Easy-to-Build 20Hz Subwoofers for Medium Size Room - diyAudio
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Old 30th April 2013, 05:50 PM   #1
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Default Easy-to-Build 20Hz Subwoofers for Medium Size Room

Howdy Experts,

I would like to create an extraordinary movie-watching experience for my family in their approximately 25 x 15 foot media room. At this point, I'm considering building a couple line arrays for the front speakers while repurposing the rear ceiling speakers with better drivers. This room has a vaulted ceiling and a carpeted floor. The TV will be placed on one of the short sides of the room.

What type of subwoofers would you recommend that I build if I would like 20hz or better bass extension. I could build two and place them in the two corners next to the TV. Size is not a big issue since this is a dedicated media room. I was dreaming of building a tapped horn for each corner but I am completely open to any design as long as it is relatively easy to assemble and can reach 20hz or less. I am tentatively working with a budget of $1000 for both.

Edit: 12" or 15" drivers are what I am aiming for. There is 3.5'- 4' on each side of the TV cabinet for subwoofers.

Thanks!
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Last edited by techbiker; 30th April 2013 at 06:26 PM.
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Old 30th April 2013, 05:55 PM   #2
AndrewT is offline AndrewT  Scotland
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A 4" driver when built into the correct box with the correct EQ will reproduce 20Hz. But it will be so quiet that you can't hear it.
A 15" or 18" driver built to the same standard can give so much bass it drives you out of the room.

Look at the fletcher Munson curves and the graph of SPL vs Sd*Xmax and select your desired speaker Vd (Sd*Xmax).
Then design your box/open baffle/infinite baffle with the appropriate EQ and you are done.

You want us to tell you the answer !

The budget just went up from $900 to $1000 !
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Last edited by AndrewT; 30th April 2013 at 06:01 PM.
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Old 30th April 2013, 05:56 PM   #3
zobsky is offline zobsky  India
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Initial thoughts:
1. Can you work with infinite baffle attic mounted subwoofers ?
2. There's always the tuba HT design that is allegedly deserving of the adjective "extraordinary", if it will fit in the room.

Perhaps a sketch of your room will help other more experienced members offer advice. Where in Texas do you live?
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Old 30th April 2013, 06:06 PM   #4
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AndrewT,

My apologies for not being more specific. I see no problem using a 12"-15" driver in each subwoofer. I would certainly like to use a driver that is 10" or larger for an appropriate SPL. I will check out the fletcher-munson curves again.

Zobsky,

I will get a sketch of the room drawn up by this evening. I live in Plano (north of Dallas). I do not have much of an attic above this room though. The vaulted ceiling is the roof and the garage is directly below.

I have an excess of space though! This is why I'm so excited about this project. I could probably fit 4 Tuba HT's in there (one in each corner of the room) and not feel crowded. At the very least, one at each side of the TV would fit in fine. The TV will be enclosed by a large cabinet and I would love to have large subwoofers to fill in the sides! hehe

If I remember correctly (I'm still away at college for the next week and a half) there is about 4 feet of room on each side of the TV cabinet.

Thanks again
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Last edited by techbiker; 30th April 2013 at 06:13 PM.
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Old 30th April 2013, 07:43 PM   #5
zobsky is offline zobsky  India
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Quote:
Originally Posted by techbiker View Post
AndrewT,

My apologies for not being more specific. I see no problem using a 12"-15" driver in each subwoofer. I would certainly like to use a driver that is 10" or larger for an appropriate SPL. I will check out the fletcher-munson curves again.

Zobsky,

I will get a sketch of the room drawn up by this evening. I live in Plano (north of Dallas). I do not have much of an attic above this room though. The vaulted ceiling is the roof and the garage is directly below.

I have an excess of space though! This is why I'm so excited about this project. I could probably fit 4 Tuba HT's in there (one in each corner of the room) and not feel crowded. At the very least, one at each side of the TV would fit in fine. The TV will be enclosed by a large cabinet and I would love to have large subwoofers to fill in the sides! hehe

If I remember correctly (I'm still away at college for the next week and a half) there is about 4 feet of room on each side of the TV cabinet.

Thanks again
Okay, I live in Plano too, technically. You're welcome to borrow my line arrays and horn loaded table tuba sub / T18 sub if you wish to, before building. You'll need a truck / full size SUV though. Personally, I've given up on conventional subwoofers. If you are serious about building arrays, I can give you enough background information to get started. Likewise with TH
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Last edited by zobsky; 30th April 2013 at 07:48 PM.
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Old 30th April 2013, 07:58 PM   #6
zobsky is offline zobsky  India
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Quote:
Originally Posted by techbiker View Post
AndrewT,

My apologies for not being more specific. I see no problem using a 12"-15" driver in each subwoofer. I would certainly like to use a driver that is 10" or larger for an appropriate SPL. I will check out the fletcher-munson curves again.
Wwhen you start thinking about horns, driver size is less important than you might imagine, except maybe wrt max SPL.
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Old 30th April 2013, 08:14 PM   #7
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Zobsky, thanks very much! I might take you up on your offer.

