Wednesday, September 25, 2013

Sennheiser SK 5212-II and EK 3241 Wireless - Less Is More

Sennheiser SK 5112-II and a nickel
Shrinking spectrum and challenges to hiding a body pack transmitter are driving location and studio audio people to find better solutions. One of these solutions is the Sennheiser SK 5212-II transmitter. 

The retail price is $2,349, for just the transmitter and another $2,100 for the EK 4231 mono receiver, for a total of $4,400. 

I found a $3,750 Bundle Price online for both transmitter and receiver that also includes the AA battery power kit for the EK 4231 receiver (batteries not included). 

There's a big price difference between these pieces and a Sennheiser G3 transmitter and receiver kit for $629.95 at B&H. Read on to discover why.

Sennheiser still sells the older SK 5212-I beltpack transmitter. They have less bandwidth; 
450 - 638 Mhz 
602 - 798 MHz
762 - 960 Mhz

The newer SK 5212-II has five ranges; 
470 - 638 MHz
606 - 790 MHz
614 - 798 MHz
614 - 697 MHz 
776 - 866 MHz. 

Not all of these frequencies are usable in the US, but I've included them because this blog receives global attention (thanks and thanks for mentioning it to others!).

So what's so special about the SK 5212-II other than its size that warrants the price? More flexibility and a better sounding compander. The transmit frequencies are adjustable in 5 kHz increments. This allows more transmitters to be operating in the same area. The SK 5212-II has three power levels; High (50mW), Low (10 mW) and LoI (10 mW, I for intermod). 

Sennheiser's Ben Escobedo
I reached out to Ben Escobedo, RF Services and Field Support Engineer at Sennheiser for more information about the LoI (low intermod) power setting. According to Ben, "The low intermodulation mode (LoI) adds a special isolation circuit in the RF signal path which reduces intermodulation, however the output power is still clamped at 10mW. The difference between LoI and regular "low" power lies in the extra power consumption of 70mA vs. "low" power mode. In fact, LoI has the same power consumption as in HI mode @ 50 mW. 

The effects of LoI are seen on a scope and it does a great job reducing intermod spikes (3rd and 5th intervals). It is most useful where there is limited free spectrum and when one is running many transmitters in close proximity to each other."

Wig Pack for SK 5212 and SK 5212 II
Theatrical & News
You'll find the Sennheiser 5000 series on Broadway fitted into opera singers' chest plates and wigs. The WMB Wig Pac features pro mesh fabric tabs that allow the Wig Pac to be securely pinned to any hair piece or wig cap. 

The hook and loop closure secures antenna and audio connectors in place and protects from slight pressure and moisture. The Wig Pac is made with fabric covered neoprene, which is durable, moisture resistant, machine washable, and latex-free.

WMB makes belt and thigh mounts from sixteen to fifty-two inches and shoulder mount packs in small, medium and large.

For "no fail" broadcast applications, the talent uses two SK 5212-II, on the left and right rear hips with a wireless IFB receiver between them in the center of the back. 

In Use

After rigging the EK 3241 receiver for battery-powered bag use with the AA battery option, I used the SK 5212-II with a Sennheiser MKE-2 Gold lav on a talent playing the part of a game show host. I wish there was something remarkable I could report, but the system just worked the way it was supposed to, no problems. 

After powering up, the transmitter screen remains backlit for a short period. In that mode the screen is very readable. You can easily toggle the main control to display frequency, name or audio level, audio sensitivity, EQ, output power and channel. 

When powered up, there's a small LED inset in the top of the transmitter that glows red. It also acts as an audio peak display blinking much brighter if the audio exceeds the proper level.

Walk Test
I've been doing walk tests to determine range around my neighborhood for a decade. I hang transmitters on a certain branch of the Mount Fuji Cherry on the front lawn and take a hike until the reception begins to drop. I tried the SK 5212-II in both 10mW and 50mW at 621.000 MHz and found they both began to fall apart at almost the same spot; about 116 yards from the tree. This is consistent with the idea that, despite the power difference, there isn't that much difference with coverage at the fringe of the signal. 

