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Old 2nd June 2007, 05:27 AM   #1
Shim is offline Shim  United States
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Default CA21REX-4ohm

Hi everyone, I just wanted to introduce myself and say you have some very informative forums going here.
I have basically finished my first DIY build of the P.E. Vifa bookshelf speaker design. After spending 3 times as much money as I would have had I just bought their kit I then spent more and cleared up the mess at 1200hz with a 3rd order butterworth.
About all that is left now is to try some Clarity caps.

I have a book shelf that runs the length of my desk and the spkrs are in that. Since I almost have Diana Krall singing from in front of my desk I feel I can show my face in public. Keep in mind I have no clue what I'm doing and have tuned them by ear, but they do sound pretty good.

I just ordered those 4ohm Seas from Madisound and want to do a take on the Njord. I coudn't find any posts where ppl had used a 4 ohm driver, other than the car, and could use a point in the right direction before spending 10 times what I should
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Old 3rd June 2007, 02:08 PM   #2
Shim is offline Shim  United States
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Guess I'm the guinea pig on the 4 ohm driver front here.
Here are the specs from Mad http://www.madisound.com/catalog/pro...oducts_id=8189
Ordered the new Vifa XT25 from to go with them http://www.madisound.com/catalog/pro...7464d615850546
I figure my next good choice could be the new Peerless HDS if I'm not happy with the sound. http://www.madisound.com/catalog/pro...oducts_id=1744
The guys at Zaph gave both of them great reviews so they should be fun to mess around with.
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Old 3rd June 2007, 11:30 PM   #3
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Nothing wrong with using the 4 Ohm. It just takes a little care in designing the XO to prevent low impedences <4 Ohm, since most home amps are not very happy with that.
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Old 4th June 2007, 12:56 AM   #4
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I probably would use the second tweeter because it's 93 dB as is the woofer. xover at 2000/2500Hz or similar. can use a 1. order on woofer (maybe). The first tweeter is half the 'sensibility' output (-3dB) and half the impedance.
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Old 4th June 2007, 04:39 AM   #5
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Quote:
Originally posted by Inductor The first tweeter is half the 'sensibility' output (-3dB) and half the impedance.
And it's finicky too. But who can resist an XT25 at half its usual price?
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Old 4th June 2007, 12:39 PM   #6
sreten is online now sreten  United Kingdom
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Hi,

Accounting for 4dB baffle step you would need a 89dB tweeter.

/sreten.
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Old 4th June 2007, 12:46 PM   #7
Shim is offline Shim  United States
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Thanks for the feedback guys.
Willitwork's comment:
Quote:
And it's finicky too. But who can resist an XT25 at half its usual price?
At $27 I figure I can mess around with it in my bookshelves. They're like a testing ground, the more I read and learn I buy some bits and try something new. I always learn something and sometimes I actually improve things

"Finicky"... great I have enough junk laying around to put together a 2nd order highpass just to see how they sound. I have a pair of 2.0mH 14ga Solen inductors I couldn't get out of the Vifas fast enough, killed all the mid range and made them very inefficient, thought I would at least start there with the base and see.

Ok, here's where the newbie part really shines, what do you mean Inductor?
Quote:
designing the XO to prevent low impedences <4 Ohm, since most home amps are not very happy with that.
I will be using them on an old NAD 705 reciever that I believe are good at reading that sort of thing.

edited:
now you really have me at a disadvantage
Quote:
Accounting for 4dB baffle step you would need a 89dB tweeter.
I'm not questioning you sreten but rather asking how I determine that from the given info on these speakers. You could tell me but then I wouldn't have learned how to calculate it myself.
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Old 4th June 2007, 03:21 PM   #8
sreten is online now sreten  United Kingdom
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Hi,

The comment about low impedances is basically saying you cannot
take as many liberties with system impedance and phase angles in
the crossover design with 4 ohm drivers compared to 8 ohm drivers.

As a rule of thumb you need to reduce the reference level of a bass/mid
unit by the amount of implemented BSC to get refrence mid treble levels.

The same also applies to 3 ways (with all BSC in the bass driver).
e.g. for 4dB BSC a 90dB bass unit would be used with a 86dB mid.

/sreten.
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Old 4th June 2007, 03:33 PM   #9
sreten is online now sreten  United Kingdom
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Click the image to open in full size.

Hi,

The above shows a response designed for a series inductor (+ optional zobel).

BSC takes place mainly below 1Khz in a not too wide cabinet.
The rise in the drivers response above 1Khz is controlled by
the BSC inductor and then rolls off acoustically at around 3KHz.

This is how the Njord c/o is designed, at least for the bass/mid unit.

If you want to sim it : http://www.rjbaudio.com/Audiofiles/FRDtools.html

/sreten.
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Old 5th June 2007, 01:27 AM   #10
Shim is offline Shim  United States
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Thanks sreten, I'm still digesting
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