brydup@mac ~/cowork % cat anthem-mrx-300-learning-guide.md
# Anthem MRX 300 — Calibration Learning Guide
Written 2026-05-19 after a hands-on session solving a long-standing
boomy-bass issue and routing the front-panel input to the CD source button.
This guide pairs the practical "how" with the conceptual "why" so the
next time something sounds wrong, you can diagnose instead of fiddle.
---
## 1. Your system in one diagram
```
External Device ──RCA──> [Front Panel L/R input]
│
▼
┌────────────────────┐
│ Anthem MRX 300 │
│ (preamp + amp) │
└────────────────────┘
│ │
Front L/R │ │ SUB W (mono LFE)
pre-out OR │ │ RCA out
internal amp│ ▼
│ ┌──────────┐
▼ │ KRK 10s │
Front speakers│ sub │
└──────────┘
```
The MRX 300 is functioning as a **preamp/processor + integrated amp**. It
decodes incoming audio, applies bass management (splits signal into
sub-bound lows and full-range), then either powers the speakers directly
(binding posts) or sends line-level pre-out signals to external amps. The
KRK sub takes the mono LFE feed from the dedicated SUB W pre-out.
---
## 2. The Setup Menu tree (front-panel navigation)
The OSD via HDMI is much friendlier, but you don't always have a TV
hooked up. The 2-line 16-char front-panel display abbreviates labels
aggressively. Memorize this tree:
```
Setup Menu
├── Aud/Vid Setup
│ ├── Main Src Setup ← per-source input routing (audio/video)
│ │ └── (pick a source via the BDP/CD/TV/etc. buttons,
│ │ then set Main Audio In, Main Video In, etc.)
│ └── Adv Src Setup ← per-source advanced tweaks
│ ├── AudRecDev (Zone 2 / Rec Out assignment)
│ ├── Half Mode (legacy, leave off)
│ ├── Dolby Vol (dynamic-range compression on/off)
│ └── Bass: 0 dB (per-source tone shelf — NOT sub level)
│
├── Spkr Config ← speaker setup
│ ├── Mode (2.0 / 2.1 / 5.1 / 7.1 — sub on/off lives here)
│ └── Bass Management
│ ├── Config: Movie/Music (two independent crossover presets)
│ ├── Front: 80 Hz (crossover per channel)
│ ├── Center: 80 Hz
│ └── Surround: 80 Hz
│
├── Listener Position ← per-speaker distances (delay alignment)
│
├── Lev Calibration ← per-channel level trim in dB
│ ├── Movie Sub: 0 dB (separate trim for Movie config)
│ ├── Music Sub: 0 dB (separate trim for Music config)
│ ├── Front L / Front R: 0 dB
│ ├── Center / Surround / Aux: 0 dB
│ ├── Noise Seq: Off (built-in pink noise generator)
│ └── Dolby Level: 5 (Dolby Volume reference)
│
├── ARC ← Anthem Room Correction (needs mic + Windows PC)
│
├── General Config ← OSD settings, triggers, display options
│
└── System Info ← firmware version (yours: v50.19, the final release)
```
### Front-panel navigation primitives
| Button | Function |
|---|---|
| SETUP | Enter the Setup Menu / back out one level |
| MENU | Quick-access menu (different from Setup) |
| SELECT (center of dial) | Enter a submenu / commit a value |
| ▲ / ▼ | Scroll between menu items |
| ◀ / ▶ | Change a value / drill into a submenu |
| Source buttons (BDP/CD/TV/...) | Inside Source Setup, pick which source you're editing |
---
## 3. Bass management — the core concept
This is where most home theater confusion lives. Two distinct settings,
often conflated:
### a) Speaker size (Small vs Large)
The "size" label has nothing to do with physical size. It tells the
receiver:
- **Large** = "this speaker can play full-range; don't filter bass out
of its signal." Lows are sent to both this speaker AND the sub.
- **Small** = "this speaker can't play low bass; filter it out and route
lows to the sub instead."
If you set fronts to **Large** AND turn the sub on, lows play through
both — **doubled bass**, very common cause of boom.
The MRX 300 conflates Size + Crossover into a single setting: Sm 80Hz
means "small, with bass below 80 Hz routed to the sub."
