Size and shape of infinite baffle

[j.burtt]

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

[derf]

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

[Andy G]

just a thought.. (don't take seriously)

how can an infinite baffle have a size and shape ??

[derf]

I think he means a sealed enclosure, some literature used to refer to the two as one and the same(before the adoption of infinite baffle designs?)

[derf]

I think I took it too seriously

[boydon_lepasci]

Or perhaps he means "open baffle"? I believe Dickason's Cookbook defines infinite baffle as a sealed box with a volume at or above the driver's Vas?

[j.burtt]

I'm sorry for my ignorance on the terminology. here is a pic from Humble Homemade HIFI that shows what I am looking for.

[hitsware]

Originally posted by boydon_lepasci
Or perhaps he means "open baffle"? I believe Dickason's Cookbook defines infinite baffle as a sealed box with a volume at or above the driver's Vas?

He says at least 3 x Vas

[Andy G]

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 !!

[Andy G]

if you mean the way the mids are used in that diagram.

what you have to take into account is the frequency below which the sound from the rear of the driver will cancel the sound from the front. The size of the "open baffle" will determine this.