In this review, we will be comparing AE2 40th Anniversary and R-51M, two Passive Bookshelf speakers from Acoustic Energy and Klipsch.
Let's have a brief look at the main features
of Acoustic Energy AE2 40th Anniversary and Klipsch R-51M first before getting into our more
detailed comparison.
| Key Specs | Acoustic Energy AE2 40th Anniversary | Klipsch R-51M |
|---|
| Brand | Acoustic Energy
United Kingdom · founded 1987 | Klipsch
United States · founded 1946 |
|---|
| Design | 2-way | 2-way |
|---|
| Tweeter | 1.1" Dome | 1" Tractrix Horn |
|---|
| Woofer | 2 x 5" ceramic-coated aluminium | 5.25" Copper-spun IMG |
|---|
| Frequency response | 35-45k Hz | 62-21k Hz |
|---|
| Sensitivity | 88 dB | 93 dB |
|---|
| Impedance | 6 ohms | 8 ohms |
|---|
| Power range | up to 200 watts | Up to 85 watts |
|---|
| Weight | 14.50kg / 31.9lbs | 5.00kg / 11lbs |
|---|
| Dimensions (H x W x D) | 15.2" x 9.3" x 12.4"
385.0 x 235.0 x 315.0mm | 13.3" x 7.0" x 8.4"
338.0 x 178.0 x 215.0mm |
|---|
What size room are the Acoustic Energy AE2 40th Anniversary and Klipsch R-51M speakers good for?
The size of the room in which you are planning to use these loudspeakers is an important decision
factor. Here we have compared their suitability to various sizes of environments considering their size
and max power parameters:
| Listening Environment* |
Acoustic Energy AE2 40th Anniversary |
Klipsch R-51M |
| Near-field |
Poor |
Average |
| Small Room |
Average |
Good |
| Mid-size Room |
Good |
Average |
| Large Room |
Good |
Poor |
| Very Large Room |
Average |
Bad |
(* Approximate Room sizes: Small < 100sq. ft / 9 m2,
Mid-size: 100-220 sq. ft / 9-20 m2, Large 220-400 sq. ft / 20-36 m2, Very Large: >
400 sq. ft / 36 m2.
Average Floor Height: 9" / 2.7m. Typical room sizes differ from country to country, and the actual
listening experience changes depending on floor height, room shape, surface materials, listening
position, speaker locations, etc.)
The sections below take each area in turn: drivers, frequency response, physical size and what you get in the box.
Drivers
Both AE2 40th Anniversary and R-51M are 2-way speakers.
Acoustic Energy AE2 40th AnniversaryKlipsch R-51M
TweeterWoofer
Front view, drawn to scale - cabinets and drivers share one scale, so sizes are directly comparable. Hover a driver for its size.
| Driver |
Acoustic Energy AE2 40th Anniversary |
Klipsch R-51M |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1.1-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
2 x 5-inch
|
1 x 5.25-inch
|
AE2 40th Anniversary features a 1.1" aluminium Dome Tweeter and 2 x 5" ceramic-coated aluminium Woofer with a Crossover frequency at 2200Hz. On the other hand, the R-51M features a 1" Tractrix Horn Tweeter and 1 x 5.25" Copper-spun IMG Woofer with a Crossover frequency at 1660Hz.
Frequency Response
AE2 40th Anniversary has a frequency range of 35-45k Hz whereas R-51M has a frequency range of 62-21k Hz. With a minimum frequency of 35Hz, the AE2 40th Anniversary can go significantly deeper on the low side and provide stronger bass compared to the R-51M's min frequency of 62Hz.
The graph below depicts how these two speakers compare with the max, min and average Low Frequency values of other speakers in the Bookshelf class in our database.
Low Frequency
Bookshelf Speakers
Neither pair reaches down to 20Hz, the usual definition of full-range, which is normal for speakers of this size. If you want the bottom octave for movies or bass-heavy music, add a subwoofer to whichever you choose. Visit our Powered Subwoofers section to find out more about the available options.
Impedance and Sensitivity
AE2 40th Anniversary is a 6 ohms speaker compared to the R-51M which has a nominal impedance of 8 ohms.
