Took advantage of a lazy Sunday and decided to try measuring my Model Six's in their unrestored state, just to see what they're putting out and how they'll improve once the woofers have been resealed and the crossover recapped. To minimize room resonances, interference, or phasing issues, I placed one speaker on a table, placed the microphone 1 ft away from the grill (kept on for this test), measured the woofer and tweeter on axis separately (and measured the tweeter in normal/dark/bright mode), and then combined the two into one graph. Bear in mind, this isn't the most scientific test nor an official declaration of what a KLH Model Six should sound like, although I did make sure to correct (roughly) for errors in my measuring microphone. A Yamaha CR620 powered the speaker, and a Blue Yeti omnidirectional USB mic was used to make the measurements. These particular Sixes are the later variants, dating from the late 1960s or early 1970s, with vinyl cabs (and serial starting in ASV6), removable drivers, and recessed terminals. I'm told that the earlier models, with epoxied drivers and hermetically sealed cabinets, sound a bit different.
The woofer seems to have its greatest output between 70-500Hz before rolling off on either side, reaching its minimum output at 1,200Hz before bouncing back up and down again. I did not disconnect the tweeter during this test, so I'm unsure if anything above 1,200Hz is from the woofer or the tweeter. The -3dB points are roughly 46Hz and 1kHz, and the -10dB points are 38Hz and 1,240Hz.
Here we're measuring the effect of the tweeter switch (normal/dark/bright). Bear in mind these are uncorrected measurements, included only to show the differences in output. The tweeter seems to start taking over around 900hz and the crossover point appears to be around 1.2-1.4kHz, right where the woofer tapers off. The woofer was not disconnected, so anything below that point is off-axis response from the woofer. The 1.75" cone tweeter gives a flat enough response in the normal position up to about 12k or so, albeit with some peaks and dips (the microphone may not have been perfectly on axis).
In "Bright" mode, the tweeter output is generally raised by about +2-3dB from the "Normal" mode. The output seems to drop around 12k, which is either due to the nature of the tweeter, or the aging caps that will be replaced soon. Hopefully this switch has more of an effect once the new caps are put in.
In "Dark" mode, the tweeter output is cut significantly across the board, by about -5dB. Not sure what the hump at 2-3kHz is.
Adding it all up
In "Normal" mode, this KLH Six is a fairly flat speaker, barring some bumps around 100Hz and 2,000Hz, which could simply be due to placement or errors in my mic that weren't properly corrected. The -3dB points appear to be at 44Hz and 16.5kHz, which sounds about right for an old East Coast speaker, and pretty decent for 50 year old caps. It'll be interesting to see how this changes once the new caps and sealant are installed. Going by my own ears, I can get output up to 18khz out of these, although it is VERY beamy, thanks to the tweeter being a large paper cone. Overall balance and clarity are very good, and the music takes on that magical honeyed glow that you can just listen to for hours on end.
The woofer seems to have its greatest output between 70-500Hz before rolling off on either side, reaching its minimum output at 1,200Hz before bouncing back up and down again. I did not disconnect the tweeter during this test, so I'm unsure if anything above 1,200Hz is from the woofer or the tweeter. The -3dB points are roughly 46Hz and 1kHz, and the -10dB points are 38Hz and 1,240Hz.
Here we're measuring the effect of the tweeter switch (normal/dark/bright). Bear in mind these are uncorrected measurements, included only to show the differences in output. The tweeter seems to start taking over around 900hz and the crossover point appears to be around 1.2-1.4kHz, right where the woofer tapers off. The woofer was not disconnected, so anything below that point is off-axis response from the woofer. The 1.75" cone tweeter gives a flat enough response in the normal position up to about 12k or so, albeit with some peaks and dips (the microphone may not have been perfectly on axis).
In "Bright" mode, the tweeter output is generally raised by about +2-3dB from the "Normal" mode. The output seems to drop around 12k, which is either due to the nature of the tweeter, or the aging caps that will be replaced soon. Hopefully this switch has more of an effect once the new caps are put in.
In "Dark" mode, the tweeter output is cut significantly across the board, by about -5dB. Not sure what the hump at 2-3kHz is.
Adding it all up
In "Normal" mode, this KLH Six is a fairly flat speaker, barring some bumps around 100Hz and 2,000Hz, which could simply be due to placement or errors in my mic that weren't properly corrected. The -3dB points appear to be at 44Hz and 16.5kHz, which sounds about right for an old East Coast speaker, and pretty decent for 50 year old caps. It'll be interesting to see how this changes once the new caps and sealant are installed. Going by my own ears, I can get output up to 18khz out of these, although it is VERY beamy, thanks to the tweeter being a large paper cone. Overall balance and clarity are very good, and the music takes on that magical honeyed glow that you can just listen to for hours on end.
