Unfolded subwoofer horns...bad idea?

DrDyna

Member
2007-05-17 11:34 am
I woke up this morning with a thought that I thought merited some opinions. I had the sudden urge to try modeling a pair of subwoofer horns that are essentially unfolded, with visible drivers at say, the front of the room, firing into a horn that flared along the sides of the walls, with the mouth area exiting toward the rear of the room...or the other way around.

Before I try to model something like this, has anyone tried anything like this? I figure it would be pretty much a FLH but with no rear chamber.

Thoughts?
 

DrDyna

Member
2007-05-17 11:34 am
I'm probably doing this wrong.
 

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just a guy

Member
2006-05-12 6:59 pm
Yup, if there's no rear chamber it's a back loaded horn. If you want a constant expansion rate as shown in your pic you can use the BIB spreadsheet either as a starting point or as a complete design. But end loaded might not work so well, you might want to use the BIB's 20 or 40 percent driver position to smooth the response a bit.

I don't personally like this idea for a number of reasons but it will work if that's what you really want.

FWIW, I had an idea similar to this awhile back.
http://www.diyaudio.com/forums/subwoofers/116963-another-big-horn-dream-comments-concerns.html
Seems it was early 2008, back when I didn't know anything about anything. It also looks like that thread was the FIRST TIME I EVER USED HORNRESP. Based on that alone I'm going to have to go back and reread it for a hit of nostalgia.

This idea was much more elaborate though, half the room from floor to ceiling defined the horn. But assuming you had a room with concrete walls all you would need to do is construct a small room inside the room to define the front chamber and horn path. (Following pic is not to scale, since I had no idea what room to use for something like this.)

The red outline is a massive floor to ceiling sealed box. The walls and the box form a dual waveguide with a rapid expansion that grows to the cross sectional area of the room at the mouth.

[IMGDEAD]http://i30.tinypic.com/kd0h2r.jpg[/IMGDEAD]
 
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DrDyna

Member
2007-05-17 11:34 am
I don't personally like this idea for a number of reasons but it will work if that's what you really want.

Well, what I was hoping for was really just a flashier way to make a horn that isn't a taped horn, so aside from the straight flare, it could also "rollercoaster" a bit, which I think would look awesome. I'm just trying to get a handle on what the acoustic disadvantages might be. The hornresp output looks a little funky, but nothing I couldn't tame with the MiniDSP if I had to.

FWIW, I had an idea similar to this awhile back.

Eeeaoww...I'm not sure how well that would work..I do have 3 concrete walls down here.

Really what I envisioned was a "shelf" that ran the length of the room on each side, 13 inches tall, with a driver mounted at the back of the room and a horn mouth at the front.

The part that concerns me is the rear of the driver that's showing would be some 550 cm from where the mouth is and I'm not sure that I'm plugging data into hornresp (or maybe I did?) to see exactly what that's going to do.
 

norman bates

Member
2003-11-25 2:28 am
well, if the horn mouth fired into the corner (since you have a total cement corner), you could have a small (ish, lol) horn, but the length needs to be 1/4 wavelength of 1/2 octave lower than the mouth cutoff. Just classic rules of thumb.

So, a 30hz horn should be 12' long and have around 14ft2 mouth.

Still want a bass horn ?

I've always wanted a 100hz front horn, but based on my calculations, even an 80hz front horn would be 4.7' long and sitting on just a concrete floor, would need 16ft2 mouth. Eeek.

And I need to be a wavelength away to develop the bass (I had a keele ported W-bin), and bass wasn't present untill I was 10' away. Not sure about being so close to a subwoofer horn.

Norman
 

just a guy

Member
2006-05-12 6:59 pm
The part that concerns me is the rear of the driver that's showing would be some 550 cm from where the mouth is and I'm not sure that I'm plugging data into hornresp (or maybe I did?) to see exactly what that's going to do.

Stick it in a chamber and don't worry about it. Use a plexiglass window if you need to see the driver. Or just make an unfolded BIB with a 40 percent (or more) driver position, that will put the driver fairly close to the mouth. As long as you stay within 1/4 wavelength of the highest frequency the sub will play you have nothing to worry about. At 100 hz that's almost 3 feet, at 80 hz 3.5 feet. If you exceed that by a bit it isn't going to be a disaster.
 

DrDyna

Member
2007-05-17 11:34 am
Stick it in a chamber and don't worry about it. Use a plexiglass window if you need to see the driver. Or just make an unfolded BIB with a 40 percent (or more) driver position, that will put the driver fairly close to the mouth. As long as you stay within 1/4 wavelength of the highest frequency the sub will play you have nothing to worry about. At 100 hz that's almost 3 feet, at 80 hz 3.5 feet. If you exceed that by a bit it isn't going to be a disaster.