These two speakers also have different sensitivity levels. AE2 40th Anniversary sensitivity is rated at 88 dB and the R-51M's is rated at 93 dB. This 5 dB difference makes the Klipsch R-51M a more sensitive speaker compared to Acoustic Energy AE2 40th Anniversary, hence will play louder with the same amount of watts.
Sensitivity
Bookshelf Speakers
Power Range
Power
range is the range of input power in watts RMS that a loudspeaker is designed to handle. Staying
within that range gives nominal performance; driving the speaker beyond its maximum wattage can damage it.
AE2 40th Anniversary can handle a max power of 200 watts RMS, whereas R-51M has a max power handling value of 85 watts RMS, 115 watts less than the AE2 40th Anniversary.
Note that higher power handling does not make a speaker louder: that depends mainly on
sensitivity and impedance. The calculator below shows how loud each of these actually plays
on a real amplifier.
Which plays louder on your amplifier?
Starting with a popular amplifier - change it to the one you own, or any you are
considering, and watch both numbers move.
Acoustic Energy AE2 40th Anniversary
Input Type and Bi-Amping / Bi-Wiring
AE2 40th Anniversary features Single Gold Plated Binding Posts - 5-way type posts and R-51M has a Single Gold Plated Binding Posts - 5-way type posts. None of these speakers feature bi-amping/bi-wiring.
Klipsch R-51M's Single Gold Plated Binding Posts - 5-way terminals
Cabinet Type and Port Position
AE2 40th Anniversary has a front firing port whereas R-51M has a rear firing ports. Acoustic Energy AE2 40th Anniversary's front-firing port gives more flexibility in placement in regards to proximity to walls compared to Klipsch R-51M with its rear-firing port.
Physical Specs
The size of a speaker can sometimes be an important decision factor due to space constraints or in some cases purely for esthetic reasons. In this section, we are going to compare Acoustic Energy AE2 40th Anniversary's and Klipsch R-51M's external dimensions. Acoustic Energy AE2 40th Anniversary has external dimensions of 385.0 x 235.0 x 315.0mm (15.2 x 9.3 x 12.4inch) whereas Klipsch R-51M has external dimensions of 338.0 x 178.0 x 215.0mm (13.3 x 7.0 x 8.4inch).
Acoustic Energy AE2 40th Anniversary is clearly the larger of the two speakers. Its body is 57mm wider, 47mm taller and 100mm deeper than Klipsch R-51M.
Size, drawn to scale
Both speakers and both views share one scale, so everything here is directly comparable. Hover a box for its dimensions.
One scale for both, standing on the same surface and pushed back to the same wall, so the deeper one visibly sticks out further.
Acoustic Energy AE2 40th Anniversary needs about 93% more floor or shelf area. Acoustic Energy AE2 40th Anniversary is 100mm deeper, so it stands that much further out from the wall. Acoustic Energy AE2 40th Anniversary is 47mm taller.
Base Surface Area Comparison
Base surface area of a loudspeaker may become a determining factor when the space in your room or desk is limited.
The base surface area of the Acoustic Energy AE2 40th Anniversary is approximately 740.3cm2 / 114.7inch2 and base area of the Klipsch R-51M is approximately 382.7cm2 / 59.3inch2. The AE2 40th Anniversary requires 93% more surface area than the R-51M which gives it a small disadvantage on placement in tight spaces.
Weight Comparison The weight of a loudspeaker can become an important factor if you need to move and reposition the unit often. Weight of a speaker can also "sometimes" be an indicator of the rigidity of the enclosure and the quality of the internal components used. The Acoustic Energy AE2 40th Anniversary weighs 14.50kg / 31.9lbs and the Klipsch R-51M weighs 5.00kg / 11lbs. This makes the AE2 40th Anniversary 190% heavier than the R-51M.
Here is a comparison of how AE2 40th Anniversary and R-51M's weights compare with the average, max and min weights in Passive Bookshelf class.
Weight
All Bookshelf Speakers
Acoustic Energy AE2 40th Anniversary
What's in the Box of Klipsch R-51M?
