Help me choose a Dayton for an OB/H-frame?

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Fmstrat

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Joined 2020
#1
Hi all,


I'm looking to build an open-baffle subwoofer, likely H-frame, that is small and will be placed near-field right behind the main seat at head level in an apartment. The intent of the design (OB/H-frame) is to centralize the volume to the listener while creating as little resonance in the room that could transfer to others in the complex. I do not need heavy bass, just something to augment the surround setup I have and add a bit more to the low end.


I'm a fan of the Dayton brand, and that's what I'm using for my surround setup, so I'm wondering if anyone has any suggestions on a 10" (or MAYBE 12", space is an issue behind the couch) Dayton subwoofer to use in this design. Secondarily, any suggestions on how to do the math for the size/depth of the enclosure.


I'm somewhat experienced with speaker design, but not with open-baffle at all.



Thanks!
 
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#4
scottjoplin said:
You need to beware of cavity resonance and you will want to crossover below it, otherwise the deeper the lower the dipole peak. There's a formula for calculating the resonance on page 3: http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf
Click to expand...


Thanks! Perhaps you could help explain it a bit?


1) Was the 7.5" depth the full depth of the H-frame cabinet? Or the depth from front to center panel (making it 15" deep overall)? He goes back and forth between U and H so I'm not sure which he's speaking about.
- From the diagram on page 4, I'm thinking the H frame was 15", just want to be sure I'm reading that right.

2) In line 2 of the formula, 9.0" shows up. Where does this come from? I saw "r" so I expected 7.5" (the radius of the 15" driver) but I'm clearly missing something here. (Or is 9" the combination radius of his two drivers?)
- I don't believe it's a combo, since the FE103E and 15A would be 9.5" total. Maybe he's taking out the voice coil (https://www.parts-express.com/pedocs/specs/290-407--eminence-alpha-15a-spec-sheet.pdf ) But even that wouldn't be exact.

3) In line 5, where does "344 m/sec" come from? Is that a standard that should always be used?
- And I think I've answered this one: Speed of sound - Wikipedia



Thanks!


P.S. Funny note.. I live 25m from the article author. Hah!
 
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#6
scottjoplin said:
Sure, 7.5" is the depth from the front to the centre panel. "r effective" is what the radius would be if the cavity were circular, it's because the formula is based on pipe resonance. End correction - Wikipedia The "end correction is where the 0.6 comes from in the formula. Yep, speed of sound. 🙂
Click to expand...


Ahhh thank you. very helpful. I'm still a bit confused on the 9, though. If the "internal cross-sectional area is 16” wide and 16” tall", why 9 instead of 8? Is he counting the 3/4" sides vs just the internal baffle? And even still, that seems like it would be more than 9.


If I try calculating the radius of a 16" square with pythagorean: sqrt(((16/2)^2)*2) = 11.31 so that's not it either..
 
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#9
Given all the info provided in this thread, I've grabbed all the subwoofers from PE under or around $150. I've highlighted the ones that I think work best based on what I'm reading, and am leaning towards the RSS265HF-8 or RSS265HO-44
but I'm wondering if I'm missing something important (like 8 vs 4ohm, etc).

subwoofers.png


What do you guys think?
 
#12
joensd said:
The 830669 is not much more expensive than the 830668 but can move much more air:
Search results for "830669"
I use a single one on a narrow baffle and find it very nice for OB.
There also should be lots of "designs"/examples in h-frames out there.
Click to expand...


The problem is that's a 12" sub. Anything bigger than a 10" is getting too big for placing on the shelf behind the listener. In an ideal world, I'd use an 8", but I'm compromising size for performance with a 10".


mordikai said:
I"m curious to see how this works for you. My open baffles have always been on the floor and I figured this contributed to the output somewhat. You doing one or a pair?
You're doing headphone ob subs!
Click to expand...


Hah, sort of I guess, yea. I will of course reply here once it's built. I'll be doing a single sub vs dual.
 
#13
scottjoplin said:
Sure, 7.5" is the depth from the front to the centre panel. "r effective" is what the radius would be if the cavity were circular, it's because the formula is based on pipe resonance. End correction - Wikipedia The "end correction is where the 0.6 comes from in the formula. Yep, speed of sound. 🙂
Click to expand...


Hi Scott,


Just one more question for clarification. He says:


"The depth was selected to push the first quarter wavelength resonance above the desired crossover frequency of approximately 200 Hz"


But then his result is 262 Hz vs below 200 Hz. He goes on to say:


"Adding additional length to either the U or H frame drops the quarter wavelength resonant frequency resulting in a peaking SPL response around the crossover frequency."


Sooooo what should i target? I'm not sure I understand the math behind determining the quarter wavelength to select the right depth.
 
#14
10" may also not be the way to go here without a lot of depth.

Inside of cabinet 11x11
Cabinet depth: 6, 7, 8
344 / (4 * ((6 + .6 * (√((11*11)/3.14)))/39.37)) = 348hz
344 / (4 * ((7 + .6 * (√((11*11)/3.14)))/39.37)) = 315hz
344 / (4 * ((8 + .6 * (√((11*11)/3.14)))/39.37)) = 288hz

What if we do 12x12?
344 / (4 * ((6 + .6 * (√((12*12)/3.14)))/39.37)) = 336hz
344 / (4 * ((7 + .6 * (√((12*12)/3.14)))/39.37)) = 306hz
344 / (4 * ((8 + .6 * (√((12*12)/3.14)))/39.37)) = 280hz


 
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