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Old 18th March 2010, 09:54 PM   #31
Rudolf is online now Rudolf  Germany
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Default Immediate desaster

Today I measured the vertical response of my tiny dipole tweeter. In fact I turned the baffle 90° and rotated it horizontally:

Click the image to open in full size.

Results were much worse than I had expected. First "upward":

Click the image to open in full size.

Then in smaller steps around 0°:

Click the image to open in full size.

Things get out of control almost immediately. Even +/- 7.5 deg is not bearable. So back to the drawing board. It will take me some time to get the sticky gum away from the tweeters.

Afterwards I will again try the tweeters back-to-back and see, whether cutting away some of the baffle area has done anything helpful to that configuration.

Rudolf
Attached Images
File Type: jpg DaytonND20 tiny_3.JPG (21.8 KB, 932 views)
File Type: gif DaytonND20 tiny_vert_1.gif (39.0 KB, 671 views)
File Type: gif DaytonND20 tiny_vert_2.gif (32.1 KB, 925 views)
File Type: gif DaytonND20 tiny_vert_3.gif (37.1 KB, 929 views)
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Old 19th March 2010, 11:42 PM   #32
Rudolf is online now Rudolf  Germany
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Default This will be the last time ...

I glued the poor tiny Daytons together back to back and got a package of 3.3 x 3.3 x 3.0 cm:

Click the image to open in full size.

The resulting dipole response is possibly the best one can get with these tweeters without compromising any direction (as in my last attempt ):

Click the image to open in full size.

But there is a back side to everything - literally. The quality control of those cheap ND20FA isn't very picky - resulting in a less convincing response from the opposite driver:

Click the image to open in full size.

For comparison I show the response of the original unequalised ND20FA dipole in a small housing as presented in post #6:

Click the image to open in full size.

Can you spot the progress?
I now will take the Dayton tweeter dipoles and put them in place of the larger Monacor dipoles. If they sound better, they will stay. If not ... I donīt believe they would sell on the bay in this shape.

Rudolf
Attached Images
File Type: jpg DaytonND20 b2b_5.JPG (12.1 KB, 900 views)
File Type: gif DaytonND20 tinyb2b_c.gif (31.7 KB, 915 views)
File Type: gif DaytonND20 tinyb2b_d.gif (28.6 KB, 913 views)
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Old 20th March 2010, 05:30 AM   #33
Spatz is offline Spatz  Germany
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What about a special dipole-tweeter that uses one voicecoil for a backside and a frontside tweeter. That should be small and thin enough to work perfectly up to highest frequency. The problem is you can't use pole pieces in this configuration, but two rings of NdFeB should to pretty good as well

Here's a sketch (voicecoil is 25mm):

Click the image to open in full size.

On the pro-side:
- low fs due to "infinite" volume inside the tweeter
- wisely planned magnetics could result in a large xmax and low variances in Bl(x)
- two surrounds lead to less rocking motions and due to the symmetrically placed surrounds, linearity in suspension should increase and variances in Kms(x) should decrease
- all this results in a better behaviour at lower frequencies

And now all that as a one inch tweeter with large surround and as a three inch dome midrange, that would be nice...

Bye,

Spatz

@ Rudolf:

How dare you not publishing these results in German boards!
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Old 20th March 2010, 02:38 PM   #34
keyser is offline keyser  Netherlands
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Thank Rudolf, very informative! At this moment, for a 3-way the Neo3W still seems the best alternative (next to the much more expensive Mundorf), but the Dayton combo might be interesting to mate to a B&G Neo8 in a 4-way.
Spatz, I like your idea!
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Old 20th March 2010, 03:18 PM   #35
Spatz is offline Spatz  Germany
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Here's the sketch in a larger size:

Click the image to open in full size.
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Old 20th March 2010, 04:11 PM   #36
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I'm getting (what I think are) decent results with my Neo3 PDRW. The trick seems to be the amount of effort I put into fixing the on-axis null - too much and too little both seem to hurt the overall response. I'm still experimenting - here's my last attempt, 1800 LR4 XO to a 6.5" midrange, no foam or felt on the tweeter:

Click the image to open in full size.

The listening axis is around the 2nd or 3rd curve from the top. I plan to try a notch for that 9kHz peak, even though it'll make the on-axis response worse. It's funny how a totally different picture emerges when you look at the off-axis plots.

I agree with keyser that the non-PDR model would probably be a better choice. Well, different set of trade-offs, I guess.
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Old 21st March 2010, 01:27 AM   #37
Rudolf is online now Rudolf  Germany
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Spatz,

if your design is technically feasable - which I can't judge - it would surely help to make a very compact dipole tweeter. But I don't know, if there is a market for more than two dozen pairs worldwide.


Saurav,

- adding nothing around the tweeter that could increase the dipole length
- ignoring the 0° axis when equalizing
- listenig off axis at 15-30°

those could be the best strategies when dealing with dipole tweeters. And yes, getting those small critical areas in the response right can become a never ending story ...

Rudolf
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Old 21st March 2010, 01:40 AM   #38
Spatz is offline Spatz  Germany
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Hi Rudolf,

this design is feasible, but you need radially magnetized neodym-rings. Aurasound can do that, I dn't know who else...

Of course, these tweeters could be used in other setups as well: for example, you could put it into baffle an place a highly damped box behind it. Now you have a normal tweeter with good motor and large chamber.

Or you could place it in front of a box that is open on the front and place some damping in the box keeping some distance to the driver (5-10 cm). Thus, the directivity to the front should be perfect, but on the rearside of the box there shouldn't be any sound...

You see, this product would be quite versatile, so there should be a market for those tweeters...

Bye, Spatz
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Old 21st March 2010, 09:04 AM   #39
mige0 is offline mige0  Austria
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Quote:
Originally Posted by Spatz View Post
Hi Rudolf,

this design is feasible, but you need radially magnetized neodym-rings. Aurasound can do that, I dn't know who else...

Of course, these tweeters could be used in other setups as well: for example, you could put it into baffle an place a highly damped box behind it. Now you have a normal tweeter with good motor and large chamber.

Or you could place it in front of a box that is open on the front and place some damping in the box keeping some distance to the driver (5-10 cm). Thus, the directivity to the front should be perfect, but on the rearside of the box there shouldn't be any sound...

You see, this product would be quite versatile, so there should be a market for those tweeters...

Bye, Spatz
An in interesting idea!
depending on the inner pole piece construction, normal magnets would do IMO.

Something to keep in mind with such a design is that you basically make a "compound system" - meaning - also with their inherent disadvantages not often mentioned.
There is always "time of flight" between the two diaphragms of a compound system - in the end resulting in a energy flow back and forth between the two diaphragms that can easily be heard at bass constructions as kinda "beat frequency"

Anyway - I would love to see (hear) such a driver...

Michael
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Old 21st March 2010, 05:14 PM   #40
Paul W is offline Paul W  United States
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Quote:
depending on the inner pole piece construction, normal magnets would do IMO.
Agree...you could use a radial arrangement of small Neo cylinders inside and/or outside an off-the-shelf/replacement dome and coil assembly. Gap height could be established with tubular soft iron sleeves and/or "washers". Should be possible for an avid DIY guy.
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