168es
Hi, I’m almost to the building stage of the 168es BIB and I have some questions along the lines of recent posts by ghpicard and leglandu. My original plan was to build out of cheapest ply I could find, see how I like them and how they mate in my room. I have purchased 17mm rough ply and plan to screw them together to make tuning the damping easier. The above posts have indicated that 17mm is not thick enough so I am thinking of adding a layer of 3mm MDF at least to the internal surfaces and possibly to the outside of the box to enable me to veneer them later if I want. My question is whether to rigidly attach the MDF to with some sort of wood glue or is there going to be any benefit from using beads of a flexible adhesive like silicon in irregular pattern to give a more lossy panel.
I have been thrashing the drivers in cardboard boxes at work and they sound remarkably good even though driven by the most despicable mini system imaginable……very alive and dynamic although they can be sharp too.
Regards, Andrew.
Hi, I’m almost to the building stage of the 168es BIB and I have some questions along the lines of recent posts by ghpicard and leglandu. My original plan was to build out of cheapest ply I could find, see how I like them and how they mate in my room. I have purchased 17mm rough ply and plan to screw them together to make tuning the damping easier. The above posts have indicated that 17mm is not thick enough so I am thinking of adding a layer of 3mm MDF at least to the internal surfaces and possibly to the outside of the box to enable me to veneer them later if I want. My question is whether to rigidly attach the MDF to with some sort of wood glue or is there going to be any benefit from using beads of a flexible adhesive like silicon in irregular pattern to give a more lossy panel.
I have been thrashing the drivers in cardboard boxes at work and they sound remarkably good even though driven by the most despicable mini system imaginable……very alive and dynamic although they can be sharp too.
Regards, Andrew.
Best glue for holding bits of wood together seems to be hot animal hide glue which you can get at any craft supplier. It contracts when it dries by a substantial amount and pulls the panels together even more tightly than a standard bonding glue does.
Never tried it with mdf... Should work fine.
Aquadhere (white PVA woodworking glue) is fine too.
Drew
Never tried it with mdf... Should work fine.
Aquadhere (white PVA woodworking glue) is fine too.
Drew
Thanks Drew, yes animal skin glue is a terrific glue; I share my workshop with a cabinet maker who uses it quite regularly. Its an almost medieval process boiling it up. But I was thinking there may be an advantage in a loose attachment , allowing loss of the higher frequencies energy in the box rather than out of the mouth, but maybe using only beads of silicon to adhere the mdf panel with the majority of the surface free to vibrate may be too loose and damp bass respose as well, dont know. Try it I guess....bit irreversable though, Andrew
Pebbles:
Sorry if I created some confusion... A looong time ago GM (IIRC) suggested making the front, middle and back baffles of chipboard and the sides plywood, as a measure to better damp frequencies over the bandwidth of the horn.
In my last post I'm saying what I got for free !!! And I got enough material for four 1" boards and two 1/2" boards, so I needed to know what was suggested. It's not a matter of choice but of cost. If I had to pay for it, I would have used "plane Jane" chipboard, as it is suggested. And if I had had ply available for free, that's what I would have used.
Another issue I have is that I need to make this one shot the best one I can, so I'm being as picky as I can afford (and I can't afford much, you can rest assured of that).
So don't feel discouraged by what I said. It only applies to my specific BIB, and relates to my specific needs. Or need$, as you prefer
Gastón
P.S.: I've bought 15 mm pine ply, 5 layer, two 1.22 x 2.44 meters for 43 USD each, and I confirmed what I feared. "Premium" meant "not so damaged as the rest of the boards". Not to mention the seller (the local version of Home Depot) didn't carry 18 mm as they advertised. So you can see you aren't so bad with your materials
Sorry if I created some confusion... A looong time ago GM (IIRC) suggested making the front, middle and back baffles of chipboard and the sides plywood, as a measure to better damp frequencies over the bandwidth of the horn.
