Quote "I have a question about the part of the path above the driver. Does it have to flare at all? or is it just a nice coincidence that that area tapers which makes a nice trap? So could I make it any shape as long as the length is correct? Hmm any volume change there would do what?"
Variac: the area above the driver is not there by coincidence as this is a horn and this is part of the horn. The position along the horn where the driver fires into the horn has in most cases been adjusted to keep the driver at an acceptical hight above the floor. I would think (but I may be wrong) that the driver would best fire into the horn at the point where the cross sectional area of the horn equals the driver. Above that point on the horn the area can be tapered to Zero but it can also be kept at the same area as the driver Sd so that So=Sd. Perhaps Scott could provide a couple of simulations showing the effect of both approaches.
My thought would be to design the horn length and flair. Then set the driver at the point where the horns cross sectional area matched the driver Sd this would then be where you would mount the driver and and then adjust the crossectional area (of the horn) above this point so that it also equals Sd all the way back to the apex. Scott your comments on this approach would be appreciated.
It may be that the ideal point along the horn for the driver to be mounted would be set by the driver perameters. So you would take the driver T/S datas and calculate the approiate throat area and then position the driver at the point along the horn from the apex to where the two areas match. Regards Moray James.
Variac: the area above the driver is not there by coincidence as this is a horn and this is part of the horn. The position along the horn where the driver fires into the horn has in most cases been adjusted to keep the driver at an acceptical hight above the floor. I would think (but I may be wrong) that the driver would best fire into the horn at the point where the cross sectional area of the horn equals the driver. Above that point on the horn the area can be tapered to Zero but it can also be kept at the same area as the driver Sd so that So=Sd. Perhaps Scott could provide a couple of simulations showing the effect of both approaches.
My thought would be to design the horn length and flair. Then set the driver at the point where the horns cross sectional area matched the driver Sd this would then be where you would mount the driver and and then adjust the crossectional area (of the horn) above this point so that it also equals Sd all the way back to the apex. Scott your comments on this approach would be appreciated.
It may be that the ideal point along the horn for the driver to be mounted would be set by the driver perameters. So you would take the driver T/S datas and calculate the approiate throat area and then position the driver at the point along the horn from the apex to where the two areas match. Regards Moray James.
bibster said:
Scottmoose said:
This looks new to me and was not a consideration
when I cut wood, though I used the recommendations here
for the FE127e.
Is this bit part of the calcualtions at the BIB site?
I just made a mule (one experimental build not a pair).
From a couple listening tests I'm undecided as to what
the BIB approach does for sound.
But my test amp is a Radio Shack SA-155. I've never liked
the sound of anything through that.
Other test which sounded better was on my Yamaha
RP-U100 for dvd and soundcard streaming audio.
The only thing I'll note right now is that a tight fit to
the wall in a corner to get maximum throw from the
wall corners did not give good sound. That sound was
through the SA-155.
I plan to add some sort of round/oval baffle on to the
mule and move it out of that corner. (Maybe I'll
put some wheels on it
)
Hi there,
I have a question, I can't decide which dimension BIB to build!
It's about Fostex FE206E. I was considering to build a shorter version, 1.8 m height, as oposed to 2.2 m one. On the positive side, the shorter BIB is has got more WAF points, although I could manage to build a "proper" one as well, but receive somewhat less praise
So, I have to make a compromise:
1.Domestically accepted BIBs, (1.8m) or,
2. Two huge towers. (2.2 m)
Scottmoose, maybe you can help. If the shorter BIB is not much worse than the taller one, I'd go for that. However, if the proper one (2.2 m tall) provides much better bass response, than maybe I could take a risk and build that one.
Thanks,
Vix
I have a question, I can't decide which dimension BIB to build!
It's about Fostex FE206E. I was considering to build a shorter version, 1.8 m height, as oposed to 2.2 m one. On the positive side, the shorter BIB is has got more WAF points, although I could manage to build a "proper" one as well, but receive somewhat less praise
So, I have to make a compromise:
1.Domestically accepted BIBs, (1.8m) or,
2. Two huge towers. (2.2 m)
Scottmoose, maybe you can help. If the shorter BIB is not much worse than the taller one, I'd go for that. However, if the proper one (2.2 m tall) provides much better bass response, than maybe I could take a risk and build that one.
