This is a great resource, study and understand how it applies to your models...
Porting at Subwoofer-Builder.com
I would recommend (as a VERY rough figure) 20 m/s at max output once your high pass filter is taken into account, with flares.
Doouble checked my model and see that I have a predicted peak of about 25 m/s around tuning, powered to xmax, with the highpass filter. Consider that it's a port equivalent to a 7" diameter pipe and it's at 35 hz, that's quite a bit of output. I'm sure there's some port compression and port noise at max output, but with the system going at 110db in room it's not noticeable. I've run tone sweeps at about 6-8mm one way max displacement an noticed no real noise from the port at tuning, that would figure at about 12-15 m/s.
I have not seen a compeling reason to use triangle ports in most designs, the area to parimeter ratio is poor. They are used mainly in PA subs where they have a big box and the port is fairly short, extending only about half the length of one wall. I prefer a slot port of you are going to bring the port the entire length of the wall, since it's easier to make a 90 deg transition on the internal end. Or a large round port if you have tons of space.
Dave,
Should I calculate velocity at x-max even if I don't plan to use that much power? The Dayton HO-15 reaches x-max with 800W input; I only plan on using 300-500 watts. Of course that's RMS not peak.
Thanks,
Evan
Calculations are to be practical and "from practice" at the same time. Calculate what you are going to use. Some purists like the sound from the shuffled air. Máx. used RMS is going to be the limit as, e.g. for the 17m/s. Round over the ends with flares (round ports or squared), for better coupling and less noise. Flare Port Tubes for Speaker Cabinets - Precision Sound Products 
Need to clairify for you on this. The power rating is based on the thermal capacity of the driver, not the xmax. The driver will reach xmax with much less power operating in free air vs. a small sealed box.
300-500W OP already stated if not using more.
Now, what enclosure/tunning are you talking about?! (3.5, 4ft3/27Hz)???
For Dayton Audio RSS390HO-4 15"
Driver is a 800W driver (info) and for Xmax needs ~1200-1500W/4.0 Ohms.
ideal 82.5L/2.9-3ft³
in a 99L/3.5ft³/22Hz
(5% speed of sound ~17 meters/s or 55 feet.s)
10 cm/4" diam. gives a tube length (can make it square if you want) 41.06 cm (41cm = 16 9⁄64in) this are practicable measures and with the power you have (will have) at listening levels (not pro at max. power all the time) I don't see where is the problem, <17m/s @100.7dB for 2xspeakers @3m it's more than fine
Now, what enclosure/tunning are you talking about?! (3.5, 4ft3/27Hz)???
For Dayton Audio RSS390HO-4 15"
Driver is a 800W driver (info) and for Xmax needs ~1200-1500W/4.0 Ohms.
ideal 82.5L/2.9-3ft³
in a 99L/3.5ft³/22Hz
(5% speed of sound ~17 meters/s or 55 feet.s)
10 cm/4" diam. gives a tube length (can make it square if you want) 41.06 cm (41cm = 16 9⁄64in) this are practicable measures and with the power you have (will have) at listening levels (not pro at max. power all the time) I don't see where is the problem, <17m/s @100.7dB for 2xspeakers @3m it's more than fine
Running both drivers up to 100db total, that's what, only +10db per driver ?
+10db is 10 watts.
And yes, 10 watts you can get away with a 4" port.
Lol, I occasionally clip my dual 15's with 300watts rms into 4ohm (crest amplifier).
30 watts is fine, if you never turn it up.................
My 15's are 95db at 8ohm each (running them in parallel).
THIS UNIT HAS BEEN SPECIALLY DESIGNED TO GIVE A CLEAN EXTENDED BASS RESPONSE IN PORTED CABINETS OF APPROX
Yes, you can run a box smaller than ideal.
Here's my formulas.
