Advice on building a home audio sub....

itzvic

Member
2001-12-11 8:49 am
Hello. I am looking at builing a home audio sub.(subs) I would be using it for music about 90% of the time, but would still like it to be impressive during movies. I am in college, and would like to **** off EVERYONE on my floor during the hours my RA already limited me to using my stereo. (i played it too loud too often, now im allowed only 3 hours, 2 days a week to play my stereo) I currently have 2 audiobahn alum 10's (dual 4 ohm vc) that i had setup in my car for this purpose. I could use those, or take my brothers 4 infinity reference 12's. My choice of drivers is limited, but they both have large xmax and high power handling (11.9mm for the reference and 300 watts, and more xmax and 700rms for the audiobahns.) so i believe they will work well. My audiobahns take 1200 watts from an orion amp right now, no problem. I have read about subwoofer box building software, but have never seen it either, so its no help here. I was wondering what type of boxes would work best, and which drivers would be the best for hard pounding accurate bass. Right now, i will probably power these subs with my mackie pa amp. Its rated at 1400 watts at 4ohm bridged (700 watts x2 at 2ohms), and has an 80htz low pass crossover. I could power either the 2 audiobahns or 4 infinities quite well... I am hoping for some serious spl from these subs, that still sounds good. If anyone has some advice on what type of enclosure to build, what subs to use, or anything else on this matter...please help me out.
Thanks for the time!
-ViC
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Here are the Thiele-Small parameters for the Audiobahn Alum 10 dual voice coil. This is for the 2000 model year. The 2001 model year is very similar.

The specifications are from the following page for the 2000 and 2001 model year:
http://www.audiobahninc.com/index2.htm


Fo (Hz) 24.3
Qms 3.16
Qes 0.43
Qts 0.38
Vas (Liters) 44
Vas (Cubic Feet) 1.5
EBP 57
Revc (2 each @) Ohms 5.6
SPL (1 Watt, 1 Meter) dB 95.6
Xmas (mm) Linear Peak Power 26
Levc (mH) 1.6

I have my recommendations, but I will let Sandro give his first.
 

itzvic

Member
2001-12-11 8:49 am
winISD

Well...i tried out winISD. I am not completly sure how to use the thing but i think i got it all down. According to this program my box volume should be 72.2 l. It should also have a 10 cm wide port that is 42 cm long. This would give me an spl of about 98-100 from 30htz to 120ish, and an spl of 90-98 from 20-30. I am not sure what the group delay of phase plot are. If someone could tell me (or possibly send me a link to somewhere that it does) it might help me figure out the correct way to set this up box. My problem comes in figuring out the liter conversions! I THINK 1ml = 1 cm^3. This means that 72.2l = 72,000cm^3. If i took the cube root of this i get a sqaure box 41.6 cm by 41.6cm by 41.6cm?!?. (and it doesnt seem right!!) How would i set this up if my port is 42cm long? I know i sound like a RETARD, but i cant figure this out! Anyhows... would this setup pound? (if i figure out the right demensions?) Let me know what you think...
Thanks
ViC

in reply to the other post, i have all the tools i would ever need between my dad and i. also, i have some money to build an enclosure... I will probably use MDF so it shouldnt cost too much no matter how much i use. (my dad has expoxy and alot of other misc things i would need) I do not want to get super elaborate to create a box, and since i have 4 more weeks of break i think i could accomplish my goal, especailly becuase i dont care about the way it looks and will leave it spray painted black.
 

itzvic

Member
2001-12-11 8:49 am
Dave, im sorry you live near some ******** that play thier cerwin vega stereo too often for you to bear. Honestly im not a big nuisance. My next door nieghbor was and still is an only child. She has no idea how to deal with anything that aggrivates her. I played my stereo loudish, becuase i always have (not like my two infinity il10's can go that loud anyhow)...and she would come over and tell me to ******* die, call me and ******* and such. Thus, i was limited to my 2 days a week, for 2 hours or whatever crap they decided. Because i am limited, i feel that i will get my revenge and be the nuisance that her prissy self is to me. You know how bad it sucks to be able to listen to your stereo only twice a week?? Even at moderate levels? I think she should know when im listening to it, if it such a big deal to her. I guess the term, EVERYONE was wrong. I only intend to **** off her ok.

