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Old 10th October 2007, 08:30 PM   #1
evad is offline evad  United States
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Default Q's about Cubic feet and driver selection

This is an unbelievable forum! I've been reading for a week and haven't gotten out of the sub threads.
Please help me with a few questions. I've selected a 300W BASH amp to mate with a PE RSS315HF 12" driver in a sealed enclosure. Haven't decided on MDF or plywood yet, but leaning toward ply. I've seen several build articles with internal gross volumes of 3 cft., 2.6 cft, and 2 cft.
Am I close on actual correct build volume? Which is best for this application; the 4 ohm or the 8 ohm version of this driver? I'm guessing 4.
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Old 11th October 2007, 07:25 AM   #2
BHTX is offline BHTX  United States
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A good bit of information here, isn't there?

Pretty good choice on the driver selection. I'm looking forward to the slight possibility of using those exact models in the near future, or something similar in the RS line. I have four 15" Ascendant Audio Avalanche subwoofers lying around here (27mm xmax XBL^2 motors), but they're still sitting around here going to waste. I spent a good deal of money on them too, and a great effort trying to obtain them. Since then, several drivers have come out, I've learned more, done more research, and changed my plans and priorities. I guess that's what happens when you wait too long to start a project.

Yes, for that particular BASH amplifier, I'd definitely recommend the 4 ohm version of the RSS315HF...unless you were wanting to run two of these, in which case I'd recommend the 8 ohm version, and a bigger and better amplifier as well. Keep in mind that this plate amplifier doesn't have an LT or EQ of any kind, which really comes in handy with a sealed alignment. Phase switch isn't variable either, which is also something to consider.

With the RSS315HF-4, aim for an internal volume of 2.0 - 2.1 cubic feet (about 56.6 - 59.5 liters) for a Qtc around .7. With that size, Qtc should fall somewhere around .7 and .71. If you plan to use EQ or Linkwitz Transform, keep in mind that the larger the enclosure, the less power required from the amplifier for the system to supply those extra demands at a given output level. In that regard, the larger the better. Without any EQ, it's pretty much just personal preference. A system Q around .70 is usually considered average. Lower system Q's may not seem as loud, but often integrate better with the listening room. As previously mentioned, it all just depends on what you really want.

As for the 8 ohm version of the RSS315, it'll require about another 0.5 cubic feet to obtain the same Qtc and frequency response mentioned in the previous example. Xmax is supposedly reduced a mere 2mm. Fs might be a couple Hz higher, but Qts is also a bit higher as well, hence the slight increase in size requirements. Inductance is also shows to be 1.71mH on the 8 ohm version, up from 0.95mH on the 4 ohm (pretty darn low for this kind of driver).

As for which building material is better, MDF or ply, I often come across debates regarding the subject. I think you'll hear a large portion of the people that are into fullrange/tubes/vintage gear swear on ply or other materials more often than not, and sometimes even advise against using MDF. MDF is easier to cut, however I don't think ply creates all the massive amounts of dust that MDF will. Personally, I honestly don't possess enough experience in this area to make any comparisons between the two, much less give any advise or recommendations regarding my preference.

Anyway, hope this helps. Goodluck with your project. Update and let us know how it goes, and post some good photos!
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Old 11th October 2007, 04:37 PM   #3
evad is offline evad  United States
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Thank you very much for the detailed response. I will post my progress. 1st on the list is the WAF. IE. permission to make a mess.
For clarification, the BASH amp can be sourced from a good Texas company called Oaudio. Their's has a variable phase control. I can also buy a plate amp from another good Texas company called Rythmik. their's has a phase contol and a LT add on.
Am I correct in assuming the suggested 2.0-2.1 cft. is net internal volume? And another .25 cft. wouldn't hurt anything, but it might need some EQ?
I will purchase the 4 ohm driver. And i will build the enclosure with plywood. Mainly because it smells better. Again BHTX thanks for the confidence builder. Y'all come see us, ya hear.
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