Quad vs 5-Trumpet Train Horn: Does a Fifth Trumpet Add Real Loudness?

Our 5-Trumpet model is rated up to 150 dB and the Quad tops out at 140 dB — so it's tempting to assume the fifth trumpet is worth 10 decibels all by itself. It isn't. Here's what an extra trumpet actually buys you, what the decibel math really says, and which horn you should put your money on.

What a fifth trumpet actually does

A trumpet is not a speaker you can simply stack for more volume. It's a tuned resonating body: the compressor pushes air through a diaphragm, and the trumpet's length sets the pitch. Short trumpets play high notes, long trumpets play low ones. On a four-trumpet horn, four different lengths sound four different notes at once — that stacked chord is the signature "freight train" sound.

Add a fifth trumpet and you get exactly what the name implies: a fifth note. The 5-Trumpet Train Horn for Milwaukee® 18v Battery runs five metal trumpets, each tuned to a different pitch, which produces the widest, most layered chord in the BossHorn lineup — deeper lows and brighter highs than a quad can reach. Five bells pointed across a wider arc also spread the sound over more directions, which matters in an open parking lot or on the water.

What the fifth trumpet does not automatically do is make the horn meaningfully louder. That part is worth understanding before you spend the extra money.

The decibel math: one more trumpet barely moves the meter

Decibels are logarithmic, and that changes the arithmetic completely. When you double the number of identical sound sources, the level rises by only 3 dB — two 80 dB machines running side by side measure 83 dB together, not 160. That's the well-documented "3 dB rule" of acoustics.

Now apply it to trumpet count. Going from four trumpets to five is only a 25% increase in sources. Run that through the same formula (10 × log₁₀ of the ratio) and you get about 1 dB — and that assumes each trumpet gets just as much air as before, which a shared compressor can't actually deliver. For reference, 1 dB is right at the threshold of what a human listener can detect at all, and it takes roughly a 10 dB jump for a sound to feel twice as loud.

So the honest physics: a fifth trumpet, by itself, is worth about one barely-noticeable decibel. Any horn maker — us included — that ships a louder five-trumpet model is getting that loudness from somewhere else.

So why is the 5-Trumpet rated 10 dB higher than the Quad?

Because the tiers differ by far more than trumpet count. Loudness in an air horn is set by air pressure and airflow: how hard the compressor pushes, how much air moves through the diaphragms, and how large the trumpets are. Our 150 dB-rated models pair their trumpet arrays with a higher-output compressor stage — that hardware, not the fifth bell, is what closes the 10 dB gap.

This is the same reason we tell buyers not to shop by trumpet count alone. A cheap horn can bolt on six tiny trumpets and still get out-shouted by a well-fed quad, because the compressor behind the array does the heavy lifting. If you've read our Dual vs Quad vs Extreme tier comparison, you already know the tiers step 130 → 140 → 150 dB — and the trumpet count changes between tiers, but it's never the whole story.

Quad vs 5-Trumpet, side by side

Here's how the two models actually compare, spec for spec. Both run on the tool battery you already own — the versions below take any Milwaukee® M18™ pack, and both are also available for DeWalt® 20V MAX™ batteries.

Spec	Quad	5-Trumpet
Max rated output	Up to 140 dB	Up to 150 dB
Trumpets	4 metal trumpets, 4 sizes	5 metal trumpets, 5 pitches
Chord	Four-note chord	Five-note chord, widest spread in our lineup
Wireless remote	Up to 160 ft	Up to 160 ft
Power	Any M18™ pack, all-day runtime	Any M18™ pack, all-day runtime
Setup	Snap in a battery — no wiring, no air tank	Snap in a battery — no wiring, no air tank

The practical difference you'll hear is tone and coverage, not a night-and-day loudness gap. The 5-Trumpet fills open space with a fuller, more locomotive-like blast; the Quad gives you most of that character for less money and a slightly more compact head.

The five-note chord is a real locomotive thing

If the fifth trumpet isn't about loudness, why do people want it? Because real locomotives made five chimes famous. The Nathan AirChime K5LA — the horn most Americans picture when they hear "train" — is a five-chime unit tuned to a B-major sixth chord: D♯, F♯, G♯, B and a higher D♯. Its three-chime sibling, the K3LA, plays a leaner chord built from three of those same notes. More chimes don't make a locomotive horn dramatically louder either — they make it sound bigger, richer, more musical.

Here's the part most buyers find surprising: by federal rule, a real locomotive horn only has to produce between 96 and 110 dB(A) measured 100 feet in front of the locomotive (49 CFR §229.129). What makes a train unmistakable isn't a record-setting decibel number — it's that thick multi-note chord rolling across a mile of open ground. A five-trumpet portable horn chases that character. We break down the chord science in our guide to why train horns make a chord.

Which one should you actually buy?

Straight answers, no upsell:

• Buy the Quad if you want the best value. Four notes already read as "train" to anyone within earshot, 140 dB is genuinely loud — and as we covered in 140 dB vs 150 dB: the law of diminishing returns, the last 10 dB matters less in the real world than the spec sheet suggests.
• Buy the 5-Trumpet if the sound itself is the point. Tailgates, boats, car meets, wide-open spaces — the five-note chord and wider projection are what you're paying for, and the 150 dB rating comes along with the tier.
• Buy an Extreme if you want maximum output and the deepest tone. The Extreme Series Train Horn for Milwaukee® 18v Battery hits the same 150 dB class with four long-bore trumpets, trading the fifth note for a lower, chest-thumping voice that carries hardest on the highway.

FAQ

Is a 5-trumpet train horn louder than a quad?

Slightly, but not because of the fifth trumpet. Trumpet count alone adds about 1 dB going from four to five. Our 5-Trumpet model is rated up to 150 dB versus the Quad's 140 dB because the higher tier moves more air — the compressor and trumpet hardware do the work, and the fifth bell adds the extra chord note and wider spread.

Does the fifth trumpet drain the battery faster?

Feeding five trumpets takes more airflow per blast, but the batteries these horns run on are built for high-drain power tools. Both models run all day on a single charged M18™ pack in normal use — blasts last seconds, not minutes, so runtime is rarely the limiting factor.

Do real trains use five trumpets?

Many do. Five-chime horns like the Nathan K5LA are standard equipment on a large share of American locomotives, tuned to a five-note major-sixth chord. That's exactly the sound a five-trumpet portable horn is built to imitate.

Is there anything louder than the 5-Trumpet?

Our Extreme and Boss Series horns sit in the same 150 dB-plus class with long-bore trumpet arrays tuned for a deeper tone. If pure output and low-end punch matter more to you than the five-note chord, that's the direction to look.