See where to adjust.

Slope listens to your subwoofer and speakers in your room through the iPhone microphone and shows you what to adjust.

Free · for iPhone and iPad

Scroll to see how it works

Slope plays a sweep through your system and records it with the iPhone microphone.
First the subwoofer: the amber curve shows how it plays in your room, peaks and dips included.
Then the speakers, in cyan, on the same graph.
Where the two curves meet, Slope suggests a crossover to try.
The Summation check shows which position of the phase switch makes the bass add up better.
And it tells you what to adjust, in plain words. You decide.

Slope plays a sweep through your system and records it with the iPhone microphone.
Living room
Example
Amplifier crossover
Try about 80 Hz
Starting point: verify with the sub and speakers playing together.
Set on the sub
80 Hz
Edit
Crossover details
Summation check
Better with: Normal (0°)
Continue the check
Verification details
Suggestions
1The sub seems loud compared with the speakers: turn it down a little, 2–3 dB, listen again and measure again.
First the subwoofer: the amber curve shows how it plays in your room, peaks and dips included.
Living room
Example
Amplifier crossover
Try about 80 Hz
Starting point: verify with the sub and speakers playing together.
Set on the sub
80 Hz
Edit
Crossover details
Summation check
Better with: Normal (0°)
Continue the check
Verification details
Suggestions
1The sub seems loud compared with the speakers: turn it down a little, 2–3 dB, listen again and measure again.
Then the speakers, in cyan, on the same graph.
Living room
Example
Amplifier crossover
Try about 80 Hz
Starting point: verify with the sub and speakers playing together.
Set on the sub
80 Hz
Edit
Crossover details
Summation check
Better with: Normal (0°)
Continue the check
Verification details
Suggestions
1The sub seems loud compared with the speakers: turn it down a little, 2–3 dB, listen again and measure again.
Where the two curves meet, Slope suggests a crossover to try.
Living room
Example
Amplifier crossover
Try about 80 Hz
Starting point: verify with the sub and speakers playing together.
Set on the sub
80 Hz
Edit
Crossover details
Summation check
Better with: Normal (0°)
Continue the check
Verification details
Suggestions
1The sub seems loud compared with the speakers: turn it down a little, 2–3 dB, listen again and measure again.
The Summation check shows which position of the phase switch makes the bass add up better.
Living room
Example
Amplifier crossover
Try about 80 Hz
Starting point: verify with the sub and speakers playing together.
Set on the sub
80 Hz
Edit
Crossover details
Summation check
Better with: Normal (0°)
Continue the check
Verification details
Suggestions
1The sub seems loud compared with the speakers: turn it down a little, 2–3 dB, listen again and measure again.
And it tells you what to adjust, in plain words. You decide.
Living room
Example
Amplifier crossover
Try about 80 Hz
Starting point: verify with the sub and speakers playing together.
Set on the sub
80 Hz
Edit
Crossover details
Summation check
Better with: Normal (0°)
Continue the check
Verification details
Suggestions
1The sub seems loud compared with the speakers: turn it down a little, 2–3 dB, listen again and measure again.

From the first sweep to the last tweak.

Guided session
A step-by-step path for sub and speakers, with a level check you can repeat after adjusting the subwoofer, without measuring the speakers again.
Library
All your measurements, with two results compared side by side. Optional iCloud sync keeps them up to date on your other devices signed in to the same account.
Living room
Sub + speakers
Slope
October 6, 2026 at 8:41 PM
Key values
Subwoofer crossover
Try about 80 Hz
Subwoofer vs speaker level
+3 dB
Sub upper limit
105 Hz
Speaker lower limit
52 Hz
Highlighted peak
44 Hz
Subwoofer +10.0 dB
Highlighted dip
190 Hz
Speakers -1.2 dB
Range to try: 70–90 Hz.
Adjust the subwoofer crossover; the speakers stay full-range.
Use the nearest setting; dial markings are approximate.
Starting point: verify with the sub and speakers playing together.
Suggestions
1.The sub seems loud compared with the speakers: turn it down a little, 2–3 dB, listen again and measure again.
2.Wide overlap between the separate curves. Verify with both sources together.
Measurement conditions
Measured band
20–200 Hz
Sweep duration
15 s
Smoothing
1/6 octave
Audio output
HDMI
Speaker band
20–400 Hz
Bass management
Full-range speakers
High-pass during measurement
Without high-pass
Set on the sub
80 Hz
The iPhone microphone is not calibrated: these values are relative and meant for tuning the system, not for certifying it.
PDF summary
A one-page report with the graph, key values, suggestions and measurement conditions.

What you need

An external audio output
The sweep has to play through the speakers of your system. Headphones and the iPhone's own speaker cannot be used for measurements.
A quiet room
The less noise, the clearer the curve. The Noise check on the Measure screen tells you the conditions before you start.
An iPhone or iPad
Running iOS 17 or later. Slope uses the built-in microphone.

What to expect

Slope is a practical tuning tool: it helps you compare and adjust your system in your room.

Values for comparing
The iPhone microphone is not calibrated: use the curves to compare measurements and see the effect of an adjustment, not as certified figures.
Below 40 Hz, with care
At the lowest frequencies the readings are less reliable, and Slope marks them as such.
They hold where you measure
The result describes the spot where you hold the iPhone: measure from where you usually listen.
Slope suggests, you decide
The app changes nothing in your system: it tells you what to try, and you adjust and listen again.

Who makes Slope Hi-Fi

I develop Slope on my own. It's free, and every feature is already included. If it helps you tune your system, you can leave me a tip from the app: it unlocks nothing, but it helps me keep going.

Questions or ideas? Write to me

Try Slope in your room.

Free · for iPhone and iPad

See where to adjust.

How it works

From the first sweep to the last tweak.

Guided session

Library

PDF summary

What you need

An external audio output

A quiet room

An iPhone or iPad

Values for comparing

Below 40 Hz, with care

They hold where you measure

Slope suggests, you decide

Who makes Slope Hi-Fi

Try Slope in your room.