Hello all,
I've finally did it;
made a pair of BiB's using the Hemp FR8c
Great sound, really window shaking with techno and metal, BUT...
it seems lots of music hasn't got the <80hz bass mode so
most of the lower bass regions fall right into the responce ripple a BiB displays....
Is there any way to reduce the ripple ?
Cheers,
Empee
I've finally did it;
made a pair of BiB's using the Hemp FR8c
Great sound, really window shaking with techno and metal, BUT...
it seems lots of music hasn't got the <80hz bass mode so
most of the lower bass regions fall right into the responce ripple a BiB displays....
Is there any way to reduce the ripple ?
Cheers,
Empee
By "resonance ripple region", do you mean the midbass suckout on the graph? Are you hearing it, or just scared by the sight of the graph? When wall/ceiling/corner loaded, that suckout won't occur in the room to nearly the same extent it appears in the simulation. Do you have them against a wall or in corners?
pj
pj
Hi !
Yes, I'm referring to the suck-out as you said, and I am really hearing it.
And when I run a frequency sweep from CD, the ripple is enormous (really not enjoyable......)
Too bad,
because on bassheavy tracks they produce really fine music
They are placed against the rear wall
(will post pictures later)
Cheers,
Empee
Yes, I'm referring to the suck-out as you said, and I am really hearing it.
And when I run a frequency sweep from CD, the ripple is enormous (really not enjoyable......)
Too bad,
because on bassheavy tracks they produce really fine music
They are placed against the rear wall
(will post pictures later)
Cheers,
Empee
Have you run a frequency sweep with other speakers in the room (or other rooms)? Nothing will be flat, most rooms are +/- 20db or more. Check out the inroom response measurements that Stereophile publishes with each big speaker review (available for free online). They usually look like enormous sawtooths, even with measurements averaged from 20 different mic positions. As they prove, it doesn't matter if you have $40,000 ruler flat speakers. If you want to to be able to play sweeps and have it sound flat, the BIB is the least of your problems. You'll need to get some digital EQ and some room treatments that make the BIBs look small.
You can flatten out the BIB with a little damping. I'm using 3lbs of polyfill in each mouth (top couple of feet), and it should reduct ripple.
pj
You can flatten out the BIB with a little damping. I'm using 3lbs of polyfill in each mouth (top couple of feet), and it should reduct ripple.
pj
Where did you get those dimensions from? Did you use any of the math on the BIB site or the spreadsheets to calc. them?
This driver isn't a particularly good choice for a pipe-horn in that it needs a gigantic cabinet to perform optimally. Assuming it's tuned to the claimed 45Hz Fs of the driver, then it needs a Vb of nearly 21.5 cubic feet, or rather more than 607.5 litres if you prefer. That's a terminus CSA of 492in^2 (or 0.31753m^2). I'm not surprised you've got problems -that pipe, big as it is, really isn't large enough for the new FR8C.
Are they corner-loaded. If you've got a smaller than optimal pipe, then they really need to be pushed back as far as possible into corners to get as much help from the room as they can & fill in the dip at the 3rd harmonic. Without that, there will be a ~6db drop centred at 95Hz.
This driver isn't a particularly good choice for a pipe-horn in that it needs a gigantic cabinet to perform optimally. Assuming it's tuned to the claimed 45Hz Fs of the driver, then it needs a Vb of nearly 21.5 cubic feet, or rather more than 607.5 litres if you prefer. That's a terminus CSA of 492in^2 (or 0.31753m^2). I'm not surprised you've got problems -that pipe, big as it is, really isn't large enough for the new FR8C.
Are they corner-loaded. If you've got a smaller than optimal pipe, then they really need to be pushed back as far as possible into corners to get as much help from the room as they can & fill in the dip at the 3rd harmonic. Without that, there will be a ~6db drop centred at 95Hz.
