It would be very unusual for an OB of those dimensions to have this kind of response so my guess is that this FR data is of the nearfield response at the front or rear and not the farfield response. Even with the driver's elevated Qts, there should be a region of 6dB/oct slope due to the front+back cancellation effect. Have you made an outdoor measurement at at least 3m distance?
Edit: I see you mentioned that, yes, this is a nearfield measurement. The farfield will show more LF droop. But with the size of the thing you will get some proximity gain at LF and it might compensate for the OB/dipole cancellation to some degree, especially if you can position them not too far from your listening position.
My prototypes were measured ground plane outside so you can the behavior. This 8 driver version is scaled up from that and shows the same response pattern. I'll measure it soon.
Mean while, here's the prototype that I did to proof of concept this thing before building it with 8.
2 driver version ground plane:
Front wave (slot)
Back wave (two rear chambers)
90 degree off axis, measured at acoustic center of the front slot at 1 meter
Top line is the slot output (front wave)
2nd line is the back wave output at 1~2db lower SPL/energy
Bottom line is the 90 degree off axis, dipole cancellation as expected.
No filters or smoothing anywhere.
There is a droop in the lower frequency output as you mentioned, the knee is still in that 28hz range, but it's not bad and is a 5db from 100hz to 30hz roughly. Still, lovely response potential without DSP. With a low pass filter to kill above 110hz, it's a lovely response to fundamental A1 naturally.
Compression tests to see where the drivers met their limits; I tested this in larger slot cavities to verify it wasn't the cavity itself, it was the drivers. These drivers are not high excursion so they compressed below 28hz when they hit their excursion mechanical limits.
Here, fully compressed, mechanical limits of the drivers, increasing by 1db. No gains below 28hz, mechanical limits of the drivers' excursion. But I can keep getting output from 30hz and up as the excursion limit isn't met. So these can go a lot more if I high pass them at 30hz.
From this I scaled up the 8 driver version.
I'll measure it soon.
Very best,
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Outside wont help you as you wont get any dipole cancellation
Against the wall as you have it measures as a pseudo cardioid as the rear wave is somewhat constrained by the rear wall and you cannot model or predict how that's effecting the phase
Maybe not precise. But you can see measurements above where off axis shows dipole behavior even outside with no boundaries with a ground plane measurement. Unless that is a different effect you can explain?
Thanks!
Very best,
Ok thanks, I'll see what I can do when its dry outside again (storming).
Very best,
Sure you will. You do not need walls or boundaries for the front and rear outputs to interact. They are both propagating like a monopole below a few hundred Hz, with pressure moving outward more or less equally in every direction. At any point in space you can model the dipole response just by summing two monopole sources while accounting for phase and SPL changes due to propagation from the location of the front or rear source to the listening position, and adding these two together. I do this all the time and it is perfectly valid at low frequencies. This will not capture the effect of the tunnel resonance from the slot or H-frame, but you can measure that in the plane of the opening and then use that as your source.
Sounds good. That way you can be sure that you are capturing the dipole cancellation "droop" properly. What I suspect you are measuring now includes some LF proximity gain. You can read about that effect here:
http://musicanddesign.speakerdesign.net/Dipole-axis.html
FWIW, you are probably only a few dB off below 60Hz...
Not sure what you’re trying to say here….how I read your response is there will be no significant difference in the response of a dipole system at the listening position in a closed space with walls and a ceiling than their will be in an open space without a roof to boundaries?…..did I read that correct?
@mayhem13 :
You make measurements with a microphone. It is just recording the pressure vs time.
You listen with a sophisticated hearing system that includes your ears and your brain.
The microphone measurements does not always reflect what your brain senses through your "hearing system". This includes the effect of reflections.
With loudspeakers as the source and in a typical indoor environment there is the direct sound (first arrival), and then sounds that reach your ears later such as those from floor, ceiling, and wall reflections and multiples of these. How your brain processes the non-first-arrival sounds depends on how much later they arrive. It turns out that there is a short window after the first arrival within which your brain lumps further acoustic signals with the direct sound. This window lasts about 4 milliseconds. Within this time you typically have cabinet diffraction effects (virtual sources along the cabinet edges), floor reflections, and ceiling reflections if the ceiling is not more than 10' tall or so. Then later on will come the wall reflections unless the room is relatively small or narrow, and then finally all the multiple reflections, e.g. two walls, floor+wall, etc. Because humans have evolved to exist and make sense out of acoustic signals in reflective indoor spaces, the brain has evolved the ability to suppress the signals that arrive after about 4 milliseconds. The more that these later arrivals have the same frequency response as the first arrival, the more effective this suppression by the brain will be. You can read up on this topic in detail by searching some papers in the field of psycoacoustics.
So, back to the open baffle subwoofer, the topic of this thread. The side and rear wall reflections will arrive after the 4msec time window has passed if they are 1.5m or greater away from the source. It doesn't matter the phase of these signals, the brain is able to suppress them and you perceive only the direct sound. But your microphone will dilligently report the interference effects of these non-first-arrival sounds as long as they are within the data recorded by the measurements.
When the listening space is much larger, reflections can arrive much later, e.g. 40msec or later, and then the brain perceives these as echoes (and you perceive these later arrivals separately). But that is much larger than a domestic listening space, so it's not really germane to this conversation.
You make measurements with a microphone. It is just recording the pressure vs time.
You listen with a sophisticated hearing system that includes your ears and your brain.
The microphone measurements does not always reflect what your brain senses through your "hearing system". This includes the effect of reflections.
With loudspeakers as the source and in a typical indoor environment there is the direct sound (first arrival), and then sounds that reach your ears later such as those from floor, ceiling, and wall reflections and multiples of these. How your brain processes the non-first-arrival sounds depends on how much later they arrive. It turns out that there is a short window after the first arrival within which your brain lumps further acoustic signals with the direct sound. This window lasts about 4 milliseconds. Within this time you typically have cabinet diffraction effects (virtual sources along the cabinet edges), floor reflections, and ceiling reflections if the ceiling is not more than 10' tall or so. Then later on will come the wall reflections unless the room is relatively small or narrow, and then finally all the multiple reflections, e.g. two walls, floor+wall, etc. Because humans have evolved to exist and make sense out of acoustic signals in reflective indoor spaces, the brain has evolved the ability to suppress the signals that arrive after about 4 milliseconds. The more that these later arrivals have the same frequency response as the first arrival, the more effective this suppression by the brain will be. You can read up on this topic in detail by searching some papers in the field of psycoacoustics.
So, back to the open baffle subwoofer, the topic of this thread. The side and rear wall reflections will arrive after the 4msec time window has passed if they are 1.5m or greater away from the source. It doesn't matter the phase of these signals, the brain is able to suppress them and you perceive only the direct sound. But your microphone will dilligently report the interference effects of these non-first-arrival sounds as long as they are within the data recorded by the measurements.
When the listening space is much larger, reflections can arrive much later, e.g. 40msec or later, and then the brain perceives these as echoes (and you perceive these later arrivals separately). But that is much larger than a domestic listening space, so it's not really germane to this conversation.
@MalVeauX These subs look really nice, and measurements are not bad either. I've been thinking about a 8 driver subwoofer system with 4 boxes and 2 drivers each. My best option right now is 12" drivers into separated sealed boxes to help with transfer. So if you put 4 pcs of 12" drivers on one side, the tower will wobble too much to be comfortable? Do you absolutely recommend opposing driver placement? If you did it now again, would you do anything differently, like smaller/bigger drivers or a different number of them?
Hi,
I have 16 sealed subs for theater. Many of them stacked. You can do any number of drivers, but I like keeping the count lower to keep weight down per unit so I'm not moving extremely heavy boxes. These 8x12" cabinets are exceptions, small for the driver count, light weight drivers.
If you do 2 drivers per cabinet, you can wire them externally so you can access them individually for wiring purposes, so you can get ideal wiring depending on their impedance and amp. Or you could just go ahead and wire them in series, and then in parallel with another 2 drivers to the amp per channel.
My cabinets when I stack do not wobble, but they're not ultra light and they have 20"~30" bases they're sitting on when I stack low squatty subs. I like to stack in pairs. I could stack more, but lifting weight that high is not fun.
Opposition pairs is a great way to have zero vibration from the box if you want to stack things. Really ideal.
I did these:
4 ft^3 sealed enclosures. MX15-22 driver. Two stacked. I have 8 total. Two groups of 4 on the amp channel (4ohm series-parallel).
