It sounds like theres a large range of possibilities by varying box size and tuning. I think that in a ported system, theres no way to say how larger or smaller boxes change the overring because the port will have a huge impact.

So it sounds like a box that is a little overdamped will have the least ringing, and one where the port tuning/box size combo makes an underdamped response will tend to ring more (and I think Fb is shifted upward).

Is there also benefit in attenuated overring by making Fb about 10db lower than the part which is flat?

Could we liken it toward a sealed system. Say a Qtc=2.0 sealed box, and a ported box with its underdamped response made to closely follow it with same -3db point, will both produce high overring, and about the same amount of it too. And then take a Qtc=0.5 sealed system which rings very little, and a ported system which is made to resemble this overdamped response with the same -3db point, regardless of the ported boxes size, will both ring about the same? (and for that fact, they will both ring very little). I hope this is right, because I feel pretty comfortable with this.

If so, then I'd say the PiAligned cabinet will ring about the same as a Qtc=0.707 cabinet. But the PiAligned one is better in that it has reduced excursion and therefore distortion too. Or something like this anyway... the sealed one could of course be used lower because excursion doesn't shoot up below resonance like it does on a vented system, although I guess not really because the rolloff means its the extra bass is just too much attenuated, and using it here also means distortion is higher.

Would it distort more too if the sealed is used below cutoff and EQ'ed up to make it flat? And if the ported one was wanted to make lower bass, then we could alter the box size/tuning to make it produce the same sort of flat/slighlty overdamped curve, just with a lower -3db point. Using a vented with lower -3db point lowers excursion more than sealed with higher -3db that is used under resonance for the extra bass. So we can achieve the same results in terms of overring with vented as we can sealed, but vented has lower distortion and we can make it go deeper too with less distortion and still better overring than a sealed made to go deep.

Phase shifts in the passband are still too minor, the ringing at resonance is the problem. And the signal does not have to be very near resonance for it to be excited (although it does say this in the Acoustic Suspension vs Bass Reflex post) but either way, doesn't matter.

Vented all the way! I hope I've gotten this right this time!

Thanks!
Adrian

Cool. Its been very interesting to me too this discussion, and I've definitly learnt from it. Hopefully others have too, if they could be bothered to read something this large :P

I have one other quick thing. As an example, the LAB12 woofer, in a Qtc=0.707 sealed box has resonance at 41Hz (thats where impedance peak is too of course). PiAligned LAB12 has Fb at 21Hz. Both have similar -3db points around 35-40Hz. Does this mean, the resonance overring on the sealed box will ring at 41Hz, and on the vented will ring at 21Hz? That would indicate to me that the vented cabinet has another advantage, because resonance is at the -10db point (about), but on the sealed box for this example, the 41Hz resonance is about the -3db point. That would seem to me the PiAligned resonance overring is at a freq greatly attenuated (by ~10db) but on the sealed box, is only attenuated 3db, which is really nothing. That also means for most music with no below 30Hz content it will be harder to make the PiAligned cab ring than the Qtc=0.707 sealed box, simply because resonance on the vented is way lower. Could this be the reason why you said in another post that a PiAligned cabinet still has less overring than sealed cab with same -3db point?

Thanks!
Adrian

As I've stated before, it's more a matter of priorities - what is the best for you & your music? The overhang on impulses from a reflex box doesn't necessarily have a bad impact. AND, I might add, your room & loudspeaker placement are VERY important in this area! I think, in real life, they may have more impact on the bass sound than different alignments, as long as we are talking sound bass design (& we are, aren't we? ;-) )

Nice flat repsonse curve too, having f3 at 35Hz and f10 at 20Hz from a cabinet smaller than 2ft3. Very small size, and good extension.

For even deeper extension, consider a cabinet twice that size. It will be a little more sensitive to parameter shifts, like we're talking about here, but as a subwoofer that may be a valid trade-off. Room modes will likely dominate in-room response anyway, hence the reason for multiple subs. As I said before, it's all about intended purpose.

Great. LAB12 is pretty cool ey, except it uses Kapton instead of aluminium or black aluminium voice coil former, kapton is supposed to heat quicker and handle less power which isn't good. I think they could have used it, apparantly its not much cost difference, it would be especially good for that "high powered labhorn".

I was reading one of your older posts made in 2001 today on the high efficiency forum where you described basically what this thread is about. The post is called "Tune the cabinet as appropriate for the woofer" and it talks about Davies and your implementations etc, and more importantly, why resonance behaviour is better controlled in a vented cab and its better transient performance than the sealed.

You said The motor is a tuned resonant system, and stronger motors are more controlled at resonance, but they still lose motor control at resonance. "Sloppy" motors lose nearly all control at resonance, and can be quite loud at frequencies near resonance, but completely uncontrolled.. I agree too, at FS, the motor is more uncontrolled.

