Hi to everybody, I want to build a ported box for two subwoofers. The model of subwoofer is KFC-W112S, 12 Inches, 4Ohm, 200W RMS, 800W peak power. You can go here for more information:
Subwoofers • KFC-W112S Specifications • KENWOOD Europe
The datasheet advises (for single subwoofer) 42.5 liters box and a round port (76mm diameter and 178mm length).
Now my target is to build a box for two subwoofers with rectangular port shape (and not circular).
I tried by my self using an online software for that purpose. You can go to this link and have a look:
Subwoofer Box for 12 inch subwoofer | Ported Box | Slot
But I don't knwo if I did well... For example, I don't know what tuning frequency I should choose. Or the port area, on what basis have I to determine it? And the box volume? I chosed 42.5 L x 2 = 85 L. Is that correct?
It would be very helpful to do it by my self with paper and pen and not using a calculator...
Thank you very much!
Subwoofers • KFC-W112S Specifications • KENWOOD Europe
The datasheet advises (for single subwoofer) 42.5 liters box and a round port (76mm diameter and 178mm length).
Now my target is to build a box for two subwoofers with rectangular port shape (and not circular).
I tried by my self using an online software for that purpose. You can go to this link and have a look:
Subwoofer Box for 12 inch subwoofer | Ported Box | Slot
But I don't knwo if I did well... For example, I don't know what tuning frequency I should choose. Or the port area, on what basis have I to determine it? And the box volume? I chosed 42.5 L x 2 = 85 L. Is that correct?
It would be very helpful to do it by my self with paper and pen and not using a calculator...
Thank you very much!
edit: Factory cab is for a vehicle and according to Hornresp it's tuned to ~15.7 Hz plus its vent is too small, calculating a 25 ms vent mac at only 10 W.
Thank you for your reply!
I want to use this at home... but it can be good also for a car... I think...
You said it is not good? You intend the advised model by the constructor?
I want to use this at home... but it can be good also for a car... I think...
You said it is not good? You intend the advised model by the constructor?
Again, factory tuning sims ~15.7 Hz to blend to a car's high amplitude cabin [room] gain.
Correct, 2x driver = 2x box volume [Vb] = 85 L/3 ft^3 net and 2x vents [or one big one] required = 2x [7.6^2*pi/4] = 90.7292 cm^2/14.063"^2 to match the factory cab alignment.
Again, the factory vent is undersized, presumably to 'choke' the driver around/at tuning to increasing power handling, not something normally none in HIFI/HT/pro apps, so need to find the vent area [Av] that at max usable power will have a vent mach [speed] of < ~17 m/s, which as a general rule requires 1/4 - 1/2 the driver's piston area [Sd] depending on how high its [Xmax] power handling is.
So using in between = ~ 1/3x [480*2] = ~316.8 cm^2/49.12"^2 Vs your 300 cm^2/46.5"^2
As a general rule a driver used for other than a mobile audio app shouldn't be tuned < ~ a half octave [0.707x] Fs = 28*0.707 = 19.8 Hz, so considered to be too low for HIFI/HT apps unless horn loaded or used in multiples to handle the power required.
Regardless, HR sims your design as very underdamped [~ +6 dB/2.0 Qt/80 Hz], ~47.3 Hz tuning [Fb], so while the high Qt makes for a lot of mid-bass 'thump'/'punch', it's high tuning makes it not suitable for a mobile app AFAIK, though this tuning will be somewhat lower due to me using just a single 300 cm^2 straight pipe, but still well above the desired < Fs tuning.
Not an alignment I'd want for HIFI/HT, but know from experience there's quite a few folks around the world that are happy with such alignments, so your call.
Power wise, it sims as being able to handle 200W with a low ~10 m/s vent mach, so did a fine job of it in this respect. 😉
For a HIFI/HT app, I recommend a ~338 L/~23.8 Hz [max flat] or ~19.8 Hz with dual 12.7 cm/5" dia. or slot equivalent to get good output down to ~20 Hz, though with only ~40 W max power below ~60 Hz due to such a low Xmax, so of course best output is in a corner for HT LFE.
Thank you very much! I have learned a lot of things!
The sound quality is a target for me... I want it loud, but also good. This is the reason for what I am spending a lot of time in studying this.
I have also used another software (WinISD, what do you think about this one?), and it gave me a volume value around 330 liters and a tuning frequency near 24 Hz.
But, sice the calculated value of volume was very high compared to the constructor one (85 liters vs 330 liters), and actually it is 😱😀, I thought there was a mistake in one of the declared parameters...
I understood very well what regards ports area, except how this is related to Xmax. I can assume that the higher is the Xmax, the higher should be the port area... but which is the law that relate them together?
I have read somewhere that is good practice to choose a tuning frequency between plus and minus 10% of Fs. So, in my case, it will be from 25.2 to 30.8 Hz. It is true?
Thank you again 🙂
The sound quality is a target for me... I want it loud, but also good. This is the reason for what I am spending a lot of time in studying this.
I have also used another software (WinISD, what do you think about this one?), and it gave me a volume value around 330 liters and a tuning frequency near 24 Hz.
But, sice the calculated value of volume was very high compared to the constructor one (85 liters vs 330 liters), and actually it is 😱😀, I thought there was a mistake in one of the declared parameters...
I understood very well what regards ports area, except how this is related to Xmax. I can assume that the higher is the Xmax, the higher should be the port area... but which is the law that relate them together?
I have read somewhere that is good practice to choose a tuning frequency between plus and minus 10% of Fs. So, in my case, it will be from 25.2 to 30.8 Hz. It is true?
