In this review, we will be comparing Richmond IV and R-51M, two Passive Bookshelf speakers from Castle and Klipsch.
Let's have a brief look at the main features
of Castle Richmond IV and Klipsch R-51M first before getting into our more
detailed comparison.
| Key Specs | Castle Richmond IV | Klipsch R-51M |
|---|
| Brand | Castle
United Kingdom · founded 1973 | Klipsch
United States · founded 1946 |
|---|
| Design | 2-way | 2-way |
|---|
| Tweeter | 1.25" Soft-Dome | 1" Tractrix Horn |
|---|
| Woofer | 6" | 5.25" Copper-spun IMG |
|---|
| Frequency response | 58-22k Hz | 62-21k Hz |
|---|
| Sensitivity | 87 dB | 93 dB |
|---|
| Impedance | — | 8 ohms |
|---|
| Power range | 25-100 watts | Up to 85 watts |
|---|
| Weight | 6.30kg / 13.9lbs | 5.00kg / 11lbs |
|---|
| Dimensions (H x W x D) | 12" x 7-1/2" x 10-5/16"
305.0 x 190.0 x 262.0mm | 13.3" x 7.0" x 8.4"
338.0 x 178.0 x 215.0mm |
|---|
What size room are the Castle Richmond IV 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* |
Castle Richmond IV |
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 Richmond IV and R-51M are 2-way speakers.
Castle Richmond IVKlipsch 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 |
Castle Richmond IV |
Klipsch R-51M |
|
Driver Setup
|
2-way
|
2-way
|
|
Tweeter
|
1.25-inch
|
1-inch
|
|
Midrange
|
- |
- |
|
Woofer
|
1 x 6-inch
|
1 x 5.25-inch
|
Richmond IV features a 1.25" Soft-Dome Tweeter and 1 x 6" Woofer with a Crossover frequency at 2.6 kHz. 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
Richmond IV has a frequency range of 58-22k Hz whereas R-51M has a frequency range of 62-21k Hz. With a minimum frequency of 58Hz, the Richmond IV can go slightly deeper then 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
The maker of the Castle Richmond IV does not publish a nominal impedance, so only sensitivity can be compared here: Richmond IV is rated at 87 dB and the R-51M at 93 dB.
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.
Richmond IV can handle a max power of 100 watts RMS, whereas R-51M has a max power handling value of 85 watts RMS, 15 watts less than the Richmond IV.
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.
Input Type and Bi-Amping / Bi-Wiring
Richmond IV 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
Both Richmond IV and R-51M have rear firing ports. Rear ported speakers generally need more room between the backside of the speaker and the wall compared to sealed and front/bottom ported speakers. Placing the speakers too close to the walls may cause the bass to sound boomy.
If you are limited in space and can't get the speakers away from the backwall, check our Speakers with Front Firing Ports page.
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 Castle Richmond IV's and Klipsch R-51M's external dimensions. Castle Richmond IV has external dimensions of 305.0 x 190.0 x 262.0mm (12 x 7-1/2 x 10-5/16inch) 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 12mm narrower and 47mm less deeper than Castle Richmond IV but it is also 33mm 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.
Castle Richmond IV needs about 30% more floor or shelf area. Castle Richmond IV is 47mm deeper, so it stands that much further out from the wall. Klipsch R-51M is 33mm 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 Castle Richmond IV is approximately 497.8cm2 / 77.2inch2 and base area of the Klipsch R-51M is approximately 382.7cm2 / 59.3inch2. The Richmond IV requires 30% 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 Castle Richmond IV weighs 6.30kg / 13.9lbs and the Klipsch R-51M weighs 5.00kg / 11lbs. This makes the Richmond IV 26% heavier than the R-51M.
Here is a comparison of how Richmond IV 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 |
100 watts
vs
85 watts
|
Handle more power from your amplifier |
 Woofer Size |
6 inches
vs
5.25 inches
|
Larger woofer |
|
Low Frequency Response |
58 Hz
vs
62 Hz
|
Generates deeper bass |
 High Frequency Response |
22k Hz
vs
21k Hz
|
Generates higher frequency |
 Height |
305mm
vs
338mm
|
Easier to fit in smaller spaces |
 Sensitivity |
93 dB
vs
87 dB
|
Play louder with same amount of amplification power |
 Base Surface Area |
382cm2
vs
497cm2
|
Takes less floor space |
| General |
Castle Richmond IV |
Klipsch Reference R-51M |
| Brand |
Castle |
Klipsch |
| Speaker Type |
Bookshelf speakers |
Bookshelf speakers |
| Power Range |
25-100 watts |
Up to 85 watts |
| Sensitivity |
87 dB |
93 dB |
| Impedance |
n/a |
8 ohms |
| Frequency Response |
58-22k Hz |
62-21k Hz |
Drivers |
|
|
| Woofer Quantity |
1 |
1 |
| Woofer Size |
6" |
5.25" |
| Woofer Composition |
|
Copper-spun IMG |
| Woofer Surround Material |
n/a |
Rubber |
| Tweeter Size |
1.25" |
1" |
| Tweeter Type |
Soft-Dome |
Tractrix Horn |
| Aimable Tweeter |
No |
No |
| Midrange Driver |
No |
No |
| Crossover Frequency |
2.6 kHz |
1660Hz |
| Firing Direction |
rear |
rear |
Physical Specs |
|
|
| Height |
305.0mm (12") |
338.0mm (13.3") |
| Width |
190.0mm (7.5") |
178.0mm (7") |
| Depth |
262.0mm (10.3") |
215.0mm (8.5") |
| Weight |
6.30kg (13.9lbs) |
5.00kg (11lbs) |
| Enclosure |
Bass Reflex |
Bass Reflex |
| Finish |
n/a |
MDF/Wood-grain vinyl |
| Available Colors |
n/a |
Black |
| Mounting Bracket |
|
No |
| Recommended Stand Height |
n/a |
24-28" |
| Grille |
n/a |
Yes |
| Moisture Resistancy |
No |
No |
Connections |
|
|
| Biamp Inputs |
n/a |
No |
Other |
|
|
| Parts Warranty |
|
5 Years |
| Labor Warranty |
|
5 Years |
No single best speaker here - they are built to different priorities, and the right one depends on your room, your amplifier and what you listen to.
| Area | Better | Why |
|---|
| Bass | A | Castle Richmond IV digs deeper - 58Hz against 62Hz. A subwoofer would even that out. |
| Amplifier needs | B | Klipsch R-51M is more sensitive (93dB vs 87dB), so it goes louder on the same amplifier. |
| Headroom | evenly matched | Similar power handling (100W vs 85W). |
| Size | depends | Similar cabinet size - neither is easier to fit. |
| 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. |
A Castle Richmond IV 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 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.