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Product Review - Bohlender-Graebener 220dx Planar-Magnetic/Dynamic Hybrid Center Channel Loudspeaker - November, 2000


John Kotches

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Design: Three-way Dynamic/Planar-Magnetic/Dynamic hybrid, Acoustic suspension (sealed) enclosure 

MFR:  80 Hz – 18.5 kHz ± 3 dB

Crossover Frequencies: 325 Hz to Planar-Magnetic Midrange;
2,500 Hz to Dome Tweeter

Nominal Impedance: 4 Ohms

Crossover Slope: 12dB/Octave

Sensitivity: 88 dB/1w/1m

Maximum Input power: 250W

Size: 8" H x 39" W x 11" D

Weight: 47 Pounds

MSRP: $1,449 (Charcoal Gray),$1,649 (Aluminum (DX))

Bohlender-Graebener Corporation, 1780 Forrest Way, Carson City, Nevada 89706; E-Mail sales@bgcorp.com; Web http://www.bgcorp.com

Identity Unknown

Bohlender-Graebener (BG) isn't a household name in the audio/video business, but they're pretty well known by lovers of planar speakers. BG has a diverse operation, marketing a line of free-standing loudspeakers under the BG name. At CEDIA, BG demonstrated the Radia Series of in-wall speakers for custom home installations. They manufacture and market ribbon assemblies in a variety of lengths to the DIYers of the world. BG also custom manufactures ribbon assemblies for several well known loudspeaker companies (this is called OEM). BG's OEM clientele includes Genesis, VMPS, and newcomer Soundline Audio. Their Radia Pro line of planar-magnetic transducers is used in commercial installations.

Being a planar aficionado, I was aware of the BG name, and had seen their speakers on a few occasions. My first opportunity to hear any of their speakers (the Radia Series In-walls) was at CEDIA 2000. They were demonstrating the Radia Series in a hotel conference room. The sound quality interested me, and I discussed with the folks at BG the prospect of receiving their free-standing Center Channel for Secrets to review. It's very difficult to review in-wall speakers without modifying your listening room and possibly destroying the review sample if you don't know what you're doing. There's a reason I'm not employed in the construction industry, and my wife tells me it has something to do with having 10 thumbs.

Deconstructing Harry

Throughout this review, you'll see me using the terms ribbon and planar-magnetic interchangeably. Technically speaking, the BG driver is a planar-magnetic, not a ribbon, since the aluminum driver is attached to a mylar backing for durability. With a true ribbon driver, the metal ribbon is all by itself, with no plastic strip backing.

The ribbon material is flanked by opposing magnets on either side. The + and - electrodes are connected to the speaker binding posts, and provide the path for the audio signal. In this picture, when the electrical signal is applied, the ribbon will flex along the horizontal axis, the length of the ribbon vibrates towards and away from the computer screen, while the vertical axis is fixed. Remember, we are talking about a center channel speaker, lying on its side. For the other speakers, the ribbon would be positioned vertically.

There are some advantages to a planar driver versus conventional cone drivers. First off, they offer exceptionally low mass, so they are superb high frequency (HF) transducers. It's not unusual for the entire drive assembly (ribbon) of planars to be lighter than a conventional dome tweeter.

Unlike point source radiators, whose output drops according to the inverse square law, the planar line source decreases by 3 dB linearly for every doubling of distance. Therefore a planar speaker can start with a lower output than a dynamic loudspeaker, and end up with a higher output at the listening position. This table demonstrates the difference in outputs between the two.

 Driver type Output at 1meter Output at 2 meters Output at 4 meters
 Planar / Line Source 86dB 83dB 80dB
 Dynamic / Point Source 90dB 84 dB 78dB

I opted for the 220dx model to review. The "dx" features an aluminum fascia at the top and bottom of the grille cloth. The standard model (no suffix) has a charcoal gray fascia. Personally, I think the aluminum fascia makes this CC look like something that George Jetson would use in his home theater. Save for the BG logo on the far right of the grille cloth, the speaker is otherwise unadorned. A stand for this speaker is not manufactured, and the intended placement for this speaker is either on top of or below a RPTV or direct view set. In my listening room, it found a place below the screen of my television, and an amp stand was used to raise the speaker closer to the horizontal level of my ears.

