I am building a new set of speakers and after all the reading, I'm considering an infinite baffle (with a mid and tweet) sitting on top of the bass module.
I have modeled several Scan Speak 7or 8" drivers for the bass modules, and they look good on paper. The bass module will use 2 drivers and be approximately 14" wide by 18" deep by 42 " tall and be vented to the rear.
The mid I will be using is the Scan speak 12M/4631G 4.5" midrange.
I am considering the LCY ribbons or Scan Speak D2904/9800 or D2905/9700 for the tweets.
I will be biamping with an active X-over between the bass module and Mid, and am considering the AR series X-O between the mid and tweet. I may also go active between the mid and tweet. The x-over duties will be handled by a Marchand 3 way active X-over (XM-44).
My main question is about the infinite baffle size and performance. How big and what shape willl give you what frequency response ? Is there a specific formula that models the size of the baffle? Mid or tweet on top ? Will the LCY ribbons work well in an infinite baffle design.
My initial thoughts are 350hz and 3500hz x-over points.
These are rather pricey drivers, but if they are that good maybe it's worth it. I am also looking for recommenations of other
drivers that may perform at a similar level, but may be a little easier on the wallet ?
James
I have modeled several Scan Speak 7or 8" drivers for the bass modules, and they look good on paper. The bass module will use 2 drivers and be approximately 14" wide by 18" deep by 42 " tall and be vented to the rear.
The mid I will be using is the Scan speak 12M/4631G 4.5" midrange.
I am considering the LCY ribbons or Scan Speak D2904/9800 or D2905/9700 for the tweets.
I will be biamping with an active X-over between the bass module and Mid, and am considering the AR series X-O between the mid and tweet. I may also go active between the mid and tweet. The x-over duties will be handled by a Marchand 3 way active X-over (XM-44).
My main question is about the infinite baffle size and performance. How big and what shape willl give you what frequency response ? Is there a specific formula that models the size of the baffle? Mid or tweet on top ? Will the LCY ribbons work well in an infinite baffle design.
My initial thoughts are 350hz and 3500hz x-over points.
These are rather pricey drivers, but if they are that good maybe it's worth it. I am also looking for recommenations of other
drivers that may perform at a similar level, but may be a little easier on the wallet ?
James
I'm interested, what made you go for 7" or 8" drivers for the bass module?
Aslong as size/waf isn't too much of a factor, nothing succeeds like surface diameter, esp when it comes to the bass.
Moving up to bigger drivers will bring a noticable increases in dynamics and spl capabilities, aswell as lower distortion.
And, to be honest, there's no excuse not to have some nice big speakers in one of those big ol' American houses
Aslong as size/waf isn't too much of a factor, nothing succeeds like surface diameter, esp when it comes to the bass.
Moving up to bigger drivers will bring a noticable increases in dynamics and spl capabilities, aswell as lower distortion.
And, to be honest, there's no excuse not to have some nice big speakers in one of those big ol' American houses
it was very late last night when I had that "deep thought"..... sorry about that ! I shouldn't post when I'm asleep !!
it was really a 'play' on the terminology used, which I think is probably not the right terminology to be using, although in many other area of life we redefine words to suit our purposes I guess.
to me, an 'infinite baffle loudspeaker' is one where the driver is flush with a very large surface, eg a wall, and has a very large volume behind it eg another room, , large enough so that there cannot possibly be any box effects on the driver.
It cannot really be a moveable loudspeaker as far as I can see ??
But we could argue about terminology that all day, I guess, so I'm not going to !!
I shouldn't post when I'm asleep !!it was really a 'play' on the terminology used, which I think is probably not the right terminology to be using, although in many other area of life we redefine words to suit our purposes I guess.
to me, an 'infinite baffle loudspeaker' is one where the driver is flush with a very large surface, eg a wall, and has a very large volume behind it eg another room, , large enough so that there cannot possibly be any box effects on the driver.
It cannot really be a moveable loudspeaker as far as I can see ??
But we could argue about terminology that all day, I guess, so I'm not going to !!
that seems a reasonable assumption to me.
you can add wings or a short section at 90 degrees (good for stability too) and lower the roll-off freq that way as well. Just don't make the wings go back too far or you start creating a hollow.
T and E !! use some cheap mdf for trials, go to nice timber later !
you can add wings or a short section at 90 degrees (good for stability too) and lower the roll-off freq that way as well. Just don't make the wings go back too far or you start creating a hollow.
T and E !! use some cheap mdf for trials, go to nice timber later !
IMHO there has to be no rear wave in the listening area at all if it's going to be called "infinite" baffle. If a "really large" baffle qualifies as "infinite" then the term loses any distinct meaning. I can see what you're saying though, at some point there's likely not much audible difference between a giant open baffle and a wall.
When does open baffle become big enough to practically be considered infinite baffle?
When the baffle is big enough to have no dipole cancellation within its bandwidth. Lets say you consider the bandwidth going down to 20 Hz.
Using the formula fequal = 0.17 x 344/D
transposed gives
D = (0.17 x 344)/fequal
fequal = 20 Hz
hence
D = 2.9m
The baffle if flat would have to be 5.8m wide, and wouldn't fit in most rooms! If you really wanted it to be infinite baffle, you would have to put it in the wall.
