Terrible Idea II - Boy was I dumb - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 46 Old 08-12-2019, 07:48 AM - Thread Starter
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Subwoofer in crawl space delivering sound to patio

Last year I had an idea of using a single sub for all sorts of purposes and went through loads of gyrations to see if I could make something work. In the end, I did nothing of the sort.
To revisit my old thread and see naivety at work: https://www.avsforum.com/forum/155-d...i-am-sure.html

The 10" driver I had was used in a single sealed cabinet for several months then retired when I built these for the living room (the dual 12" cabinets attached). I am still applying finish, thus they are a bit of a mess in these photos.

Quite a bit has happened over the past year.
Bought a NAD C658 DAC with Dirac - thus have resolved my desires for DRC.
Built those subs, which are ridiculously powerful for my use.

The big development, started working on outdoor theater on the patio.
We just bought a small projector and a cheap 10' diagonal projection screen to test viability and my wife is hooked. The ability to watch 3d movies while roasting marshmallows is a big hit. She has totally bought into the idea of setting up surround sound back there too.

The plan for next year (thus homework now).
- Install two poles to hold a 15' diagonal screen. The poles will be installed above the retaining wall; the poles and screen will be removable - This is have no problem with, at all.
- Buy five outdoor speakers for basic surround setup. These will have to be under $200 a pair (she bought into it but $1000 on outdoor speakers is a NO GO). I am considering something from OSD Acoustics. Simple sealed boxes.

Why I am posting this?
Under the sliding glass doors (which will go away soon) is a conditioned crawl space (the photo is about some insurance work, ignore the red oval).
I would like to build a cabinet in the crawl space that will feed through the wall to the patio.
Initial thought is a band pass cabinet where the ports are extended out of the cabinet through the wall. I could use plugs to close them off when not in use.

Needs:
I do not need extreme volume - as you can see I have neighbors close by.
I really do not need to hit below 40hz. In fact, 30hz is about as low as I would like to go; I am not trying to create a THX experience, just a nice experience.
Would like to keep the driver cost below $400 total (1, 2, or 4 drivers would need to come in around $400 total).
Amplification will be resolved in the future.

I am open to suggestions and ridicule.
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post #2 of 46 Old 08-12-2019, 04:03 PM
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A more descriptive title would likely get you more help.

Anyway, I like the bandpass idea.

Your SPL and freq requirements should make this a straightforward project.

Sounds like the much-discussed and affordable 12" JBL's would work, though BP boxes can be tricky due to sensitivity to parameter values.

It's not clear what exactly need help with.

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post #3 of 46 Old 08-12-2019, 04:30 PM - Thread Starter
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You are correct, horrible title - I'll update it after this response.

Where do I need help?
- I have very little knowledge of drivers, driver selection, or design parameters for a complex cabinet.
- Is bandpass really the best application or are there other designs to consider that would be easier to execute?
- I initially thought some sort of manifold (two drivers feeding a chamber ported through the wall) type setup would be good but fear a large cutout would be required in the crawlspace wall; I would like to keep the cutout under 192 square inches.

What are reasonable drivers for this project? I assume aluminum or CF with rubber surround due to changing seasons.
What are reasonable driver parameters for bandpass?
Are there any drivers known for use in bandpass cabinets?
1x18", 2x15" or 2x12" reasonable?

I assume, if the design calls for a 12" long 4" diameter port - and that port is on the exterior of the front chamber, I should subtract the volume of the port from the front chamber?
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post #4 of 46 Old 08-12-2019, 06:07 PM
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I'm surprised they haven't complained of the noise yet.

Do you never get any wind there or only setup the screen during movie-night?

In any case, I'd probably go with a pair of PA-460's ported to 30hz and place them directly behind your seating.
That's the only way to get sufficient bass without killing the bank or frying small animals at a distance.
Those drivers are so efficient that amplification could literally be anything, but an nu1000dsp is the best match (parallel 4-ohms).
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post #5 of 46 Old 08-12-2019, 08:06 PM - Thread Starter
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Currently using my Elac UB5 for sound - hauling them in and out each night. My neighbors seem to live with their blinds closed and air conditioning on; so far no complaints. I've even asked them and they are fine. Obviously, no bass from the Elacs.

