Micro Speaker for POS Terminals and Payment Devices
A payment terminal speaks in public. It announces a completed transaction, a declined card, and sometimes an amount, in a space where the person standing behind the counter is not the only person listening. That single fact changes the acoustic problem more than any datasheet figure: the driver has to be heard by the customer without being heard by the queue, and it has to do so while a printer, a scanner and a second card reader are all running.
1. A Payment Device Talks to Two Audiences
Short answer: A payment terminal has at least two acoustic audiences with different privacy expectations, so the specification should separate what the customer must hear from what only the operator needs.
Most consumer audio design assumes one listener at a designed distance. A payment terminal breaks that assumption immediately. The customer needs confirmation that the transaction was accepted; the operator needs to hear the amount, the card type, or the failure reason; and the person behind them in a queue should hear as little of it as possible. The device therefore performs at least two different jobs with one transducer, at different times, at different levels, and with different privacy expectations attached.
This is why a payment terminal's audio specification is longer than its acoustic specification. Before any driver is chosen, the product has to define which prompts are public, which are private, and how the product changes behaviour when a headset is connected or a privacy mode is entered. A terminal that treats every prompt as a public announcement will be complained about in a queue; one that treats confirmation as private will leave the customer unsure whether the payment went through. The driver cannot resolve either question.
2. The Counter Is a Loud Place
Short answer: Retail environments combine continuous broadband noise from HVAC and printers with short high-level transients, so the prompt has to clear a variable noise floor without becoming unpleasant at close range.
A counter area is acoustically hostile in a specific way. There is usually continuous background noise from ventilation and refrigeration, intermittent noise from a receipt printer, and a thermal printer in some formats that runs during the transaction itself. A card terminal sitting on that counter is also handled at close range, often picked up and turned toward the customer, so the distance between listener and driver varies over a wide range during a single transaction.
That variability is the part that datasheets do not describe. A prompt tuned to be clearly audible at 1.5 m will be harsh when the terminal is held at 200 mm, which is the distance it is actually used at. The relevant design target is therefore not one distance but a range, and the specification should state the level at the far end of that range as the audible requirement and the level at the near end as the comfort limit. A device that satisfies only the first will be returned for being shrill; a device that satisfies only the second will not be heard over the printer.
Table 1: The three noise sources on a payment counter and what each one does to the prompt
Noise source | Character of the noise | Effect on prompt design |
Ventilation and refrigeration | Continuous, broadband, stable level | Sets the floor the prompt must clear; broadband noise masks the speech band specifically |
Receipt printer | Intermittent, mid and high band, unpredictable onset | A prompt that starts during printing is masked; the timing of the announcement relative to the print matters as much as its level |
Thermal printer | Continuous during a transaction, low frequency heavy | Competes with the prompt's low end and can cause the speaker to be pushed harder to be heard |
Queue and store ambience | Speech shaped, level varies with trading | The one source that sounds like the content itself, so it is the hardest to separate from the prompt |
Second card reader or scanner | Short bursts at unpredictable timing | A competing announcement from another device on the same counter; acoustic separation here is a placement problem |
3. The Cavity Behind a Terminal Is Often Someone Else's
Short answer: In a counter device the deepest available volume is frequently reserved for the printer, battery or main board, so the acoustic decision is usually made by packaging before a driver is selected.
Payment terminals are dense. The display, the card slot, the printer mechanism, the battery, the main board and the antenna all compete for the same internal volume, and the region left for a speaker is frequently a thin front-facing pocket beside the display or a slot along the housing parting line. In that situation the driver is being asked to perform in a cavity nobody designed for acoustics, and the choice of a nominally more powerful part does not recover the lost output.
The useful engineering move is to separate the acoustic cavity from the packaging cavity wherever the form factor allows. A boxed platform that carries its own volume makes the speaker independent of the space remaining after the printer and board are placed, which in a counter device is often the difference between a controlled acoustic result and an uncontrolled one. Where the product must be a bare driver in a shared pocket, the layout should reserve the pocket as a defined cavity with a defined opening rather than accepting the gap that the housing happens to leave.
4. Handheld and Desktop Are Different Problems
Short answer: A handheld terminal is held at close range in a quiet hand-held pose, while a desktop terminal speaks across a counter; the level and band requirements of the two do not converge on the same part.
