Single vs multi frequency explained: what the kHz number actually decides
Frequency is the spec beginners are told to care about and the one the explanations agree about least. One shop page says single frequency, another says multi, a third says "multi-frequency" about a machine that only ever runs one frequency at a time — and two popular guides give opposite rules for which frequency suits which target. Underneath the marketing there are really three different designs, one consistent pattern for what low and high frequencies do, and a choice that should start with where you hunt rather than with the technology. This guide separates the three designs, reconciles the contradictory advice against what the manufacturers themselves state, and ends with a spec-sheet check that takes about two minutes on any model you are considering.
What a kilohertz actually is
The frequency number is how fast the detector's transmitted field cycles, measured in kilohertz — thousands of cycles per second. A retailer explainer from LP Metal Detecting puts the typical single-frequency range at about 5 to 20 kHz: the machine transmits at that one rate, listens to the return signal, and builds everything it tells you — the tone, the target ID, the depth estimate — from that single conversation with the ground. Change the frequency and you change the conversation, because different frequencies interact differently with different targets and different soils. That interaction, not the number itself, is what you are actually choosing.
Low vs high frequency: reconciling the contradictory advice
Start with the pattern both major manufacturers state, because it is the yardstick for judging everything else. Minelab's Multi-IQ material describes it directly: low frequencies — its example is 5 kHz — are more responsive to high conductors, such as large silver targets, while high frequencies — its example is 40 kHz — are more responsive to low conductors, such as small gold nuggets. The Nokta Legend manual applies the same pattern in its own settings advice: 4 kHz is the suggested single frequency for large silver coins, while 20 and 40 kHz are the suggestions for shallow jewellery. UK retailer Joan Allen states the matching depth side of the trade: lower frequencies penetrate deeper but sacrifice sensitivity to small objects, and higher frequencies offer excellent sensitivity to small targets near the surface.
Now the contradiction a beginner will meet in the wild. One widely read retailer frequency guide states that the best frequency for large objects is 7 kHz or higher and for smaller objects 7 kHz or lower — the reverse of the manufacturer pattern — while elsewhere on the same page advising 10 kHz and lower for coins and 14 kHz and higher for gold, which agrees with the pattern. A page cannot have both rules. The manufacturer statements, the second half of that same guide, and the other retailer explainers all line up on one side: low frequency favours depth and large, high-conductivity targets; high frequency favours small, low-conductivity targets near the surface. When a source disagrees with that, treat the source — not the pattern — as the problem. One honest caveat, also from Minelab: its own frequency diagram is representative only, and actual sensitivity always depends on the target's type and size, the ground conditions, and the detector's settings. Frequency tilts the odds; it does not guarantee an outcome on any single target.
The three designs compared
Most explanations offer two categories. There are three, and the middle one is where the confusion — and most of the marketing — lives.
| Design | What it actually does | Strength | Limit |
|---|---|---|---|
| Fixed single frequency | Runs one frequency, chosen by the manufacturer, every hunt | Simple, typically lighter and more affordable, lower battery draw (Joan Allen) | The one frequency is a compromise; mineralized ground can severely affect it and saltwater beaches are a known struggle |
| Selectable single frequencies | Offers a list of frequencies but runs one at a time — the Legend manual lists 4, 10, 15, 20 and 40 kHz | Lets you tilt the machine toward a target class or step away from electrical interference by switching | Still one frequency at a time; Minelab is explicit that switchable singles do not match simultaneous multi for target ID accuracy at depth |
| Simultaneous multi-frequency | Transmits, receives and processes more than one frequency concurrently — Minelab's definition of the term | Maximum sensitivity across target types and sizes at once, with ground noise minimised, especially in saltwater (Minelab) | More processing and cost; and modes can restrict you — on the Legend, Beach mode requires Multi rather than offering it as a choice |
The definitional point matters when money is involved. Minelab states that when it uses the term "multi-frequency" it means simultaneous — more than one frequency transmitted, received and processed at the same time — and it draws the line exactly at switchable machines that claim the multi-frequency label. A selectable-single machine is a perfectly good design with real advantages; it is simply not doing the simultaneous thing, and it should not be priced or judged as if it were.
Which design fits which site: a decision framework
Work through these questions in order. The site comes first because frequency problems are site problems: the same machine that is calm in a park can be unusable on wet salt sand, and no frequency feature fixes hunting the wrong design in the wrong place.