I'm going to have to read some about BIB.

Oh...yeah, that looks like it could be a winner.

Edit2 grrr...bib calc is 404.
 
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So, really, the act of unfolding a tapped horn so that the driver back isn't at s2/s3 pretty much destroys it?

A tapped horn can't be unfolded, it HAS to tap into the line at 2 different spots, somewhat near the beginning and end of the line.

Edit2 grrr...bib calc is 404.

I've got a couple of different versions I can email to you. I recommend you run the results through MJK's BIB worksheet though, especially if you are considering changing the driver position. I can do that for you as well once you have something you like with the calculator.
 

DrDyna

Member
2007-05-17 11:34 am
I sent you an email but I couldn't add any attachments. You will have to email me back so I have your email address and then I can send you an email through hotmail with attachments.

No problem, and thank you!

Yeah, I figured unfolding the tapped horn would break it, I just didn't realize that it would pretty much completely break it, lol.

The more I think about the BIB, the more it seems like what I want to do, I just have to prototype one to see how it stands up to the other 4 designs I have kicking around before I start making dust with expensive BB ply.
 
While still just a mere lad, back in the '70s, while looking for speakers which finally wound up being Altec A7-500s, in the back of a store in Minneapolis, MN was a horn that must have been 20 feet long and about 8' by 8' at the mouth being built. Sure wish I could have heard it...
 

DrDyna

Member
2007-05-17 11:34 am
Ha! That looks exactly like the pic I posted but this one doesn't extend all the way from floor to ceiling so it's much, much smaller.

[IMGDEAD]http://img209.imageshack.us/img209/7042/estrade31024x768qs8.jpg[/IMGDEAD]

Wow, that is fantastic..I could see something like that in my space downstairs.

Honestly, I've experimented with LLT vented, T-TQWT, Tapped Horn (which I loved for some source material and despised for others) and most recently, a T-QWP and one of the things I considered was unfolding the T-QWP into a "monolith" because it'd be easy, but I'm really open to anything...

The BIB is giving me something to think about, simply because of the name, and for the frequency I'd try to tune it to, it'd probably be massive.

Edit: Perhaps massive isn't the right word, see attached.
 

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Wow, that is fantastic..I could see something like that in my space downstairs.

You would need some pretty tall ceilings for that to work.

The BIB is giving me something to think about, simply because of the name, and for the frequency I'd try to tune it to, it'd probably be massive.

Edit: Perhaps massive isn't the right word, see attached.

It's actually pretty small if you unfold it and put it on the wall, the mouth is only 163 sq inches so for most of it's length it wouldn't even be big enough to form an effective shelf. But it is long, which is not unexpected. Conical pipe/horns are the longest type of horn there is. If you want to shorten it you need to either change the flare or make the throat larger or both, but if you do that it won't be a BIB anymore.

By comparison though, the bass stand/stage is several times larger, the BIB really isn't all that big in comparison.
 
Wait, is that bass horn stand really as simple as it looks? I'm looking at this drawing and at first I thought something was missing, but it appears that it's just a top and bottom with a single curved piece.

That's all you need to make a horn. There's a spreadsheet in that thread to work out the dimensions for your. You could fold it a bit to make it smaller and use up some of the dead space in the middle if you wanted to.

But remember, this isn't going to be simple or cheap to build. It's going to need to tie into the walls and the top of it is a whole new floor for half of the room. You could build the BIB with a hundred dollars in an hour or two, the bass stand/stage would take thousands of dollars and probably a few weeks to do right. It is a nice, simple concept, but implementation would be anything but simple.
 
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DrDyna

Member
2007-05-17 11:34 am
That's all you need to make a horn. There's a spreadsheet in that thread to work out the dimensions for your. You could fold it a bit to make it smaller and use up some of the dead space in the middle if you wanted to.

But remember, this isn't going to be simple or cheap to build. It's going to need to tie into the walls and the top of it is a whole new floor for half of the room. You could build the BIB with a hundred dollars in an hour or two, the bass stand/stage would take thousands of dollars and probably a few weeks to do right. It is a nice, simple concept, but implementation would be anything but simple.

Yeah, I could see that being ~ 10 sheets of material or more, depending. The only concern I have with it really is while the back wall and left wall where I'd build it are concrete, the right wall is a standard drywall construction, so I'd be into re-doing that wall as well. I'm not really opposed to lots of work, I've pretty much built the room as it is, and it would give me an excuse to get rid of the ugly carpet that's down there at the moment.

The other issue is...if we were to ever sell the house..it would be pretty much married to it.

I'm sure it would be a sound and sight to behold under my projector screen though.

I suppose all my questions about the original idea have been answered, thanks for all the input and suggestions, it's much appreciated.