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Old 25th August 2013, 12:18 AM   #11
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Quote:
Originally Posted by Face View Post
I don't believe this is correct.
I agree.

The distortion is also lower in the lower range.

The wave guide negates the 40k hz extension because it doesnt boost over 15K although I dont hear a difference in air on the top end vs the bare tweeter. It is by far my favorite tweeter now that 1500 and above is clean from the wave guide. Dispersion is now as good as it gets.
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Old 25th August 2013, 09:08 AM   #12
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Based on the PMs I'm getting a clarification is in order.

The XT25tg60 is much cleaner on the low end than the XT25tg30. If you look for test for the sonus faber XT25tg61 which is also the same motor as the 60 and the Scan speak 2604/8330 you see the low end being far cleaner. With the wave guide and a cap a 1500 cross with a 440hz res peak is perfectly ok.

Forum members get it in their heads that the XT25tg30 has worse limitations, they dismiss the 60 as the same unit and it isnt. With a wave guide the 60 has none of those limitations.
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Old 25th August 2013, 10:34 AM   #13
ODougbo is offline ODougbo  United States
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Thanks for posting SpinMonster - I know lots of folks have XT25TG30-04s and no projects to use them in.
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Old 25th August 2013, 04:00 PM   #14
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Quote:
Originally Posted by Face View Post
I don't believe this is correct.
Test it in FEMM, if you have a Hall sensor in your phone (most do) this can be directly measured around the periphery will help you understand the bucking action. Troels Gravesen has tested adding a bucking magnet to boost the spl often getting upwards of a 1.5dB gain. Not huge but better than nothing. The main reason for not much gain is the magnet is on the outside of the magnetic circuit atop of the T pole. Adding a ferrous metal can would help reduce stray fields a bit more. Mu metal should provide best shielding with a bucking magnet.

I'm not asking anyone to simply take my word for it, but am asking to test and read up on the subject.
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Old 25th August 2013, 04:23 PM   #15
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Quote:
Originally Posted by SpinMonster View Post
Based on the PMs I'm getting a clarification is in order.

The XT25tg60 is much cleaner on the low end than the XT25tg30. If you look for test for the sonus faber XT25tg61 which is also the same motor as the 60 and the Scan speak 2604/8330 you see the low end being far cleaner. With the wave guide and a cap a 1500 cross with a 440hz res peak is perfectly ok.

Forum members get it in their heads that the XT25tg30 has worse limitations, they dismiss the 60 as the same unit and it isnt. With a wave guide the 60 has none of those limitations.
It still has rather highish distortion at the low end. The waveguide help reduce this and provides better low end reinforcement. Still to low of a crossover point for my tastes, not that I dislike the 60. It certainly does perform better than the 30
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Old 25th August 2013, 05:02 PM   #16
seanny is offline seanny  United States
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Face's quote applies to a double magnet speaker that have 2 magnets between metal plates. A bucking magnet is a magnet attacted outside a finished speaker.

A bucking magnet increases Bl by 3%.
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Old 25th August 2013, 10:22 PM   #17
gedlee is offline gedlee  United States
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Originally Posted by Greebster View Post
The design intent of the extra magnet is to provide shielding of stray magnetic fields, commonly called a bucking magnet. The increase in gain was unintentional, but we'll take whatever we can on that front
This is absolutely correct by the way. There is some gap flux addition, but the main effect is stray field reduction. The front plate also gets saturated, which reduces flux modulation. It is a Band-Aid however since this technique is an expensive waste of magnet volume.

Why is there a Hall sensor in a cell phone? How can it be used as you indicate?
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Old 25th August 2013, 10:39 PM   #18
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Originally Posted by seanny View Post
Face's quote applies to a double magnet speaker that have 2 magnets between metal plates. A bucking magnet is a magnet attacted outside a finished speaker.

A bucking magnet increases Bl by 3%.
Face's post was taken directly from the advertisement literature talking about the goal of the second magnet on the 60. The company's goal was to increase efficiency, lower res freq, and lower distortion. The fact that it reduces stray mag fields in the world of flat panel TVs isnt as important as it once was.

