I mostly filled the gaps between layers and the marks from the clamps, sanded yesterday, round two today. I wanted to make the gluing surfaces flat and square, so I did that with an orbital sander. And that is all that I will do before gluing to the front board, top and bottom. Then, I will try to make the chambers look nice from the front. The plan is to use short thick wood screws - maybe drywall screws would work well.
Nice work Pelanj!
The baffle width plus U depth controls the bass extension. I’m at about 27in wide total “width” with wings and 12in wide front baffle. I am getting about 44Hz -3dB with the high Qts drivers. The depth of the slot chamber controls the upper extension and works out to be about 470Hz. The SLOB design provides overs a decade of frequency response and does so with good powerful slam and lower distortion than plain single front facing OB dipole.
It’s good to utilize the natural upper falloff with the electrical filter and you get a free 4th order for the price of a 2nd order filter.
The baffle width plus U depth controls the bass extension. I’m at about 27in wide total “width” with wings and 12in wide front baffle. I am getting about 44Hz -3dB with the high Qts drivers. The depth of the slot chamber controls the upper extension and works out to be about 470Hz. The SLOB design provides overs a decade of frequency response and does so with good powerful slam and lower distortion than plain single front facing OB dipole.
It’s good to utilize the natural upper falloff with the electrical filter and you get a free 4th order for the price of a 2nd order filter.
Drives me only marginally less crazy than all the new 'genders'...
Very impressive design.
Does that make ~470Hz your quarter wave slot depth at 7.1" / 182mm?
Thats just super smart.
For other SLOB designers is there any danger of getting a high resonance boost with high distortion pushing up to quarter wave resonance? Say a slot peak at 400Hz then HD3 at 1200Hz goes right into the sensitive midrange band.
If the upper 1/4 wave falloff is 400Hz (as determined by slot depth), there won’t be much getting through at 1200Hz (even if it is the 3rd harmonic) because slot is an acoustic filter that suppresses all sources of sound whether primary or unintended higher order distortion.
Here is the raw response of my SLOB. No electrical filter running full range electrically. You can see the higher order distortions are quite suppressed. The higher peaks near 200Hz to 400Hz were caused by steel basket ringing and were greatly reduced by Noico added to the frame.
Here is the raw response of my SLOB. No electrical filter running full range electrically. You can see the higher order distortions are quite suppressed. The higher peaks near 200Hz to 400Hz were caused by steel basket ringing and were greatly reduced by Noico added to the frame.
Wow. Thats super smart. Thanks for pointing out how the higher order HD is effectively suppressed.
I see HD is very low. Extraordinary for using such cheap drivers.
Your work in this field is outstanding. Dont expect any recognition for years.
..though in this case I knew the acronym.
It at least has been around for a while now (2011):
https://www.firstwatt.com/pdf/art_slob.pdf
Nice work! Can I ask why you chose to use a wide conventional OB vs a U-shaped one with a narrower front profile like what I did on XSD? It’s much less imposing and wife-friendly. The benefits of dipole bass are still there and perhaps even deeper bass extension.
I used this style to visually match to the horn that will be used with it. It is almost 62 cm wide, so I used 60 cm boards to their full width. I might add internal wings for bass extension, I got some extra boards for that.
I have just measured the chamber depth and it is 175 mm, which translates to 490 Hz cut off, which should be a great match to the large horn. The picture shows the prototype horn on a table with similar dimensions as the SLOB.
I have just measured the chamber depth and it is 175 mm, which translates to 490 Hz cut off, which should be a great match to the large horn. The picture shows the prototype horn on a table with similar dimensions as the SLOB.
Attachments
Looking good! I see that the very soft wood is giving you plenty of "challenges" but it sure looks nice. Are the screws holding OK?
What's next? Drivers in then some measurements?
Do you have a measurement mic? Im very curious to see if you can replicate XRX's amazing freq and THD response, right through the quarter wave peak and out the other side.
The screws hold fine, I just need to get some shorter ones for driver mounting. Because of the screws, I will add a layer of thin plywood to the top, bottom and front.
I have a UMIK-1 for measurements. I also need to get some speaker wire, I found out I am out of it.
I have a UMIK-1 for measurements. I also need to get some speaker wire, I found out I am out of it.
Hi Pelanj,
Makes sense to match your 62cm wide horn - that is big! 490Hz is a good place for a crossover to a mid range driver. How low can your horn go? Probably 700Hz is my guess. So not quite low enough to skip a mid range.
Makes sense to match your 62cm wide horn - that is big! 490Hz is a good place for a crossover to a mid range driver. How low can your horn go? Probably 700Hz is my guess. So not quite low enough to skip a mid range.
I find Spax self tapping drywall screws in #8 size work well for wood (ply, MDF, solid, or anything else, concrete, steel, … almost universal).
SPAX #8 x 1-1/4in. Flat Head Unidrive Zinc Coated Screw - 1 LB Box https://a.co/d/c0TNpfV
It is waiting for being finished - I already have the extra plywood panels cut, but I cannot decide how the back and chambers should be done - black paint or transparent lacquer are the two top options. When I decide, I will glue on the external plywood panels, apply the final clear coats and then the woofers will be installed.
For those that have built the (6) driver SLOB ... would there any advantage in driving it with a (6) channel amplifier? My guess would be an increase in sensitivity of 18dB for the whole unit that way through mutual coupling. I ask because of the interest here of using the SLOB with a large horn. Six cheap 8" .. 85dB 1w/1m drivers could produce 102dB 1w/1m total output that way. Splitting the line level signal into (6) is straight forward. Thoughts?