Well, as long as the voltage per driver is the same, you get no gain from using separate amplifiers IMHO. The nice thing about this arrangement is that you can feed a lot of power and have quite a lot of driver area in a small footprint (especially if folded as the original). And the cavity is not too deep, so it can play high enough to match a large horn. I still do not understand what the slot loading does. The 2x12 version can make 115 dB/1m, 40 - 200 Hz but needs an EQ and 200 W amplifier. https://www.diyaudio.com/community/threads/slob-2x12-subwoofer-for-near-field.384529/
For slot size, please refer to XRK971's original thread: https://www.diyaudio.com/community/threads/cheap-and-fast-ob-literally.249984/
Also if you refer to Papa’s original SLOB article I believe he says about 1/3 of combined Sd as a rule of 👍
Edit: Papa says “ The six woofers are mounted in a chamber formed by laminating five layers of 0.75 inch particle board, and are arranged to squeeze the air out a front slot 2.25 inches wide and having about one third of their combined piston area.”
Edit: Papa says “ The six woofers are mounted in a chamber formed by laminating five layers of 0.75 inch particle board, and are arranged to squeeze the air out a front slot 2.25 inches wide and having about one third of their combined piston area.”
Last edited:
Re:'what the slot loading does' - it acts as a low pass filter
Re:'XRK971's original thread' - couldn't see any calculation there, but I didn't trawl though all 36 pages....
Re:'a rule of 👍' = guesswork
Re:'XRK971's original thread' - couldn't see any calculation there, but I didn't trawl though all 36 pages....
Re:'a rule of 👍' = guesswork
I don’t think there is any advantage in using separate amps for each driver. You may in fact, have more distortion because when the drivers are connected in series parallel and the opposing driver is flipped magnet in on one side - the combination of suspension hysteresis and it’s interaction with voice coil and BL may help to cancel distortion.
Slot width: you want some loading on the cone. You don’t want it too narrow as that increases velocity and you get turbulence and motor has to fight hard. Too big and you don’t get slot loading. I try to adjust it to about 1/3 of cone Sd area. Plus make it wide enough to fit magnet and basket inside.
Slot width: you want some loading on the cone. You don’t want it too narrow as that increases velocity and you get turbulence and motor has to fight hard. Too big and you don’t get slot loading. I try to adjust it to about 1/3 of cone Sd area. Plus make it wide enough to fit magnet and basket inside.
Maybe it was the other thread - 1/3 Sd sounds good to me. The 212 slot I made was seriously undersized being around 1/7 of combined Sd and it introduced a nasty 10 dB peak at 220 Hz. I had to EQ it out.
I do not understand what it does (if it does) anything to the low end. Maybe it lowers the resonance frequency a bit and I get much less dipole loss than I would have expected from a baffle of this size - most probably measurement error or the room comes in. In any case, the bass from the 2x12 box is really nice, not boomy, but tight. But maybe that is actually because of the MEH used with it.
I do not understand what it does (if it does) anything to the low end. Maybe it lowers the resonance frequency a bit and I get much less dipole loss than I would have expected from a baffle of this size - most probably measurement error or the room comes in. In any case, the bass from the 2x12 box is really nice, not boomy, but tight. But maybe that is actually because of the MEH used with it.
Re:'what it does to the low end' - nothing, it cuts the high frequencies, which is why I'd like to see an exact formula
Regarding calculations for slot depth and upper bandwidth. It’s simple 1/4 wave theory. A 6.5in woofer will have about 7.0in deep slot. 7in x 0.0254m/in to get meters and divide speed of sound 342m/sec by depth and divide by 4 since quarter wave and the quarter wave cancellation dip on that slot depth is 480Hz. Longer depth and it’s a lower frequency and vice versa. What nice is if you use that natural falloff in combination with the electrical low pass filter at the same frequency, you will get a steeper slope for the cost of a lower order filter.
Do you happen to know if the article explores the chamber modes or does it look at the chamber as a simple low pass?
