What would be the best rule of thumb regarding the baffle width on the slot loaded portion? I have two 18" woofers I was going to maybe try as per the article, and it is mentioned that baffle dimensions weren't as critical. Was that in regard to the FR panel or the Slot Loaded woofers? Does the reduced rearward output make the wide baffle less necessary?
I'd suggest a trial before the final decision. The optimal ratio would probably be different in different drivers and rooms.
For my 18" woofer, I feel 30% Sd for slot's CSA is too small, which gives an over emphasized bottom end.
It's cool to have that effect of Dinosaur footsteps. It almost gives a sense that the whole room is pressurized (by this dipole sub) ! But it gets tiresome pretty soon. After some other trials, I built it 40% eventually.
For my 18" woofer, I feel 30% Sd for slot's CSA is too small, which gives an over emphasized bottom end.
It's cool to have that effect of Dinosaur footsteps. It almost gives a sense that the whole room is pressurized (by this dipole sub) ! But it gets tiresome pretty soon. After some other trials, I built it 40% eventually.
To add to CLS's reply, if you remove the wings, you'll get very little bass since the way the woofer is mounted, you're nearly in the dipole "dead spot"....
You might be better off with a horizontal ripole arrangement if height is an issue.
I'm been slowly reading through this thread, and re-reading Nelson Pass's SLOB article for some time, noodling on a way to add more bass to my current open-baffle rig, without using larger woofers, or a huge baffle.
I currently use 3 extremely modest ($12.50ish each, sad 4.5mm X-Max, excursion limited at 30Hz at a paltry 4-5W each,) MCM 55-1240 8in woofers on each side. (Fs 40Hz, Qts 0.74,) with a vintage Dukane paper cone + whizzer FR driver on top, and a single Linaeum tweeter mounted on top of the baffle. The baffle is just a 4ft piece of "1x12" pine board, with shelf standards screwed to the back, shelf brackets installed upside down to form legs.
Thanks to the wild mis-match of efficiencies, the system is tri-amped after an active 4-way crossover. I cross at 110-120Hz, 6-7Khz at 18db/oct, and use a high-pass filter at ~35Hz when I want to play loud. (Damn 4.5mm x-max.)
They sound fantastic at reasonable volume, within about 3m, don't look half bad, but I can't play anywhere near "Party Level" without either using a high-pass filter to limit bass extension, or adding more/larger woofers.
I'm sold on the idea of a super-narrow W-frame for appearance sake, and already own a dozen of these MCM woofers.
My proposed solution is similar to the InDiBA 16.2 concept, but I'm using 6 8in drivers per side, laminating the entire cabinet out of 16 pieces of 18mm, (what passes for "3/4" here,) plywood cut like Nelson's manifold, sandwiched together with 12 long threaded rods & barrel nuts.
Renderings attached.
(I intend to angle the bottom Linaeum slightly down, the top one slightly up, hopefully giving better vertical dispersion as well as 6db headroom. The SLOB manifold measures 31.75 tall, 11.75 deep, 11.38 wide. Overall height, without feet/spikes, is 44.2in.)
I'm perfectly happy with extension to 35Hz, (The woofers are excursion-limited at only 4-5W at 35Hz,) so I'm more interested in the perceived near-field gain from Nelson's design than I am in the Fs reduction and Qts increase of the ripoles.
With only a 2-board-wide opening in front, the ratio of Sd to front slot area is about 5.7:1. With 4-board wide openings in the back, Sd to slot area ratio is about 2.3:1.
My questions to all who have played with S.L.O.B.s, or ripoles:
Will I enjoy the benefits of either "trick" with this arrangement?
Must I widen the center/front slot by a board to eliminate losses?
(This would bring the ratio of Sd:Slot area down to 3.8:1)
Is the 2:1 ratio between the area of the front slot and back slot enough to create the pressure differential essential to Nelson's design?
Are the slots too deep in back? (They are deeper than the central slot on purpose... I wanted to simulate a wider baffle.)
Any guidance appreciated.
Eric.
I currently use 3 extremely modest ($12.50ish each, sad 4.5mm X-Max, excursion limited at 30Hz at a paltry 4-5W each,) MCM 55-1240 8in woofers on each side. (Fs 40Hz, Qts 0.74,) with a vintage Dukane paper cone + whizzer FR driver on top, and a single Linaeum tweeter mounted on top of the baffle. The baffle is just a 4ft piece of "1x12" pine board, with shelf standards screwed to the back, shelf brackets installed upside down to form legs.
