Equipment Review No. 3  -  April 2003

Acoustic Research Model AW791
Wireless 900MHz Surround Sound Headphones
$299.99

Specs:
40mm elements with neodymium magnets
Freq. Response: 20-20K
S/N: >70dB
Stereo separation: >35dB
20bit DAC with Dolby Digital decoder
Virtual Surround technology (Q Sound)
Three separate transmission channels
Effective range: up to 300 ft.
Optical input: EIAJ standard
Digital sampling rates: 32K, 44.1K, 48K
PCM in AES/EBU format
Base is recharger for batteries

Includes:
3 ft. Toslink digital optical cable
7v AC power supply
3 AAA Ni-MH rechargeable batteries with 4 hr. Life

Acoustic Research Accessories Division of Recoton Accessories Inc.
2950 Lake Emma Road, Lake Mary, FL 32746
407-833-1660 www.recoton.com

Intro

These phones offer a combination of three very attractive features for those prone to watching movies with 5.1 surround soundtracks at times that would disturb others in the area who are not watching. The surround feature could even be attractive to those who have not yet set up a 5.1 surround speaker system for home theater. That’s the first feature; the second is being cordless - which means no more tripping over long cables - as screens get larger we sit further back from them, right? The third feature is the much greater range from the source possible with the 900MHz system vs. the older infrared approach - allowing even the freedom to work outdoors close to the house while listening in many cases. Another nice feature of this unit is that it automatically recharges the batteries while it sits at rest on its stand - some of the wireless phones (such as the Amphony we reviewed here earlier) don’t include a recharger.

I originally requested the AR phones for review because of the somewhat misleading advertising mentioning Dolby Labs. It led me to believe these were the first stand-alone headphones available in the U.S. incorporating the Dolby Headphone technology developed by Lake of Australia. I later learned from Dolby that they are not - the Dolby license only pertains to the initial decoding of the 5.1 DD datastream, not to the special HRTF processing that creates five virtual speakers outside of your head - which I have heard and which is extremely convincing in its effect. Dolby tells me so far it is only available on a Pioneer headphone system available only in Japan. The AR phones license the virtual surround technology they employ from the Canadian firm Q Sound (about which we haven’t heard much lately). Yet they strangely omit mention of that in any of the literature or advertising connected with the AW791.

It’s often a great convenience to use headphones and much more of a convenience to use wireless headphones, but it should be remembered that - as audiophiles learned early in the replacement of LPs with CDs - that convenience comes at the cost of compromised sonic fidelity. None of the wireless phones - even the most expensive - equal the sonics of a good pair of wired phones such as the Grados or Sennheisers. And if you use them with a dedicated headphone amp, even more so. And not just the overall fidelity but some very annoying artifacts come up with both types of wireless phones. The infrared signal is blocked by any opaque object in the path between the transmitter and your head. Just turning your head a little can cause serious hiss, distortion or complete loss of signal. Phones using the newer 900MHz FM stereo signal can go thru walls and doors, and have a much greater distance range, but remember the analog FM stereo system has plenty of impaired sonic quality to begin with. There’s no way it can equal a good pair of wired phones.

Hooking Up

The AW791 comes with a very useful DVD of Set Up Instructions that takes you efficiently thru the whole process. There are sections on Preparing, Connecting, Listening, Troubleshooting, and then a handy section of about a half dozen of Dolby Labs’ 5.1 movie trailers that we’ve all seen/heard in the theaters. They all emphasize an exaggerated surround field that is perfect for demonstrating 5.1 playback, whether via virtual surround phones or the real thing via loudspeakers.

The AW791 Transmitter should be placed close to your audio system and in a location where the phones can be stored on it for recharging. It can be fed from up to three different audio components - two digital and one analog. The two digital input connections comprise both standard coaxial and Toslink (for which the cable is provided), thus making it useable with a wide variety of digital and analog AV components. In addition to these four jacks, there is the 7v jack for the AC wall wart plus the three position switch to select among the three different input connections.

Operation

Moving to the front of the base transmitter, we have a row of four small red LEDs flanked by a larger switch button at each end of the row. The furthest right button selects among the three inputs, the same as the slide switch on the back of the unit. (Confusing because of conflicting nomenclature: On the rear they are called Input Select, but on the front Channel Select.) The second, third and fourth small LEDs light to indicate which input has been chosen: coax digital, optical digital, or analog. The first of the LEDs is controlled by the larger button on the far left, and it switches the virtual surround feature on and off.

