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Simi's Official 12" subwoofer build.

audiozaz said:
I guess 37Hz is kinda low and would not have the sub cover much, I guess the 50Hz filter is a good starting point. The B'waves will still take care of the punch region.

IG
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My problem with my mains is mostly at low volume... I have to start dumping a lot of juice into them to get a good bass, and I have to start backing off the bass. They can honestly shake the neighbors house across the street, and he has told me they have... but at low volume, they just don't have the bottom end I want. Especially after moving them onto a different wall, and I don't have them sitting catty corner in the corners like I did that really helped re-enforce the bass...

Guess this is one of the things you have to consider when using pro drivers.. they are meant to sound their best when you have some real power into them.. but at low volumes, they still sound great, just not much punch.


OH.. and I hope for others thinking about a sub build, I hope all this info these guys are giving helps you understand better too.... I got a minor grasp of things, but these guys sure make it easier to understand so you can latch onto more and end up with a better product. :thmbsp:
 
similost said:
Yep.. makes a lot more sense to me now.. thanks... faster roll off basically... .Now I just gotta start understanding octives... I mean I understand and octive in music, I just don't in speakers... but I know each music note is a hz of one or another... same principle to speakers?
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Yes sir!!:yes:
 
similost said:
Huh... I like this idea.. BUT... and this is only cause I don't know any better... if you did something like this, how would you know what size to cut the hole, then how far to move it to get your tuning you want?

I mean... say I decide to tune the box at 28hz with just strictly the size of the slot... then say I want to try 23hz.... so if I make the slot longer (deeper into it with an extension piece(like a slide pipe sorta)) into the box then would that start tuning me downwards to 23hz? Or would it start tuning it up? Seems if I remember, longer is lower, right?
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My grasp of the mathematical aspect is somewhat nill :thumbsdn:

I would start would a slot, and rectangular insert like a slide pipe :yes:,
Push the port until it hit the back of the enclosure, then back off 1/2" at a time until I was able to "hear" the best response. Longer is lower.

Sorry I cannot add anything on the technical aspect.
 
Numerical example...

If you choose 50Hz as your filter and 12dB/octave as your slope then at 100Hz (up one octave) the sound will be down by 12dB relative to 50. At 200Hz it will be down 24dB relative to 50. So if you're smokin along at 100dB as your nominal level the sub will be playing 50Hz at 100dB, 100Hz at 88dB, and 200Hz at 76dB.

With an 18dB/octave slope it would be 100dB at 50Hz, 82dB at 100Hz, and 64dB at 200Hz.

The steeper slope keeps the sub from interfering with your mains.

Note: this is a simplistic example. The filter knee (50Hz in this example) is not actually flat, it's the point where the response has rolled off 3dB so all the numbers would need to be adjusted for that and the fact that the filter has not reached the final slope yet. However, it's good enough to get the idea across.
 
Thanks Ray!! My ability to explain is next to nil. vocab is lacking.:sigh:
Not to mention my typing abilities.
 
HUGE help in understanding it Ray, and yes, now I can see the need for a 18db slope, and I think that's what I really want...

So, that got me to looking around, and I found the perfect little gadget..
http://store.hlabs.com/pk4/store.pl?view_product=26

Well... I'm getitng clost to starting to order things now.

Box size... CHECK...
Crossover, CHECK
Port, Pretty much Check, A slot seems to be my best bet...

Drivers, pretty much a check, unless someone can point out a more sensitive driver, at no more than about $150 per driver. I've been looking around hard and heavy, but it's hard to find them even upwards of 90db AND be 20hz Fs or below.
 
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Hot damn.. holding my bonus in my hand right now... SUBS.. HERE I COME :D

:banana:

I wasn't even thinking of a check when this idea started.. it was started over the need.. not money to burn... LOL..
 
Interesting device, the FMod adjustable box.

Other interesting gadgets I'd like to play with, albeit ~3x cost, are the miniDSP units. http://www.minidsp.com/ I think you can go pretty wild with slopes and such with these and the various plugins you buy to load on them.
 
hhhmm.. that minidsp is cool looking.. you think that would be overkill for my project? This will be a set it and forget it kinda deal..
 
