Wireless Multi-Channel Audio Systems | Wideband wireless, explained for people who have to buy it
WMAS stands for Wideband Multichannel Audio System. Instead of giving every microphone its own narrow slice of RF, a WMAS puts one wide channel — 6 MHz in the US, 8 MHz in Europe — on the air and time-slices many bidirectional audio links inside it. Sennheiser Spectera is the first shipping product built on it. The FCC legalized the approach in 2024.
That is the whole idea. What follows is what it actually means for spectrum, for hardware, and for whether it belongs in your building.
What is WMAS, and how is it different from conventional wireless?
A conventional wireless microphone system is a collection of independent narrowband radios. Each transmitter occupies roughly 200 kHz of spectrum, and a coordination step spaces them apart so their intermodulation products do not land on each other. That spacing is the hidden cost: a large part of a TV channel is left empty on purpose, as guard space between carriers. In-ear monitors then need their own separate block of spectrum, usually in a different band, with their own antennas and their own coordination.
A WMAS inverts that. The system occupies one contiguous wideband RF channel and manages everything inside it as a single scheduled resource. Sennheiser describes Spectera's air interface as a proprietary variant of OFDM-TDMA — orthogonal frequency-division multiplexing for the carrier structure, time-division multiple access for who transmits when. Because the base station controls the schedule, there is no intermodulation coordination between links to perform. There is one channel, and the system allocates slots inside it.
Two consequences follow, and they are the reason the industry is paying attention.
Microphones and IEMs share the same channel. The link is bidirectional. The same RF channel carries talent audio up and monitor audio down, which removes the separate IEM band, the separate transmit antenna system, and the separate coordination exercise.
Diversity gets much deeper. Spreading a link across a wide channel means many independent frequency paths per link. Sennheiser states 40-fold diversity in an 8 MHz RF channel and 30-fold diversity in a 6 MHz TV channel. Conventional true diversity uses two. That is the practical difference between a dropout being a design problem and a dropout being unlikely.
| Conventional narrowband | WMAS | |
|---|---|---|
| Spectrum model | One narrow carrier per link, spaced apart | One wide channel, links scheduled inside it |
| Coordination | Intermodulation study per system | Handled by the base station scheduler |
| Mics and IEMs | Separate bands, separate antennas | Same channel, same antenna, bidirectional |
| Diversity | Typically two paths | 30-fold in 6 MHz, 40-fold in 8 MHz |
| Adding a channel | New receiver, new coordination pass | Configuration change inside the existing channel |
| Rack footprint | Scales with channel count | 1RU base station regardless of link count |
How does Sennheiser Spectera actually work?
Spectera is three pieces of hardware and a control application.
The Spectera Base Station is a 1RU rack device supporting up to 64 audio links — 32 inputs and 32 outputs — across up to two wideband RF channels. It carries four antenna ports, two power supplies, primary and secondary Dante connections, and two slots for optional redundant MADI, available as BNC or optical cards. It performs permanent spectrum sensing while it runs, rather than only at setup.
The DAD is the part that changes how a room gets cabled. It is a transceiving antenna that handles microphone signals, IEM signals, and control data at the same time, on one RJ45 connection over Cat5e, powered by PoE from the base station. IP 54 rated, in 10, 25, and 50 metre cable options, with fibre conversion available for longer runs. For anyone who has pulled coax and installed splitters and boosters for a large wireless deployment, that is the sentence worth rereading: the antenna infrastructure becomes structured cable.
The SEK bodypack is a transmitter and a receiver in one body. A 3-pin connector takes the microphone or instrument; a 3.5 mm jack feeds the earpieces. One pack, one battery, one belt clip, where a presenter or performer previously wore two. It runs on the BA 70 rechargeable battery for up to seven hours, and the display retains information when the pack is powered down. UHF and 1.4 GHz variants are available; a handheld SKM is on the roadmap, along with SMPTE ST 2110 support.
Audio-side specifications: 32-bit float internal processing, AES 256 CTR encryption, dual mono transmission to keep in-ear channels separated, and latency down as low as 0.7 milliseconds for IEM use. Control is LinkDesk on Mac or PC, plus a browser WebUI.