Thanks to the wild mis-match of efficiencies, the system is tri-amped after an active 4-way crossover. I cross at 110-120Hz, 6-7Khz at 18db/oct, and use a high-pass filter at ~35Hz when I want to play loud. (Damn 4.5mm x-max.)
They sound fantastic at reasonable volume, within about 3m, don't look half bad, but I can't play anywhere near "Party Level" without either using a high-pass filter to limit bass extension, or adding more/larger woofers.
I'm sold on the idea of a super-narrow W-frame for appearance sake, and already own a dozen of these MCM woofers.
My proposed solution is similar to the InDiBA 16.2 concept, but I'm using 6 8in drivers per side, laminating the entire cabinet out of 16 pieces of 18mm, (what passes for "3/4" here,) plywood cut like Nelson's manifold, sandwiched together with 12 long threaded rods & barrel nuts.
Renderings attached.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
(I intend to angle the bottom Linaeum slightly down, the top one slightly up, hopefully giving better vertical dispersion as well as 6db headroom. The SLOB manifold measures 31.75 tall, 11.75 deep, 11.38 wide. Overall height, without feet/spikes, is 44.2in.)
I'm perfectly happy with extension to 35Hz, (The woofers are excursion-limited at only 4-5W at 35Hz,) so I'm more interested in the perceived near-field gain from Nelson's design than I am in the Fs reduction and Qts increase of the ripoles.
With only a 2-board-wide opening in front, the ratio of Sd to front slot area is about 5.7:1. With 4-board wide openings in the back, Sd to slot area ratio is about 2.3:1.
My questions to all who have played with S.L.O.B.s, or ripoles:
Will I enjoy the benefits of either "trick" with this arrangement?
Must I widen the center/front slot by a board to eliminate losses?
(This would bring the ratio of Sd:Slot area down to 3.8:1)
Is the 2:1 ratio between the area of the front slot and back slot enough to create the pressure differential essential to Nelson's design?
Are the slots too deep in back? (They are deeper than the central slot on purpose... I wanted to simulate a wider baffle.)
Any guidance appreciated.
Eric.
Last edited:
You might want to read this thread
http://www.diyaudio.com/forums/multi-way/252593-novel-open-baffle-construction-techniques.html
Flip one side of the drivers so that they are in push-pull mode to reduce 2nd order harmonic distortion.
http://www.diyaudio.com/forums/multi-way/252593-novel-open-baffle-construction-techniques.html
Flip one side of the drivers so that they are in push-pull mode to reduce 2nd order harmonic distortion.
This has been discussed many times in this thread, and in others, I'm still unclear as to whether it is really necessary to physically orient the woofers in the same direction, (mag to cone, instead of cone to cone,) or if reversing the polarity to one of 2 woofers sharing the same cavity produces the same effect.
(The cones would be moving in the same direction with just the polarity flip.)
Is the reduction in 2nd order harmonics more profound with the physical flip?
Can you please clarify?
KG.DiVA 4.2
I missed this thread for too long, sorry, but back again.
@ xrk971.
Your link is a good way to all discussions about near and far field effects of dipoles. Yes there is an effect but normal use is in the area of 2..3m (6.5'..10') and in this distance it's only effective at very low frequency.
@ Eric
Can you provide type and/or TSPs of your speaker? I think a dipol with woffers excursion-limited at only 4-5W at 35Hz is not the best choice.
If depth of your cabinet is not limited you should think about 4x 10" with excursion as max as possible.
@all
Here is my construction of 2013.
An open baffle or call it dipole with 4x10" as V-array in a normal waste water tube (KG300) with diameter of 319mm and a hight of 1050mm.
Pls use extended view.
With digital XOver it runs down to 25 Hz. More details you'll find here at DIY Hifi at the end of that thread.
br
Wolfgang
I missed this thread for too long, sorry, but back again.
@ xrk971.
Your link is a good way to all discussions about near and far field effects of dipoles. Yes there is an effect but normal use is in the area of 2..3m (6.5'..10') and in this distance it's only effective at very low frequency.
@ Eric
Can you provide type and/or TSPs of your speaker? I think a dipol with woffers excursion-limited at only 4-5W at 35Hz is not the best choice.
If depth of your cabinet is not limited you should think about 4x 10" with excursion as max as possible.
@all
Here is my construction of 2013.
An open baffle or call it dipole with 4x10" as V-array in a normal waste water tube (KG300) with diameter of 319mm and a hight of 1050mm.
Pls use extended view.
