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compression driver throats

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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Topic: compression driver throats
    Posted: 14 October 2012 at 3:33pm
iv been reading into comp horns a bit today doing a bit of pondering as u do.
my question is as follows;   what profile would u usualy find in the throat of a comp driver?

i understand the importance of realising the comp is the start of the horn and that it is critical especialy for the highest frequencys for it to follow suit with the angle or flare type of the throat of the horn.

i  asume it would have to be either tactrix or conical ?

if using a single point source box either side ,no arraying issues, is there any better choice than a conical horn?
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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2012 at 3:40pm
just to add for clarification,the tannoy vq speaker that uses the bms coaxial,that horn is that a tactrix?
i gotta get it clear in my head 
tactrix= kinda conical but with an ever increasing flare rate?Shift+R improves the quality of this image. Shift+A improves the quality of all images on this page.Shift+R improves the quality of this image. Shift+A improves the quality of all images on this page.
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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2012 at 8:18pm


anybody?Shift+R improves the quality of this image. Shift+A improves the quality of all images on this page.

perhaps i should start a new thread in the general section lol
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minaximal View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote minaximal Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2012 at 8:36pm
Hi, yes throat angles are important and often ignored.

The tannoy VQ is a type of oblate spheroid, basically a conical horn with a smooth short transition as close to the throat as possible, a very similar initial start profile to the peavey quadratic waveguide horns.

for upper end off axis response there is no better than a type of oblate spheroid, the only drawback is the need to have a shelving filter to boost 6db the upper end frequencies, but at least unlike normal constant directivity horns the beamwidth doesn't narrow anything like them on an OS or strsight conical.

there is no set throat flare rate and all comps vary, for single stack a wide dispersion conical or OS would be great for off axis, but will also array better due to minimal beaming.

Here's my list of known exit angles:

CP750Nd – 24º
CP850Nd – 7º
CP755Nd – 12º60’
SMC65Nd – 15º
CP385Nd – 16º30’
cd10    - 16º30’
SMC225Nd – 13º1’

B&C

1"
DE250 14.6°
DE10 7.7°
DE12 24°
DE400TN 20.7°
DE400 31°
DE500 17°
DE200 9.9°

2"
DE85TN 34.5°
DE750TN 22°
DE950TN 17°

BMS

4524       20º
4538       21.8º
4544       20.6º
4550       14º
4554       26.7º
4555       30º
4590/4590p 1º
4591       1º
4540nd     14º
4552nd     24º
4592nd     10º
4594nd     3º
4595nd     10.8º

cheers al



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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2012 at 6:48pm
good stuff minaximal ,some realy usefull information there mate :-D

id like to start a project building my own comp horns, my plan is to scour the web on different ways of going about building them.im sure i saw somewhere  someone use lots of if u like gaskets of mdf stuck together forming the profile, does that make sense?
seems to be alot going for the idea of not having to pick  an off the shelve comp horn,to much of a compromise!
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matty w View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2012 at 7:01pm
sorry for bad punctuation my phones hardwork and im tired lol

surely using an off the shelf horn is a bit like being able to buy an off the shelf bass horn and then finding the best driver for  it,its just not cricket! u design the horn to the driver.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 16 October 2012 at 8:42am
would imagine the angle of throat is a good indication of drivers intended use.
the de950tn is an interesting 1!
will look into it later when iv got more time.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 16 October 2012 at 8:45am
sorry de 85tn i mean 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote minaximal Quote  Post ReplyReply Direct Link To This Post Posted: 16 October 2012 at 1:05pm
Originally posted by matty w matty w wrote:

..im sure i saw somewhere  someone use lots of if u like gaskets of mdf stuck together forming the profile, does that make sense?..


Did you mean this thread? http://forum.speakerplans.com/how-to-make-a-circular-waveguide-in-pictures_topic39526.html

Steve B, has also posted threads about making circular waveguides, and theres been more technical talk on the DIY audio forum about exit angles etc.

al


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Non-Smoking Man Quote  Post ReplyReply Direct Link To This Post Posted: 16 October 2012 at 3:55pm
Google Jack Bouska for a high level discussion of waveguide theory (also Earl Geddes re 'Oblate Spheroid flare shaping). And what a system he has! (Not pro audio as such but use of pro audio drivers.)
Science over Religion
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 16 October 2012 at 4:19pm
It is easy to get way to anal about such things as throat angles etc. Whilst obviously the ideal would be to have the comp driver perfectly matched to the horn throat, I have heard way too many examples of duo's that on the face of it just will not work correctly together actually making a really nice noise.

Got to admit though that sound wise an OS horn perfectly matched to the comp does sound a bit special, not always the best dispersion pattern for P.A though :)

Tony
www.forteaudio.eu - BMS - db-Mark Processors - Lexon (SAE)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 16 October 2012 at 10:21pm

If you follow the link to minaximal’s thread on horn construction, it gives a good idea of how to go about constructing a round horn. A couple of things that I have found are that mdf makes a better plug and don’t use hub pullers to release the horn from the mould.

Due to how ply is constructed, when you turn it on the lathe, you are cutting along the grain, then across the grain, then along the grain…… If you are not careful you can get little ridges forming as you turn the plug. Mdf is more consistent. I always glue and screw the layers together and coat the wood with resin once shaped. I then finish off with increasingly finer grades of wet and dry up to 1200 grit. Finally I use T-cut before polishing with a release wax. Once I have made the initial horn from the turned plug, I make a second mould from that and put the wooden plug away.

Using hub pullers concentrates all the pressure on two or three small points on the flange which can cause cracking. One way round this is to make an extremely thick flange. I use a frame that supports practically the whole area of the flange and then use a steel bar fractionally smaller than the throat and tap out the mould with a hammer. I use both wax and release agent, and rarely have problems with sticking moulds. If you go with this method, ensure that you polish all traces of wax off the mould before applying the PVA release agent. If you have problems with the release agent not flowing, you can reduce the surface tension by adding a few drops of washing up liquid; this stops it beading.

There were some useful videos by hornmaster showing how the horns were made once the mould had been finished.

Before you get to all of the above you need to design your horn.

Call me cynical, but I would suggest that the throat angles of compression drivers have more to do with the distance from the diaphragm/phase plug exit and the throat exit, which has to be one of the standard sizes. The actual diaphragm size also comes into this too.

One of the advantages of designing your own stuff is that you get to decide which areas of the design can be compromised and which cannot. There is a lot of information about the different aspects of design out there on the internet so I won’t go into any great detail at the moment.

Exponential and tractrix horns give increasing directivity with increasing frequency. This compensates somewhat for the fall off in power response to maintain a level on axis frequency response. Conic horns (this includes the OS and similar horns) have a more constant coverage but require more compensation eq to give a flat frequency response.

Abrupt changes in the flare profile (line array slots and traditional CD horns) will introduce ripples in the response, but may enable better pattern control. The size of the horn will determine how low a frequency the horn will maintain good pattern control. Depending on what you are using in the frequency band below the horn, it is sometimes better to lose some control so that the polar response of the two frequency ranges match at the crossover point.

For one off projects where the horn is designed for just the one box, look at the system as a whole and try and maintain an even power response through the crossover region. If possible, build and measure the mid section below the horn to give you a good idea of how low the horn needs to go and how to match up the dispersion patterns. As you are designing the horn. you have more flexibility that way rather than designing the horn and trying to match that with a suitable cone mid driver.

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