Pa d1000.1 subsonic filter??

IrishChamp

It's adjustable but is it always on? Subsonic filters are only needed with ported Enclosures correct? Seems strange that it would not be defeatable. I loved my pa1200.1 but this is nice and small. Hmmmm....

On a side note:
Polks site has the specs of this amp listed differently in two places.
On the main info page:
500 @ 4 ohms
800 @ 2 ohms
1200 @ 1 ohm

Under Technical Specs:
500 @ 4 ohms
1000 @ 2 ohms
1250 @ 1 ohm

What's correct? What's listed in the manual or on the box?

pentoncm

You are correct, subsonic filters are usually not necessary with sealed enclosures. There may be some benefit depending on the sub whether it can make the bass a little cleaner sounding. You could try setting it around 20 or 25 Hz if you want and see how that sounds.

IrishChamp

I'm Installing two mm1240's and trying to decide if I should get a d1000.1 or another 1200.1

pentoncm

I vote for the 1200.1 because you can defeat the subsonic filter. I don't like that the d1000.1 only goes down to 20Hz for the subsonic but it is on a 12db/octave slope. That means its gonna start cutting all the way up at 35 to 40Hz or so. I would just opt the 1200.1 and keep the subsonic off. I have the Alpine MRX-50 and although I can't defeat the subsonic I turn it all the way down to 5Hz which shouldn't be affecting anything audible.

IrishChamp

Why on earth would they make it non defeat able, this baffles me. I can't believe it's really as bad as it sounds? Most of Polks subs are designed primarily for sealed enclosures with plenty of xmax for low end excursion.

IrishChamp

Pentoncm,
Wouldn't a 20hz 12db slope subsonic filter start cutting at 20hz (cut 3db at 20hz) and be attenuated 12db+3db by 10hz?

IrishChamp

Also noticed the overall frequency response of the amp is listed as 20hz to 200hz so it seems that a subsonic filter turned down to 20hz would not really do anything, correct??
All the mono amps but the Pa880 are similar frequency range, the 880 is 10hz to 30khz and it doesn't have a subsonic filter at all.

pentoncm

Yes you are correct that the filter would cut at -3db at 20Hz but it doesn't just start cutting there. The problem with a 12db/octave filter is that it is very shallow causing cutting pretty far from the crossover point.

I have attached the frequency response to show you what it looks like if you were to set your subsonic at 20Hz and the LPF at 80Hz. Notice how nowhere on the curve do you ever reach 0db. Every point on the sub is cut, this will not sound good in my opinion. You end up boosting a narrow 31 to 50 range while cutting out everything on the edges. This simulation was using a relatively high LPF of 80Hz, using this frequency at 12db/octave will certainly cause sub localization towards the rear.

Notice how the situation gets much worse when you use a better LPF at 60Hz.

It really isn't necessary to use a subsonic filter. You need to use one in a ported box because beneath the tuning frequency the sub acts as though it is in free air and will "unload". So you have to use a subsonic to protect the sub. In a sealed box the air inside supports the sub at all times so it is many times more stable than a sub in a ported box. There isn't much information under 30Hz anyway even in techno. You would have to be playing movie soundtracks or listening to pipe organs.

Less signal manipulation is always better. A 12db/octave crossover (subsonic filter) will cause a phase shift in the crossover region as well further complicating tuning.

IrishChamp

thanks.
If this is accurate this amp is a poore choice for any situation ported or sealed.

IrishChamp

I'm leaning towards getting the pa 1200.1, had one before and liked it, guy I sold it to said it was much more detailed And controlled bass than his previous amp (don't remember what he had before).
Also, there is a JL audio g max (1200 @ 2 ohms) for sale on diyma, how do you think it would compare to the Polk 1200.1 in SQ?
I have an older slash JL amp, I like the sound from the pa500.4 better.