't have a clue at what point it might be obviously audible depending on seating location.
hi GM...
ok i understand what you mean globally,
but i seriously thought that the planar wave would work with a lot fewer % of the area of the wall covered by drivers ... i understand that it is frequency dependent
yet i have not sorted out what kind of XO i would like to work with ..since i do not have all the details worked
out ( this system is getting seriously tedious and complicated the further it grows... too many entricate details wich need assumptions right now to work with,
or require direct inputs of correct details to be able to determine and decide on components and details ...)
will an array of 18 or 15" sub permit me to go higher in the frequency of the crossovers ?
down to what hz is the bass required to come from the correct direction and situation ?
i do believe that up to a certain hz, the bass will start to be more directional and behave differently VS sub-bass systems ?
all this is seriously related, and i have yet to determine what kind of XO and driver sizing the line arrays will permit me as far as combing and driver spacing ..
Have you seen/read the paper on double bass array ?
have you seen/heard any examples of sub bass arrays
used to form mirror images and simulate a planar wave?
what i read and understood,
is that by correct placement of drviers on the front wall,
sub abss drivers are able to produce some kind of planar wave ( as distributed as it can be ...i do not have sufficient knowledge for that part ) wich will react in the room and travel through it as if it was confined in a horn/tube and behave as a near field @ -3db for doubling distance ...
what i wanted to work with is trying to eliminate the side and vertical room modes as much as possible without having to resort to bass traps, having the rear of the room as absorptive as possible for bass
( probably 2" of some wool or fiber + some back spacing
thus reducing a maximum the front/back modal )
What you are reffering to as distribution of the planar wave, doesn't sound radiate spherically at sub bass frequencies ? won't it all scatter and make some kind of big mess of a planar wave even if drivers are more sparce?
my mental image of it happening in 3d is of scaling spheres merging into each others at mid driver distance,
but i cannot think of what will happen afterwards?
will the waves continue to spread after colliding or will they merge and make some sort of field with higher and lower densities of pressure, constantly evolving and mixing until there is no more energy ?
i have felt once sub bass from a long port sitting right in front of it ...was big
and i can tell you that when the bass hits you,
it is something alot more than just sitting in a place where a spherical wave hits you partly while it grows to loose its power ...
am i dreaming or ?
bjorno:
thanks for the simulation and links
the room pressure distribution isn't supposed to be as your plots show, as i was told that with a planar wave type of config, the pressure moves evenly through the room as if it was going through a tunnel or a horn tube
so i am not sure what to do with your polar plots ..
though very instructive
Then, your html simulator doesn't show much info for different frequencies and would need to assume for only 3db of loss on distance ( if the theory of the planar wave behaving as nearfield is correct)
i believe that i will need to emulate the driver's response and calculate attenuation VS distance by myself, and then find a suitable SPL at the lower Hz i am looking for, the rest can be filtered out
that is IF the NO MODAL of the planar wave works correclty thus assuming no room gain for the sub bass frequencies ...
to be seen ...
please let me know if you guys have more info or think of something else that would help
could i use HornResp to calculate the SPL the system would achieve and then use the distance to calculate the loss ??
ok i understand what you mean globally,
but i seriously thought that the planar wave would work with a lot fewer % of the area of the wall covered by drivers ... i understand that it is frequency dependent
yet i have not sorted out what kind of XO i would like to work with ..since i do not have all the details worked
out ( this system is getting seriously tedious and complicated the further it grows... too many entricate details wich need assumptions right now to work with,
or require direct inputs of correct details to be able to determine and decide on components and details ...)
will an array of 18 or 15" sub permit me to go higher in the frequency of the crossovers ?
down to what hz is the bass required to come from the correct direction and situation ?
i do believe that up to a certain hz, the bass will start to be more directional and behave differently VS sub-bass systems ?
all this is seriously related, and i have yet to determine what kind of XO and driver sizing the line arrays will permit me as far as combing and driver spacing ..