Then you say In a sealed box - we have damping, but we have no acoustic impedance rise at the woofers resonant frequency. . What I thought is, in free air, all woofers have rise/peak in impedance at its fs. In a sealed box, isn't this shifted upward to the box resonance point? Because thats where the impedance peak shows up on the box modelling programs, the peak is shifted to the sealed box resonance. I thought that in the box, resonance overring is at box resonance, and not woofer fs, and in a sealed system woofer resonance is usually about 10db down from the passband on a qtc=0.707 system, so would that not mean its more important for impedance rise to be at box resonance and not woofer resonance? (or maybe the sealed box shifts woofer resonance up to box resonance which could be why I dont understand this, I'm not sure).

And lastly, you state And in a bass reflex system, the acoustic impedance of the enclosure becomes very high at the Helmholtz resonant frequency, which serves to limit cone movement. What I've thought is the vented box creates two impedance peaks, and the Helmholtz (Fb) is at the trough of this, or the lowet point between the two impedance peaks. But you say its the opposite? You do say acoustical impedance though, I think that might be different from electrical impedance which I'm talking about. I have never heard of acoustical impedance before though or what it does except that you can graph it in Hornresp :P Can you please explain the difference to me?

BTW: It said in the sealed box, theres no impedance rise at woofer resonance. But for the vented box you said it is (so its better damped, lower cone movement/ringing), but you said the acoustical impedance rise is at Helmholtz resonance. Helmholtz is not always at woofer fs... can you please explain to me what this meant?

I think computer programs should simulate acoustical impedance then if its important to damping, but I guess its not absolutely needed that we see it because we can see damping from the FR.

Thanks!
Adrian

But in a bass-reflex speaker, we have one extra item - the Helmholtz resonator. Since there are two resonant systems, we can have conditions that cause the two to be in-phase and others that cause them to be out-of-phase. That introduces additional reactive components for damping, by introducing an additional resonator. It's sort of like adding another spring with a counterweight.

These are mechanical and pneumatic properties. The electrical impedance will reflect these conditions, and the electro-magnetic system will add some properties of its own. But even without the electro-magnetic part of the system, you still have a mass/spring resonant system in a sealed box, and a pair of resonators in a vented box.

Actually, the reason why horns are working so well is that they work as impedance transformers - on the acoustic side! A driver is 'born' with a natural high acoustic impedance (speaking in popular terms, we have a rather heavy diaphragm trying to move some light air), & the air's acoustic impedance is low. So the horn offers a high acoustic impedance at the throat (for the benefit of the driver), & through the length of the horn this is converted to a low acoustic impedance, at the mouth.

Closed & reflex boxes aren't very good at this transformation, sad to say, they stink - so the efficiency for them is max ~5%. But they are MUCH easier to handle when it comes to size in the bass area. The pay (again!) - bigger amps.

Btw., the LAB 12 offers very good performance in reasonably sized boxes - too bad they are not easy to get a hold on in my country.

So it seems that the sealed box shifts resonance upward. The resonant frequency of the box/woofer system is Fo. But does this shift Fs upward too..... ? I'd assume that any ringing will occur at Fo too, where the electrical impedance peak is. If the box shifts Fs up to form box resonance Fo, then we can say that Fs=Fo in a sealed box. So fs may be 20Hz free air, fs may be shifted to say 40Hz in a sealed box. All motors are more uncontrolled near resonance. If the new Fs is 40Hz, thats pretty bad because instead of being uncontrolled at 20Hz, its now uncontrolled at 40Hz, which is much higher, and its also the sealed box resonant so that means it will be more uncontrolled and also ring at the same time more and sealed box resonance is usually in the passband too which makes it even worse.

The vented cabinet has the Helmholtz resonator too, and its this frequency where any ringing is. Does the vented box shift Fs at all? If it doesn't, then thats good because it may be that neither Fb or Fs is in the passband. But if a sealed box shifts Fs upward to box resonance so that Fs=Fo, that means the motor is uncontrolled at higher freq, and the box is also making it ring here too and usually in the passband. Is this correct? Half correct?

The "Frequencies of interest" post says the bass reflex cab has Fo too, I thought it was only on a sealed, unless we block the port. It says however the enclosed woofers resonant freq in a vented box is Fo, and is near Fh, which indicates that the vented box might shift Fs up to near Fh. Or something :P Maybe I'm being too picky.

Thanks!
Adrian

I just re-read your Electrical, mechanical and pneumatic properties post. The sealed box modifies the speakers mechanical properties and it raises Fs and changes its Qts. It does that by changing its spring stiffness and resistance because of the air pressure in the box. Therefore we can say that Fs=Fo, right?

So the question is: All motors are more uncontrolled near Fs. Because the sealed system shifts Fs upward by modifying its spring stiffness, does that mean its now uncontrolled at the shifted frequency instead of the lower free air Fs. I think it might not, because the motor strength is not changed and is helping damp the driver. I would think the new boxed-Fs is more controlled than free-air Fs because the box would lower the drivers Qms. That seems like the reason its different, but doesn't make it worse, only better which I guess is how sealed system damping works, in a basic way.

The vented box has a port, so I'd assume it does not modify its spring stiffness/resistance and therefore a driver in a vented box won't change Fs. The Helmholtz resonator tunes the system instead. Does it change any of the drivers Q pameters like the sealed box does? I guess not either.

Thanks!
Adrian