With digital XOver it runs down to 25 Hz. More details you'll find here at DIY Hifi at the end of that thread.
br
Wolfgang
The motor strength and compliance of the suspension as a function of excursion is often non-symmetric, that is to say it changes differently when the cone moved towards the magnet than away from it. You can "cancel" or at least "average out" these non-linearities by using two drivers set up so that when one is moving "in" the other is moving "out". Placing them close together causes the wavefronts to combine and add.
If you have four of them, you could have a two of them with the cones facing each other and the other two with magnets facing each other, however, its not always a good thing to put to magnets in close proximity so (my guess is) that the cone-to-magnet orientation may be the preferred one.
Concrete S.L.O.B. block mold???
Gnom,
I already own 12 of these, and have a total of ~$160 into said dozen, am married to 'em, flaws and all. I chose them because they offered the best Xmax and efficiency I could find for the money, with a high Qts, in an 8in size. I started fiddling with open back / open baffles as a result of picking up a pair of late 1970's Dukane PA speakers that had 4 of the 8in paper wide-range drivers mounted in a hideous shallow sealed plywood box, with a single, (dead,) Motorola piezo horn tweeter mounted in the middle. So, this exercise started by trying to squeeze the most fun out of 4 8in holes in an open-back box, hence the choice of less-than-optimal-for-bass 8in woofers.
I've been listening to three of these woofers per side, one trio in a simple narrow baffle, (The board is roughly 11.25 x 36, LOTS of cancellation,) the other in the lower 3 holes of the original Dukane cabinet with the back removed, both sides with a single Linaeum tweeter atop, for 2+ years, with a grin. Any improvement from what I'm running now is gravy.
Since I already own all of the drivers, I'm only looking to implement Nelson's slot loading scheme, not reinvent the wheel with different drivers. (The 8in full-ranger is probably not the best choice for wide dispersion up to 6khz either.)
My goal is to put the original 6 8in woofers + 6 more into "proper" baffles to add 6db of headroom before I'm excursion limited, and eliminate some of the cancellation I'm suffering in the lowest octave on the narrow plain baffle.
Specs for the MCM 15-1240 are as follows:
Fs=37Hz (advertised as 40Hz)
Qts=0.74
Qes=0.96
Qms=3.22
Vas=61.05L
Sd=211cm^2
Re=5.9ohms
Vd=89.78cm^3
Xmax=4.25mm
Pe=40W program / 80W peak (advertised... baloney)
Le=0.74mH
Mmd=17.15g
Mms=18.89g
Cms=0.00098m/N
BL=6.19N/A
SPL (1W/1m)=86.9db
To muddy the water even more, since the local seller who was offering nice Maple-faced 11-ply 18mm wood for $15 per half-sheet has vanished, I'm looking into making a concrete mold out of the endless supply of crappy construction grade 3/4in plywood downstairs.
With 30mm thick walls, a "module" made for a single pair of 8in woofers should weigh about 98lbs using no filler. With some polystyrene filler, I should be able to get the weight down to ~80lbs so I can make one from a single bag of mix. Ultimately, it'd be nice to build 3 sets of 6 modules, using a single mold set, allowing me gift a couple sets, make use of 6 of the 7 surviving Dukane drivers, which I quite like. (Who doesn't like 600lbs of concrete as a gift?)
Given the stupid mass of concrete baffles, and my desire to keep these as narrow as possible, am I really losing out on much keeping the woofers arranged cone-to-cone, running them in opposite phase? (It appears that there is much asymmetry to the shape and volume of each chamber, and further constriction of the front/center slot, going magnet-to-cone.)
Attached is a quickie mockup of said 98lb concrete mold, made with 19mm wood. The front slot form will be screwed to the top of the mold. The rear slot forms to the bottom of the mold, the round through hole forms, (visible as discs between the drivers and front slot form,) screwed to the front slot form, unscrewed during de-molding, after the rear slot forms are removed.
De-molded, the block, (kinda looks like a giant cinder block,) measures 276x276x345mm, (10.87 x 10.87 x 13.58in)
My wood-cutting laziness knows no bounds... I'd rather do it once, then play with concrete
That said, (it's been several hours since I wrote the above post, never hit the "submit" button,) I'd love to contribute a design that consumes $10 worth of crappy wood, can be used to make an arbitrary size array of 8in woofers in this slot loaded arrangement for $5 worth of Quickrete per pair.
Eric.
Gnom,
I already own 12 of these, and have a total of ~$160 into said dozen, am married to 'em, flaws and all. I chose them because they offered the best Xmax and efficiency I could find for the money, with a high Qts, in an 8in size. I started fiddling with open back / open baffles as a result of picking up a pair of late 1970's Dukane PA speakers that had 4 of the 8in paper wide-range drivers mounted in a hideous shallow sealed plywood box, with a single, (dead,) Motorola piezo horn tweeter mounted in the middle. So, this exercise started by trying to squeeze the most fun out of 4 8in holes in an open-back box, hence the choice of less-than-optimal-for-bass 8in woofers.
