20mm vs 23mm vs 28mm Micro Speaker: Which Size Fits?

20mm vs 23mm vs 28mm Micro Speaker: Which Size Is Right for Your Product?

Three round micro speaker diameters cover a large share of the compact products currently in production. A 20 mm driver fits a tight internal pocket but leaves little structure around it. A 23 mm driver usually arrives as a potted unit with a composite diaphragm, which changes what the product can do. A 28 mm driver fits only where the product was designed around it, and it changes the low-frequency budget more than its footprint suggests. Choosing between them is mostly a question of which constraint the product actually has.

The diameter is not the parameter buyers usually think about. It is a proxy for three other things that matter more: how much magnetic structure fits inside, how much internal height the product can spend, and how the radiating structure behaves once it is installed. Two products of the same diameter can sit at very different points in the catalogue, and the difference is usually height and construction rather than diameter.

1. What Diameter Actually Determines

Short answer: Diameter sets the outer envelope and therefore the mounting opening and the room left for structure around the driver. It does not by itself determine sensitivity, resonance or power — those follow from the magnet, the height and the construction inside that envelope.

This distinction is the reason diameter comparisons go wrong. A 20 mm driver is available in thin, low-power versions and in versions that need a defined host cavity; both share the same diameter. When a comparison is made between diameters, the useful question is what was built inside each one, and under what measurement conditions the figures were taken.

Height is the parameter buyers under-budget. Going from a 5 mm frame to a 10 or 12 mm potted body inside the same diameter does not give the same product; it gives a product with a different acoustic behaviour, a different mounting height and a different cost. Product designers who fix the diameter first and choose the height afterwards usually end up redesigning the internal stack.

2. Why the Three Diameters Behave Differently

Short answer: The three diameters differ in construction, not in size alone: a thin magnet frame with no front cover, a potted composite-diaphragm unit, and a taller frame or potted body with more internal volume behind the diaphragm.

A 20 mm round magnetic driver in a thin frame is the most straightforward option: it is fitted where a rear cavity exists and measured after mounting. A 23 mm pot-type unit with a composite diaphragm and a polyurethane edge is a different object: it is a more complete acoustic structure, described by the catalogue as suitable for voice and Bluetooth products, and it occupies considerably more height than its diameter suggests. A 28 mm driver appears in two distinct forms, a 5 mm iron frame for alarm and voice products and a 10 mm potted version with a lower published resonance.

The practical consequence is that diameter predicts the mounting problem more reliably than it predicts the acoustic result. Where the product is designed first, the useful sequence is the reverse: define the acoustic target, then choose the construction, then check whether the envelope still fits.

3. Published Data Across the Three Diameters

Short answer: Published sensitivity, resonance and power for round drivers between 13 mm and 36 mm in one catalogue. Each figure is stated with its test condition; sensitivity and resonance values measured in different cavities are not comparable.

Table 1: Illustrative round-driver comparison observed across one published sample catalogue. All sensitivity figures are quoted at 2 kHz / 10 cm at the stated test power, and resonance values at the stated test voltage. They are catalogue values, not a recommendation for a specific product.