In my last post I'm saying what I got for free !!! And I got enough material for four 1" boards and two 1/2" boards, so I needed to know what was suggested. It's not a matter of choice but of cost. If I had to pay for it, I would have used "plane Jane" chipboard, as it is suggested. And if I had had ply available for free, that's what I would have used.
Another issue I have is that I need to make this one shot the best one I can, so I'm being as picky as I can afford (and I can't afford much, you can rest assured of that).
So don't feel discouraged by what I said. It only applies to my specific BIB, and relates to my specific needs. Or need$, as you prefer
Gastón
P.S.: I've bought 15 mm pine ply, 5 layer, two 1.22 x 2.44 meters for 43 USD each, and I confirmed what I feared. "Premium" meant "not so damaged as the rest of the boards". Not to mention the seller (the local version of Home Depot) didn't carry 18 mm as they advertised. So you can see you aren't so bad with your materials
I do not think that a BIB will necessarily be significantly better by optimizing a single parameter such as material stiffness.
A BIB will have a lot of acoustic resonances (that is why it works). It will have diffractions and reflections, esp. from the internal baffle through the cone. There will be room reflections, and there will be a mixture of material resonances.
A nice blend of all this may make a very listenable result.
Damping most of the fairly benign material resonances spread over a wide frequency band, might leave only the nasty ones.
Modest material thickness, and selective bracing for larger panels may be good enough - and save some money and keep the weight down
SveinB
A BIB will have a lot of acoustic resonances (that is why it works). It will have diffractions and reflections, esp. from the internal baffle through the cone. There will be room reflections, and there will be a mixture of material resonances.
A nice blend of all this may make a very listenable result.
Damping most of the fairly benign material resonances spread over a wide frequency band, might leave only the nasty ones.
Modest material thickness, and selective bracing for larger panels may be good enough - and save some money and keep the weight down
SveinB
ghpicard said:
Greets!
I hope I didn't, at least not as a general rule-of-thumb. Now, where a BIB panel is going to be snug up against another boundary such as the bottom/floor junction, MDF, or better still, an even more lossy material such as the cheapest particleboard (PB) you can find works well to create a constrained layer damped panel composite. To use it on other panels though requires a fairly tight fit, so just pushed in the corner up against any baseboards won't work well unless a filler piece is added, which can be any lossy PB.
Never tried it, but one can argue using thick open cell foam as a bottom panel or wall spacer if a good seal around the cab's perimeter can be made, though finding the right density to get its BW EQ'd ~flat in-room could be a time consuming, tedious affair, but for the perfectionist could be an elegant acoustical solution to an acoustic problem.
The internal baffle can be a lossy 3/4" Pb in fairly narrow pipes, though at some as yet undetermined width it must be braced well with strips of void free plywood or similarly rigid material bonded on edge at a golden or acoustic ratio centered along ~80% of its axial length (i.e. parallel to the side walls) on at least one side to keep from rolling off too much of its BW. FYI, it need not span/ be bonded to the opposite wall to work well, so you can use long scraps of at least 1.5" width since they won't be visible except potentially to giants.
Anyway, any normally visible panel, i.e. baffle, side(s) should always be a very rigid, stable, void free material since it's essentially free standing and that once positioned in-room, the perimeter of the mouth be extremely rigid to keep it from 'ringing', just like any other horn mouth.
GM
GM said:
Greets!
I hope I didn't, at least not as a general rule-of-thumb. Now, where a BIB panel is going to be snug up against another boundary such as the bottom/floor junction, MDF, or better still, an even more lossy material such as the cheapest particleboard (PB) you can find works well to create a constrained layer damped panel composite. To use it on other panels though requires a fairly tight fit, so just pushed in the corner up against any baseboards won't work well unless a filler piece is added, which can be any lossy PB.
Never tried it, but one can argue using thick open cell foam as a bottom panel or wall spacer if a good seal around the cab's perimeter can be made, though finding the right density to get its BW EQ'd ~flat in-room could be a time consuming, tedious affair, but for the perfectionist could be an elegant acoustical solution to an acoustic problem.
