# Ask..how to calculate end get ideal size box floorstanding

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#### haryojo

Hi..dear all
let me introduce my self...I'm agus from indonesia
I have problem to build the box speaker..

I have sbacoustic driver and want to build the floorstanding speaker. But I dont know how to calculate and get the ideal size and volume of the box. I plan to make the 3 way speaker with that drivers.
For all master audio, help me please to calculate it.
Thanks a lot of.

Driver :
Woofer : SB accoustic 5 inch
Mid Woofer : SB accoustic 4inch

T/S :

1. Woofer 5" SB15NRX C30-4
Nominal Impedance = 4 ohm
DC resistance, Re = 3,1 ohm
Voice coil inductance, Le = 0.12 mH
Effective piston area, Sd = 82 cm2
Voice coil diameter = 30.5 mm
Voice coil height = 15 mm
Air gap height = 5 mm
Linear coil travel (p-p) = 10 mm
Magnetic flux density = 1.0 T
Magnet weight = 0.54 kg
Net weight = 1.48 kg
Free air resonance, Fs = 41 Hz
Sensitivity (2.83 V/1m) = 91 dB
Mechanical Q-factor, Qms = 5.3
Electrical Q-factor, Qes = 0.31
Total Q-factor, Qts = 0.29
Moving mass incl.air, md = 8.6 g
Force factor, Bl = 4.7 tm
Equivalent volume, Vas = 16.7 liters
Compliance, Cms = 1.75 mm/N
Mechanical loss, Rm = 0.42 kg/s
Rated power handling = 50 watt

2. Woofer 4" SB12NRXF25-4
Nominal Impedance = 4 ohm
DC resistance, Re = 3,1 ohm
Voice coil inductance, Le = 0.27 mH
Effective piston area, Sd = 50 cm2
Voice coil diameter = 25.4 mm
Voice coil height = 15 mm
Air gap height = 5 mm
Linear coil travel (p-p) = 10 mm
Magnetic flux density = 0.84 T
Magnet weight = 0.32 kg
Net weight = 0.75 kg
Free air resonance, Fs = 61 Hz
Sensitivity (2.83 V/1m) = 87 dB
Mechanical Q-factor, Qms = 5.3
Electrical Q-factor, Qes = 0.53
Total Q-factor, Qts = 0.48
Moving mass incl.air, md = 5.8 g
Force factor, Bl = 3.6 tm
Equivalent volume, Vas = 4.1 liters
Compliance, Cms = 1.17 mm/N
Mechanical loss, Rm = 0.42 kg/s
Rated power handling = 30 watt

Nominal Impedance = 4 ohm
Nominal impedance [ohm] 4
Voice coil resistance [ohm] 3.0
Nominal power [W] 140
Short term max power [W] 950
Long term max power [W] 400
Operating power [W] 5.3
Sensitivity [dB] 91.5
Frequency range [kHz] 1.5-40
Free air resonance [Hz] 500
Voice coil diameter [mm] 25
Voice coil height [mm] 2.2
Air gap height [mm] 3.2
Voice coil inductance [mH] -
Eff. diaphragm Area [cm²] 5.4
Moving mass [g] 0.30
Magnet weight [g]/[oz] 240/8.5
Force factor [Bl] 2.5
VAS [l] 0.017
Qms 2.50
Qes 0.71
Qts : 0.55

#### chlorofille

Hello Haryojo,

It is very unusual that you use a tiny woofer(5'') for a 3 way. Looks like you are better off building a small 2 way using the 5'' SB midwoofer + Vifa tweeter. The specs of the 5'' midwoofer point to an optimal box of 5 litre bass reflex, port tuned to 50Hz. F3 is 71Hz using a 40mm diameter, 250mm long port.