The rear panel is all business, and its only distinguishing feature is the binding post assembly pictured here. The fascia extends slightly beyond the enclosure, and a gasket affords a tight seal between the end of the cabinet and the end of the fascia. The speaker cannot be bi-wired, and BG has no plans to add the capability due to insufficient demand for this feature.

Use of the adjective unadorned doesn't mean that interesting things aren't afoot . . . just that the interesting bits are hidden away by the speaker grille cloth. This speaker is a 3-way design - with a pair of 6.5" woofers in an acoustic suspension (sealed) enclosure working from 80 Hz - 325 Hz. For the crucial midrange, the BG planar magnetic driver carries 325 Hz - 2.5 kHz, and finally, for the high frequency portion, a 1" neodymium tweeter takes over. A picture is worth a thousand words, so here's a diagram I drew of the workings behind the grille cloth (shown below).

Each woofer driver is in a discrete enclosure, acoustically isolated from the midrange-tweeter assembly. The midrange ribbon looks like two pieces in the diagram, but BG reports that it is a single 22" ribbon divided by the tweeter assembly. I have no way of checking this physically short of breaking into the enclosure. The cabinet behind the midrange is sealed and damped, making this a monopole planar driver rather than the more familiar dipole configuration (where sound comes out the front and back). Since the intended installation of this speaker is either on top of or below a television set, there is insufficient space behind the speaker to allow the back wave from the planar driver to propagate as it would on a vertically oriented speaker. This makes BG's choice to dampen the back wave understandable.

Another design decision made was to use a standard metal dome tweeter to handle frequencies above 2.5 kHz. The problem with using the ribbon for all frequencies above 325 Hz is that the planar reaches the point of beaming - where the frequency to be reproduced is shorter than the length (or width) of the planar driver being used at approximately 3 kHz. By returning to the conventional dome tweeter above 2.5 kHz, the worst of the beaming effect is avoided. The center channel is used for voice reproduction in movies, and the majority of human speech falls in the frequency range of 300 Hz - 3 kHz. This allows for an excellent match with the other loudspeakers in BG's lineup.

Stop, Look and Listen

I listened to a variety of material, but I'm going to focus on a few select recordings, some familiar to everyone, and some not. I have a fair-sized collection of DTS music CDs (23 at last count) that I used extensively for listening tests. To accentuate the center channel (at the expense of everything else), on most recordings, I trimmed the center channel up 6.0 to 8.0 dB. From time to time, I also sat even with my mains (dipole radiators) and listened to the center channel - drastically out of context, but it helped me focus.

I heard Lyle Lovett's She Makes Me Feel Good on a DTS demo disc, and went out the next day and purchased the DTS encoded CD of "Joshua Judges Ruth". It's a superb stereo recording, and the translation to DTS encoding was given great care. While the use of surrounds is aggressive at times, I enjoy the perspective that's presented. Baltimore is an engaging ballad, and I tend to just sit through this song without moving. Through the 220dx, I was transfixed by the palpable presence of the lead vocals in my listening room. Given its quiet intensity, the illusion that a person is singing in your room becomes more eerie as you hear subtle nuances of the performance. At one point in the song, the vocal line is, "And as I breathe she breathes no more", with more trailing off in volume as if the singer is using his last breath to utter the word. The track She's Already Made Up Her Mind has a larger instrumentation, and the acoustic guitar in the center channel is at times strummed very lightly, while at others, very hard. The timbral differences between these two are readily apparent, as are the the individual notes when arpeggiated chords are struck in succession. The kick (bass) drum is convincingly recreated in the center channel by a combination of two events. First, the subwoofer is only firing from 80 Hz and below, and secondly, the harmonic series being reproduced in the center channel gives the impression that a lower fundamental is being created out of the center channel. Combined, you have no way of knowing that the 220dx isn't covering the entire kick, except by putting your hand over the cone of the powered subwoofer.

