C400.4 amp crossover?

Systems

I just bought my new Polk C400.4 today that is hooked up to a Pioneer Premier 840 head unit. Should I turn the crossovers off on the amp and do all my adjusting with the head unit? There is alot of eq adjustments that can be done in the head unit alone and my front DX3065 Polk components have there own crossovers. My rear speakers are the DB525.

MacLeod

I would use the high pass filters on the amp. It cuts out all frequencies below 80 Hz which would only distort your components anyway. Now if you dont have a sub then you may want to use them with the x-overs off til you get a sub. Other than that Id let the Polk x-overs handle the distributing chores and fine tune with the Pioneer.

exalted512

Originally posted by MacLeod
I would use the high pass filters on the amp. It cuts out all frequencies below 80 Hz which would only distort your components anyway. Now if you dont have a sub then you may want to use them with the x-overs off til you get a sub. Other than that Id let the Polk x-overs handle the distributing chores and fine tune with the Pioneer.

agreed
-Cody

neomagus00

id use the highpass at say 80 on the HU for all channels, then use no xover on the amp, then use the provided xovers with the components. id say the hu xover is more precise, cause you're only within maybe +- 5% on the amp... at 80 Hz, it could be passing a 70 Hz signal... at the limits of volume this could be bad.

MacLeod

Well Im not so sure about that my man, the 400.4 has a 24 db x-over slope which is pretty damn steep. Id say you werent getting anything over what you set it at. Plus I doubt the HU x-over has that steep a slope.

neomagus00

i looked it up, you're right, it's 12 dB/oct. i was talking about the tolerances in the actual amp components... e.g. in the momo xover, all the inductors/caps etc. are 5% tolerance

worst case theoretical scenario, 5% tolerance on a standard 24 dB/oct. xover, and i set it at 80 Hz (the -3 dB point), it could concievably play as low as 66 Hz (also the -3dB point). a half-octave isn't much, but at excursion limits, 66 vs. 80 can make a difference.

in order for us (including me!) to see if this matters, let's assume the amp's xover is badly screwed-up (xovering at 66 instead of 80, but still within manufacturing limits) but with a slope of 24, and the hu's is fine, with a slope of 12.

if we're accounting for maximum excursion at 80 Hz and we have a perfect speaker (one where the BL curve is linear, so twice excursion = twice volume OR twice excursion = same volume at half frequency... SOMEONE CHECK THIS!! i'm kinda running off instinct here!)... roughing out the logarithic bit of freqency and kinda winging it here (but pretty close nonetheless), our amp is over-driving our speaker by about 50%... it's at 1.5 max excursion at 66 Hz, cause the amp isn't cutting anything off here yet. 150% excursion = dead speaker. or, less volume higher up on the spectrum if we dial down gains so this overdriving is within speaker's limits. in reality, though, we're not gonna get 150% excursion, cause BL curves are way nonlinear, but there's severe over-excursion nonetheless, and much badness. or, look at it the other way, and the amp is xovering at almost 100 Hz, and you're losing some musical info. louder, yes, but less full. add in multiple amps and multiple uncertainties and you can get an unbalanced response or less volume than possible... all avoidable by hitting a button on the HU.

ah, let's check to see if the hu's gonna hurt that speaker with only 12 dB/oct. xovered at 80 again, output at 40 Hz is a mere (70-12) 58 dB... and a 12 dB reduction is a 4X power reduction, translating to 2X excursion (cause 1/2 frequency) MINUS 4X excursion (cause 1/4 power) and we get a net 50% excursion. with the effect decreasing as we near the xover point, but at no point is the 12 dB/oct failing us.

please tell me im right, its late and im tired, so i hope i got all this straight...

MacLeod

Dont ask me bro. You lost me within the first sentence!

Im not very educated on the physics or inner workings of electronics. Pretty much all I know is how much they cost and which ones look the coolest!

Ive tried to read up on it some but if there aint a lot of pictures I get bored and fall asleep!

Ya know that brains/brawn thing? Well I fall more into the brawn side!! LOL

Which isnt good beacuse ya know the old saying,"the strong take it from the weak and the smart take it from the strong".

exalted512

Originally posted by neomagus00
i looked it up, you're right, it's 12 dB/oct. i was talking about the tolerances in the actual amp components... e.g. in the momo xover, all the inductors/caps etc. are 5% tolerance

worst case theoretical scenario, 5% tolerance on a standard 24 dB/oct. xover, and i set it at 80 Hz (the -3 dB point), it could concievably play as low as 66 Hz (also the -3dB point). a half-octave isn't much, but at excursion limits, 66 vs. 80 can make a difference.

in order for us (including me!) to see if this matters, let's assume the amp's xover is badly screwed-up (xovering at 66 instead of 80, but still within manufacturing limits) but with a slope of 24, and the hu's is fine, with a slope of 12.

if we're accounting for maximum excursion at 80 Hz and we have a perfect speaker (one where the BL curve is linear, so twice excursion = twice volume OR twice excursion = same volume at half frequency... SOMEONE CHECK THIS!! i'm kinda running off instinct here!)... roughing out the logarithic bit of freqency and kinda winging it here (but pretty close nonetheless), our amp is over-driving our speaker by about 50%... it's at 1.5 max excursion at 66 Hz, cause the amp isn't cutting anything off here yet. 150% excursion = dead speaker. or, less volume higher up on the spectrum if we dial down gains so this overdriving is within speaker's limits. in reality, though, we're not gonna get 150% excursion, cause BL curves are way nonlinear, but there's severe over-excursion nonetheless, and much badness. or, look at it the other way, and the amp is xovering at almost 100 Hz, and you're losing some musical info. louder, yes, but less full. add in multiple amps and multiple uncertainties and you can get an unbalanced response or less volume than possible... all avoidable by hitting a button on the HU.

ah, let's check to see if the hu's gonna hurt that speaker with only 12 dB/oct. xovered at 80 again, output at 40 Hz is a mere (70-12) 58 dB... and a 12 dB reduction is a 4X power reduction, translating to 2X excursion (cause 1/2 frequency) MINUS 4X excursion (cause 1/4 power) and we get a net 50% excursion. with the effect decreasing as we near the xover point, but at no point is the 12 dB/oct failing us.

please tell me im right, its late and im tired, so i hope i got all this straight...

scientifically, im pretty sure youre right...the only thing im not sure about is "twice excursion = twice volume OR twice excursion = same volume at half frequency"
but as you claim, that is the perfect speaker, of which there is none, so you cant really go off of any that
in realiy, there are sound differences in the differenent crossover slopes, it could blend them better having a 24 slope rather than a 12, but it could also make it sound worse, depending on the distance between the speakers, where theyre mounted, how good they are on or off axis, and the acoustics of the vehicle
so yes, you are correct, but your assumptions are in the perfect enviroment with a perfect speaker, of which, there are none:)
-Cody

MacLeod

And plus, the differences will be so slight that most people would never know the difference.

So I guess the answer is, use either the HU or the amp x-over. Both will work fine.

neomagus00

yes! half an hour of work for... (drumroll, please!)... a completely ambiguous answer!

no, anyways, he's right, all this babble says that either's good. and the point was made that a 12 and a 24 dB/oct slope will allow speakers to blend in different ways... try both slopes

AustinKP

Originally posted by MacLeod
Which isnt good beacuse ya know the old saying,"the strong take it from the weak and the smart take it from the strong".

I've never heard that saying before. I like that last part. Gives me hope *sniff*