These are the others. These are bigger. 6 ft^3 each. HT18 V3 driver each. I stack them in 2's. That's 12 ft^3 stacked as a fat tower with two 18's.
Otherwise, using 12's, I would probably just do 4 drivers per enclosures, 8~12 ft^3 single towers. No stacking. And do opposition pairs. 2 on the front. 2 on the back. For position I would face them so the drivers are the same distance to the listener, so drivers would fire to the sides and the blank wall of the sub pointed at the listener. Two towers like that. 8 total 12's. Opposition pairs with no cabinet vibration. Two channels total needed.
Very best,
Thanks for your reply, you seem to have lots of experience with these things. The upper picture is something that I had in mind. I thought that I could do slightly smaller cabinets and have total of 8 pcs of 12" drivers to match the output of the 15" (upper) bass woofers of my main speakers.
You say that opposing firing woofers would be ideal and I concur, but my only problem is placement in my listening room. It would be a lot easier to stack array of 4 facing forward than opposing woofers. But then I thought of wobbling if going for lighter cabs, but I guess that would be a problem only at ridiculously loud volumes. Maybe I could to rearrange my furniture a bit 🙂 I will need to plan this through. Thanks again for yor thoughts.
Regards,
Jukka
You say that opposing firing woofers would be ideal and I concur, but my only problem is placement in my listening room. It would be a lot easier to stack array of 4 facing forward than opposing woofers. But then I thought of wobbling if going for lighter cabs, but I guess that would be a problem only at ridiculously loud volumes. Maybe I could to rearrange my furniture a bit 🙂 I will need to plan this through. Thanks again for yor thoughts.
Regards,
Jukka
You could do smaller cabinets, smaller drivers, it's all about what bandwidth and SPL you want. My system is focused on 10hz as its peak in the house curve. So I have lots of larger drivers in larger volumes stacked up. It's for theater. But if you are doing music or not focused on infrasonic, 12's can easily do 20hz and up no problem. 8 x 12's can do 20hz and above very nicely in a typical room. They wouldn't need full excursion or high power even.
If you were going very tall and very light weight, then sure, opposing pairs would be ideal. They can have an inch or two between them for vent pole clearance. It's not that different than the width if they face you unless they're huge magnet drivers with high depth. But yea unless your cabs are unbalanced to begin with, the drivers will not walk off the top. You can put a material that makes them moving or sliding nearly impossible. I use pantry shelf liner between cabinets, its a foam rubbery paper that keeps cups and dishes from sliding in cupboards and works great between cabinets when stacking, they don't budge and mine are moving 20mm excursion one way.
Very best,
Cab design - Horn resp needs a learning curve, advanced level of wood work, - difficult construction and production - large form factor - below ia a suggestion following kef compact design philosophy based on tech barrier resolution.
kef -
https://soundstagesimplifi.com/index.php/equipment-reviews/191-kef-kc62-powered-subwoofer
6.5" driver x 2 ; 10" x 10" x 10" , -3db @ 11hz , 105 db ; 1000W
Project -
Easier - DSP, https://vi.aliexpress.com/item/1005005880012900.html?spm=a2g0o.cart.0.0.240938da3cPtUT&mp=1&pdp_npi=5@dis!USD!USD 39.90!USD 36.71!!USD 36.71!!!@2103246617460595194447152e2c05!12000034681998126!ct!BR!137474716!!1!0&gatewayAdapt=glo2vnm
or mini dsp
Any powerful class D you like - > 1k for x 2 drivers. 1.4 to 1.6k w better.
A driver like , in place of - the advanced 6.5inch KEF driver - 2 x 8" driver with a suspension system like SD series can be used.
https://sundownaudio.com/products/s...oofer-sub-neo-sd4?_pos=8&_sid=fae8345cb&_ss=r
https://sundownaudio.com/products/x-series-v-3-8-800w-x-8-subwoofer-used?_pos=5&_sid=fae8345cb&_ss=r
DSP - 40USD, DSP ing & eq critical to the project
Driver - x 2 - 700USD (350@)
Amp -
Small Cabinet - easy to execute, lesser construction difficulties. good looks, convenient, diy awe factor - small cab for the output