Have you seen/read the paper on double bass array ?
have you seen/heard any examples of sub bass arrays
used to form mirror images and simulate a planar wave?
what i read and understood,
is that by correct placement of drviers on the front wall,
sub abss drivers are able to produce some kind of planar wave ( as distributed as it can be ...i do not have sufficient knowledge for that part ) wich will react in the room and travel through it as if it was confined in a horn/tube and behave as a near field @ -3db for doubling distance ...
what i wanted to work with is trying to eliminate the side and vertical room modes as much as possible without having to resort to bass traps, having the rear of the room as absorptive as possible for bass
( probably 2" of some wool or fiber + some back spacing
thus reducing a maximum the front/back modal )
What you are reffering to as distribution of the planar wave, doesn't sound radiate spherically at sub bass frequencies ? won't it all scatter and make some kind of big mess of a planar wave even if drivers are more sparce?
my mental image of it happening in 3d is of scaling spheres merging into each others at mid driver distance,
but i cannot think of what will happen afterwards?
will the waves continue to spread after colliding or will they merge and make some sort of field with higher and lower densities of pressure, constantly evolving and mixing until there is no more energy ?
i have felt once sub bass from a long port sitting right in front of it ...was big
and i can tell you that when the bass hits you,
it is something alot more than just sitting in a place where a spherical wave hits you partly while it grows to loose its power ...
am i dreaming or ?
bjorno:
thanks for the simulation and links
the room pressure distribution isn't supposed to be as your plots show, as i was told that with a planar wave type of config, the pressure moves evenly through the room as if it was going through a tunnel or a horn tube
so i am not sure what to do with your polar plots ..
though very instructive
Then, your html simulator doesn't show much info for different frequencies and would need to assume for only 3db of loss on distance ( if the theory of the planar wave behaving as nearfield is correct)
i believe that i will need to emulate the driver's response and calculate attenuation VS distance by myself, and then find a suitable SPL at the lower Hz i am looking for, the rest can be filtered out
that is IF the NO MODAL of the planar wave works correclty thus assuming no room gain for the sub bass frequencies ...
to be seen ...
please let me know if you guys have more info or think of something else that would help
could i use HornResp to calculate the SPL the system would achieve and then use the distance to calculate the loss ??
If the room is long enough, wouldn't a huge horn be possible by making the mouth out of multiple small (but deep)cabinets ? Each horn driven by a single 10 or 12" driver. Then the horn mouths would all butt up next to each other and eliminate any problems from driver spacing.
Kind of like the way the labhorn is only 1/6th of the proper full size horn.
Cheers,
Rob.
Kind of like the way the labhorn is only 1/6th of the proper full size horn.
Cheers,
Rob.
very nice idea indee Rob ....
gives me good thinking ..
i do not have a few feet to spare ( 25' long .. gotta fit 2 rows of seats and need some distance because of the 120" screen )
what if, i use some extensions like horns, from the 15 or 18" that would all meet up to each other
maybe like 2-3 feet long extensions, wouldn't that work also ? it does not have to behave like horns, but i can clearly see that it would make for a complete wall movement type ...wouldn't be too hard to do either..
i'll make a 3d sketch tonight ...
would i have any problems with that ?
would it raise sensitiviity a bit by matching impedance with air a very little more?
gives me good thinking ..
i do not have a few feet to spare ( 25' long .. gotta fit 2 rows of seats and need some distance because of the 120" screen )
what if, i use some extensions like horns, from the 15 or 18" that would all meet up to each other
maybe like 2-3 feet long extensions, wouldn't that work also ? it does not have to behave like horns, but i can clearly see that it would make for a complete wall movement type ...wouldn't be too hard to do either..
i'll make a 3d sketch tonight ...
would i have any problems with that ?
would it raise sensitiviity a bit by matching impedance with air a very little more?
Such a short / small horn would (I think) be pretty useless at sub frequencies. You really need the length to drive it properly. That said with that many drivers / Power handling you should be able to EQ the response below the horns cut off to whatever you want.
I think the best way would be to model a horn with a mouth the size of the rearwall, and divide it into the number of cabinets you want, then model the horn with that number of drivers sd, and the combined throat / rear chambers etc.. Hornresp can do this but is size limited in the mouth size.
I'm not the best man to be giving horn design help though, but there are people here who are very knowledgable.
Cheers,
Rob.
I think the best way would be to model a horn with a mouth the size of the rearwall, and divide it into the number of cabinets you want, then model the horn with that number of drivers sd, and the combined throat / rear chambers etc.. Hornresp can do this but is size limited in the mouth size.
I'm not the best man to be giving horn design help though, but there are people here who are very knowledgable.
Cheers,
Rob.
i have given up on horns some time ago
due to some problems that can't be dealt with easily..