It takes less than 15 minutes to completely setup the screen. In total, about 40 minutes to have everything completely dialed in. I can put it all away in roughly 15 minutes. Next year I will have something better for the screen setup and the speakers will all be installed.

The crawlspace is directly behind the seating area, so that is covered.

I like the $90 speaker, but would they work in some sort of Bandpass cabinet?

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post #6 of 46 Old 08-13-2019, 07:08 AM - Thread Starter
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If I could I would delete this thread and start over. I should be more to the point in the future.
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post #7 of 46 Old 08-13-2019, 07:31 AM
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I have to say I am having a hard time discerning exactly what it is you are trying to do. What is the exact budget? What are the exact dimensions of this crawl space? Are we building a sub or mains speakers?
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post #8 of 46 Old 08-13-2019, 08:30 AM - Thread Starter
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Quote:
Originally Posted by buggers View Post
I have to say I am having a hard time discerning exactly what it is you are trying to do. What is the exact budget? What are the exact dimensions of this crawl space? Are we building a sub or mains speakers?
Thus, I would love to delete this thread and start over.

Location information:
- Patio is located at the back of the house where I have an addition.
- The addition has a large crawlspace with concrete floor and considered a "conditioned space" (it gets some heat and AC in the space).
- The crawlspace is 12'x24' with 40" high ceiling (quite roomy).
- I do have neighbors roughly 15' either side of my house. For this reason I would like to limit the sub to 30hz and above - actually 40hz+ would be just fine, I am sure.

Parameters
- I would like a sub located in the crawlspace to deliver sound to the patio through the crawlspace wall.
- I would prefer not to cut 18" holes in the walls.
- I imagine a 4th order bandpass cabinet may be a good fit; the wall penetrations would be limited to the diameter of the ports.
- As noted above I have neighbors, no need to reach 130db at 35hz. Though, I would like to some headroom to protect the drivers from extreme dynamics.
- I imagine crossing over to the sub somewhere between 60-80hz.
- I am not trying to create a high fidelity THX experience, just want something decent with a bit of bottom end.

I am open to:
- single or multiple cabinets.
- single or multiple drivers per cabinet.
- 12", 15" or 18" drivers.
- I mentioned 4th order band pass but open to other ideas so long as it does not result in a large hole in the wall or placing cabinets on the patio.
- If possible I would like to limit the cost of drivers to $400 total, $500 may be something I could swing.


I initially thought of some sort of manifold IB cabinet but figured that would require something like a 10"x17" hole in the wall.

I am totally open to suggestions and would be wildly appreciative of somebody leading me by the nose through the process.
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post #9 of 46 Old 08-13-2019, 09:54 AM
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Quote:
Originally Posted by iH8usrnames View Post
... I would like to limit the sub to 30hz and above - actually 40hz+ would be just fine, I am sure.

In that case, why not save yourself a lot of trouble and get some PA speakers for L and R.

Noah
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post #10 of 46 Old 08-13-2019, 10:50 AM
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post #11 of 46 Old 08-13-2019, 11:10 AM
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Although 21" is all the rage, I believe the PA modeled pretty good in the Devastator. Have you checked that thread? I'd opt away from all of the others since they'd be larger and lower tuned.

I'm pretty sure this exact application was the intended use in the first place.
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post #12 of 46 Old 08-13-2019, 11:20 AM - Thread Starter
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Quote:
Originally Posted by noah katz View Post
In that case, why not save yourself a lot of trouble and get some PA speakers for L and R.
I am 50 years old and have no desire to haul out big stupid speakers and run 120v and audio cables to them when I want to watch a movie.

This has happened several times now, I come with a specific question and I get responses that has NOTHING to do with the question.
I already specified I am going to install small sealed all weather speakers, so how is suggesting five large PA speakers even in the ball park of my question?
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post #13 of 46 Old 08-13-2019, 11:27 AM - Thread Starter
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Quote:
Originally Posted by notfastenough View Post
Although 21" is all the rage, I believe the PA modeled pretty good in the Devastator. Have you checked that thread? I'd opt away from all of the others since they'd be larger and lower tuned.

