Equilibria
12-30-06, 05:03 PM
I can't get it to play test tones properly!
I'll explain. Started my first DIY (which turns out to be an IB) sub at the start of december, just finished mounting the amp and getting the BFD 1124P plugged in yesterday. The sub consists of:
2 MJ-18's from Mach 5 Audio (8Ohm version)
1 Bash300 Amp from Creative Sound
1 Behringer Feedback Destroyer 1124P from ... Long and McQuade (I think)
All of this was purchased in Canada
My father and I built the enclosure ourselves out of 5/8" stran board doubled up (so the whole thing is 1 1/4") with the layers rabbitted together for strength. We changed the Bash to have a HP filter set at fc=12 and Q=0.7 (I think its R25=43KOhm and R26=84KOhm, maybe other way around). Finding those resistors is not hard if you read the description on the instruction sheet that comes with the amp (adjacent to the phase switch) and just look underneath the resistors as best as possible to make out the 25 and 26. We took the PCB off the amp, too tight an area otherwise. The drivers are wired in parallel to get 4Ohm.
Now onto the problems. First off, the fact that the inputs/outputs on the BFD are balanced gave us some grief. As Radio Shack barely exists in Canada now, had to go across the border and pick up some dual RCA (L/R) to balanced 1/4" adapters. Problem was, it introduced hum into our system (barely audible, but still there). My father has done a lot of electronics work so figured we should just make our own connectors. That just made it worse. I ended up doing what I should have done in the first place and looked up online the best way to connect a reciever to the BFD - single RCA to mono 1/4". Ended up just modifiying our homemade balanced jacks to unbalanced. Still getting the same hum I did with the radio shack purchased adapters. Did more research - turns out my satellite (Bell HD, non-PVR) was feeding a ground loop through its component outs into my Onkyo SR-602. Disconnected those (we rarely watch TV in the theatre room, so its only temporary) and no more hum, problem solved.
Next problem, and the one that still stands. Tried to setup everything last night with the BFD and RoomEQ just to see the response and so forth. Running through the setup with RoomEQ and setting everything up worked okay, until I had to run the sweep to actually measure the room. The subs wont respond below 30~35 hz. I know about amp limiting to some extent, and so I tried going straight from computer to amp, and just running a tone generator. to play 10 hz, I had to crank the amp to about 60% before the drivers started moving (and they moved... so did my house). Is there some sort of output I have to drive the sub with before it moves? It seems to work fine when I'm just playing a movie or xbox, regardless of the output level. Maybe this is normal, it just seems strange to me, I mean standard drivers (speaker or sub size) can take much smaller amounts of power from my reciever and they output the respective intensity, however the sub when connected to my computer, needs a lot of volume to output anything (and then it really kicks in).
Other than this, if I bypass the BFD and go straight from reciever to amp, WOTW feels amazing. I've demo'd it to a few friends - the movie will never feel adequate on any other setup. When listening to music and sitting in front of the sub, when the bass kicks in I nearly fall over...
But back on topic, any ideas about the sub testing? What am I doing wrong? Thanks
I'll explain. Started my first DIY (which turns out to be an IB) sub at the start of december, just finished mounting the amp and getting the BFD 1124P plugged in yesterday. The sub consists of:
2 MJ-18's from Mach 5 Audio (8Ohm version)
1 Bash300 Amp from Creative Sound
1 Behringer Feedback Destroyer 1124P from ... Long and McQuade (I think)
All of this was purchased in Canada
My father and I built the enclosure ourselves out of 5/8" stran board doubled up (so the whole thing is 1 1/4") with the layers rabbitted together for strength. We changed the Bash to have a HP filter set at fc=12 and Q=0.7 (I think its R25=43KOhm and R26=84KOhm, maybe other way around). Finding those resistors is not hard if you read the description on the instruction sheet that comes with the amp (adjacent to the phase switch) and just look underneath the resistors as best as possible to make out the 25 and 26. We took the PCB off the amp, too tight an area otherwise. The drivers are wired in parallel to get 4Ohm.
Now onto the problems. First off, the fact that the inputs/outputs on the BFD are balanced gave us some grief. As Radio Shack barely exists in Canada now, had to go across the border and pick up some dual RCA (L/R) to balanced 1/4" adapters. Problem was, it introduced hum into our system (barely audible, but still there). My father has done a lot of electronics work so figured we should just make our own connectors. That just made it worse. I ended up doing what I should have done in the first place and looked up online the best way to connect a reciever to the BFD - single RCA to mono 1/4". Ended up just modifiying our homemade balanced jacks to unbalanced. Still getting the same hum I did with the radio shack purchased adapters. Did more research - turns out my satellite (Bell HD, non-PVR) was feeding a ground loop through its component outs into my Onkyo SR-602. Disconnected those (we rarely watch TV in the theatre room, so its only temporary) and no more hum, problem solved.
Next problem, and the one that still stands. Tried to setup everything last night with the BFD and RoomEQ just to see the response and so forth. Running through the setup with RoomEQ and setting everything up worked okay, until I had to run the sweep to actually measure the room. The subs wont respond below 30~35 hz. I know about amp limiting to some extent, and so I tried going straight from computer to amp, and just running a tone generator. to play 10 hz, I had to crank the amp to about 60% before the drivers started moving (and they moved... so did my house). Is there some sort of output I have to drive the sub with before it moves? It seems to work fine when I'm just playing a movie or xbox, regardless of the output level. Maybe this is normal, it just seems strange to me, I mean standard drivers (speaker or sub size) can take much smaller amounts of power from my reciever and they output the respective intensity, however the sub when connected to my computer, needs a lot of volume to output anything (and then it really kicks in).
Other than this, if I bypass the BFD and go straight from reciever to amp, WOTW feels amazing. I've demo'd it to a few friends - the movie will never feel adequate on any other setup. When listening to music and sitting in front of the sub, when the bass kicks in I nearly fall over...
But back on topic, any ideas about the sub testing? What am I doing wrong? Thanks