I recently built two medium size cornu spiral horns with my girlfriend (these use 3" drivers) and their low-end presence definitely surprises. I'm eager to get back to Plano in order to get access to speaker building tools.

This brings up an important question (or at least one of which I have not heard a definitive answer to). Isn't there more in a subwoofer design than simply average/ maximum SPL? I often hear designers discussing distortion levels, etc. Don't larger drivers usually have more of a capacity to "effortlessly" reproduce audio, even in horn applications?

My current understanding is that larger tapped horns using larger drivers are generally able to reach lower. Since space is not a large issue in this application (only time requirements are), I wouldn't mind realizing any benefits of a 15" driver over a 12" driver.
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Last edited by techbiker; 30th April 2013 at 08:23 PM.
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Old 30th April 2013, 08:38 PM   #8
zobsky is offline zobsky  India
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Quote:
Originally Posted by techbiker View Post
Zobsky, thanks very much! I might take you up on your offer.

I recently built two medium size cornu spiral horns with my girlfriend (these use 3" drivers) and their low-end presence definitely surprises. I'm eager to get back to Plano in order to get access to speaker building tools.

This brings up an important question (or at least one of which I have not heard a definitive answer to). Isn't there more in a subwoofer design than simply average/ maximum SPL? I often hear designers discussing distortion levels, etc. Don't larger drivers usually have more of a capacity to "effortlessly" reproduce audio, even in horn applications?

My current understanding is that larger tapped horns using larger drivers are generally able to reach lower. Since space is not a large issue in this application (only time requirements are), I wouldn't mind realizing any benefits of a 15" driver over a 12" driver.

Some of reasons I prefer horn subs:
1. For the same SPL, the driver moves significantly less than a conventional subwoofer, achieving lesser distortion without the need for fancy motors. Horns just sound clean and hit harder than other designs I've built (virtually every thing out there - sealed, ported, push-push ported, aperiodic, open baffle, dipole, transmission line, T-TQWT, ripole). I've heard open baffle subs sound cleaner, but they (at least the ones I built) wimped out at deep bass/higher SPLs.
2. Think of the air plug within the horn as a mass load on the driver, lowering the resonant frequency of the system without having to depend totally on the T/S specs of the raw driver.
3. The air plug also damps the motion of the driver better. Think about striking a bell in air vs striking it underwater.
4. One reason to use smaller drivers is so that you can employ a longer gradual taper from throat to mouth. The longer horn length acts as a quarter / half wave resonator at lower frequencies than a shorter horn using a larger driver might. The end result is deeper bass.
5. I agree that larger drivers can sound somewhat more effortless than smaller drivers, but it's not a black and white truth , rather a range of acceptable grays
6. Larger drivers will work in (large) horns. Just understand that the enclosures can get large. TH are better in that regard as they lie between ported boxes and true horns in efficiency and size and can be built as monoliths that take up relatively little floor space. They do have a more restricted bandwidth than true horns, typically 1.5 - 2 octaves, so keep that in mind. A 20 Hz typically starts getting weird around 60 - 90 Hz. See Tapped Horns


A major criticizm of horn subwoofers is that they sometimes tend to have non linear in room measurements, due to undersized. To this, I say
1. If it sounds good, it is.
2. At low frequencies, there's a lot of interference from room modes. Put a perfectly measuring sub in an average room,measure it and see what the response looks like.
Hope that helps
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Last edited by zobsky; 30th April 2013 at 08:51 PM.
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Old 19th January 2014, 10:43 PM   #9
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Zobsky, I too live in the Plano area. I have a home theater room that is 20'x 18' with 10' ceiling. I have a 5.1 system that consist of M & K speakers all around and the original Sunfire subwoofer. These diy horn subs interest me. I have been reading a post on a different site for a F-20 horn sub. I have just asked how the F-20 (or two) would sound compared to my Sunfire as a reference.

I have need for a sub downstairs in a much reduced 5.0 family room setting and the although the the Sunfire would be overkill it would make my wife happier than even a moderate sized store bought. So in reality I know what the Sunfire sounds like but I am wondering if I can build a decent horn sub or two that would sound better for and if so could you give me some links to your plans/component selections?
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Old 19th January 2014, 11:46 PM   #10
zobsky is offline zobsky  India
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Quote:
Originally Posted by jjjbrim View Post
Zobsky, I too live in the Plano area. I have a home theater room that is 20'x 18' with 10' ceiling. I have a 5.1 system that consist of M & K speakers all around and the original Sunfire subwoofer. These diy horn subs interest me. I have been reading a post on a different site for a F-20 horn sub. I have just asked how the F-20 (or two) would sound compared to my Sunfire as a reference.

I have need for a sub downstairs in a much reduced 5.0 family room setting and the although the the Sunfire would be overkill it would make my wife happier than even a moderate sized store bought. So in reality I know what the Sunfire sounds like but I am wondering if I can build a decent horn sub or two that would sound better for and if so could you give me some links to your plans/component selections?
I can do a bit better than that. I have a " relatively small" tuba T18 that I can loan you so you can get a taste of horn bass . Message me if interested
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