( mainly delay ... )in an ht setup
you say that having short but really flared ports at the noutput of each drivers wouldn't work ?
the waves won't follow the ports because of the size?
i do not care much if it doesn't change the sensitivity and impedance of the units, but i do care if it resolves the problem associated with driver spacing ...
so if'd be to port/flare a 18" driver for it to be double or triple its size ( something like 27" by 27" ports
by approx 2' long, would the wave follow and output similar as with a horn mouth ?
due to some problems that can't be dealt with easily..
( mainly delay ... )in an ht setup
you say that having short but really flared ports at the noutput of each drivers wouldn't work ?
the waves won't follow the ports because of the size?
i do not care much if it doesn't change the sensitivity and impedance of the units, but i do care if it resolves the problem associated with driver spacing ...
so if'd be to port/flare a 18" driver for it to be double or triple its size ( something like 27" by 27" ports
by approx 2' long, would the wave follow and output similar as with a horn mouth ?
In a home theater setup the delay is very easily dealt with by adding the horn length to the 'normal' measurement when setting up the listening positions on the processor. ie: when it asks for distence to sub, just measure to the mouth then add the horn length.
You may be onto something wrt the short 'horns'. If a wall of 80Hz horns will couple properly, and launch a single wave from 80Hz upto the 160Hz GM mentioned, then if you have a lot of drivers and a lot of EQ you may have a solution. I wouldn't really think of it as a horn though - more a 'waveguide' as you're not really horn loading in its useable bandwidth. However, personally I'd still try for horn loading as low as possible (30Hz ?) for ultra low distortion.
As I said though, there's better people than me here to answer that Q.
Rob.
You may be onto something wrt the short 'horns'. If a wall of 80Hz horns will couple properly, and launch a single wave from 80Hz upto the 160Hz GM mentioned, then if you have a lot of drivers and a lot of EQ you may have a solution. I wouldn't really think of it as a horn though - more a 'waveguide' as you're not really horn loading in its useable bandwidth. However, personally I'd still try for horn loading as low as possible (30Hz ?) for ultra low distortion.
As I said though, there's better people than me here to answer that Q.
Rob.
Hi ROB,
will not be using a regular processor..
everything will be from computer
with all individual DACs and all ...
so delay work is to be avoided as much as possible
to be able to keep clear of potential complexity...
waveguides is what you call this type of "horn mouth"
then waveguides it would be ...
GM: could you please elaborate on that?
what exactly do you mean by polar overlap ?
is there any formula or rules to use when calculating that? i guess that it is hz dependent?
And how would the wave collapse?
what happens when the wave collapse?
also would like to understand how to plot the BW vs this phenomenon you are pointing !
i really need to learn more of that area of accoustics!!!
will not be using a regular processor..
everything will be from computer
with all individual DACs and all ...
so delay work is to be avoided as much as possible
to be able to keep clear of potential complexity...
waveguides is what you call this type of "horn mouth"
then waveguides it would be ...
GM: could you please elaborate on that?
what exactly do you mean by polar overlap ?
is there any formula or rules to use when calculating that? i guess that it is hz dependent?
And how would the wave collapse?
what happens when the wave collapse?
also would like to understand how to plot the BW vs this phenomenon you are pointing !
i really need to learn more of that area of accoustics!!!
Greets!
If you understand it's frequency dependent, then why the problem with the spacing since the former dictates the latter? I mean you can use a line array's 1 WL spacing, but it will be ~planar over only a narrow BW. Obviously, the smaller the driver, the shorter the spacing potential, ergo the higher the BW before it all collapses into an array of beaming sources rolling off faster with distance than the lower frequencies.
I've read lots of papers, which specific one are you referring to?
I've built a pair of mirrored woofer 'infinite' line arrays at one end of a long basement using (4) 15" drivers/channel), but not a LF planar array, though I've experienced them at large outdoor concerts, so irrelevant WRT this app. We needed the line arrays to XO at 500 Hz/2nd order and it was abysmal sounding, so a lesson learned and the drivers were rearranged into mirrored corner loaded quad bipoles with the HF horns offset above them. Strange looking, but it worked well. Tried it in a regular stick built room and the relatively lossey wall construction compared to a below grade basement transformed it into a so-so performer until I stiffened/damped the corners.
A point source driver radiates spherically until it reaches its TL mode. Many sub drivers have such large dustcaps though that it typically has no usable BW IMO above its 1/2 space point or ~13560"/pi/effective diameter, so for a 15" it could be as low as ~300 Hz for an ultra high Xmax unit. Overlapping sound waves sum their particles, not 'scatter', so if unimpeded it will ~maintain its shape as air friction over distance causes its eventual complete decay. This distance is great enough for low frequencies that we can ignore it though.
