Do USB audio adapters supply bias voltage for lavalier condenser mics, and is TRS better than TRRS?

Question

I give a lot of live (but recorded) seminars over zoom and need high voice quality. At home I use a Rode NT5 plugged into a focusrite 2i2 in a room with some sound treatment, and am pleased with the results. However, I also sometimes need to have zoom meetings while traveling, when I can't bring all of this gear with me and am likely in a place with worse acoustics. Right now I use a cheap USB lav mic which doesn't sound great, and I would like to upgrade to a higher quality pro lav mic, possibly the Shure twinplex TL47, which sounds good to me in tests on youtube.

My laptop has a TRRS port, but I can't use this for the microphone, because if I plug in a cable it mutes my speakers, preventing me from hearing if someone in my audience has a question. Hence, I'm hoping to get a small USB adapter and use this to plug in the lav mic, so it shows up as a separate USB sound device. My questions:

• Is it better to get a microphone with a 3.5mm TRS or 3.5mm TRRS connector/adapter? Presumably TRRS is an unbalanced signal, but I don't know if TRS connectors are typically for a stereo signal, a balanced mono signal, or a mono signal with a separate connector for power. Is it easy to convert in both directions, or is one of them more general? (Though I'd typically plug into my laptop, in certain situations I might want to plug the mic into my phone [TRRS] or mirrorless camera [TRS], so I'd like to be able to adapt to whichever connector I don't get.)

• Do most USB audio adapters supply bias voltage? I definitely can't lug a proper mic pre-amp around, so am hoping to use a small USB-to-TRRS or USB-to-two-TRS connector cable. Unfortunately, none of the audio adapters I see mention anything about bias voltage. I don't know if this is because all conforming 3.5mm TRRS audio sockets supply bias voltage to the microphone and hence it goes without saying, or because no adapters do this and hence none would work with a condenser mic.

• Any suggestions on lavalier mics to consider if I like the sound of the Rode NT5? (In particular, I like that the NT5 makes my voice sound less "boomy" and tiring than my current USB lavalier mic, which I was using previously all the time.)

Answer 1

There are some USB audio adapters which provide 5 or 7 channel output on 3.5mm TRS sockets. Those tend to have microphone inputs with bias voltage on them, too. Only problem is that the quality is not better than that of the average microphone input on a laptop.

As a rule: anybody who has the temerity to provide a 3.5mm phone socket for a microphone will provide plugin power. Mono microphone inputs can have separate bias voltage on the ring (though this old Soundblaster convention likely is pretty dead these days and you have the ring either open or connected to the tip).

TRRS inputs have microphone input and bias voltage on the same connection (once the second R, but these days it is more likely to have it on S if I remember correctly and instead have signal ground on the second R) but those are basically only used on combined headphone outputs.

Good USB audio adapters invariably have XLR inputs with +48V phantom power. There are adapters for using them with electret microphones with bias voltage: if you take a look at clip-on instrument microphones at some mail order music store, you'll find that they often have phantom power adapters bundled, and those are also available separately. They have a variety of connectors, but 3.5mm TRS and mini-XLR (used by AKG microphones/wireless with 4V through 4.7kOhm bias if I remember correctly, TA3M in the adapter) are common.

If you are looking for a brand product, Røde has the VXLR+ adapter for their video mics (note that the + sign is important or it will not provide plugin power), also 3.5mm TRS.

By now there is a deluge of cheap noname adapters of probably differing quality.

If you want TRRS, it will usually be the easiest option to use a laptop adapter splitting TRRS into a microphone input and a headphone output. I haven't heard of an XLR-to-TRRS adapter yet and it seems somewhat pointless since XLR does not provide a headphone output signal.

Answer 2

If you're getting an external USB audio interface, get one that supports phantom power [48v].

The Shure [& many other pro-level lav mics] comes with interchangeable adaptors for connectivity to different manufacturers' body packs etc as well as 'regular' XLR. If you don't need to consider wireless integration, then XLR is the 'safe option'.

I can't find the info on Shure's site, but B&H says it will run on phantom power between 11 & 52v.

If you are considering spending $£€ 400 or so on a lav mic, don't ignore the DPA mics. I've never used the Shure myself so I have no comparison, but I've had the DPA 4060 for 20 years or so & consider it to be one of the best mics I've owned. They also have similar multiple connectivity options.

btw, mics that plug into a laptop's headset jack are all cheap high impedance mics. Pro-level low impedance mics won't work that way. Don't even bother ;)

Of course, if you are powering from a body pack/wireless transmitter, then each mic manufacturer will use their own bias voltage, meaning you have to be careful to match one to the other. Using the XLR adaptor instead makes the use of phantom a more 'universal' solution.