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Discussion Starter · #1 ·
The Sub: 15" Dayton Quatro DIY, 5.5 cu.ft., 4" flared port 11" long, 240w PE plate amp. Tuned roughly 18 hz. (WinISD claims that my box has to be 7cuft for this to be possible, box has magic eggcrate lining)


The problem: EQ'd roughly flat to 20hz, but I have at least a 10db peak from 18hz down to 16hz. (graph at home, me at work, but you get the idea).


The Question: What to do? Should I 1) dance around for joy that room gain is giving me this huge low end thump? 2) Shorten the port to move the tuning up some 3) Call Behringer and tell them I need to EQ sub 20hz frequencies or 4) stuff the port for music and continue dancing?


I'm getting a little boomy occasionaly with music (though not nearly as bad since re-EQing, room wizard is handy, so are 1hz increment test tones) but have no complaints otherwise.


thoughts, advice?
 

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How much music actually goes down to 16Hz? ;)


I'd try tuning it higher, yes. If you can't do it with that, you might want to move the sub. If both of those fail to help, then yes, EQ it out.
 

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A peak at 18hz is not going to translate to a "low-end thump".

It's more likely to create the impression that the bass is "slow", due to excessive room mode ringing, which will tend to recur at multiples of that 18hz frequency.

It will also tend to accentuate infrasonic room and street noise from the recording studio, and little if any recorded music or LFE content.


I'm guessing that your room has at least one dimension of at least 30' and your listening position is close to a wall.

Try moving the sub and/or listening position into more moderate zones; the response will be flatter.

Accurate bass is good bass.

All other forms are bad.


BTW, that's an impressive subwoofer!
 

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Discussion Starter · #5 ·
Quote:
You could also tune lower to extend the usable low end.
Heh, I probably don't want to do that. I don't have the model handy, but I believe at it's current tuning I'm tickling the mechanical limits of the driver around 20-25hz at higher SPLs (granted higher than I'm likely to push it in it's current environment). Tuning it lower, I think would exacerbate that little problem.


Quote:
I'm guessing that your room has at least one dimension of at least 30' and your listening position is close to a wall.

Try moving the sub and/or listening position into more moderate zones; the response will be flatter.
Close, sort of. ;) Room is 9.5'x15', but listening position is 4 ft off the sidewalls and 10 ft from the front wall. Sub is in front left corner. I can't really move it, it's much to big to go anywhere else.


I'll play with it some more tonight. The only real solution I can think of is moving the tuning up to 20ish or so.
 

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Originally Posted by snickelfritz
I'm surprised you're getting such a large peak at 18hz in such a small room!

What's the output at 35hz look like?
I agree. You should be starting to see the start of room gain around 33 Hz in that size room.


OTOH, your subwoofer could anechoically exhibit an EBS type alignment, where there is a sag in the FR above Fb. The only way to determine this would be to measure the subwoofer in 1/2 space away from reflective structures.


If this is the case, this sag in the FR might be coupling with room gain to yield a flat FR nearly down to around 20 Hz. Then as you approach Fb, the FR recovers, and this (combined with room gain) suddenly shows a big peak in the response.


Considering how insensitive the human ear is to frequencies in the 16-18 Hz region, a moderate gain in that region isn't terribly detrimental IMO. I'd worry much more about peaks and nulls in the 35-120 Hz bandwidth.


If you plot your FR against some equal loudness curves at your preferred playback level, you might find that a boost at 16-18 Hz will be perceived as equally loud when compared to higher frequencies.
 

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Discussion Starter · #8 ·
Interesting. Just reading up on EBS alignments, and it's entirely possible this sub is exhibiting some EBS qualities. The driver actually reacts to the box as if it were 40% bigger than it actually is, given the tuning and length of port. Hmmm.


This weekend I will get some graphs up, both with EQ, and without. I still need to plot 80-120 anyway, and we can discuss reality vs theory. RIght now with eq, I have an ever so slight house curve from 80-20hz.


If I recall correctly, the biggest peak I had to tame was in the 40hz area.


Thanks so far.
 

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"The driver actually reacts to the box as if it were 40% bigger than it actually is, given the tuning and length of port. Hmmm."


I agree with the "Hmmmm" :)


I think it's more accurate to say the box *is* 40% bigger.


My understanding is that above Fb a vented box behaves similarly to a sealed box, ergo EBS' gradual rolloff associated with big box/low Qts.


Then in the region of Fb the output is boosted by the second resonant spring/mass system comprised of the vent mass and box air spring.
 

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Discussion Starter · #10 ·
Well it is a 5.5cuft box. Per the model however, for the sub to be tuned to 18hz with a 4" diameter port that's 11" long, the box would have to be roughly 7.5cu ft. Hence the magic eggcrate foam comment.


First time building a sub, so I'll readily admit I only vaguely know what I'm talking about. :) I just have this hump down there.
 

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I've also found that foam lining the walls reduces Fb significantly. That's not from EBS, that's from absorbing the heat of compression and reducing the pressure rise.


Also, did you include end corrections for the port? Its effective length is longer than its actual length because it takes some distance for the the air flow to spread out (if it hasn't spread out it's the same as if it's still in the tube).
 

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Discussion Starter · #12 ·
heh, move along nothing to see... the peak was a collection of misreads, actually down about 4 at 16hz. At the moment anyway, need another day to re-EQ everything. Mostly pleased with the cruve though.
 
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