Thank you again 🙂
You're welcome!
There are several different basic T/S theory design routines; FWIW I use the Margolis-Small's HP 67/97 & 41C calculator program for max flat [default] alignments out of several decades of habit as opposed to computer software: AES E-Library » Personal Calculator Programs for Approximate Vented-Box and Closed-Box Loudspeaker System Design
net volume [Vb] [L] = 20*Vas*Qts'^3.3
box tuning [Fb] [Hz] = 0.42*Fs*Qts'^-0.96
Before joining the WWW, more advanced computer software available at affordable prices, I used its vent formulas:
dv min. [cm] = [[20*Vd^0.5]/Fb^0.25]/10
Vd [cm] = [Sd * Xmax/10]
L' = 2350/[Fb^2*Vb]
lv [mm] = [L'*dv^2] - [0.73*dv]
dv [mm] = 10*[-85 + [0.85^2 + [4*L'*lv]]^0.5]/[2*L']
Qts' = Qts + any added series resistance [Rs]: Calculate new Qts with Series Resistor
WinISD's box alignment is close to mine, so probably uses the same math since my sim has some extra series resistance for wiring that makes mine a little bigger, tuned a little lower.
Correct.
Not sure what 'law' you're referring to, but assume the vent math answers it.
Can't recall seeing/hearing this 10% rule-of-thumb [ROT], just know from long experience that it will severely limit one's driver options for a given desired alignment.
Typically no upper limit, just a ~ 1/2 octave [0.707x] below it, but it really depends on box, room loading and of course Xmax.
Nowadays it's not uncommon to tune down to Fs/2 for some HIFI/HT apps.
OK, the 338 L alignment in theory gets you whatever SQ the driver's specs, construction can do, but even duals doesn't have enough efficiency and/or Xmax to go 'loud', at least by mine [>120 dB/listening position = [4] more drivers] or even THX's lower reference [115 dB/listening position = [2] more].
Put your two in a well constructed [rigid/massive] corner though and now it's ~115 dB/m at only 20 W [Xmax], though in theory it will drop 6 dB/doubling distance, so -6 dB/2 m, -12 dB/4 m, etc., to the listening position.
Thank you all for your replies 🙂
One thing I don't understand very well is why I need a so large volume, about 160L for one subwoofer, even if it isn't very powerful... Does the RMS power deal with volume value? I can assume that the more is the power, the more should be the volume, because of a larger airflow... Is this true?
In some videos I have seen powerful subwoofers (1000 - 2500 WRMS) with a relatively small box... I am not sure, but by my eye I can assume, for example, 100L for one of them... So, I don't understand why I need about 330L for two subwoofers and 400W RMS... Which is my mistake?
One thing I don't understand very well is why I need a so large volume, about 160L for one subwoofer, even if it isn't very powerful... Does the RMS power deal with volume value? I can assume that the more is the power, the more should be the volume, because of a larger airflow... Is this true?
In some videos I have seen powerful subwoofers (1000 - 2500 WRMS) with a relatively small box... I am not sure, but by my eye I can assume, for example, 100L for one of them... So, I don't understand why I need about 330L for two subwoofers and 400W RMS... Which is my mistake?
You're welcome!
Well, going back to my earlier post and looking at the box math: Building a ported box for two subwoofer
Notice that until [Vas] gets quite large or its effective motor thrength [Qts'] gets quite small [very powerful] it's the [Qts'] that dominates.
From this it becomes obvious that as the motor weakens [higher Qts'], the larger the box's [Vb] acoustic mass [restoring 'spring'] must be to allow the driver to accurately track the signal and if [Vas] is large, then [Vb] typically runs into the 10s of ft^3/100s of liters for just one speaker.
Need two, then 2x [Vb], 2x vent or make one big one with the same total area [Av] and adjust vent length as required due to differing pipe end corrections.
From this it's also obvious that power handling per se has nothing to do with box size/tuning, so no.
Where higher power comes into play is that as [Xmax] rises, so goes the vent size to offset the cab's increasing pressure with increasing [Xmax] on the vent's open pipe 1/2 WL resonances, which in turn increases box size unless it's external, such as using the vent as a pole for a speaker riser/stand: Resonances of open air columns
Well, going back to my earlier post and looking at the box math: Building a ported box for two subwoofer
Notice that until [Vas] gets quite large or its effective motor thrength [Qts'] gets quite small [very powerful] it's the [Qts'] that dominates.
From this it becomes obvious that as the motor weakens [higher Qts'], the larger the box's [Vb] acoustic mass [restoring 'spring'] must be to allow the driver to accurately track the signal and if [Vas] is large, then [Vb] typically runs into the 10s of ft^3/100s of liters for just one speaker.
Need two, then 2x [Vb], 2x vent or make one big one with the same total area [Av] and adjust vent length as required due to differing pipe end corrections.
From this it's also obvious that power handling per se has nothing to do with box size/tuning, so no.
Where higher power comes into play is that as [Xmax] rises, so goes the vent size to offset the cab's increasing pressure with increasing [Xmax] on the vent's open pipe 1/2 WL resonances, which in turn increases box size unless it's external, such as using the vent as a pole for a speaker riser/stand: Resonances of open air columns
Hoffman's Law = small, loud, and low...pick 2.
You want a high powered small loud box, then it won't play low in a 2 Pi space.
T-TQWT = small and low for a TH.
You want a high powered small loud box, then it won't play low in a 2 Pi space.
T-TQWT = small and low for a TH.