polk mm12 freq response question

Scoop

I had a bass test cd and the mm12 was poinding... (just to clarify, the sub is broken in properly)

i realized i had the subsonic filter on, 20hz-50hz was off.

Heres a little of my situation, I am running the sub off speaker wire line-out-converted to RCA, going to a RF amp and to the sub. I'm not sure on the voltage but the L-o-c is supposed to drop it from 20 to 5-8. Anyhow, its not RCA setup because my car has fiber optics and you basically cant do it...

Will the sub be fine playing 20hz to 50hz? or is it safer to just leave it off?

AustinKP

what kind of enclosure is it in? With a ported/vented enclosure, you have to be careful to not let the sub play below the tuning frequency, or it can quickly overexcurt - ruining the sub. In a sealed box, a SSF isn't necessary. The natural rolloff of the sub will keep it from dying on you.

neomagus00

if the sub is playing from 20-50, that's not a subsonic... subsonic cuts stuff below 20 (subsonic is a stupid name, it's a frickin highpass set at 15-20 Hz)... but austin's right, if you're in a sealed box, no biggie... in a ported box you'll need that 'subsonic' filter or you'll wreck the thing, eventually... so it sounds like you're talking about a lowpass set at 50 Hz, which is fine but a little low... 80 Hz is the standard cutoff, because the lower the sub is set to start, the lower your mains have to play...

and what kinda car has fibre optics?? sounds neato...

Scoop

its an 04 Saab 9-3.

anyhow, i meant the filter thats 20hz-50hz...

its the polk momo that comes in the momo enclosure with a grill.

MacLeod

A subsonic filter that cuts out at 50 Hz? Usually SSF's cut out at 15 Hz. Cant be a crossover cause who would low pass their sub at 20 Hz?

Either way, it doesnt sound right. Leave it off.

A subsonic filter isnt there to really spare the sub but rather to keep the amp from having to reproduce frequencies you cant hear anyway so why waste the power on them.

neomagus00

whoa, where do the 04's have fibre optics? i have an 00, and i sure don't have any light beams flying around my car...

and yeah, whatever funky filter you're talking about, it's one-of-a-kind (as you've described it), so kill it.

MacLeod

I just caught that too.

Fiber optics? In a car?

Man, I really need to keep up with the times!

Scoop

the whole audio setup is fiber optic.

well, the headunit and SID (stock cpu onboard) use the mostnet fiber optic (which carries audio, info, etc). The fiber optic run throughout the car, tells of any errors (even says if the tire pressure is low, if the lights go out, etc etc). It also goes to pioneer amps (one 5 channel, and another 2 or 4 i forgot). From the amp, it has copper wire running to the speakers in the doors (at 2ohms...6 1/2s retarded yes...). I tapped that copper wire (with very limited room at that)

there is 1 headunit that takes in fiber optic. $900 clarion. thats it =/

MacLeod

Ya gotta love technology!

neomagus00

indeed... i didn't know saab has already implemented the tire pressure sensors (they're required OEM by like 2008 or somesuch)... is the fibre optic stuff your doing? or is it new for this year?

oh, and just out of curiosity, you have the T8 module, right?

AustinKP

I wonder why Saab chose to use fiber for all the signals like that. It is orders of magnitude more difficult than copper to repair. If something happened to the cable, it would most likely be cheaper to run a whole new cable than to try to fix it.

Second, it's not really needed for something like low tire pressure sensors. Nothing like that requires a perfect signal. Any old copper wire would work. Now for the audio, that's great because fiber is completely immune to any interference.

The 2 ohm speakers, I'd actually prefer. I'd rather my polks be 2 than 4 ohms because then I could get the power they want to them with the same amp I already have. Mine puts out 85x4 @ 4 ohms, but 170x4 at 2 ohms; just what the MM6's want.

-Austin

MacLeod

Yeah, but then your amp would be working much harder. This is the same as bridging a 4 channel into a 2 channel which is something Im not real fond of.

THD tends to go up to 3% at 2 ohm loads.

audiobliss

And I'm sure that if the speakers were rated at 2 ohms....they'd need a lot more power...lol.......just a viscious circle...

MacLeod

Not really. ID has some components that are 2 ohms but take the same power as their 4 ohm counterparts.

audiobliss

Oh; that's cool. Are their components pretty good? As good as their subs?

MacLeod

They are pretty highly regarded.

Ive only heard a set once a few years ago on a soundboard but they were pretty good.

neomagus00

their HLCD tweeters and powersupplies/eqs seem to be pretty well-regarded, too...

exalted512

ID anything=:D
-Cody

AustinKP

Originally posted by MacLeod
THD tends to go up to 3% at 2 ohm loads.

Nah...even at two ohms, it's still less than like 1/10%. When THD for an amp at 4 ohms is measured in the hundredths, the THD doubles at 2 ohms. That sounds like a lot, but it's still in the hundredths. Not an audible difference by any means.

neomagus00

assuming the amp is capable of putting out full power at half its rated load... lots of amps will make say 1.5 times their 4-ohm power at 2 ohms, and pushing it even that high is pretty rough on the amp - that thing is running flat-out, and that's assuming the user isn't trying to get 2x the power... at lower wattages, though, yeah, it just doubles the THD ( and halves the damping factor)

audiobliss

Originally posted by neomagus00
and halves the damping factor

Ahhh......hadn't even thought about that....

MacLeod

Originally posted by AustinKP
Nah...even at two ohms, it's still less than like 1/10%. When THD for an amp at 4 ohms is measured in the hundredths, the THD doubles at 2 ohms. That sounds like a lot, but it's still in the hundredths. Not an audible difference by any means.

Yeah, that would be another of my infamous type-o's. That should have been 0.3%. :rolleyes: