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Discussion Starter #1
Additional Chapters by lilmike:


Chapters 1a,2,3:

http://www.avsforum.com/avs-vb/showt...2#post17831932


Tapped horn tutorial:

http://www.avsforum.com/avs-vb/showt...4#post17835074



OK folks, as promised, a simple HornResp Tutorial for how to design an offset driver, conical, front loaded horn.


Here are the basics:




The Left purple and blue areas are the horn 'throat', the Rightmost area is the horn 'mouth'. The S1, S2, S3, Vrc and Lrc are parameters we will change in hornresp to design a horn....


OK, here's the hornresp input box:




The driver I chose is the 12" Dayton DVC, so go ahead and fill in its parameters in your hornresp program....and double click the 'Nd' until you get an 'OD' like you see circled....


Now, lets get the OD letters to turn black, to say everything is OK with the inputs. Input the following values for Ang, Eg, S1, S2, S3, S4, L12, L23, L34 and Vrc and Lrc (see pic below):


What we're inputting is that the horn is standing in a field with no boundaries nearby (Ang), and that we are feeding the driver 2 Volts. We are also saying that the horn has a straight throat chamber (areas S1=S2=S3) where the driver will mount, and there will be 20cm in front of the center of the driver cone, and 20cm behind the center of the driver cone. I chose 20cm to give a little room past the driver flanges. The horn flares from 100sqcm (S3) to 1000sqcm (S4) over 400cm of length. S1 to S2 is the blue part in the above diagram, S2 to S3 is the purple part, and S3 to S4 is the yellow part. Vrc is the volume of the rear chamber, and Lrc is the height of the rear chamber.


MAKE SURE YOU DOUBLE CLICK on the L12, L23 and L34 boxes so that they say CON, so you can enter a length.


Here's what you should have so far:




Now click 'CALCULATE' and say 'YES' to the suppression of rear chamber resonances....and you get an spl graph.




You can see the response is far from ideal, but this is a tutorial on what you can adjust, and what it does....


So, lets adjust one factor at a time.


To adjust throat volume, make S1=S2=S3, and make them all the same value. In this case, I am doubling them:




And the change in response (original response in grey).




You can see that the low end of the response smoothed out some! By making the throat smaller than original, it will make the response peaks bigger.


So, what happens if we change the mouth area (S4)?




S4 has been doubled.


Here's what we get (original again in grey):




You can see that adding mouth size increases sensitivity and the height of the peaks and valleys, and decreases extension...


Now, what about length (L34)?




Horn length (L34) has been doubled, here's what we get (original in grey):




Response is just about as ragged, but you gained extension to lower frequencies....


Now, here's what happens when you change the size of the driver chamber (Vrc):




We have made the chamber 1/2 as small as before. Here's what we get (original in grey):




By making the driver chamber smaller, we get a 'boost' in response at the 'low corner' of the horn, before response drops off the cliff. To tame that boost, simply increase rear chamber size.


So, let's say you want a horn that will play well to 30Hz (for recorded, bass-heavy music, but no movies). We play with ONLY 4 THINGS: Throat chamber size, Mouth Area, Length, and Rear Chamber size. A bit of fooling around, and I get this (took 3 min):




Which gives this for response:




The box is 262 liters. Compared to a DVC in a 100 liter box:




Compared to two DVCs in 100 liter boxes (with 2V into each):




Compared to three DVCs in 100 liter boxes (with 2V into each):




So it takes 3x the drivers with 3x the power in sealed boxes to get close to the same sensitivity as the horn.


But what about max output/excursion?


Xmax limited output for the horn (around 22V in):




Excursion:




Now, the three sealed boxes output at Xmax (18V into EACH BOX):




And excursion:




Now you're raising your BULLSH*T FLAG....."The excursion max is at 10Hz, way below the 30Hz you need, you dumb*ss!!!"


Yup, you are right. But look at the excursions for both the three sealed and the horn at 30Hz..... they are just over a milimeter or so of each other.....So I consider it a decently fair comparison, hypothetical though it may be.....and, for the record, I didn't optimize the sealed box for the DVC. 100 liters seemed like a nice round number.....


But you get the point. With a horn, you get more ragged response, a larger box, but more output in a passband with less power.


But how often will you play your sub in an open field? Chances are, not very....so you can change the 'ANG' parameter in hornresp to show you how the sub will play when next to a wall (1.0 x Pi), or in a corner (0.5 x Pi). Here's the same 30Hz DVC 12" horn inside in a corner, with only 2V in, compared to it in an open field (open field in grey):




You can see that the difference is HUGE. You not only get more output, but the response is smoother, and you get more extension! To get the same performance in an open field, you'd need 4 of the horns stacked together....boundaries are good for bass with standard speakers, but GREAT for bass with horns...



Hope this helps folks.....



JSS
 

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What you've labeled as the first driver segment is actually part of the throat chamber. It would be the first driver segment in a tapped horn, but that's not what you have pictured there. The way you have it pictured the second driver segment also could be considered throat chamber, though it gets a bit muddy. To be safe one usually considers the beginning of the horn to be past where the cone exposure lies, except in a tapped horn.
 

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Here is a pic to help out.
 
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Discussion Starter #6

Quote:
Originally Posted by Bill Fitzmaurice /forum/post/17824035


What you've labeled as the first driver segment is actually part of the throat chamber. It would be the first driver segment in a tapped horn, but that's not what you have pictured there. The way you have it pictured the second driver segment also could be considered throat chamber, though it gets a bit muddy. To be safe one usually considers the beginning of the horn to be past where the cone exposure lies, except in a tapped horn.


I just wanted to keep things simple, with less jargon, and I am using the recommended inputs for an offset driver according to hornresp. Just For the record, quotes from my first post:

"The Left purple and blue areas are the horn 'throat'"


And,

"We are also saying that the horn has a straight throat chamber (areas S1=S2=S3)"


Also, this tutorial is not intended to be an 'end-all' reference work or anything. This is just so people won't be so afraid of hornresp, and it descibes how I go about screwing around with OD horns....


Basically, for a certain driver, you can get a certain horn to behave well. Some drivers are good, others suck. Just play around and see what you get....and post your results if you find a good one!


JSS
 

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Discussion Starter #7
Thanks for the props, guys....now get to designing/modeling! Drivers I have found work well in OD conical horns: Dayton DVC 12" and 15", AE AV15-H, B&C TBX 15". Please add to the list if you find one that behaves well....


Soho,


Thanks so much for the drawings.



Lilmike,


You are up next for the Tapped Horn Tutorial, and more advanced tutorials....I limit myself to these OD horns and tapped horns with essentially a single, conical 'segment'. MUCH easier to fold that way...I know there is much more out there, though...TEACH US!!!


The folding tutorial will be a royal ***** to put together (may have to do a video or something, individual images wouldn't be as instructive), so it'll be a little while before I get to it...



JSS
 

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Here is a picture to show what Hornresp expects of an OD horn with no Throat Chamber.

 

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Discussion Starter #9

Quote:
Originally Posted by soho54 /forum/post/17824492


Here is a picture to show what Hornresp expects of an OD horn with no Throat Chamber.


Nice! Thanks....


A note:


from S2 to S3 (green side) in the diagram above is not necessary to model a driver in an offset horn in hornresp. You can just go straight from S2 (center of driver) to the mouth of the horn which will be S3 (the purple side) . The reason I don't is so I can have a straight portion, and a single conical portion. It makes it easier to design and fold....no having to match up 2 conical sections to have the same expansion rate, to have a nice, flat surface to mount the driver to....


Very nice drawing....


JSS
 

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The reason to use three chambers is when your are using different flare rates in different portions of the horn.


