Ultimax UM15-22 and 2 Passive Radiators

everettT

everettT

Audioholic Spartan
What cubic foot would you recommend for sealed? The Parts Express recommendation is 3.98ft3 but that seems small. Thoughts?
That flat pack size is sufficient, especially with an external amp.
 
TLS Guy

TLS Guy

Seriously, I have no life.
I'm not sure if you are referring to the 18" or 15" UM. I have not modeled the 15" but I have the 18". The optimal internal box volume is 2.75 Cu.ft sealed. You would have to add driver volume and bracing to that to get Vbt. That gives you an F3 of 31 Hz and Qtc of 0.7 which is pretty good. The PE box gets you a Q of 0.64 and an F3 of 29 Hz. However the PE box does not provide enough restoring force and cone excursion becomes excessive well before 20 Hz even without EQ and is not the correct box size for that driver. It is not too small but too big. The optimal volume of air inside the enclose for that driver is 2.75 cu.ft anf I'll stand by that.
 
F

Fochops

Audiophyte
I'm not sure if you are referring to the 18" or 15" UM. I have not modeled the 15" but I have the 18". The optimal internal box volume is 2.75 Cu.ft sealed. You would have to add driver volume and bracing to that to get Vbt. That gives you an F3 of 31 Hz and Qtc of 0.7 which is pretty good. The PE box gets you a Q of 0.64 and an F3 of 29 Hz. However the PE box does not provide enough restoring force and cone excursion becomes excessive well before 20 Hz even without EQ and is not the correct box size for that driver. It is not too small but too big. The optimal volume of air inside the enclose for that driver is 2.75 cu.ft anf I'll stand by that.
So 2.75 cu.ft for the 18? Then likely the 15 would need to be a tad smaller?
 
TLS Guy

TLS Guy

Seriously, I have no life.
So 2.75 cu.ft for the 18? Then likely the 15 would need to be a tad smaller?
Yes it would. However remember with a sealed speaker the only thing moving air is the speaker cone. That is inefficient and more so the smaller the cone. With other alignments that is not so but appears so. What really matters is Fs, sensitivity/efficiency and displacement. Fs is really of over riding importance to bass extension, but not output. Increased cone size usually equates to heavier which means lower Fs also reduced excursion for the same output. Then another issue, the higher the flux density and therefore sensitivity the lower the bass extension. Horns, pipes and Helmholtz resonators are much more efficient couplers in that order. Pipes also have a property of encircling which enables them to defy the distance square law which makes them particularly effective for low bass duty.

This has really been brought home to me in our new very large lower great room space open to the upper level via the stairs. One Dayton 10" driver fills the space with little power, so much so that I have not stopped reducing its volume. The bass it totally even in the space. It takes little power. I'm now more convinced than ever that the optimal alignment for a sub is a reverse tapered aperiodically damped transmission line. The perceived quality of the bass is also much better than other alignments.
I have been convinced for a long time that the only reason to build a sealed sub is that you don't have room for something better.
 

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