Flat frequency response

I am often surprised by the number of speakers with "gee-whiz bang" technology but can't even get speaker design 101 right. I can see the benefit of avoiding a lot of signal processing but preferences notwithstanding, flat frequency response seems like the logical place to start and then progress from there.

1) Why is it so hard to achieve?

2) Does it matter?

3) Is it reasonable to say when you skip the basics you are only progressing on a flawed foundation.



I agree with you.  I'm often surprised when I get to the measurements part of a Stereophile speaker review, and read about strange anomalies of the design, and then see a not-so-good waterfall plot from a very expensive speaker.

It might be because a speaker that measures ruler flat sounds like crap in an actual room.  Just a semi-educated guess. 

but can’t even get speaker design 101 right.


Can you please point us to speakers you have designed in the past? A write-up or measurements of them? Where did you take Speaker Design 101?  Is there a particular author /  engineer whose course or book on speaker design you are referring to?

That’s the sort of background I would expect from a post that claims speakers are not designed correctly.

My guess, based on your questions is that you have none of that background, but are interested audiophile who is trying to understand the meaning of frequency response measurements. 




Speakers with completely flat responses do not sound good. I have read articles from more than one speaker designer that attests to the fact that flat response speakers sound dry and lifeless. One sticks in my mind of a designer that could not decide between releasing his speaker which tested nearly perfectly flat or release it with great sound. In one case you sell to the specification people and in the other dedicated audio folks


This simply puts speakers in the same category as all other high end audio stuff. A simple measure or two does not characterize performance to the human ear. So, to design great audio equipment… the important, very time consuming part is human listening tests and tweaking to make it sound good.

A waterfall plot shows decay times describing the acoustics in that particular ROOM


Thanks !



Where did you take Speaker Design 101? Is there a particular author / engineer whose course or book on speaker design you are referring to?

You make a good point. I have not seen flat FR as a design goal in any text. I should have put "Speaker Design 101" in quotes. My bad.

My guess, based on your questions is that you have none of that background,

Very cool you have that skill but IMHO should not be a requirement to have an opinion or yours would be the only response here, haha. With your design experience, I would be interested what you think about "1) Why is it so hard to achieve?"

Yes I do but I would rather example JA saying things like "That midrange deviation from flat will give vocals a nasal quality." Disclaimer: this is from memory, not an exact quote. I just used quotes for clarity.

But enough about me, back to the topic on hand, I am guessing your answer to "2) Does it matter?" would be no?



Theres lots to learn on the topic of frequency response.

Are you familiar with "The Harman Curve"? That could be a fun place to start!

Any quality company around $1k and up will do computer simulation 

and frequency phase plots and account for peaks in the Xover .

thsts another area ,having owned a Audio store for a decade and being a die hard Audiophile that’s one area 95% of all mfg  go cheap why because of $$ either Chinese capacitors or low average Solen caps , and cheap ceramic resistors 

even inductors tiny Bobbins, or sledge hammer type .

I bought a 5 year old Dynaudio ,they are very good Jantzen open core inductors 

caps and resistors ok , I put in muncher higher grade parts ,a solid 15% improvement many people don’t understand ,it’s the 🧠 or ♥️ of your loudspeaker ,

the entire Signal goes through there , Even $25 k martens ,Magico A5 and Wilsons , they use decent rated a 9 on the capacitir scale ,Mundorfs best caps are their supreme in several flavors,marten and Magico use the much cheaper Evo caps why ? They get 50% off .rule of thumb 25% no more goes into the build including packaging ,the rest R&D overhead and markup ,this too applies to electronics.

that’s why I highly recommended to upgrade any loudspeaker Xover you plan on keep a major Sonic upgrade.

I concur, speakers that are designed to be flat responsively are boring.  Give me one that brings life to the party [without being obnoxious].

I tuned my room by ears with one hundred Helmoltz resonators... It takes me one year of incremental tuning process...The results was not perfect at all in term of flat frequencies response  just totally astounding FOR ME.... 😊


A flat frequency response made some sense between two pieces of gear as a dac and an amplifier for exemple ...

But electronic engineering is not acoustic...Here frequencies responses ask for a more deep investigation ...

The answer from acoustic and psycho-acoustic is more complex and way more nuanced because here we introduce the specific ears coupled to a specific brain in a specific small room ...




Here an article by an acousticuian who teach studio acoustic ( the underlining is mine )  :


«The Hunt For Your Prefered Tonal Balance

First, as you are shaping your music, you’ll automatically gravitate towards a tonal (frequency) balance that resembles your own personal taste.

Some people generally prefer more bass, some less. Some like more present highs and “forward” mids, some prefer a “neutral” representation.

If you’ve ever applied EQ to a speaker system for a client for tonal shaping purposes, you’ll know that a balance they like can be drastically different from what you like.

The point is that you have developed your very own preferred subjective frequency balance through years of listening to your favourite music on various speakers and headphones, at different volumes, throughout different periods of your life, etc.

That subjective frequency balance is personal to you, and you alone.

That’s why acoustician Bob Hodas says:

“I have yet to find an engineer or studio owner who actually wanted a “flat” room. Experience shows that a flat room has no personality and is no fun to work in. Equally important, working in a flat room does not necessarily ensure a recording that sounds good elsewhere.” – Source

The problem is that if the frequency response of your system does not mirror your personal taste, you’ll constantly be over-compensating for it.