Yes, to be brutally honest, they're too small for the driver, unless you're corner-loading them (which is generally needed to mostly kill the 3rd harmonic dip anyway). Especially as the Hemp driver has an upward-tilting FR. Sorry. What method did you use for selecting these dimensions BTW? How far along the horn is the driver tapped in?
Most drivers can, in principle, be loaded in a pipe-horn, but its best if you design the box for the driver. If it's not possible to properly corner-load the enclosures, then I would be inclined to do something else with your drivers. In a fully sized pipe-horn they'll outperform many other speakers, but they will be very large -too much so for many people, so something mass-loaded will probably be the best bet.
FWIW, you can try damping things a bit & see how far you get. I don't know what you're doing at the moment, but try lightly stuffing the point above the driver & a layer on the internal base, and either line the terminus about 12in from the top down on all faces, or hang a pennant of damping material (carpet underlay or whatever) down the 2nd half of the flare.
Most drivers can, in principle, be loaded in a pipe-horn, but its best if you design the box for the driver. If it's not possible to properly corner-load the enclosures, then I would be inclined to do something else with your drivers. In a fully sized pipe-horn they'll outperform many other speakers, but they will be very large -too much so for many people, so something mass-loaded will probably be the best bet.
FWIW, you can try damping things a bit & see how far you get. I don't know what you're doing at the moment, but try lightly stuffing the point above the driver & a layer on the internal base, and either line the terminus about 12in from the top down on all faces, or hang a pennant of damping material (carpet underlay or whatever) down the 2nd half of the flare.
Hi Scott !
I got them backed up against the wall,
but will try if things improve by shoving them in the corners...
Have some stuffing above the driver, carpet right behind the
driver, carpet on the base.
But if I was to buy a new set of drivers for these pipe's,
what would you suggest ?
I it possible to derrive the drivers specs from a given pipe ?
driver is 850mm from closed end
(btw, the dimensions are my own, and I derrived them from
the initial Hemp-BiB dimensions as in that HUGE BiB-thread,
in combination with the available space in my room, standard
sheet size, WAF... And there was this saying by one of the
participants in that thread stating "how forgiving these pipes are"
plus I didn't want to bother you and others asking for sims and all.....
I got them backed up against the wall,
but will try if things improve by shoving them in the corners...
Have some stuffing above the driver, carpet right behind the
driver, carpet on the base.
But if I was to buy a new set of drivers for these pipe's,
what would you suggest ?
I it possible to derrive the drivers specs from a given pipe ?
driver is 850mm from closed end
(btw, the dimensions are my own, and I derrived them from
the initial Hemp-BiB dimensions as in that HUGE BiB-thread,
in combination with the available space in my room, standard
sheet size, WAF... And there was this saying by one of the
participants in that thread stating "how forgiving these pipes are"
plus I didn't want to bother you and others asking for sims and all.....
That's what the spreadsheets were for -to make sizing the cabinets easy for people. It's a pity Jeff hasn't uploaded any to the site, but the raw math is there.
Unfortunately most of those early cabinet dimensions on the site were done before an optimal volume calculation for a pipe-horn was worked out (by GM), so they are now superceded. The Hemp ones were also for the earlier FR8, not the new FR8c.
Pipe-horns are quite forgiving within reason, mainly due to their relative high volume, but even this does have some limits. The relative lack of volume in your pipes won't be helping, but more of an issue is your current driver position, which from your description is slightly too low, so the null will be a couple of db greater than in the more optimal location.
Unfortunately most of those early cabinet dimensions on the site were done before an optimal volume calculation for a pipe-horn was worked out (by GM), so they are now superceded. The Hemp ones were also for the earlier FR8, not the new FR8c.
Pipe-horns are quite forgiving within reason, mainly due to their relative high volume, but even this does have some limits. The relative lack of volume in your pipes won't be helping, but more of an issue is your current driver position, which from your description is slightly too low, so the null will be a couple of db greater than in the more optimal location.