What a starting system costs
| Component | SKU | Price | Notes |
|---|---|---|---|
| Spectera Base Station 1RU | 509162 | $9,999 | Up to 64 links, dual PSU, Dante |
| DAD Antenna, UHF | 509169 | $1,599 | PoE over Cat5e, IP 54 |
| DAD Antenna, 1G4 | 509170 | $1,599 | 1350–1400 and 1435–1525 MHz |
| SEK Bodypack, UHF | 509164 | $1,999 | Mic transmit and IEM receive in one pack |
| SEK Bodypack, 1G4 | 509163 | $1,999 | 1.4 GHz variant |
| MADI card, BNC / optical | 509293 / 509295 | $159 | Optional, redundant pair supported |
| BA 70 battery | 508860 | $55 | Up to 7 hours per pack |
| L 70 charger, 2-bay | 508861 | $75 | Cascadable |
The base station also requires a one-time activation license keyed to the regulatory zone it will operate in, which is how Sennheiser keeps a unit compliant with local rules. Confirm the zone license for your region at order time rather than after delivery.
Is WMAS legal in the United States?
Yes, since November 18, 2024. The FCC adopted WMAS rules in February 2024 and they took effect that November. The specifics matter, because they constrain what a US system can do.
In the TV bands, a WMAS may occupy a maximum bandwidth of 6 megahertz and must operate entirely within a single TV channel. It cannot straddle two. In several bands outside the TV spectrum, up to 20 megahertz is permitted where the spectrum allows.
The FCC also attached a spectral efficiency condition: a WMAS must be capable of providing at least three audio channels per megahertz in an operational mode, though not necessarily at all times. In a 6 MHz US TV channel that sets a regulatory floor of 18 audio channels. It exists to stop a manufacturer from occupying a whole TV channel with a handful of links and calling it wideband.
| Band | Licensed (Part 74) | Unlicensed (Part 15) |
|---|---|---|
| UHF-TV | 250 mW conducted | 100 mW EIRP for 1–6 MHz bandwidth; 50 mW EIRP up to 1 MHz |
| VHF-TV | 50 mW EIRP | 50 mW EIRP up to 1 MHz |
| 600 MHz duplex gap | 20 mW EIRP (653–657 MHz) | 20 mW EIRP (657–663 MHz) |
| 941.5–944 MHz and other microwave bands | 1 W conducted | — |
The gap between 250 mW licensed and 100 mW unlicensed in UHF is the single most consequential number in that table, and it raises the question most buyers skip.
Do you qualify for a Part 74 license?
Part 74 eligibility historically covered broadcasters and TV and film production companies. Since 2014 it also covers professional sound companies and venues that routinely use 50 or more wireless microphones, where wireless is integral to the major productions or events they host. A performing arts center, a large house of worship, or an arena can often qualify. A corporate campus with a dozen conference rooms generally cannot, and will operate unlicensed at the lower power limit. That is not a reason to avoid WMAS; it is a reason to design coverage around 100 mW rather than assume 250 mW and discover the difference at commissioning.
How much usable spectrum is actually left?
This is where US deployments diverge from the datasheet. The SEK bodypack's UHF variant tunes 470–608 MHz and 630–698 MHz. In the United States, the upper portion of that hardware range is not available for wireless microphones. The 600 MHz incentive auction and repack reassigned it to mobile carriers.
Under 47 CFR 15.236, unlicensed wireless microphone operation in the US is permitted in 54–72 MHz, 76–88 MHz, 174–216 MHz, 470–608 MHz, 614–616 MHz, and 657–663 MHz. Channel 37 at 608–614 MHz is reserved for radio astronomy and medical telemetry. The practical consequence for a WMAS, which needs a full contiguous 6 MHz TV channel, is that 470–608 MHz is the working range. Everything above it is either too narrow to hold a wideband channel or unavailable.
That is 138 MHz, shared with television broadcast, and in a major metropolitan market a meaningful share of it is occupied. This is the honest case both for and against WMAS. Against: the spectrum you have is finite and getting no larger. For: efficiency inside a scarce resource is exactly the problem WMAS was designed to solve, and the alternative is a narrowband system leaving guard space empty in spectrum you cannot replace. The 1.4 GHz variant exists partly to sidestep the argument, and where regulations permit its use it removes the TV-band contention entirely.
Where does WMAS make sense, and where does it not?
WMAS earns its cost in specific situations rather than generally.
It makes sense when a venue runs both microphones and in-ear monitors and currently coordinates them as two systems; when link count is high enough that rack space, antenna distribution, and coordination labor are real line items; when performers or presenters are currently wearing two body packs; when the RF environment is congested and deep diversity is worth paying for; or when channel count changes from event to event and reconfiguring inside one channel beats re-coordinating a rack.
