Compression driver as a phase plug

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   I've been thinking about coaxial horns and seeing the phase ball thingy in the martin cabs got me thinking: the shape of some CDs is not too far from a ball (although at very high frequency the departures are probably significant) so why not use a compression driver of an appropriate shape to do this same job in a coaxial horn?

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Steak'n'ale Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 31 January 2008 Status: Offline Points: 165	Post Options Post Reply Quote Steak'n'ale Report Post Thanks(0) Quote Reply Topic: Compression driver as a phase plug Posted: 29 July 2008 at 11:16am
	I've been thinking about coaxial horns and seeing the phase ball thingy in the martin cabs got me thinking: the shape of some CDs is not too far from a ball (although at very high frequency the departures are probably significant) so why not use a compression driver of an appropriate shape to do this same job in a coaxial horn?

ceharden Members Profile Send Private Message Find Members Posts Add to Buddy List The 10,000 Points Club Joined: 05 June 2005 Location: Southampton Status: Offline Points: 11776	Post Options Post Reply Quote ceharden Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 11:20am
	D&B did it in the C4 tops....

darkmatter Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 26 February 2005 Location: LDN Status: Offline Points: 2425	Post Options Post Reply Quote darkmatter Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 11:20am
	its kind of been done, the problem is where you put the cd horn. some turbosound coaxial cabs have used that idea i think.

Steak'n'ale Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 31 January 2008 Status: Offline Points: 165	Post Options Post Reply Quote Steak'n'ale Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 11:36am
	Ok, so its not only possible but a fairly good idea if those guys have done it. Theres plenty of posts on here about hornresp being crap to model mid/hi, what would I use to model this. I'm a bit new on this whole modelling thing but I'm not so interested in doing bassbins. Would it be better to just give it a go and see how it sounds?

Deadbeat Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 12 March 2008 Location: Singularity Status: Offline Points: 3167	Post Options Post Reply Quote Deadbeat Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 11:40am
	davey t made a topic about this a few weeks back I think. The dynacord coax tops use a similar thing. I think you'd need a sort of 'fairing' to make the shape of the back end of the comp smoother and more phase plug like. This is the Tannoy cab that has a similar thing going on. http://www.tannoy-speakers.com/s.php?product=87&title=iQ10&s= This is an patent relating to a wedge with a similar thing. Lifted from my patent thread. The comp is mounted behind the driver and is similar to a coax driver, the comp's horn is the phase plug (not the comp but similar...) http://www.google.com/patents?id=rzs7AAAAEBAJ&printsec=abstract&zoom=turbosound#PPA2,M1
	Away on extended leave.

Deadbeat Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 12 March 2008 Location: Singularity Status: Offline Points: 3167	Post Options Post Reply Quote Deadbeat Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 11:42am
	Here's why some say hornresp isn't good for modelling in HF. Lifted from diyaudio wiki: How high can you model before the results become inaccurate? Hornresp models the power response of the horn. This is different than the on-axis response which you might measure with a microphone. The power response is what you would measure at a point if sound radiated evenly in all directions away from the horn, within the solid angle specified in the ANG input. So the modeled results should be fairly accurate up to the frequency where the horn starts to have directivity - where the polar pattern starts to narrow. This is typically at the frequency where the wavelength falls below the diameter of the horn mouth. Above this frequency, Hornresp will predict lower SPL levels than what you would measure on-axis. Hornresp now includes tools to investigate this effect. Once you calculate the model, go to the SPL Response chart. Under Tools, select Directivity. If you enter a blank input, you will see the power response. If you enter 0, you will see a prediction of the on-axis response. You can also enter other angles. Also under tools, you can look at the Pattern tool. This will predict the polar pattern at the frequency you input and show you the DI, directivity index at that frequency. Directivity index is a number in dB giving the gain over what the level of the power response is. If you're that bothered, use Akabak.
	Away on extended leave.

Steak'n'ale Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 31 January 2008 Status: Offline Points: 165	Post Options Post Reply Quote Steak'n'ale Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 11:47am
	That tannoy looks quite interesting in the way they use the HF horn. A DIY approach to do something similar would be to build a pyramidal box around the horn, shouldn't be a problem as they all have concave sides.

Deadbeat Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 12 March 2008 Location: Singularity Status: Offline Points: 3167	Post Options Post Reply Quote Deadbeat Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 11:57am
	I think the comp is mounted through the back of the driver. You might be able to do this with pipe and some very very careful driver modification. look here: http://www.google.com/patents?id=8fozAAAAEBAJ&printsec=abstract&zoom=4&dq=inassignee:tannoy#PPA1,M1
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Steak'n'ale Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 31 January 2008 Status: Offline Points: 165	Post Options Post Reply Quote Steak'n'ale Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 12:05pm
	Thats just a coaxial driver init?

Deadbeat Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 12 March 2008 Location: Singularity Status: Offline Points: 3167	Post Options Post Reply Quote Deadbeat Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 12:22pm
	Think like Tony Andrews and have the phase plug mounted through the driver. Then think like Alex Garner and have the compression driver mounted through the driver. You end up with the Tannoy iQ10. Look at the first patent linked for a similar thing.
	Away on extended leave.

_djk_ Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 23 November 2004 Location: United States Status: Offline Points: 6002	Post Options Post Reply Quote _djk_ Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 3:53pm
	Hornresp is accurate in prediction power response. When you are inside a building, Hornresp will tell you what the response will be beyond the critical distance. The critical distance is the distance at which the direct sound energy and the reflected sound enegy are equal. Beyond this point the direct sound drops at the inverse square with distance, while the reflected sound stays the same. What does this mean? A non-CD horn may measure flat on-axis in the nearfield, but in a large room it will have the same roll-off that Hornsesp predicts. The critical distance for most large rooms is under 20 foot. Edited by _djk_ - 29 July 2008 at 3:54pm
	djk

_djk_ Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 23 November 2004 Location: United States Status: Offline Points: 6002	Post Options Post Reply Quote _djk_ Report Post Thanks(0) Quote Reply Posted: 29 July 2008 at 10:16pm
	"so why not use a compression driver of an appropriate shape to do this same job in a coaxial horn? " http://www.google.com/patents?id=MtgkAAAAEBAJ&pg=PA3&dq=patronis&source=gbs_selected_pages&cad=1_1#PPA3,M1 Edited by _djk_ - 29 July 2008 at 10:18pm
	djk

Compression driver as a phase plug

How high can you model before the results become inaccurate?