15" Re MX enclosure question

[chief_bignut 10+ year member]

ok i ended up going 4.75^3 after sub dispacement right around 32hz. will begin cutting and assembly this afternoon. will take pics and post em up if anyone is interested to see how this turns out

 

[chief_bignut 10+ year member]

the mx isnt new. its been reconed by team psi i believe. i bought it used from dman_1 on caco. i think hes here too. if it blows ill simply have it reconed again. no biggie

 

[PV Audio 5,000+ posts]

If I can be honest, and I know I'll get shot for this, but that speaker isn't optimized to work ported in the slightest. Richard Small, the guy who you in part owe all speaker parameters to, made a guideline called the EBP which is Fs/Qes. A EBP below 50 means the speaker should be sealed and around or over 100 means it should be ported. This speaker has a EBP of 37. It has that because it's electrical Q, or in a simplified way, how free the cone is to movement due to the electrical parts, is very high. A high Q of anything means that something is very free to resonate or oscillate. For example: if you strike a bell and it rings very briefly will have a very low Q while if it rings for hours, it has a very high Q. This speaker's Qes isn't low enough to warrant a ported box because it could break up easily.

I'm not saying to not port it since 98% of ca.com is hellbent on doing it, I'm just saying that you might want to consider what enclosure the speaker was designed to be in. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[PV Audio 5,000+ posts]

Also, that speaker is going to have a MONSTROUS spike in group delay around tuning frequency which I don't know if you're a SQ guy or not, is fairly undesirable. Just to make my point, if you do a sealed box at 3.28 cubic feet net with moderate damping inside (fiberglass, polyfill, whatever), you'll have a rolloff point of 34.47 and it will be flat as a 5 year old girl's chest until that point. If you port it at 5 cubes, you'll end up with a rolloff of 26.21hz. You're thinking hey, that sounds great! Yeah, no. The ported box is going to be very peaky and it only rolls off tha tlow because at around 40hz, you'll have about 7-8db gain which will correspond to incredibly muddy sounding bass along with a HUGE amount of group delay. With the sealed, the the group delay and phase are both flat all across while the ported boxes have horrible plots: sharp bends, undamped oscillations, and other bad stuff. The only way you can get a flat response with that speaker is to throw it in a very large ported box tuned low, aka, 8.6+ cubic feet tuned to 17hz. What is happening is that the speaker has such a low resonant frequency that it needs a ported box with a Q to match it. Smaller boxes have a Q that's far too high and they end up being peaky. Just think about it or if you don't understand something I've said, just ask. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[chief_bignut 10+ year member]

im not all that big on sq. dont get me wrong i like it to sound good but i like it to be loud as well and at the same time still be able to pick up the lows. i picked up this 15" as a temp sub. i may find another non working mx and send them both in to team psi and have them make identicle subs and go from there.

 

[PV Audio 5,000+ posts]

Alrighty, just wanted to let you know //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[chief_bignut 10+ year member]

ok so im re-doing the design before i cut anything out. my external dimensions are 35*20*19 which gives me an internal volume of 7.69^3 if im not mistaken so then after sub displacement (.22^3 feet) im left with 7.47=7.5 im rounding up. ok so with a slot port 6x20 (120 sq " of port) and a length of 23.25" im right around 32hz. if i did the math right. so the external measurments of the port tell me that the port takes up 2.09^3 which leaves me with an internal volume of 5.41 after port and after sub. is this still too big of a box for the sub?? anyone correct me if im wrong on these measurments plz. any input is helpful

 

[chief_bignut 10+ year member]

Anyone? Come on guys