LF Rise in Redgum Amps
When we asked Ian Robinson the reason for the boost in the low-frequency response of the Magnificata he provided two responses, one short and simple, the other longer involving technicalities and psychoacoustics. His short reply: ‘I consider that the introduction of a consistently graded lift is a much more accurate way of gaining a believable musical result.’
His long reply: ‘I have yet to observe any speaker in any price bracket that can’t benefit from a lift of +1dB at 40Hz or +3dB at 20Hz. So if we are to get anywhere near to attaining the desired “flat” response from a speaker (though that remains contrary to the laws of physics), it has to be approached via creating a flat response from the entire system. Take, for example, the effect at 20Hz. This being the same frequency range where conventional speakers are falling dramatically (if there is any response worth reporting at all), hooked up with a Redgum as part of the system, their response is 3dB up i.e. 3dB above the accepted range at a point where even the best speakers are usually 30–40dB down. Doing the maths, 30dB down, countered by 3dB up… maybe it is mathematically ambitious to consider that to be a rising response in the total scheme of things! Rather it can be seen as a slight moderating effect to the system. As to answering the question: “But why do it?”, the drop in these frequencies are heading into the range where we feel more than we hear. So rather than being a countermeasure just to “extend the bass” for quotable specs, it is done for reasons of musicality. At these frequencies, feeling the impact of an instrument becomes more critical than hearing it for the perceived realism of the music. Despite what any speaker manufacturer claims, independent graphs always show a falling response of the bottom end.You can’t beat physics! But you can work with it, as psychoacoustics has shown how the perceived realism of instruments is affected by changes in other/unrelated sections of the frequency range. Said not as a justification, but more as an industry reality check, ... recently, I have become aware that speakers which are internally bi- or tri-amped often use this principle to extend the bass. So, yes, my design inclusion (but one focused on a systemic result) was implemented sooner, but for better reasons than just improving the look of the specs! Indeed, the presence of a similar “rise” has been a part of each Redgum amplifier’s design over the past 22+ years. But it must be stated that considering the price point of the speakers that are likely to be used with an amplifier of this price, and thus their likelihood of having a decent extended frequency range, the “rise” in the Magnificata is an extremely subtle one in application. Simply put, as part of the interplay of a system, it is there to give “feeling” to the instruments.’