Small room sub tuning - flat vs. smooth roll-off - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 11 Old 07-24-2015, 08:02 PM - Thread Starter
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Small room sub tuning - flat vs. smooth roll-off

Hello!

I’m working on a subwoofer for my office using a Focal 33 V1 driver that I acquired for cheap from a friend. It’ll be used in a small room of about 4 x 2.3 meters (13 x 7.5 feet) with open doors on each of the smaller walls.

This subwoofer will be used exclusively with music at low listening volumes. I don’t need Earth shaking bass. My goal is sound quality and I hate boomy bass.

My question is about the enclosure tuning for this build. All other variables being equal (port velocity, cone excursion, group delay), should I aim for the most flat reproduction, or a smooth and more natural roll-off, expecting that I’ll have some room gain on the lower frequencies? I’m afraid a flat simulated anechoic response will actually sound boomy in room conditions.

To sum up, what would you do?




Option A - deeper and flat response - 54 liters tuned to 26hz (green line)
-3db = 28hz / -6db = 24hz

Option B - natural roll-off like a sealed box - 35 liters tuned to 23hz (orange line)
-3db = 38hz / -6db = 29hz

Option C
- buy a measurement microphone, measure my room and then decide.

Both simulations include a a 20hz 4th order high pass and a 2db boost at 25hz that are built in my plate amp. I’m also using a 100hz low pass filter to integrate with my bookshelves.
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post #2 of 11 Old 07-25-2015, 12:05 AM
 
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Option C. Obviously measurements are better than speculation. Is this a trick question?




From a purely speculative point of view. Something that models nearly flat. So that with room gain you have a rising response into the lower frequencies. You should get room gain starting at about 43hz and below, based on a 13ft max dimension of your room.


Don't forget about Equal-loudness contours. Especially with listening at low volumes. You can see how the contour lines are steeper at low volumes and flatten out at the volume goes up.


Ears are less sensitive to low frequencies than high frequencies.


https://en.wikipedia.org/wiki/Equal-loudness_contour


Try building a couple boxes, it can't take more than part of a day and $20 in materials for something that size.


Why not build sealed?
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post #3 of 11 Old 07-25-2015, 02:55 AM
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the pretty curves will be out the window as soon as you put the sub in your room.


if you have eq capability, the larger cab is better simply because it is more efficient.


boomy bass is almost always a room resonance effect, so again, eq, placement, and absorption will in all likelihood matter more than a big or small cab.
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post #4 of 11 Old 07-25-2015, 05:50 AM - Thread Starter
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Thank you for the feedback, guys.

It's not a trick question at all. I've been reading a lot lately, but nothing trumps real world experience. I cannot understand by looking at the response alone how something will sound.

Getting a measurement mic and building multiple boxes would be a great learning experience. That's what I'll do, ultimately.

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Originally Posted by More is Better View Post
Why not build sealed?
This driver models poorly sealed. F3 of 54hz / F6 of 40hz, including the small EQ bump at 25hz. The small box with lower tuning has a roll off similar of the sealed version, but with more extension. I read some articles by Curt Campbell that support this idea. Seems to be a good compromise, but the port is long, increasing the complexity of the cabinet construction and requiring two elbows to fit.

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if you have eq capability, the larger cab is better simply because it is more efficient.
If I EQ the larger box to have a similar response curve of the smaller box, would they both sound equal? Again, no trick question, just trying to learn from your experience.
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post #5 of 11 Old 07-25-2015, 08:44 AM
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Quote:
Originally Posted by gcaltanetti View Post
If I EQ the larger box to have a similar response curve of the smaller box, would they both sound equal? Again, no trick question, just trying to learn from your experience.

that's pretty much right. but again, those differences are going to be small differences compared to the effect that the room has on your result.

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post #6 of 11 Old 07-25-2015, 09:28 AM - Thread Starter
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Thanks. Data-Bass has an interesting article that corroborates that: Sealed vs Bass Reflex vs Tapped Horn.

