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HSD Sound Systems · Subwoofer

HSD Battleaxe

Model 21FLH28

The renowned 21-inch FLH, usable output down to 25 Hz.

The BattleAxe is a high-intensity 21" front-loaded horn subwoofer engineered for deep bass extension and extreme power handling. Designed for demanding professional applications, it delivers usable output down to 25 Hz, making it the go-to for large-scale venues and events that demand superior low-end reinforcement. Hand-built by Hennessey Sound Design in Massachusetts, and backed by a 5-year limited warranty.

$7,100 retail

Built to order. Quote includes freight, system design, and current lead time.

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HSD Sound Systems Battleaxe subwoofer by Hennessey Sound Design

Amplification

Passive cabinet, amplification required
The BattleAxe is offered with a 4- or 8-ohm driver. With the 4-ohm driver, one BattleAxe per 2,500 W channel of a KP Series 4-10KP / KD Series 4-10KD is a one-to-one match, four subs per amp.
1 amp channelper cabinet, 4 or 8Ω
Driver
1×21″front-loaded horn
Response
28Hzto 150 Hz (-3 dB); 22 Hz at -10 dB
Power
2,500Wcontinuous (5,000 W program)
Sensitivity
107 dB1W/1m
HSD Sound Systems Battleaxe subwoofer, alternate angle

Full specifications

HSD Battleaxe (21FLH28) specs

Factory specifications from Hennessey Sound Design. Download the cut sheet for drawings and driver details.

Frequency Response28 Hz - 150 Hz (-3 dB); 22 Hz - 250 Hz (-10 dB)
Sensitivity107 dB (1W/1m)
Drivers1 x 21" (front-loaded horn)
Power Handling2,500 W continuous (5,000 W program)
Impedance4 or 8 ohms (driver option)
Dimensions25.5" W x 50" H x 52.5" D
Weight340 lbs
Connectors2 x NL4
HSD Battleaxe cut sheet (PDF)

Why buy from Fullblast

An HSD system is a build, not a box. We manage the whole thing.

01

Authorized HSD dealer

Fullblast Sound is one of only three authorized HSD Sound Systems dealers in the United States. Factory pricing, factory support, and a direct line to the Massachusetts shop on every order.

02

Real dealer support

We spec the system against your room and application, handle freight and logistics, and stay on call after delivery. Talk to us before you order and we will get the design right the first time.

03

Nationwide freight

Every HSD cabinet ships crated freight from the factory. We quote and coordinate delivery to your dock or venue anywhere in the country as part of the system price.

04

Financing available

Spread an HSD system across payments instead of a single check. See financing options or ask for terms with your quote.

Get a real quote

Send a system spec, not a price shopping number

Tell us the room, the audience size, and what you run today. We come back with the right HSD build, amplification, freight, and current factory lead time. One short form.

Request Quote Or call 210.489.0492

Same business day response.

Buyer research

Questions buyers ask about the Battleaxe

Common pre-purchase questions on the HSD Battleaxe.

Q1

Why is the BattleAxe HSD's best-known cabinet?

It is the box that built the brand's festival reputation: a 21″ front-loaded horn with usable output down to 25 Hz, 2,500 W continuous handling, and 107 dB sensitivity. For large-scale venues and events that demand real sub-bass pressure, not just extension on a spec sheet, the BattleAxe has been the go-to.

Q2

What amplifier drives the BattleAxe?

It is offered with a 4- or 8-ohm driver ($7,100 either way). With the 4-ohm driver, one BattleAxe sits one-to-one on a 2,500 W channel of the HSD KP Series 4-10KP or KD Series 4-10KD, four subs per four-channel amp. Choose the 8-ohm driver when you want to parallel pairs per channel on higher-power KD models; we will spec the right combination for your wall.

Q3

BattleAxe, Battlehawk, Tomahawk, or Sherman?

All 21″-class FLH subs (the Sherman is a 24). The BattleAxe ($7,100) is the renowned original. The Battlehawk ($7,500) is its evolution, flatter response and 3,000 W handling. The Tomahawk ($6,100) cuts 100 lbs for touring. The Sherman ($10,600) is the 24″ flagship: one Sherman equals two BattleAxes. The right answer depends on whether weight, budget, or output leads your spec.

Q4

What goes on top of a BattleAxe wall?

The classic HSD stack adds Cannon bandpass horns for the 65–220 Hz band and Mantarray 60 or Haymaker tops above. Its stable 50″-tall cabinet is the base layer the rest of the wall is designed around.

Q5

What are the build terms on a BattleAxe order?

Every BattleAxe is built to order in Massachusetts, with lead times typically around 90 days. It carries a 5-year limited warranty, free factory training is included, and custom paint is available for $500 per cabinet. We will walk you through ordering and payment when we quote your system.

System design

This pairs well with

The BattleAxe is the foundation stone of the signature HSD wall.

Punch layer

Cannon bandpass horn

Designed specifically to ride on FLH sub stacks. Cannons over BattleAxes own everything from 25 to 220 Hz.

Tops

Haymaker 3-way

Large-format tri-amped top with waveguide options, the full-range finish over a BattleAxe base.

Amplification

HSD KD Series 4-10KD

2,500 W per channel into 4 ohms: a one-to-one match for 4-ohm BattleAxes, four per amp.

Explore the HSD lineup

Where the Battleaxe sits in the catalog

One cabinet in a system. See the full HSD Sound Systems hub.

Point-source tops

HaymakerTri-amped 18/10/4×1 point source. Selectable waveguides. UppercutMedium-format tri-amped top. Full range to 45 Hz. SouthpawHigh-mid extension for fills, delays, monitors. 50 lbs. Mantarray 60Array-optimized 60×40 point source. Mantarray 90Wide 90×40 coverage, reaches 90 Hz alone.

Mid-bass horns

HammerDual-18 FLH mid-bass. 108 dB sensitivity. V-HornCompact 15″ mid-bass horn. Van-friendly. Cannon18″ bandpass horn. Rides on big sub stacks.

Subwoofers

WarhammerDual-18 FLH sub. Sustained 140 dB+. Switchback18″ FLH to 32 Hz. Truck-pack footprint. EagleCluster-optimized 18″ FLH to 29 Hz.
BattleaxeThe renowned 21″ FLH. Usable to 25 Hz.
BattlehawkThe BattleAxe evolved. 3,000 W, flatter response. Tomahawk21″ FLH, 100 lbs lighter. Built for the road. Sherman24″ flagship. One Sherman = two BattleAxes.

Monitors

DJ18 Monitor18″ booth sub to 27 Hz. Passive or powered. Reference 12Coaxial 12″ reference monitor. 80×80.

Line array

BallistaMedium-format line array module. Four-way passive.

Amplifiers

KP Series Amplifiers2–4 ch DSP amps, up to 10 kW. FIR at 96 kHz. KD Series Amplifiers4-ch Class-D, up to 20 kW. Universal voltage.

Documentation

Cut sheet

HSD Battleaxe cut sheet (PDF) Full HSD Sound Systems lineup

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