### b) Crossover frequency
The frequency where the speaker's signal gets split: above the
crossover stays with the speaker, below goes to the sub. **80 Hz is the
THX standard** and works for almost all speakers smaller than floor-
standing towers. Going lower (60, 40 Hz) only makes sense if your
fronts genuinely play deep bass cleanly. When in doubt, 80 Hz.
### c) Movie vs Music configs
The MRX 300 keeps **two independent bass management presets**:
- **Movie**: typically same speakers at 80 Hz, but you can set fronts to
Large if you want music-style passthrough during movies (rare).
- **Music**: some people prefer no sub at all here (front L/R Large,
sub off) for stereo purism. Others keep them identical to Movie. We
set both to 80 Hz across the board — clean and consistent.
You don't switch between them manually — the receiver picks Movie vs
Music based on the **listening mode** in use (Dolby Digital, DTS,
Stereo, etc.).
---
## 4. Slope-stacking — the gotcha that solved your boom
Your KRK 10s has its own **internal low-pass crossover** (the knob on
the back, 50-130 Hz range). The receiver also has a crossover (80 Hz).
If both are set near each other, **two filters stack**:
```
Receiver filter ↘
↘ ↘
↘ ↘ ← combined slope is steeper than designed
↘ ↘
↘ ↘
KRK internal filter ↘ ↘ ↘
↘ ↘ ↘
↘ ↘
```
This creates two problems:
1. A **lump** in the response right around the crossover region (audible
as "boomy")
2. A **steeper rolloff** below the crossover (you lose deep bass)
**The fix**: open the sub's internal filter as wide as possible, so
only the receiver's filter is active. On the KRK 10s, that means
**turning Low-Pass Freq fully clockwise to 130 Hz** (the highest
setting). The KRK 10s doesn't have a Bypass position — 130 Hz is the
practical equivalent.
Now the receiver dictates the crossover at 80 Hz, the KRK passes
everything below 130 Hz, and the actual crossover point is the
receiver's clean 80 Hz filter alone.
**This single change usually fixes more "boomy sub" complaints than any
amount of level trimming.**
---
## 5. Level calibration vs tone control vs sub volume — three distinct knobs
People mix these up constantly:
| Setting | Where it lives | What it does |
|---|---|---|
| **Sub level (in Lev Calibration)** | Setup → Lev Calibration → Movie/Music Sub | Per-channel digital trim. The "real" sub volume from the receiver's perspective. Adjust here. |
| **Bass tone control** | Adv Src Setup → Bass: 0 dB | Per-source bass *shelf* (boosts or cuts everything below ~250 Hz). Equivalent to the bass knob on a stereo amp. NOT a sub-specific control. |
| **Sub's physical gain knob** | On the back of the sub | Analog gain on the sub's own amp. Set once to 0 dB and forget. Let the receiver do precision trim. |
**Rule**: trim with the receiver, never the sub. Once the sub knob is
set, leaving it alone means your calibration is reproducible. If you
ever swap the sub, the receiver settings remain meaningful relative to
the new sub's 0 dB position.
---
## 6. Phase (0° vs 180°)
The PHASE switch on the sub flips the polarity of its driver. Sound
waves from the sub and your fronts meet around the crossover region
(80-150 Hz). If they're **in phase**, they reinforce; if **out of
phase**, they cancel.
Cancellation isn't always silence — it's often a *suckout* (notch in
the response) that makes the bass sound thin or weak in certain
frequencies. Reinforcement isn't always good either — it can cause the
boomy lump we just fixed.
**The test**: flip the switch, listen for 20-30 seconds to the same
track, decide which sounds tighter. There's no "correct" position
a priori — it depends on the sub's distance from the fronts and the
geometry of your room.
**Common outcomes:**
- Sub far from fronts, behind/beside seating → 180° often correct
- Sub front of room, near fronts → 0° often correct
- No audible difference → either works; pick one and leave it
---
## 7. Source assignments — how Aud/Vid Setup works
The MRX 300 has source buttons (BDP, CD, TV, SAT, GAME, AUX, iPod,
Tuner). Each one is a **label that maps to**:
- A physical audio input (HDMI 1-4, Coax 1-2, Optical 1-3, Analog 1-6,
or Front Panel)
- A physical video input (same)
- A default listening mode
- A per-source level offset
- A per-source bass tone shelf
- A name (you can rename "CD" to "Turntable" etc.)
