Sealed box frequency question

ryanosaur

ryanosaur

Audioholic Overlord
Hi all! I’ve read the speaker design books through 1 time and am starting to work my way through some longhand speaker math. My first project is going to be a subwoofer, and as I’m still teaching myself through the equations with the goal right now of just getting the theory down, I’m already stumbling on a question:
In sealed boxes, how does one go about getting a good strong low extension?
My first run through with a Dayton ultimax 12” driver gave me a larger than recommended box and a Fb of between 34Hz and 29, depending on playing with Qtc(did .707 and .669 just to experiment.)
I don’t necessarily mind a large box, and I recognize this might not be the right driver for the goal... What should I look for in the specs that will help me achieve around -3dB at 20Hz? Is it just as simple as finding a low Fs?
Many thanks!
 
TheWarrior

TheWarrior

Audioholic Ninja
Deep bass from a sealed box requires Power and DSP, as well as a driver optimally chosen for the application.

If you are using the UM12-22, that will also require the acoustics of a car's interior to achieve any significant bass, as that was its intended application.

But achieving -3dB @ 20Hz at EVERY seat in a room, requires more than one subwoofer. The advantage of sealed subs is that they need far less cabinet volume than ported subs, so you can hide more of them around.

You may need 4 subs to get equal bass at all seats, but 1 or two of them may only need to play the first octave (20 hz-40hz) to bring the low bass up to the relative sound level.
 
ryanosaur

ryanosaur

Audioholic Overlord
Thank you. Just to be clear, I’m not really in a serious design phase here. I selected several different drivers to practice the math and theory on... just to learn about doing it the hard way. I won’t be able to use a CAD type program for a while due to costs and budget.
I started with this Dayton because it had a low EBP, and I had seen some people comment that they were decent for home audio. I’ll also be running through the process with a ScanSpeak, Morel, and AE drivers.

@TheWarrior, I saw some instances where a driver specified car audio in the description, but not very often on the sites I visited. How do I tell the primary usage? Is there something ‘coded’ into the parameters that I can learn to identify? Or maybe a better question is how to tell a good hi fi driver from one not so appropriate to a high end home rig?
Again, thank you!
 
William Lemmerhirt

William Lemmerhirt

Audioholic Overlord
Hola amigo! @tlsguy is a wizard and has designed/built many speakers. He’s also very generous with his knowledge, and maybe he’ll drop in her. I know he’s very busy atm.

Anyways, as the warrior indicated, to simply equal the output it can take as many as 4 sealed boxes. I am personally not a fan, and I believe mark(tlsguy) has voiced his dislike as well.
Despite that, more to your question.
IMO, FS is a quick indication of a drivers intended purpose. Higher FS of say, 30hz would indicate a sub that isn’t meant for HT FS since it’s very difficult to get a sub to play below its FS without dis too, and without pushing it to death. Output in a sealed application takes a lot of power and a lot of excursion. And when you start to EQ the bottom end to increase output, it will quickly introduce distortion, and power requirements This and all the extra excursion creates heat, and is very bad for driver parts. Other T/S parameters I don’t remember so much off hand, but the ones(qts?) that refer to a high or low Q, are important to note, as that will indicate a one note wonder, or a linear controlled bass source. Hopefully someone can elaborate as I just haven’t had my mind there for awhile.

Also, ported subs aren’t that much more difficult(academically at least) to build than sealed, and given your hands on approach, and seemingly good skills should be easy.

Winisd, bassbox pro, and sonosub builder(sorry no links this time brother) are great resources to use, and simulate with unit you go to put blade to wood.

Not sure anything useful here, but even a little bit can go a long way. Have fun!
 
