According to Stereophile magazine, the top ('A' ranked) room correction or room EQ devices are:
1) Audyssey Sound Equalizer, $2500
This is a device intended for use in home theater systems. It has 8 analog line level inputs and 8 analog line level outputs and would therefore be typically placed between a pre/pro and power amplifier. It offers increased filter resolution (requiring more DSP power) compared to the Audyssey algorithms included in many home theater receivers. The analog inputs and outputs of course mean that two potentially sound degrading digital conversions occur (one on input and one on output). The Audyssey Sound Equalizer package does not include a measurement microphone or calibration software, since it is intended to be set up and calibrated by a dealer.
2) Meridian 861 with MRC room correction, $18,995
This is multi-channel device based on Meridian's unique decay time approach to room correction (see these two blog posts for more information - here
). Measurement and filter generation are automated but Meridian allow the user to adjust the filters after generation. In my view it is critical that any room correction device offers users this adjustment capability since there is almost always a sound quality improvement that can be made by manual fine tuning. The device only operates below 200Hz, the frequency at which room behavior is dominated by modes. Removing modal resonance, which are audible as boomy, bloated and 'one note' bass is perhaps the biggest impact that room correction can have on sound quality and therefore it makes sense to confine any device to this application. For those that want Meridian Room Correction (MRC) but can't afford the 861, the same capability is available in the G61R and G68.
3) Rives Audio sub-PARC and PARC, $5000 / $3200
The Rives Audio approach relies on a user or dealer measuring the system's frequency response using a separate measurement rig. The correction filters must then be manually calculated and set on the devices front panel. Whilst this approach allows for maximum flexibility it has drawbacks in that additional measurement equipment and knowledge must be acquired to set the filters correctly. The Rives device is unique amongst the devices in this list as the correction filters are implemented in the analog domain. This means the device is particularly useful for audiophiles whose systems are based on an analog front end such as a turntable. The majority of other devices operate in the digital domain and must therefore perform an analog to digital conversion on the input side and a digital to analog conversion on the output side. The device offers three parametric EQ filters; although this sounds like a small number generally in my experience I have found that three filters is enough to significantly reduce the negative impact of the major length, width and height axial room modes that all peak in the center of a room. The difference between the two devices is that the sub-PARC is designed for use with a single passive (i.e. non-amplified) subwoofer and contains a 1200W amplifier for this purpose.
4) SVSound AS-EQ1, $799
Designed for use with either single or dual subwoofers, the AS-EQ1 is based on a implementation of Audyssey's DSP room EQ code. Plug in the included measurement microphone and install the custom Windows based software onto your computer and you are ready to go! Because it uses Audyssey code many locations in the room are measured (up to 32) before the correction filters are generated. This makes it particularly suitable for use in a multi-seat home theater where the bass response and therefore degree of correction required will vary significantly from seat to seat. The drawbacks with this unit are that there is no digital input, meaning that the incoming signal is converted from analog to digital and back again, and that there is no manual target frequency response adjustment - you have to accept the correction filters it generates for you. The DSP in the AS-EQ1 also introduces 7.5ms of delay or latency which must be corrected for through the 'distance' controls in a pre/pro (this can also be approximated using the phase control on the sub for two channel systems).
5) Velodyne SMS-1, $749
The Velodyne Subwoofer Management System (SMS-1) is a device intended for use with a subwoofer. It is basically a standalone implementation of the digital room correction capability built into Velodyne subs like the Digital Drive series. There are 8 bands of parametric EQ available. The device ships with a measurement microphone and the measurement and control functionality is configurable via a connection to a television or projector. This is good in some ways (no PC is required) and bad in others (often an audiophile two channel system will not have a television available for hookup!). One of the nice things about the SMS-1 is that whilst measurement and EQ generation capabilities are automated all of the filters can be manually adjusted.
6) Z-Systems RDP-1 Reference, $4000
The RDP-1 is no longer available, Z-Systems seeming to have chosen to concentrate on the pro audio market. The RDP-1 was a four band parametric EQ device operating in the digital domain (and with digital inputs!). It could also function as a digital preamplifier, since it contained a digital volume control and input selector. Of course being a standalone parametric EQ it meant that the user had to have a separate measurement and filter generation capability. The modern replacement for the RDP-1 is the Z-Q2, which has only AES digital inputs and offers four bands of digital parametric EQ.
Do you agree with Sterephile's list or do you think there are others that should be added? How important is the ability for the room EQ device to automatically generate correction filters? What do you think about the multiple digital to analog and analog to digital conversions? Is the capability to manually adjust room correction filters important to you? Please add your comments!