Hi all not posted for a while
I built a PA a couple of years ago which is 2 tops, 2 15” (modded b&c design) kicks/subs depending on setup and one dual 15” PPSL sub I built to beef up on the lows when neccesary.
I think it starts to roll off around 45/50hz but that’s fine for my needs. However what isn’t fine is that with the current drivers at least, it sounds horrendously fluffy with any significant power put into it, don’t know if it counts as chuff in this box layout unless chuffing means all forms of sound pressure/cone interference?
The drivers have been in a while so I can’t remember what they are, they are some neo-d low end drivers, nothing very fancy, maybe a spanish make? Anyway the rig sounds much better without the sub as the kicks can take a lot more signal without complaining, renders it almost useless really as they also go as low
My question I guess is - is there anything I can do about the chuffing? I designed the box to have the smallest ‘plenum’ (slot) possible and make it taper out like a horn, and built out the internal corners, again to reduce volume of slot, as I read it is desirable to get the drivers as close together as possible, and as a joiner I fancied the challenge, but most PPSL subs just have a rectangular slot.
This was my design:
If I can save the box and get it to work by rebuilding the slot part, it might be worth it, it seems a handy way to squeeze 2 drivers into a small space!
I built a PA a couple of years ago which is 2 tops, 2 15” (modded b&c design) kicks/subs depending on setup and one dual 15” PPSL sub I built to beef up on the lows when neccesary.
I think it starts to roll off around 45/50hz but that’s fine for my needs. However what isn’t fine is that with the current drivers at least, it sounds horrendously fluffy with any significant power put into it, don’t know if it counts as chuff in this box layout unless chuffing means all forms of sound pressure/cone interference?
The drivers have been in a while so I can’t remember what they are, they are some neo-d low end drivers, nothing very fancy, maybe a spanish make? Anyway the rig sounds much better without the sub as the kicks can take a lot more signal without complaining, renders it almost useless really as they also go as low
My question I guess is - is there anything I can do about the chuffing? I designed the box to have the smallest ‘plenum’ (slot) possible and make it taper out like a horn, and built out the internal corners, again to reduce volume of slot, as I read it is desirable to get the drivers as close together as possible, and as a joiner I fancied the challenge, but most PPSL subs just have a rectangular slot.
This was my design:
If I can save the box and get it to work by rebuilding the slot part, it might be worth it, it seems a handy way to squeeze 2 drivers into a small space!
Try to round over any edge that is in contact with high velocity air, usually all vent edges. The vent divider would better be removed or at least rounded over.
Edit: you could try to find the frequency/ies where the speakers make chuffing noise to get an idea what the problem is. Use a sine generator and slowly sweep through the low frequency range.
Edit: you could try to find the frequency/ies where the speakers make chuffing noise to get an idea what the problem is. Use a sine generator and slowly sweep through the low frequency range.
Ok thanks, maybe it’s not chuff then actually, it’s definitely coming from the drivers. They move without crunch manually so it makes me think it’s the air interfering with the movement of the cones? Can’t hurt to try rounding things though if I have to deconstruct it
If it starts to roll off at 45/50Hz, it's tuning (Fb) is probably around that frequency, the cabinet needs to be high passed around 40Hz, or the flapping of the cone blowing air will sound "horrendously fluffy with any significant power put into it". Below Fb, the cone and port output go out of phase, and the cone "unloads", moving like it has no cabinet.
If the driver has a vented pole piece, it will also chuff more below Fb, as the cone flaps uselessly.
Your other subs may (probably..) have a lower Fb than the PPSL.
Anyway, run a moderate level sine wave through your subs, the cone movement will be lower at the Fb frequency than above or below. Use a BW24 HP a few Hz below Fb.
If you would like to lower the Fb, you could experiment reducing the port volume something like in this exaggerated diagram:
As STV suggested, rounding all vent (and plenum) edges will reduce noise, but that's probably not the problem- port noise is hard to hear over most music.