Choose a bandwidth extending down to 40 Hz and then the baffle "only" needs to be 2.9m wide.
Regarding that design, the mid driver is much too small to operate in open baffle mode. It would bottom with a moderate amount of power, and require eq to even go flat down to a point where you would cross to the woofer.
To get fequal at 200 Hz requires a 600mm wide front baffle, or 300mm wide plus 450mm deep wings. Unfortunately the wings don't help the sound, and take away the openess of an OB design. Hence you need a driver that can move more air even for a midrange OB. That tiny driver won't have a chance of keeping up with those midbasses in terms of output.
I'd say a 6.5" driver is a minimum for an OB, and an 8" is probably a better choice. I'd also consider going with OB bass as well.
Something like Behringer Ultradrive is worth considering for a project like this, or perhaps you should look at Linkwitz site as he has a cheapish prototype you can build, even a passive version.
I think for the bass drivers you are looking at not infinite baffle but acoustic suspension. If you have a certain box volume to VAS ratio you may consider a box to be infinite baffle - I think it is about 10.
When the baffle is big enough to have no dipole cancellation within its bandwidth. Lets say you consider the bandwidth going down to 20 Hz.
Using the formula fequal = 0.17 x 344/D
transposed gives
D = (0.17 x 344)/fequal
fequal = 20 Hz
hence
D = 2.9m
The baffle if flat would have to be 5.8m wide, and wouldn't fit in most rooms! If you really wanted it to be infinite baffle, you would have to put it in the wall.
Choose a bandwidth extending down to 40 Hz and then the baffle "only" needs to be 2.9m wide.
Regarding that design, the mid driver is much too small to operate in open baffle mode. It would bottom with a moderate amount of power, and require eq to even go flat down to a point where you would cross to the woofer.
To get fequal at 200 Hz requires a 600mm wide front baffle, or 300mm wide plus 450mm deep wings. Unfortunately the wings don't help the sound, and take away the openess of an OB design. Hence you need a driver that can move more air even for a midrange OB. That tiny driver won't have a chance of keeping up with those midbasses in terms of output.
I'd say a 6.5" driver is a minimum for an OB, and an 8" is probably a better choice. I'd also consider going with OB bass as well.
Something like Behringer Ultradrive is worth considering for a project like this, or perhaps you should look at Linkwitz site as he has a cheapish prototype you can build, even a passive version.
I think for the bass drivers you are looking at not infinite baffle but acoustic suspension. If you have a certain box volume to VAS ratio you may consider a box to be infinite baffle - I think it is about 10.
Derf, in that case the path difference (D) is so large that it would not likely have any dipole cancellation within the audible bandwidth. IB is probably most used with subwoofers, where drivers are ceiling mounted, and the volume of the attic space is the "infinite" air volume, or at least large enough to be considered as infinite.
it's not only the low frequencies that come around the baffle though, pushing the low frequency diploe rolloff down below the audio range is fine, but above that you still have higher frequency back waves bouncing around the room interacting with the front wave. Assuming it's a round baffle (as using a single number for D does) you get a comb filtered high frequency response, and still figure of 8 radiation pattern right?
Infinite baffle using a wall has no out of phase rear radiation interacting with the front wave at all, avoids baffle step compensation and box resonances, but has it's own problems I imagine. The wall is a pressure peak for some room modes and a presure node for others, so you'd get an all or nothing excitation of them I guess.
Infinite baffle using a wall has no out of phase rear radiation interacting with the front wave at all, avoids baffle step compensation and box resonances, but has it's own problems I imagine. The wall is a pressure peak for some room modes and a presure node for others, so you'd get an all or nothing excitation of them I guess.
From Vifa's (DST) site:
Conditions for measurements
--------------------------------------------------------------------------------
This is a short description of the measuring methods used at vifa/scan-speak.
FREQUENCY RESPONSE
The frequency response curves are measured in one of vifa/scan-speaks anechoic chambers.
The chambers are 6x7x8 meters which gives a lower cut-off frequency at 100 Hz.
The curves are measured in 0°, 30° and 60° with microphones in a distance of 1 meter. The input voltage is 2.83 V.
One of the walls in the anechoic chamber is without damping material and acts like an infinite baffle (2-pi room) for the driver. Behind the driver is a closed box - typically at 320 litres.
cheers,
AJ
Conditions for measurements
--------------------------------------------------------------------------------
This is a short description of the measuring methods used at vifa/scan-speak.
FREQUENCY RESPONSE
The frequency response curves are measured in one of vifa/scan-speaks anechoic chambers.
The chambers are 6x7x8 meters which gives a lower cut-off frequency at 100 Hz.
The curves are measured in 0°, 30° and 60° with microphones in a distance of 1 meter. The input voltage is 2.83 V.
One of the walls in the anechoic chamber is without damping material and acts like an infinite baffle (2-pi room) for the driver. Behind the driver is a closed box - typically at 320 litres.
An externally hosted image should be here but it was not working when we last tested it.
cheers,
AJ
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