A handheld payment terminal is used at arm's length or closer, usually in a quiet interaction, often with the device partly covering the customer's view. A desktop or counter-mounted terminal does the opposite: it sits at a fixed distance, faces outward, and has to compete with store noise. The two therefore want different levels and different amounts of low-frequency content, and they have entirely different constraints on power, because a handheld device runs from a battery that has to survive a working day.
Table 2: Published drivers used in payment and point-of-sale equipment
Model | Format and published size | Published sensitivity and power | Published F0 | Fit for payment-device work |
HS003650H | Round magnetic, φ36 × 5.0 mm | 97 dB at 2 kHz / 10 cm / 2.0 W | 500 Hz ±15% | Counter-mounted units where the prompt must project across a fixed distance |
HS002850H50 | Iron frame, φ28 × 5.0 mm | 97 dB at 2 kHz / 10 cm / 2.0 W | 600 Hz ±15% | A thinner frame than the round magnet class for a shallow front pocket |
HS003050H | Round magnetic, φ30 × 5.0 mm | 97 dB at 2 kHz / 10 cm / 2.0 W | 550 Hz ±15% | Catalogue applications for point-of-sale equipment; a mainstream counter choice |
HS002038H | Round magnetic, φ20 × 3.8 mm | 93 dB at 2 kHz / 10 cm / 1.0 W | 800 Hz ±15% | Handheld units where depth is the binding constraint and the room is quiet |
HS002045H | Round magnetic, φ20 × 4.5 mm, leaf spring | 94 dB at 2 kHz / 10 cm / 1.0 W | 600 Hz ±15% | The same footprint with a lower resonance, for a slightly larger pocket |
HS204130H30 | Round magnetic, 20 × 14 × 3.0 mm | 90 dB at 2 kHz / 10 cm / 1.0 W | 900 Hz ±15% | Rectangular format for a housing with a wide, shallow cavity; no bass required |
HS203045H45 | Round magnetic, 20 × 30 × 4.5 mm | 97 dB at 2 kHz / 10 cm / 0.8 W | 800 Hz ±15% | A long narrow cavity where level is needed but power budget is tight |
HS001846H | Large round magnetic, φ18 × 4.6 mm | 94 ±3 dB at 2 kHz / 10 cm, 2.83 Vrms | 500 Hz ±15% | A compact part with a tolerance band specified rather than a single figure |
HS-BX-3520 | BOX platform, 35 × 20 × 16 mm | 97 dB at 2 kHz / 10 cm / 2.0 W | 900 Hz ±15% | Counter terminals where the module must define its own cavity |
HS-BX-2514-YJT01 | BOX platform, 38 × 16 × 9 mm | 95 dB at 2 kHz / 10 cm / 3.0 W | 750 Hz ±15% | A shallow boxed option for a counter unit with limited internal depth |
HS-BX-4020 | BOX platform, 58 × 22 × 10 mm | 97 dB at 2 kHz / 10 cm / 2.0 W | 1250 Hz ±15% | Confirmation-only prompts in a wide, very thin housing; no low-frequency target |
HS-BX-5017 | BOX platform, 50 × 17 × 9.1 mm | 95 dB at 2 kHz / 10 cm / 2.0 W | 1400 Hz ±15% | A shallow narrow slot where intelligibility of a short confirmation is the only goal |
The read-across between the two formats is worth stating. The round-magnet parts in the φ20 to φ36 range are listed for point-of-sale equipment in this catalogue and are the mainstream counter choice; the boxed platforms cover the shallow housings where the packaging decision would otherwise dominate. The two rectangular drivers at 3.0 mm and 4.5 mm show the trade directly: the wider part reaches 97 dB on 0.8 W where the narrower one reaches 90 dB on 1.0 W, and which of those is better depends on how much width the cavity has and how much power the battery can afford.
5. Public Prompts and Private Confirmation
Short answer: Where a prompt must be private, the acoustic solution is usually a directed outlet or a headset path rather than a quieter driver, because privacy is a radiation-pattern problem.
Amounts, card numbers and authorisation details should not be audible to a queue. There are three ways to handle that, and they cost very different amounts. The first is a headset or wired output for the operator, leaving the driver to carry public confirmation only; this is the cleanest solution and the most common in higher-value terminals. The second is a restricted-radiation outlet facing the operator, which relies on the housing geometry and the position of the user rather than on electronics. The third is a very low level on the driver itself, which is the least reliable of the three because the audibility threshold in a real counter environment moves with the store's noise level.