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You have to make an impedance plot, you should see what kind of box you have created. Then, as mentioned in post #2 do a manual sweep with a generator. Find the critical frequency, you will probaply feel the air pulsating if it comes from the vented pole piece of a driver for example.
A look at the 3-d picture shows the posibility that you accidentely constructed a band pass cabinet. In this case it would help to integrate half of the lower vent to the box volume. Then install the missing vent into the upper end of the box. That would synchronize both volumes.The baffles carrying the drivers may turn the inner volume into two chambers resonating.
A look at the 3-d picture shows the posibility that you accidentely constructed a band pass cabinet. In this case it would help to integrate half of the lower vent to the box volume. Then install the missing vent into the upper end of the box. That would synchronize both volumes.The baffles carrying the drivers may turn the inner volume into two chambers resonating.
Are all of the cabinets on the ground used as subs? One problem I see is if they so not match in the low end they could cancel at some frequencies. The middle cab being different from the sides could be a problem.
Thanks all, very interesting and helpful! The drivers definitely have vents at the back and are definitely flapping around so it sounds like you’re all ok the right track
Reducing port volume could be achieved by filling the vent space with material? Sorry @weltersys I don’t quite understand your diagram - and turbowatch you are suggesting something similar but blocking half the vent and adding half sized one to balance at the top, fairly major surgery but it would be nice to save the box
Reducing port volume could be achieved by filling the vent space with material? Sorry @weltersys I don’t quite understand your diagram - and turbowatch you are suggesting something similar but blocking half the vent and adding half sized one to balance at the top, fairly major surgery but it would be nice to save the box
Your box chamber is open to the section above the plenum, as is standard for PPSL cabinets, no need to add an upper port.
My suggestion to lower the Fb (if you find it higher than the other subs) was to add a "V" on either side of the port divider panel. This would make the port tapered on the inside and out. Tapered ports reduce turbulence.
An easier approach would be reducing the port area with two straight sections the same dimensions as your present port divider with a cover in front, leaving the back open to the cabinet inside, similar to the "step down" (lower Fb) mode in the EV TL cabinets when the center section is covered.
Placing the cabinet on it's side (cones vertical rather than horizontal) will prevent cone sag over time.
My suggestion to lower the Fb (if you find it higher than the other subs) was to add a "V" on either side of the port divider panel. This would make the port tapered on the inside and out. Tapered ports reduce turbulence.
An easier approach would be reducing the port area with two straight sections the same dimensions as your present port divider with a cover in front, leaving the back open to the cabinet inside, similar to the "step down" (lower Fb) mode in the EV TL cabinets when the center section is covered.
Placing the cabinet on it's side (cones vertical rather than horizontal) will prevent cone sag over time.
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If you can't store the speakers laying on the side, just swap the lower and the upper driver every 1/2 years.
I'd bet a lot on that's the solution.
E: At which frequency do you cross the subs and the infra? ..you DO cross them over.. please say you do.
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Haha yes I do cross over, fear not. I think 80/90 or 100hz I can’t remember last settings. Thanks that’s a nice solution to swap the drivers occasionally although they are both technically the same way ‘up’? Does it still help? No reason I can’t store it on side though as well.
Can definitely high pass just below Fb, might be nice to get the most out of Fb with port modification first. Also, I think I already run it with a high pass but maybe it’s too low, I’ll check next time I get it all fired up
Can definitely high pass just below Fb, might be nice to get the most out of Fb with port modification first. Also, I think I already run it with a high pass but maybe it’s too low, I’ll check next time I get it all fired up
Thanks for explaining, that is much appreciated and I think I can quite easily try making a few additions to add to the port and experiment and see what gets good results 🙂
facepalm ...... noooo... The two subs on which the tops are mounted on. And the bigger one between them. So no xo between these? They are tuned differently, no?
Yeah when I use all of them in a kinda 2.1 I cross to the bigger one around 100, but if not using that obviously run the two others low, which is currently preferable because of these issues!
