when you design a box in WinISD, what input power would you choose to design the enclosure if your drivers RMS is e.g. 60W. (monitoring for cone excursion). I have heard loads of people saying to design an enclosure for 2/3 of the woofers RMS.
Suspension is only so stiff or so loose
So the box has to be a certain size regardless for whatever alignment
your using.
The only thing I can think of is many times people use max power in WinIsd
to design the velocity needed for the port. So they assume it needs to be much bigger
than needed, hence the port is too long to fit in the box.
Aside from high Qts speakers which may be difficult to understand in a model.
You hit QB3 for ported or use .5 to .8 Qtc for sealed and that is the box size.
But yes it is rather rare to use a speaker at full thermal rating.
Real world power used is much less.
So the box has to be a certain size regardless for whatever alignment
your using.
The only thing I can think of is many times people use max power in WinIsd
to design the velocity needed for the port. So they assume it needs to be much bigger
than needed, hence the port is too long to fit in the box.
Aside from high Qts speakers which may be difficult to understand in a model.
You hit QB3 for ported or use .5 to .8 Qtc for sealed and that is the box size.
But yes it is rather rare to use a speaker at full thermal rating.
Real world power used is much less.
There are two types of power handling: excursion limited and thermal limited, where the adhesives and coil coating are failing. Keep in mind, with some driver and box combinations, the thermal limit is reached first, like a small sealed box. With others, the mechanical limit is reached first.
With that out of the way, we can speak to linearity. Some drivers are already starting to exhibit non-linear tendencies at 1/10th the AES power handling, and your mileage may vary.
Power handling is a calculated figure with pink noise generally from Fs to 10Fs, based on the voltage applied before failure ( of the driver in free-air, with ample cooling, not in a box ) on the rated minimum impedance value. Of course, by that point, near failure the DC resistance rises, reducing the amount of current through the coil.
Also, depending on the compliance linearity of the spider, and the motor strength linearity, it may take more or less power than a mathematical model based on small signal level predicts vs the actual cone excursion experienced in box with the same amount of power ( voltage ) applied.
Hopefully that helps.
With that out of the way, we can speak to linearity. Some drivers are already starting to exhibit non-linear tendencies at 1/10th the AES power handling, and your mileage may vary.
Power handling is a calculated figure with pink noise generally from Fs to 10Fs, based on the voltage applied before failure ( of the driver in free-air, with ample cooling, not in a box ) on the rated minimum impedance value. Of course, by that point, near failure the DC resistance rises, reducing the amount of current through the coil.
Also, depending on the compliance linearity of the spider, and the motor strength linearity, it may take more or less power than a mathematical model based on small signal level predicts vs the actual cone excursion experienced in box with the same amount of power ( voltage ) applied.
Hopefully that helps.
For this I'm usually thinking of the power of the amplifier I'm expecting to hook it up to. You can go harder on a sealed enclosure as the box limits that. Ported box lets excursion go wild below tuning frequency - the more bandwidth you have below tuning (the higher you tune) the more risk you take here.
The power I usually enter into WINISD is the rated power. The excursion, port air velocity, SPL etc. are updated as this is entered. Of course any value could be entered but the highest definitely makes sense.
FWIW, the pioneers used Fb = measured Vas/1.44, Fb = 1.56x measured Fs for prosound to ensure a relatively reliable long life and served me well using up to ~7-8 mm, so maybe ~ 'bulletproof' with higher power/Xmax based on a lone experience with a dual JBL 2242H LFE cinema sub that pumped out an estimated 130+ dB/30 Hz @ 2/3 back from the screen wall after hard pegging my 'el cheapo' RS 120 dB meter.
2/3 of max driver power will be way way OTT; if designing a ported box it will give a very inappropriate and likely infeasible port.
I suggest this example.
Estimate your maximum listening volume; often this will be in the mid 80s to high 80s dB range; allow a bit more possibly for bass transients.
For an example I'll say we might design for 95dB.
Check your speaker sensitivity; for an example I'll say 85dB/watt
Find the power to give this volume; some simple maths, but I'm lazy. A doubling of power will give +3dB so for this example:
2 watt gives 88dB
4 watt gives 91dB
8 watt gives 94dB
So for our 95dB criterion we need a bit over 8 watt, I'd guess 9 watts would be near enough to use for the box/port design.
I've just done exactly this process for my possible MTM design.
The speaker is expected to be 90dB/watt, I don't listen loud, the amp is 3.5 watt. I guess 93dB max giving 2 watts and modelling this in WINisd gives a reasonable size port with velocity within limits.
Hope this helps.
I suggest this example.
Estimate your maximum listening volume; often this will be in the mid 80s to high 80s dB range; allow a bit more possibly for bass transients.
For an example I'll say we might design for 95dB.
Check your speaker sensitivity; for an example I'll say 85dB/watt
Find the power to give this volume; some simple maths, but I'm lazy. A doubling of power will give +3dB so for this example:
2 watt gives 88dB
4 watt gives 91dB
8 watt gives 94dB
So for our 95dB criterion we need a bit over 8 watt, I'd guess 9 watts would be near enough to use for the box/port design.
I've just done exactly this process for my possible MTM design.
The speaker is expected to be 90dB/watt, I don't listen loud, the amp is 3.5 watt. I guess 93dB max giving 2 watts and modelling this in WINisd gives a reasonable size port with velocity within limits.
Hope this helps.
exactly!
And below tuning frequency any ported speaker will reach/exceed Xmax with very little power.
So to make any sense the max power indication needs to be related to a frequency range and the music/sound-specific energy distribution and crest factor.
The "usual practise" is that you need to have enough headroom and/or safety measures to keep your drivers safe.
Hifi speakers usually have lots of headroom regarding thermal power for reasonable listening levels. you will not hear the thermal limit, however, thus be careful with thermally sensible tweeters.
Woofers usually tolerate quite a lot of exceeding Xmax before being damaged and have much more thermal inertia, thus tolerate more thermal (peak) power.
Yes, that's the catch. However much you reduce this term called power, you can't go below this frequency. This value is therefore the limit for the said loudspeaker design.
For example, if I have a driver that's rated 250W and tuned at 40Hz, there's no way I'm going to be able to 'extract' anything substantial below 40Hz, even at lower power levels. So I'd enter full power and watch where the excursion reaches, as this is only a simulation and nothing is at the risk of blowing.
Note that this design would still work at a lower power as the port velocity, excursion, SPL, VA etc are all going to be lesser than their corresponding values in the simulation. In reality, I'd also add a second order high-pass filter at tuning frequency to keep the excursion within limits.