WRT bass traps, they shouldn't be needed since you'll effectively be in the 'vent' with a ~uniform particle density, so the sub's BW intensity will be fairly constant throughout the room. Unfortunately the rest of the system won't unless you make them planar also.
AFA modeling a large array, EASE is the only program I know of that can do it with any degree of accuracy, though of course you'll have to use drivers with EASE data: http://www.renkus-heinz.com/ease/index.html
Anyway, I'm not really following some of your thoughts or Qs and haven't kept up with all the different versions of your build, so can't really contribute much, but I've given you what you need to work it out for a ~planar sub system that will turn your room into the equivalent of a sub-bass to ~160 Hz BW 1/2 WL resonator with a deep notch at its midpoint. If you can damp it at the other end well enough it will turn into a damped 1/4 WL resonator with notches at its odd harmonics, so in either case you want the XO point/slope to roll it off below these notches and ideally taper your walls and ceiling into a horn to help with a rapid decay of 'slap' echo just like in any concert hall.
GM
If you understand it's frequency dependent, then why the problem with the spacing since the former dictates the latter? I mean you can use a line array's 1 WL spacing, but it will be ~planar over only a narrow BW. Obviously, the smaller the driver, the shorter the spacing potential, ergo the higher the BW before it all collapses into an array of beaming sources rolling off faster with distance than the lower frequencies.
I've read lots of papers, which specific one are you referring to?
I've built a pair of mirrored woofer 'infinite' line arrays at one end of a long basement using (4) 15" drivers/channel), but not a LF planar array, though I've experienced them at large outdoor concerts, so irrelevant WRT this app. We needed the line arrays to XO at 500 Hz/2nd order and it was abysmal sounding, so a lesson learned and the drivers were rearranged into mirrored corner loaded quad bipoles with the HF horns offset above them. Strange looking, but it worked well. Tried it in a regular stick built room and the relatively lossey wall construction compared to a below grade basement transformed it into a so-so performer until I stiffened/damped the corners.
A point source driver radiates spherically until it reaches its TL mode. Many sub drivers have such large dustcaps though that it typically has no usable BW IMO above its 1/2 space point or ~13560"/pi/effective diameter, so for a 15" it could be as low as ~300 Hz for an ultra high Xmax unit. Overlapping sound waves sum their particles, not 'scatter', so if unimpeded it will ~maintain its shape as air friction over distance causes its eventual complete decay. This distance is great enough for low frequencies that we can ignore it though.
WRT bass traps, they shouldn't be needed since you'll effectively be in the 'vent' with a ~uniform particle density, so the sub's BW intensity will be fairly constant throughout the room. Unfortunately the rest of the system won't unless you make them planar also.
AFA modeling a large array, EASE is the only program I know of that can do it with any degree of accuracy, though of course you'll have to use drivers with EASE data: http://www.renkus-heinz.com/ease/index.html
Anyway, I'm not really following some of your thoughts or Qs and haven't kept up with all the different versions of your build, so can't really contribute much, but I've given you what you need to work it out for a ~planar sub system that will turn your room into the equivalent of a sub-bass to ~160 Hz BW 1/2 WL resonator with a deep notch at its midpoint. If you can damp it at the other end well enough it will turn into a damped 1/4 WL resonator with notches at its odd harmonics, so in either case you want the XO point/slope to roll it off below these notches and ideally taper your walls and ceiling into a horn to help with a rapid decay of 'slap' echo just like in any concert hall.
GM
RobWells said:
How so? I mean the spacing will be further apart than with point sources, so the planar field will collapse quicker with increasing frequency and depending on the horn's design it could be much worse due to its increasing beaming and off-axis 'shrouding' of the driver.
With multiple small horns, you'd actually be better off IMO putting fewer of them in a traditional cluster to keep the drivers as close together as practical and suspend them to reflect off a curved sound (front) wall with the mains facing forward. Basically a heart attack serious version of the 901.
ok GM
well first off..to show how limited my understanding and knowledge of all this is...i had to re-read your last 2 posts approximatly 10 times before starting to get a few things of what you typped
First thing, as you seem very experienced and knowledgeable about all those things,
is there a book or a place where i could read more of accoustics VS real world application and understand a bit more of theories and applications?
i have read master handbook of accoustics a few times,
it clears up a few things everytime, but it doesnt' give definite answers and doesn't relate me much to real world applications of the theories of accoustics.
then ...