His post along with mine was to explain to Dave Pellegrene what the difference between the 30 and 60 were from the wave guide use perspective because Dave asked in post 2 for a clarification of what the 60 was.

All dave needed to know in terms of wave guides was that the 60 is a 30 with a second magnet on it, therefore the diaphragm and mounting are the same.
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Old 25th August 2013, 11:19 PM   #19
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Originally Posted by Greebster View Post
It still has rather highish distortion at the low end. The waveguide help reduce this and provides better low end reinforcement. Still to low of a crossover point for my tastes, not that I dislike the 60. It certainly does perform better than the 30
You arent giving the wave guide's contribution its credit of how much it lowers distortion. Using a cap on any tweeter with a wave guide lowers distortion under the level of a bare 1" dome. I dont have measurement equipment but the way the XT25 is used here counters any statement about its low end distortion. I think the lack of interest in this thread is that people saw the two drivers used and dismissed it as garbage. Maybe it is. All I know is I have a great sounding speaker free of the criticisms of these drivers. I figured it would have people take another look at waveguides. I'm not pushing these drivers. Now that I know how Dave's wave guides sound, I will build a system using the best available parts with no costs cut.To illustrate for others who aren't aware of Zaph's tests for wave guides added to a tweeter..............

This is the 27-TDFC bare response
Click the image to open in full size.

This is the lift with a small 6" wave guide (I used a 8" wide for the XT25 = more low end lift)
Click the image to open in full size.

This is the response with a 3.3 cap on it:
Click the image to open in full size.

Here is the bare tweeter distortion plot
Click the image to open in full size.

Here is the distortion plot with guide and cap. The F2 distortion is down by 25db at 2000hz.
Click the image to open in full size.

No way the XT25 with a guide is worse low end distortion above 1700 than any bare tweeter after you reshape the low end to counter for the rising wave guide lift. Above 2500, the XT25's performance is already reference level. Its dispersion with a wave guide for me makes it as good as it gets. For some reason, likely its phase plug, makes it interact better with a wave guide than most tweeters. Once back to a flat response with the 8" guide and cap I used, I can apply any slope curve with active crossing and get a low end that is better than any bare tweeter. The power handling is unreal. I have an extra 10db from the guide so I need a fraction of a watt to hit the same SPL.

People just have it in for the XT25 because they read about its distortion and they dismiss it with generalized statements. Their loss. A wave guide and cap shaing the response back to flat lowers the noise at 2000hz 20db and the resonant frequency ringing in lower by something like 30db.

You cant just pop a 3.3 or 4 cap onto a bare 1" because it would be down 10db in its response in the low end. The 60 with a wave guide used like this is the equal of any 1" dome in distortion....or better.

Last edited by SpinMonster; 25th August 2013 at 11:38 PM.
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Old 26th August 2013, 12:15 AM   #20
Pallas is offline Pallas  Pakistan
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Quote:
Originally Posted by SpinMonster View Post
***I think the lack of interest in this thread is that people saw the two drivers used and dismissed it as garbage.***
I doubt that's the case. It looks like a very nicely thought-out and executed project. What I find especially interesting is that the measurements seem to show that Dave's WG removes the actual problem I've heard from the Vifa and ScanSpeak ring radiators: extremely extremely narrow treble dispersion.

Quote:
Originally Posted by SpinMonster View Post
Now that I know how Dave's wave guides sound, I will build a system using the best available parts with no costs cut.
That, by contrast, I suspect that would end up disappointing. Not because it wouldn't be good, but because there wouldn't be much improvement from what you already have. Probably get more people on forums to ooh and aah if you're able to throw out brand names like Audio Technology, Accuton, Scan Revelator, etc, but ultimately speakers really boil down to three things: listening axis FR, dispersion, and output capability. Your current project looks well-sorted for a speaker of that size. I'd say be happy, and add multiple subs.
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