I've been listening to three of these woofers per side, one trio in a simple narrow baffle, (The board is roughly 11.25 x 36, LOTS of cancellation,) the other in the lower 3 holes of the original Dukane cabinet with the back removed, both sides with a single Linaeum tweeter atop, for 2+ years, with a grin. Any improvement from what I'm running now is gravy.
Since I already own all of the drivers, I'm only looking to implement Nelson's slot loading scheme, not reinvent the wheel with different drivers. (The 8in full-ranger is probably not the best choice for wide dispersion up to 6khz either.)
My goal is to put the original 6 8in woofers + 6 more into "proper" baffles to add 6db of headroom before I'm excursion limited, and eliminate some of the cancellation I'm suffering in the lowest octave on the narrow plain baffle.
Specs for the MCM 15-1240 are as follows:
Fs=37Hz (advertised as 40Hz)
Qts=0.74
Qes=0.96
Qms=3.22
Vas=61.05L
Sd=211cm^2
Re=5.9ohms
Vd=89.78cm^3
Xmax=4.25mm
Pe=40W program / 80W peak (advertised... baloney)
Le=0.74mH
Mmd=17.15g
Mms=18.89g
Cms=0.00098m/N
BL=6.19N/A
SPL (1W/1m)=86.9db
To muddy the water even more, since the local seller who was offering nice Maple-faced 11-ply 18mm wood for $15 per half-sheet has vanished, I'm looking into making a concrete mold out of the endless supply of crappy construction grade 3/4in plywood downstairs.
With 30mm thick walls, a "module" made for a single pair of 8in woofers should weigh about 98lbs using no filler. With some polystyrene filler, I should be able to get the weight down to ~80lbs so I can make one from a single bag of mix. Ultimately, it'd be nice to build 3 sets of 6 modules, using a single mold set, allowing me gift a couple sets, make use of 6 of the 7 surviving Dukane drivers, which I quite like. (Who doesn't like 600lbs of concrete as a gift?)
Given the stupid mass of concrete baffles, and my desire to keep these as narrow as possible, am I really losing out on much keeping the woofers arranged cone-to-cone, running them in opposite phase? (It appears that there is much asymmetry to the shape and volume of each chamber, and further constriction of the front/center slot, going magnet-to-cone.)
Attached is a quickie mockup of said 98lb concrete mold, made with 19mm wood. The front slot form will be screwed to the top of the mold. The rear slot forms to the bottom of the mold, the round through hole forms, (visible as discs between the drivers and front slot form,) screwed to the front slot form, unscrewed during de-molding, after the rear slot forms are removed.
De-molded, the block, (kinda looks like a giant cinder block,) measures 276x276x345mm, (10.87 x 10.87 x 13.58in)
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
My wood-cutting laziness knows no bounds... I'd rather do it once, then play with concrete
That said, (it's been several hours since I wrote the above post, never hit the "submit" button,) I'd love to contribute a design that consumes $10 worth of crappy wood, can be used to make an arbitrary size array of 8in woofers in this slot loaded arrangement for $5 worth of Quickrete per pair.
Eric.
Someday I'll learn to attach image links:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I missed this thread for too long, sorry, but back again
@all
Here is my construction of 2013.
An open baffle or call it dipole with 4x10" as V-array in a normal waste water tube (KG300) with diameter of 319mm and a hight of 1050mm.
Pls use extended view.
With digital XOver it runs down to 25 Hz. More details you'll find here at DIY Hifi at the end of that thread.
br
Wolfgang
Hi Wolfgang,
Just a question, the "tweeter" is FRS5X? If so what about your impression?
Regards,
Peter
Sound of...
Hi Peter
The FRS5X used as dipol is well described by Rudolf @dipolplus.de. It's a good compromise of bandwidth and cost.
Build in my dipol system it is easier to control the hights than the room modes.
I use it with passive XOver since i built it and it is quite as good as my new 2014 construction used with digital XOver and full open baffle.
br
Wolfgang
Hi Peter
The FRS5X used as dipol is well described by Rudolf @dipolplus.de. It's a good compromise of bandwidth and cost.
Build in my dipol system it is easier to control the hights than the room modes.
I use it with passive XOver since i built it and it is quite as good as my new 2014 construction used with digital XOver and full open baffle.
br
Wolfgang
Thanks Wolfgang,
I will order four of them to play with. Not a big deal at this price
Peter
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