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And he wants to build a sub. Already has a Dayton dvc 15" driver and plans on putting it in a small sealed enclosure. He'll be using a Linkwitz type circuit to EQ it relatively flat, a la:

http://sound.westhost.com/project48.htm


While this circuit offers many advantages (ie a pretty flat curve right without expensive PEQ's) the disadvantage is, of course, the extreme gain in the low frequencies...If he wants to be flat to 20Hz, he'd need ~19dB of gain there! Meaning, the excursion there is outrageously higher and definitely becomes the limiting factor.


So here's the meat of the problem. He'll be using it almost exclusively for music. And as a result, he's in the mindset (not entirely wrong) that he doesn't really need to go down to 20Hz, thereby allowing considerably higher power handling. But he's thinking that he could HP at 40-50Hz without losing anything, seeing as how most of the 'bass sensation' is in the 60-120 Hz range.


Now I know that that's just silliness. A bass guitar outputs a 34Hz note. Several of the largest harmonics in a kick drum are in that area. So anybody have any clever ideas on how to convince the guy that there's content worth saving? And what a more reasonable target would be?


Thanks in advance!


PS, sadly my sub capabilities are pretty nonexistant right now to to budgetary constraints, so I can't just throw in Pink Flyod's Welcome to the Machine and literally rock his world. And before I get a torrent of "Just do a THT!!!!11!!1one", he's getting married and has an extremely tight SAF to contend with. So stuck with a very small enclosure, I'm afraid.
 

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Quote:
Originally Posted by Starkiller4299 /forum/post/18289486


And he wants to build a sub. Already has a Dayton dvc 15" driver and plans on putting it in a small sealed enclosure. He'll be using a Linkwitz type circuit to EQ it relatively flat, a la:

http://sound.westhost.com/project48.htm


While this circuit offers many advantages (ie a pretty flat curve right without expensive PEQ's) the disadvantage is, of course, the extreme gain in the low frequencies...If he wants to be flat to 20Hz, he'd need ~19dB of gain there! Meaning, the excursion there is outrageously higher and definitely becomes the limiting factor.

Most music has little last octave content, with even electronic music you think has low bass having last octave peaks over 10dB down from the rest of the spectrum.

http://sound.westhost.com/linkwitz-transform.htm#power


If you're really interested it's straight forward to rip your music, build some IIR filters in GNU Octave (their free Matlab clone), and see where your peak values are.


You're not going to have problems as long as you keep things vaguely reasonable, and if you do a reasonable sized amplifier will clip before you bottom the driver.

Quote:
So here's the meat of the problem. He'll be using it almost exclusively for music. And as a result, he's in the mindset (not entirely wrong) that he doesn't really need to go down to 20Hz, thereby allowing considerably higher power handling. But he's thinking that he could HP at 40-50Hz without losing anything, seeing as how most of the 'bass sensation' is in the 60-120 Hz range.

With music he can equalize it so that it's flat anechoic down to 20Hz, although matching the bottom end to room gain is a better idea.


I have Linkwitz Orion dipoles (with 18dB/octave excursion increase for constant SPL instead of 12dB in a sealed box) with 25dB of equalization at 20Hz overcoming dipole roll-off and low Q in my living room equalized for a pair of real poles at 20Hz (Q=.5) with output at xmax of 82dB @ 20Hz/100dB @ 40Hz and another 5dB until they bottom. In seven years I've never bottomed them on music, even rock and techno averaging 95dBC.


His roll-off is 6dB/octave better, he has more displacement (that's a pair of 10" drivers per side), and he's picking up 3-5dB more for each room boundary the sub woofer is near depending on wall construction.


He'll probably find Siegfried Linkwitz's spread sheets useful in determining output limits

www.linkwitzlab.com/spl_max1.xls


and Linkwitz Transform component values

http://www.linkwitzlab.com/pz-eql.xls

Quote:
PS, sadly my sub capabilities are pretty nonexistant right now to to budgetary constraints, so I can't just throw in Pink Flyod's Welcome to the Machine and literally rock his world. And before I get a torrent of "Just do a THT!!!!11!!1one", he's getting married and has an extremely tight SAF to contend with. So stuck with a very small enclosure, I'm afraid.

He may be better off evaluating his actual output requirements and building something using a smaller driver which is more compliant in a smaller box. For instance I have a pair of Linkwitz Pluto+ in our bedroom which put a 10" driver in a .5 cubic foot box equalized to Fp = 20Hz and Qp = .5 (I should move the poles higher in frequency to account for room gain). My wife liked them so much that she thought we should get a nicer stereo rack (in the bedroom, with a canopy bed and the requisite 12 pillows) to match.
 

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get spectrumlab running. it is free and will let your buddy know what he needs given his listenting preferences. i'll bite my tongue with respect to what i would suggest.
 

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Quote:
Originally Posted by Starkiller4299 /forum/post/18289486


So here's the meat of the problem. He'll be using it almost exclusively for music. And as a result, he's in the mindset (not entirely wrong) that he doesn't really need to go down to 20Hz, thereby allowing considerably higher power handling. But he's thinking that he could HP at 40-50Hz without losing anything, seeing as how most of the 'bass sensation' is in the 60-120 Hz range.


Now I know that that's just silliness. A bass guitar outputs a 34Hz note. Several of the largest harmonics in a kick drum are in that area. So anybody have any clever ideas on how to convince the guy that there's content worth saving? And what a more reasonable target would be?.

There is very, very little musical content below 40hz.

A 4 string BG is 41Hz for low E and 31Hz for B. However, the fundamental content is much reduced even on an open E (2H and 3H dominate), and even less on an open B. Our brains compensate and fill in missing fundamentals. The prime range for bass drums is nearer 100Hz, and a spectrum was posted only a few days ago that shows the same.


To get the same SPL at 20Hz vs 40hz is going to require 4x the excursion, which means a lot more distortion where it will be audible. Model it, add LT for a reasonable F3 and Qt, see where it will run out of excursion and add a simple 2nd order HP (2 resistors and 2 caps) to limit it below Xmax limits. You might find it also then interfaces with the room better as room gain will artificially add the the LT EQ and may make the LF sound bloated.


If you tell me the actual Dayton driver and post the T/S (link to datasheet) and the size of the box, I can sim the filters and box in a few minutes.
 

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"There is very, very little musical content below 40hz."


alpha niner is right about that more or less, so i give a +1 to his post.
 
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