Steely Dan's first new album in almost 20 years, "Two Against Nature", was also a PBS concert special that was subsequently released on DVD in Dolby Digital and DTS encoding. I used the DTS encoded soundtrack for my listening tests. The entire DVD is an exceptional recording of a tight band. Elliott Scheiner did the mixdown of this DVD (as well as the Eagles' "Hell Freezes Over"), so it has a very aggressive use of surround channels. I'm not sure if watching the video is necessarily a good thing, because it seems like Donald Fagen is perfecting the dirty old man look. The track Josie and FM are what I'll be commenting on, and my comments apply equally to the two tracks. This disc doesn't seem to have a tremendous amount of reverberation, so it's pretty dry. Throughout I got the impression that Donald Fagen's voice was a touch brittle and thin, with just the slightest bit of edge to his voice. Donald Fagen has never had a big fat voice, and the thinness is fully attributable to his vocal chords. The slight edge is evidenced on my Reference Center Channel, the Magnepan CC-1, and is also present when he speaks, so my conclusion is that it's endemic to the recording. The drum kit is mixed into the center channel, and Ricky Lawson kicks some serious butt. The strength of his snare drum strikes and the splash of his cymbal strikes are reproduced with wonderful authenticity without edge or harshness. I'm dying to hear what this sounds like on either DVD-Audio, or multi-channel SACD as opposed to the lossy compression codecs currently in use (DD and DTS).

James Taylor's "Live at the Beacon Theater" is the best sounding Dolby Digital encoded music disc I've heard to date. It's also an excellent choice for center channel auditioning with JTs voice and guitar, plus the bass and most of the drum kit in the center channel. As with the Steely Dan disc, the bass transition is seamless, with no detectable separation between the higher notes above 80 Hz, and the lower notes, down to about 31 Hz. For all you sticklers for detail, the bassist uses a 5 string bass, with an additional B-String below the traditional E-string. Steve Jordan is a top-notch percussionist, and hearing his playing with all the appropriate crispness and sharpness of a drum kit on a home theater disc is a blast. On the track Your Smiling Face, even the differences between JTs thumb and fingers when plucking his guitar are rendered with crystalline precision. Near the end, when JT is belting out notes at the top of his vocal range, the timbral difference between his tessitura and the top of his register are rendered truly, without causing overemphasis due to a lack of smooth frequency response from the speaker. Finally, I backed down the center channel to a balanced level with the rest of the speakers to listen to Shower the People. The out chorus features one of the backup singers (Arnold McCuller) singing over the rest of the backup singers and JT. When the moment arrived, JTs voice dropped down and blended perfectly with the other backup singers across the front of the soundstage.

Logical Conclusion

Given its asking price (US$1450 - $1650 depending on finish), the 220dx is a fairly expensive center channel. Paying attention to the physical specification at the beginning of the review demonstrates that this is a physically large center channel speaker. (I photographed the 220dx on top of a piano bench so you could have a perspective on its size.) The use of the ribbon midrange requires the physical size. With respect to the price, I'm happy to say that the 220dx delivers all the expected performance, and then some. Dialogue is crisp and clear . . .  my wife doesn't ask, "What did they just say?" Singing voices and instruments are rendered with clarity and nearly lifelike characteristics.

It has sufficient bass response, so that by the time the transition from this speaker to the subwoofer occurs, the sound isn't localized. At any volume in my room that was listenable, the 220dx produced no signs that it was straining to produce the desired volume. Its only sonic weakness was a slightly boxy sound on recordings that tend towards a closed off or boxy timbre.

The "limited" treble extension of this speaker (-3 dB at 18.5 kHz) never was noticeable to my ears during the course of this review.

It is plain to see why Bohlender-Graebener has some great speaker manufacturers as OEM customers.

Reference System

Golden Theater GTX-1 Preamp/Processor
B&K Reference 30 Preamp/Processor
Aragon 8008x3B Amplifier
Toshiba SD-3108 DVD (digital transport)
Echostar 5000 DSS Receiver
JVC S3500U S-VHS VCR
Homegrown Audio Super Silver analog interconnects
Harmonic Tech Cyberlink Silver digital interconnects
Better Cables speaker cable

Referenced Recordings/Movies

 Lyle Lovett "Joshua Judges Ruth"  HDS 7102-54430-2-7
 Steely Dan "Two Against Nature" ID9584CGDVD
 James Taylor "Live at the Beacon Theater"  

- John Kotches -

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Copyright 2000 Secrets of Home Theater & High Fidelity
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