Replacing an 8 ohm tweeter with a 4 or 6 ohm tweeter? - diyAudio
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Old 28th April 2012, 11:59 PM   #1
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Default Replacing an 8 ohm tweeter with a 4 or 6 ohm tweeter?

I have Wilmslow audios k100s which have these tweeters which are 8 ohms Europe Audio
I want to replace them with these tweeters which are 4 ohms http://www.scan-speak.dk/datasheet/pdf/d3004-662000.pdf
There are another 6 ohm possibility, but this would be my choice if possible. What is the easiest way to intergrate them.
Thanks
Regards
CL
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Old 29th April 2012, 12:32 AM   #2
tvrgeek is offline tvrgeek  United States
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First, that is 8 Ohm NOMINAL impedance. It does not really tell you what the impedance through the crossover region is. You have to measure it.

Second, why are you talking about replacing a very very good tweeter with a very expensive one and not talking about your 40 or so years experience in crossovers voicing. If you don't have that level of experience, you will not like the outcome. The crossover is 90% of the sound. The quality difference between these two drivers is splitting hairs. From very very good to "What on earth can we possible do better, and man are you going to pay for it" ultra high end range. I have the 40 years off and on, and am not ready for an air-circ yet. Maybe this summer.

Replacing the tweeter means redoing the crossover, so correct padding is not a problem. Tweeters are far more efficient than the midrange, so they are padded anyway. Sometimes this is done with an L-pad, but I go through the extra effort to prototype until I have it right to just use a series resistor. It makes the caps in the tweeter smaller, and reduces the distortion in the power amp by being a higher impedance load. As an example, the speakers I am building right now have a 6.2 Ohm Re. 8 Ohm "nominal" Seas tweeter. They require 9 Ohms series resistance by the time the crossover was complete with all the notches and shelves to match the mid exactly.
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Old 29th April 2012, 12:55 AM   #3
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I am thinking to change the tweeters as one of the originals is fried. I managed to fix it as the break in the coil is in the free air gap so I soldered a tail on to it just for now, but they need replacing. I can buy the same again or just a coil, but I thought about fitting tweeters with a more even response. I contacted Wilmslow and they said this was a drop in replacement, but I am sceptical that it wont need impedence matching somehow which is why I posted here. If we asume the crossover is perfect for the original tweeter, cant we just add a series resistor? The original tweeter has a coil resistance of 5.6 ohms and the new possibility has a coil resistance of 3.0 ohms, would not a 2.5 ohm non inductive resistor in series balance things out? The sensitivity of both tweeters is around the same.
Regards
CL

Last edited by cafe latte; 29th April 2012 at 12:59 AM.
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Old 29th April 2012, 01:53 AM   #4
AllenB is offline AllenB  Australia
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Hi cafe latte, the interaction between your average driver and crossover is complex enough that it can be difficult to predict the outcome. If Wilmslow say these are a drop in replacement, they are suggesting you should do nothing else. If you added the resistor it would probably have unwanted effects.

You don't have to settle for this though. You could redesign the crossover, although this would be difficult as you'd need to match the effort of the designer if you want to see a benefit.

On the other hand you could merely supervise the swap by making reasonable measurements of the speakers before and after adding the new tweeters. This should get you close.
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Old 29th April 2012, 02:15 AM   #5
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Thanks Allen,
How much gain differences does 4,6 or 8 ohms actually make?
I have been doing a bit or research on the Wilmslow site. They list the Vifa d27tg-35-06 (the original tweeter Wilmslow used in their k100 kit). They now use the ones in mine which is the scanspeak d2608-9130. Anyway I noted they list the vifa as a drop in replacement for the kef t27 also, and they list the scanspeak D2905/950000 as a drop in replacement for the Kefs too (also apparently a possibility for my speakers), yet the vifa's are 92db, 6ohms and have a dc resistance of 4.6 ohms and the classics are 90db 6 ohms and have a dc resistance of 4.7 ohms
The tweeters in my speakers (the d2608-9130) are 91db, 8 ohms and have a dc resistance of 5.6 ohms. The ones I thout about fitting which they also said were fine are 91.6db 4 ohms with a 3 ohm dc resistance. To me all these tweeter look very different in specs surely they cant all be a match?
Thanks
CL
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Old 29th April 2012, 02:19 AM   #6
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If Wilmslow are telling you that the tweeter is a drop in replacement then they are telling you bull crap and simply want to make a sale. This also throws the original loudspeakers crossover into question too as no decent crossover designer would ever tell you that it's a drop in replacement.

As has been said the 913 is one heck of a tweeter and the 6620 is only marginally better, if better at all. You can buy replacement coils for the 913 and they are easy and cheap to replace, doing so makes the most sense. Also if all you've done is snapped the fragile tinsel lead and have managed to repair the break, then you don't even need to replace the dome/coil assembly.
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Old 29th April 2012, 02:31 AM   #7
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Quote:
Originally Posted by cafe latte View Post
To me all these tweeter look very different in specs surely they cant all be a match?
Thanks
CL
They are different and are not drop in replacements. Some will probably drop in and do so fairly decently, some others wont even come close.

You asked how much of a difference it makes and it makes a lot. Looking at the DC resistance of the 913 and 6620 you're comparing 5.6 with 3 ohms. This almost by a factor of 2. In other words if you had a filter designed to work for the first driver it would be out by a lot for the second.

Below is just that happening. The blue trace is a transfer function for the 5.6 DCR tweeter with a 2nd order electrical filter applied and the red is what happens if you replace it with a 3ohm DCR tweeter. Not pretty.

Click the image to open in full size.
Attached Images
File Type: gif 5.6vs3.GIF (66.5 KB, 156 views)
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Old 29th April 2012, 02:38 AM   #8
AllenB is offline AllenB  Australia
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As far as the 4, 6 or 8 ohms is concerned, there is enough other stuff going on that these numbers aren't all that important. The other specs won't do much for you either, except the sensitivity which should be the same or better than what you replace. These numbers won't say much for how it sounds.

As far as the "drop-in" is concerned, it's already been mentioned too many times in this thread. I'd have to agree with 5th and add that you'll need to do some sensible tweaking at the very least.

I've used the d27tg and the 950000. The Vifa is a good inexpensive dome tweeter but if you're looking at the scan-speak and you haven't shied away from the price, then leave the vifa. The 950000 can be clean sounding, maybe a little 'accurate' sounding for whatever that means
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Old 29th April 2012, 02:55 AM   #9
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Ok if I want to upgrade my tweeters then how can I do it without messing things up? Is there a high quality tweeter that I could use that would need little modding? Also if I went for the d3004662000 could it be intergrated easily with some modding? As far as i am aware the k100s cross over at around 3000 hz if this helps
Regards
CL
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Old 29th April 2012, 03:13 AM   #10
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I cant help wondering if Wilmslow have not changed the crossover since they used the Vifas which were 92db and 6 ohms with a dc resistance of 4.6. If that is the case, then d3004662000 which are 91.6, 4 ohms and a dc resistance of 3 ohms looks maybe a bit better? Still if this were the case it would make the ones fitted badily match from what you guys have said.
Regards
CL
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