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jwc

Bass horn ideas again. A possible build. Need criticism.

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I would like to have some opinions on designing bass horns and want to know if Im way off base. Why am I doing thiseducation and most likely will build one for the hell of it.

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Now a couple of things I want to keep standard for right now. Stick with me.

Driver Bobs woofer only one per bass bin

Throat 78 sq in

Slot 3 x 13

Non ported for now

Exponential

Now I started off with a 60Hz Fc with a ¼ wavelength. Easy build but it got a little large. H x W x D was 42 x 52 x 21. Now this is just too big. It was shaped like the jubilee. Jumping to a 70Hz cutoff with a ¼ wavelength was a reasonable size. But why not just build a La Scala. For nowthats no fun.

So then I thoughtOkit will sit in the Corner and lets try 1/8 wavelength. Now I have read/browsed Bruce Edgars Showhorn. He made a 50Hz cutoff for a 12 inch driver at 1/8 wavelength. However, not pure exponential but partially hyperbolic.

Anyhow, thought I would try the 50Hz cutoff at 1/8 wavelength. I used a slightly different throat and calculated mouth area. I also split the horn like in the scala. Is there a real problem with using 1/8 wavelength?

Mouth 5.15 sq ft

Horn length 49 inches on both sides

Now basically I have a jubilee shaped cabinet;

H x W x D is 41.5 x 42 x 22 (external). Pure Exponential.

Now the way I did it was a way that I knew I could build it. Couple of things to notice. The sealed chamber is large. About 5.8 cu ft. Just less than a Cornwall actually being at 6.2 cu ft. Is there a problem with this?

The driver can be taken in and out of the back like a cornwall. If I needed to, I could make the sealed chamber smaller and keep the same horn.

Now does anyone think it is a bad idea to use masonite for the outer side walls of the cabinet to get the EXACT exponential curve for the second half of the horn. Was thinking of trying to layer 4 different 3/16 masonite glued together one at a time. Is there a problem with this?

Take a look at the image. It is the top view of only one side of the cabinet. The straight columns of the horn have vertical ramps to keep a constant horn throughout. No dead space.

Jc

post-16499-138193046515_thumb.jpg

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I can assume much higher than a Khorn but maybe not as much as a scala. There is one 90 degree turn and one 180 degree turn. More turns...more demise of the upper end. The Jubilee does this also but has 12 inch drivers....may be more forgiving.

You can see where in the turns that I sketched out a plan to place "buffers" in those corners to get a smoother transition.

Now after that first 90 degree turn, I chose not to flare horizontally but vertically. This makes for easier build but creates a larger sealed chamber. With that sized chamber, I could place a port in the throat with good results. This would change my throat size and I would have to reconfigure the flare but that is not a big deal. I thought I would try it first w/o a port since the port makes for a complicated throat configuration and I have never built a Bass horn before.

Now a port in the horn with a 15 inch driver would make for some really low frequency production.......some loss of spl?....not sure. have considered placing a port below the 3 x 13 slot. The port opening could be 3 x 13 also with depth I would have to calculate later. HOWEVER, with the driver and port installation from the back, I could change out port sizes to try different responses. Keeping the first flare at a 3" depth with two slots of 3 x 13 will give a thraot of 156 sq inches. Actually that would be an easier build...i think.....man I'm rambling.

jc

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What is the rest of the system that you plan to use with the bass bin?

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Mike you are getting ahead of me. Its a good question...but I can't answer it. You know I'm just sort of an actual hands on experimentor.

If you are asking this to know 2 way or 3 way. Not sure. I however, have no problem with 3 way.

jc

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well it's a bit more complicated than just deciding the frequency response. [;)]

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Guest " "

jwcullison

Since you asked for input, and from reading some your past post, you can recognize input as well as recognizing someone who is just trying to be critical just for the sake of being critical.

So here is some input, you may have already considered this notion, but in the event you have not, also attach is a diagram to try to communicate my point.

Your design strikes me as being well optimized for the lower end of the sound spectrum, if that was your goal, congrats. Now I'm not sure what the effective crossover point would be at the upper band of your cabinet. I am going to guess, that you will certainly need to go 3-way, and perhaps, 4-way.

I have attached a drawing, which, from the top view, shows greater flares than your design. The attached drawing will have a higher upper bass and mid-bass operating range, and of course, it's lower operating band is no where near the lower operating band of your design. These are trade off decisions.

If you want to go 2-way, some changes may be in order, along the lines of the channel flare rate in the attached diagram.

However, if 3-way was your goal, and you can support a low mid cutoff, IMO, your design will work just fine.

I hope this info is helpful, and my apologies if my recommendations and input are out of line and items you already considered.

post-22082-1381930465751_thumb.jpg

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Yes I want the criticism.

Yes I have thought of some of your thoughts. I want it to go low but I do not know how to predict the high cutoff. Any thoughts there?

I'm not thinking of a "system" when doing this. You remember from the last thread you participated in, I was just trying to get down the bare basics. The throat was a big hang up for me. Well, this thread was to just take it a step further. Just trying to see if I understand it enough just to get the match/physics right. Now your last post is helpful. Telling me it may not go as high as I though it might. Curious if it would get to 500Hz.

No I wouldn't want to do 4-way. Right now..I just looking for flaws in bass horn design. I guess so far is that there is no Basic design problem and at this point may need to think about things ahead as you and Mike may be suggesting.

But to reinterate some of the underlined questions at the start of the thread. Any thoughts on those?