Here are the items that come with the R-51M:
- 2 Bookshelf loudspeakers
- 2 Grilles (installed)
- 8 Self-adhesive rubber feet
- Quick Setup Guide
- Important Safety Instructions
- Warranty Information
 Max Input Power |
200 watts
vs
85 watts
|
Handle more power from your amplifier |
 Number of Woofers |
2
vs
1
|
More woofers |
|
Low Frequency Response |
35 Hz
vs
62 Hz
|
Generates deeper bass |
 High Frequency Response |
45k Hz
vs
21k Hz
|
Generates higher frequency |
 Port Position |
Front
vs
Rear
|
Gives more flexibility placing close to walls |
 Sensitivity |
93 dB
vs
88 dB
|
Play louder with same amount of amplification power |
 Nominal Impedance |
8 ohms
vs
6 ohms
|
Less selective with amplifiers |
|
Woofer Size |
5.25 inches
vs
5 inches
|
Larger woofer |
 Height |
338mm
vs
385mm
|
Easier to fit in smaller spaces |
 Base Surface Area |
382cm2
vs
740cm2
|
Takes less floor space |
 Price per pair* |
359USD
vs
3699USD
|
costs less (*prices may change depending on the seller, location and time) |
| General |
Acoustic Energy AE2 40th Anniversary |
Klipsch Reference R-51M |
| Brand |
Acoustic Energy |
Klipsch |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
up to 200 watts |
Up to 85 watts |
| Sensitivity |
88 dB |
93 dB |
| Impedance |
6 ohms |
8 ohms |
| Frequency Response |
35-45k Hz |
62-21k Hz |
Drivers |
|
|
| Woofer Quantity |
2 |
1 |
| Woofer Size |
5" |
5.25" |
| Woofer Composition |
ceramic-coated aluminium |
Copper-spun IMG |
| Woofer Surround Material |
n/a |
Rubber |
| Tweeter Size |
1.1" |
1" |
| Tweeter Type |
Dome |
Tractrix Horn |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
2200Hz |
1660Hz |
| Firing Direction |
front |
rear |
Physical Specs |
|
|
| Height |
385.0mm (15.2") |
338.0mm (13.3") |
| Width |
235.0mm (9.3") |
178.0mm (7") |
| Depth |
315.0mm (12.4") |
215.0mm (8.5") |
| Weight |
14.50kg (31.9lbs) |
5.00kg (11lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
RSC constrained-layer HDF/bitumen, ten-coat high gloss |
MDF/Wood-grain vinyl |
| Available Colors |
High Gloss Walnut,High Gloss Black |
Black |
| Mounting Bracket |
No |
No |
| Recommended Stand Height |
n/a |
24-28" |
| Grille |
Yes |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Biamp Inputs |
No |
No |
Other |
|
|
| Parts Warranty |
|
5 Years |
| Labor Warranty |
|
5 Years |
These sit in different price classes - Acoustic Energy AE2 40th Anniversary costs roughly 10.3x what Klipsch R-51M does. Expect it to lead on paper; the question is whether the gap is audible enough in your room to be worth it.
| Area | Better | Why |
|---|
| Bass | A | Acoustic Energy AE2 40th Anniversary digs deeper - 35Hz against 62Hz. |
| Amplifier needs | B | Klipsch R-51M is more sensitive (93dB vs 88dB), so it goes louder on the same amplifier. |
| Amplifier match | B | Klipsch R-51M is the easier load at 8 ohms. |
| Headroom | A | Acoustic Energy AE2 40th Anniversary takes more power (200W vs 85W) - more in hand in a big room. |
| Size | depends | Klipsch R-51M is easier to place; Acoustic Energy AE2 40th Anniversary is bigger, which usually goes with fuller bass. Your room decides. |
| Expandability | depends | Neither adds bi-amping, a sub output or height drivers. Klipsch R-51M sits in a wider range (5 models), so a matched surround system is easier later. |
| Price | B | Klipsch R-51M is cheaper - $359 against $3,699, about 90% less; arguably a different class. |
A Acoustic Energy AE2 40th Anniversary B Klipsch R-51M
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both speakers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
Neither runs away with it - they trade advantages. Let the "depends" rows and your own room settle it. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 62Hz anyway, which makes the cheaper Klipsch R-51M much easier to justify. Match it to your room: we rate Acoustic Energy AE2 40th Anniversary the better fit for a mid-size room, a large room and a very large room, and Klipsch R-51M for near-field listening and a small room.
And remember what a spec sheet cannot show: how each looks in your room and whether the finish suits it, what dealer support and warranty are like where you live, and how they actually sound to you. If you can hear them first - ideally with your own music - that will tell you more than any number above.