William Lemmerhirt

William Lemmerhirt

Audioholic Overlord
I guess too, part of selecting a sealed box size is determining the right amount of back spring. Iirc too big, and it will unload the driver like a ported sub playing below tune. Too small and you’ll lose efficiency and extension. Maybe I’m ten miles off but that stands out...
 
ryanosaur

ryanosaur

Audioholic Overlord
William, anything that helps reinforce what I've read and keeps me aiming in the right direction is useful! Thank you!
I guess my interest in the sealed concept comes from commentary from many sources that building a sealed system is somehow more cohesive in SQ, as well as being a good starting place. But even that is getting ahead of where I am right now just focusing on solidifying my grasp on the theory and math.

I have 3 drivers selected for my "play dates" with EBPs <50 which indicate closed box. Of those, the Dayton mentioned above has the highest Fs @ 26Hz, two have Fs @ 21Hz. Q: still being somewhat mysterious to me in terms of understanding low vs high, I might be erroneously focusing on Qts (total system Q for the driver?).
That Dayton is .59, while the other two have a Qts of .43. (But that coincidence in matching Fs and Qts is where the similarities end between the Morel and AE drivers, so I am expecting to see slight variations as I play with the numbers.)

For Ported boxes, I have specs from Peerless, Morel, AE, ScanSpeak, and a different Dayton to play with. Three of them are close enough in EBP I might figure them for both Ported and Sealed.

Getting to the point where the numbers have meaning to me is my goal. When I can, I'll have to get a PC to run any programs, as I'm a Mac man, and I can't find anything that will work. I've fooled around with a couple online calculators with varying levels results. None of which struck me as proper...
...like the one that modeled a port tube about 3x longer than the box with it seemingly impaling the box and not actually venting. *facepalm

:)
 
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William Lemmerhirt

William Lemmerhirt

Audioholic Overlord
Only have a sec...
AFAIK winisd and bassbox etc work with Mac. Not sure but think so. I’ll see if I can find out later. Also, IMO and many others, sealed being tighter, easier to integrate etc is a myth and proper integration of either is key. In a proper integration, I doubt you’d be able to tell which was which, until of course you get down into the HT realm of bass where the ported box will have a. Big advantage. Of course with enough sealed boxes, this can be addressed too, but to me, the real estate would be better occupied with ported subs. Yes for music too.
I understand your looking at this academically atm but just sharing some thoughts.
 
ryanosaur

ryanosaur

Audioholic Overlord
Dig it! ;)
I'm a ponderous thinker... apparently a trait of us Sag's, though I'm not really an astrology kinda guy.

I'll look into those, too. It would be nice to be able to confirm my math against a model! :) Thanks!!!
 
William Lemmerhirt

William Lemmerhirt

Audioholic Overlord
Dig it! ;)
I'm a ponderous thinker... apparently a trait of us Sag's, though I'm not really an astrology kinda guy.

I'll look into those, too. It would be nice to be able to confirm my math against a model! :) Thanks!!!
lol! I’m not too much either but it’s funny how accurate some of it can be. I’m a Gemini for example. Yep, I have dual(ing) personalities, and other traits. Lol!

:( nope. *sigh
;)
Bummer...
 
Swerd

Swerd

Audioholic Warlord
Q: still being somewhat mysterious to me in terms of understanding low vs high
I think of Q for a bass driver/cabinet combination as unit-less ratio that describes the slope of a roll-off curve. It is associated with a variation in sound. Qualitatively, I would say a low Q bass (0.7 or lower) sounds "dry or restrained" and a high Q (approaching 1.0 or higher) bass sounds "fat or boomy". It can vary some with the driver and the room.

High Q values do provide greater SPL, but create a muddier sound that masks bass detail. If you have Ray Alden's book, Speaker Building 201, look in the chapter on sealed bass cabinets and look where he discusses how high Q bass alignments allow bass drivers to ring or reverberate, but low Q damps the ringing, at the expense of SPL. There is a good figure that compares the frequency vs. SPL curve to the SPL vs. time curve of different Q values. (If I had my book at my fingertips, I'd tell you the page number.) Basically, low Q = high fidelity, but there seems to be a wide range in individual tastes for this.