This decoupling means you can wire anything to anything. Want CD to
play from the front-panel RCA jacks? Set Main Audio In = Fnt Analog.
Want TV to use the optical input? Set Main Audio In = Optical 1. The
labels on the buttons are arbitrary — they're for your convenience.
The setting lives in **Setup → Aud/Vid Setup → Main Src Setup**, then
press the source button to pick which source you're editing.
---
## 8. The SUB W jack — why you almost missed it
The MRX 300 rear panel labels the subwoofer output SUB W (Subwoofer)
in the **7.1CH MAIN PRE-OUT** block. Two things make it confusing:
1. **It's a single mono jack**, not part of an L/R pair. Both CENTER
and SUB W are mono channels, and the receiver layout puts them in
the same column to save space: CENTER (white, top row) and SUB W
(red, bottom row).
2. **The red color suggests "R" of a stereo pair**, but it's not — it's
just how the panel was color-coded for visual distinction from the
white CENTER jack above it.
Always trust the printed labels, not the color coding. Most pre-outs
use white = L / red = R for stereo pairs, but standalone mono outputs
(Center, Sub) break the pattern.
---
## 9. ARC — the long-term fix you haven't run yet
Anthem Room Correction is the MRX 300's killer feature and the
*correct* answer to most "the bass is uneven" complaints. It works by:
1. Playing **frequency sweeps** through each speaker
2. Recording the room's actual response with a **calibrated mic** at
multiple listening positions
3. Calculating the deviation from ideal flat response (these deviations
are **room modes** — frequencies the room amplifies or cancels)
4. Building a **parametric EQ filter** that inverts those deviations
5. Uploading the filter back to the MRX 300, which applies it in real-
time to all incoming audio
What you need:
| Requirement | Status |
|---|---|
| ARC mic (came in the original box, looks like a small black mic + USB) | Check your packaging |
| Mic stand (a camera tripod works) | Available |
| Windows PC | Need to find one — ARC1 is Windows-only |
| USB cable from mic to PC | Probably with the mic |
| Software: Anthem ARC1 (free download from Anthem) | Free |
| 30-60 minutes of quiet | Plan for an evening |
ARC measures from 4-5 listening positions to characterize the *zone*
where you sit, not just one spot. The end result is much more dramatic
than level trim alone — it doesn't just adjust volumes, it actively
cancels out the room's acoustic problems.
If you can't find a Windows PC: a friend's machine, a cheap used
ThinkPad, or a Boot Camp / Parallels install on a Mac all work. ARC is
worth the friction.
---
## 10. Calibration discipline — the rules you should follow
After today's session, these are the habits that keep the system
reliable:
1. **Sub gain knob set once, never touched.** All sub volume changes
happen at the receiver.
2. **Sub's internal crossover always wide open (130 Hz on the 10s).**
The receiver does the crossover.
3. **All speakers Small @ 80 Hz** unless you have specific reason
otherwise.
4. **Movie and Music configs match** until you have a deliberate reason
to differ.
5. **Volume always starts low after touching settings.** -30 dB
before playing the first test track.
6. **Trust the labels, not the colors.** Especially around the SUB W
vs CENTER confusion.
7. **A/B between music services when diagnosing.** Source mastering
varies wildly and can fake out your perception.
8. **Capture the final values somewhere persistent.** (This guide.)
