Rane AC 24 Active Crossover

Since the inception of the company, Rane Corporation of Mukilteo, Washington has been a popular source of professional audio componentry. Signal control is their game, and contractors can find a diverse product group; including mixers, equalizers, compressors, delays, and crossovers, the latter of which is the focus of this review. The new flagship of the Rane crossover line, the AC 24 ($999).
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Since the inception of the company, Rane Corporation of Mukilteo, Washington has been a popular source of professional audio componentry. Signal control is their game, and contractors can find a diverse product group; including mixers, equalizers, compressors, delays, and crossovers, the latter of which is the focus of this review. The new flagship of the Rane crossover line, the AC 24 ($999).
Product PointsApplication: Sound reinforcement, installation

Key Features: Dual four-way or three-way crossover; delay; multiband limiter; analog interface, security cover

Price: $999

Contact: Rane at 425-355-6000, Web Site.

Plus:

+ Sonically accurate

+ Excellent user interface

+ Useful multiband limiting and delay

Minus:

- None

The Score: A first-class DSP based crossover incorporating an analog style user interface that has all the bases covered.
Features

The AC 24 is a dual-channel four-way unit, incorporating 4th-order 24 dB per octave Linkwitz-Riley filters, signal delay, and limiting functions in a two-rackspace package. The channels can be linked for stereo operation, and the AC 24 can also be used as a dual three-way crossover, if needed. The unit incorporates DSP, yet has an analog-style user interface. This is refreshing in this age of click-and-drag operating systems, when a system without PC control (heaven forbid!) is preferred.

Each channel of the AC 24 has an overall level control and clip indicator LED, low, mid, high-mid, and high output level controls, mute switches for each range, limit controls (and low-limit link switch) with threshold indicator LEDs for each range, and 0 to 10ms delay controls for each range, as well. Crossover cutoff frequency controls lie between these ranges; they are adjustable from 31.5 Hz to 315 Hz, 160 Hz to 1.6 kHz, and 1.25 kHz to 12.5 kHz, respectively. A defeatable constant directivity (CD) horn EQ is included, for high-mid and high-frequency horn adjustment, with control of each from 2 kHz to 8 kHz.

Finally, a low frequency mono summing switch and stereo link switch complete the front panel topology. As one can see, a very extensive set of operational parameters.

The rear panel jackfield includes panel mount XLR female input jacks for channels A and B, individual XLR male band outputs each with polarity switches, and XLR male sum outputs for each channel. Input impedance is a high 7.33kohms, and output impedance a low 100 ohms, which makes for good impedance matching with most equipment. The three-way/four-way mode selection switch is at the bottom left, near the IEC power cord connector. The AC 24 uses an internal power supply, as opposed to the wallwart style units found on some other Rane products.

Obviously, for correct setup of a crossover such as this one, which has so many fine-tuning capabilities, an audio analyzer is necessary. For example, with a multi-way enclosure, you may not have the specifications for the individual drivers within the box. An analyzer can help determine where the drivers roll off. Setting gain for individual drivers requires a dB meter. If you are unsure of the acoustic centers of the drivers in the box relative to each other for the purposes of delay adjustment, an analyzer can help in this way, as well. Suffice it to say, that if you are unclear at all about any aspect of a multi-way enclosure that you intend to crossover electronically, an analyzer gives you an edge.

In Use

In a recent situation at a local club, there had been complaints about the sound; general muddiness and no articulation in the homebrew stacks. These were three way boxes, with a 15-inch JBL woofer, 10-inch JBL mid, and a Community radial horn with compression driver mounted on top. Thinking this may be a good chance to try the AC 24, I bypassed the older analog crossover (brand name withheld), inserted the AC 24, and shot some pink noise through the amplifier/individual driver sets. After noting the frequency responses of the individual drivers on my New Frontier DSP2010-EX analyzer with a calibrated Josephson measurement mic, I set the crossover points with the crossover in three-way mode, stereo link activated. I then noticed there was a noticeable horizontal displacement between the voice coils of the drivers, especially the mid-high horn. I then calculated the delay settings by dividing the distance in inches between the farthest back driver voice coil and the others by 13.57, giving me delay in milliseconds (the farthest back voice coil would have no delay), and adjusted the bands accordingly. Then, with program source engaged and board set at maximum output before clipping, I set the gain levels on the EQ and AC 24, and finally, tweaked the limiter section.

Upon listening to the results, I was surprised to find such a difference in response of the system. While changing the gain stage (which was negligible) may have had some effect, I was surprised by the change in clarity and the life that was breathed into this system. While I did not expect the delay section to have this dramatic of an effect in the closefield, it seemed like some of the comb filter-type anomalies were greatly reduced. Useable sound coverage was increased. Multiband limiting also worked well, focusing on offending program material parts in a way that didn't give the impression of pumping or squeezing the signal.

Summary

It is great to have a DSP based crossover with analog style interface available. There could be a lot of retrofit possibilities for contractors with this unit, especially if the customer is not ready to dive into the mouse click set. The AC 24 is built with a tough, attractive fit-and-finish in the Rane tradition. Sonically superior, with all the features needed, a great overall product.