Model	Diameter × height	Construction	Published sensitivity	Published F0	Impedance	Rated / max power
HS001342H42	φ13 × 4.2 mm	Round magnetic	88 dB at 0.5 W	1000 Hz ±15%	8 ±15% Ohm	0.5 / — W
HS001534H39	φ15 × 3.4 mm	Round magnetic	90 dB at 0.8 W	800 Hz ±15%	8 ±15% Ohm	— / —
HS001846H	φ18 × 4.6 mm	Large round magnetic	94 dB at 2.5 W	500 Hz ±15%	4 ±15% Ohm	— / —
HS002038H	φ20 × 3.8 mm	Round magnetic, solder type	93 dB at 1.0 W	800 Hz ±15%	8 ±15% Ohm	0.8 / 1.0 W
HS002045H	φ20 × 4.5 mm	Round magnetic, leaf spring	94 dB at 1.0 W	600 Hz ±15%	8 ±15% Ohm	0.8 / 1.0 W
HS0023123H123	φ23 × 12.3 mm	Pot-type, composite diaphragm, PU edge	95 dB at 2.0 W	400 Hz ±15%	4 ±15% Ohm	2.0 / 2.5 W
HS002850H50	φ28 × 5.0 mm	Iron frame	97 dB at 2.0 W	600 Hz ±15%	8 ±15% Ohm	2.0 / 2.5 W
HS0028110H110	φ28 × 10.0 mm	Pot-type large magnetic	96 dB at 2.0 W	350 Hz ±15%	4 ±15% Ohm	2.0 / 2.5 W
HS003050H	φ30 × 5.0 mm	Round magnetic	97 dB at 2.0 W	550 Hz ±15%	8 ±15% Ohm	— / —
HS003050H50	φ30 × 5.0 mm	Round magnetic	98 dB at 2.5 W	500 Hz ±15%	4 ±15% Ohm	— / —
HS0034140H140	φ34 × 9.0 mm	Pot-type large magnetic	98 dB at 2.0 W	300 Hz ±15%	4 ±15% Ohm	— / —
HS003650H	φ36 × 5.0 mm	Round magnetic	97 dB at 2.0 W	500 Hz ±15%	8 ±15% Ohm	— / —

Read across the table rather than down it. The step from φ20 × 4.5 mm to φ23 × 12.3 mm changes resonance from 600 Hz to 400 Hz and rated power from 0.8 W to 2.0 W, but the height goes from 4.5 mm to 12.3 mm. That is the trade a diameter-first decision misses.

The two φ28 entries show the same point from the other direction: at one diameter, the 5 mm frame gives 600 Hz at 8 Ω and the 10 mm potted body gives 350 Hz at 4 Ω. Choosing between them is a height and impedance decision, not a diameter decision.

4. How to Choose Between 20, 23 and 28 mm

Short answer: Choose by the tightest real constraint: internal height for a potted unit, mounting opening for a frame type, available rear volume for anything measured after installation, and the impedance the amplifier can drive.

1. Fix the maximum internal height first, not the diameter. A potted unit at 10 to 12 mm is a different structural decision from a 4 to 5 mm frame type.

2. Establish whether a rear cavity exists. If it does, frame types measured after mounting are usually simpler; if it does not, a driver requiring a defined host cavity or a module with its own volume should be evaluated instead.

3. Compare published figures only at identical test conditions — same distance, same test power, same cavity volume.

4. Check the impedance against the amplifier rail. The 4 Ω options in this range need a different rail headroom than the 8 Ω ones at the same power.

5. If the product carries music rather than speech, weight the resonance and excursion figures more heavily than the mid-band sensitivity.

6. Ask the supplier to state which of the three diameters would be chosen for the assembled product and what would have to change to move to the next one.

Project Case Study (Hongsheng)

A wellness device for listening during rest specified a thickness limit of 12.5 mm together with a rated power of 2 W, distortion below 1% and a resonance low enough to give audible bass. In that envelope a single driver could not meet all three, so Hongsheng first supplied an existing potted unit with a resonance of 280 Hz for the customer to evaluate. The customer accepted the sound but the 16.5 mm height of that unit exceeded the available envelope, so the specification was renegotiated to 13.5 mm and a custom φ40 diaphragm was designed. The resulting single-point resonance was 120 Hz and 230 Hz once assembled in its cavity, with measured sensitivity of 98 ± 3 dB at 2 kHz, 2.83 Vrms input, 10 cm, and a rubber diaphragm that kept distortion extremely low. Rated power settled at 1.0 W with a maximum of 1.5 W, below the original 2 W request. Two passive radiators were fitted, one on each face, to add low-frequency output while reducing enclosure vibration. Four iterations were produced before the customer accepted the result, which is now in production use. Hongsheng can supply either a potted unit of this class or a custom-diaphragm route once the available thickness, cavity size and power target are stated, and can say plainly when the combination requested is not physically available.

