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High Efficiency Speaker Asylum Need speakers that can rock with just one watt? You found da place. |
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In Reply to: Bass control with low powered tube amps posted by tomtom58 on October 24, 2016 at 07:41:16:
Regardless of how powerful the woofer's magnet is, its effective electrical Q is modified by the amplifier's output impedance. This effect is the sum total of damping factor's influence on the bass region, and it is easy to model: A 4-ohm output impedance will raise the electrical Q of a nominal 8-ohm woofer, assuming a 6-ohm voice coil resistance, by a factor (6+4)/6 = 1.67. This is true no matter how powerful the woofer's magnet is.If we started out with a 16-ohm woofer (voice coil resistance of 12 ohms), then an amp with an output impedance of 4 ohms would raise the electrical Q by a factor of (12+4)/12 = 1.33, or half as much.
I design speakers to work well with a wide range of amplifier damping factors, from solid state to the Atma-Sphere S-30 OTL tube amp (which has a lower damping factor than most SET amps). The approach I use is to keep the impedance curve fairly high and as smooth as is reasonably feasible, and typically use multiple pluggable ports to adjust the box tuning. In practice, I can get about 1/3 octave deeper extension with a low-damping-factor tube amp, once the port tuning is adjusted.
The Klipsch Forte uses a passive radiator, as I recall, so you could theoretically add mass to it to lower the tuning frequency.
But before doing that, try adding a pound or so of well-fluffed Polyfill inside the enclosure. This will reduce the magnitude of the upper bass impedance peak, which is the one that makes the most difference in the bass region. You could theoretically get a 1.5 dB ballpark reduction in output at that frequency, which would be beneficial if that speaker/amp/room combination is giving you bass boom.
(If the Forte's impedance curve has significant peaks and dips elsewhere in the spectrum, those can cause changes in the frequency response that are harder to address.)
Of course changing speaker and/or listener locations to reduce boundary reinforcement can help too, but heavily stuffing the box is a trick that might be worth having up your sleeve.
Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
Edits: 10/25/16 10/25/16
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- Stuffing - Duke 13:32:07 10/25/16 (0)
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