I've wondering about this too. @xrk971 would love to learn your view?
How would the midbass (from 150Hz or so and up) compare with a great OB driver, such as AE LO15 on a small baffle?
The 8x6.5" would have about 50% more cone surface than the 1x15" plus slot loading would load the lower midbass and deliver the impact X describes (and OB often are short of), and maybe the coloring in the upper range is the trade-off?
I haven’t used an AE driver before but if you look at the response of the SLOB drivers here, there is no horn coloration. I got rid of the pesky 200Hz distortion peak by adding Noico to the woofer basket. The ones with magnet in the chamber had a ringing mode like a bell. There is some output near 2k but it’s down -40dB. The trick is to put the second order electrical system the same place as the slot first cancellation frequency. That makes 4th order filter with fewer components.
This was first Xo:
Current one is more like this with more midbass:
This was first Xo:
Current one is more like this with more midbass:
Hi Xrk was reading the article & am a little lost : are arranged to squeeze the air out a front slot 2.25 inches wide and having about one third of their combined piston area. I believe the 2.25 inch width is arrived fron 1/3 surface area of the 8 inch woofer cone. Does one third combined piston area refers to the slot height & if so how do we arrive at the depth of the chamber ? Sorry for the noob questionI am thinking of going with something along the lines of this aproach by Nelson Pass "The slot loaded Open Baffle": The Slot Loaded Open Baffle Project Article By Nelson Pass
But do it in modular 2-drive units that can be stacked as you need more surface area.
Thanks again
The depth should be as shallow as possible and that is limited by the diameter of the driver surround. I suppose one could make a partial opening from driver cone to chamber (maybe 1/2 of diameter) to reduce chamber depth even more. That creates a different band pass effect like a synergy horn side injection. Then you would want lower Qts more powerful drivers.
The slot cross sectional area needs to be less than combined Sd of the two cones in order to provide loading or resistance. This has effect of controlling cone motion to reduce distortion. So if Sd is 120cm2 for one driver x 2 is 240cm2. Then slot cross section is 240/3 or 80cm2. The slot width needs to be big enough to allow space for magnet to sit inside. 80cm2 would be 2.25in x 5.5in tall. Thats exactly my slot cross sectional area. The slot cross sectional area reduction by 1/3 also has effect of increasing air velocity in front by 3x while air velocity in back is not accelerated and this is what provides the extra dynamic punch asymmetrically to the front with some more directionality. There is about a 2.5dB effective gain in sensitivity vs a plain wide open baffle.
Series parallel eight x 8ohm drivers to 4ohms gives a 12dB boost in sensitivity at the same voltage vs 8ohm single driver. Add 2.5dB gain from slot loading. Take away about 6dB loss from open baffle and we are at a net 8.5dB overall gain from nominal rating of the woofer, or 93.5dB for 85dB nominal. That’s incredibly sensitive and a whole lot of bass for a narrow U baffle dipole.
The slot cross sectional area needs to be less than combined Sd of the two cones in order to provide loading or resistance. This has effect of controlling cone motion to reduce distortion. So if Sd is 120cm2 for one driver x 2 is 240cm2. Then slot cross section is 240/3 or 80cm2. The slot width needs to be big enough to allow space for magnet to sit inside. 80cm2 would be 2.25in x 5.5in tall. Thats exactly my slot cross sectional area. The slot cross sectional area reduction by 1/3 also has effect of increasing air velocity in front by 3x while air velocity in back is not accelerated and this is what provides the extra dynamic punch asymmetrically to the front with some more directionality. There is about a 2.5dB effective gain in sensitivity vs a plain wide open baffle.
Series parallel eight x 8ohm drivers to 4ohms gives a 12dB boost in sensitivity at the same voltage vs 8ohm single driver. Add 2.5dB gain from slot loading. Take away about 6dB loss from open baffle and we are at a net 8.5dB overall gain from nominal rating of the woofer, or 93.5dB for 85dB nominal. That’s incredibly sensitive and a whole lot of bass for a narrow U baffle dipole.