-ViC

BTW does it inflate your pathetic ego to come on here and bash someone who is trying to build thier own stereo for thier own listening pleasure? Im sure it does, since you are so pathetic you find it easier to tell off me, who you dont know, then the guy upstairs. Grow some balls, and go yell at that guy so you dont have to come on here and be an ***...thanks.
 

itzvic

Member
2001-12-11 8:49 am
I know it sucks to deal with someone like that, honestly... But this flame war type deal is lame as hell. Anyhow, good luck on the finals... and next sememester build a giant sub and mount it up against the ceiling, then proceed to play bass testers all day long while you go to the library. Im sure they will get the picture after a few hours.
peace
-ViC
 
Sonotube subs can be built with minimal problems. I built one with a Shiva driver, and its easily the best stub I've heard given what it cost me to build.

However, make sure that your driver is suitable for use in the downfiring position, or you will experience cone sag, and eventually ruin the driver. I think that the aluminum cone Audiobahn's shouldnt have that problem, seeing as they are well constructed drivers.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Itzvic:

As a newcomer to speakers, you should be made aware that with ported boxes, you have a wide range of sizes that work well. The "ideal size" that so many programs give you is only one of them.

The bigger the box, the deeper the bass. Each of your speakers will go down to 17 Hz in a 3 cubic foot box or fit into a 3/4 cubic foot box with a cutoff of 34 Hz, and all stops in between. Double the size if you want to fit 2 speakers in one box.

Tell us how big of a box you are willing to tolerate, and we can give advice on the way to go.

Some time ago, a paper was written where the authors checked for the low frequency content available on CD's and videotapes, (this was the '80's). CD's had the lowest frequency sound. Only 5 CD's, they found, had any notes beneath 16 Hz. So 16 Hz is really a goal to go for if you can achieve it, assuming you are willing to tolerate a box that big.
 
thank you for the info keltikwizard, I'll try to say something meaningful!

First, the parameters looks a bit strange, given the VAS and an effective diaphgram diameter of about 8" (classical 'mid-suspension' measure) the calculated mass (Mas) is 163 grams and the sensitivity is 85 dB SpL with 2.83V/1mt
I assumed the parameters are measured on one voice coil, wiring them in parallel we have 3dB more at 2.83V, still far away from the 95dB/1mt declared by the manufacturer.

So said, it looks a well designed speaker for subwoofer use in small enclosures, maybe ideal for car

The best alignment I've found is this one:

- bandpass 6th order (i.e. double reflex ) detuned

box 1
**********
Physical volume Vb1: 37.5 lt
Virtual Volume Vb1 : 41.5lt
Acoustic filler (glasswool, dacron fiber) : on the walls, 3-4 cm thick

Tuning freq. Fb1: 30 Hz
Duct : Diameter : 12 cm
lenght : 83 cm


Box 2
**********
Physical volume Vb2 : 21 lt
Virtual volume vb2 : 23 lt
Acoustic filler : on the walls, 3-4 cm thick like above

Tuning freq: Fb2 52 Hz

Duct : diameter 10 cm (4")
lenght : 31 cm

(I've used an Italian software named Audio for Windows, winISD is very nice to use but you cannot simulate the effect of the acoustic filler on volume and Q factors)

This will give you an spl of about 89 db/1mt 2.83V - 1 col driven, with a lower f-3 of about 30 Hz and an upper f-3 of about 70 Hz
Yes, it is a real subwoofer, don't even talk about mid-bass! anyway, with these parameters the unit is probably a bit 'slow' to properly reproduce percussions and high-speed transients. Just speculations, I never heard this little animal at work.


Tips: Duct lenght problem. Yes, the smaller the enclosure and the lower the frequency the duct are awfully big. One trick is to build them with a rectangular shape (of the same area and lenght of the round one) around the box
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_|_________|

A rule of the thumb in case of big ducts is to assume that 1/3 of their volume contributes to the unit load, and so reduce the box volume accordingly.

Reducing the duct area brings a reduction in lenght too, but also an increase in air speed that will bring turbulence noises; the values I give you are (in my opinion) the smallest 'safe' areas.

bye
sandro