Thanks,
Vix
Scottmoose said:
Scott, you've written this many times. Since I'm sure you know what you're talking about, there must be something I'm missing. My understanding has been that a conical horn has the same flare as a cone (seems obvious enough
). A cone has a cross section that is proportional to the square of the distance along the length. Consider a cone (or anything with the same flare) with a length L and terminus cross section Sm. Half way along the length (L/2) the cross section will be Sm/4.The BIB most definitely has a cross section that is linearly proportional to the distance along the length. Half way along its length (basically, at the fold) the cross section is Sm/2.
So what am I missing? This has bugged me for a long time.
I'm confused by this too, no doubt for the same reason as above. I just don't see how the ratio of WxD changes the flare rate. No matter what WxD happens to be, the cross section at the fold (half way along the pipe) is Sm/2.
Again, what am I missing?
moray james said:
As I've already demonstrated my ignorance on this design, I probably have no business responding, but my ignorance knows no boundaries.
My understanding is that the driver placement has more to do with the cab's functioning as a transmission line than as a horn. Simply put, the transmission line has many resonant modes. The only one you really want to excite is the 1/4 wave mode. You want to keep from exciting the 3/4, 5/4, ... modes as much as possible. Different driver positions along the length of the pipe will excite (or won't excite) different modes to different degrees. Ultimately, the choice of position is a compromise, but presumably some compromises are much better than others.
-- Dave
Re: Re: BIB question: sm for radio shack 40-1285D
See above example. GM is the better person to ask regarding the details of this one, as his background knowledge is frightening, and I follow his guidance -Greg is the horn guru as far as I'm concerned. FWIW you also need to remember we're firing into a corner which is automatically a 1/8 space conical expansion and forms an extension of the enclosure.
Re the driver placement, you're quite correct -the location is related to 1/4 wave resonance theory and achieving the best possible balance between preserving first-mode gain, and minimising the activation of harmonics. The ideal theoretical place is actually around 0.434 line-length, but given that would put the driver on the floor, we go for half that which provides the best practical compromise and puts the driver conveniently at ~ear-height in the vast majority of cases. Strictly speaking, most expanding pipes are variations on the horn theme as they are end-loaded, and positively tapered, & therefore posesses both odd and even harmonic modes. With 1/2 wavelength tuning, which is notionally ideal for a horn, putting velocity highest at the throat, the BIB falls into this definition.
GM said:
See above example. GM is the better person to ask regarding the details of this one, as his background knowledge is frightening, and I follow his guidance -Greg is the horn guru as far as I'm concerned. FWIW you also need to remember we're firing into a corner which is automatically a 1/8 space conical expansion and forms an extension of the enclosure.
Re the driver placement, you're quite correct -the location is related to 1/4 wave resonance theory and achieving the best possible balance between preserving first-mode gain, and minimising the activation of harmonics. The ideal theoretical place is actually around 0.434 line-length, but given that would put the driver on the floor, we go for half that which provides the best practical compromise and puts the driver conveniently at ~ear-height in the vast majority of cases. Strictly speaking, most expanding pipes are variations on the horn theme as they are end-loaded, and positively tapered, & therefore posesses both odd and even harmonic modes. With 1/2 wavelength tuning, which is notionally ideal for a horn, putting velocity highest at the throat, the BIB falls into this definition.
Hey Scott,
So... does that mean, if you had high ceilings (10-11 feet) and used one of the fe127 or fe103 (edit or even Supravox 165lb! etc.) in a BIB that had been 'straightened out' to its full length of ca 100 inches, so it is like a big cone and put the driver at an 'ideal' .434 its length (therefore getting it at a suitable 43.4inches off the floor) it would sound pretty good? Just an idea....
Cheers Stroop
So... does that mean, if you had high ceilings (10-11 feet) and used one of the fe127 or fe103 (edit or even Supravox 165lb! etc.) in a BIB that had been 'straightened out' to its full length of ca 100 inches, so it is like a big cone and put the driver at an 'ideal' .434 its length (therefore getting it at a suitable 43.4inches off the floor) it would sound pretty good? Just an idea....
Cheers Stroop
Right. Providing you have a tall enough ceiling, no reason at all why you can't do exactly that. You'd just need to juggle the damping material a little as the bend helps attenuate some of the unwanted HF that goes into the horn. I really should look into a chambered version of a BIB at some point, but I never seem to have the time. I'm in the middle of a Nagaoka style double back-horn that I'm designing with Dave at the moment, and I just haven't had chance to look at the blasted thing for over a week. Sorry Dave. Work's taken over a bit recently, aside from a couple of quick posts. Hense the lack of sims. After Wednesday I should have a bit more time on my hands. Hopefully.
Hi,
Well, made some testboxes over the weekend, and I must admit that I'm impressed... I'm not so experienced at building (nor listening!!) but I really like this..
