Altec VOTT 828 tests


49A. Sound pressure for cond. Mike M23 and dyn. Mike ES-58-S versus frequency. Great differencies in mike sensitivity (25 - 53 db versus test range).
Observe text for overlay 1 and overlay 3. Hasling proff. Mixer precision bandwidth: 10 Hz -0,1 dB 20 KHz -0,4 dB (bal. In/bal.out with 2 transformers).
The red curve is for cond. Mike M23 with phantom power 48 V reg. Mike preamp sensitivity has the same settings for the two tests, with fixed gain positions (10 pos. switch) so the differences in sensitivity is easily measured as vertical height is calibrated in log. dB, 10 dB per horizantal line. Differences in sensitivity and frequency range is simply the distance between the two curves. The swept frequency range is from 20 Hz to 1100 Hz. Red curve shows fine working range from 700 Hz and down. Fine linearity to 30 Hz for a bass horn .
The blue curve is the dyn. Mike ES-58-S with off switch. Drops from 200 Hz to 30 Hz, smooth roll off 20 dB like it should (vocal mike), around 50 dB from 200 to 20 Hz.
The speaker in the VOTT enclosure is Altec 416-8B, restored by Per Hasling, with very low Fs (22,0 Hz) and high compliance again, as when it left the Altec Factory, or even better.
My wings (triangles, they can get 30 cm wider in each side) are in the positions you can see on my web page
The measurements on this page are made with the mikes level with the center of the dustcap, and mikes 85 cm from the enclosure front. Software is SpectraPRO.
Copyrigt Hasling Audio. April. 30. 2011.


49B. Sound pressure curve versus frequency from the ported area added (violet curve) over the 2 mike curves are also taken with M23 mike (red curve is Cond. Mike M23, blue is the dyn. mike ES-58-S). Swept frequency is linear from 20 - 300 Hz. for all. Volume from power amp have been increased a little to get free of the red curve. Red and blue are the curves taken with mikes level with the center of the dustcap of the 416-8B, 85 cm from the enclosure front, see page 49A. Frequency linearity in the port is excellent.
Hasling Audio Systems, Denmark. Software is SpectraPRO
Copyright Hasling Audio. April. 30. 2011.