Hi can you help me with a problem.
I want to build some 3 way speakers using the SB29NRX75-6 as bass units.
I do not want the cabinets to be too large (WAF) so intend to make them about 40 litres internal. If I make them sealed the bass is just a bit lacking so I was thinking of making them ported but then the bass may be a bit too much.
My idea is to just use a 50mm port of the correct length which would mean not increasing the cabinet internal size too much to compensate and then filling the port tube with some very open cell foam to get something in between sealed and ported.
Do you think this will work or will it just end up with the same performance as sealed.
I want to build some 3 way speakers using the SB29NRX75-6 as bass units.
I do not want the cabinets to be too large (WAF) so intend to make them about 40 litres internal. If I make them sealed the bass is just a bit lacking so I was thinking of making them ported but then the bass may be a bit too much.
My idea is to just use a 50mm port of the correct length which would mean not increasing the cabinet internal size too much to compensate and then filling the port tube with some very open cell foam to get something in between sealed and ported.
Do you think this will work or will it just end up with the same performance as sealed.
Last edited:
"Very" open cell foam will have almost no effect on the port response.
With an undersized ported cabinet tuned low (near or Fs), the bass will not be "too much", it will roll off towards Fb (box tuning) then drop more rapidly than a sealed cabinet below. The sealed cabinet will start to drop off at a higher frequency.
Room modes may cause certain bass frequencies to be too loud (or not loud enough), but that is independent of design.
The SB29NRX75-6 has an Xmax of 11mm, the suggested 3" (76mm) diameter port is already a bit on the small size, 50mm may chuff a bit if you plan to use the full capability of the driver, which is more likely in an undersized cabinet...
With an undersized ported cabinet tuned low (near or Fs), the bass will not be "too much", it will roll off towards Fb (box tuning) then drop more rapidly than a sealed cabinet below. The sealed cabinet will start to drop off at a higher frequency.
Room modes may cause certain bass frequencies to be too loud (or not loud enough), but that is independent of design.
The SB29NRX75-6 has an Xmax of 11mm, the suggested 3" (76mm) diameter port is already a bit on the small size, 50mm may chuff a bit if you plan to use the full capability of the driver, which is more likely in an undersized cabinet...
much better idea would be to use a DSP parametric EQ and a measurement mic to get the response you want.
40L sealed is pretty close to ideal with a Qtc~ .66, f3~ 42hz and a nice shallow roll off.
40L ported is a bit undersized but does lower the f3 to ~31hz with a steeper roll off.
You could build it sealed and see how you like it and if you don't add a 75mm port about 20" long, which tunes it to ~ 24hz. You could also build it with the port and plug it if needed, which is what I typically do.
40L ported is a bit undersized but does lower the f3 to ~31hz with a steeper roll off.
You could build it sealed and see how you like it and if you don't add a 75mm port about 20" long, which tunes it to ~ 24hz. You could also build it with the port and plug it if needed, which is what I typically do.
Not by much. I doubt your significant other can tell the difference between a 40 or 45 or 50litre enclosure. 75mm is kinda average for a 290mm woofer.
"50mm may chuff a bit" - how many people actually play at a level that would cause chuffing in a home environment? - only the deaf or drunk. 50mm is fine
while I agree that port size calculation are often a little conservative around here, I think 50mm in an under sized box with a 10" woofer is less than ideal but he can try and if he has issues he can stuff the port or go bigger. I'm always for trying things, worse case he learns what chuffing sounds like.
Woofer and box sizes go hand in hand, that is because the larger the surface area of the cone, the more the pressure of the box will act on it.
All things short, I believe the driver itself would not work well, what you really want is a 8" as a woofer to match a 40 litre box.
Oon
All things short, I believe the driver itself would not work well, what you really want is a 8" as a woofer to match a 40 litre box.
Oon
Going back to my original thought, would an open foam bung whilst not doing much slow down the air and stop chuffing and at the same time give a performance between sealed and ported.
The open cell foams used in air filters cause a resistance on the air.
The open cell foams used in air filters cause a resistance on the air.
Not really. If you damp the port resonance it becomes weaker and broader in frequency leading to it largely ceasing to contribute to the output. Unless carefully designed you will get an uneven frequency response and even if it is carefully designed a gently falling sealed response may well work better for most rooms in a home. This follows from room gain and a reduction in the level of the intrusive lowest frequency room resonances.
If you do control the room response with something like distributed subs things start leaning more towards porting but for uncontrolled rooms the gentle roll-off of a sealed speaker with a decent amount of cone area tends to be a good compromise between hearing low frequencies and not being overpowered by room boom. This assumes an interest in sound quality for conventional music. If you value such things as exploding planets in films and perhaps loud deep organ music things may be different.
If small box has to be tuned low and you dont have place for big enough vent you can try a passive radiator.
With little thinking and experimenting you can even make it by yourself using speaker suspension and cardboard disc or self made weighted cone
With little thinking and experimenting you can even make it by yourself using speaker suspension and cardboard disc or self made weighted cone
look up aperiodic vent.
Do you have a sketch of your speaker. You seem to be hemming and hawing about a cm here a few litres there. If space is that tight how are you going to position them in the room properly. Maybe you should just go with a smaller woofer or just accept the SB 10" in a sealed enclosure which could probably be as small as 30-35 litres. You won't learn much until you start to build and experience these things yourself. At this point you don't know and we don't know what you like and what compromises you can live with.
Understand that air doesn't flow through the port. The air inside the port acts just like the cone on a driver. That volume of air is what excites the air outside the port, just like the pistonic motion of the cone driver does. The chuffing is a result of that volume of port air being too small to react to the pressure produced by the cone driver quick enough. It "chokes".
Have spent some time working on dimensions and ports etc.
Can now fit a 70mm dia port.
After deducting all the internal components, port crossover and driver etc I get 40 litres, assuming damping will add approx 10 % to this I have 44 litres.
Do you think I will now be ok.
Can now fit a 70mm dia port.
After deducting all the internal components, port crossover and driver etc I get 40 litres, assuming damping will add approx 10 % to this I have 44 litres.
Do you think I will now be ok.
Last edited:
With your size constraints you're better off w/sealed. EQ the bottom end to suit.
You can't stuff a reflex enclosure w/damping to gain volume.
You haven't touched on the tuning frequency you have arrived at w/70mm port. How long is the pipe? I'm guessing it is too high which will give you peaky response in the low end and drop like a rock.
You can't stuff a reflex enclosure w/damping to gain volume.
You haven't touched on the tuning frequency you have arrived at w/70mm port. How long is the pipe? I'm guessing it is too high which will give you peaky response in the low end and drop like a rock.
Do you intend to place these speakers on stands? If so, you have the option to use the stand tube as the port which would be largely outside the speakers enabling you to get closer to the optimum cabinet volume and the optimum port length.