The internal baffle can be a lossy 3/4" Pb in fairly narrow pipes, though at some as yet undetermined width it must be braced well with strips of void free plywood or similarly rigid material bonded on edge at a golden or acoustic ratio centered along ~80% of its axial length (i.e. parallel to the side walls) on at least one side to keep from rolling off too much of its BW. FYI, it need not span/ be bonded to the opposite wall to work well, so you can use long scraps of at least 1.5" width since they won't be visible except potentially to giants.
Anyway, any normally visible panel, i.e. baffle, side(s) should always be a very rigid, stable, void free material since it's essentially free standing and that once positioned in-room, the perimeter of the mouth be extremely rigid to keep it from 'ringing', just like any other horn mouth.
GM
Greets, GM !
Thanks for your detailed explanation. You can blame the coarse generalization on me. I totally agree that the "chipboard inside" has its limitations when we start to think of big builds. I was thinking that diagonal bracing in the baffle (and sides) was the way to go, so your suggestion of parallel bracing is most interesting.
Gastón
168es BIB
Hi, thanks for all replies and comments. Ghpicard, no confusion caused, I had just realised my materials were probably a bit on the skinny side and was wondering what would be the most advantageous way to increase their thickness without replacing them.
Now let me see if I understand the posts correctly. Leaving aside GM's elegant solution involving open celled foam to line interior and tune BW to room response which would be beyond my current level of experience, is what I'm after basically a rigid pipe with a lossy internal baffle and possibly base, with bracing for the mouth?. On the standard 168es BIB would bracing be nescessary at the mouth and is it OK to be internal as in two pieces of dowel spanning both pairs of sides, which I would prefer as it is not visible(any issues re terminus area and/or reflections?) or outside the BIB which is probably better because it avoids any above issues but would be an eyesore? Regards, Andrew
Hi, thanks for all replies and comments. Ghpicard, no confusion caused, I had just realised my materials were probably a bit on the skinny side and was wondering what would be the most advantageous way to increase their thickness without replacing them.
Now let me see if I understand the posts correctly. Leaving aside GM's elegant solution involving open celled foam to line interior and tune BW to room response which would be beyond my current level of experience, is what I'm after basically a rigid pipe with a lossy internal baffle and possibly base, with bracing for the mouth?. On the standard 168es BIB would bracing be nescessary at the mouth and is it OK to be internal as in two pieces of dowel spanning both pairs of sides, which I would prefer as it is not visible(any issues re terminus area and/or reflections?) or outside the BIB which is probably better because it avoids any above issues but would be an eyesore? Regards, Andrew
Re: 168es BIB
Greets!
You're welcome!
Hmm, I didn't mention the side walls as I figured the diagonal internal baffle would be sufficient, at least I didn't add any to the few large pipe horns I did except in the mouth area. In these areas a nominally parallel brace would actually be on the diagonal due to the taper, right?
WRT the internal baffle itself, my cabs were wide/flat, so even with 3/4" no-void marine grade plywood it needed bracing and for lack of thought/education beyond not wanting to add undue turbulence in the horn's passband (as opposed to its TL BW where the WLs were somewhat > in size WRT the horn's CSA) I used a parallel brace on the front and rear, each off-set at a 1:1.4 acoustic ratio popular back then.
Anyway, in theory, opposing diagonal braces on the internal baffle and its 'parallel' wall would help decay the pipe's upper harmonics, so maybe these should be standard pieces regardless of whether it needs extra bracing or not.
Any experimenters willing to 'tackle' this one?
GM
ghpicard said:
Greets!
You're welcome!
Hmm, I didn't mention the side walls as I figured the diagonal internal baffle would be sufficient, at least I didn't add any to the few large pipe horns I did except in the mouth area. In these areas a nominally parallel brace would actually be on the diagonal due to the taper, right?
WRT the internal baffle itself, my cabs were wide/flat, so even with 3/4" no-void marine grade plywood it needed bracing and for lack of thought/education beyond not wanting to add undue turbulence in the horn's passband (as opposed to its TL BW where the WLs were somewhat > in size WRT the horn's CSA) I used a parallel brace on the front and rear, each off-set at a 1:1.4 acoustic ratio popular back then.