I'm pretty sure this exact application was the intended use in the first place.
Are you referring to the PA 460? I fiddled with that in WinISD for a few minutes but nothing extensive.

I am not aware of the "Devastator". I will look for it.
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post #14 of 46 Old 08-13-2019, 01:04 PM
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Quote:
Originally Posted by iH8usrnames View Post
I already specified I am going to install small sealed all weather speakers, so how is suggesting five large PA speakers even in the ball park of my question?

You're also having some trouble reading; I suggested PA only for L/R, which saves you a lot of time and expense not dealing with subs, but I take your point.

For your requirements they may not need to be that big, but I guess you want to keep them very small?

Another benefit of PA is that the directivity will keep the sound more contained, and require less bass because it will be closer to the listening area.

Noah
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post #15 of 46 Old 08-13-2019, 02:21 PM
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Quote:
Originally Posted by iH8usrnames View Post
Are you referring to the PA 460? I fiddled with that in WinISD for a few minutes but nothing extensive.

I am not aware of the "Devastator". I will look for it.
And honestly, if you're not looking for oodles of output, you could probably scale it down to a 15" Dayton PA driver. However, it would require being modeled again in Hornresp/WINisd and the layout redone accordingly.
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post #16 of 46 Old 08-13-2019, 02:48 PM - Thread Starter
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I just worked over the PA460 again and it is extremely promising, and cheap.

I am not against having the ability to create obscene bass, its not my motivation. The way I see it, if the cabinet can produce 115db and I never use it over 100db, that is a safety margin.

I will see how the 12 and 15" drivers model later tonight.

Screen caps from WinISD included.
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post #17 of 46 Old 08-13-2019, 02:51 PM - Thread Starter
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Quote:
Originally Posted by noah katz View Post
You're also having some trouble reading; I suggested PA only for L/R, which saves you a lot of time and expense not dealing with subs, but I take your point.

For your requirements they may not need to be that big, but I guess you want to keep them very small?

Another benefit of PA is that the directivity will keep the sound more contained, and require less bass because it will be closer to the listening area.
I stand correct, you did specify L&R. either way, I am not interested in hauling big boxes around. I would like this to be as simple to use as possible so my wife does not need me to set everything up each time. Everything will be hardwired in place 24x7.

Also, I apologize. Work has been a melt down today and I have a bit of misdirected anger. FYI, never use AT&T for MPLS; our circuit has been down all day and we've been getting the run around with them.
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post #18 of 46 Old 08-13-2019, 05:48 PM
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I would not use the PA-460 in a bandpass box.
In fact I wouldn't use bandpass at all... they tend to have horrible sound quality.

Just stick with ported, the PA-460 can be ran up to 300hz.
Mid-bass is 50-300hz, which is the frequencies you "feel in your chest".
<30hz is for earthquake simulations, which won't be very possible on dirt or concrete (2nd-story floors made of plywood is a different story.)

99% of music and movies is >30hz. Rock/Metal/Pop/Dance/Country/Classical/Techno/Explosions/Cat Scares/etc
A 30hz ported box should be plenty...
100db is cop-calling levels for most people (and 115db definitely would be....)

That said, SPL drops 6db per doubling of distance, so you lose about ~10db in the first ~10ft, and you'd be down -16db at 20ft etc.
That's why you want the subs to be as close to your seat as reasonably-possible, same for the LCR's but you must maintain some of that "big screen" sound which only happens with distance and big/efficient speakers.

A normal cinema that seats 200 people often has 10-50kW and all the speakers are big PA floorstanders, obviously that is overkill for your situation.
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post #19 of 46 Old 08-13-2019, 06:09 PM
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Quote:
Originally Posted by iH8usrnames View Post
I have a bit of misdirected anger. FYI, never use AT&T for MPLS; our circuit has been down all day and we've been getting the run around with them.
I guess we are fairly lucky where I work, their internet is within the same optical cable as the inter-city 911 service, a dedicated strand all the way back to the ISP's main data center, which has UPS's and generators. (and so do we).