It does not make sense when the requirement is four handheld microphones in a ballroom. Two channels of a well-chosen conventional digital system will do that for a fraction of the price, and a Sennheiser EW-DX pair covers it properly. WMAS is also the wrong answer where no bodypacks are in use, since the handheld SKM is still on the roadmap rather than in the catalog. And it is premature where a facility has not yet done a spectrum scan, because the first question a wideband system asks is whether a full clean TV channel exists in that building.
The strategic argument is separate from the project argument. WMAS is now in the FCC rules, ETSI has standardized it, and Spectera has been shipping since April 25, 2025. It is a direction the industry is moving, not a single product. For a venue planning a ten-year infrastructure cycle, that matters more than the specification sheet does.
Frequently asked questions
What does WMAS mean in wireless audio?
WMAS stands for Wideband Multichannel Audio System. It is a method of operating wireless microphones and in-ear monitors in which many audio links share one wide radio channel — up to 6 MHz in the US TV bands, 8 MHz in Europe — rather than each link occupying its own narrow carrier. The system's base station schedules transmissions inside that channel, so links do not need to be spaced apart to avoid intermodulation the way conventional wireless does. Because the channel is wide, each link can be spread across many frequencies at once, which produces far deeper diversity than the two-antenna arrangement conventional systems use. WMAS is defined in ETSI standards for Europe and was adopted into FCC rules for the United States effective November 18, 2024. Sennheiser Spectera is the first commercially shipping WMAS product.
Can Spectera transmit microphones and in-ear monitors on the same channel?
Yes, and that is the central design difference rather than a feature. Spectera's links are bidirectional, so a single RF channel carries microphone audio from the performer and monitor audio back to them, using the same DAD transceiving antenna for both directions plus the control data. The SEK bodypack reflects this: one pack contains both the microphone transmitter and the IEM receiver, with a 3-pin input for the microphone and a 3.5 mm output for earpieces, so a performer wears one device instead of two. Practically, this removes the separate IEM transmit band, the separate transmit antenna and combiner, and the separate frequency coordination exercise for monitors. It also removes a common failure mode, which is a monitor system coordinated correctly against itself but incorrectly against the microphone system, a fault that typically surfaces only when both are running at full channel count during a live event.
How much power can a WMAS transmit in the United States?
It depends on the band and on whether the operator holds an FCC Part 74 license. Licensed operation in the UHF-TV band permits 250 mW conducted power. Unlicensed operation under Part 15 in the TV bands permits 100 mW EIRP for a system using between 1 and 6 MHz of bandwidth, and 50 mW EIRP for systems up to 1 MHz. In the VHF-TV bands the licensed limit is 50 mW EIRP. In the 600 MHz duplex gap the limit is 20 mW EIRP for both licensed operation at 653–657 MHz and unlicensed operation at 657–663 MHz. Certain bands outside the TV spectrum, including 941.5–944 MHz, permit 1 W conducted power under a license. Design coverage against the limit that applies to the operator, not the highest number on the page, because the difference between 250 mW and 100 mW is a real difference in usable range and in how many antenna positions a building needs.
Who is eligible for an FCC Part 74 wireless microphone license?
Part 74 eligibility covers broadcasters and television and film production companies, and since 2014 it also covers professional sound companies and venues that routinely use 50 or more wireless microphones, where wireless microphone use is an integral part of the major productions or events they host. The 50-microphone threshold is about routine operational use rather than a one-time count, so a venue that hires in wireless for an annual event generally does not qualify on that basis. The distinction matters for system design because licensed operation in UHF permits 250 mW conducted while unlicensed operation permits 100 mW EIRP, and coverage planning built on the wrong assumption produces a system that works in commissioning and fails at the back of the room. Confirm eligibility before the RF design is finished, not after the antenna positions are already cut into the ceiling.
Next steps
Creation Networks designs and installs wireless microphone systems, in-ear monitor systems, WMAS and Sennheiser Spectera deployments, RF coordination and spectrum surveys, and antenna distribution for performing arts centers, houses of worship, arenas, higher education, and government facilities nationwide. Browse the Sennheiser catalog or the full professional microphone range.
Before specifying a wideband system, the first deliverable is a spectrum scan of the actual building. If a clean 6 MHz TV channel is not available where the system has to work, that answers the question faster than any datasheet. Talk to an AV design advisor about scanning your space.
Creation Networks, Inc. — nationwide commercial AV integrator, CTS-D certified, based in Concord, CA and Incline Village, NV. Design, engineering, programming, installation, and support from a single point of contact since 2006. Call 888-230-3661 or email sales@creationnetworks.net.
