Two questions about Forte II's

[pzannucci]

More area with the passive and load for more extension.  Ports will be smaller and load less in that size box.  If you use ports it will likely be tuned higher if you are looking for a reasonable output in reference to the woofer.  That means do not over drive the woofer under tuning point otherwise you can get in trouble quick when the woofer unloads.

[moray james]

8 hours ago, pzannucci said:

More area with the passive and load for more extension.  Ports will be smaller and load less in that size box.  If you use ports it will likely be tuned higher if you are looking for a reasonable output in reference to the woofer.  That means do not over drive the woofer under tuning point otherwise you can get in trouble quick when the woofer unloads.

A large passive will behave like a large vent and that means reduced turbulence and distortion as compared to a smaller passive or smaller vent but a passive and a vent do the same thing and if you can tune a passive you can tune a vent to the same frequency, yes at some point the passive will win out due to loss of internal volume that a vent would take up but were are not talking about extremes such as that here. If you use a vent or a passive to achieve a desired load at a chosen frequency the is no difference to the tuned frequency one system does not have any real advantage so far as tuning extension goes aside from the obvious consequence of using a large diametre vent and the required vent length and associated vent volume loss neither method is better or worse really from a practical point of view.  

   The woofer will determine the lowest frequency that it can be tuned to and not the vent or passive, it is the woofer which activates the vent/passive. If I use a passive to tune a Forte to 38 Hz. or I use a couple of vents to do the same thing it will result in two systems sounding so close few could tell the difference. A single larger vent is going to get long and eat up cabinet volume while two smaller vent will achieve the desired tuning without eating up much internal volume. I would imagine you could match the two methods to within a Hz. or two of each other. Remember that the woofer has to be able to generate on its own in the cabinet enough energy at the chosen frequency to excite the vent air or the passive mass into a full resonance in order to damp the woofer. Once the woofers ability to output enough energy rolls off with frequency you simply can no longer use the woofer to excite a vent or a passive as your energy source (the woofer) has in effect run out of steam to do that job any more.

   Tuning lower and lower simply by adjusting the vent or passive is not how it works as I said it is the woofer in the cabinet which will by its natural system resonance determine how low you can tune it. Now you can cheat a little and tune just below system resonance but these are all tweaks and trade offs, basically you can tune to a bit below system resonance a few Hz and that is the end of it and if you need/want more extension than that then you need to make system design changes like a larger cabinet volume or a different woofer or both. You also want to design in some sort of safety margin and not design right to the hairy edge or you will end up with reliability issues. I hope that I have made some sense of this.

[pzannucci]

2 hours ago, moray james said:

A large passive will behave like a large vent and that means reduced turbulence and distortion as compared to a smaller passive or smaller vent but a passive and a vent do the same thing and if you can tune a passive you can tune a vent to the same frequency, yes at some point the passive will win out due to loss of internal volume that a vent would take up but were are not talking about extremes such as that here. If you use a vent or a passive to achieve a desired load at a chosen frequency the is no difference to the tuned frequency one system does not have any real advantage so far as tuning extension goes aside from the obvious consequence of using a large diametre vent and the required vent length and associated vent volume loss neither method is better or worse really from a practical point of view.  

   The woofer will determine the lowest frequency that it can be tuned to and not the vent or passive, it is the woofer which activates the vent/passive. If I use a passive to tune a Forte to 38 Hz. or I use a couple of vents to do the same thing it will result in two systems sounding so close few could tell the difference. A single larger vent is going to get long and eat up cabinet volume while two smaller vent will achieve the desired tuning without eating up much internal volume. I would imagine you could match the two methods to within a Hz. or two of each other. Remember that the woofer has to be able to generate on its own in the cabinet enough energy at the chosen frequency to excite the vent air or the passive mass into a full resonance in order to damp the woofer. Once the woofers ability to output enough energy rolls off with frequency you simply can no longer use the woofer to excite a vent or a passive as your energy source (the woofer) has in effect run out of steam to do that job any more.

   Tuning lower and lower simply by adjusting the vent or passive is not how it works as I said it is the woofer in the cabinet which will by its natural system resonance determine how low you can tune it. Now you can cheat a little and tune just below system resonance but these are all tweaks and trade offs, basically you can tune to a bit below system resonance a few Hz and that is the end of it and if you need/want more extension than that then you need to make system design changes like a larger cabinet volume or a different woofer or both. You also want to design in some sort of safety margin and not design right to the hairy edge or you will end up with reliability issues. I hope that I have made some sense of this.

Can't discount the area / volume pushed and hard to get that with a small box and ports.  That will determine to some extent the amount of output capability for the port / passive, of course dependent on some other items.  In a cabinet that small, the ports would need to be small or very long to tune low enough to get an actual 32hz -3db point.  Of course below that there is a 24db drop.

 

To me, you will likely get higher output (re woofer output) with the passive compared to smaller ports in the smaller box.

 

The noise with smaller ports is another consideration.  All this works hand in hand.

 

They will sound somewhat different as you stated.  Not sure which I like better.  Comparing my two KLF-20 woofers in a 5cf front box slot ported box to around 31hz vs the same woofers with two rear mounted 12" passives close to the same tuning, the passives sounded cleaner but the port sounded more alive.  I might have liked the extra noise from the slot port or something though I know there are other factors that can't be quantified.