What is Frequency Response and Why Does it Matter for Speakers?

Speaker frequency response indicates how evenly it reproduces the full range of audible tones. Ideal is a flat line - no exaggerated or missing bands. Factors like driver size, enclosure, crossover affect response. Irregular curves cause tonal imbalance. Optimizing position & room acoustics improves flatter in-room response. Prioritize smooth, extended response for natural, high-fidelity sound.

By: Aleksey Makohon Date: 10 / 27, 2023

If you've ever shopped for speakers or headphones, you've probably come across the term "frequency response" in the product specs. This is one of the key measurements that determines how a speaker or headphone will sound. But what exactly does it mean and why does it matter?

In simple terms, frequency response refers to the range of bass, midrange, and treble frequencies that a speaker can accurately reproduce. It's a measurement of a speaker's tonal balance - whether certain frequencies are exaggerated or lacking. The ideal frequency response is flat and even across the entire audible spectrum from the lowest bass tones to the highest treble.

Frequency response table with common ranges

Frequency Subset	Frequency Range	Description
Sub-bass	16-60 Hz	Extreme low end, felt more than heard. Provides sense of power and rumble.
Bass	60-250 Hz	Fundamentals of bass instruments, kick drum, lower registers of many instruments. Gives body and warmth.
Lower midrange	250-500 Hz	Where fundamentals lie for brass and low woodwinds. Adds richness and depth.
Midrange	500 Hz-2 kHz	Vital for natural vocal reproduction. Critical for overall tonal balance.
Upper midrange	2-4 kHz	Presence range where details emerge. Can cause harshness if exaggerated.
Presence	4-6 kHz	Boosted in this range increases perception of clarity and intimacy.
Brilliance	6-20 kHz	High treble for air and sparkle. Extends perceived bandwidth.

When a speaker has a flat frequency response, it will sound natural and balanced. No single element of the sound will stand out. You'll hear the music as the artist and producer intended. Vocals will have the proper presence and detail. Instruments will have realistic timbre and imaging. Bass will be tight and impactful without booming or muddying up the mids. Treble will sparkle without harsh sibilance or sounding shrill.

On the other hand, spikes and dips in a speaker's frequency response lead to tonal imbalances. A peak in the upper midrange might make vocals sound shouty and fatiguing. A dip in the treble region can make music sound dull and lifeless. Rolled-off bass gives the impression of weak low end punch. These response irregularities color the sound and distort the tonality compared to the original recording.

So when researching speakers, looking at the published frequency response graphs can give you insight into how colored or neutral the speakers will sound. Smooth, extended response tends to correlate with accurate reproduction. Irregular response indicates some elements of the sound will likely be exaggerated while others are deficient. This directly impacts listening enjoyment, so frequency response deserves careful evaluation.

Reading and Interpreting Frequency Response Graphs

The Ideal: Flat and Straight

As mentioned, the ideal frequency response graph shows a straight, flat line at 0 dB across the entire specified frequency range. This indicates neutral, uncolored sound reproduction. No tonal balance bias or distortion is introduced by the speaker. You hear exactly what's in the source audio without alteration.

Variations from Flat

In real-world speakers, some variation from a perfectly flat response is inevitable. However, well-engineered speakers with advanced driver and crossover design can achieve remarkably flat response across most or all of the audible range. Small ±2 dB deviations are generally considered inconsequential.

Problematic Peaks and Dips

Larger peaks, dips, and irregularities indicate significant coloration and alteration of the original tonality. A peak of +6 dB at 2 kHz will make vocals sound harsh and piercing. A -3 dB dip at 100 Hz results in weak, unsatisfying bass. These distortions negatively impact sound quality.

Look for Smoothness and Extension

When evaluating frequency response graphs, look for speakers that maintain the smoothest possible curve through the midrange and treble, without drastic spikes and dips. Check that the bass extension doesn't roll off prematurely. The flatter and wider the response, the more accurately the speaker reproduces the complete audio spectrum.

Beware of Exaggerated Graph Scales

Some manufacturers exaggerate or condense the vertical dB scale to make the response graph look flatter than it really is. Zoom in on the scale values to make sure you're seeing an honest representation of the measurements.

What Design Factors Influence a Speaker's Frequency Response?