Anyway, I ran into one, little, issue:
I made the testboxes out of the cheapest 15mm I could find: Particle board (Alway makes me think of the TMBG song... particle man.. ).
(No, no pics, I'll make some when I yank up the real ones, okay?)
I thought I'd make them (the REAL ones) out of 15mm multiply, so I'd TEST with the same thickness.
I made the boxes in according with the 'right' proportions (1:sqrt(2)) so inner dims are 14 wide, 19.8+15mm depth. (Fostex FE127e, 43sq." Sm)
When I wanted to insert the driver @ 49.5 off of the top, well..... I couldn't..
I had to 'double' the baflle with 5mm, and even then the drive allmost touches the inner baffle, and , me thinks, the driver sort of completely blocks the passway over there.
Should I, for the REAL ones, do (both) the following things ?
1: Opt for the 63 sq." version (with more bass, I'd like that I think..)
2a: Opt for a suprabaffle or-whatever-that's-called.
2b: Opt for a (locally) thicker baffle, by adding (say) a 22mm thick square, same width as the cabinet.
I prefer 2b over 2a as I think it has higher WAF.
With either option, I think I recall it's good practice to chamfer the inside of the mounting-hole, right?
Thanks for your help,
Bibster
Well, made some testboxes over the weekend, and I must admit that I'm impressed... I'm not so experienced at building (nor listening!!) but I really like this..
Anyway, I ran into one, little, issue:
I made the testboxes out of the cheapest 15mm I could find: Particle board (Alway makes me think of the TMBG song... particle man..
).(No, no pics, I'll make some when I yank up the real ones, okay?)
I thought I'd make them (the REAL ones) out of 15mm multiply, so I'd TEST with the same thickness.
I made the boxes in according with the 'right' proportions (1:sqrt(2)) so inner dims are 14 wide, 19.8+15mm depth. (Fostex FE127e, 43sq." Sm)
When I wanted to insert the driver @ 49.5 off of the top, well..... I couldn't..
I had to 'double' the baflle with 5mm, and even then the drive allmost touches the inner baffle, and , me thinks, the driver sort of completely blocks the passway over there.
Should I, for the REAL ones, do (both) the following things ?
1: Opt for the 63 sq." version (with more bass, I'd like that I think..)
2a: Opt for a suprabaffle or-whatever-that's-called.
2b: Opt for a (locally) thicker baffle, by adding (say) a 22mm thick square, same width as the cabinet.
I prefer 2b over 2a as I think it has higher WAF.
With either option, I think I recall it's good practice to chamfer the inside of the mounting-hole, right?
Thanks for your help,
Bibster
The Hemp BIB's are upstairs and playing. I actually got them set up last night. They sound fantastic. They are entirely different from the previous set up with these drivers, sealed boxes and a TL sub. They have an incredible amount of bass. My sealed enclosures didn't have BSC, so I'm used to a lean, slightly bright sound. These sound like the heavyweights they are, though they are very agile. The bass on some recordings sounds really tight and quick, on others it sounds bloated. Either way, it sounds much flatter, clearer and more articulate than my previous set up. The midbass quality is stunning.
They drivers hardy move at average listening levels. The cabinets vibrate less than the previous enclosures, which is interesting given the size of the unbraced sections. I was planning to add some exterior bracing, but I don't think it will be necessary. Nothing but bass is coming out of the mouths. Both panel resonances and midrange through the horns were concerns of mine.
So far the only downside is the driver height. My chair isn't that high. I listen off axis anyway so the tonal balance is fine, but the sound is way up in the air. My old enclosures were too low, and I got used to them, so I'm sure I'll get used to this.
I hate to make judgements without listening longer, but overall they seem to be a big step up. I'll post some pics later. I also hope to make some SPL measurements.
Paul
construction details again: dims: Scottmoose's of zilla's site (sm is actually 201). Due to an error I decided not to correct, the aspect ratio is 1.46. All 18mm Baltic Birch ply, front baffles are double thick. They have a handle/brace across the mouth, I'll post a pic of it. They each have a pound of acoustuff. Half of it is teased from just below the driver to the top of the line. The other half is in the bottom. I used PL Premium Polyurethane construction adhesive as glue. I highly recommend it if you can't cut to with 1/64". I can't. It's a pleasure to work with, just don't get it on anything.
They drivers hardy move at average listening levels. The cabinets vibrate less than the previous enclosures, which is interesting given the size of the unbraced sections. I was planning to add some exterior bracing, but I don't think it will be necessary. Nothing but bass is coming out of the mouths. Both panel resonances and midrange through the horns were concerns of mine.
