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Sansui SP-3005 project confusion

Posted by maxhifi (A) on October 4, 2016 at 23:01:53

Picked up a pair of these rather unique speakers a few years back in very poor shape, cabinets had got wet at some point (by previous owner) and bottoms totally rotted out. Left them in the garage as a future project Recently I Decided to have some fun, removed and tested all components and all drivers are good. Claimed sensitivity is 96 dB 1W/ 1m so that's why posting here.

Decided to then do some reverse engineering to figure out what the original design was all about.This is where I got a bit confused,

Woofers seem pretty good quality., 12" paper cone drivers with fairly heavy ceramic magnets

I measured the following parameters

Fs = 36.4 hz
Qms = 2.93
Qes = 0.987
Qts = 0.738
Vas = 2.22 ft^3

Volume of enclosure is 2.3 cubic feet, and port is really weird, 5.5 inches diameter and 2.75 inches long.

If I treat the enclosure as a helmholtz resonator, and use the basic formula for calculating resonant frequency, the box resonates at about 70Hz.

What confuses me is when I enter everything into boxplot 3.0, it gives a pretty nice response when I set h = 0.5. ( h being Fs/Fb), but the vent calculator tells me the port should be 14 inches long.

If I adjust h so that boxplot gives me a 2.75 inch port, the response it graphs has a massive peak which makes no sense at all, with h = 0.5 the response actually looks good.

My intention in reverse engineering is to evaluate if the original design has any potential to sound good before I bother with making new enclosures. I must be missing something, I don't really understand the discrepancy between the boxplot vent length result and the helmholtz resonant frequency calculation.

Update: I initially misinterpreted what h means in Boxplot. Assuming I measured the driver parameters correctly, the design indeed does have a big ugly peak, and is therefore not really suitable for hi-fi sound reproduction as-is.

Edits: 10/05/16 10/05/16

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Kimber Kable

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