It is just a generic diagram of the two most common options. A way to visualize what you are doing.
 

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Here is an OD with a Throat Chamber

 

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Great work JSS! 2010 is looking good for a bass horn. Now I just have to learn how to fold them
 

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Quote:
Originally Posted by maxmercy /forum/post/17824352


Thanks for the props, guys....now get to designing/modeling! Drivers I have found work well in OD conical horns: Dayton DVC 12" and 15", AE AV15-H, B&C TBX 15". Please add to the list if you find one that behaves well....


Soho,


Thanks so much for the drawings.



Lilmike,


You are up next for the Tapped Horn Tutorial, and more advanced tutorials....I limit myself to these OD horns and tapped horns with essentially a single, conical 'segment'. MUCH easier to fold that way...I know there is much more out there, though...TEACH US!!!


The folding tutorial will be a royal ***** to put together (may have to do a video or something, individual images wouldn't be as instructive), so it'll be a little while before I get to it...



JSS

Just say when boss. Tapped horn design is tricky, but McBean gave us a wizard that helps visualize things while designing. I can crank out a simple sim in a few minutes, and I can spend the next year tweaking it. When I look back at what I've done, often times the subtle difference in response due to the added complexity is not worth the added construction effort.


Seriously, thanks for the effort. For the graphically challenged, the illustrations in this thread are priceless.
 

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Quote:
Originally Posted by Antripodean /forum/post/17824914


Great work JSS! 2010 is looking good for a bass horn. Now I just have to learn how to fold them

Draw pictures.


Seriously - plot a scale picture of the horn, then cut it into pieces and shuffle the parts around so that they fit inside the box. It usually works best when you start with the big end. As MaxMercy says, conical horns fold lots easier.


Happy 2010 all!!!
 

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fantastic writeup!


a comment about how the peaks and dips will not be as large in life as in model, should be part of this.


also useful might be some rules of thumb about how large/small the various dimensions can be. for example, how small can one make the rear chamber volume, how small the area of the throat can be relative to the area of cone, etc.


i once saw a horn folding graphic that made it pretty intuitive for me. now, that i understand what is going on, folding a horn is pretty much just geometry. i'll see i can dig it up.


again, great write up.
 

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Per LTD02 comments,


As he mentioned the simulated peaks and dips will be less than as they appear in the models. The Q of the peaks and dips will be less than shown, and the dips seem to be more over-emphasized than the peaks. The models are based on walls made from unobtainium that is infinitely hard and doesn't resonate. I believe D. McBean called it non-resonate kryptonite.
The models also do not take into account acoustic losses within the horn path. That said it is best to eliminate as much rippling as possible, but you do not need to get obsessive over it.


The dimensions are all pretty much what ever you can get to work. The only thing to really keep in mind is the compression ratio, and the mouth size.


The compression ratio in an OD horn is set by the ratio of the Area of the Driver surface divided by the area of S2. The amount of compression a driver can take before destroying the cone is not something you can be sure of, without exceeding it. A safe general rule of thumb for an unknown driver is to keep it below 3:1 with what you consider a stout driver, and around 2-2.5:1 for a regular driver. EDIT: I forgot to add that this is for 12" drivers. As they get bigger you need to go down in compression, and with smaller drivers you can get away with higher compression.


The mouth size will determine the efficiency and low frequency response of your horn. If you make it to small overall efficiency will go down, and low frequency response will taper off, and get very ripply.
 

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I will add that the math to figure out ideal sizes for the various chambers and lengths are posted online, if you check out MJKs transmission line site, the math used to derive his various TLs variation will apply quite well here. This is true with tapped horns as well.

http://www.quarter-wave.com/
 

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Horns also need to be at least a quarter wavelength long at the low corner your are after.


If you have the space the maximum efficiency will be reached with a half wavelength horn.
 

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Discussion Starter #20
UPDATE:


Added a graphic showing what boundary loading does the horn designed in Post #1...


JSS
 
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