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Old 5th January 2013, 02:36 PM   #231
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I have got 4 microphones, but I don't know how good they are, one came with my ONKYO Receiver , which is used to set the speakers up! 2 are SONY ones I bought nearly 40 years ago. Just ruined another 2 diaphragms on my 4' x 2' ferrite planars, moving them into the garage, but I won't be rebuilding them yet. so delicate 12 um Mylar. I'm getting worse as I get older.
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Last edited by JAMESBOS; 5th January 2013 at 02:40 PM.
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Old 6th January 2013, 12:18 PM   #232
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Maybe you can find a curve of the Onkyo somewhere online, where people have used it in REW.

The Panasonic capsules are about $2 or so and definitely good enough for measurements.
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Old 22nd February 2013, 08:31 AM   #233
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I have had a rethink on the epsilon layout, must do more experimentation, will get back when finished, more rebuilds, again,c'est la vie.!!?
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Old 23rd February 2013, 04:34 AM   #234
gootee is offline gootee  United States
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Good. Enjoy! Some day I hope to have time to try similar things.

You can download free software, such as ARTA, that will let you use a mic in conjunction with a computer sound card, to perform speaker measurements. You might need a mic preamp. If you post the mics' makes and model numbers, someone might be able to say exactly how it might be able to be done, with one of your mics.

Cheers,

Tom
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Old 23rd February 2013, 06:55 PM   #235
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Have found out using the epsilon layout when you use 12.7 mm wide neo magnets is a waste of time. The one I rebuilt using the epsilon layout is 8 Db down on a ferrite magnet one using 18 mm wide ferrite magnets. You live and learn. Whereas the ferrite 18 mm wide magnets use 2 foils on the magnet body you can only get 1 foil on the 12.7 mm neo magnets this is the secret to the difference in the sensitivity.So the 60 x 40 using 18 mm wide magnets with the epsilon layout is 8 Db more sensitive than a 4' x 2' one using the epsilon layout and 12.7 mm wide Neo magnets. C'est La Vie.
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Old 23rd February 2013, 07:41 PM   #236
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Henry so are you saying there is no advantage using neo,s over ferrite magnets,thats good cost wise when i get around to reverse engineering my epsilons as i wish build a larger pair and the cost of the magnets is a big factor.
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Old 23rd February 2013, 09:18 PM   #237
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Are the thicknesses of the magnets the same?

The distance of the foil to the magnets will be a big contributing factor to the difference in sensitivity.

Also the total resistance of each foil will make a difference as well as this determines how much current is flowing through the Voice Coil as the current is directly related to the magnetic field.

If all else is the same then then doubling of the current in the foil by either doubling the voltage or adding a second foil then you should get an increase in sensitivity.

If you double the voltage with the two foils this will maintain the same current as a single foil providing that they are in series.
But as there are two foils contributing to the magnetic field this should increase the sensitivity by 6db.

Also the sensitivity will drop by 6db if the distance of the foil to the magnets is doubled and it will be increase by 6db if it is halved.
So therefore if you are talking about a distance of an 1/8" then as little as 1/32" to 1/16" can make a big difference in your end sensitivity.

Neo's are definitely more powerful when comparing them to a ferrite of exactly the same size.

Earlier (in another thread) I had shown how I made a simple magentometer to measure the field strength of the magents and I had found that by stacking them was just like connecting battery's in series and every time you doubled the number of magnets in the stack (thickness) the field strength was doubled as well.

How to make a good transformer for ribbon tweeter?

It was very simple to make using a an EMI core torn out of a dead PC supply.
I very useful tool indeed when working with magnets.

Cheers!!!

jer

Last edited by geraldfryjr; 23rd February 2013 at 09:47 PM.
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Old 24th February 2013, 12:08 AM   #238
WrineX is offline WrineX  Netherlands
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Quote:
If you double the voltage with the two foils this will maintain the same current as a single foil providing that they are in series.
But as there are two foils contributing to the magnetic field this should increase the sensitivity by 6db.
did not notice this btw. i did a setup with 2 coils with foil on top of eachother(spaced by some tape), measured one coil then 2 in series, i ended up with an increase of only 1.5 dB, ofc there was extra weight of the foil + the tape that serperated them from eachother. so i can imagine a little bit more dB gain if the extra weight whas not there.

while in paralel it increased by 6 dB.

am i missing something ?
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Old 24th February 2013, 12:40 AM   #239
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I may be wrong in my estimation as I was thinking originally it might only be a 3db increase.
I am not good with math when it comes to converting db's in my head.
So 1.5 db may very well be the correct factor.

jer
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Old 24th February 2013, 09:58 AM   #240
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Quote:
Originally Posted by brian t View Post
Henry so are you saying there is no advantage using neo,s over ferrite magnets,thats good cost wise when i get around to reverse engineering my epsilons as i wish build a larger pair and the cost of the magnets is a big factor.
Yes there is no advantage in using the epsilon layout with 12.7 mm wide neos against 18 mm ferrites.I am listening to a ferrite planar 60 x 40 mm on the left, against a 4' x 2' neo one on the right. I have to run the neo one 8 Db higher to get them equal in volume. The ferrites are 50 x 18 x 10 mm and the neos are 50 x 12.7 x 3 mm. When I used the normal layout of the tape they were equal in sensitivity on the neo one. Also the ferrite ones are a lot smaller and about the same weight.The resistance of both are 6.6 ohms exactly. I am in the process of working out the layout for some 25 mm wide ferrites I have.Not easy at my age. I'm glad I don't have to rebuild all my 60 x 40 planars, I have 11 in the living room hanging from the ceiling. Iwill only have to re-build about 10 ferrite ones,again.!! C'est la vie.
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