flapping

PoweredByDodge

hi guys... i'm runnin 4 DX 12's in dual chambers (2 subs per chamber .. 8 ohm subs) off an mtx 81000d.

now its giving me hell.

box is at spec. 0.80 cubic per sub sealed.

the amp seems to flap them uncontrollably on tracks with good bass (some industrial heavy metal / rap / even country!).

the gain is only at 60% with the "bass boost" at 1/8 th so its barely figuring in.

in theory i shoudl be able to put the boost at half or more and the gain at 70%.

i am very displeased with the low damping factor of themtx 81000d... its only rated at 100... thats pathetic... zapco's cheapest bottom of the barrell amps have damping factors of over 850!

i'm just wondering if you think that getting an amp with a higher damping factor and less thd (81000d is at 1.3% tested thd / 1200 rms / and damping of 100 at 12.5 volts)... and if an amp with better ratings would help better control thewoofersand make them function "TIGHTLY" instead of uncontrolled.

??????

TrappedUnder Ice

Vinnie..I already told you you were overdriving your subs..thus the flapping noise..

Have a nice day buddy

Thom

There's more to it than that, I think. What kind of head unit are you using (what's the output voltage)?

PoweredByDodge

Well I'm using an alpine 7864 head w/ dual 4 volt outs... one out goes to my amps for highs, the other to the 81000d for the subs. So 4v max is probably like 2 or 2.2 vrms.

there's got to be something more to it, because i've run half this configuration before - the 500d and two dx 10's and it was immensely better sounding.

PoweredByDodge

note --- i tried parallelling the front and rear outputs so that i'd get juice into the amp... same problem... tried reducing it by splicing of to another amp at the same time... same effect.

(yes i've been trying just about every dumb thing i can think of...lol)

TrappedUnder Ice

Let me ask you this...if you were too turn the gains down on your sub amp..and then run the "heavy bass" tracks..does it still do it?

PoweredByDodge

in order to make it "perfect" i have to turn the gain to 1/4, the bass EQ off, and keep the volume low.. then itsounds ok, and woud pass for "good", but its so quiet that if you have the high's on you cant even tell the subs are on

TrappedUnder Ice

Too me..sounds like either something is wrong with the enclosure..or the subs. If you decrease the gain and it sounds good..then you are 0verdriving the subs with that amp..wich is what I thought in the first place.

Now..why are we overdriving the sub...that is the question. Is it the subs just cant handle it..or cant handle it in that enclosure.? Dont really know. or have the subs already suffered the damage..thus cant take the "higher" power? :rolleyes:

BTW..I should be in chat tonight..Thomas...

PoweredByDodge

For anyone who cares to know (I already told Thomas -- my wise old Yoda like friend) ... the dx's testing is complete. Each speaker tried in a "perfecT" sealed 0.88 cubic 3/4 inch mdf box with no poly fill and exactly 400 watts of power.

the speaker fell on its face --- all 4 of them.

Different amps (meterd for output) gave the same result... so then we went to our buddies at circuit city and pulled about 6 subs off the shelf.. all in appropriately sized sealed boxes. Polk will be hapy to know that the best sounding of them all --- and pulling in a grand total power handling of about 625 watts before distorting / making funky sounds... was the MOMO 12 inch in the sealed lexan backed box made by polk.

The dx sounds like a bloody lawnmower gone bad -- it broke up long before the alpine type R as well as even the crappy mtx 8000... the only thing that performed worse was the Coustic sub (more junk from Mitek - MTX corp) If I had a "good" / new dx 12 here i'd compare it head to head with the 4 i've got to see if its just that these subs are blown or not... but i' haven't so I can't tell you. However.. I am leaning strongly toward them being in some way damaged -- one of my buddies, a veteran installer at CC agrees with me that hte voice coil seems to be going in almost all of them.

This is kind of ridiculous out of a 2 1/2 month old subwoofer-- yup 2 1/2 months not 2 1/2 years.

Putting only about 300 - 370 watts per sub on these things (depending on 12.5 volt versus 13.8 volt amp power) I am shocked as hell.

The funny part of the day was when the alpine type R crapped the bed and died with about 500 wrms...

I'd have bought 4 momo 12's in the lexan boxes on the spot -- as I really did like them.. however at 399 bucks each. thats almost as ridiculous as the dx's going bad on me.

Instead. I went and snagged 2 Image Dynamics IDMAX dual 4 ohm coil jobbers. gonna put a big sign on back of the truck "150 db's or bust".

anybody who wants the dx's (they maintain integrity and sound quality up to about 275 - 300 watts -- more as long as its not a bass heavy rap track) you can have them for 75 bucks each -- email poweredbydodgev8@aol.com

If I can't sell them I'm gonna ship em out to polk repairs out in California as they're under warranty and have them fixed or send me a new set -- then sell them for 100 each to cover the fact that i had to pay shipping on the repair/rework.