Vented box alignments and Qtc

[SaSi]

With sealed enclosures we have the "well-known" alignments as per Qtc value. The lower the Qtc, the better the transient response.

With vented enclosures we have lots of different alignments. However I see no reference to Qtc for them. Is there a correlation between alignment and Qtc?

If I "sort" the responses of the alignments suggested by WinISD, I see that the bigger boxes are also tuned lower and exhibit lower group delay figures and a less steep rolloff before f3 (bass shelf) while the smaller boxes are tuned higher and show a steeper rolloff or even a bump.

I would expect the larger boxes to behave better in transients and exhibit a lower Qtc. Is that correct? Is there a correlation between box size, vent tuning frequency and Qtc?

[gedlee]

Originally Posted by SaSi

With sealed enclosures we have the "well-known" alignments as per Qtc value. The lower the Qtc, the better the transient response.

With vented enclosures we have lots of different alignments. However I see no reference to Qtc for them. Is there a correlation between alignment and Qtc?

If I "sort" the responses of the alignments suggested by WinISD, I see that the bigger boxes are also tuned lower and exhibit lower group delay figures and a less steep rolloff before f3 (bass shelf) while the smaller boxes are tuned higher and show a steeper rolloff or even a bump.

I would expect the larger boxes to behave better in transients and exhibit a lower Qtc. Is that correct? Is there a correlation between box size, vent tuning frequency and Qtc?

As a system all forms of enclosure have a "Q" which depends on the alignment. But since there are two resonances to consider - the driver and the box, a single Q as is possible with a closed box, is not as easy for a ported one. But the Q is simply that of the finished systems HP response.

But I wouldn't worry too much about things like "Q" and transient response for woofers in real rooms. It all gets washed away by the room.

[Ron E]

Qtc is not a concept that works for vented boxes. A vented box becomes at the limit a closed box when the tuning frequency is 0Hz, or the port losses are made so high as to effectively close the box. This is the limit for transient response. For any given box size, this Fb=0 condition represents the best transient response possible for a ported box.

It is said that the SC4 alignments represent good transient response. An EBS aligned vented box can approach the transient response of a sealed box, essentially, with the ringing of the port (which you will never hear if it is <40Hz) overlaid.

Tailoring the response to match the room is arguably more important than any concept such as Q in either vented or sealed boxes.

[gedlee]

Originally Posted by Ron E

Tailoring the response to match the room is arguably more important than any concept such as Q in either vented or sealed boxes.

Or just use any old box and driver - as long as it has enough "capability" (Power handling, excursion, etc.) -and don't worry about any of that Thiele-Small stuff, just fix the whole shebang with EQ in-situ. Multiple subs assumed of course.

[SaSi]

Thanks for the informative replies. What I am worried about is group delay in specific that is much higher with vented enclosures compared to sealed. I have tried several WinISD simulations showing different group delay values peaking in the 15 ~ 30msec range around resonance.

I have yet to find any definitive answer as to how audible this delay can be in the 20 ~ 30Hz region. (The port in my simulations is tuned at 18~20Hz and the enclosure is 160lt with two compound drivers having Fs=23 and Vas=250).

[gedlee]

Originally Posted by SaSi

Thanks for the informative replies. What I am worried about is group delay in specific that is much higher with vented enclosures compared to sealed. I have tried several WinISD simulations showing different group delay values peaking in the 15 ~ 30msec range around resonance.

I have yet to find any definitive answer as to how audible this delay can be in the 20 ~ 30Hz region. (The port in my simulations is tuned at 18~20Hz and the enclosure is 160lt with two compound drivers having Fs=23 and Vas=250).

Its not audible. Just build whatever is easiest, but make sure that there are several of them. Different types and tunings can actually help. One ported, one closed, one dipole. Its all in the setup.