While the ideal is a perfectly flat frequency response, the real-world design of the speaker drivers, enclosure, crossover, and other elements naturally impacts and limits the overall response profile. Here are some of the key factors that affect the frequency response in different regions.

Speaker Driver Size

Larger speaker drivers with bigger cones or diaphragms can move more air and reproduce lower frequencies than smaller drivers.

Woofers in the 6.5" to 8" range may reach down to 45-55 Hz before rolling off.
Larger 10" to 12" woofers extend response further into true deep bass territory - 30 Hz or lower.

So using multiple woofers in various sizes allows a speaker to cover both mid-bass punch and sub-bass rumble.

Enclosure Type

The enclosure or cabinet plays a big role in low frequency response by controlling woofer backwave reflections.

Sealed boxes offer tighter, more accurate bass, but less extension.
Ported or bass reflex designs boost the bottom octaves but can suffer port noise.
Transmission lines and infinite baffles aim for deep bass without boom.

Crossover Network

The crossover directs different frequency bands to the appropriate drivers. The crossover design impacts phase coherence and driver integration through the midrange down to woofer cutoff point. High-order crossovers tend to enable smoother, more extended response across the driver hand-off region.

Number and Combination of Drivers

Having separate woofers, midrange drivers, and tweeters (aka multiple way speakers) allows each transducer to be optimized for its portion of the frequency spectrum. This divides the audio bandwidth for specialization rather than demanding full-range reproduction from a single driver. The right driver complement extends and smoothes overall response.

How Non-Flat Frequency Response Affects Sound Quality

When a speaker deviates significantly from flat, neutral response, it introduces tonal coloration that can degrade sound quality in several ways:

Peaked Response

A peak or spike in the frequency response graph indicates that particular frequency range will be exaggerated and more prominent in the speaker's sound.

For example, a +3 dB spike around 2 kHz will make vocals shouty and sibilant. A peak around 100 Hz over-emphasizes mid-bass, creating a boomy, muddy effect. These response irregularities distort the natural tonal balance.

Rolled-Off Highs or Lows

On the flip side, dips and downward slopes in certain frequency bands cause those ranges to be recessed.

Rolled-off treble makes music sound dull, lacking sparkle and airiness. Rolled-off bass removes impact and warmth, leaving an unnaturally thin sound. The overall presentation lacks detail and completeness.

Irregular Response

Multiple peaks and dips throughout the frequency range lead to an irregular, uneven response full of tonal coloration.

This causes a disjointed sound where different instruments and vocal ranges are thrust forward or recede back at different times. The coherent imaging of the stereo soundstage is negatively affected. The ear constantly has to adapt to changing tonal balances.

Listen for Natural, Realistic Sound

The most natural, realistic sound comes from speakers with smooth, extended frequency response across the audible spectrum, free of significant peaks, dips or irregularities.

This allows you to hear music as the recording engineer and artist intended - with the correct harmonic structure and spectral balance intact.

So beware of response anomalies when evaluating speakers - they directly impact fidelity and listening experience even if some deviations are inevitable in affordable designs. Prioritize smoothness and listen for natural tonal balance.

How Speaker Frequency Response is Measured

There are a few main methods used to test and quantify a speaker's frequency response during design and manufacturing. The resulting measurements are usually published in marketing materials as graphs that aim to represent the speaker's sound.

Anechoic Chamber Testing

The most accurate way to measure raw frequency response is by placing the speaker in an anechoic chamber - a room designed to absorb sound reflections.

A microphone is positioned where the listener's head would be. Electronic test signals are fed to the speaker and the microphone data is analyzed to plot amplitude versus frequency. This shows the inherent response uninfluenced by room interactions. Professional reviewers often analyze speakers this way.

In-Room Measurement

Real-world listening happens in normal rooms where speakers interact with the environment. So many experts find in-room measurement more useful for understanding perceived frequency response.

This involves placing a calibration microphone at the prime listening position while sweeping test tones through the speaker positioned normally in the room. Room correction software accounts for the impact of the room's acoustics. This indicates how tonal balance is affected by speaker placement.

Look for Wide, Smooth Response

When interpreting published frequency response graphs, you generally want to see the curve maintain as flat and smooth a profile as possible across as wide a frequency range as possible.

Watch for any obvious, sharp peaks or spikes which indicate boosted frequencies. Dips or downward slopes suggest missing energy in those bands. The wider and flatter the overall curve, the more accurately the speaker reproduces the complete audio spectrum.

