Hey, guys
I was curious as to what effect a large cabinet would have upon a driver, as compared to the same driver in a small cabinet (And for the sake of exercise, what would the effects be for an overly large or an overly small cabinet be as well)
Is it primarily distortion characteristics?
(Also, hopefully we can keep this idea towards sealed cabinets for the sake of convinience)
Much love/Many thanks in advance everyone
I was curious as to what effect a large cabinet would have upon a driver, as compared to the same driver in a small cabinet (And for the sake of exercise, what would the effects be for an overly large or an overly small cabinet be as well)
Is it primarily distortion characteristics?
(Also, hopefully we can keep this idea towards sealed cabinets for the sake of convinience)
Much love/Many thanks in advance everyone
Hi,
Box size related to Vas changes driver Fs to Fbox and driver Qts to Qbox.
Fbox is always > Fs and Qbox > Qts.
Sealed boxes have a target Qbox, typically 0.5 to 1.0,
often 0.7, noting the the target cannot be below Qts.
Too small and Fbox and Qbox are too high.
Too big Qbox can be too low, and generally
Vbox should be less then Vas, except for
small high Qts drivers.
The major penalty in using the wrong box
for a driver is another driver would be
better suited for the chosen box volume.
The right box totally depends on the driver.
(As does whether sealed or vented suits.)
rgds, sreten.
Box size related to Vas changes driver Fs to Fbox and driver Qts to Qbox.
Fbox is always > Fs and Qbox > Qts.
Sealed boxes have a target Qbox, typically 0.5 to 1.0,
often 0.7, noting the the target cannot be below Qts.
Too small and Fbox and Qbox are too high.
Too big Qbox can be too low, and generally
Vbox should be less then Vas, except for
small high Qts drivers.
The major penalty in using the wrong box
for a driver is another driver would be
better suited for the chosen box volume.
The right box totally depends on the driver.
(As does whether sealed or vented suits.)
rgds, sreten.
For sealed boxes, changing the internal volume affects the Q of the system's resonant frequency. A higher Q (small box) allows the resonance to be more sharp, more peaked, louder at the peak. A lower Q has no resonant peaking, and better damping (dryer sound) and louder at very low frequencies.
The best way to visualize this is to download a free speaker box simulator like WinISD Beta, and experiment with changing the box volume, see how it affects the FR.
The best way to visualize this is to download a free speaker box simulator like WinISD Beta, and experiment with changing the box volume, see how it affects the FR.
Assume you equalize the response so that the large box and small box have the same frequency response. This is easily done with, for example, a Linkwitz Transform equalizer.
In that case, the driver in the larger box will have lower distortion.
In that case, the driver in the larger box will have lower distortion.
can you explain why the larger box will have less distortion? It needs less power from the amp for the same cone movement, sure. I always thought same cone movement gives same spl and same distortion.
On a slightly different issue, people have commented that the greater surface area of a larger box means that colouration can be a bigger problem when compared to a smaller box. So more work has to be done to reduce panel vibrations.
It's because, for the same displacement volume, the air in the smaller box undergoes more significant compression and rarefraction. The pressure changes in the box are causing distortion by changing the air-spring compliance along with the cone displacement, and the smaller the box the worse this effect is. Sigfried Linkwitz has some tool (a spreadsheet I think) that estimates this, and it can be on the order of a couple of percent to 10% or so. Of course this is most apparent with a subwoofer type application. But you could also say that a larger box, stuffed, compared to a smaller one with the same stuffing density would better adsorb the backwave. Sound waves generated from the rear of the cone that are not fully adsorbed by the box and which re-radiate back out through the cone also create distortion. The way I see it, the same driver in a larger box should produce less distortion. The limits are more of a practical nature when it comes to box volume, although one can point to driver power handling and the need (possibly) to boost power at lower frequencies as a constraint on box size.
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A larger box has more air to compress and so has less resistance on the cone moving backwards and forwards.
A smaller box has less air so resists the cone movement more.
A smaller box has less air so resists the cone movement more.
I don't believe you are correct. The SPL generated by a closed box loudspeaker is simply proportional to the cone velocity, therefore the identical SPL (for the same driver in a small or large box) implies the same cone velocity (excursion).
The smaller box with the transform will likely be less efficient in general, and probably requires a significant amount of "lift" (power boost) at the lowest frequencies.
From Elliot:
If you are trying to get more bass out of a driver than it produces in a box then one does have to worry about excursion.
dave
If you are trying to get more bass out of a driver than it produces in a box then one does have to worry about excursion.
dave
I found the distortion estimation (accounting only for 2nd order distortion) by S.Linkwitz. This is taken from his spreadsheet "closed-box1.xls".
distortion in % = 0.014*Sd*Xmax/Vbox
Sd is the cone area in cm^2
Xmax is the peak excursion in mm
Vbox is the internal box volume in liters
You can easily see that Vbox is in the denominator so that a larger box would reduce this distortion source.
Feel free to plug in some values from your favorite woofer/subwoofer...
distortion in % = 0.014*Sd*Xmax/Vbox
Sd is the cone area in cm^2
Xmax is the peak excursion in mm
Vbox is the internal box volume in liters
You can easily see that Vbox is in the denominator so that a larger box would reduce this distortion source.
Feel free to plug in some values from your favorite woofer/subwoofer...
The bigger problem with small boxes is that, when EQ'd to the response of a big one, you're throwing more power in at the low end.
Distortion increases with power input, too. I suspect that's a much bigger problem than the expansion and compression of the air: using a high-power subwoofer in a small sealed box, I get 4.7% distortion. That's with ~1kW input. Wonder what the distortion from the motor would be...
Chris
Distortion increases with power input, too. I suspect that's a much bigger problem than the expansion and compression of the air: using a high-power subwoofer in a small sealed box, I get 4.7% distortion. That's with ~1kW input. Wonder what the distortion from the motor would be...
Chris
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Can you provide some data to back up this claim?
Long term "power compression" effects are something else, and don't generate "distortion" - they only change the frequency response and decrease efficiency. That's not distortion.
Charlie, one distortion mechanism that increases with larger power input is flux modulation. Copper or aluminium rings help, but only to a point.
Hi,
You can't make a generalisation into an absolute truth.
A generalisation will not apply to all drivers and cases.
It has assumptions that may not be true.
That distortion depends only on that equation is wrong.
Assuming it does is guessing wrong. I'm not guessing.
I proffer a very educated opinion that that equation refers
to the implicit known asymmetry of compressing air
in boxes and nothing else at all, certainly appears so.
(The equation clearly indicates a pressure relation.)
In real life it is nothing like as bad as a poor suspension
and the lower the ratio of Vbox to Vas the better mostly.
rgds, sreten.
For small boxes with high pressures the driver is
deliberately designed such that the pressure
asymmetry tends to cancel driver asymmetry.
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