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Looking for advice on how to improve bass response in my system without losing clarity.
I have 604B's in custom cabinets that sound quick with excellent tone. If I add subs, I am concerned that the additional xovers will dirty the waters. What to do???
Add an active subwoofer and cross it over under 100hz. Be certain to high-pass the Altecs. 604s /515s/803s/416s are not low-frequency shakers by any measure.
My recommendations include Bag End's ELF dual-integrator line (http://www.bagend.com/) and the Velodyne servo-controlled subs. Both exhibit excellent phase behavior and very low distortion.
The Bag End dual-integrator assisted subwoofer systems are especially fascinating; their passband is below the driver/enclosure system resonance!
These systems utilize a fairly low-Q driver (with a large Xmax obviously) in a small sealed enclosure with an overall system Q=0.707 (second-order Butterworth, maximally flat) and fairly high -3dB point (~80-100hz).
Two integrators are cascaded in series resulting in a 12dB/octave slope; when used in conjunction with the driver/enclosure, the integrators flatten the driver/enclosure second-order (-12dB/octave) slope below the system resonance and also creates a 12dB/octave low-pass response above system resonance. Very cool and has the obvious benefit of more consistent, predictable phase behavior, especially over standard sealed or vented designs operated above system resonance.
The downfall? This system requires exceptionally large amplification. For example, if you're running 1 watt at 80hz, you'll require 251 watts at 20hz with the attendent extreme driver excursion to achieve the same SPL; you're adding +24dB boost two octaves below ;-)
The Bag End ELF uses an ingenious concealment circuit that limits or `slides' the low frequency limit of the integrators to keep driver excursion within physical limits; hence, the higher the SPL, the higher the low frequency limit of the integrators. Note that this feature does NOT limit the dynamic range as a standard amplitude limiter would and its audible effects far less noticeable as well.
No, I don't work for Bag End ;-) though their ELF dual integrator system is by far the best I've heard by a long shot (IMHO, of course). Another well-engineered, innovative system by Long/Wickersham, the team who developed the UREI 800-series control room monitor line.
Anyhow, add an active subwoofer; the improvements in imaging and lower distortion are well worth the effort.
BobR