> Here's the natural response of a GPA 288H on a 511E horn . This is unEQed . It was published ( a couple years back as a stamp-size pic ) by GPA .
> Enlarged , it clearly shows the 8K & 10K dips and 12.5K peak in response . These are part of the normal response curve for most all, 288(s) and shouldn't be viewed as "problem" areas, when diagnosing the health of a 288 . .
> If I were you ( living overseas ) , I would have a competent speaker tech ( with test gear ) measure your drivers ( on your horns ) for frequency response & diaphragm fit . Compare to the first pic .
> A healthy 288-8K ( with healthy diaphragms that are seated properly ) will measure very close to what you see above ( since GPAs 288H is closely modeled on the 288-8K, excluding the magnet type ) ..
> For use without a tweeter ( on the 511E ) one needs a midrange suppression/ HF lift circuit in place, to make the driver sound HiFi .
> If you want to experiment with this sort of circuit then copy the top portion of the following pic . Vary the capacitance of C-1, from 3uF to 6uF, according to taste .
Here are two "looks" at my 288-8K ( on an EH-500 radial horn / this horn is similar in size to the 811 ) . This curve is passively EQed and is here to demonstrate the FR that the driver is capable of on a smallish horn . ( Focus on the curve with 1/3 octave smoothing, since this closer to the resolution of most peoples ears ) .
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