I think I'm trapped on the mindset that some subwoofers sound "tight", others "loose". From what I understood so far, those qualities are directly dependent on the in-room frequency response, and not the modeled design itself. (as long as the design has no inherent problems)

I'll probably run this sub with a DSP, so maybe the best idea is aim for the better theoretical frequency response, as a starting point, and use the DSP and room treatments to minimize any problems.
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post #7 of 11 Old 07-26-2015, 04:53 AM
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Definitely get some sort of way to add DSP so that you can fine taylor the in room response and take care of any potential boomyness that the room itself might induce. If you already have the amp, I would suggest either a MiniDsp or perhaps even JRiver. being that this is going to be soley a music setup in your office, I would assume that it might not be practical having a bunch of equipment in there, and I am also assuming that the room already has a computer. So instead of having an AVR or preamp with an outboard DSP unit such as the MiniDsp, a CD player, ect...why not just rip your entire music collection onto your computer, buy a subscription to JRiver, and run the computer straight into your speaker and subwoofer amplifiers! You can get as good or better EQ options in JRiver compared to a MiniDsp, you also will not need an AVR/preamp or a CD Player or a MiniDsp. Therefor giving you better options to fine tune everything and save on clutter. That is what I would do, and is actually what I did for my music setup.

Only other thing that I might suggest is to perhaps add some room treatments, if you can.
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post #8 of 11 Old 07-26-2015, 11:35 AM
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Quote:
Originally Posted by gcaltanetti View Post
I think I'm trapped on the mindset that some subwoofers sound "tight", others "loose". From what I understood so far, those qualities are directly dependent on the in-room frequency response, and not the modeled design itself. (as long as the design has no inherent problems)
"Tight, Loose", such subjective terminology is valid, however your suspicions are partially correct; the FR must be free from significant resonances that result in peaky response. But equally as important is the time domain, as you must damp the energy from ringing. A smooth FR response combined with a well damped time domain behavior, allows for the bass detail and impactful transients to convey the experience of what the artist intended.

From 300Hz or so and below, the room is the overwhelming dominant factor in the reproduction. Coincidentally, below that point is where approx. 90 percent of the energy in a recorded piece exists. Again, owned by the room... it creates massive energy peaks in magnitude, and can easily obscure the subsequent transient detail because of the smearing elicited by the poorly damped energy that doesn’t dissipate quickly enough.

You want tightness and bass detail? Damp the lingering energy.


Yes, there exists theoretical differences between various subwoofer alignments and approaches. But in a well executed/best practices sub of any type or alignment, the room absolutely owns the sound we experience.

That said;
Careful placement and experimentation in placement.
Parametric EQ'ing of resultant peaks (address FR dips via relative phase/distance/placement, not EQ)
LF damping w/bass traps, etc.(for high resolution bass in small rooms, such treatment is vital and almost always hugely impactful, ... I'm talking jaw dropping, "why the hell did I wait so long", stuff)



Best of luck
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post #9 of 11 Old 07-26-2015, 04:56 PM - Thread Starter
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Thank you all for your suggestions.

I think I'll model the subwoofer for the best theoretical model and work on some room treatments. This room is my office first and foremost, but I think it's possible to improve the sound response without making it look like a studio room.

First action will be buying a calibration microphone, probably the UMIK-1, maybe with the individual calibration provided by cross-spectrum.com. This will be a great learning tool, it's actually something that I wanted to invest for a long time. Only after that I'll build the sub. At first it'll be used with a pair of Audioengine A2 speakers that I frankly don't like too much.

End goal is to pair the new sub with DIY bookshelves, something like the Continuum, by Jeff Bagby, or the Speedsters, by Paul Carmody. I want an integrated look, so I'll probably drive those with a plate amp with DSP by MiniDSP or Hypex. This will allow me to keep a clean look and also have DSP control, including the sub output.

Look for my build thread in the next few months.
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post #10 of 11 Old 07-27-2015, 12:27 AM
 
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Sounds like a good plan. For the little bit of extra $ I think its a no brainer to get the mic from CSL if they are available. I even waited a few months for one when I could have got the regular one immediately.
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post #11 of 11 Old 07-27-2015, 05:58 PM
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Quote:
Originally Posted by gcaltanetti View Post
It’ll be used in a small room of about 4 x 2.3 meters (13 x 7.5 feet) with open doors on each of the smaller walls.
The open doors may reduce room gain a bunch.

Noah
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