RL-P18 D2 LLT in a 350-400l enclosure?

[coctostan]

I see that most RL-P18 D2s are in 550-650l enclosures. That is too big for me. What about a 400l sono tuned to ~13.5-14hz? Would this be advisable over a RL-P15 D2 in 300l sono tuned to ~15hz?

My models show the 15 flatter, but more output from the 18 and more extension. Would my room ~3000cu ft room help out?

I really don't know what a good curve should look like. Thanks.

[Bradley]

I am/was somewhat in the same boat as you are... arriving at the conclusion that a 650 liter sonotube wouldn't integrate well into my HT space, and instead looking at box in the neighborhood of 15 ft^3 (425 liters). I looked at a 15" driver solution but ultimately decided on the RL-P18 because of the large advantage it has in displacement, with only a modest increase in cost. The exact tuning frequency seems to be a matter of opinion and preference, assuming you stay within the handful of well established guidelines concerning port length, port air velocity, and cone excursion. At 15 cubit feet, SteveC suggested a 16.5 Hz tune with the RL-P18 D2. You can go lower as long as port length doesn't get too long and raise the specter of a first port resonance less than 190-200 Hz. I don't know that the 3000 cubit foot room will help or hurt. My understanding is that it will have a bit less room gain at low frequences than, say, a 2000 cubic foot room. But I don't know how to measure or quantify that. Either way, the 18" driver will produce ample output and presumably you can use a BFD to EQ it to a fairly flat in-room FR response curve.

Hope that helps.

[coctostan]

So which is better:

RL-P18 - 425 liter - 16.5hz - 8 in dia port

or

RL-P15 - 300 liter - 15hz - 6 in dia port

Obviously the 18 is a little bigger, but that would still be doable for me. I know it won't have the extension of a 600 liter enclosure, but it looks pretty similar to the 15 with more output.

[Scott S]

If youre just making one woofer and SPL is important Id go for the 18. Personally, I wouldnt go that small. I would go for at least 500 liters for the 18 and tune around 14-15hz but thats me. I did two RLp18s each in a 725liter box tuned to 11hz.

[Bradley]

"What Scott said."

If you can swing it, go with the RL-P18. It can move/sweep 6.5 liters of air, compared to about 4 liters for the RL-P15. Here is the transfer function for the two subwoofer alignments as you described:



Above 15 Hz the 18" driver walks away from the 15" handily. At 15Hz the RL-P15 is about done and the RL-18 is dropping off too due to the 16.5 Hz tune (and box size). But one potentially serious problem I see with the 15" plan is the port air velocity. If you feed it 500W, your port air velocity hits 34 m/s which is twice the ideal maximum of 17 m/s (5% the speed of sound).

[Scott S]

Yep! Thanks Bradley for supplying those charts!

The 8" port and bigger box will surely come in handy, especially when considering port speed. If you had the choice Id go with a slightly bigger box and/or a lower tune. At least 14hz (15hz max unless youre a SPL hound) with the 18. *nods*

[WillyD]

Even in the 425liter enclosure I'd drop the tune to 15Hz.

[Blaser]

With only 425 L, I would tune the box to 17-18. This is more reasonable and will be easier to build. Bear in mind that most commercial subs are tuned even higher and still many of them sound very good.
Depth is fine but say 13 Hz is not a priority when using 425 L. You might even be unable to hear a difference between a sub tuned 13 and the other tuned 17 Hz, but there will be a noticeable SPL difference though (in a 3000 cu ft room).

[Blaser]

Max,

Any news? What did you decide? Any pics? Your experience may be useful for people who would like to have RL-P18s but do not want a 600L box...