- Will you hunt wet salt sand or shallow salt water regularly? If yes, simultaneous multi-frequency moves to the top of the list. Minelab names saltwater as the condition its simultaneous processing specifically quietens, single-frequency machines are documented to struggle there, and some beach modes will not let you leave Multi anyway. Occasional dry-sand trips do not create the same requirement — dry sand is far more forgiving.
- Is your hunting mostly parks, yards and fields for coins and dropped jewellery? Then any of the three designs can work, and the choice becomes about targets and budget. A fixed single-frequency machine in the typical range is the simple, affordable option; a selectable-single machine adds the ability to drop to a low frequency such as 4 kHz for large silver or rise for small shallow jewellery, following the pattern above.
- Are small, low-conductivity targets the point — tiny gold, fine chains, small relics? Prioritise access to genuinely high frequencies, whether as a selectable single (20 or 40 kHz on the Legend's list) or inside a simultaneous design. Note the restriction pattern before buying: on the Legend, Goldfield mode restricts the lower single frequencies, which is the manufacturer steering you to the same conclusion.
- Do you hunt near power lines, fences or other electrical interference? Selectable frequencies earn their keep here too: the Legend manual lists electromagnetic interference as a reason to run a single frequency, because stepping to a different single frequency can move the machine away from the interference in a way a fixed machine cannot.
Notice what is not on the list: brand, and the raw count of frequencies. Five selectable singles and a simultaneous mode in one machine — the Legend's arrangement — is a flexibility story, not proof that more numbers on the box find more targets at your sites.
Verify it on the spec sheet: a two-minute check
Before any frequency claim influences a purchase, run this check on the manufacturer's own specification or manual. It uses the Legend and the EQUINOX line as worked examples because both publish the relevant lines clearly.
- Find the operating-frequency line. One number means a fixed single-frequency design. A list of numbers means, at minimum, selectable singles. The word "simultaneous" — or a named simultaneous technology — is the claim that separates the third design from the second.
- Check whether the list is really all usable. Minelab's own footnote for the EQUINOX 600 states that 20 kHz and 40 kHz are not available as single operating frequencies on that model, even though they sit inside its multi-frequency range. A frequency that exists only inside the simultaneous blend is not a selectable single, whatever the headline range implies.
- Check the mode restrictions. In the Legend manual, Beach mode requires Multi frequency and Goldfield mode restricts the lower singles. Restrictions are not defects — they are the manufacturer telling you which design each site actually needs, in writing.
- Match the result to your framework answer. If step 1 of the framework put you on salt water and the spec sheet shows a fixed single frequency, that is a mismatch no discount fixes. If your sites are parks and the sheet shows selectable singles covering a low and a high option, the machine fits the decision you actually made.
What success looks like
Success is being able to say, in one sentence, which of the three designs a machine is and why that design suits your main site — before price enters the conversation. The frequency-to-target pattern stops being a pair of competing slogans and becomes one rule you can apply: low for depth and large high conductors, high for small low conductors near the surface, with ground and settings always having a say. And when a listing says "multi-frequency," the first question is automatic: simultaneous, or selectable? The spec sheet answers it, every time.
FAQ
Is a higher kHz number simply better? No. Higher frequencies are more responsive to small, low-conductivity targets near the surface and give up depth and stability to get it; lower frequencies do the reverse. "Better" only exists relative to a target and a site.
A detector lists five frequencies. Is it multi-frequency? Only if it runs them simultaneously. A list such as 4, 10, 15, 20 and 40 kHz that the machine runs one at a time is a selectable-single design — useful, but a different thing, and manufacturers such as Minelab draw exactly that distinction.
Why does beach mode force multi-frequency on some machines? Because conductive salt is the condition simultaneous processing is built to quieten. The Legend manual makes Beach mode Multi-only; that restriction is the manufacturer encoding the site-first rule into the machine.
Can a single-frequency machine work at the beach at all? On dry sand, generally yes. Wet salt sand is the documented weak point: retailer and manufacturer sources alike describe single-frequency machines struggling with mineralization and false signals there, which is precisely the gap simultaneous designs were built to close.
Detector capabilities, site rules and permissions vary by place and model. This guide is general information about how frequency designs work — always check local laws and get permission before detecting on any land, and verify specifications against the manufacturer's current manual for the exact model you are considering.