Here are some preliminary results about the effect of BH5.
With the help of a Radio Shack sound pressure meter, I measured the frequency response of my two 626R. Both were placed side by side on a coffee table. A dense polyurethane foam was used to isolate the speaker cabinet from the table wood. The Radio Shack microphone was placed about one foot from the two woofers. Measurements were repeated two times. The second time the L/R speaker connections were reversed. I used the Stereophile CD test for the test tones. The treble and mid pads were set to their minimum values (no sound from the ribbons).
RF : speaker lined with black open cell rubberfoam (about 1/2 inch thickness), no stuffing
BH5: speaker lined with BlackHole 5 (about 1 inch thick), no stuffing
Freq (Hz) RF (db) BH5(db)
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1000 82/83 86/86
200 101/101 101/100
160 100/100 101/100
125 100/99 102/100
100 98/98 99/99
80 98/98 99/99
63 94/94 95/95
50 91/91 92/91
40 84/84 86/87
31.5 81/81 81/81
25 81/81 82/82
20 75/75 75/76
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The first thing that surprised me is the level of the 1Khz tone, knowing that the crossover is set at 166 Hz - I thought that I would not have much sound at 1K. When playing music in this setup, I can hear much more than just the low frequencies.
I played two Jazz tracks from the test CD. I paid attention to the bass level and thightness. I did not notice a major difference between to two speakers. However, both speakers sound slightly different.
My conclusion is that lining the cabinet with rubber foam or BH5 increases slighltly the amount of bass. In a previous listening test, I compared an empty 626R with one already lined with rubber foam and there was a bass increase in the latter.
Rocket wrote:
it is supposed to clean up the mids in the speaker
I don't think that the VMPS speakers would benefit much from BH5 for the mid frequencies. Most of the mids are coming from the ribbon panel which has its own enclosure.
Bruno