So far the only downside is the driver height. My chair isn't that high. I listen off axis anyway so the tonal balance is fine, but the sound is way up in the air. My old enclosures were too low, and I got used to them, so I'm sure I'll get used to this.
I hate to make judgements without listening longer, but overall they seem to be a big step up. I'll post some pics later. I also hope to make some SPL measurements.
Paul
construction details again: dims: Scottmoose's of zilla's site (sm is actually 201). Due to an error I decided not to correct, the aspect ratio is 1.46. All 18mm Baltic Birch ply, front baffles are double thick. They have a handle/brace across the mouth, I'll post a pic of it. They each have a pound of acoustuff. Half of it is teased from just below the driver to the top of the line. The other half is in the bottom. I used PL Premium Polyurethane construction adhesive as glue. I highly recommend it if you can't cut to with 1/64". I can't. It's a pleasure to work with, just don't get it on anything.
I wionder if anyone has experience with what happens when the mouth of the horn is more than , say two feet from the ceiling. Does this affect the bass output because there are only 2 planes involved (the walls) vs. three planes (walls and ceiling)? I suspect it works pretty well either way, and in fact, all three affect the out put even if the mouth is 3 or 4' from the ceiling, but it would be nice to know the optimal spacing.
I have dodged a bullet in my one BIB test mule in that
I can reposition the back panel enough to compensate
for that difference in the measures for completion of the
horn as stated in the post above #1877.
I was too lazy to trim off the bit of excess on the
glued up commercial shelving I used and so by releasing the
glue joint with a putty knife could likely make the
adjustment.
other things first though.
Sonic impact t-amps are backordered at Parts Express
until January of 2007. This puts many things on hold.
But I'm ready to try the build with a supra baffle made from
a ready-to-paint plaque from the Hobby Lobby. Finding
the exact center of an elipse came close by eye but still
not professional grade and off by a bit. I got some round
ones as well and may run into the same centering
problems.
And a question: For ceiling loading (which seems muddy
if the BIB is tight and square to the corner) will angling
out to allow for better dispersion of the driver to the
listener position improve tonal balance. I have yet to
try the BIB at a 45d angle from the wall and an improved
amp over the Radio Shack SA 155.
I can reposition the back panel enough to compensate
for that difference in the measures for completion of the
horn as stated in the post above #1877.
I was too lazy to trim off the bit of excess on the
glued up commercial shelving I used and so by releasing the
glue joint with a putty knife could likely make the
adjustment.
other things first though.
Sonic impact t-amps are backordered at Parts Express
until January of 2007. This puts many things on hold.
But I'm ready to try the build with a supra baffle made from
a ready-to-paint plaque from the Hobby Lobby. Finding
the exact center of an elipse came close by eye but still
not professional grade and off by a bit. I got some round
ones as well and may run into the same centering
problems.
And a question: For ceiling loading (which seems muddy
if the BIB is tight and square to the corner) will angling
out to allow for better dispersion of the driver to the
listener position improve tonal balance. I have yet to
try the BIB at a 45d angle from the wall and an improved
amp over the Radio Shack SA 155.
Re: The big bear has gone....
My sympathies to Terry's wife Leslie and the family.
Please keep us informed of the need for help with
expenses via the auction that is now in progress. I was
working up a donation of a build and thought I had more
time.
Terry will be remembered in the work that we build and
have built from his inspiration.
GM said:
My sympathies to Terry's wife Leslie and the family.
Please keep us informed of the need for help with
expenses via the auction that is now in progress. I was
working up a donation of a build and thought I had more
time.
Terry will be remembered in the work that we build and
have built from his inspiration.
Amen to that. Godspeed my friend. And my heartfelt sympathy to Leslie at this difficult time.
Thank you Greg, for letting us know. I wish I'd known Terry better. I think this thread actually contains his last on-line contribution. He was a craftsman, a canny speaker designer, and an enthusiast who tried to help people consider different options rather than following a proscribed path.
More importantly, he was just a decent bloke. The world is a little emptier for his passing. But we'll remember him in our work. It's a good memory and memento to have.
Scott
Thank you Greg, for letting us know. I wish I'd known Terry better. I think this thread actually contains his last on-line contribution. He was a craftsman, a canny speaker designer, and an enthusiast who tried to help people consider different options rather than following a proscribed path.
More importantly, he was just a decent bloke. The world is a little emptier for his passing. But we'll remember him in our work. It's a good memory and memento to have.
Scott