#### cosmindaniel12

My thoughts exactly. The SB15 has lower distortions in the midrange than the SB12, so you would better build a 2 ways with the sb15 and the Vifa tweeter crossed around 2000-2500 Hz.
I would recommend a 7 liters bass reflex with a 4 cm port, 13-14 cm long. Should get you down to a 60Hz F3. Or a 4 liters sealed, but you'll only get a 100 Hz F3.
If you want a 3 ways floorstander, buy a couple of paper cone 18 cm woofers and add the sb15 and the vifa tweeter. The SB15 doesn't work well in a large enclosure, and the distortions in the bass are greater than most cheap 18 woofers...

#### haryojo

Hello Haryojo,

It is very unusual that you use a tiny woofer(5'') for a 3 way. Looks like you are better off building a small 2 way using the 5'' SB midwoofer + Vifa tweeter. The specs of the 5'' midwoofer point to an optimal box of 5 litre bass reflex, port tuned to 50Hz. F3 is 71Hz using a 40mm diameter, 250mm long port.

You are right..its unusual. at first concept..i plan build the speaker with compotition : dual 5" woofer + 4" midwoofer + vifa tweeter. It cause my room not to large(only 3x3 m). also, what the reason for my choise (floorstanding concept) cause, i hope to get the detail more, i like jazz music or classic. I think your suggestion about 2 way..reasonable.. but i dont understand read of calculating by litre..how about...in HxWxD?

#### haryojo

Distortion

My thoughts exactly. The SB15 has lower distortions in the midrange than the SB12, so you would better build a 2 ways with the sb15 and the Vifa tweeter crossed around 2000-2500 Hz.
I would recommend a 7 liters bass reflex with a 4 cm port, 13-14 cm long. Should get you down to a 60Hz F3. Or a 4 liters sealed, but you'll only get a 100 Hz F3.
If you want a 3 ways floorstander, buy a couple of paper cone 18 cm woofers and add the sb15 and the vifa tweeter. The SB15 doesn't work well in a large enclosure, and the distortions in the bass are greater than most cheap 18 woofers...

dear..cosmindaniel12
what d'you mean of distortion..may be you can show me the effect or the sound character of SB15. Your sugestion for 3 way to buy 18 cm paper cone woofers (it means 7") ...well i don't like "big" size woofer. I plan build the slim box. at first concept..i plan to build in dual 5" woofer+4"+vifa tweeter. Bass not priority then detail..But i don't understand calculating with litre..may be using dimension (HxWxD)...cu

#### chlorofille

Haryojo,

The box size for 7 litre 2 way bass reflex with Vifa tweeter + SB 5'' is :

300mm X 190mm X 208mm (external dimensions, using 18mm thick MDF/plywood)
I suggest you don't go for 3 way as it does not offer any benefit. The difference in clarity between that 4'' and 5'' is very small, and furthermore the 5'' has a higher sensitivity to better match the Vifa tweeter for a 2 way design.

What about the crossover? For a 2 way it can be quite simple, but it will get complex and costly when you design/build a 3 way crossover. Who is going to design the crossover for you?

#### haryojo

Haryojo,

The box size for 7 litre 2 way bass reflex with Vifa tweeter + SB 5'' is :

300mm X 190mm X 208mm (external dimensions, using 18mm thick MDF/plywood)
I suggest you don't go for 3 way as it does not offer any benefit. The difference in clarity between that 4'' and 5'' is very small, and furthermore the 5'' has a higher sensitivity to better match the Vifa tweeter for a 2 way design.

What about the crossover? For a 2 way it can be quite simple, but it will get complex and costly when you design/build a 3 way crossover. Who is going to design the crossover for you?

Well dear chlorofille..
the dimension 300 mm, it means the speaker box category : bookshelf..right?
how about..if the box keep floorstanding (height :75 cm)? it can be?
And the design of crossover? not yet sir. I wish you be helpfull with me...haha
thanks a lot of...

#### cosmindaniel12

dear..cosmindaniel12
what d'you mean of distortion..may be you can show me the effect or the sound character of SB15. Your sugestion for 3 way to buy 18 cm paper cone woofers (it means 7") ...well i don't like "big" size woofer. I plan build the slim box. at first concept..i plan to build in dual 5" woofer+4"+vifa tweeter. Bass not priority then detail..But i don't understand calculating with litre..may be using dimension (HxWxD)...cu

Haryojo... 7 liters mean 0.25 cu ft. Any more than that for each SB15 woofer would make the bass muddy and boomy, due to a greater group delay. The size is calculated using the Thiele-Small parameters of the speaker, from the SB-Acoustics page.

