18SW1P Enclosure questions

[asnn]

Hello guys,

I would like some help with my subwoofer design. I want to build and enclosure for selenium's 18SW1P.

The design attached here uses numbers that i got from selenium's website. According to selenium's calculation, if the sub is in a box with 3 ducts of 13cm and a vb of 300 i should get a F3 of 30hz and a Fb of 34hz.

I am looking for a sub that can go at very low frequencies but still put out a clear bass. So i would like some help double checking this calculations, and maybe even changing the type the box for something that would better suit my needs.

I made the design using Sketchup, and it was my very first attempt using a 3D modelling program, so bear with me.

If you need any more information to help me plz ask!

 

[asnn]

Thiele-Small and other specs

I tried to attache the spec sheet but it was a bit too big.
So here is a bit more information about the Selenium's 18SW1P



SPECIFICATIONS
Nominal diamet er . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460 (18) mm ( i n )
Nominal impedance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 ohms
Mi ni mum impedance @ 106 Hz. . . . . . . . . . . . . . . . . . . . . . . 7.0 ohms
Power handling
Musical program . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 600 watts
AES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 watts
Sensi t i vi t y ( 1W/ 1m) averaged f r o m 80 t o 250 Hz . . . . . . . . . 97 dB S P L
Power compr essi on @ 0 dB ( nom. power) . . . . . . . . . . . . . . 3.3 dB
Power compr essi on @ - 3 dB ( nom. power)/2 . . . . . . . . . . . . 2.8 dB
Power compr essi on @ - 10 dB ( nom. power)/ 10. . . . . . . . . . 0.7 dB
Frequency respons e @ -10 dB . . . . . . . . . . . . . . . . 30 t o 2, 500 Hz

THIELE-SMALL PARAMETERS
Fs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Hz
Vas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 (13. 344) l (ft )
Qt s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.34
Qes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.35
Qms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10. 93
no (half space) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.03 %
Sd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.1194 (185. 07) m (in )
Vd ( S d x Xmax) . . . . . . . . . . . . . . . . . . . . . . . . . 1,134.3 ( 69. 22) c m ( i n )
Xmax (max. excursi on (peak) with 1 0% di st or t i on) . . . 9. 3 ( 0. 37) mm( i n )
Xlim (max. excursi on (peak) bef or e physi cal damage) 25. 0 ( 0. 98) mm( i n )

ADDITIONAL PARAMETERS
bL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20.7 Tmβ
Flux density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.90 T
Voice coil diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 (4) mm ( i n )
Voice coil winding length . . . . . . . . . . . . . . . . . . . . 39.7 ( 130. 3) m (ft)
Wi re t emperature coeffi ci ent of resi stance ( ) . . . . . 0.00372 1/ °Cα 2 5
Maxi mum voice coi l operating t emper at ur e. . . . . . . . 275 ( 527) ° C ( ° F)
vc (max. voi ce coi l operating t emp. / max. power) . . 0.34 ( 0. 66) °C/ W( °F/ W)θ
Hvc ( voi ce coi l wi ndi ng dept h) . . . . . . . . . . . . . . . . . 32.0 ( 1. 26) mm ( i n )
Hag ( a i r gap hei ght ) . . . . . . . . . . . . . . . . . . . . . . . . . 13.5 ( 0. 53) mm ( i n )
Re . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 ohms
Mms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147. 3 (0.325) g (lb)
Cms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198. 6 m/ Nµ
Rms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 k g/s

NON-LINEAR PARAMETERS
Le @ Fs (voi ce c o i l inductance @ Fs) . . . . . . . . . . . . . . 10. 694 mH
Le @ 1 kHz ( voi ce coil i nduct ance @ 1 kHz) . . . . . . . . . . 2. 152 mH
Le @ 20 kHz ( voi ce coil i nduct ance @ 20 kHz) . . . . . . . . 0. 508 mH
Red @ Fs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.77 ohms
Red @ 1 kHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. 88 ohms
Red @ 20 kHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80. 23 ohms
Krm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14. 375 ohms
Kxm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145. 290 mH
Erm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0. 735
Exm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0. 518


ADDITIONAL INFORMATION
Magnet material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Barium ferrite
Magnet weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,440 (120) g ( oz )
Magnet diameter x dept h . . . . . . . . . . . . . . 220 x 24 (8.66 x 0. 95) mm ( i n)
Magnetic assembly weight . . . . . . . . . . . . . . . . . . 11,200 (24. 69) g ( l b)
Frame material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aluminum
Frame finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Black epoxy
Magnet i c assembl y steel f i ni sh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zinc-plated
Voice coil materi al . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flat CCAW
Voice coil former materi al . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fiber glass
Cone mat eri al . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Non pressed long fiber pulp
Volume displaced b y woofer . . . . . . . . . . . . . . . . . . . . 8.6 (0.304) l (ft)
Net weight. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14, 180 (31. 26) g (lb)
Gross weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15, 400 (33. 95) g (lb)
Carton dimensions ( W x D x H) . . . . . . 48 x 48 x 24 (18.9x18.9x9.5) cm (in)

 

[Cal Weldon]

I am looking for a sub that can go at very low frequencies but still put out a clear bass.

Hi asnn,

The Selenium is not a subwoofer as such. It is a sub by PA standards but not hi-fi. You will get clear clean bass but it won't go low as you can see by your calculations.

 

[wg_ski]

From his post in the amps section, I figured he would be using it for PA work, DJ ing, that sort of thing. From the specs, the driver pretty much looks like the PV Lowrider. 30 Hz is pretty low for PA - most of the pro's try to save their backs and live with a lot higher f3.

