Ah yes, the BIB-thread liveth and reigneth itinually (loose variation on a Lee Perry album title).
The 15" Fanes I have now calculate into a BIB that is far too large for me, but it keeps whispering in my ear. "Build me... Build me...."
The 15" Fanes I have now calculate into a BIB that is far too large for me, but it keeps whispering in my ear. "Build me... Build me...."
Missed this......... You read about 'tophats' then to extend designs to taller ceilings, so depending on the driver can be an option.
GM
Right, totally forgot about some of these drivers having huge magnets and/or deep frames.
GM
A ~5 ft^3 net BIB is too big?! For what, a closet? Or is the driver's measured Vas much larger than its published ~203 L spec?
GM
GM
Qts is 0.7, so (0.7^1.25)*203*20= 2599.5 liters. The minimal version is 1805 liters.
Or am I calculating that wrong?
5 cubic feet seems small. According to a conversion tool, it's 141 liters.
Or am I calculating that wrong?
5 cubic feet seems small. According to a conversion tool, it's 141 liters.
My minimal calculation would suggest 63.7 cubic feet. That's what the formula poops out as minimal for my Tangband W69-1042.
I was basically ignoring the parts of the calculator that determine's net Vb same as we've done to adjust path length, etc., and why I implied it would be an under damped mid-bass tuning to keep the size as low as practical, which according to the pioneers is Vas/1.44.
After all, the standard BIB is under damped and performs well in room, so seems reasonable that maintaining the same tuning, but with a net Vb that will only strongly load it to the mid bass will work too, though admittedly I've only done it with my BIB variant from long ago, which is more akin to a ML-horn, so might not.
Only one way to know for sure.
GM
After all, the standard BIB is under damped and performs well in room, so seems reasonable that maintaining the same tuning, but with a net Vb that will only strongly load it to the mid bass will work too, though admittedly I've only done it with my BIB variant from long ago, which is more akin to a ML-horn, so might not.
Only one way to know for sure.
GM
I being a student here, am really keen on setting clear a few questions on BIB speakers. Could any of you please offer your insights and experience?
1. With the Vb required being so much greater than the Vas, does the driver tend to behave as if working in free air? Also does it mean that the system Q will be only nominally higher than the Qts?
2. How much increase in sensitivity can be expected from a driver used in a BIB?
3. Since there is no coupling chamber nor a constricted throat opening into the expanding pipe, am i right in my understanding that there won't be a 1st order low pass working on the output of the driver from the mouth? Does it also mean that the sensitivity lift will be heard all through the frequency band of the mid-bass cone?
4. Since the Vb is going to be too large, i understand the driver would work very very lightly loaded. With the Fostex 6" driver having only 1 mm of Xmax and Cms > 1, how would it take even 3-4 watts without bottoming out?
I look forward to some light on this. Please do excuse me if you find my questions silly! 🙂
Thanks!
sujat
1. With the Vb required being so much greater than the Vas, does the driver tend to behave as if working in free air? Also does it mean that the system Q will be only nominally higher than the Qts?
2. How much increase in sensitivity can be expected from a driver used in a BIB?
3. Since there is no coupling chamber nor a constricted throat opening into the expanding pipe, am i right in my understanding that there won't be a 1st order low pass working on the output of the driver from the mouth? Does it also mean that the sensitivity lift will be heard all through the frequency band of the mid-bass cone?
4. Since the Vb is going to be too large, i understand the driver would work very very lightly loaded. With the Fostex 6" driver having only 1 mm of Xmax and Cms > 1, how would it take even 3-4 watts without bottoming out?
I look forward to some light on this. Please do excuse me if you find my questions silly! 🙂
Thanks!
sujat
1. No, it's working against a full WL conical horn loading [which isn't much]. System Q [sysQ] will be lower than the driver's as shown in the impedance plot Vs IB.
2. Depends on room loading; referenced to mid band efficiency, none.
3. There is a coupling chamber of sorts created by the impedance mismatch at the driver, so from there back to the tip of the horn is the low pass filter, but it's so lossy it won't peter out till it reaches the driver's upper mass corner [Fhm], hence the need for some damping.
4. It won't, actually it will really only have small fractions of Xmax available due to being tuned so far below Fs, but due to the horn gain in room that's similar to the super high cabin gain in a mobile audio app there's your built in baffle step compensation [BSC], so combined with the driver's high mid band efficiency it's already loud enough that a 'flea' power amp is sufficient. The only real advantage to higher power is for EQing the driver around/above its [Fhm].
Fhm = 2*Fs/Qts'
Qts' = Qts + any added series resistance [Rs]: HiFi Loudspeaker Design
You're welcome! Quite astute actually. Are you a 'student' student or just one here WRT the BIB?
GM
2. Depends on room loading; referenced to mid band efficiency, none.
3. There is a coupling chamber of sorts created by the impedance mismatch at the driver, so from there back to the tip of the horn is the low pass filter, but it's so lossy it won't peter out till it reaches the driver's upper mass corner [Fhm], hence the need for some damping.
4. It won't, actually it will really only have small fractions of Xmax available due to being tuned so far below Fs, but due to the horn gain in room that's similar to the super high cabin gain in a mobile audio app there's your built in baffle step compensation [BSC], so combined with the driver's high mid band efficiency it's already loud enough that a 'flea' power amp is sufficient. The only real advantage to higher power is for EQing the driver around/above its [Fhm].
Fhm = 2*Fs/Qts'
Qts' = Qts + any added series resistance [Rs]: HiFi Loudspeaker Design
You're welcome! Quite astute actually. Are you a 'student' student or just one here WRT the BIB?
GM
Thank you for such considerate treatment of my questions, GM! I am really not as familiar as you with the technical behaviour of driver-cabinet systems. I will need some time to allow this to assimilate.
True, I'm on the 'slippery slope' to 74 and still learning, though too often nowadays it's stuff I've forgotten. 
GM
GM
Hmm, the horn has a large acoustic mass it's working against that shifts the system tuning lower whereas the ~aperiodic box is an acoustic resistor.
GM
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What about it? The BIB is tuned a full octave below Fs [Fs/2] and since it's a 'fast' expanding [low gain] conical horn with lots of air mass, its pipe horn action turns it into 'chop suey' 😉: http://www.quarter-wave.com/General/Fostex_FE-167E_BIB_Design.pdf
Speaker wiring at minimum, usually ~0.5 ohm unless using the wire size as an inline resistor; then any resistive components in frequency shaping filters and last, but least, the high output impedance of an amp's output transformers, which can double the driver's effective Qts all by itself.
GM
You're welcome!
I know it well enough in my own way to design horns, etc., but don't have the higher math skills to work it out 100% correctly, so sometimes one the horn gurus will correct me for whatever reason, so being a student other than just a DIYer wanting a little help with a build, best to have Bjorn elaborate and/or correct my responses.
GM