Which is safer...a closed box..or a vented one...when it comes to over-excursion of a subwoofer...there is some indication that a vented one is safer but not below fb...if the woofers/box combination gives an fb of around 20..what are the chances it will be going lower than that?
The reason I am asking is because I have two Tempest subs(sealed) and I am powering them with 750 watts each in parallel..and I was wondering if they can take the excursion..I know they will take the thermal tolerance because they are rated at 750 watts.......
The reason I am asking is because I have two Tempest subs(sealed) and I am powering them with 750 watts each in parallel..and I was wondering if they can take the excursion..I know they will take the thermal tolerance because they are rated at 750 watts.......
Excursion depends on box size (and tuning frequency for vented boxes). Smaller boxes have better power handling, but somewhat less bass. Venting reduces excursion at tuning, but excursion at ~1.5 x Fb is the same as for a sealed, and excursion below tuning is much more than a sealed box.
Chances are you could rip your woofers apart in sealed or vented boxes with the amount of power you have, but I think sealed would be slightly safer.
In a 100 liter sealed box per woofer, the power handling at 20Hz is only 300 Watts, according to my simulation....Reducing box size to 60L would give you twice the displacement limited powerhandling, at the expense of a higher Q. If I were going to pound on them, it's probably what I would do.... Although, If I were going for max SPL, I wouldn't use tempests, I'd probably use LABHorns...
YMMV
Chances are you could rip your woofers apart in sealed or vented boxes with the amount of power you have, but I think sealed would be slightly safer.
In a 100 liter sealed box per woofer, the power handling at 20Hz is only 300 Watts, according to my simulation....Reducing box size to 60L would give you twice the displacement limited powerhandling, at the expense of a higher Q. If I were going to pound on them, it's probably what I would do.... Although, If I were going for max SPL, I wouldn't use tempests, I'd probably use LABHorns...
YMMV
It also depends heavily on the driver construction, how well
it is designed to cope with "overexcursion". Some cheap
drivers are very poor, some better drivers have progressive
stiffness suspensions and shrug off being driven past linear
excursion limits.
For digital sources (not vinyl) subsonics below 20Hz are very
clean and basically not a concern regarding overexcursion.
Reflexes have a huge advantage in max SPL over sealed
at low frequencies so I'd suggest reflex is the best bet.
🙂 sreten.
it is designed to cope with "overexcursion". Some cheap
drivers are very poor, some better drivers have progressive
stiffness suspensions and shrug off being driven past linear
excursion limits.
For digital sources (not vinyl) subsonics below 20Hz are very
clean and basically not a concern regarding overexcursion.
Reflexes have a huge advantage in max SPL over sealed
at low frequencies so I'd suggest reflex is the best bet.
🙂 sreten.
Apples and Oranges
How much of an advantage is it really, say right at f3? I thought it was only like 3dB.
I agree that if you take a speaker designed for a vented box, like one with an EBP over 100, and simulate it in a sealed box, you will notice it typically runs out of XMAX in the bottom octave or so. A speaker like that will not be able to put out a lot of SPL at low frequencies.
On the other hand, if you use a speaker designed for a sealed box, one with a low EBP and plenty of XMAX, you WILL be able to produce a lot of SPL at low frequency.
In fact, at frequencies BELOW f3, the sealed box will put out a significantly higher SPL because it only rolls off at 12db/octave not 24dB/octave like the vented box.
I think it's like comparing apples to oranges, because vented and sealed boxes each need their own type of speaker to work well.
sreten said:
How much of an advantage is it really, say right at f3? I thought it was only like 3dB.
I agree that if you take a speaker designed for a vented box, like one with an EBP over 100, and simulate it in a sealed box, you will notice it typically runs out of XMAX in the bottom octave or so. A speaker like that will not be able to put out a lot of SPL at low frequencies.
On the other hand, if you use a speaker designed for a sealed box, one with a low EBP and plenty of XMAX, you WILL be able to produce a lot of SPL at low frequency.
In fact, at frequencies BELOW f3, the sealed box will put out a significantly higher SPL because it only rolls off at 12db/octave not 24dB/octave like the vented box.
I think it's like comparing apples to oranges, because vented and sealed boxes each need their own type of speaker to work well.
Oh yeah...
Oh yeah... a sealed box at q=1.1 will be a bit "peaky", but it has the highest power handling of any sealed alignment. And the smallest box size. Transient response not quite perfect, but this is low bass, right? The ear is not so sensitive there.
I have made nice sealed subwoofers, q=1.1, and they sound very rich and thick. They have quite a "thump" to them as there is still useable output well below f3, like at 15 Hz. My vote says that sealed boxes have a much greater feeling of 'solidity' that vented boxes at roughly equal f3.
