I was asked to build a bespoke speaker for real bookshelf mounting. The size was restricted to 10 liters of internal volume. Bass reflex was out of reach, because every realizable port would have limited the output first and mostly by the infamous chuffing. Passive drones would be too heavy to stand the test of time with sagging and so on. The excursion limit of contemporary drivers was better used in a sealed box with Linkwitz biquad equalization.
But, not at least due to Erin's measurements the inevitable intermodulation came into focus. 3%, let alone 10% was found to be inacceptable. Even half a percent was felt objectionable in the region of some hundreds Hz and up. Above 1..2kHz the impact of IM, to my ears, declines.
In consequence the design was chosen to be: 6,5" woofer sealed, eq'ed, 3,5" midrange from 250Hz (!!) up to 2kHz, and a dome tweeter, hence a 3-way in 10 liters. The result is, especially due to bookshelf mounting, astonishingly well behaved. Even with big fat bass content the sound remains clear and crisp. Following bass lines, revealing the moods of human talk and the like are all as good as with a huge speaker. The comparison to an alternative 2-way of similar size was a hilarious attempt--no question.
=> So, what to do with a floor standing speaker, 21cm wide, 40 liters internal volume?! Should I use two 7" drivers in parallel up to 500Hz, or better one driver just for the bass (reflexed), and the second as a dedicated low-midrange from 180Hz to 500Hz? The latter would spare out any excursion induced intermodulation for the mids, while the bass would be heavily contaminated.
To use both for bass wouldn't yield that much of additional output, because power is limited to 50Watts @ 8 Ohms, 70Watts @ 4 Ohms. That's not enough to hit the excursion limit of the chosen drivers.
Any ideas how to optimise the design?
But, not at least due to Erin's measurements the inevitable intermodulation came into focus. 3%, let alone 10% was found to be inacceptable. Even half a percent was felt objectionable in the region of some hundreds Hz and up. Above 1..2kHz the impact of IM, to my ears, declines.
In consequence the design was chosen to be: 6,5" woofer sealed, eq'ed, 3,5" midrange from 250Hz (!!) up to 2kHz, and a dome tweeter, hence a 3-way in 10 liters. The result is, especially due to bookshelf mounting, astonishingly well behaved. Even with big fat bass content the sound remains clear and crisp. Following bass lines, revealing the moods of human talk and the like are all as good as with a huge speaker. The comparison to an alternative 2-way of similar size was a hilarious attempt--no question.
=> So, what to do with a floor standing speaker, 21cm wide, 40 liters internal volume?! Should I use two 7" drivers in parallel up to 500Hz, or better one driver just for the bass (reflexed), and the second as a dedicated low-midrange from 180Hz to 500Hz? The latter would spare out any excursion induced intermodulation for the mids, while the bass would be heavily contaminated.
To use both for bass wouldn't yield that much of additional output, because power is limited to 50Watts @ 8 Ohms, 70Watts @ 4 Ohms. That's not enough to hit the excursion limit of the chosen drivers.
Any ideas how to optimise the design?