This matters at component-selection time because the first solution changes the driver requirement entirely — it becomes a small, low-power part in a device that is otherwise quiet — while the second leaves the acoustic design in the housing and the third looks like a driver choice and behaves like an acoustics problem. Deciding this after the housing is frozen means redesigning an outlet, which is one of the more expensive changes late in a programme.
6. Power and Duty Cycle in a Battery Device
Short answer: A payment terminal's audio energy is trivial against its display and radio budget, so the real constraint is peak current during a short prompt, not total consumption.
It is easy to assume a payment terminal has no power problem. In practice the display backlight, the radio, the printer and any card-reader module dominate, and the speaker's contribution to average consumption is small. The constraint that matters is different: prompts are short and infrequent, but the instantaneous current during a prompt has to sit inside the amplifier's capability at the battery voltage, which is lowest at the end of a working day. A part that is comfortable at nominal rail may clip or shut down at the end of the shift.
The specification should therefore state the drive condition, the load, the rail voltage at the low point, and the required level at the intended distance, and should require a distortion figure at that condition rather than at the datasheet maximum. Thermal duration is rarely the limit in a payment device; headroom at low battery is. A part driven at a fraction of its rating will also tend to survive a long working day better, which matters for a device that is on for twelve hours.
7. Project Case: Counter-Mounted Payment Terminal
Project Case Study (Hongsheng)
A side-exit portable camera programme failed for a structural reason, and the sequence of fixes is the useful part. The customer had tried several drivers without reaching the target, because the original design placed the driver so that its sound had to leave through the side of the housing while no front cavity had been designed. The result was sound trapped inside the body: the output was muffled, and the 15 × 11 mm driver's requirement for a rear cavity was not met, which added noise coloration rather than clarity.
Hongsheng's engineering team overturned the original arrangement and worked from the customer's mechanical and board files instead. The rear cavity was enlarged first. The boss height around the driver was lowered by 1.75 mm, and the boss was redesigned so that it extended out level with the PCB and the board could cover it, forming a sealed rear cavity with the board rather than an open pocket. Where the cavity was still short, space was found elsewhere in the housing and the cavity extended again. The sound outlet, originally a round hole, was changed to a long slot, because a round hole was below 10% of the required open area; the slot was lengthened by 1.70 mm in each direction. The front cavity step height was then set to 1.2 mm with a 2.3 mm sealing step, and the driver assembly was reworked to reduce production defects. A hand-built sample was produced to demonstrate the result before any tooling was committed.
The cavity specification that came out of this work is the part worth carrying forward for any side-exit or narrow-body product: a rear cavity between 0.8 and 1.0 cc, a front cavity of 0.1 to 0.15 cc for a side exit, a front cavity throat length below 0.6 mm, and a front cavity height of 0.8 to 1.2 mm, with 1.2 mm giving the largest output. Hongsheng's contribution was participation in the joint design from the start rather than supplying a part into a frozen structure, and the practical lesson is that a driver of this class requires the cavity to be designed with it. Hongsheng revised the driver boss height by 1.75 mm, Hongsheng extended the boss to meet the PCB plane, and Hongsheng specified the front-cavity step at 1.2 mm with a 2.3 mm sealing step, so the cavity was designed with the part rather than after it. Hongsheng can supply the sealed BOX route for an enclosure with no room for a defined cavity, and can review the outlet geometry against the front-cavity figures before a tooling commitment is made.
One-line conclusion: the outlet was below 10% of the required open area — no driver change would have fixed that.
8. Confirming a Payment Terminal Driver with the Supplier
Short answer: For payment devices the questions that change the answer are about the acoustic cavity, the drive condition and the repeatability of the level, not about the datasheet headline.
1. Ask for in-cavity level and resonance measured in a housing with comparable volume and front opening, not only free-air figures.
2. State the two listening distances you need to satisfy and ask what level is required at each, in the band that carries speech detail.
3. Ask which published test condition each figure refers to: distance, applied voltage, power, cavity volume and the presence of a grille.
4. Ask whether a boxed platform brings its own acoustic volume or expects a defined host cavity, and what changes if the host volume differs.
