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Like so many of other peeps here, I am spending WAY more time than I care to admit going back and forth between my last few choices of subs. I’ve narrowed it down to the HSU VTF 3.5 or the Monolith THX 12. Quite honestly, I’m reaching the upper end of my budget with all the other basement finishes I’m currently undertaking, so the difference of $100 to ship the HSU actually means something at this point (especially if something happens and I would need to throw another $100 to return it). Right now I’m planning to start with a high-quality single and almost certainly add a second, matching sub a little bit down the line. Both of these should be available in a year or two, so getting a match shouldn’t be a problem.

ANYWAY... that all being said, I don’t want to go cheap or lack performance (which I don’t think I’ll really do regardless of which I choose). The theater/rec room I’m putting my system in is actually 15’ x 31’ x 8.5’ (3,950 CF). However, the portion of the room that will be used for the actual theater and sound system is only about half of that... perhaps 15’ x 17’, making the volume only around 2,200 CF.

Stupid newb question... do I need to take the ENTIRE volume of the unbroken room into account when making my final decision on a sub or just the portion where I actually plan to be watching movies? My guess is the former but want to make sure.
 

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Tactile response requires pressurization so the entire space matters. A suspended floor will help, as will placing the subs nearfield.

If you're uncertain, consider doing a no-cost, in-home demo with, say, an SVS PB-2000. If you like what it does but feel that you need just a bit more, add another PB-2000 and you're done. If you're seriously underwhelmed, return it and get the HSU or Monolith.
 

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Tactile response requires pressurization so the entire space matters. A suspended floor will help, as will placing the subs nearfield.

If you're uncertain, consider doing a no-cost, in-home demo with, say, an SVS PB-2000. If you like what it does but feel that you need just a bit more, add another PB-2000 and you're done. If you're seriously underwhelmed, return it and get the HSU or Monolith.

I second this. Try a PB-2000 in your space and learn to calibrate it properly. Evaluate all the possible subwoofer locations and document them with REW. Send the PB-2000 back and then come back to this forum. With more data you can get much better suggestions AND you will have a better idea of how much bass you want.
 

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Like so many of other peeps here, I am spending WAY more time than I care to admit going back and forth between my last few choices of subs. I’ve narrowed it down to the HSU VTF 3.5 or the Monolith THX 12. Quite honestly, I’m reaching the upper end of my budget with all the other basement finishes I’m currently undertaking, so the difference of $100 to ship the HSU actually means something at this point (especially if something happens and I would need to throw another $100 to return it). Right now I’m planning to start with a high-quality single and almost certainly add a second, matching sub a little bit down the line. Both of these should be available in a year or two, so getting a match shouldn’t be a problem.

ANYWAY... that all being said, I don’t want to go cheap or lack performance (which I don’t think I’ll really do regardless of which I choose). The theater/rec room I’m putting my system in is actually 15’ x 31’ x 8.5’ (3,950 CF). However, the portion of the room that will be used for the actual theater and sound system is only about half of that... perhaps 15’ x 17’, making the volume only around 2,200 CF.

Stupid newb question... do I need to take the ENTIRE volume of the unbroken room into account when making my final decision on a sub or just the portion where I actually plan to be watching movies? My guess is the former but want to make sure.
Here's a quick lesson on how sound work, for the basic law of Physics.

When it come to your speakers, either the mains or any surrounds one. They only care about the physical distance where they are, to your MLP (Main Listening Position).

On the other hand, due to their lower frequencies. Sub/s try to fill any open space, not just to your MLP. Therefore, in your case you are looking at filling a 3950^3 space.

Since you have a fairly big room, my advise would be to buy for now. The best single sub you can afford for now, without starving your family. And arm yourself with lot's of patience to get another in the future. In this Hobby, patience is your best friend for not ending-up with the "What If" syndrome stuck in your head.

Made the mistake myself many time in the past, of buying just enough. Only to be more costly at the end, and since than. I like to say, "Buy Once and Cry Once" since then:)

By the way, there is no stupid question. Only the ones not ask when in dough, since you do not know what you don't know


Darth
 

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I'm going to be something a voice of dissent here.

The room size will dictate where boundary reinforcement nodes begin. Basically, the resonance node created by the longest dimension so that you get a ~3dB (maybe 6dB, CRS these days) gain per octave below that corner frequency. Larger rooms will inherently not start their boundary reinforcement until a lower frequency. This can present a problem for designs that plan for this reinforcement, depending on what the designer's idea of an average room dimension is.

Otherwise, your SPL will mainly be determined by the distance between the driver and the listener, regardless of frequency. At worst, you'll lose maybe 2-3dB due to "cabin gain" SPL if the same sub were placed in a real 15x17 room versus your 15x31 room with the MLP is 15' in both cases.

When evaluating subwoofers, keep in mind that most manufacturers and independent measurement reviews are using ground plane (ie. outdoor) SPL numbers. You will always get more output when placed in a real room at the same distance.

For example, I have a ~1 ft^3 sealed 12" DIY unit in a 22'x20'x9' living room that's open to a 2 story foyer/staircase/cat walk. My boundary reinforcement works well with the natural low end rolloff of my design (predicted f3 mid 30s) such that I still get good usable output into the mid to low 20Hz range at the MLP about 12'-14' from the sub, which is effectively corner loaded. This is my casual, everyday TV system, not the much smaller dedicated theater room upstairs that has a pair of 4 ft^3 ported subs in it. However, I still can get more than adequate SPL levels from the little sealed sub, even if they're not exactly rock concert level like the dedicated room. IIRC, since I don't have the measurements on this computer, I'm still easily getting low 90+dBs at the in-room listening position, which tracks nicely with the predicted ground plane simulations. YMMV and all that.

In the end, it comes down to *your* performance requirements and expectations. IME, whether we're talking 20Hz, or 6Ghz, your primary measured output is determined by distance. You can increase the measured output by adding walls\ceiling or 8' parabolic dishes as needed. :)

-Brent
 
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