At home I use a 6 1/2 inch woofer in my folded voigt style speakers, only 4 foot tall, length of line is 7 ft. sounds great, the midbass is far superior to ported designs, and people cannot believe the amount of subbass that comes from them, people are always looking for the seperate sub bass unit that does not exist. I am very interested to hear how awsome the results will be with a 12". Wow interesting plan
tinitus said:From what I can read the BIB is a compromise by simulating a number of drivers.... from 5" to 8" .... with a fixed length
Are you really sure this will work with a 12"
I am not good in maths ... but dont you get a big change in exstension of the horn when the slanted inner baffle is that much wider in relation to the BIBs with smaller drivers
Good questions. Answering them in order:
No. I occasionally restrict line-length with low Fs drivers to keep cabinet height, and driver position to reasonable levels. In a BIB, horn length is determined by 1/2 the wavelength of the tuning frequency. Usually this is set to Fs, or just below, but if you've a low Fs driver things can get out of hand, so I tune a bit higher. FWIW, I've built a pair with the Fostex FF225K for a friend before now, which were 89in tall, approximately 178in line length to math their 38Hz Fs. Sound was -er, rather impressive. Like my FF165K boxes, but larger. In this case, we've a 45Hz Fs, which equates to a half-wavelength of roughly 150in.
Oh yes indeed. Of course it will work with a 12in driver. The physics doesn't change just because it's got a hefty cone area. Higher Vas & Qt simply require a larger box (cone-area per se has little to do with it).
No. Vb needs to swamp, or come close to swamping, the driver's Vas. Width and depth dimensions are usually selected to preserve the conical horn profile (depth needs to be 1.414 times width) though there is plenty of room for experiment here. Terry Cain's original cabinet had a 1:2.2 ratio for example. So long as CSA is preserved, you can try different things out. The internal baffle terminates in the centre of the cabinet, the same distance from the floor as from the internal front and rear walls.
The point above the driver needs a light layer of stuffing, and a nice thick carpet of the stuff on the internal base will absorb any stray HF and damp out reflections. Beyond that, stuff to taste once in-room. Because they use the room as part of the speaker, they all need somewhat different quantities, though most of the time, the above is all that you'll find necessary.
Deflector panels are a bad idea BTW guys -the bass we want couldn't care less if a corner is smooth or not, but the unwanted HF does. So abrupt is the order of the day.
Doesn't sound too scientific I know, but it works. The more we learn, the more we forget. These simple, traditional corner horns are as effective now as they ever were. 3 watts into these will blow your windows out. And they do dynamics like little else you will ever hear from full range, or wide-range, drivers.
punkrokr1701 said:
Miracle!!! We are all in agreement- or as close as is possible for this group. Punkrockr- I really think these will do it for you. It is amazing that you will get your wish at about a quarter of the budget we had gotten up to! The only expense is the 12" driver at this time, and a lot of plywood or MDF.
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=290-409&scqty=2
I got their actual price and it's $58 each. So for under $150 including shipping you will have all you need to get started. You can add the tweeter later, after the cabinets are finished and even after you have tried them with just the 12" at first if you want..
If the cost of plywood is too much you CAN use MDF (medium density fiberboard) . MDF is available in lumber yards and Home Depot type places. It is like a very dense particle board (DON"T use particle board!) The good thing about it is that it is only about $25 a sheet in 3/4" thickness. The bad things are: It is very heavy. Each speaker will use about two and a half sheets minimum so you and your dad should try picking up two sheets together in the store and decide if you can or want to carry a speaker of more than that weight, plus the driver weight.. The other bad thing is that it isn't anyways near as strong as plywood, so if you move the speakers much the corners will be damaged and worse. Of course at that weight, you probably won't be moving them much, unless you are thrown out of your house because the police keep coming due to neighbors reporting too loud music.....
Many people prefer the sound of Plywood in this use, but the differences are sure to be subtle enough to not matter to you. Still plywood is the best choice, and I found someting called "imported birch" at about $40 a sheet which worked very well for my big home speakers. So check different places...
Seems like you will need six sheets....
Hey Scott! the 16.5" dimension is a small problem. If the internal width were 16", then we could get 3 pieces from one of the pieces of plywood. (actually 2 saw kerfs would eat up another 1/4" so the optimal would be 15 and 11/12's ! . So can it be made a tad deeper front to back? and a smidge narrower? We would get three from a sheet. The sides could be more than two feet as we will probably cut one side and one front or back from a sheet...The saw could be set and cut the 4 fronts and backs , and 4 internal baffles in one shot.
THIS isn't a big deal, as only one sheet will probably have 3 side strips cut from it, so don't compromise if it is a problem...
I will draw up plans, and it would be nice to fix this if possible, but it isn't essential...
Punkrockr: this will take a couple of days or more to draw up!.