Here's the link:
https://worldradiohistory.com/UK/Wireless-World/60s/Wireless-World-1968-04.pdf
"Use of Slit.-The next factor to be dealt with was the directivity of the units. ...; the diffraction from the edges of the slit will make the radiation more nearly omnidirectional in the horizontal plane. There is, however, a limitation to this device: the Helmholtz resonator formed by the mass reactance of the slit and the compliance of the air enclosed between the slit and the cone increases the output to an undesirable extent in the region of the resonance frequency, but acts as a low-pass filter above the resonance, severely reducing the output at high frequencies. The minimum slit width which could be employed without either of these two effects becoming excessive was found to be 100 mm and it would appear at first sight that this width, which amounts to only a third of a wavelength at 1 kHz, should be quite small enough for this purpose."
https://worldradiohistory.com/UK/Wireless-World/60s/Wireless-World-1968-04.pdf
"Use of Slit.-The next factor to be dealt with was the directivity of the units. ...; the diffraction from the edges of the slit will make the radiation more nearly omnidirectional in the horizontal plane. There is, however, a limitation to this device: the Helmholtz resonator formed by the mass reactance of the slit and the compliance of the air enclosed between the slit and the cone increases the output to an undesirable extent in the region of the resonance frequency, but acts as a low-pass filter above the resonance, severely reducing the output at high frequencies. The minimum slit width which could be employed without either of these two effects becoming excessive was found to be 100 mm and it would appear at first sight that this width, which amounts to only a third of a wavelength at 1 kHz, should be quite small enough for this purpose."
@chromenuts
This is quite similar to my cunundrum: I have an 18" Faital in H OB frame driven by Hypex UcD400. Not fully in love with midbass impact from my Faitals - granted, they weren't designed for OB. I'm considering a SLOB per XRK's and AE Dipole 15. I was thinking the SLOB would have more impact...but that wasn't your experience.
I think there were a lot of different factors that attributed to a less than satisfactory result with my SLOB project.
kazap touched on a lot of what was going through my mind as possible reasons in the post following mine.
I’m not ruling out the possibility that I may take another stab at slot loading with some AE Dipole 18 that I have two pair of.
kazap touched on a lot of what was going through my mind as possible reasons in the post following mine.
I’m not ruling out the possibility that I may take another stab at slot loading with some AE Dipole 18 that I have two pair of.
Pardon my ignorance -- I thought the SLOB nee AMT3 was an arrayed line-source (like AMT1 for HF) projecting forward with lower dispersion (except for controllable omni-horizontal diffraction effect mentioned in Harwood quote above). Hence good match for horn.
I'm trying to understand as well the slot-loaded port radiation pattern in the context of an MLTL (or my "TLonken" fullrange). Near the speaker the line-port (1-pi?) well-dominates the cone's LF output (4-pi around the speaker), more so the lower the frequency (so not just mouth area < Sd). Does the slot (and the SLOB) function as a line-source for LF?
Thanks.
I'm trying to understand as well the slot-loaded port radiation pattern in the context of an MLTL (or my "TLonken" fullrange). Near the speaker the line-port (1-pi?) well-dominates the cone's LF output (4-pi around the speaker), more so the lower the frequency (so not just mouth area < Sd). Does the slot (and the SLOB) function as a line-source for LF?
Thanks.
Last edited:
After some thinking, I just went with black paint, two or most probably three layers with sanding in-between. This unit is a testing one anyway, so it does not need to look super good, just good enough. First layer is to be sanded, but most probably in January.
There are some machining errors anyway due to the properties of the wood used. If I ever build a proper pair, it will use Paulownia only for the chambers. The wood is too soft for the main body, the good old birch plywood is just the best, and most expensive, too.
There are some machining errors anyway due to the properties of the wood used. If I ever build a proper pair, it will use Paulownia only for the chambers. The wood is too soft for the main body, the good old birch plywood is just the best, and most expensive, too.
It would appear that you want LF drivers with quiet motors for a SLOB, being the rear of the driver is exposed with some of them radiating backwards out from the rear and not being inside the slot.
How does one calculate the group gain of multiple LF drivers in a SLOB ie. dB/w from the sum of drivers vs just a single?