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Many thanks again for your kind advice Xrk. I see that your design is different to Nelson's his is a long vertical slot with no dividers between the woofers where else yours is divided in individual chambers. Woofer facing is also different. Do you find any advantage with arrangement over Nelson's ?
If you look carefully, I think there are dividers between the woofers on Nelson Pass’ design. They have been painted black so not as obvious. It gives the design more structural integrity to have a divider to hold the two plates together. There is a log of pressure generated and so it’s important to give it extra support there.
Would the GRS version of the planar NEO8 work ( possibly with a wave guide like the tweeter ) ???
GRS 8" Planar Mid
PDF Spec Sheet
GRS 8" Planar Mid
PDF Spec Sheet
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How far from the speakers are you listening? Is this materially perceivable at 10 feet from them, playing music at 85dB or so? Dynamic punch in bass/midbass is where small baffle OB is a trade-off for me, so maybe this could do the trick?
I think GRS 8in is a good idea and I considered using it as well without a mic but sensitivity is only 85dB or less down at 400Hz. Dip at 800Hz to 80dB or so. Maybe a mid is still needed. The SLOB woofers are so sensitive that you need to match it with high sensitivity drivers in mid and tweeter.
I listen about 2.5m away and 10ft or about 3m would still be very good. I have walked around the room and even at 15ft it’s still palpable dynamics. The neat thing is very little effect of room modes. The bass is very uniform.
I listen about 2.5m away and 10ft or about 3m would still be very good. I have walked around the room and even at 15ft it’s still palpable dynamics. The neat thing is very little effect of room modes. The bass is very uniform.
HI XRK thanks again for the tutorial. Re : 80cm2 would be 2.25in x 5.5in tall. How does one arrive at the width of the slot, do you measure the cone diameter first & adjust width dimension till cross section area equals 80 cm2. Sorry if this sound stupid, trying to get hold & understand this.
Many thanks again
The width of 2.25in was matter of convenience as it was 3 layers of 3/4in thick MDF sandwiched by two layers that provide the mounting panel and covers. Why 3 layers was to make it big enough to fit the driver basket and magnet inside the chamber and be about the correct slot width to give 1/3 Sd of both drivers. The height of the slot was diameter of the cutout hole diameter (~5.5in) for the driver. It just happened to be about right. You can be off a little - it is ok to be a bit larger or smaller. You can also adjust it with an exit aperture cut to exactly the size you want placed on the baffle.
You can clearly see the 3 layers that make up the middle stack for the slot width here. And the height of the slot matches the cutout hole.
You can clearly see the 3 layers that make up the middle stack for the slot width here. And the height of the slot matches the cutout hole.
Not a good idea to cross it too low, it will distort. I use it only 1kHz and up. Mid definitelly recommended.
Thanks, Adason,
Yes, that was the other reason I forgot to mention. Distortion below 2kHz is probably pretty bad.
I have been playing around making a brand new XO for the 5MR450NDY. It took a lot rejiggering. Changing the mid is a new XO from scratch unfortunately. The mid is handling the whole decade from 470Hz to 4700Hz for good telephone band coherency. Distortion should be about 20dB lower than 6FE100 at 1kHz.
Yes, that was the other reason I forgot to mention. Distortion below 2kHz is probably pretty bad.
I have been playing around making a brand new XO for the 5MR450NDY. It took a lot rejiggering. Changing the mid is a new XO from scratch unfortunately. The mid is handling the whole decade from 470Hz to 4700Hz for good telephone band coherency. Distortion should be about 20dB lower than 6FE100 at 1kHz.
Hi XRK advice again pls, how do you calculated the bandwidth of the chamber for different sizes of woofers ?
Also would it perform better if we have a bigger chamber & adding a venturi like slotted mouth piece, perhaps
it would help loading the woofers better & also increases the slotted port velocity.
Thanks again
Also would it perform better if we have a bigger chamber & adding a venturi like slotted mouth piece, perhaps
it would help loading the woofers better & also increases the slotted port velocity.
Thanks again