Checking the very helpful online Sennheiser Interactive Frequency Finder, I noticed a Construction Permit for WMJF LD a 5kW just five miles down the road. Never heard of them, but the station is part of Towson University. John MacKerron, who hired me to teach there as an adjunct decades ago, is now the Chair of the TV/Film Department. A long telephone call later, WMJF LD is dark, so my test accurately reflects what the potential capabilities of both power settings are. 

Golden Sound
With the Sennheiser MKE-2 Gold, the overall sound of the wireless was very smooth and no hiss to the point of sounding perhaps rolled off a bit on the top relative to a Sennheiser G2. I have a 24-bit WAV file using the MKE-2 Gold, SK 5212-II and EK 3241 available for download from my DropBox account - HERE.  Battery life for the single AA battery was very good. As we approached 5 hours, we still had juice in the alkaline battery, with the transmitter running at 50 mW.

The 3000 and 5000 Series Sennheiser wireless use HiDyn Plus companding. (Sennheiser uses HDX on their 2000 and Evolution Series.) During my use of the SK 5212-II and EK 3241, I didn't hear any artifacts. The frequency response of the system goes down to 50 Hz. The Sennheiser G3, shows specs that roll off at 80Hz. 

The SK 5212-II operates over an impressive 184 MHz bandwidth. Its input may be adjusted from -30 dB mic level to +40 dB line level in 1 dB steps. For acoustical environments with problematic low frequencies, it has a 120Hz High-Pass filter. I found menu navigation very easy on the SL-5212-II

EK 3241 Receiver with
one of four external battery options
EK 3241 Receiver
The EK 3241 analog, single channel receiver uses two antennas. It's True Diversity, meaning there are not just dual antennas, but dual antennas and dual receivers. The EK 3241 is compatible with a number of Sennheiser transmitters. Currently, there are three different versions; 

450-626 MHz
590-834 MHz
798-960 MHz. 

When you order the receiver, you specify which 36 MHz bandwidth within each of the three versions you want. You also want to be aware of what frequencies are legally available and where there are likely holes in your area before buying any gear. Like the SK 5212-II, the EK 3241 receiver is also tunable in 5 kHz steps. 32 custom frequencies have already been programmed within the switching bandwidth of 36 MHz; in addition, you can store another 20 frequencies in steps of 5 kHz into the user bank. 

EK 3241 Battery Kit
Base plate with XLR and External DC jack
Optional Kits
Although the EK 3241 receiver has optional kits for Thompson, Sony, Panasonic or Ikegami cameras, it can also be used in the bag, running on two or three AA batteries. AA battery operation requires optional kit parts, but provides a very handy operation. 

You just remove two screws from the bottom plate of the receiver, remove the bottom plate, slide the kit shell on and re-attach the bottom plate, locking the shell into place. A smaller clip shown below holds two AA cells that slide into the shell and a three battery clip is also available. There's a small LCD strip on each clip that indicates battery life.

At one point the last LCD power mark on the battery display began blinking, signaling that power loss was imminent. The receiver continued to work, but later on, after having turned the receiver off, it would not power up, even though the LCD battery meter was still blinking. I installed new batteries and the receiver started right up.
EK 3241 B50 Battery Box
with LCD battery meter.

In addition to an assortment of four battery boxes, the EK 3241 also has an external DC power jack and cable for larger, longer lasting DC supplies. There are also a headphone output and QuadPack options for four receivers. 

The manual suggests not operating the transmitter and receiver closer that five meters apart to avoid overloading the receiver.
Menu navigation on the EK 3241 is tougher than on the SK 5212-II, due to the small window, no back-lighting and menu structure. It's not a deal breaker and most adjustments are not that difficult, but I wouldn't take the receiver on a gig without getting to know it. One very handy feature is being able to read the transmitter battery level from the receiver window.

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