Hello,
ive built a box for my subwoofer boschmann v-1250sni that has about 70liters of capacity(i THINK that was the recommended capacity in the only manual i had found at that moment and it wasnt in english so im not sure that was the capacity recommendation). the sound is great on low volume, and at high volume at some soundtracks, but mostly i get some kind of strange rattling or something like that, like there wouldnt be enough air in the box. the sub is fine and not broken for sure, but i think its the box that is causing problems. it is sealed at the moment, but ive been thinking that adding a port would solve the problem somehow?
ive built a box for my subwoofer boschmann v-1250sni that has about 70liters of capacity(i THINK that was the recommended capacity in the only manual i had found at that moment and it wasnt in english so im not sure that was the capacity recommendation). the sound is great on low volume, and at high volume at some soundtracks, but mostly i get some kind of strange rattling or something like that, like there wouldnt be enough air in the box. the sub is fine and not broken for sure, but i think its the box that is causing problems. it is sealed at the moment, but ive been thinking that adding a port would solve the problem somehow?
Boschmann V-1250SNI - Głośniki Samochodowe Archiwum - Car & Home Audio Sklep i dont understand polish language, but i thought Vas = 70l was the capacity recommendation, might be completely wrong though
So making my box 10 liters smaller size as a sealed one, or 20 liters smaller as a ported one should fix the problem? is there anything to do with my 70l box?
Is it the box itself that is rattling? Play it loudly whilst its rattling, and press hard on each wall to feel for excess vibration and yhe noise being eliminated by your hand. If it's the box, brace it internally
Parametry T/S:
Fs 32,40 Hz
Zo 60,31
Sd 2,70
Dia 30
BL 13,52
no 0,63
SPL 90 dB
Qms 6,34
Qes 0,37
Qts 0,35
Vas 70,19 L = the driver's compliance spec.
Cms 241,75
Mms 99,86
Mmd 94,33
Xmax 10,5 mm
Basic sealed box math for max flat [0.707 Qtc] alignment:
a = [0.707/0.35]^2 - 1 = ~3.0804
net volume [Vb] [L] = 70.19 L /~3.0804 = ~23.00 L
box tuning [Fc] = [~3.0804 + 1]^0.5 * 32.4 Hz = ~65.45 Hz
From this we see that the 70 L box is much too large for sealed and in theory shouldn't normally be any larger for vented, so my SWAG is that the driver's 'rattling' is due to extreme over excursion since box Qtc = ~0.35, ergo has about as much control over it as if it was in free air.
In short, it has way too much air in the box, so either vent it or add scrap wood, bricks, whatever that's dense that reduces it to ~23 L with the understanding it will become mostly a mid-bass sealed box alignment.
All that said, published specs can be pretty far off from what your driver's specs actually are, so while the math is good, the results may not mirror it.
GM
damn i missed the capacity COMPLETELY 🙁 so putting this speaker in a much smaller box would fix the rattling but it would not be able to play the lower frequencies?
Correct, one can only choose two of these three: TA Speaker Topics: Loudspeaker Design Tradeoffs
Physics, it's the Law! 🙁
At this point, best overall to vent it.
GM
Physics, it's the Law! 🙁
At this point, best overall to vent it.
GM
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Vent it on 70l box? or make a new one with 27l capacity? and vent it by adding rectangular hole on the side of the front, or adding a tube in some place? sorry for many stupid questions, im still a newbie at this 🙁
Basically, the Qts of the driver make it a better candidate for a ported enclosure rather than sealed. You would need to reduce the box volume to ~44L and add a 30cm long x 10cm diameter tube as a port. All three of the above values are important.
The size of the box matters. Think of the air inside as providing a "spring" behind the cone of the driver. This a referred to as acoustic suspension.
For a sealed box design the stiffness of the spring is dependent on the volume of the box. If the box is too large, the spring is too soft and doesn't support the cone at lower frequencies. If the box is too small, the spring ends up too stiff and prevents to the cone from reaching the lower frequencies.
A ported enclosure operates in a similar but not identical manner. In this case, the spring tends to want to vibrate (resonate) at a specific frequency which is slightly offset from where the driver wants to resonate on its own (the Fs value). This helps extend the low frequency of the driver.
The volume of a sealed box design will not be the same as the volume of a ported box for the same driver.
-b
The size of the box matters. Think of the air inside as providing a "spring" behind the cone of the driver. This a referred to as acoustic suspension.
For a sealed box design the stiffness of the spring is dependent on the volume of the box. If the box is too large, the spring is too soft and doesn't support the cone at lower frequencies. If the box is too small, the spring ends up too stiff and prevents to the cone from reaching the lower frequencies.
A ported enclosure operates in a similar but not identical manner. In this case, the spring tends to want to vibrate (resonate) at a specific frequency which is slightly offset from where the driver wants to resonate on its own (the Fs value). This helps extend the low frequency of the driver.
The volume of a sealed box design will not be the same as the volume of a ported box for the same driver.
-b
Finding the tube you described seems harder than bending the laws of physics! Anyway, thank you very much for the information! There is a lot to learn about these things for me.
You can start with the closest diameter tube you can get and then adjust the length of the port. Port length and diameter go hand in hand. If you increase the diameter and want the same frequency response, you have to increase the length. More specifically, if you increase the port area (pi*r^2), you have to increase the length by the same proportion. There's an additional correction, but if you aren't changing the diameter of the tube by much, that won't make much difference.
And in the US, PVC pipe is sold in 4" diameter (10.16cm).
And in the US, PVC pipe is sold in 4" diameter (10.16cm).
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