Thanks for the input

jc

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Are you using wavecalc JW, or just raw equations?http://www.users.bigpond.com/dmcbean/

I know it won't be able to predict your folds perfectly, but you can get an idea of how each variable can affect the response and go from there.

3 things to keep in mind with your design:

The height of the cabinet. I know it's just a standalone unit right now, but you should keep in mind what kind of midrange you'll slap down on top of it.

Polar response. Your exit paths should be trying to guide the wavefront in the direction that you want it to go.

Similar to that concept is maintaining the sound bubble. That sharp 90 degree bend on the inside is going to introduce diffraction effects and the HF response isn't going to couple very well. I think a design similar to what speakerfritz posted a picture of would would work better.

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Guest " "

"Curious if it would get to 500Hz."

IMO, as hands on speaker builder (trial and error method), is that it will not, and if there is no flare at all after the first bend, may not reach 350hz.

You can help the response curve by adding 45-degree wood fillets in your 90-degree bends and adjusting the tunnel width accordingly. Another consideration that may help keep your design template is to cut the corners off the bends at the 90-degree turns opposite where you put the 45-degree wood fillets. And in keeping with you design, if you were to gradually expand the width of the path, the resulting re-orientation would be closer to the drawing I provided, with out radically changing your design model.

I tried to find a blueprint that was closer to your design, with the minor changes, I saw one somewhere, just can't recall where. If I find one, will post it.

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What will go on top is up for grabs at this point. I am no polar response expert by all means but haven't gotten that critcal (yet).

Mike...Is that program free. I may have to mess with it some.

I have done previously what you said about eliminating the 90 degree. Remember there is a constant flare there vertically. Now if I were to flare horizontally there...couple of issues. The cabinet would be very short. For me to flare partially vertical and partial horizontal is almost impossible to build...at least for me.

The vertical flare was to gain height as a 50Hz horn folding in a horizontal plane will get you over 50 inches in width. Also..the horn you posted is huge. In that case I could build a wide la scala and turn it on its end. That actually would work for a 60Hz cutoff and look pretty good. Any thoughts what the dispersion of a la scala bass bin turned on its side? I gave this some thought.

I had planned already to put the 45 degree buffers in there. Will have to think how I can get rid of the 90 degrees w/o getting to wide and short. This would get me back to where I started almost and have to go with the suggestion of two drivers to get a bigger throat or narrowing the intial flare to 2" depth as opposed to 3" depth.

Just now typing this...I have an idea...may have to sketch it tonight.

jc

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Guest " "

"...I have an idea...may have to sketch it tonight"

Look forward to seeing it.

I'll continue to look for a closer "existng" match to your design model.

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1/8 wavelength works when you're in 1/8th space - so if you pull the driver outta the corner you will lose a lot of bass.

No problem with having a large cabinet behind the driver. You can almost think of a horn as a big low pass filter with gain. Your design would make it very easy to adjust the rear volume too and later add ports when you feel like it.

I like your idea with the masonite and is something I've thought about doing too. However, I would be inclined to build it with 2 or 3 layers and then add bracing as needed. It'll be easier, cheaper, lighter, and you will probably need to add bracing regardless of the width anyway.

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Guys. Doesn't the jubilee have the same type 90 degree bend?

jc

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1/8 wavelength works when you're in 1/8th space - so if you pull the driver outta the corner you will lose a lot of bass.

No problem with having a large cabinet behind the driver. You can almost think of a horn as a big low pass filter with gain. Your design would make it very easy to adjust the rear volume too and later add ports when you feel like it.

I like your idea with the masonite and is something I've thought about doing too. However, I would be inclined to build it with 2 or 3 layers and then add bracing as needed. It'll be easier, cheaper, lighter, and you will probably need to add bracing regardless of the width anyway.

Yes...that is what I was thinking....same line of thought. The basic horn principles are getting me somewhere.[<:o)]

jc

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jwcullison

Jubilee has 1, but uses a 45 degree fillet. If I were to build the Jubilee, I would cut off the corner at that 90 degree turn.

Your design has 2 90 degree turns, and a 3rd turn that, while not 90 degree, is very agressive, none of your 3 turns have 45 degree fillets.

Jubilee exist path expands along its lenth.

The LaScala has 1 90 degree turn, with out fillets or cutoff corners, and rumbles at 400hz. W-bins are known for issues above 400hz.

There is another implementation of the w-bin that does not rumble at 400hz, if you want i can post it. I don't want to drift your thread off topic, so I'll wait for your OK.

post-22082-1381930465871_thumb.gif

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Of course......keep em coming. Very much interested.

Yes. See your point. The first two bends will have 45 degree fillets. I Just didn't draw them there. You can see the markings of where I will put them.

The 3rd turn will be pure exponential as I am thinking of masonite on the entire side of the cabinets.

So where is the other "potential" problem with the "w".

thanks

jc

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jwcullison

Other issues with w-bin enclosures can be mitagated by flaring the intial stretch of the horn lenth. This helps reduce wave bounce back into the driver.

This can be done in one of two ways. At the dog house face where the horn throat is, or at the cabinet shell where the horn throat waves are targeted.

See attached diagram that illustrates the taper of the dog house on the horn throat side.

I don't have a diagham of putting the taper at the cabinet shell where the horn throat is, but I do use this approach often.

I 'll post a few pics of hybrids as well.

post-22082-13819304664244_thumb.jpg

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jwcullison

hybrid

notice horn throat area

post-22082-13819304664714_thumb.jpg

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jwcullison

another hybrid

notice horn throat area

post-22082-13819304664984_thumb.jpg

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