But that is for your ears...
Oh yeah... a sealed box at q=1.1 will be a bit "peaky", but it has the highest power handling of any sealed alignment. And the smallest box size. Transient response not quite perfect, but this is low bass, right? The ear is not so sensitive there.
I have made nice sealed subwoofers, q=1.1, and they sound very rich and thick. They have quite a "thump" to them as there is still useable output well below f3, like at 15 Hz. My vote says that sealed boxes have a much greater feeling of 'solidity' that vented boxes at roughly equal f3.
But that is for your ears...
A speaker that is suitable for sealed or reflex in a bigger box :
Around port frequency before cutoff max SPL is +12dB for the reflex.
This reduces to ~ 6dB ~ 2/3 of an octave above port frequency.
Above these frequencies excursion limited bass becomes similar.
Apples and oranges yes, but the other way round, a reflex
alignment will push out the equivalent of 4 sealed drivers,
(around the port fequency) and need less power to do so.
But you do need a bigger box (than for one sealed driver).
🙂 sreten.
Around port frequency before cutoff max SPL is +12dB for the reflex.
This reduces to ~ 6dB ~ 2/3 of an octave above port frequency.
Above these frequencies excursion limited bass becomes similar.
Apples and oranges yes, but the other way round, a reflex
alignment will push out the equivalent of 4 sealed drivers,
(around the port fequency) and need less power to do so.
But you do need a bigger box (than for one sealed driver).
🙂 sreten.
Yes, I see what you are saying... when you pick one driver with intermediate characteristics-- one that can be used either vented or sealed-- it will inevitably tune to a higher f3 when put into a sealed box.
Because the f3 is higher, it rolls off sooner so of course the max SPL you can get at the lowest frequencies is diminished.
But when you look at the curves you supplied, it's clear that the vented box's output is not 12 dB higher at all frequencies. Way above resonance, the curves are nearly the same. The sealed box has a higher f3, that's all.
My contention is that if you get a driver with the low EBP, low fs, and high XMAX that you would want anyway for a sealed box, that problem will largely correct itself and the f3 would be lower. Then there would be little difference at resonance, and a marked advantage for the sealed box below resonance.
On the curve you supplied, see how the sealed box has higher output at REALLY low frequencies, like 15 Hz. In my opinion, that is what contributes to a sealed box often sounding more "solid" even when the f3 is slightly higher than a comparable vented box. Though not as much a higher f3 as in your example. I'm sure that in the example you gave the sealed box would sound thinner at the very low end. That's why you have to get a driver that is specially suited to the sealed box. Apples and oranges again.
But in answer to the original question--sorry, almost forgot!-- The one thing you really have to worry about with vented enclosures is subsonic signal getting in, because the cone motion is hardly controlled at all below resonance. For example if your vented box has an f3 of 40 Hz (not absurd) and you crank up the bass so a lot of 20Hz signal is getting through, (assume modern electronica or hip-hop music) the cones will fly all over the place and maybe tear up. So add a subsonic filter to take out frequencies below resonance if you go with vented box. At least, if you are worried about high-power use and durability.
Because the f3 is higher, it rolls off sooner so of course the max SPL you can get at the lowest frequencies is diminished.
But when you look at the curves you supplied, it's clear that the vented box's output is not 12 dB higher at all frequencies. Way above resonance, the curves are nearly the same. The sealed box has a higher f3, that's all.
My contention is that if you get a driver with the low EBP, low fs, and high XMAX that you would want anyway for a sealed box, that problem will largely correct itself and the f3 would be lower. Then there would be little difference at resonance, and a marked advantage for the sealed box below resonance.
On the curve you supplied, see how the sealed box has higher output at REALLY low frequencies, like 15 Hz. In my opinion, that is what contributes to a sealed box often sounding more "solid" even when the f3 is slightly higher than a comparable vented box. Though not as much a higher f3 as in your example. I'm sure that in the example you gave the sealed box would sound thinner at the very low end. That's why you have to get a driver that is specially suited to the sealed box. Apples and oranges again.
But in answer to the original question--sorry, almost forgot!-- The one thing you really have to worry about with vented enclosures is subsonic signal getting in, because the cone motion is hardly controlled at all below resonance. For example if your vented box has an f3 of 40 Hz (not absurd) and you crank up the bass so a lot of 20Hz signal is getting through, (assume modern electronica or hip-hop music) the cones will fly all over the place and maybe tear up. So add a subsonic filter to take out frequencies below resonance if you go with vented box. At least, if you are worried about high-power use and durability.
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