The Subwoofer DIY Page
The Subwoofer DIY Page - Ported Systems: Box Calculations
Vb = 20*Qts^3.3*Vas
Fb = (Vas/Vb)^0.31*Fs
F3 = (Vas/Vb)^0.44*Fs
dBpeak = 20*LOG(Qts*(Vas/Vb)^0.3/0.4)
where,
Vb = net box volume (litres)
Fb = box resonant frequency (Hz)
F3 = -3dB frequency (Hz)
dBpeak = maximum peak or dip in system response
and
The Subwoofer DIY Page v1.1 - Sealed Systems: Box Calculations
Qr = Qtc/Qts
Vr = Qr^2-1
Vb = Vas/Vr
Fb = Qr*Fs
F3 = Fb*((1/Qtc^2-2+((1/Qtc^2-2)^2+4)^0.5)/2)^0.5
If Qtc>(1/2)^.5
then dBpeak = 20*log(Qtc^2/(Qtc^2-0.25)^0.5)
Else dBpeak = 0
where,
Vb = net box volume (litres)
Fb = box resonant frequency (Hz)
F3 = -3dB frequency (Hz)
dBpeak = maximum peak or dip in system response
If I wanted the most of my 15's, I'd need 8ft3 each for tuning and F3 around 31-33hz, and I'd use a bigger port than the single 4".
But even I compromise, putting both in a single 8ft3 box and tune to 27hz.
And with a single 4" port (for dual 15" with 8mm Xmax), I havn't heard chuffing
If I listen to bass sine waves, I'm sure I'd spot it, but, eh, whatever.
Norman
+10db is 10 watts.
And yes, 10 watts you can get away with a 4" port.
Lol, I occasionally clip my dual 15's with 300watts rms into 4ohm (crest amplifier).
30 watts is fine, if you never turn it up.................
My 15's are 95db at 8ohm each (running them in parallel).
THIS UNIT HAS BEEN SPECIALLY DESIGNED TO GIVE A CLEAN EXTENDED BASS RESPONSE IN PORTED CABINETS OF APPROX
Yes, you can run a box smaller than ideal.
Here's my formulas.
The Subwoofer DIY Page
The Subwoofer DIY Page - Ported Systems: Box Calculations
Vb = 20*Qts^3.3*Vas
Fb = (Vas/Vb)^0.31*Fs
F3 = (Vas/Vb)^0.44*Fs
dBpeak = 20*LOG(Qts*(Vas/Vb)^0.3/0.4)
where,
Vb = net box volume (litres)
Fb = box resonant frequency (Hz)
F3 = -3dB frequency (Hz)
dBpeak = maximum peak or dip in system response
and
The Subwoofer DIY Page v1.1 - Sealed Systems: Box Calculations
Qr = Qtc/Qts
Vr = Qr^2-1
Vb = Vas/Vr
Fb = Qr*Fs
F3 = Fb*((1/Qtc^2-2+((1/Qtc^2-2)^2+4)^0.5)/2)^0.5
If Qtc>(1/2)^.5
then dBpeak = 20*log(Qtc^2/(Qtc^2-0.25)^0.5)
Else dBpeak = 0
where,
Vb = net box volume (litres)
Fb = box resonant frequency (Hz)
F3 = -3dB frequency (Hz)
dBpeak = maximum peak or dip in system response
If I wanted the most of my 15's, I'd need 8ft3 each for tuning and F3 around 31-33hz, and I'd use a bigger port than the single 4".
But even I compromise, putting both in a single 8ft3 box and tune to 27hz.
And with a single 4" port (for dual 15" with 8mm Xmax), I havn't heard chuffing
If I listen to bass sine waves, I'm sure I'd spot it, but, eh, whatever.
Norman
Hi,
I can recommend You the Epic12. It's a truely good driver for small closed casings. I use two of them in a global shaped concrete casing of 60cm OD.
Crossed over at 50 Hz the working range is almost completely below the room modes and the drivers are for most working below their Fb. At such low frequencies the voicecoils Le doesn't matter at all.
At a forst glance it seems that none of the other recommendations took room acoustics into account. At these low frequencies the room functions rather like a pressure chamber with an theoretical increase in SPL of +12dB/oct with decreasing frequency. Below its Fb the drivers show a -12dB/oct decrease.
So room and sub complement each other, resulting in a more constant/linear output level. The efficiency of such a system is quit high, especially the more you place it towards an room edge. Equalization is probabely needed, but to a much lower degree than typical free-field simulations indicate.