this system was intended only for LF
i dind't not originally want to use it at anything above 100hz ..probably something like 70-80hz XO point ..
there shall be more than enough mid bass drivers to cover the ranges of the 100hz +
( the main lousdpeakers are supposed to be floor to ceiling OB line arrays of mid woofers and tweeters,
for front side and rear louspeakers, placed for near field listening )
is this a realistic XO point for that kind of system?
possible XO point?
the paper i was reffering to, is the german paper on the subject of the Double Bass Arrays
that you helped link in the DBA questionning thread
http://www.sennheiser.com/klein-hummel/globals.nsf/resources/tmt2002.PDF/$File/tmt2002.PDF
"A point source driver radiates spherically until it reaches its TL mode"
what is TL mode?
"...above its 1/2 space point or ~13560"/pi/effective diameter..."
what is 1/2 space point?
i do undertand that 13560" is sound speed
divised by effective diameter, what exacly does PI
do in there? related to half space?
i have yet to grast the notion of full space, 1/2 space, 1/4 space and so on ...
half space is half of a sphere ??
thus where the driver moves to "plane" ?
"Overlapping sound waves sum their particles, not 'scatter', so if unimpeded it will ~maintain its shape as air friction over distance causes its eventual complete decay. This distance is great enough for low frequencies that we can ignore it though."
please elaborate..i do not completly understand that statement ...
i am very visual, and unfortunatly, sound waves aren't easy to see...do you have any videos of moving sound waves ( simulations maybe ) that would express that kind of behavior?
"Anyway, I'm not really following some of your thoughts or Qs and haven't kept up with all the different versions of your build, so can't really contribute much""
you have already contributed alot with all your advanced information , and my version is always evolving with my perception and understanding of the different compromises and choices
my goal is simple, best possible performance for HT setup within my 25' by 20' room
and for me, HT = dynamics
that is one of the main reason why i am trying to move on with alot of drivers
"...what you need to work it out for a ~planar sub system that will turn your room into the equivalent of a sub-bass to ~160 Hz BW 1/2 WL resonator with a deep notch at its midpoint... "
what you mean is that it would turn my room into a
"tube like" where the bass would move on in a planar form ? why do you say 1/2 WL resonator ?
and why the deep notch at the midpoint?
i do not understand why there would be a deep notch...
is it because of the reflected delayed waves from the back that would "sum" with the front waves at midpoint?
that would be the equivalent of a 1/2WL mode ?
"...If you can damp it at the other end well enough it will turn into a damped 1/4 WL resonator with notches at its odd harmonics, so in either case you want the XO point/slope to roll it off below these notches and ideally taper your walls and ceiling into a horn to help with a rapid decay of 'slap' echo just like in any concert hall...."
how can it turn to a 1/4WL resonator if there is no back waves boucing off the rear ?( assuming perfect absorption.. )
odd harmonics? again like modal resonances?
taper the walls into a horn... going smaller at the back or bigger at the back ?
i would assume smaller because of the losses ...
lastly... i do not still understand how a planar wave can be assumed..i seriously thought that in sub bass, with a distributed array of drivers just like in the DBA thread and paper, one could assume some kind of near perfect planar wavefront up to a certain frequ.
still missing some information as how waves behave with eachother at this low frequencies going out spherically from the drivers ....
and i thank you again for your time and effort
to help me understand more and have a better final plan for my big project
well first off..to show how limited my understanding and knowledge of all this is...i had to re-read your last 2 posts approximatly 10 times before starting to get a few things of what you typped
First thing, as you seem very experienced and knowledgeable about all those things,
is there a book or a place where i could read more of accoustics VS real world application and understand a bit more of theories and applications?
i have read master handbook of accoustics a few times,
it clears up a few things everytime, but it doesnt' give definite answers and doesn't relate me much to real world applications of the theories of accoustics.
then ...
this system was intended only for LF
i dind't not originally want to use it at anything above 100hz ..probably something like 70-80hz XO point ..
there shall be more than enough mid bass drivers to cover the ranges of the 100hz +
( the main lousdpeakers are supposed to be floor to ceiling OB line arrays of mid woofers and tweeters,
for front side and rear louspeakers, placed for near field listening )
is this a realistic XO point for that kind of system?
possible XO point?
the paper i was reffering to, is the german paper on the subject of the Double Bass Arrays
that you helped link in the DBA questionning thread
http://www.sennheiser.com/klein-hummel/globals.nsf/resources/tmt2002.PDF/$File/tmt2002.PDF
"A point source driver radiates spherically until it reaches its TL mode"
what is TL mode?
