That does seem strange. I always thought that sealed enclosures rolled off at a much shallower rate compared to ported.
So in theory going deeper, but with a longer roll off, compared to higher output to the -3db point, and then rolling off steeper….
Am I not understanding something?
So in theory going deeper, but with a longer roll off, compared to higher output to the -3db point, and then rolling off steeper….
Am I not understanding something?
But not "...and Justice" because there's no bass on that album 😆
Because it's a 'stick a sock in it' stuffed vent, not a sealed plug, so in retrospect should have called it ~aperiodic, though having built mostly this type of alignment I called it a 'critically damped' reflex as I found it the best compromise for getting the prominent 'toe tapping' (mid) bass folks wanted once against a wall, corner.
So I thought it over, it’s definitely going to be a closed box. I’m gonna pick up some plywood next week, hopefully, this time I’m going to try to avoid the super expensive birch ply. The prices have gone insane here in Austria.
If the sealed enclosure has the same effective volume as the vented enclosure, then the closed-box low-frequency alignment will have a slow roll off in the bottom end. This will generally behave more like a Bessel closed-box low-frequency alignment, rather than a standard B2 (Butterworth) low-frequency alignment.
Since this is a subwoofer application, you will find that the typical 80-Hz Linkwitz–Riley 4th-order low-pass filter will significantly reduce the woofer's response. You can boost the low end of the subwoofer's response to flatten and extend its low-frequency performance.
There's a bit of a transition zone where the roll-off rates can be somewhat similar. This might also have something to do with the vented response having a peak in its response function, as well as having a port that is relatively lossy. Below about 30Hz the roll-off rates are starting to be quite different, with the vented box being the steeper of the two (as expected).
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If there is appropriate DSP processing available, then some EQ can serve to significantly modify the effective Q of the sealed+DSP system. An important consideration is to get a set of accurate Thiele–Small parameters for the driver. This will enable some reasonably accurate simulations to be performed to explore available options for DSP/EQ response shaping and enclosure sizing.
Fortunately, the only TSP info I could find, other ones I posted earlier in this thread. The driver is apparently normally used for car Audio. I read mention of there being some TSP data in an old issue of hobby hi-fi, the German magazine. But I could not find it.
The Hypex Ds400 I’m using does have some controls, I think I’m going to go for 50 L sealed, and see what I end up for a response, then I can start to play with DSP and taylor the response…
I plugged the above set of Thiele–Small parameters into VituixCAD's enclosure modeller. Then I selected a 50-litre closed-box enclosure.
Looking through the (short) Hypex DS4.0 plate amplifier users manual, I was able to determine that it provides a 3rd-order 18dB/octave low-pass filter, which I assume is a Butterworth topology. There is also a 4th-order 24dB/octave high-pass filter set to 12Hz, which I also assumed is a Butterworth topology.
The DS4.0 also has a "Bassboost" EQ capability, where the frequency can be set between 20Hz and 50Hz, and the boost level can range from 0dB to +6dB. For the purpose of the VituixCAD model, I assumed that this EQ can be modelled as a parametric EQ with a Q=2.0, and the frequency and amplitude can be dialled in by the user.
An example configuration is shown below. The low-pass filter has been chosen to have an acoustic −3dB point of 80Hz. The low-frequency response is −3dB at 28.7Hz, which seems a quite good result. Here the plate amplifier is set to provide a nominal input of 50W re 8 ohms, and a peak driver excursion of about 11mm is reached at that power level.
Below is a slightly different configuration, where I have aimed for the response to be −6dB at 80Hz. This allowed me to slightly reduce the frequency of the Bassboost EQ from 31.5Hz to 29Hz, which has also lowered the −3dB low-frequency cut-off to 26.3Hz. There is a small drop in overall output as a result of these changes.
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Wow witwald! You have really helped me tremendously!! Thanks for your time!
Ok, so sealed @ ca. 50 liters looked like a winner for my goal, i will start cutting wood next week. I really appreciate everyone who has helped me narrow down what would best suit my situation.
Cheers!!😎
Ok, so sealed @ ca. 50 liters looked like a winner for my goal, i will start cutting wood next week. I really appreciate everyone who has helped me narrow down what would best suit my situation.
Cheers!!😎