The 12.5 mm limit and the 2 W target could not both be kept; the resolution was a thinner-than-requested power rating in exchange for a resonance the application actually used.

Hongsheng publishes round drivers from φ13 mm to φ45 mm across thin frame, iron frame and pot-type constructions, so each of the three diameters can be evaluated against more than one construction rather than a single option. Hongsheng can compare the constructions that fit a given envelope and identify which one would meet the stated target.

5. Frequently Asked Questions

Q1: Is a larger diameter always the better choice?

No. A larger diameter offers more internal volume and usually lower resonance, but it also requires a larger mounting opening and often more internal height. In a product with a fixed pocket and a tight stack, the smaller frame type with a defined host cavity is frequently the only option that fits.

Q2: Why do two drivers of the same diameter have very different resonance figures?

Because the construction differs. Within one diameter, the catalogue lists thin frame types, iron frame types and potted bodies with composite diaphragms, and these differ in the volume behind the diaphragm and in the radiating structure. Height is usually the visible indicator of which is which.

Q3: How do I compare sensitivity figures from different datasheets?

Check the measurement distance, the applied voltage and the cavity volume behind the driver. A figure quoted at 2 kHz / 10 cm at 1.0 W is not comparable with one quoted at 1 W in a larger cavity. Without the three conditions, differences of several decibels may describe the test rather than the product.

Q4: What does the pot-type construction change in a compact product?

It removes the requirement to reserve a rear cavity, because the unit is a more complete acoustic structure, but it occupies more height and usually presents a 4 Ω load. Where internal depth is available and the amplifier can drive 4 Ω, it is often the shorter route to a lower resonance than a bare driver in a shallow cavity.

Q5: Does a lower published resonance automatically sound better?

No. A lower resonance gives more low-frequency output in the same cavity, but audible quality at the listening position also depends on level in the speech and presence bands, on distortion, and on whether the cavity behind the driver is defined. Two drivers with different resonance figures can be indistinguishable in use.

Q6: What should be confirmed before locking a diameter?

The maximum internal height, the mounting opening available, whether a rear cavity exists and its volume, the impedance the amplifier will drive, the power the rail can supply, and the band the product actually needs. These six answers determine the construction, and the diameter follows from that.

Q7: Can a supplier tell me which diameter to use before I have a design?

A supplier can narrow it down from the envelope and the acoustic target, but a reliable answer needs the available height, the cavity situation and the level required at the listening position. Where those three are not yet fixed, an evaluation of more than one diameter is usually more useful than a single recommendation.

6. Summary

Diameter is a useful proxy for the mounting problem and a poor proxy for the acoustic result. Within each of the 20, 23 and 28 mm options, published sensitivities range from 93 to 97 dB and resonances from 350 to 800 Hz, and the difference is produced by height and construction rather than by the outside dimension. Fixing the maximum internal height and the cavity situation first is what makes a shortlist meaningful. Hongsheng can compare the diameter options available for a given envelope and identify which construction would meet the stated target, and can state plainly where the stated combination is not available. Selection always belongs in the product specification and in measurements made in the assembled product.

Next step If you are choosing between round micro speaker diameters for a compact product, the shortest route to a shortlist worth testing is to state five things: the maximum internal height available, the mounting opening the front face can provide, whether a rear cavity exists and its volume, the impedance the amplifier will drive, and the level required at the listening position. With those specified, our engineering team can compare the constructions that fit the envelope, or state plainly which diameter and which height would need to change if the first proposal does not reach the target.

More in This Series

· How a shallow housing changes the result, and when a BOX platform is the right route →https://www.hsdz-spk.com/news/575.html

· Choosing between rectangular 20 × 30 mm and 20 × 40 mm formats in compact devices → https://www.hsdz-spk.com/news/577.html