THIS isn't a big deal, as only one sheet will probably have 3 side strips cut from it, so don't compromise if it is a problem...
I will draw up plans, and it would be nice to fix this if possible, but it isn't essential...
Punkrockr: this will take a couple of days or more to draw up!.
You can reduce the width by 0.5in. Just boost depth to 24.25in to maintain Vb and you should be fine. it departs from the ~ideal conical, but not by much.
The drivers are PA, the BIB type cabinet less so (apart from the size). Frankly, I wouldn't worry too much about origins anyway. I see nothing that suggests this should not work, and be a very entertaining, inexpensive project.
Path starts at the point at the top, expands downward, then flares back up and vents out of the top of the cabinet.
The drivers are PA, the BIB type cabinet less so (apart from the size). Frankly, I wouldn't worry too much about origins anyway. I see nothing that suggests this should not work, and be a very entertaining, inexpensive project.
Path starts at the point at the top, expands downward, then flares back up and vents out of the top of the cabinet.
Internal depth of the terminus is 24.25in. Assuming 3/4in build material (& I suspect doubling the side panels might be a good move BTW) add 2.25in to that for a total external cabinet depth of 26.5in. Nothing really... (though I did a dipole horn that's 32in deep a while back).
So the internal baffle needs to terminate centrally; 12 1/8 inches from the front and rear internal baffles, and the same distance from the internal base.
So the internal baffle needs to terminate centrally; 12 1/8 inches from the front and rear internal baffles, and the same distance from the internal base.
How about this link?
http://melhuish.org/audio/DIYTQ8.html
I guess I'm still skeptical about "full range drivers", since you have what's really a mechanical crossover. It just seems like black magic to me, regardless of how much everyone likes it.
Regardless, if the midrange isn't to your liking I don't see any reason why you couldn't substitute the Beta 12 CX in its place at a later date.
http://melhuish.org/audio/DIYTQ8.html
I guess I'm still skeptical about "full range drivers", since you have what's really a mechanical crossover. It just seems like black magic to me, regardless of how much everyone likes it.
Regardless, if the midrange isn't to your liking I don't see any reason why you couldn't substitute the Beta 12 CX in its place at a later date.
Good to see you work it out
Knowing what a good 8" can do in a horn, I am sure Punk will be amazed with lots of bass
As to "PA" origin of driver, I am sure it will work fine for rockandroll.... propably Punk will like the "bite"
A wrong crossover can do a lot of worse things to a speaker
In this case it might be enough to have a cheap Selenium slothorn supertweeter with a single small condensator
Knowing what a good 8" can do in a horn, I am sure Punk will be amazed with lots of bass
As to "PA" origin of driver, I am sure it will work fine for rockandroll.... propably Punk will like the "bite"
A wrong crossover can do a lot of worse things to a speaker
In this case it might be enough to have a cheap Selenium slothorn supertweeter with a single small condensator
So let me see if I understand this BIB thing and what we are doing here. Information on TL stuff is a bit scattered, and there are so many flavors that it's hard to know exactly what's what.
The BIB is a back loaded horn, more or less. It is an almost conical horn with the pointy end near the driver and the open end pointing up. The length is folded in 1/2.
The length of the horn is determined by the Fs of the driver. Length equals 1/2 wavelength of driver Fs +/- a few Hz for tuning reasons. So it's a twisted or folded half wave tube. The driver is cut into the cone somewhere near the pointy end.
Width of box = driver width?
Depth = 1.414 width.
Mouth area is WxD
Length = 1/2 Fs wavelength - folded.
Baffle wall starts in top front corner and descends to center point of box depth equidistant from back, front, bottom.
Sound about right?
Seems simple enough.
What determines Fo (or Z) - the driver placement?
How can the box be "optimized"?
The BIB is a back loaded horn, more or less. It is an almost conical horn with the pointy end near the driver and the open end pointing up. The length is folded in 1/2.
The length of the horn is determined by the Fs of the driver. Length equals 1/2 wavelength of driver Fs +/- a few Hz for tuning reasons. So it's a twisted or folded half wave tube. The driver is cut into the cone somewhere near the pointy end.
Width of box = driver width?
Depth = 1.414 width.
Mouth area is WxD
Length = 1/2 Fs wavelength - folded.
Baffle wall starts in top front corner and descends to center point of box depth equidistant from back, front, bottom.
Sound about right?
Seems simple enough.
What determines Fo (or Z) - the driver placement?
How can the box be "optimized"?
You're there more or less. It's a 1/4 wave enclosure with a line length of 1/2 wavelength of the tuning frequency (it can't be a 1/2 wave enclosure though unless it's open at both ends ;-)
Width of the box is determined by how much Vb you need to swamp the driver's Vas. Depth you've identified. You're spot on with the location of the internal baffle. It's an So=0 pipe (So being the CSA of the sealed end, which in this case comes to a point, and effectively has no surface area at all) for maximum pipe gain over the widest possible frequency range. Driver placement in the line is determined by needing to minimise the harmonic null F3, though there is a little leeway if needed.