Anyway, in theory, opposing diagonal braces on the internal baffle and its 'parallel' wall would help decay the pipe's upper harmonics, so maybe these should be standard pieces regardless of whether it needs extra bracing or not.
Any experimenters willing to 'tackle' this one?
GM
If I understand you , you are suggesting that the cabinet be "cut in half on the vertical axis with a divider/brace?
Would this be an opportunity to try my idea of tuning each side a little differently to "average out" the big dips?
Anyone able to play with this? What would shift the dips? a different sized chamber above the driver? a longer chamber? make the divider brace offset from the center? Maybe someone with the worksheets could do some computer simulation?
The two horns would just average out and behave like the combined horn does ?
hmmmm
Would this be an opportunity to try my idea of tuning each side a little differently to "average out" the big dips?
Anyone able to play with this? What would shift the dips? a different sized chamber above the driver? a longer chamber? make the divider brace offset from the center? Maybe someone with the worksheets could do some computer simulation?
The two horns would just average out and behave like the combined horn does ?
hmmmm
With adding a brace, either wood or the dowels, the pennants mentioned earlier in the thread may become easier. The braces could be wrapped with dampening creating a filter. Or, if dowels were used, the pennant could be attached to it and then the top sides. You could experiment with its tension and amount to filter out unwanted HF.
Variac said:
As far as I understand, the bracing would be affixing > 1.5" ply (i.e.) strips like if they were internal fins, so no "double paralleled horn" effect.
Now, as I only got 15 mm pine ply (that seems not have been seasoned at all and is warping more and more by the hour
) for the sides I am thinking in placing one or two of this "fins" on each side, keeping the ratio of distance in the terminus and the lower portion.i.e. if I have at the bend:
internal baffle + 1/3 * (depth/2) + fin + 1/3 * (depth/2) + fin + 1/3 * (depth/2) + back baffle
I would have at the terminus:
front baffle + 1/3 depth + fin + 1/3 depth + fin + 1/3 depth + back baffle
The 1/3 depth separation is arbitrary and only as an example. The real one should be some uneven ratio.
Also, as GM said, perhaps parallel to the back and of different length depending on the distance to the back (to avoid much disturbance to the baffle) is a better idea.
Gastón
OK- about that tapered chamber above the driver. Is its length important, or are we just changing the length to adjust the volume?
Does it have to taper?
If the second, then I'm tempted to space the driver well away from the rest of the box ( like , say a 6" thick suprabaffle) and get more distance behind the driver to get less reflexion back through the driver..
Its sometimes hard to figure out what is done for convenience with the BIB and what is done because it is a theoretical best. They sound so good, that a little more box complexity would be OK by me..
Does it have to taper?
If the second, then I'm tempted to space the driver well away from the rest of the box ( like , say a 6" thick suprabaffle) and get more distance behind the driver to get less reflexion back through the driver..
Its sometimes hard to figure out what is done for convenience with the BIB and what is done because it is a theoretical best. They sound so good, that a little more box complexity would be OK by me..
OK, the BIB is a chamberless (pipe) horn notionally intended for corner placement, though that last is not critical providing it's damped properly, and expanding in a linear fashion. Basically, imagine drawing a linear horn, folding it in half, and then tapping the driver into this horn at Z distance along the flare to help supress the harmonic modes as much as possible (you'd need a much larger pipe & a more complicated flare profile to erradicate them, just like any horn).
