Legis,
The 15" push pull (one driver has the magnet in the slot) slot loaded cabinets I recently built had around a 3 dB peak at 180 Hz, easily tamed with DSP, as can be seen in the green response compared to the raw white response. I'd expect an 18" slot to be no different other than the frequency. The PP arrangement is probably less peaky than a cone to cone arrangement, though.
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For the luxury of 100cm depth, I'd like to propose the attached design.
In fact it's more or less like I've mentioned previously, similar to the MB section, just somewhat bigger overall, and with a smaller slot-loaded throat.
For reducing the 1/4 wavelength resonance, 2 ramps in the throat chamber might help.
In the case of face to face, the ramps can even cover some of the cone area. As to the effect of such 2-stage compression, I'm not so sure...
The sketches are not to scale, of course. But if the driver is 18", then the overall width might approach 1.5m.
Mmwhahahaha .....
BTW, this has some other benefits:
1. time align with other sections of the system
2. coherent in the look with the MB section
3. there's still possibility to play with cardioid by the stuffing in the rear space
....
Have fun.
In fact it's more or less like I've mentioned previously, similar to the MB section, just somewhat bigger overall, and with a smaller slot-loaded throat.
For reducing the 1/4 wavelength resonance, 2 ramps in the throat chamber might help.
In the case of face to face, the ramps can even cover some of the cone area. As to the effect of such 2-stage compression, I'm not so sure...
The sketches are not to scale, of course. But if the driver is 18", then the overall width might approach 1.5m.
Mmwhahahaha .....
BTW, this has some other benefits:
1. time align with other sections of the system
2. coherent in the look with the MB section
3. there's still possibility to play with cardioid by the stuffing in the rear space
....
Have fun.
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Elias, something like that. Midst googling I happened to come across the Cessaro horn speakers: Cessaro ::*Gamma I
Those desing choises give many ideas. I like the frame consept. Much less brutal looking than "piled-up PA system" -look.
Those desing choises give many ideas. I like the frame consept. Much less brutal looking than "piled-up PA system" -look.
Another brain fart for <100Hz band that would sit quite nicely in a Cessaro-like frame. Time aligment will be done with DSP, but naturally "passive-xo compatible" aligment of drivers does not hurt as a bonus.
FYI the 18" woofers are modified BMS 18N860's (picture: http://i817.photobucket.com/albums/zz95/LegisActio/BMS%2018%20inch%20woofers/BMS_sanded4_zps6c5e081c.jpg). They are quite deep bastards, around 27cm with the phase plug holding bolt and it's plywood "washer".
FYI the 18" woofers are modified BMS 18N860's (picture: http://i817.photobucket.com/albums/zz95/LegisActio/BMS%2018%20inch%20woofers/BMS_sanded4_zps6c5e081c.jpg). They are quite deep bastards, around 27cm with the phase plug holding bolt and it's plywood "washer".
An externally hosted image should be here but it was not working when we last tested it.
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I could start with the sim I did for CLS's slot loaded push pull bandpass sub: http://www.diyaudio.com/forums/subwoofers/255959-sim-slbp_pp-maybe-more.html
Then simply close the vent leading to the slot and add resistive vents to the back and/or sides.
But then ask yourself the question if the sound below 100 Hz is omni, why not just make it a slot loaded band pass? They are very flat and wide bandwidth:
A similar design but with a pair of $62 ea Infinity budget 1260W woofers:
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I have had them in U-frames and regular closed boxes (only two of them as infra subs) before.
That PPSL looks cool, thanks xrk971. I have been reading the PPSL thread for 20-30 pages now, it looks promising based on ppls comments. I might do a convertable PPSL box, the front slot, back wall and top could be removable for easy disassembly and try/fail.
It might be a good thing that I have strenghtened the cones with carbon fiber sheet and epoxy on the backside of the cone. They are very rigid, and could deform less under compression situations. Also the de-dustcapping reduced the "running noise" (air blowing through the motor) to literally non-existent, so putting another woofer motor facing the outside will not generate noises under long strokes if the slot ifself does not start to chuff.