How does one calculate the group gain of multiple LF drivers in a SLOB ie. dB/w from the sum of drivers vs just a single?
+3 dB efficiency increase forget doubling the driver's
eg 1 driver 0, 2 drivers +3, 4 drivers +6
lastly, each halving of the impedance results in another 3 dB increase in effective sensitivity
So, assuming, for instance an 80 dB/wm 8 ohm speaker and a PP array wired in 2 series groups of 4 paralleled resulting in 4 ohm effective impedance , the effective sensitivity would be
80+3+3+3 ( increasing number of drivers) +3 (halving the effective impedance) resulting in an effective sensitivity of 93
This calculation ignores any bandpass gain from the slot or any reduction in spl with distance as a result of the nearfield array effect
Thank you.
Fully understand. Yet you are the only one I know of that has tried a SLOB and AE Dipoles, so it's a valuable data point. I will either need to import 16x 6" or 2x AE 15" so either path will be a hassle.
SLOB has the forward reinforcement that seems appealing compared to my 18" Faitals in OB that sound a bit thin in the low midbass. But the Dipole15 are supposed to be better there too. Oh well 🙂
Your Dipole15 from post #18 seem to be rather close to the front wall. Can I ask how far are they, how low do they reach, and if you supplement them with subs?
Thanks again!
Hi Lewinski
I don’t want to wander from the OP topic too much.
I guess SLOB and OB room placement concerns are similar enough.
While my long term OB project evolved over the last few years I came across the Liionidas article.
Since my project was already very similar, and I had just come across a pair of used Crystal 10 I wanted to try, I decided to use it as a guide to make adjustments.
Leon included a room placement map in his article. My room mimics the basic guidlines for placement. (Image)
It resulted in a little more room on the sides of the panels and a back space of at least 24 in (60 cm) toed in towards the listening position slightly wide of on axis.
There is no sub woofer in this system. I don’t feel the need for one. Perhaps if it was a home theater system that would be different. It is only for music.
I play everything from classical guitar and piano to dubstep, jazz and rock on this system throughout the day.
I can say there is no contest as to the amount of good clean bass output coming from the dipole 15 in the OB. My SLOB didn’t come close.
It should be noted that I am now using a pair of Hypex FA502 amps to drive the AE dipoles as opposed to the bridged Rotel HT amps I was using to drive the SLOB.
I’m sure the he Hypex would produce more ouput if I tried it with the SLOB, but the bass extension would still not be there.
I have not taken measurements for a while. This system was tuned by ear.
I was hoping to take some soon as I’d like to get a clearer picture of what’s going on with my current Sonido field coils up top and decide if I should try a tweeter with them.
I have the feeling there is some better resolution in the top end to be had.
I don’t want to wander from the OP topic too much.
I guess SLOB and OB room placement concerns are similar enough.
While my long term OB project evolved over the last few years I came across the Liionidas article.
Since my project was already very similar, and I had just come across a pair of used Crystal 10 I wanted to try, I decided to use it as a guide to make adjustments.
Leon included a room placement map in his article. My room mimics the basic guidlines for placement. (Image)
It resulted in a little more room on the sides of the panels and a back space of at least 24 in (60 cm) toed in towards the listening position slightly wide of on axis.
There is no sub woofer in this system. I don’t feel the need for one. Perhaps if it was a home theater system that would be different. It is only for music.
I play everything from classical guitar and piano to dubstep, jazz and rock on this system throughout the day.
I can say there is no contest as to the amount of good clean bass output coming from the dipole 15 in the OB. My SLOB didn’t come close.
It should be noted that I am now using a pair of Hypex FA502 amps to drive the AE dipoles as opposed to the bridged Rotel HT amps I was using to drive the SLOB.
I’m sure the he Hypex would produce more ouput if I tried it with the SLOB, but the bass extension would still not be there.
I have not taken measurements for a while. This system was tuned by ear.
I was hoping to take some soon as I’d like to get a clearer picture of what’s going on with my current Sonido field coils up top and decide if I should try a tweeter with them.
I have the feeling there is some better resolution in the top end to be had.
