As a neophyte to speaker design and a newbie on this group it appears that I may have yet to ask my obligatory stupid question. (I recognize that appearances can be deceiving. The jury's still out on one question.) The stupid question is a rite of passage. Maybe this one is totally daft.
What's to keep me from boosting the sub bass in my office system with a passive filter between the amp and the crossovers? Muscle the notes out, as it were. The room is only about 14x14x10 feet. The amp is a solid 40 watts per channel and the speakers (Lynn Olson Ariels) are pretty efficient. Playing music CD's I can't ever turn the volume knob more than about 1/7 of its rotation.
When I use a test CD, 60Hz is loud, 40Hz is pretty good, 30Hz is weak, and 20Hz is virtually inaudible. But if I crank up the amp at 30 and 40Hz, the speakers don't appear to have excessive excursion, and they sound good. Say I put a low pass filter in parallel with a resistor or pot between the amp and the crossovers -- what then? Let's say the filter had a cutoff around 30Hz, phase correctness, and a sharp rolloff. Wouldn't that not only boost the weak frequencies, but also allow more fine control with the volume knob on the amp?
What's to keep me from boosting the sub bass in my office system with a passive filter between the amp and the crossovers? Muscle the notes out, as it were. The room is only about 14x14x10 feet. The amp is a solid 40 watts per channel and the speakers (Lynn Olson Ariels) are pretty efficient. Playing music CD's I can't ever turn the volume knob more than about 1/7 of its rotation.
When I use a test CD, 60Hz is loud, 40Hz is pretty good, 30Hz is weak, and 20Hz is virtually inaudible. But if I crank up the amp at 30 and 40Hz, the speakers don't appear to have excessive excursion, and they sound good. Say I put a low pass filter in parallel with a resistor or pot between the amp and the crossovers -- what then? Let's say the filter had a cutoff around 30Hz, phase correctness, and a sharp rolloff. Wouldn't that not only boost the weak frequencies, but also allow more fine control with the volume knob on the amp?
There are no dumb questions, just dumb people asking questions. And since you're in the South Bay and you're still employed, how dumb could you be?
Anyway, you can eq at the cost of gain, distortion, and max SPL. But you'll probably want to do an active eq, so gain won't be the issue. And active eq lets you actually compensate for the rolloff with a mirror-image function, which you can't do with a passive circuit. If it were my system, I'd bung together an opamp-based Linkwitz transform circuit, plug it in, and see if the cone excursion looks to be too much. An afternoon's work and maybe $20 in parts is pretty low risk.
Anyway, you can eq at the cost of gain, distortion, and max SPL. But you'll probably want to do an active eq, so gain won't be the issue. And active eq lets you actually compensate for the rolloff with a mirror-image function, which you can't do with a passive circuit. If it were my system, I'd bung together an opamp-based Linkwitz transform circuit, plug it in, and see if the cone excursion looks to be too much. An afternoon's work and maybe $20 in parts is pretty low risk.
7V said:
Ah, now that IS dumb.
Yesssssss! I knew I could do it!
But, but, but... I can't bear the thought of "wasting" the power amp part. I only got it a couple of weeks ago. The return policy is 7 days. Besides, I really like it. It's a Rotel RA-02 with keen-o blue LED's and a matching CD player.
Oh, yeah, we have a very strict dumb question quota. Watch it, Mac!
Yeah, you definitely don't want to do this at speaker level. The tape loop is the way to go, or if you're one of those people like me who says, "@!#$ the warranty!" you can add a set of power amp in jacks with a couple minutes of drilling and wiring. Or if you're ambitious, you could incorporate the eq board right inside the Rotel, snaking your power from it.
Yeah, you definitely don't want to do this at speaker level. The tape loop is the way to go, or if you're one of those people like me who says, "@!#$ the warranty!" you can add a set of power amp in jacks with a couple minutes of drilling and wiring. Or if you're ambitious, you could incorporate the eq board right inside the Rotel, snaking your power from it.
SY said:Oh, yeah, we have a very strict dumb question quota. Watch it, Mac!
Yeah, you definitely don't want to do this at speaker level. The tape loop is the way to go, or if you're one of those people like me who says, "@!#$ the warranty!" ...
Right arm, brother! I always lose the receipts anyway.
I like it! I was thinking maybe batteries, but digging into a brand new piece of equipment gets my heart racing. I had my factory fresh 2002 Z28 convertible two days before I was under the hood with a Drimmel, opening up the air intake box. That bad boy now has the torque converter it was born to have and double diamond cross braces on the subframes.
Woo. I spaced. Now I'm cruising the net looking for design info on active EQ's and op amps.
OK, now if you're REALLY ambitious, you'll get a service manual and scour the schematic for a likely candidate stage where you can change the feedback loop to include the EQ.
A Dremel tool is a good thing to have. I've got a pretty high-tech printing press at work that was built by a couple of guys squatting in the corner with a saw, a Black and Decker drill, and a Dremel, carving hunks of aluminum and tool steel with loving care.
A Dremel tool is a good thing to have. I've got a pretty high-tech printing press at work that was built by a couple of guys squatting in the corner with a saw, a Black and Decker drill, and a Dremel, carving hunks of aluminum and tool steel with loving care.
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