Rogers LS4a - tweeters - diyAudio
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Old 1st May 2013, 12:25 PM   #1
stax92 is offline stax92  United Kingdom
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Default Rogers LS4a - tweeters

Hello all

I've been enjoying the site for quite a while but had nothing to say... until now.

I have a pair of these and when I bought them a tweeter was blown. I replaced both with Vifa DX19TD05-04 units on recommendation from a fella at Wilmslow Audio. They sounded fine for ages but I recently wondered if they could sound better so I spoke to a fella at Falcon Acoustics, top bloke, very knowledgeable and helpful, about the crossovers (whether to recap).

He mentioned that the original tweeters were made by SEAS for Rogers and that a more accurate replacement would be the 19TAFD/G. I've since seen a post on the net somewhere quoting a rep at SEAS saying the same thing so my friend at Falcon is probably right. So I bought a pair.

The problem is that the Vifa ones (similar price) sound much better in the Rogers boxes than their replacement SEAS - far more detailed. Where it gets confusing is that the basic specs of both aren't very similar at all.

Nominal Impedance for the Vifa is 4ohm/ SEAS is 8ohm. Sensitivity is 90.7 versus 88. DC resistance is 2.9ohm versus 6.2. Voice coil inductance is 0.017mH versus 0.05mH. The frequency range for the SEAS is 4-20kHz but the spec sheet for the Vifa doesn't specify it.

My question is that the crossover will have been designed for the SEAS so how can the Vifa sound noticeably better even when the basic specs are so different? I don't have schematic of the crossover I'm afraid and I'm no electronics expert.

I'm confused?? Have I got poor hearing or quirky tastes?

Last edited by stax92; 1st May 2013 at 03:36 PM.
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Old 2nd May 2013, 12:05 PM   #2
stax92 is offline stax92  United Kingdom
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I suppose what I'm getting at is because the Vifas have a lower impedance and higher sensitivity then I'm getting more out of the top end and that suits my tastes, the source, the position of the speakers etc. - does that sound about right?

Still confused about my failed upgrade!
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Old 2nd May 2013, 01:07 PM   #3
LJNorth is offline LJNorth  United Kingdom
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I think you have had no other replies as your story is a common one. A shop offered you a less-than-optimal replacement product (driver and crossover matching is far more complex than nominal impedance and nominal sensitivity). You fitted the replacement and you noted and became accustomed to an increase in 'detail'. Actually the replacement tweeter was most likely not suited to the original design, but without measurement equipment you will be unable to determine quite how sub-optimal the result is (you would probably be shocked by the measured result of your DIY replacements).
You now like the inaccurate reproduction of your sub-optimal system, I suppose this is good so why change? Unless you wish to return the design to its original spec. (hifi) , there is not a lot to be done. In essence you wish to have a permanent in-built tone control in your crossover, but what is wrong with the one on the front of your amp?
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Old 2nd May 2013, 01:12 PM   #4
AndrewT is offline AndrewT  Scotland
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LJ, has a point.
Getting used to an incorrect replay is very difficult for the brain to undo.
That's why measurement is so important. Are you actually comparing like to like?
The measurement cannot tell you it is nice to listen to. It can tell your the levels are similar, or same, or grossly different.
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Old 2nd May 2013, 02:41 PM   #5
stax92 is offline stax92  United Kingdom
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Cheers fellas. Sounds about right although the inaccurate reproduction sounds more like being in a room with live music so I'll stick with the 'wrong' ones. With the SEAS replacements the 'original' spec speakers sound very humdrum - even considering they're hardly high end. Maybe they just reveal a weakness in my amp (Cambridge Audio A1 fed by a modded Caiman DAC) so I'll dust them off and give them a go when I change that. Thanks again.
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Old 2nd May 2013, 03:32 PM   #6
LJNorth is offline LJNorth  United Kingdom
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I like the idea of the loudspeakers sounding more lifelike, but beware - you can fall in to the trap of your hifi sounding 'realer-than-real', I did it a while ago with some speakers I tweaked by ear, then went to a concert (first in a while) and was a little disappointed in the lack of treble from the singers, i suppose they need better tweeters as well.
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Old 2nd May 2013, 09:30 PM   #7
stax92 is offline stax92  United Kingdom
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Fair point, very good post and food for thought. I'll listen to them with that in mind - it's all part of the mix. And yes, real life can be rather disappointing sometimes
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Old 5th June 2013, 09:00 AM   #8
stax92 is offline stax92  United Kingdom
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After a month of listening to the new tweeters I'd like to thank you both for your replies. I put the old ones back in just to test them out and they sounded very harsh this time. With the SEAS tweeters the bass sounds better, as does the treble and it all seems more 'natural'.
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Old 5th June 2013, 05:30 PM   #9
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You can tweak SEAS tweeter to better suit your taste by changing L-pad resistors in Rogers crossover. Also, it is possible that original condition (with SEAS tweeter) actually does not have enough HF energy to give flat response, that there is too much HF roll off. It all depends on acoustics of your room. Rogers is tuned to give flat response in anechoic room + BBC school of loudspeakers tends to keep HF response a little on dark side. That is the reason why old loudspeakers used to have L-pad pots. Each individual room requires different HF setting to give flat response. It is very likely that a couple of dBs are missing in the HF range, so Vifa tweeter can in fact be right choice for flat response.
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Old 5th June 2013, 06:12 PM   #10
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Quote:
Originally Posted by stax92 View Post
my amp (Cambridge Audio A1 fed by a modded Caiman DAC) so I'll dust them off and give them a go when I change that. Thanks again.
The A1 is actually a real good amp, worth more than some many times the cost. Ive yet to find an amp that sounds better for less than 3 times the price (and I dont even have an external DAC).

I love the A1 so much that I bought another, and Im planning an active preamp and xover front end.
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Last edited by mondogenerator; 5th June 2013 at 06:16 PM.
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