That CSA is a little larger than mine. If you compare the Hemp simulations posted on zillaspeak, ScottMooses and GM's, it sure appears to me that the smaller, longer set (ScottMooses sim) has a smaller midbass suckout than the larger set (6db versus 10db). The larger dims do have more gain at low frequencies, but a lack of low frequencies isn't your problem, is it?
My guess is that your cabs are plenty big enough. The new spreadsheet gives results that are far larger than the enclosures many folks have had success with (most of the cabinets built before the spreadsheet came out). Besides, MJK's software doesn't lie, and it shows that smaller dims can work fine, especially if they are tuned lower (as yours are). My BIB's are too small, by the spreadsheet, but they have too much gain as is. I can't imagine that I could make an "optimal" set work at all unless I had a far larger room.
You did get the driver position correct, right? 764.5mm from the top of the line? If not, that could create weird response.
My guess, again, is that you are hearing room modes. They can be even more noticeable as your BIB's are probably putting out significantly more bass than you are used to. Have you tried any damping in the back half? Don't give up when you've hardly begun. There are plenty of options to explore. Also, if you've got a more conventional set of speakers around, hook them up and play that frequency sweep. You'll be surprised.
pj
My guess is that your cabs are plenty big enough. The new spreadsheet gives results that are far larger than the enclosures many folks have had success with (most of the cabinets built before the spreadsheet came out). Besides, MJK's software doesn't lie, and it shows that smaller dims can work fine, especially if they are tuned lower (as yours are). My BIB's are too small, by the spreadsheet, but they have too much gain as is. I can't imagine that I could make an "optimal" set work at all unless I had a far larger room.
You did get the driver position correct, right? 764.5mm from the top of the line? If not, that could create weird response.
My guess, again, is that you are hearing room modes. They can be even more noticeable as your BIB's are probably putting out significantly more bass than you are used to. Have you tried any damping in the back half? Don't give up when you've hardly begun. There are plenty of options to explore. Also, if you've got a more conventional set of speakers around, hook them up and play that frequency sweep. You'll be surprised.
pj
pjanda1 said:
They're about 3in too far down, which will increase the null.
In principle yes, smaller than optimal CSAs can work well, though the driver has a harder time of it, and they don't produce as much gain as they can. Big gain = good. You can never have too much LF gain, you can always damp it down if necessary.
I had similar problems with my BIB's, and I couldn' t live with the bass ripple. With this design there will always be a certain amount of bass ripple. Despite what people would try to convince you - it is a quarter wave design which always has nulls in the terminus response. With a Transmission Line they avoid this by killing the response of all the terminus output apart from the main line resonance - they achieve this with heavy stuffing.
What I did "successfully", was mass load my pipes. I now have absolutely no noticable ripple and they go down very low. Unfortunately you will have to trade off some of the bass volume to get the smoothing. It sounds as if you have plenty of bass to trade off though.
What you are attempting to achieve is convert the terminus into a reflex port.
Make a wooden plate to cover over the complete mouth of the terminus, then mount on the end of this a piece of wood as wide as the speakers internal width and about 2inchs long. This will form an L shaped baffle that sits over the terminus and forms a "reflex" pipe into the enclosure. Place this over the opening and then adjust the size of the opening until you get a satisfactory bass response. I found that all I needed was a gap at the terminus of about 1inch. Once you have established the correct size of opening cut the baffle so that it slips inside the terminus and glue it in place. I will guarantee that this will save the day and will absolutely not sound like a conventional reflex design.
Try it with some corrigated cardboard just to get a feel for what you are trying to achieve.
The BIB is a variant of the Voigt pipe. If you look back to most of the successful implementations of the Voigt concept, you will see that almost all of them are designed on the mass loading principle. The Voigt pipe fell out of fashion with the diy speaker building community because it rarely satisfactorily dealt with the ripple problem. The BIB seems to work because it pushes the ripple down to frequencies where most people can happily ignore it. This married to the ability to minimise it with modern computer simulations. However mass loading is still the prefered method for getting the best out of the voight style pipe.