5. For a handheld device, give the rail voltage at end of discharge and ask for the distortion and level data at that condition.
6. Ask whether the part has been used in a terminal where a printer or a second reader runs during the prompt, and how it performed.
7. Confirm the mechanical interface and the recommended acoustic opening, including any foam, gasket or mesh the drawing assumes.
8. Confirm how a change of magnet grade, raw material or adhesive in the motor would be communicated before it reaches production.
9. FAQ on POS and Payment Device Speakers
Q1: How loud should a payment terminal prompt be?
It has to clear the counter noise floor at the distance the customer actually stands, without being harsh when the device is picked up and held at 200 mm. Those two requirements usually conflict, so the specification should state the audible requirement at the far distance and the comfort limit at the near distance, and the driver should be chosen against both.
Q2: Should a payment terminal speak the transaction amount aloud?
Not in most retail environments, because the queue can hear it. The usual arrangement is a public acceptance confirmation plus a private amount or authorisation channel through a headset or a restricted outlet aimed at the operator. That decision affects the driver requirement substantially, so it belongs in the acoustic specification rather than in the firmware specification.
Q3: Is a more powerful driver the answer to a quiet terminal?
Usually not. If the prompt is masked by the noise floor, the first question is whether the cavity is defined at all; a louder part in an undefined cavity gains less than the datasheet difference suggests. Adding power to compensate for a poorly defined acoustic path also costs battery, which in a handheld terminal is not free.
Q4: How much cavity volume does a counter terminal need?
The honest answer is that it is set by the low-frequency target, not by the driver. Sealing a driver into a smaller cavity raises the in-cavity resonance rather than lowering it, following FC = Fs × √(1 + Vas / Vb). For a payment prompt that only has to carry a short confirmation, a very small cavity is perfectly workable and is the right answer.
Q5: Can the same driver serve a handheld and a countertop terminal?
The format can be shared, but the operating point should not be. A handheld is used at close range in a quiet interaction, a countertop unit projects across noise. Using the handheld part in a counter unit usually means driving it harder, which raises distortion and consumes battery; using the counter part in a handheld gives more level than the product needs at a higher cost than the BOM should carry.
Q6: What is the effect of the printer on prompt design?
It depends on the printer. A receipt printer produces intermittent mid and high band noise that masks a prompt starting at the same moment, so the timing of the announcement relative to the print operation can matter as much as its level. A thermal printer runs continuously during a transaction and competes mostly with the low end. Where a collision is unavoidable, the product's own sequencing is usually the cheapest fix.
Q7: Do I need a sealed driver for a payment terminal?
Only where the device is exposed to moisture or dust at the level the product definition requires. Note that the IP rating is claimed for the housing, not for the driver. A counter terminal in a dry retail environment usually needs no special acoustic sealing, and adding it removes the design freedom on the front face for no acoustic benefit.
10. Summary: Public and Private Audio in a Payment Device
Payment terminal audio is a public-and-private problem wearing an acoustic costume. The driver has to make a short confirmation audible across a noisy counter and comfortable in the customer's hand, while details that the queue should not hear go somewhere else. That means the acoustic specification has to come first: the two listening distances, the public and private prompt split, the drive condition at end of battery, and the cavity the product can genuinely afford after the printer and board are placed. Only then does the format question matter, and it is a comparatively easy one — round-magnet parts in the φ20 to φ36 range cover counter-mounted units, boxed platforms cover shallow housings, and rectangular parts cover a wide shallow pocket. Terminals that write the two-distance target and the public-private split into the specification before the enclosure is frozen are the ones that avoid reopening the acoustic design later.
Next step If you are evaluating a micro speaker for a payment terminal or point-of-sale product, the shortest route to a configuration worth testing is to state five things: the space available for the driver and its cavity, the impedance the amplifier will drive, the power the rail can supply, the target level at the intended listening position, and the cavity left after the printer and board are placed. With those specified, our engineering team can recommend a suitable configuration for evaluation, or state plainly which part of the acoustic design has to change first.
More in This Series
· How a shallow housing changes the acoustic result, and when a BOX platform is the right route →https://www.hsdz-spk.com/news/569.html
· What to check in a supplier's data before approving a part for a battery device →https://www.hsdz-spk.com/news/571.html