XXLS Large vented Sub

[Svante]

Well, I am aware that XLS and XXLS are usually used in smaller boxes, mostly then with a passive radiator, since the vent would become to long in a small box.

I made the simulation of a 240 litre box, mainly since LageB suggested such a big box. Indeed, if you strive for a Butterworth response, the box should be that large. However, this dimensioning does not take any room effects into account, and depending on the room it might be wise to build some sloping in the response into the system.

Also, If LageB wants the response of a 90 litre box, but has the room for a big box, there is always the opportunity to build a 180 litre box with two drivers. This opens for some nice possibilities of balancing the inertia of the cones by making them move in opposite directions (by monting the drivers on opposite sides of the box). (X)XLS subs have a tendency to "walk" as you play them loud. 😀

I don't see why you would want the rumble filter, though, other than that you could reduce the box volume a but further with these connected. You hardly need to remove frequencies below 20 Hz, there isn't much of that on CDs. For vinyl, however, it might be beneficial. I would also consider using a higher crossover frequency than 40 Hz, 80-90 Hz is generally recommended by people I know and trust.

Much of the above are opinions and of course opinions may be different. But those are mine. 🙂

 

[paulspencer]

I don't see why you would want the rumble filter, though, other than that you could reduce the box volume a but further with these connected. You hardly need to remove frequencies below 20 Hz, there isn't much of that on CDs. For vinyl, however, it might be beneficial. I would also consider using a higher crossover frequency than 40 Hz, 80-90 Hz is generally recommended by people I know and trust.

The idea of a vented sub is to lower distortion and get more SPL down low. In some cases, however, where there is significant content below tuning, lack of a rumble filter will cause absurd excursions. The result of this is that you have more useable output from a sealed sub!

If you have a sealed sub and only use it for music, then fine ... no rumble filter is really necessary, although even then it's still a good idea sometimes.

but ...

If you have a vented sub, you will likely want it for DVDs and then you would be nutty to not use a rumble filter, if you unless you sub has FAR more output potential than you intend to use.

I would also consider using a higher crossover frequency than 40 Hz, 80-90 Hz is generally recommended by people I know and trust.

My guess would be that the SS woofers would be more articulate in that range. Going up that high would suggest also that stereo subs or at least dual mono would be appropriate.

 

[LageB]

Thanks you guys for your continous help.

For your reference, my set-up is a FR Driver (sealed) Fostex F200A that I cut off at 90Hz and the let my Scan-Speak 10" stereo Modules (also sealed) run the frequences below 90Hz, using digital filter XO both for high pass FR and and low pass SS.

The sound is faboulus (I think) but sometimes I lack force in the 20-40 Hz region.

Now, I have huge empty space avaialble in the courner of my listening room, under stairs (1.5M3) that I can "fill" if I want.

So, I have been searching for an efficient Subwoofer (that's why vented) that should operate only 20-40Hz region. When I made simulations of the XXLS, it seemed like a feasible idea. As mentioned, size is no problem.

If you have other proposal for my application, I am very keen to listen to any ideas.

Thanks again

LageB

 

[SSassen]

I spotted a contradiction in terms:

The idea of a vented sub is to lower distortion and get more SPL down low.

If low distortion is what you're after then a vented subwoofer is not the way to go, vented = more distortion, rather the opposite. A closed box will yield far better results. With enough surface area and a large Xmax you can then simply compensate by boosting the curve in the lower regions. This will, provided proper units are used and boost isn't excessive, result in lower distortion and similar SPL but a much cleaner bass overall. You just need to keep an eye out for the total Qtc, target for that is around 0.5, hit that mark and you got a very articulate closed sub that will certainly have better control than a vented one.

For example two XLS12s in a 50 liter closed box will give you a F3 of 55Hz with a Qtc of 0.51. Add a 500-watt amp and you can safely boost to 6dB in the lower regions without stressing the amp or the woofers too much. With the room-gain added you'll easily be able to achieve a flat response and an SPL of 100dB at 20Hz.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com

 

[paulspencer]

If low distortion is what you're after then a vented subwoofer is not the way to go, vented = more distortion, rather the opposite.

I'd like to see some measurements to back that up. Measurements I've seen have indicated that vented subs have lower distortion. They weren't taken with a view to to prove either way, hence they need to be taken with some caution.

A closed box will yield far better results.

I think this is a bit of an audiophile myth. I would say "it depends..."

If you compare a sealed vs vented sub using the same driver, and they are designed to get the same response, you will find at 6db more output for the vented version is typical in the lowest octave of its response. The excursion of the vented sub will be much less, and if it is designed well the distortion should be much lower.

With enough surface area and a large Xmax you can then simply compensate by boosting the curve in the lower regions. This will, provided proper units are used and boost isn't excessive, result in lower distortion and similar SPL but a much cleaner bass overall.

If you compare a single vented sub vs a pair of sealed subs using the same driver and both are producing the same SPL, the distortion of the sealed subs would be less in the midbass but this is not really a fair comparison.

 

[SSassen]

Of course I made a broad generalization, but what I was trying to get across that it is easier to construct a low distortion closed box subwoofer than a bass-reflex one, esp. if you don't know what to look for when things don't sound right to you or don't have the tools to accurately measure the performance.

Most diy-subs that I've heard suffer from a over-excursed woofer or a bass reflex port of too small a diameter. Other common mistakes made are boosting the driver below the Fs of the driver + enclosure, not taking group delay into account when tuning low, hence driving it into the audible spectrum exponentially increasing harmonic distortion, etc. etc.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com

 

[paulspencer]

So if I understand correctly, you are not saying that vented subs have higher distortion, but that poorly designed vented subs do?