Shoog
What I did "successfully", was mass load my pipes. I now have absolutely no noticable ripple and they go down very low. Unfortunately you will have to trade off some of the bass volume to get the smoothing. It sounds as if you have plenty of bass to trade off though.
What you are attempting to achieve is convert the terminus into a reflex port.
Make a wooden plate to cover over the complete mouth of the terminus, then mount on the end of this a piece of wood as wide as the speakers internal width and about 2inchs long. This will form an L shaped baffle that sits over the terminus and forms a "reflex" pipe into the enclosure. Place this over the opening and then adjust the size of the opening until you get a satisfactory bass response. I found that all I needed was a gap at the terminus of about 1inch. Once you have established the correct size of opening cut the baffle so that it slips inside the terminus and glue it in place. I will guarantee that this will save the day and will absolutely not sound like a conventional reflex design.
Try it with some corrigated cardboard just to get a feel for what you are trying to achieve.
The BIB is a variant of the Voigt pipe. If you look back to most of the successful implementations of the Voigt concept, you will see that almost all of them are designed on the mass loading principle. The Voigt pipe fell out of fashion with the diy speaker building community because it rarely satisfactorily dealt with the ripple problem. The BIB seems to work because it pushes the ripple down to frequencies where most people can happily ignore it. This married to the ability to minimise it with modern computer simulations. However mass loading is still the prefered method for getting the best out of the voight style pipe.
Shoog
Hi!
Hey, that sound like a cunning plan
Unfortunatly I do not have / had much time to spend on my audio,
but last night I finally moved the pipes into the corners...
That helps a lot !
the suckout is now more a ripple, meaning there is a least some midbass.
I can listen to them now, but will try the reflex port-idea,
when I get the time...
Still I'm thinking,
"will a FE167E work better in there pipes ?"
Hey, that sound like a cunning plan
Unfortunatly I do not have / had much time to spend on my audio,
but last night I finally moved the pipes into the corners...
That helps a lot !
the suckout is now more a ripple, meaning there is a least some midbass.
I can listen to them now, but will try the reflex port-idea,
when I get the time...
Still I'm thinking,
"will a FE167E work better in there pipes ?"
Shoog said:
It's a chamberless tapped horn intened for 1/8 space placement and tuned to 1/2 wavelength of the design Fc. As such, it's positively tapered toward the mouth, has a QW fundamental and being as horn, both odd and even order harmonic structure. Mass loading can be useful, particularly if the pipe isn't big enough for the driver requirements, but with these particular pipes you have to be careful in applying it otherwise you'll actually increase the null at F3.
Kind of. The Voigt (no 'h': P.G.A.H. Voigt you know
) Pipe was created by the Lowther Club of Norway for the Lowther PM6c, & they appear to have used a traditional BR proceedure & sized the vent to approximately equal the Sd of the driver. The pipe itself is nominally 1/4 wavelength of a design frequency (though this takes no accout of the line taper -it's not long enough; or the vent CSA needs dramatically reducing to get reasonable performance, assuming Vb is appropriate to the driver). It doesn't expand sufficiently to develop any significant 1/2 wave action, so it's a TQWT (i.e. negatively tapered toward the throat). As such it's only distantly related to Voigt's patents, in this case lines 94 - 105 on page 4 of his 1936 patent application with reference to 1/4 wavelength tuning. The BIB OTOH, despite the apparantly similar appearance, is much closer in concept to Voigt's ideas, deliberately using room boundaries, preferably a corner, to complete the horn expansion (see attached from Voigt's 1933 patent on sound distribution and also page 5 of the aforementioned 1936 patent), and aiming for maximum wide BW gain. Using 1/2 wavelength tuning also gives maximum efficiency for a horn.
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