I don't ever recall it having any downtime for years now, but if it ever has it was sub-second only.
and in case the physical wire gets cut, it automatically switches to wireless air-fiber. Fancy pants stuff batman...
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post #20 of 46 Old 08-13-2019, 06:45 PM - Thread Starter
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I guess we are fairly lucky where I work, their internet is within the same optical cable as the inter-city 911 service, a dedicated strand all the way back to the ISP's main data center, which has UPS's and generators. (and so do we).
AT&T MPLS circuit lost loads of routes and AT&T being AT&T, it took several hours to even get in contact with the correct department to get help. We would open a ticket and they would reply, "Circuit is up, closing ticket". WTF! IT IS NOT THE CIRCUIT DUMMIES, ITS YOUR ROUTES!
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post #21 of 46 Old 08-13-2019, 07:27 PM - Thread Starter
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Quote:
Originally Posted by BassThatHz View Post
I would not use the PA-460 in a bandpass box.
In fact I wouldn't use bandpass at all... they tend to have horrible sound quality.

Just stick with ported, the PA-460 can be ran up to 300hz.
Mid-bass is 50-300hz, which is the frequencies you "feel in your chest".
<30hz is for earthquake simulations, which won't be very possible on dirt or concrete (2nd-story floors made of plywood is a different story.)

99% of music and movies is >30hz. Rock/Metal/Pop/Dance/Country/Classical/Techno/Explosions/Cat Scares/etc
A 30hz ported box should be plenty...
I really feel like 40hz would be just fine. Right now I am using a pair of Elac UB5's in my family room without a sub and get a disturbing rumble from them and they only go down to 46hz.

I cannot stress enough how much I DO NOT want a sub cabinet on the patio, or under a chair, or under/as table, or under couch.
I intend to have three speakers mounted to the retaining wall and two mounted to the house.
All of them will be white (not wildly intrusive or clashing) with 6.5" drivers in sealed cabinets.

Quote:
100db is cop-calling levels for most people (and 115db definitely would be....)
I cannot say I have ever spent time with a DB meter while listening to music, so I will take your word for it. I believe everyone here gets what I desire, some reasonable low end for music or movies.

Quote:
That said, SPL drops 6db per doubling of distance, so you lose about ~10db in the first ~10ft, and you'd be down -16db at 20ft etc. That's why you want the subs to be as close to your seat as reasonably-possible, same for the LCR's but you must maintain some of that "big screen" sound which only happens with distance and big/efficient speakers.
Inverse square law, same applies to light; I spent years as a professional photographer.

I have been using my Elacs on the patio for movies, placing them about 12 feet away from us and slightly in front of the screen. Saturday I placed them about 20" away from the retaining wall, about 2' behind the screen, and it was much better; seemed much more integrated with film instead of just squawking at us.

Quote:
A normal cinema that seats 200 people often has 10-50kW and all the speakers are big PA floorstanders, obviously that is overkill for your situation.
50k/200=250watts per viewer. If I expect no more than 6 viewers I should have a 1500 watt system, right? <-- THAT IS A JOKE


As I said before, the crawl space used to be vented, each vent was roughly 8"x10". A total of three across the addition directly at the patio.

I had two ideas prior to bandpass, maybe they were better?
1. IB manifold, as shown below, leveraging those penetrations by opening them back up. My concerns:
- if IB, how will those wave in the crawlspace affect the family room; rattle it to pieces?
- is the opening required to be equal to the radiating surface of the cone? If so, that would be very limiting.
2. I then thought about a pair of ported cabinets as a manifold. Imagine the image below with each driver in an enclosed cabinet and the ports also feeding the manifold. Concerns:
- the wall penetration, I assume having the ports and drivers feeding a manifold would really jack up the math.

As I write this I wonder if this would be reasonable.
Have two ported boxes feeding a manifold to the patio and redirecting the ports directly outside?

If I have two 12" drivers feeding a manifold, how large an opening to I need? I have ABSOLUTELY no idea.