The built-in DAC in the unit is an unusual feature. (We just received the Grace headphone amp for review and it also has a DAC.) Most preamps and receivers now have a digital out so this can go directly to the AW791 and you won’t really need the other inputs. If you use only the analog inputs you won’t get any digital processing - just analog Pro Logic (I) decoding of surround sound and analog Q Sound virtual surround processing. I hooked my unit’s optical input directly to the Toslink Out on my best DVD player, a Sony 9000ES and the coax input to the digital output of my Sunfire Theater Grand III Preamp. Another disappointment occurred when the DVD I was listening to refused to get a signal thru the AW791. The manual has a single line at the bottom of one page: “this product does not decode DTS.” The digital inputs also to not accept 96K digital datastreams; therefore the 96K music DADs will not play on it even if your DVD player outputs them properly.

The headphone has a compartment for all three batteries on one side which is easily accessible. The phones also operate with standard AAA batteries as well as the rechargeable batteries - which is a good thing since the contacts in the base were too short to properly make connection with the phones for recharging. (AR tells me this fault is being corrected immediately.) The On/Off switch on the right earpiece turns on a red LED at the same location on the left earpiece. The right side also has the volume control. The phones are quite light, they swivel, and there is a self-adjusting headband, so they are very comfortable to wear for those three-hour movies.

Processing Modes

You have a choice of four different modes depending on the nature of the input and whether you have the Virtual Surround button in an on or off setting. Dolby Digital 5.1 will be decoded and then spatialized to create a virtual 3D effect of a five-speaker surround system around you if the button is on. With the button off the same DD 5.1 input will be decoded as two-channel if it is plain stereo and as virtual surround if it is Pro Logic Surround. For analog and PCM inputs, having the switch in Virtual mode creates a 3D room environment by using first Dolby Pro Logic decoding and then Q Sound. If the switch is off, a standard stereo signal is passed thru to the headphones.

Listening

First I compared the basic sound quality of the phones without the virtual surround processing to my Amphony Model 1000 2.4 Gig wireless phones, as well as my Grado and AKG wired phones. Well, first and probably needless to report, there’s no comparison to the corded phones. At all. If you want the best fidelity it still requires a cable. I found the Amphony to sound rather dulled on string tone and piano, such as on the stereo mixes of the chamber music DVD-As from the Tacet label. But they sound very musical. The ARs, however, were extremely peaky, raspy although more open and cleaner-sounding in comparison. The peaky response was intensified by the high level of hiss and frequent high-pitched noises resulting from moving my head or body, even when within a foot or two of the transmitter. The artifacts were similar to that experienced with my older Sennheiser wireless headphones which used the infrared principle. The ARs seem to have a bit more stereo separation than the Amphonys. Only 35dB isn’t very good but that’s due to the limitations of the antiquated FM stereo format, not the phones proper.

A strange reversal occurred with the Amphony and AR phones which I can’t explain. I feel compelled to report on it since it shows both that perhaps my bad experience with the ARs is peculiar to my environment and yours might be just fine, and also that there are many unexpected factors that impinge on the successful use of wireless headphones. When I reviewed the Amphonys I complained that although the signal was very clean within the same room as the transmitter - even 30 feet away - when I went into my office in an adjoining room it was impossible to listen to the phones due to the serious distortion and noise. Also, the first evening I hooked up the ARs and watched a surround sound DVD they had no artifacts from head movement - just a bit of hiss.

The next day and in the days since that, the situation was just reversed: Suddenly I can listen to my Amphony phones clearly in my office, while I’m getting serious artifacts even close to the AR transmitter, as described above. Can’t explain this.

Bottom Line

So would you be happy listening to a DD 5.1 surround movie soundtrack late at night with these phones on the Virtual Surround setting. Probably not. The effect is minimal - if you play the THX surround channel setup test the sounds from the left and right surround speakers sound just about the same as those from the front left and right. The main difference seems to be a filling in of the center sonic image, but at a high elevation. It reminded me of the very subtle HeadRoom Processor, except that it kept the center fill-in in a straight line left to right. However, when I played back the various Dolby Surround theater demos on the AR How-To DVD, there was a fuller and more spectacular playback of the multichannel sources than with the Virtual Surround defeated. But surround sound it was not. By the way, the LFE signal in the THX test doesn’t produce any sound whatever in the phones - but then one wouldn’t expect phones to handle that subterranean region anyway.

The literature from AR states as one point, “[The Virtual Surround switch is used] to alternate between watching a surround movie and listening to music.” Well, if it works well, why would you want to listen in plain stereo when you can have surround sound? It also instructs that, “All CDs, cassettes and radio should be experienced with the Virtual Surround Sound OFF.” Same objection, plus how about all the Dolby Pro Logic CDs out there and all the other processes such as UHJ Ambisonics and binaural - which abound in the sort of ambient “difference information” which any virtual surround processor can use to create often astounding surround fields?

I’m afraid these phones are not quite ready for prime time. I await the first reasonably-priced stand-alone headphones with true Dolby Headphone. In the meantime, if you’re in the market for an AV receiver, check out the several models now appearing from various Japanese manufacturers which include a Dolby Headphone jack.

- John Sunier

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