Is there any way around that problem ???, ...bigger port would be to long ???Definitely go for the HO, I'd say. That's too small for a HF in a vented config. A 315HO in 3cuft gross with a 4"x24" or so round port would reach down real low. Would need an HPF and I'd maybe only recommend 300W, as port velocity will be an issue in the low 20s.
Problem is I'm trying to keep the box as close to 3cuft max as possible !:coocoo:For sure. Are you building your own box? If so, then ya you could use a larger port and the gross volume of the box would get bigger. A slot port or multiple round ports would probably be best for 3cuft net.
ya, that's your limiting factor then. The 4x24" port plus sub displacement will come close to .25cuft. That's what I was considering in my first post. Less usable net volume by using a larger port would hurt your lowend extension, but allow you some more power.Problem is I'm trying to keep the box as close to 3cuft max as possible !:coocoo:
Are there 4.5" or 5 " ports that would reduce the velocity enough, without being to long ??ya, that's your limiting factor then. The 4x24" port plus sub displacement will come close to .25cuft. That's what I was considering in my first post. Less usable net volume by using a larger port would hurt your lowend extension, but allow you some more power.
The "HO" has a thicker cone material than the "HF" so would be the more appropriate driver for HT; it takes a lot more punishment before breakup.
You're on the right path with your modeling.
Just trying to figure out how to get (1) 4" PORT for a 3-3.5 net enclosure without port noise ?
Do 5" PORTS exsist ?
that's right.I believe the larger the port size in diameter the longer the port has to be for tuning. I might be wrong though.
Without modeling it to check, I'm not sure if five inch diameter would be enough. If you can wait a couple days I will be able to get to it. A lot of people use PVC pipe instead of the black plastic ports. That, or build in a slot port.
So assuming .4cuft for the port volume, then.
So, RSS315 HO 44, 3.4cuft net, 5x35" round port. Looks good with 300W and assuming the sub amp has a standard HPF @ 17Hz. You could *probably* run 500W without audible problems, but I'd recommend 300W.
Hey Brent , now you know why im so confused,..one says one thing and the other something else.?brent_s said:Just to add my .02 since Randy's been PMing me on another forum about this. I don't get the "HF needs a much larger box" concern. While the Vas of the HF-4 is slightly larger than the HO-44, if needed, one can run the HF-4 ported down to about 2.5 ft^3 and still get very useable 20Hz output at the expense of efficiency. It's still less than 6dB down at 20Hz anehoic; room gain can easily make that flat in room. In the end, Hoffman's in control...low, loud, small; pick 2.
In 3.4 ft^3 tuned to 20Hz with 300 watts, no HPF. My models say the 315HO-44 will have ~1.5dB advantage over the 315HF-4. Above 25Hz, the 315HF-4 pulls away growing to a 2.3dB advantage from 40Hz up. IOW, that extra heavy coil and cone mass start to cost you once the driver efficiency breaks away from being controlled by the enclosure.
Speaking of power, Randy, you haven't said how you plan to power these subs. The HO-44 is a dual 4 ohm driver. You'll either need to present 2 ohms to your amp or you need an amp capable of delivering 300-500 watts into 2/8 ohms. Plate amps don't like 2 ohm loads unless you get into something like the SpeakerPower stuff Seaton uses. A pro amp could do it, but you've got to eliminate the fan noise and provide a HPF solution.
It comes down to a matter of taste, but with typical room gain, I prefer alignments that are 3-4dB down anechoic at 20Hz (unless you're going for single digits). If you're flat/peaked anechoic at 20Hz, you're likely going to have some bloat in room...of course, depending on taste, this "house curve" could be considered a good thing. The HO-44 model shows a peak right above tuning typical of an oversized enclosure. Add a typical HPF, such as the ones used in the BASH300/BASH500 amps and that peak is about 2dB @ 23Hz.
Regarding durability of the HF-4. I've been running a pair of HF-4s in 3.5 ft^3 with a 17Hz tune (measured) in my theater room for several years. No HPF in place, amp's -3dB point is 3Hz. Granted, I don't listen at Reference level, but nothing's caused them to make a bad noise yet. I agree that 300 watts is a better "no worries" number for the HF-4, but with an appropriate HPF, the rising impedance below tuning, and an Xsus of 21mm*, it should be okay with a [email protected] amp as long as one backs off the throttle if something starts to sound strained.
*Since the HO-44 came out years later than the original HF-4/HO-4 drivers and long after the original drivers' designer had left P-E, it's an unknown if the HO-44 shares the same Xsus as the rest of the series.