That PPSL looks cool, thanks xrk971. I have been reading the PPSL thread for 20-30 pages now, it looks promising based on ppls comments. I might do a convertable PPSL box, the front slot, back wall and top could be removable for easy disassembly and try/fail.
It might be a good thing that I have strenghtened the cones with carbon fiber sheet and epoxy on the backside of the cone. They are very rigid, and could deform less under compression situations. Also the de-dustcapping reduced the "running noise" (air blowing through the motor) to literally non-existent, so putting another woofer motor facing the outside will not generate noises under long strokes if the slot ifself does not start to chuff.
An externally hosted image should be here but it was not working when we last tested it.
" Also the de-dustcapping reduced the "running noise" (air blowing through the motor) to literally non-existent, so putting another woofer motor facing the outside will not generate noises under long strokes if the slot ifself does not start to chuff."
Have not had the slot 'chuff ' but have replaced a solid dust cap with a felt one (4.5" felt dustcap over a 3" coil) and sealed the vent through the magnet.
Have not had the slot 'chuff ' but have replaced a solid dust cap with a felt one (4.5" felt dustcap over a 3" coil) and sealed the vent through the magnet.
Doesn't removing the dust cap and sealing the motor vent hole really kill the principal mechanism of cooling the voice coil for high power loads? For home use it is probably not an issue but a 1kW pro driver running at max sustained SPL needs to dissipate the equivalent of a hair dryer. Without that air noise the could will fry as there is minimal conduction from the coil former to the frame as it is mounted on non thermally conductive spider and paper cone.
My one experience with a slot loaded push pull open baffle was very positive. I used 6 x 6.5 in high Qts cheap woofers. The bass is very natural sounding and actually digs deep without wall shake. If I were to build a wooden speaker my next build would indeed be a slot loaded push pull OB with maybe 8 x 8 in drivers each side for the sub woofers.
http://www.diyaudio.com/forums/full-range/249984-cheap-fast-ob-literally.html
A very promising approach to clean bass generation - and with DSP can really be implemented quickly and effectively.
My one experience with a slot loaded push pull open baffle was very positive. I used 6 x 6.5 in high Qts cheap woofers. The bass is very natural sounding and actually digs deep without wall shake. If I were to build a wooden speaker my next build would indeed be a slot loaded push pull OB with maybe 8 x 8 in drivers each side for the sub woofers.
http://www.diyaudio.com/forums/full-range/249984-cheap-fast-ob-literally.html
A very promising approach to clean bass generation - and with DSP can really be implemented quickly and effectively.
If on OB, don't worry about the cooling. It won't go any high power operation. It's excursion limited. (I guess it won't take more than 50W each)
If in sealed, I'm not 100% sure. But with cone area of 4x 18" in domestic use, I don't worry very much, either. The weak link is human. Mmwhahahaha...
If in sealed, I'm not 100% sure. But with cone area of 4x 18" in domestic use, I don't worry very much, either. The weak link is human. Mmwhahahaha...
Heat transfers from point to point in various ways but yes, at least the long term cooling is reduced, but I have no idea by how much. The air still moves in the air gap but not as much/fast as with forced cooling that compresses the air through the motor at various points. Short term power handling might not alter ás much.
My aluminum phase plugs weight over 2,5kg per piece, they also help with the cooling and act as a heat stabilising buffer. I got them mainly because they also act as a (fourth) shorting ring, but I deliberately made them as big as possible to maximize the heat buffering and make their DCR very small. At first I though of rosewood bullet shaped phase plugs, but decied to make aluminum plugs for the aforementioned reasons.
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Off topic:
I found some old measurements of 18N860 with and without the phase plugs.
