Mark K's Speaker Pages
...when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science...Lord Kelvin
Seas 27TBCD/GB-DXT small horn tweeter
Can Seas deliver the goods on a horn loaded tweeter? I purchased a pair for my own testing curiosity from Madisound.
Manufacturer's link- Seas 27TBCD/GB-DXT -forever more referred to as "the DXT tweeter." The meaningful reflection free interval on the impulse is ~7.125-2.8ms, or thereabouts, if you're interested in the resolution of the graph.
On axis frequency response at one meter
Certainly, a bit of a droop, but smooth, very smooth and easily correctable in the crossover. Or, leave a little droop if that's your preference.
Off axis family at 1 meter
Well, this is impressive. Remarkably extended off axis performance, and remarkably smooth and somewhat better than the typical 1" dome in dispersion. Note my baffle rotation assembly probably overestimates the drop at 60 degrees by 1-2dB, so really, the tweeter off axis 60 degree response is probably only ~5-6dB.
I shudder to show this (no really new information here), but some folks like it. It's very smooth, a reflection of the on axis smooth nature of the FR.
Impedance
A little bit of variation. Not sure why Seas didn't use ferrofluid and changed the design a little bit. (See Zaph's comments on impedance variation.)
What you've all been waiting for-some SL style 3 tone nonlinear distortion bursts.
Are you a pretender, or a contender. Let's jump right in with a 1k series.
Well, I didn't expect this. Remember, we're driving it in the middle of it's impedance hump. This is actually in the same league, though not quite, as the 27TBFC/G. Wow.
Now, at 1.3k. Well, this is even better. Still too much distortion to be crossed at 1.3k for my tastes, but very respectable.
Now at 1.5k. First unit one then unit two. Well, would you look at that. Eminently usable at 1.5k. Both test similarly.
Last, at 2k.
Conclusion
Well, Seas has produced another winner.
The highs-Smooth on axis frequency response, and controlled, smooth off axis response as well. The driver lends itself well to a second order crossover. (See Zaph's circuit.) As a bonus, distortion is low and the horn sets the AC further back, making phase alignment easier. Though not quite the distortion champ (that distinction is still held by the 27TBFC/G), based on these distortion measurements the usable lower limit of this tweeter is 1.5k.
The lows-well the price of Seas tweeters is climbing, and the impedance variation/lack of ferrofluid.