 

[asnn]

Re: Re: 18SW1P Enclosure questions

The Selenium is not a subwoofer as such. It is a sub by PA standards but not hi-fi. You will get clear clean bass but it won't go low as you can see by your calculations.

I am not planning to use this 18" monster in a Hi-Fi set up. This is meant for PA use. And the calculations, as i said, are not mine they are from selenium's website. The box design was indeed made by me, and i am a little skeptical about a volume of 300 liters. What do you think? Another thing that i am not so sure about is the placement of the ducts. Does it matter where in the box i put them?

From his post in the amps section, I figured he would be using it for PA work, DJ ing, that sort of thing. From the specs, the driver pretty much looks like the PV Lowrider. 30 Hz is pretty low for PA - most of the pro's try to save their backs and live with a lot higher f3.

Thanks for you help here and in the amp section
I am not sure if i should know this by now… but is there a particular reason to stay away from very low frequencies in the PA system?

 

[Cal Weldon]

I use quite a few Selenium pieces and find they are well built and quite rugged. It seems only the tweeters get noticed but the woofers are no slouch. Good bang for the buck.

Stay away from low frequencies as they really suck up the power. By sacrificing the low end you get more volume.

Duct placement is not a huge thing but don't put rear ports right behind the driver.

 

[asnn]

I use quite a few Selenium pieces and find they are well built and quite rugged. It seems only the tweeters get noticed but the woofers are no slouch. Good bang for the buck.

Here in Brazil there are not that many options, Selenium is one of the best if not the best national brand, and bringing from outside the country and paying taxes is out of the question.

Stay away from low frequencies as they really suck up the power. By sacrificing the low end you get more volume.

If that is the only issue i dont mind giving up some volume. I am planning on using this sub to punch along trance tracks, and they are heavily based on sub frequencies.

Duct placement is not a huge thing but don't put rear ports right behind the driver.

So is the design i made a good choice? Will it give me the low frequencies, maybe not as low as i had previously thought, but low enough to make a box this big worth bulding.
If it is not good, i wouldn’t mind hearing that i got it all wrong and should start it all from scratch.

 

[Cal Weldon]

Here in Brazil there are not that many options, Selenium is one of the best if not the best national brand, and bringing from outside the country and paying taxes is out of the question.

I was quite happy to support your economy. I heard good things and was not disappointed

If that is the only issue i dont mind giving up some volume. I am planning on using this sub to punch along trance tracks, and they are heavily based on sub frequencies.[/B]

The issue is the woofer was designed to deliver lotsa sound but won't travel very far so can't deliver low bass. It is very sensitive but there's a trade off. You can't force it to be a subwoofer.

So is the design i made a good choice? Will it give me the low frequencies, maybe not as low as i had previously thought, but low enough to make a box this big worth bulding.
If it is not good, i wouldn’t mind hearing that i got it all wrong and should start it all from scratch. [/B]

I'm not the expert but I wonder if this woofer is going do what you want. It's a chest thumper not a floor rumbler.

 

[wg_ski]

It is a "floor rumbler" compared to a lot of the stuff that's out there. Should be capable of 30 Hz in an EBS-type alignment. The catch is the power handling will drop to about 600W, and that means if you want a lot of output down that low you need more than one. That's where the 'wall of woofers' comes in.


Most of the pro's will state (quite adamantly) that anything below 40 or 50 Hz is a waste. Not in my experience - I usually boost the half octave below 40 to get that shuddering, throbbing bass that breaks down your defenses. Just going from a 40Hz capable system down to 30 with any type of dance music feels like being let out of jail. But threre isn't a whole lot below 30 - the dBx 120A subharmonic synth will only put out tones down to 26 Hz. If you high pass there you won't miss it. Getting below that with any type of PA requires either multiple esoteric drivers with a quarter million watts behind them or a truck full of lab horns.

 

[wg_ski]

Here in Brazil there are not that many options, Selenium is one of the best if not the best national brand, and bringing from outside the country and paying taxes is out of the question.

Selenium:Brazil :: Eminence:USA.

That makes Eminence cheaper here. But they are a bit behind the curve on drivers in the 600 watt and up class, and Selenium has stomped them on compression drivers since the 90's.

 

[asnn]

I am actually very surprised to know people use selenium's in other countries. It might be very ignorant from my part, but if i had the chance to choose from all the brands you guys in America or Europe can choose from, i dont know if selenium would be in the list.

In a couple of days i should be posting a couple of pictures of the box i am bulding.

 

[Cal Weldon]

You are not very kind to your countrymen. Dollar for dollar they got my vote and I had to purchase through PE in the states. Not very patriotic but the Canadian offerings didn't meet my needs.

 

[asnn]

You are not very kind to your countrymen. Dollar for dollar they got my vote and I had to purchase through PE in the states. Not very patriotic but the Canadian offerings didn't meet my needs.

I am acutally very happy to hear that and i am slowly changing my mind about national brands. But it is brazilian nature not to value national products but the deeper i dig in the PA world the more i find out that we do have some very good brands in here.

Now i have a question related to the enclosure i am building. Should i use some kind of damping material inside the box, something like glass fiber or memory foam?
I know in a sealed box damping is essential, but i am not so sure if i should use damping in a vented enclosure.

 

[wg_ski]

Add too much damping and you'll detune the box. Sort of like lowering Qms of the driver. You just want to damp out any higher frequency reflections that might come through the cone or the port and produce high Q peaks or dips. If you cross over low enough, you don't need any in principle because those box modes should be well above the crossover. I just line three sides with fiberglass and call it good on sub or full range cabs.