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Old 9th April 2006, 01:14 PM   #1
Fossil is offline Fossil  Singapore
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Default What could be wrong?

I have a pair of Usher spkrs which use the Vifa TC26TG05-06 tweeters. It's a 6 ohms 90db unit.

Out of vanity, I replaced it with a pair of XT25 ring radiator without changing the X-over. As the XT is 4 ohms and 91.5db, I expected higher high freq energy but, on the contrary, I'm hearing less.

How is this so?
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Old 9th April 2006, 01:39 PM   #2
BWRX is offline BWRX  United States
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http://www.d-s-t.com/link/vifa/data/tc26tg05-06d.htm this site says your original tweeter has 92dB sensitivity.

If you look at the frequency response graphs of the tweeters (you can find them on madisound's site) you'll see that the FR measurements were taken at 2.83V @ 1m. 2.83V with an 8ohm speaker is 1W, but is 2W for a 4ohm speaker. If the XT25 were tested at 1W @ 1m you'd see that it would be less sensitive than your original tweeter. Some numbers by themselves can be misleading. Sensitivity is one of those numbers. Output power of an amplifier is a more infamous example
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Old 9th April 2006, 02:08 PM   #3
Fossil is offline Fossil  Singapore
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Oops! My mistake on the db!

OK, so the XT is 0.5db lower. But shouldn't the higher power output for the same signal (V) more than compensate for this difference?
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Old 9th April 2006, 02:13 PM   #4
Fossil is offline Fossil  Singapore
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Oops again!

I think I took a far too simplistic view on the compensation for the tweeter!!

I'll play with some numbers and see how I can revise the L-pad values.

Sorry for wasting the time of all thsoe who have read this thread!
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Old 9th April 2006, 02:27 PM   #5
tade is offline tade  United States
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I think it is cool that you got an answer so quickly. Sometimes my braing has a stupid malfunction and the members of this forum are more than hapy to set mine straight in a jiffy!
Good luck with your project.
BTW, how do the ring radiators sound?
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Old 9th April 2006, 02:48 PM   #6
Fossil is offline Fossil  Singapore
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hmmm...
Using the L-pad calculator from lalena and then plugging in the numbers into excel, I still couldn't quite understand what is happening.

With the woofer at 86db and the tweeter at 92db and assuming they only compensate it by 5db (I think they usually under compensate so that the speaker sounds brighter n more lively), I got R1 = 2.6 and R2 = 7.7.

Then I put these values with the 4ohms and I get a oervall imp of abt 5.2 ohms (close enough) and a reduction of 3.6db. Therefore the output shd be around 88db, right?

Yet somewhat the overall presentation is very muffled...
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Old 9th April 2006, 09:44 PM   #7
BWRX is offline BWRX  United States
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Like I said earlier, the XT25 tweeter is 91.5dB with 2W@1m, not with 1W.

http://www.madisound.com/pdf/vifa/xt25tg30-04e.pdf

So it would be more like 88.5dB with 1W@1m, which is a lower sensitivity than you used with your calculations. You need to pad it down much less to bring the treble back up.
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Old 10th April 2006, 02:23 AM   #8
Fossil is offline Fossil  Singapore
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ah!! now I see!!

I've never noticed that different manufacturers present their curves differently, ie, SS/Vifa using 2.83V/m while some use 1W/m.

Many thanks!!
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Old 10th April 2006, 10:03 AM   #9
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Fossil

I've never noticed that different manufacturers present their curves differently,
ie, SS/Vifa using 2.83V/m while some use 1W/m.
Hi,

they all use 2.83V, which is often misrepresented as 1W,
especially when manafacturers quote 4 ohm driver sensitivity.

/sreten.
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Old 10th April 2006, 11:48 AM   #10
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Hi, Fossil.
Can you post your complete set up.
Woofer
Tweeter
Wo filter Cap
Wo filter Induct
Tw filter Cap
Tw filter Induct
and the L-pad (if) you are using.
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