Bassreflex on the other hand always leads to a peak in SPL because of the linear behaviour of the driver below its Fb and a -24dB/oct drop below the tuning frequency. Imho thats on of the reasons BR always sucks sonically. It simply doesn't fit room acoustics.
For the Epic: use a small but very stiff casing of a internal volume giving You a Qts of about 0.8-0.85. Use a amplifier of 300-500W and possibility of lowfreq xover of 60Hz or less and the possibility of Eq/of +3 to+6dB and 16-20Hz subsonic and You'll be fine at low effort.
jauu
Calvin
I can recommend You the Epic12. It's a truely good driver for small closed casings. I use two of them in a global shaped concrete casing of 60cm OD.
Crossed over at 50 Hz the working range is almost completely below the room modes and the drivers are for most working below their Fb. At such low frequencies the voicecoils Le doesn't matter at all.
At a forst glance it seems that none of the other recommendations took room acoustics into account. At these low frequencies the room functions rather like a pressure chamber with an theoretical increase in SPL of +12dB/oct with decreasing frequency. Below its Fb the drivers show a -12dB/oct decrease.
So room and sub complement each other, resulting in a more constant/linear output level. The efficiency of such a system is quit high, especially the more you place it towards an room edge. Equalization is probabely needed, but to a much lower degree than typical free-field simulations indicate.
Bassreflex on the other hand always leads to a peak in SPL because of the linear behaviour of the driver below its Fb and a -24dB/oct drop below the tuning frequency. Imho thats on of the reasons BR always sucks sonically. It simply doesn't fit room acoustics.
For the Epic: use a small but very stiff casing of a internal volume giving You a Qts of about 0.8-0.85. Use a amplifier of 300-500W and possibility of lowfreq xover of 60Hz or less and the possibility of Eq/of +3 to+6dB and 16-20Hz subsonic and You'll be fine at low effort.
jauu
Calvin
I was able to model a HO15 in a large box with a low tune and have it hit xmax with about 350w, with a proper high pass filter applied. If you were to operate it in free air, such as in an infinite baffle or dipole sub, it would reach xmax with even less power.
I understand it makes more power but if SQ is the objective, the higher impedance will result in a higher damping factor. There is a point with many amps where it deteriorates to mud.
The Alpine 1522D has a nice flat BL and hits 21hz in a 3.7 cube box tuned to 21. Others have posted that its a great budget $200 sub. I've used it and was pretty impressed. It would be my choice before the Dayton 15 on box size alone. If you're only using 300 or 500watts, you can get away with a 4" port and its efficient being a 15. 20mm Xmax although, I've never been able to bottom it out with an EP4000 on my small liv room system...and I've tried.
Hi,
The voicecoils Re is the parameter, that is responsible for low efficiency.
Also it spoils the damping factor.
For the magnetic drive system only the L of the voicecoil produces driving force.
Seen from the magnetic drive system, the Re is rather part of the output impedance of the amplifier. Calculations taking the Re into account show, that damping factors of the amplifier of more than 10-20 (hence output impedance values below 100mOhm) make hardly any difference.
In fact a lower Re would actually result in higher damping factors as seen from the voicecoil.
The amplifier needs to be capable to drive a low impedance, but then one may think of current driving amplifiers instead of the classical voltage driving amplifier feeding into very low impedance drivers as one can find among some car audio basses with multiple, which may be parallel connected then.
jauu
Calvin
The voicecoils Re is the parameter, that is responsible for low efficiency.
Also it spoils the damping factor.
For the magnetic drive system only the L of the voicecoil produces driving force.
Seen from the magnetic drive system, the Re is rather part of the output impedance of the amplifier. Calculations taking the Re into account show, that damping factors of the amplifier of more than 10-20 (hence output impedance values below 100mOhm) make hardly any difference.
In fact a lower Re would actually result in higher damping factors as seen from the voicecoil.
The amplifier needs to be capable to drive a low impedance, but then one may think of current driving amplifiers instead of the classical voltage driving amplifier feeding into very low impedance drivers as one can find among some car audio basses with multiple, which may be parallel connected then.
jauu
Calvin
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