FWIW...I think this is your choice...change the jumpers, listen, change the jumpers etc...Like the fact that it's passive and transparent as well.

PFMOD LP-1 low pass adjustable crossover. By removing factory jumpers in the you can select 42hz to 200hz in 16 points at 18 db per octave. The LP-1 has two input channels and two bypass output channels in addition to the mono-mixed low pass outputs. Passive device so there is no noise or distortion (transparent to your system).
 
Yeah, I like the fact it's passive and not active. One less point to be injecting electrical noise. And the part about being adjustable is the biggest selling point to me. I gotta thank Ray for turning me onto the fmod that caused me to search that word and find this.

Which got me to thinking about the port for this... being adjustable... that way, I can also tune it to what ever other speakers I may one day use with them... so here's my idea...

Cut the port slot large enough so that it's tuned say around 30hz, then take like a 1/4" piece of ply and slot it, and then use wing nuts on bolts to tighten and loosen it on the outside of the front baffle (or I could put it inside with a nice knob to move it with...) , and be able to slide it to close up the port to drop the tuning lower....

Waddaya think?
 
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You could make the baffle in two pieces, one of them accommodating the slot. Make the slot-baffle removable for easy adjustment of dimension of the slot or lengthening the port. If you dado in a gasket material on the periphery of the slot-baffle or on the cabinet, it will seal tight.

Too bad the Shiva isn't for sale anymore (at least I can't find a source). I think 3.0 cu. ft. is ideal for it. What are you going to be pushing these subs with, Simi?
 
similost said:
Yeah, I like the fact it's passive and not active. One less point to be injecting electrical noise. And the part about being adjustable is the biggest selling point to me. I gotta thank Ray for turning me onto the fmod that caused me to search that word and find this.

Which got me to thinking about the port for this... being adjustable... that way, I can also tune it to what ever other speakers I may one day use with them... so here's my idea...

Cut the port slot large enough so that it's tuned say around 30hz, then take like a 1/4" piece of ply and slot it, and then use wing nuts on bolts to tighten and loosen it on the outside of the front baffle (or I could put it inside with a nice knob to move it with...) , and be able to slide it to close up the port to drop the tuning lower....

Waddaya think?
Click to expand...

Sounds good but, I would worry about a 30hz note and a 1/4" piece of ply getting the pulp rattled out of it....:scratch2: 1/2" maybe :scratch2:
 
Yeah.. 1/2"... I kinda forget subs rattle stuff apart... Not used to using a true sub, (much less two) but after hearing my brother's cheaper sub last weekend... :thmbsp:.....

I knew.... it had to be done... :screwy:

Oh.. and OK.. 25hz on the slot? Could also allow me to use different drivers later if I want. I think that would be the highest I'd ever want to go on the Fs of a driver..

Which reminds me.. been shopping drivers all day, and I can't seem to find many 12" sub drivers that are much over 87db without starting to drop a huge pile of cash, that also has an Fs below 21. I'm kinda finding drivers with the specs of this GR driver are fairly far apart, especially at this price point... We'll see... I can always upgrade if I make a tunable slot..
 
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Those GR drivers look like they offer a nice price/performance ratio. Can't wait to hear about your impressions of them.
 
Pretty much what I was thinking Kyle, but then I keep thinking about the 200w part, and it being mentioned it's 85db.... and knowing me...... ... Genies appear..

So I keep thinking back to this LAB-12 driver... The sensitivity is 89db, and the Fs is only 4 hz higher than the GR driver, and it handles twice the wattage...

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=290-570

Oh man.. what to do, what to do. Not a whole lot more money, and I think they would perform very similar... Tune the box to say like 24hz or so...

Any feedback on this much appreciated... because I'd like to order what ever I'm gonna order today.
 
Do you have a way to dial in some bass boost near Fs? More power capacity and higher efficiency just might work better than a slightly lower Fs.
 
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