Question for John Marsh re: Seas tweeters

[LNeilB]

John,

Do you feel that the Seas 27TDFC and 27TBFC/G are easily interchangeable?
The curves for both are really close....

[JonMarsh]

Basically, yes. There are some differences which could result in subtle voicing differences, but the H1212 is a fine tweeter- much better than the H400, for example, which I used in the mid 90's. Most important is that the impedance curves are quite similar.

[LNeilB]

Comparison

How would you compare/contrast the H1212 and the RS28 tweeters? Is there a clear winner?

[LNeilB]

And before I forget....

I often see you recommend removal of diffusors, lenses and the like from tweeters to make them sound better. If I'm not mistaken, it should be easy to disassemble the H1212 faceplate and pull out the clear lens Seas puts on the grille. Do you think this will reduce sibilant emphasis a bit?

[JonMarsh]

Do you think the H1212 has a sibilant emphasis?

I'd look at it closely with shaped sine bursts over a wide rante of frequencies before drawing conclusions. There is a lot of variation in diffuser structures- Vifa and MB Quart had some pretty nasty ones, IMO.

The "problem" with having a transparent tweeter in your system, is that it will be revealing of issues elsewhere in your system. This can include source program quality, your source electrtonics (particularly a lot of CD players), amplifier electronics quality, even cables... The Focal TC120dx2 series is often accused of sibilance or brightness or whatever, mostly unjustified in my opinion- it was just reproducing what was fed to it.

If cost is a parameter, the H1212 is probably the winner. Non-linear distortion is very close, though the RS28 seems to be a bit cleaner with regards to upper range harmonics- less high order distortion. But we're talking pretty low levels for both.

~Jon

[LNeilB]

That's great!

Thanks Jon!

I won't worry about splitting hairs between those two tweeters. But I'm still not certain about the diffuser lens. I'm guessing I should leave it alone unless I can measure it. I do recall having seen Totem reshape it in one of their speakers, adding a large hole in the center of it.

Neil

[JonMarsh]

The hole in the center thing is common- DLR did that with his mod to the Dayton- would be interesting to do a detailed comparison (another thing on my long "to do" list).

~Jon

[Dennis H]

Those diffusor thingies in the center seem backwards to me. That's the part of the dome you DON'T want to block because it's nice and flat and makes a good piston. Why not a ring of felt to block the outside where the slope of the dome is steepest and presents the most phase problems above 10K? A bonus would be a 1" tweet with a polar pattern like a 3/4".

[LNeilB]

I think....

Unless I am mistaken, isn't the diffusor there to improve off-axis response? If it does so at the expense of on-axis sound quality, I think the hole in the middle if the lens is the way to go.

[Mark K]

Unless I am mistaken, isn't the diffusor there to improve off-axis response? If it does so at the expense of on-axis sound quality, I think the hole in the middle if the lens is the way to go.

The diffusor usually is there to prop up the sag in FR that occurs on axis.

I did linear distortion measurements of the RS28 with and without the diffusor and they were roughly the same.

IMHO, if you can go through the effort to equalize the FR irregularity, it may be worth it to take off the diffusor. But on a well implimented one, it's probably not worth it to "just take it off" without eq'ing it.