---
## 11. Your current settings (snapshot 2026-05-19)
```
SOURCE: CD
Main Audio In: Fnt Analog (front-panel L/R RCA)
Dolby Vol: On (per default — could try Off for music-only listening)
SPEAKER CONFIG (Bass Management):
Movie config:
Front: Sm 80Hz
Center: Sm 80Hz
Surround: Sm 80Hz
Music config: (assumed same — re-verify)
LEV CALIBRATION:
Movie Sub: -10 dB
Music Sub: -10 dB
All other channels: 0 dB (uncalibrated — ARC will fix this)
KRK 10s SUB:
Volume: 0 dB
Low-Pass Freq: 130 Hz (fully clockwise)
Phase: 0° (unverified — try 180° in a future test)
Input: Single RCA (orange/red) into LINE IN, from receiver's SUB W
FIRMWARE: v50.19 (latest/final for MRX 300)
```
---
## 12. Quick troubleshooting reference
| Symptom | Most likely cause | First thing to try |
|---|---|---|
| Sub too loud | Slope-stacking, level trim, or room mode | Open KRK Low-Pass to 130 Hz → drop Movie/Music Sub trim |
| Sub too quiet | Level trim too low, or sub off in Mode | Verify Mode is 5.1/7.1, raise Sub trim |
| Bass thin / weak | Phase cancellation | Flip KRK Phase 0°↔180°, listen |
| One channel quiet | Cable not seated, or per-channel level trim | Push cable, check Lev Calibration |
| Source plays through wrong speakers | Source setup wrong input/listening mode | Aud/Vid Setup → Main Src Setup, fix Main Audio In |
| No sound from source | Wrong input mapping, or volume muted | Aud/Vid Setup → Main Src Setup, check input |
| Bass changes drastically between songs | Source/streaming service mastering | A/B between services, or accept variance |
| Bass uneven across listening positions | Room mode | ARC is the fix; placement helps short-term |
---
## 13. Glossary
- **Pre-out**: line-level signal output from the receiver's preamp section, intended to feed an external power amp.
- **LFE (Low-Frequency Effects)**: the dedicated ".1" channel in 5.1/7.1 audio. Always mono. Carries explicit sub content from movies/games.
- **Bass management**: the receiver's process of taking full-range signals from each channel, filtering out the lows, and routing those lows to the sub.
- **Crossover**: the frequency where signal is split between a speaker and the sub.
- **Slope**: how steep the cutoff is at the crossover frequency. Standard is 24 dB/octave (Linkwitz-Riley 4th order).
- **Room mode**: a specific frequency the room amplifies (or cancels) due to its dimensions. Usually 20-200 Hz. Cannot be EQ'd away with simple bass knobs — needs parametric EQ.
- **Phase**: the timing relationship between the sub's driver and the main speakers at the crossover point.
- **ARC (Anthem Room Correction)**: Anthem's automated EQ/calibration system. The killer feature of this receiver.
- **Listening mode**: the decoder/processor for incoming audio (Stereo, Dolby Digital, DTS, AnthemLogic Music/Cinema, etc.). Different modes route channels differently.
- **OSD (On-Screen Display)**: the receiver's menu shown via HDMI on a connected TV. Much more readable than the front panel.
---
## 14. Reference: keyboard-style summary of menu paths
```
Set CD source to front-panel input:
SETUP → ▼ Aud/Vid Setup → SELECT
→ ▼ Main Src Setup → SELECT
→ press CD button
→ ▼ Main Audio In → ◀/▶ until "Fnt Analog"
→ SELECT → SETUP × 3 to exit
Set speakers to Small @ 80 Hz:
SETUP → ▼ Spkr Config → SELECT
→ ▼ Bass Management → SELECT
→ ▼ Front: ◀/▶ to 80 Hz
→ ▼ Center: ◀/▶ to 80 Hz
→ ▼ Surround: ◀/▶ to 80 Hz
→ ▲ Config: ◀/▶ to Music (then repeat above)
→ SETUP × 3 to exit
Drop sub level:
SETUP → ▼ Lev Calibration → SELECT
→ ▼ to Movie Sub: ◀ ◀ ◀ ◀ ◀ (each press = -1 dB)
→ ▼ to Music Sub: ◀ ◀ ◀ ◀ ◀
→ SETUP × 2 to exit
```
---
That's the lot. The MRX 300 is a 2010-era processor with surprisingly
deep capability — ARC alone keeps it competitive with much newer gear.
Treat it as a preamp/processor that happens to have built-in amps and
the system unlocks: feed any source into any input, use external amps
when you want better front L/R sound, and let the receiver do all the
bass management math centrally.
brydup@mac ~/cowork %