The cabinet I posted for this driver theoretically is about the optimal as it is. It could do with being a little larger, but it'd be daft to go much further -it's big enough as it is. There's no way of taking it further in the theory because these corner horns don't have a mouth of their own per se, just a terminus. It's the room that forms the mouth, so until it's in position, you won't know what damping modifications to make to best match it to your own room.
Best
Scott
Width of the box is determined by how much Vb you need to swamp the driver's Vas. Depth you've identified. You're spot on with the location of the internal baffle. It's an So=0 pipe (So being the CSA of the sealed end, which in this case comes to a point, and effectively has no surface area at all) for maximum pipe gain over the widest possible frequency range. Driver placement in the line is determined by needing to minimise the harmonic null F3, though there is a little leeway if needed.
The cabinet I posted for this driver theoretically is about the optimal as it is. It could do with being a little larger, but it'd be daft to go much further -it's big enough as it is. There's no way of taking it further in the theory because these corner horns don't have a mouth of their own per se, just a terminus. It's the room that forms the mouth, so until it's in position, you won't know what damping modifications to make to best match it to your own room.
Best
Scott
It's 1/8 space the terminus fires into, and we've also got extremely powerful 1/4 wave resonant action so we can bring that down considerably. Technically they're horns due to the positive taper and end-loading, but the physics is nothing fancy -see Martin King's Classic TL alignment tables for straight & tapered lines.
There is indeed a dip in the midbass, but it's not that severe -it's actually a consequence of the driver positioning -ideally it should be elsewhere for a flat response, preferably at about 0.416 line length, but that would put the driver just about on the floor, so we compromise here by using the next best thing that's closest to ear-height. These specific cabinets will be very powerful to 30Hz (~ flat, ignoring a little of ripple) with a final cut off of around 18-19Hz.
Best
Scott
There is indeed a dip in the midbass, but it's not that severe -it's actually a consequence of the driver positioning -ideally it should be elsewhere for a flat response, preferably at about 0.416 line length, but that would put the driver just about on the floor, so we compromise here by using the next best thing that's closest to ear-height. These specific cabinets will be very powerful to 30Hz (~ flat, ignoring a little of ripple) with a final cut off of around 18-19Hz.
Best
Scott
Whoops, I didn't move Andrew T's interesting post from the old thread and don't know how to at the moment, but here it is :
As has been posted around here , very little rock is anywhere near as low as 35hz. The lowest note of an electric bass is 42 hz I believe, but most of its output even at that note is the first resonance, at double that. So, for Punkr, this is a theorectical discussion.
However, a lot of these have been made, and seem to work, so I see no problem for him.
Hey Mr. Moose, is there an optimal distance from the top of the box to the ceiling? Maybe we can customize Punkr's cabinet optimally..
As has been posted around here , very little rock is anywhere near as low as 35hz. The lowest note of an electric bass is 42 hz I believe, but most of its output even at that note is the first resonance, at double that. So, for Punkr, this is a theorectical discussion.
However, a lot of these have been made, and seem to work, so I see no problem for him.
Hey Mr. Moose, is there an optimal distance from the top of the box to the ceiling? Maybe we can customize Punkr's cabinet optimally..
Wrong. And right as well. Why wrong? The BIB's gain back wave begins at 1/2 wavelength, it's positive tapered and end loaded. That, by definition, is a horn. Of course, life being what it is, you're also 100% correct at the same time, because all of the above also applies to TQWTs, which are in reality horn, not TL varients. So it's both, because both are effectively the same thing. My head hurts now. One of those gray areas that's developed over the last few decades. GM took me through this some time ago.
Re optimal distance, ideally, it needs to be such as to ~'perfectly' continue the conical expansion, but it'd need someone with more math ability than me to figure it out. An 8 - 12 foot ceiling is usually a good compromise. More than that and you start to loose a bit of the LF, depending on the height of the enclosure of course.
So it's both, because both are effectively the same thing. My head hurts now. One of those gray areas that's developed over the last few decades. GM took me through this some time ago.Re optimal distance, ideally, it needs to be such as to ~'perfectly' continue the conical expansion, but it'd need someone with more math ability than me to figure it out. An 8 - 12 foot ceiling is usually a good compromise. More than that and you start to loose a bit of the LF, depending on the height of the enclosure of course.
Joe's point that someone could substitute a 12" with a coaxial tweeter into this design at some point is a good one. I hope someone will try that . There are a WHOLE lot of 12" drivers out there with a coax horn tweeter. Of course for this design, at this time, we will stick with the Eminence 12" whizzer cone model, which has its own advantages..
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