The Zdriver position (Z distance along the flare) is selected for practical reasons. For a tall pipe, generally 0.2 - 0.217 line length is used as this position gives the best supression of harmonic resonances while keeping the driver vagely near ear-height. For an inverted type of enclosure (usually for drivers with a relatively high Fs), I favour the 0.416 line length Zdriver position Martin King suggests in his TL Alignment Tables for a 1:10 expanding line, which although not the same as an So=0 pipe is a good starting point. This is actually superior to the 0.217 line length in terms of flat response once damped, but for an upward venting design, or a tall inverted cabinet, would either put the driver on the floor, or about 3 foot over the listeners head, which isn't much use except for sub-bass duties, where directionality is less of an issue. I should mention at this point that Greg isn't convinced this is the best location for the driver; neither it would appear is Tom Danley (both of whom are audio Gods, despite their modesty), although the latter's TOP tapped horn subwoofer is using a different expansion ratio & AFAIK is a trunkated pipe rather than an So=0 design, both of which affect the optimal driver position, to say nothing of the TOP using the radiation from both sides of the driver to drive the line. I've no reason to doubt Greg (or TD), & I'll never have his experience & knowledge; I'm simply going by what the sims I've run indicates. YMMV.
FWIW, you could always add a chamber, with the driver in it, as a pod-like addition to the side, & tap in at the appropriate distance along the line. I'm not sure how much difference it would make though, as you'll still be activating the line-harmonics with the fundamental, and it's one more complicating factor. The (better IMO) alternative would be to design a regular, chambered BLH from scratch specifically intended for upward-venting like the familiar basic BIB.
The Zdriver position (Z distance along the flare) is selected for practical reasons. For a tall pipe, generally 0.2 - 0.217 line length is used as this position gives the best supression of harmonic resonances while keeping the driver vagely near ear-height. For an inverted type of enclosure (usually for drivers with a relatively high Fs), I favour the 0.416 line length Zdriver position Martin King suggests in his TL Alignment Tables for a 1:10 expanding line, which although not the same as an So=0 pipe is a good starting point. This is actually superior to the 0.217 line length in terms of flat response once damped, but for an upward venting design, or a tall inverted cabinet, would either put the driver on the floor, or about 3 foot over the listeners head, which isn't much use except for sub-bass duties, where directionality is less of an issue. I should mention at this point that Greg isn't convinced this is the best location for the driver; neither it would appear is Tom Danley (both of whom are audio Gods, despite their modesty), although the latter's TOP tapped horn subwoofer is using a different expansion ratio & AFAIK is a trunkated pipe rather than an So=0 design, both of which affect the optimal driver position, to say nothing of the TOP using the radiation from both sides of the driver to drive the line. I've no reason to doubt Greg (or TD), & I'll never have his experience & knowledge; I'm simply going by what the sims I've run indicates. YMMV.
FWIW, you could always add a chamber, with the driver in it, as a pod-like addition to the side, & tap in at the appropriate distance along the line. I'm not sure how much difference it would make though, as you'll still be activating the line-harmonics with the fundamental, and it's one more complicating factor. The (better IMO) alternative would be to design a regular, chambered BLH from scratch specifically intended for upward-venting like the familiar basic BIB.
No worries. Best would be the triangular braces Greg's suggesting if you can cut them. Like those shown in the attached render of a sub-horn version I did with Dave for the CSS Subduction 12in unit.
Generally speaking, I like the BIB the way it is (appropriately damped & braced). Quick, simple & big sound per £ value.
Generally speaking, I like the BIB the way it is (appropriately damped & braced). Quick, simple & big sound per £ value.
Attachments
Sloping top on BIB
Hi, one last (unlikely) little question before I duck off and build something. I read earlier in this thread that sloping the top of the BIB back toward the rear was a good idea for smoothing the entry of the sound into the room; I might have this as an option in my prototype. Would this be a 45 degree(roughly) slope and where would I then assume the line terminated when calculating the dimensions? Halfway down the slope, at the rear or does it not matter a fraction of an iota (whatever that is)? As always, grateful for advice, Andrew
Hi, one last (unlikely) little question before I duck off and build something. I read earlier in this thread that sloping the top of the BIB back toward the rear was a good idea for smoothing the entry of the sound into the room; I might have this as an option in my prototype. Would this be a 45 degree(roughly) slope and where would I then assume the line terminated when calculating the dimensions? Halfway down the slope, at the rear or does it not matter a fraction of an iota (whatever that is)? As always, grateful for advice, Andrew