Beware of Response Graph Manipulation

Some brands exaggerate or condense the vertical dB scale ratios to make response curves appear flatter when zoomed out. Make sure you look closely at the axis values. Also beware of exaggerated horizontal frequency scales that hide missing bass or treble extension. Evaluate graphs carefully when comparing speakers.

Tips for Getting the Best Frequency Response

While no speaker has perfectly flat response, there are some helpful tips for optimizing a system to get as smooth and extended a frequency response as possible:

Choose Speakers with Inherently Smooth Response

Prioritize speakers designed and engineered for linear response over a wide bandwidth.
Look at measured response graphs and read professional reviews.
In general, higher-end audiophile speakers aim for neutrality.

Use EQ to Correct Obvious Irregularities

Room correction EQ can help fix severe spikes or dips in certain bands.
But use gently. Excessive EQ risks new distortions.

Proper Positioning Controls Bass

Placing speakers close to walls boosts bass, moving them out flattens response.
Experiment with toe-in angle to balance treble and bass.

Upgrade Crossover Components

Higher quality crossover parts like poly or oil caps enable smoother driver integration.
But focus first on speakers designed well in the first place.

Trust Your Ears

Measurements reveal helpful insights but don't replace listening.
Choose speakers that sound balanced, natural, and realistic to your ears.

Getting flat response isn't the ultimate goal - listening enjoyment and emotional engagement matter more. But evaluating frequency response does give you valuable guidance for choosing speakers and positioning them optimally. With care and common sense, you can craft a system that sounds fantastic.

FAQ

What is the audible frequency range for humans?

The typical healthy human ear can hear frequencies between 20 Hz on the low end and 20,000 Hz (20 kHz) on the high end. However, our hearing is less sensitive at the extremes.

What does a perfectly flat frequency response look like on a graph?

The ideal response is a straight horizontal line at 0 dB across the entire audible spectrum, indicating equal amplification of all frequencies. This would represent perfectly neutral, uncolored sound.

How much deviation from flat response is acceptable?

It depends on the amplitude of peaks and dips. Small ±2 dB variations are generally not very noticeable. Larger spikes or dips above 5 dB will result in clearly audible coloration. Multiple irregularities cause a disjointed sound.

Do all speakers and headphones alter the frequency response?

Yes, every transducer will deviate somewhat from perfectly flat response due to physical design limitations. However, high-end audiophile models aim to minimize alterations as much as possible.

Should I only choose speakers with a ±3 dB response?

While flatter is generally better, moderate response deviations don't necessarily ruin sound quality if they occur evenly across the spectrum rather than concentrated in one narrow band. Listen to the speaker's tonal balance.

Will equalization fix a speaker's frequency response issues?

EQ can help reduce obvious peaks or dips, but excessive EQ often introduces new issues. It's better to choose inherently well-designed speakers when possible. EQ should be used sparingly.

Which matters more - frequency response or distortion?

Both significantly impact sound quality and should be optimized in speaker design. Low distortion allows you to appreciate the benefits of smooth, extended frequency response.

How can I improve bass response in my room?

Corner placement, proximity to walls, and acoustic treatment can help reinforce and tighten bass response. But start with capable speakers designed to reproduce low frequencies at your listening volume.

Conclusion: Why Frequency Response Matters

In the quest for high-fidelity sound reproduction, few specs are as important as a speaker's frequency response. This measure of how evenly a speaker reproduces the full spectrum from bass to treble reveals its tonal balance and neutrality.

While no speaker can achieve perfectly flat response across all audible frequencies, smooth and extended response should be a top priority. Careful engineering of the drivers, crossover, enclosure, and other elements can minimize peaks, dips, and irregularities that color the sound.

Pay close attention to published frequency response measurements and graphs when researching speakers. Look for as flat and wide a curve as possible without drastic deviations. Listen for natural tonality without exaggerated or recessed bands.

Proper positioning and room acoustics further help smooth out response dips and peaks. Some careful equalization can also compensate for defined errors in certain frequency ranges.

But above all, trust your ears. Choose speakers that sound clear, balanced, and realistic. The most accurate, lifelike sound comes from transducers designed from the ground up to deliver neutral, uncolored frequency response, preserving the fidelity of your music as the artist intended.