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post #22 of 46 Old 08-14-2019, 04:22 AM
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The PA-460 is a good choice. 12" drivers are not going to cut it. Don't fire the port into a manifold, just fire it to the opening outside.
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post #23 of 46 Old 08-14-2019, 06:39 AM - Thread Starter
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Quote:
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The PA-460 is a good choice. 12" drivers are not going to cut it. Don't fire the port into a manifold, just fire it to the opening outside.
The PA460 appears to be the magic bullet.
It is capable of going much lower and louder than required; fortunately we have low pass filters and volume knobs to control that.
The cabinet size is very reasonable.
The port length is suitable length to penetrate the wall.

The only question I'm left with is how large would the manifold opening need to be for the driver?
Obviously I am not going to cut a 18" diameter hole in the wall.
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post #24 of 46 Old 08-14-2019, 07:06 AM
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Do you mean what size of a hole for the port to fire into the yard? That depends on what size of a port you are using. Let's get the box dimensions and port size determined first.
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post #25 of 46 Old 08-14-2019, 07:24 AM - Thread Starter
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Quote:
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Do you mean what size of a hole for the port to fire into the yard? That depends on what size of a port you are using. Let's get the box dimensions and port size determined first.
No. Cabinet size, port diameter and length are fairly straight forward.
I'm calling it a manifold but I suppose that would be incorrect as it is a single driver feeding it.


I made this CAD drawing to give you a sense of what I hope to accomplish.


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post #26 of 46 Old 08-14-2019, 07:47 AM
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That's not going to work. Like I said before do not use a "manifold".
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post #27 of 46 Old 08-14-2019, 08:12 AM - Thread Starter
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Quote:
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That's not going to work. Like I said before do not use a "manifold".
You said "Don't fire the port into a manifold, just fire it to the opening outside."

The port is not going through a manifold, it is directed through the wall to the exterior.
The front wave of the driver is directed into a chamber which opens through an 8x16" hole in exterior wall. <-- if I do not use s method similar to this, I am not sure what to do?

8x16 is an arbitrary number as I do not know how to properly calculate the size requirement.
I would think the proper method would be area of cone*xmax of driver.
To make is simple I just simply multiplied 254*.5 = resulting in a 127sq inchs.

This may be insanely wrong, but an attempt.
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post #28 of 46 Old 08-14-2019, 08:33 AM
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I should have said do fire the port or the driver into a manifold or chamber like structure, as that will screw up the porting of the box. Fire one of them out of a hole in the wall.
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post #29 of 46 Old 08-14-2019, 10:02 AM - Thread Starter
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I must be missing something pretty obvious.

The idea is not unlike the Electrovoice S-181 with three exceptions:
- The ports would be on the outside of the box in order to feed through the crawlspace wall.
- Are area containing the driver would be be extended 6" to exit through the crawlspace wall.
- The driver would be mounted the opposite direction as the 181 so that all electrical connections would be inside the box.

I am not arguing with you, I am trying to understand why this would be the wrong thing to do?

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post #30 of 46 Old 08-14-2019, 11:35 AM
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Quote:
Originally Posted by iH8usrnames View Post
... I am not interested in hauling big boxes around. I would like this to be as simple to use as possible so my wife does not need me to set everything up each time. Everything will be hardwired in place 24x7.

If everything is permanently mounted, why the reference to hauling out PA speakers?

Maybe there are some reasonably sized PA speakers with 10" or 8" woofers.

Also some of the speakers that look like rocks have 8" woofers and may be sufficient

https://www.google.com/search?q=spea...hrome&ie=UTF-8


Barring that, I think the concepts shown in both your manifold and ported sketches are feasible.

My guess is that you could go down in manifold cross sectional area to about half the cone area w/o issue.

Maybe that could be determined more precisely by modeling as a bandpass with a tiny front volume.

I don't think IB rattling the house would be an issue, especially if you HP filter it to your 30 - 40 Hz requirement.


Quote:
Originally Posted by iH8usrnames View Post
Also, I apologize.

No problem, I've experienced the same frustration with both work and left field forum responses

Noah

Last edited by noah katz; 08-14-2019 at 11:43 AM.
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