The SB15 has lower distortions because it has a copper cap on pole piece, which the SB12 doesn't have. Distortion measurements here:

Zaph|Audio for the SB15

If you take a look in the comparison chart there (Zaph|Audio) at the SB15 distortion graphs, you'll see that this driver has superb performance between 200-300 Hz up to 3-4 kHz. Used at the base of a 3-way, there are way cheaper drivers with better performance! Used as a midrange, it's one of the best options available!
Plus, as chlorofille mentioned, the SB15 has a better sensitivity.

If you are set on building a 3-ways, choose other woofers, and try to use the SB15 as a midrange.

One more thing, if you are using 2 woofers, pick 2 8 ohms woofers, not the 4 ohms. This way you'll get 4 ohms by using the woofers in parallel.

But if you have no experience in building crossovers, try to stick on a 2-ways (it's A LOT easier to mess up a 3 ways crossover than a 2-ways!!!) or try a proven and tested design.

Last edited:

#### haryojo

2 woofer in paralel

Haryojo... 7 liters mean 0.25 cu ft. Any more than that for each SB15 woofer would make the bass muddy and boomy, due to a greater group delay. The size is calculated using the Thiele-Small parameters of the speaker, from the SB-Acoustics page.

The SB15 has lower distortions because it has a copper cap on pole piece, which the SB12 doesn't have. Distortion measurements here:

Zaph|Audio for the SB15

If you take a look in the comparison chart there (Zaph|Audio) at the SB15 distortion graphs, you'll see that this driver has superb performance between 200-300 Hz up to 3-4 kHz. Used at the base of a 3-way, there are way cheaper drivers with better performance! Used as a midrange, it's one of the best options available!
Plus, as chlorofille mentioned, the SB15 has a better sensitivity.

If you are set on building a 3-ways, choose other woofers, and try to use the SB15 as a midrange.

One more thing, if you are using 2 woofers, pick 2 8 ohms woofers, not the 4 ohms. This way you'll get 4 ohms by using the woofers in parallel.

But if you have no experience in building crossovers, try to stick on a 2-ways (it's A LOT easier to mess up a 3 ways crossover than a 2-ways!!!) or try a proven and tested design.

weel...
may be you right..i have to build in 2 way. But, what about using 2 woofers SB15 8 ohms woofer and set in paralel + tweeter..does it mean 2 way crossover?

#### haryojo

Haryojo... 7 liters mean 0.25 cu ft. Any more than that for each SB15 woofer would make the bass muddy and boomy, due to a greater group delay. The size is calculated using the Thiele-Small parameters of the speaker, from the SB-Acoustics page.

The SB15 has lower distortions because it has a copper cap on pole piece, which the SB12 doesn't have. Distortion measurements here:

Zaph|Audio for the SB15

If you take a look in the comparison chart there (Zaph|Audio) at the SB15 distortion graphs, you'll see that this driver has superb performance between 200-300 Hz up to 3-4 kHz. Used at the base of a 3-way, there are way cheaper drivers with better performance! Used as a midrange, it's one of the best options available!
Plus, as chlorofille mentioned, the SB15 has a better sensitivity.

If you are set on building a 3-ways, choose other woofers, and try to use the SB15 as a midrange.

One more thing, if you are using 2 woofers, pick 2 8 ohms woofers, not the 4 ohms. This way you'll get 4 ohms by using the woofers in parallel.

But if you have no experience in building crossovers, try to stick on a 2-ways (it's A LOT easier to mess up a 3 ways crossover than a 2-ways!!!) or try a proven and tested design.

if you not recomend SB15 in 3 way, what about if I change with woofer SB Acoustics 6" SB17NRX35 for bass, SB 15 for mid and vifa tweeter...

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This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.