100Hz 106dB/1m:
Without phase plug / With phase plug / Difference
H3: 0,153% (-56,3dB) / 0,100% (-60dB) / -3,7dB
H4: 0,0201% (-53,4dB) / 0,288% (-50,8dB) / + 2,6dB
H5: 0,166% (-55,6dB) / 0,0771% (-62,3dB) / -6,7dB
H6: 0,0155% (-76,2dB) / 0,0123% (-78,2dB) / -2dB
H7: 0,0702% (-63,1dB / 0,0207% (-73,7dB) / -10,6dB
H8: 0,0098% (-80,2dB) / 0,0096% (-80,4dB) / -0,2dB
H9: 0,0332% (-69,6dB) / 0,0123% (-78,2dB) / -8,6dB
130Hz 103dB/1m:
Without phase plug / With phase plug / Difference
H3: 0,262% (-51.6dB) / 0,0970% (-60,3dB) / -8,7dB
H4: 0,0287% (-70.8dB) / 0,0111% (-79,1dB) / -8,3dB
H5: 0,284% (-50,9dB) / 0,125% (-58,1dB) / -7,2dB
H6: 0,0345% (-69,2dB) / 0,0191% (-74,4dB) / -5,2dB
H7: 0,0936% (-60,6dB) / 0,0360% (-68,9dB) / -8,3dB
H8: 0,0276% (-71,2dB) / 0,0067% (-83,5dB) / -12,3dB
H9: 0,0107% (-79,4dB) / 0,0037% (-88,6dB) / -9,2dB
Quite big difference, H2 rises for some reason (whatever that may be?) and higher order harmonics go lower in general. I believe the high order harmonic reduction comes from more linear Le(X) with the phase plugs on. I will do some more measurements in the future. Interesting to see how low distortion figures one can get with the even order cancellation of PPSL with generally low distortion woofers.
I found some old measurements of 18N860 with and without the phase plugs.
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.
100Hz 106dB/1m:
Without phase plug / With phase plug / Difference
H3: 0,153% (-56,3dB) / 0,100% (-60dB) / -3,7dB
H4: 0,0201% (-53,4dB) / 0,288% (-50,8dB) / + 2,6dB
H5: 0,166% (-55,6dB) / 0,0771% (-62,3dB) / -6,7dB
H6: 0,0155% (-76,2dB) / 0,0123% (-78,2dB) / -2dB
H7: 0,0702% (-63,1dB / 0,0207% (-73,7dB) / -10,6dB
H8: 0,0098% (-80,2dB) / 0,0096% (-80,4dB) / -0,2dB
H9: 0,0332% (-69,6dB) / 0,0123% (-78,2dB) / -8,6dB
130Hz 103dB/1m:
Without phase plug / With phase plug / Difference
H3: 0,262% (-51.6dB) / 0,0970% (-60,3dB) / -8,7dB
H4: 0,0287% (-70.8dB) / 0,0111% (-79,1dB) / -8,3dB
H5: 0,284% (-50,9dB) / 0,125% (-58,1dB) / -7,2dB
H6: 0,0345% (-69,2dB) / 0,0191% (-74,4dB) / -5,2dB
H7: 0,0936% (-60,6dB) / 0,0360% (-68,9dB) / -8,3dB
H8: 0,0276% (-71,2dB) / 0,0067% (-83,5dB) / -12,3dB
H9: 0,0107% (-79,4dB) / 0,0037% (-88,6dB) / -9,2dB
Quite big difference, H2 rises for some reason (whatever that may be?) and higher order harmonics go lower in general. I believe the high order harmonic reduction comes from more linear Le(X) with the phase plugs on. I will do some more measurements in the future. Interesting to see how low distortion figures one can get with the even order cancellation of PPSL with generally low distortion woofers.
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Legis,
Are those measurements with the bare drivers or U frames? A -8dB reduction in 3rd harmonic at 10 Hz is huge! Very impressive upgrade. Do you just bolt the aluminum phase plug onto the central iron motor core where the vent hole normally goes? The Eddy current shorting seems to be doing the trick though. Can you post some photos of the mod? Thanks for sharing.
X
Are those measurements with the bare drivers or U frames? A -8dB reduction in 3rd harmonic at 10 Hz is huge! Very impressive upgrade. Do you just bolt the aluminum phase plug onto the central iron motor core where the vent hole normally goes? The Eddy current shorting seems to be doing the trick though. Can you post some photos of the mod? Thanks for sharing.
X
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