TragicMagic

Hey guys,
I just ordered a Kenwood KAC-8501D amp. Looking at the specs for this unit, the LPF can be dialed in the range of 50-200Hz, and the Subsonic/Infrasonic filter is selectable between 15 or 25Hz. Because Kenwood screwed up the information on their website I'm uncertain as to whether the LPF slope is -12db/octave, or -24db/octave. Both are listed in two different areas. Right now, it doesn't matter.

My question is this. If I set the LPF to 80Hz, is that the frequency at which the amp starts to attenuate higher frequencies, or does it attenuate before 80Hz, with 80 being the cut-off point? Logic would suggest that the amp would begin to cut-off frequencies from 80Hz and upward, until the -db removed all traces of that signal.
But now I go back to the -12db or -24db. The amp is going to power a Cadence 8" sub is a sealed box. If the slope is steep at -24db/octave, would it be wise to raise the LPF, so I don't cut too many frequencies from being amplified? I want a nice roll off from the bass to the mids being produced from the four 6.5's.

Dukk

Usually the crossover point, 80hz in this case, is actually the -3db point. This is done so that if both the low pass speaker and high pass speaker are -3db at that frequency, their combined output theoretically sums to zero.

80hz is a good start regardless of slope. Maybe the deck is 24db low pass and 12db high pass? That's not uncommon.

TragicMagic

To clarify, the KAC-8501D is a mono amplifier. It only has the Low Pass Filter and an Infrasonic filter. I plan on running an 8" Cadence (dual 2ohm voice coil), with an RMS of 250W, at 4 ohms, with which the amp will output 300W.




On Kenwood's website the "general info" tab claims a -12db slope, while the "specifications" tab claims a -24db slope. And their user's manual (opened in Acrobat Reader) doesn't have any information regarding the slope of the LPF.

JohnnyRock1588

iTrader: (22)

If im reading your post correctly your concerned about having the amp be fixed at 12 or 24db slopes.

24db is recommended for most sub stages as a general rule of thumb DEPENDING on your system configuration of course. So you wont need to worry about it as its not a big deal.

also if your head unit has the option to switch your slope from 12 to 24 then just do it on the head unit.

when lowpassed you are cutting frequencies above that point ( 80hz in your case )

what what rest of your system consist of?

TragicMagic

I'm more concerned with knowing if the slope starts at the LPF set point, or ends on the LPF set point.
If the subwoofer is rated to play 28-750Hz I don't see a reason to cut off the higher frequencies too early, at 80Hz. Even if I set it at 150Hz, I think I wouldn't be misusing/abusing the sub. Cadence S1W8 D2
The system is going to have an Excelon HDC-x696 headunit. It's going to power the stock 6.5's in the doors, and the stock tweeters at the bottom of the A pillars.

I just checked the owner's manual for the deck, on Kenwood's site. It states that for the high pass, and low pass, that "frequencies below(HP) or above(LP) the specified value are cut off". There's no mention of a slope at all...

Ah well, I'll just have to play with it, and see what it sounds like...

Sonic

iTrader: (1)

It all comes down to what sounds good to you, however, you dont want to cross the sub too high for it to play vocals because it would draw the sound stage to the back of the vehicle, the same can be said for the rear speakers.

For subs, steeper the slope the better, 24 or 18 db slope not 12. For the rest of the system a 12 db slope is prefered for smooth transition.

TragicMagic

I have a website bookmarked with audio files for different Hertz tones. Judging by what I hear with the 100 or 125 Hz tone, I feel confident that the 8" can reproduce up to that range, without sounding "muddy" and still not effect the staging much at all. Pure Test Sounds - MP3 - From 20 Hz to 20.000Hz @ -10dB

Now, if I can determine that the slope is -24db, I'll stay closer to 125Hz -as subsequent frequencies will be cut off more sharply. If its the -12db slope, then I'd stay close to 100Hz, since the cut off would be more gradual. I'd prefer the 2nd of the two scenarios.

Also, the woofer is going to be installed in the cabin of the car, not in the trunk. There's a space between the back of the centre armrest/console and the middle back seat. There's enough room for a small sealed box. When I have a passenger in that seat, they'll have the sub between their legs - which might feel nice. lol

Sonic

iTrader: (1)

Sounds like a plan, a bit of tweaking and you will find what you are looking for, and yes that passenger may feel nice in that seat lol.....

Dukk

Regardless of the slope, the specified frequency is usually the -3db point. If the crossover point is continuously variable then it doesn't really matter, nor does it matter what the value is that you set it at as long as it returns the best sound.