"...above its 1/2 space point or ~13560"/pi/effective diameter..."
what is 1/2 space point?
i do undertand that 13560" is sound speed
divised by effective diameter, what exacly does PI
do in there? related to half space?
i have yet to grast the notion of full space, 1/2 space, 1/4 space and so on ...
half space is half of a sphere ??
thus where the driver moves to "plane" ?
"Overlapping sound waves sum their particles, not 'scatter', so if unimpeded it will ~maintain its shape as air friction over distance causes its eventual complete decay. This distance is great enough for low frequencies that we can ignore it though."
please elaborate..i do not completly understand that statement ...
i am very visual, and unfortunatly, sound waves aren't easy to see...do you have any videos of moving sound waves ( simulations maybe ) that would express that kind of behavior?
"Anyway, I'm not really following some of your thoughts or Qs and haven't kept up with all the different versions of your build, so can't really contribute much""
you have already contributed alot with all your advanced information , and my version is always evolving with my perception and understanding of the different compromises and choices
my goal is simple, best possible performance for HT setup within my 25' by 20' room
and for me, HT = dynamics
that is one of the main reason why i am trying to move on with alot of drivers
"...what you need to work it out for a ~planar sub system that will turn your room into the equivalent of a sub-bass to ~160 Hz BW 1/2 WL resonator with a deep notch at its midpoint... "
what you mean is that it would turn my room into a
"tube like" where the bass would move on in a planar form ? why do you say 1/2 WL resonator ?
and why the deep notch at the midpoint?
i do not understand why there would be a deep notch...
is it because of the reflected delayed waves from the back that would "sum" with the front waves at midpoint?
that would be the equivalent of a 1/2WL mode ?
"...If you can damp it at the other end well enough it will turn into a damped 1/4 WL resonator with notches at its odd harmonics, so in either case you want the XO point/slope to roll it off below these notches and ideally taper your walls and ceiling into a horn to help with a rapid decay of 'slap' echo just like in any concert hall...."
how can it turn to a 1/4WL resonator if there is no back waves boucing off the rear ?( assuming perfect absorption.. )
odd harmonics? again like modal resonances?
taper the walls into a horn... going smaller at the back or bigger at the back ?
i would assume smaller because of the losses ...
lastly... i do not still understand how a planar wave can be assumed..i seriously thought that in sub bass, with a distributed array of drivers just like in the DBA thread and paper, one could assume some kind of near perfect planar wavefront up to a certain frequ.
still missing some information as how waves behave with eachother at this low frequencies going out spherically from the drivers ....
and i thank you again for your time and effort
to help me understand more and have a better final plan for my big project
Yes, you do, it's painfully obvious you're asking about designing/making something that you don't have a clue what it is or at least my understanding of what a planar wave array is and how it should perform and I don't know how to explain it any more simply than I already have without resorting to a bunch of sketches that I don't have time to do without devoting all my forums time on it, which I'm not willing to do. I mean I've already given you all the rules, math (complete with example) you need to get the job done AFAIK.
By wave collapse I mean there's not enough driver output overlap for a given frequency, so each driver will be a distinct source instead of part of a whole.
'Sound is round', so you can draw it to scale with a compass or in a drafting program to see how much overlap there is for a given frequency, driver c-t-c- and driver/wall spacing.
AFA learning this stuff, I imagine all this is taught in one form or another at an engineering college since it's just physics, but not being able to do advanced math, mine's mostly from experience with a little help from my more educated friends and books like this one: http://www.amazon.com/Sound-System-...2923326?ie=UTF8&s=books&qid=1192773926&sr=8-1
Anyway, it's after 2 am, maybe someone in a different time zone can/will be able to either better explain it or point you to some websites that do.
By wave collapse I mean there's not enough driver output overlap for a given frequency, so each driver will be a distinct source instead of part of a whole.
'Sound is round', so you can draw it to scale with a compass or in a drafting program to see how much overlap there is for a given frequency, driver c-t-c- and driver/wall spacing.
AFA learning this stuff, I imagine all this is taught in one form or another at an engineering college since it's just physics, but not being able to do advanced math, mine's mostly from experience with a little help from my more educated friends and books like this one: http://www.amazon.com/Sound-System-...2923326?ie=UTF8&s=books&qid=1192773926&sr=8-1
Anyway, it's after 2 am, maybe someone in a different time zone can/will be able to either better explain it or point you to some websites that do.
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