In this review, we will be comparing AE500 Mark II and R-51M, two Passive Bookshelf speakers from Acoustic Energy and Klipsch.
Let's have a brief look at the main features
of AE500 Mark II and Klipsch R-51M first before getting into our more
detailed comparison.
| Key Specs | AE500 Mark II | 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 | 5" carbon fibre cone | 5.25" Copper-spun IMG |
|---|
| Frequency response | 45-26k Hz | 62-21k Hz |
|---|
| Sensitivity | 87 dB | 93 dB |
|---|
| Impedance | 8 ohms | 8 ohms |
|---|
| Power range | up to 120 watts | Up to 85 watts |
|---|
| Weight | 7.50kg / 16.5lbs | 5.00kg / 11lbs |
|---|
| Dimensions (H x W x D) | 12.2" x 7.3" x 10.6"
310.0 x 185.0 x 270.0mm | 13.3" x 7.0" x 8.4"
338.0 x 178.0 x 215.0mm |
|---|
What size room are the AE500 Mark II 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* |
AE500 Mark II |
Klipsch R-51M |
| Near-field |
Average |
Average |
| Small Room |
Good |
Good |
| Mid-size Room |
Average |
Average |
| Large Room |
Poor |
Poor |
| Very Large Room |
Bad |
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 AE500 Mark II and R-51M are 2-way speakers.
AE500 Mark IIKlipsch 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 |
AE500 Mark II |
Klipsch R-51M |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1.1-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 5-inch
|
1 x 5.25-inch
|
AE500 Mark II features a 1.1" soft dome Dome Tweeter and 1 x 5" carbon fibre cone Woofer with a Crossover frequency at 3.2kHz. 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
AE500 Mark II has a frequency range of 45-26k Hz whereas R-51M has a frequency range of 62-21k Hz. With a minimum frequency of 45Hz, the AE500 Mark II 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
AE500 Mark II and R-51M have the same Impedance of 8 ohms but where they differ is the sensitivity levels. AE500 Mark II sensitivity is rated at 87 dB and the R-51M's is at 93 dB. This 6 dB difference makes the Klipsch R-51M a more sensitive speaker compared to AE500 Mark II, 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.
AE500 Mark II can handle a max power of 120 watts RMS, whereas R-51M has a max power handling value of 85 watts RMS, 35 watts less than the AE500 Mark II.
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.
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 AE500 Mark II's and Klipsch R-51M's external dimensions. AE500 Mark II has external dimensions of 310.0 x 185.0 x 270.0mm (12.2 x 7.3 x 10.6inch) whereas Klipsch R-51M has external dimensions of 338.0 x 178.0 x 215.0mm (13.3 x 7.0 x 8.4inch).
Klipsch R-51M is 7mm narrower and 55mm less deeper than AE500 Mark II but it is also 28mm taller.
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.
AE500 Mark II needs about 31% more floor or shelf area. AE500 Mark II is 55mm deeper, so it stands that much further out from the wall. Klipsch R-51M is 28mm 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 AE500 Mark II is approximately 499.5cm2 / 77.4inch2 and base area of the Klipsch R-51M is approximately 382.7cm2 / 59.3inch2. The AE500 Mark II requires 31% 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 AE500 Mark II weighs 7.50kg / 16.5lbs and the Klipsch R-51M weighs 5.00kg / 11lbs. This makes the AE500 Mark II 50% heavier than the R-51M.
Here is a comparison of how AE500 Mark II and R-51M's weights compare with the average, max and min weights in Passive Bookshelf class.
Weight
All Bookshelf Speakers
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 |
120 watts
vs
85 watts
|
Handle more power from your amplifier |
 Low Frequency Response |
45 Hz
vs
62 Hz
|
Generates deeper bass |
 High Frequency Response |
26k Hz
vs
21k Hz
|
Generates higher frequency |
 Height |
310mm
vs
338mm
|
Easier to fit in smaller spaces |
 Sensitivity |
93 dB
vs
87 dB
|
Play louder with same amount of amplification power |
|
Woofer Size |
5.25 inches
vs
5 inches
|
Larger woofer |
 Base Surface Area |
382cm2
vs
499cm2
|
Takes less floor space |
| General |
Acoustic Energy AE500 Mark II |
Klipsch Reference R-51M |
| Brand |
Acoustic Energy |
Klipsch |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
up to 120 watts |
Up to 85 watts |
| Sensitivity |
87 dB |
93 dB |
| Impedance |
8 ohms |
8 ohms |
| Frequency Response |
45-26k Hz |
62-21k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
5" |
5.25" |
| Woofer Composition |
carbon fibre cone |
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 |
3.2kHz |
1660Hz |
| Firing Direction |
n/a |
rear |
Physical Specs |
|
|
| Height |
310.0mm (12.2") |
338.0mm (13.3") |
| Width |
185.0mm (7.3") |
178.0mm (7") |
| Depth |
270.0mm (10.6") |
215.0mm (8.5") |
| Weight |
7.50kg (16.5lbs) |
5.00kg (11lbs) |
| Enclosure |
|
Bass Reflex |
| Finish |
n/a |
MDF/Wood-grain vinyl |
| Available Colors |
Piano Gloss White,Piano Gloss Black,American Walnut wood veneer |
Black |
| Mounting Bracket |
|
No |
| Recommended Stand Height |
n/a |
24-28" |
| Grille |
Yes |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Biamp Inputs |
n/a |
No |
Other |
|
|
| Parts Warranty |
|
5 Years |
| Labor Warranty |
|
5 Years |
A generation apart: AE500 Mark II is the newer design, against a 2018 model. Newer is not automatically better, but the older one is more likely to be discounted or near run-out.
| Area | Better | Why |
|---|
| Bass | A | AE500 Mark II digs deeper - 45Hz against 62Hz. |
| Amplifier needs | B | Klipsch R-51M is more sensitive (93dB vs 87dB), so it goes louder on the same amplifier. |
| Headroom | A | AE500 Mark II takes more power (120W vs 85W) - more in hand in a big room. |
| Size | depends | Similar cabinet size - neither is easier to fit. |
A AE500 Mark II 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?
AE500 Mark II has the edge on paper, though the margin is not large. The rows marked "depends" may matter more to you than the score does. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 62Hz anyway, so judge these on the other rows instead. If your amplifier is modest, vintage or valve-based, Klipsch R-51M is the safer partner - the other will want more current or more watts to sound its best.
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.