In general, the larger the sealed cabinet, the lower the Q. Below is a combined plot of several different sealed cabinet volumes for the same woofer, a JBL 123A. I did this several years ago, but kept the result. You can see volumes ranging from 2.0 to 5.9 ft³, and calculated Q values ranging from 0.7 to 1.0:
Q=0.7, dark blue curve, F3=38.8 Hz​
Q=0.8, red curve, F3=44.4​
Q=0.9 green curve, F3=50.5​
Q=1.0 turquoise curve, F3=56.7​

I didn't calculate a cabinet volume for lower than 0.7, such as Q=0.5. This is the so-called critically damped Q value, but for this driver it the cabinet would have been way too large.

1550607032542.png
 
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KEW

KEW

Audioholic Overlord
I think you should shoot for DIY'ing one of these!
https://www.funkaudio.ca/store/p26/Funk_Audio_21.0.html
I figure if @Steve81 chose it for his system, it is probably an excellent performer!
Also, at $8,000 to $8,300, the potential for you to save money is much greater than some piddlin' 12 to 15 subwoofer!

PS: I am impressed by how close the speaker fits to the exterior walls of this cabinet!
Also intrigued that the driver is indicated as "Hand-built in house by Funk Audio". I may be wrong, but had the opinion that Funk was a very small operation (like Salk) and did not know "DIY'ing" drivers was a thing!
 
ryanosaur

ryanosaur

Audioholic Overlord
Hi Swerd... Yes, thank you. I 'get' most of that, but since I can't really explain it yet, as an epistemic kinda guy, I would have to say I don't 'know' it. :)
I saw another graph on a website as I was trying to help myself understand it better... they showed the knee and rolloff more pronounced to help illustrate it, but almost identical info! Again, thank you!
 
lovinthehd

lovinthehd

Audioholic Jedi
I think you should shoot for DIY'ing one of these!
https://www.funkaudio.ca/store/p26/Funk_Audio_21.0.html
I figure if @Steve81 chose it for his system, it is probably an excellent performer!
Also, at $8,000 to $8,300, the potential for you to save money is much greater than some piddlin' 12 to 15 subwoofer!

PS: I am impressed by how close the speaker fits to the exterior walls of this cabinet!
Also intrigued that the driver is indicated as "Hand-built in house by Funk Audio". I may be wrong, but had the opinion that Funk was a very small operation (like Salk) and did not know "DIY'ing" drivers was a thing!
Believe Funk also put together their own amps. Didn't know they offered a diy option, tho. You can buy a hand built subwoofer driver from Stereo Integrity for their HST drivers....
 
ryanosaur

ryanosaur

Audioholic Overlord
Sweet. Custom made drivers. Gotta draw the line somewhere! :p As if I weren't looking at almost $600 drivers already.:rolleyes:

If I could build something half-as-cool as a Funk sub, I'd be stoked!

I might've stated this elsewhere, but secretly, I want to replace the x-13s in my room with something that might be a better pairing for the Phil rig. Totally happy with them, don't misunderstand, but having matching Raals and Revelators all around me is an intriguing concept. Then I could put the x-13s in the greatroom. Win/win. But if I were to do that, I need to get my 15-16Hz extension for pipe organ.

I really appreciate you guys chiming in! I know I'm gonna have more questions as I work through this.
 
ryanosaur

ryanosaur

Audioholic Overlord
Quit messing around with those puny mid woofers. Go for 24", and get two of them.
Thanks, Swerd. I've only got roughly 155'2 floor plan to work with. :)
But let me run it past the lady for the greatroom.
 
KEW

KEW

Audioholic Overlord
Believe Funk also put together their own amps. Didn't know they offered a diy option, tho. You can buy a hand built subwoofer driver from Stereo Integrity for their HST drivers....
I didn't mean to imply they offered a DIY kit. Just suggesting using the Funk as an objective in a "go big or go home" mentality!:D
 

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