What is best box volume for ported woofer ?

[Ramon Cota]

I can model the same woofer in 60 l bass reflex box as well as 120 l , with simillar gentle slope rolloff the only difference being bass extension. Now i know for sealed box we have Qtc parameter that is supposed to give best transient response when 0.57 ( if i remember correctly ) but how does it translate to ported boxes ? Doest biggest extension and volume yield best quality fast and tight bass or should i sacrifice extension and aim for smaller box ?

 

[Matt_Holland]

Big box with tuning to give flat response or shallow roll off.

The box volume for best damping in a reflex cabinet (assuming you’re using a woofer with suitable parameters) has an equivalent sealed box Qtc of around 0.5.

 

[Duke]

Doest biggest extension and volume yield best quality fast and tight bass or should i sacrifice extension and aim for smaller box ?

Ime the in-room frequency response curve is the best single predictor of bass quality. To this end, and assuming you have a woofer well suited for such, imo there is an argument for building the bigger box and making provisions for adjusting the tuning frequency based on the actual in-room performance. I like to use multiple pluggable ports when possible.

Big box with tuning to give flat response or shallow roll off.

The box volume for best damping in a reflex cabinet (assuming you’re using a woofer with suitable parameters) has an equivalent sealed box Qtc of around 0.5.

And imo this is a really good approach, again with multiple pluggable ports if feasible.

 

[Ramon Cota]

Big box with tuning to give flat response or shallow roll off.

The box volume for best damping in a reflex cabinet (assuming you’re using a woofer with suitable parameters) has an equivalent sealed box Qtc of around 0.5.

Okay , so i simulated two drivers in winisd and these are results :
sb 34nrxl - 101 l for qtc 0,5 sealed f3 61hz f6 41 hz
37 l for qtc 0.707 sealed f3 59.8 hz f6 45,5 hz

sb 23nrxs - 158 l for qtc 0,5 sealed f3 54 hz f6 35,5 hz
40 l for qtc 0.707 sealed f3 52 hz f6 39.5 hz

according to what you say , 101 l would be perfect for sb34 ported ? The thing is i have sb23 currently in ported 40 l , that would mean the box is severely undersized ?

 

[DVDdoug]

A box can be too big and you might get boomy bass. Often a smaller than "optimum" box is used for practical/marketing purposes. That's often the case with "small" sealed active subwoofers which are EQ'd to extend the bass range down.

with simillar gentle slope rolloff the only difference being bass extension.

Welll... That's kinda' an important thing!

best quality fast and tight bass or should i sacrifice extension and aim for smaller box ?

I don't know what that means but smooth deep-extended bass is usually fine.

To me "tight" means "restricted". I don't know what "fast" means either. You can't change the speed of sound and the actual velocity of the cone depends on the frequency and amplitude. (And since it's low frequency, woofers don't move as fast as midrange speakers or tweeters.) The higher frequency drivers also reproduce the "transients".

 

[Ramon Cota]

A box can be too big and you might get boomy bass. Often a smaller than "optimum" box is used for practical/marketing purposes. That's often the case with "small" sealed active subwoofers which are EQ'd to extend the bass range down.


Welll... That's kinda' an important thing!


I don't know what that means but smooth deep-extended bass is usually fine.

To me "tight" means "restricted". I don't know what "fast" means either. You can't change the speed of sound and the actual velocity of the cone depends on the frequency and amplitude. (And since it's low frequency, woofers don't move as fast as midrange speakers or tweeters.) The higher frequency drivers also reproduce the "transients".

frankly i neither know what these adjectives mean but i read them mentioned alot on serious audio forums so they maybe are real. I read somewhere that some woofers in too big ported box can be unresponsive , or not have enough " slam" , crazy...

 

[Matt_Holland]

Okay , so i simulated two drivers in winisd and these are results :
sb 34nrxl - 101 l for qtc 0,5 sealed f3 61hz f6 41 hz
37 l for qtc 0.707 sealed f3 59.8 hz f6 45,5 hz

sb 23nrxs - 158 l for qtc 0,5 sealed f3 54 hz f6 35,5 hz
40 l for qtc 0.707 sealed f3 52 hz f6 39.5 hz

according to what you say , 101 l would be perfect for sb34 ported ? The thing is i have sb23 currently in ported 40 l , that would mean the box is severely undersized ?

Doesn’t WinISD give you a recommended ported box size?

Just play around with box size and tuning frequency until you get the response shape and group delay you prefer.

Your woofer Qts should be low ideally as well. A rough rule of thumb for a porter box is that the equivalent sealed box Qtc value should be no lower than the value of the woofer Qts.

Woofer Qts in the range of 0.3-0.6 is usually good for ported boxes.