Getting To The Promised Land of the “Flat Frequency Response”

Of course, no matter how good you become at referencing and keeping your taste in line, it will not compensate for a serious lack of information. You cannot judge what you cannot hear. If the frequency response at your listening position is simply too crooked to start off with, no skill in the world can make up for it.

That’s why the basic requirement for your home studio is this:

Your frequency response should be balanced to match your taste, and nothing should be drastically missing.

Once you’ve got that, you’re good to go. The rest is up to you and navigating the choppy waters of “taste drift”. Interestingly, looking at the big picture, your room’s frequency response suddenly becomes a non-issue.

You’ll then realize that the really important acoustic aspects of your room are less about frequency, and much more about time.

Because the way that reflections mess with your perception of the sound stage and dynamics, and the way that resonances and excessive reverb cause masking, is not something you can cure with skill and technique.

“Contrary to popular belief the big problem with bass in hifi is not lumpy bass, standing waves, room modes, hot spots and suckouts. The big problem is sound masking.” – Art Noxon

And solving those issues, more than anything, will help you get what you want. A sound that you can trust, a sound that lets you reliably make decisions, one mix after the other.

Sure, you won’t be able to say: “My room is perfectly flat”, but then why would you want that anyway.

Instead you’ll be able to say: “I know and trust my room. I can hear every little detail. And I know that the decisions I make translate perfectly and exactly how I expect them to.”»

From :




I pretty much agree that speakers should be flat but the music should not be flat. The problem is most music is produced badly.


Floyd Toole’s book is documented research on this subject and worth a read (linked below). The short version is people like flat response on and off axis and like some side wall bounce. Now as we are all super into audio we might different just a bit here and there.

When I got into this hobby 20 years ago I read all the tech. I was amazed and drank the cool-aid of brands like B&W. I read the white papers, even bought a pair. Only to have a grating sound and chase electronics. B&W is a good example of making a great speaker sound bad. Now I use speakers with good old paper drivers and big boxes….

My current speakers have 0.5 db adjustments for the treble and mid treble and those 0.5db adjustments make a profound effect on the sound.

I think other things that are hard to measure like dynamics play a huge favor. The measurements will have you thinking a small genelec speaker will sound better than big wilson audios. I can assure you they don’t. The dynamics of those big wilson just sound more real. Something that is missed in measurements. But yes flat measurements are a basic requirement for speakers for me. I will not even audition speakers that are not flat. Then they need to bring the other things.



I’ve never envied speaker manufacturers because they have an impossible task of designing a component to work in a room that does not measure flat and will vary greatly in size and overall dimensions.  And, as we all know here, the room has a huge impact on what we ultimately hear.  Yeah, room correction software and/or room treatments can and do help greatly, but still, I’d much rather make cables and take the much higher profit margins and transportability.  God bless speaker manufacturers!

Anyone who wants to hold up "flat" as ideal needs to at least investigate the B&K or the Harman speaker curves. There’s a lot of stuff written there. Also the East Coast vs. West Coast sound. How Klipsch and AR were sounding different from JBL and why.

Also, take a look at the work Floyd Toole has done in terms of determining bass levels vs. user preferences.

Then there’s the issue of hearing and volume. Some speakers really bring out the best at low volumes while others need to be played loud.

This is just the tip of the iceberg when it comes to deciding what a speaker output should be like.






Back when I was an avid amateur speaker builder, I borrowed some test equipment from a technician so I could fine-tune a crossover design, my target being the "holy grail" of flat frequency response. As I got closer and closer to "flat", the sound got worse and worse. Still I persevered, firm in my faith that once I reached "the promised land" of flat measured frequency response, everything would fall into place and the angels would sing.

Well, that didn’t happen. When I finally arrived at "flat" response (plus or minus about .75 dB indicated at the microphone location except for the peaks and dips in the bass region), the sound was harsh and bright and imo unlistenable.

After this highly unsettling experience I started spending as much of my spare time as I could in the library of a nearby university, poring though audio industry journals trying to figure out what had gone wrong and what the solutions might be. Here are the conclusions I eventually arrived at:

1. The in-room response at the listening position dominates perceived tonal balance, and the most natural-sounding in-room response has a gently downward-sloping trend as we go up in frequency (the Harman Curve being an example of this).

2. The spectral discrepancy between the first-arrival sound and the in-room reflection field should be minimized.

3. This means that BOTH the first-arrival sound AND the in-room reflections should have approximately the same gentle downward-slope as we go up in frequency.

Therefore, in my opinion, “getting the basics right” includes getting the first-arrival sound right, and getting the reflection field right.


speaker manufacturer



The book you need to read is Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms by Floyd E. Toole now in its third edition. It will answer a lot of your questions.

I honestly prefer the house curve in my room. This is where the the bass region is above the reference level and trending at a downward slope where the up end of the frequency response(20k) is probably at about 6db/oct. In linear scale, theoretically this will give you a flat response but not in FFT.

One other thing to remember is that having a good frequency response is only the tip of the iceberg. How it sound is another thing.

From what I’ve read, and experiences from my attempts at building speakers, it does seem to be important that the overall power output be smooth, with a downward tilt of some sort toward the treble. It really is difficult to get a speaker to simultaneously have a flat, smooth on-axis response while also having a smooth but downward tilted response off axis at all angles. There’s a ton of stuff that goes on between the drivers and cabinet baffle, port, internal enclosure resonances, etc. interacting with each other that make getting the off axis response smooth at all angles a can of worms. If you can’t solve all of that, then some compromises here and there might not be all that audible, while allowing the speaker to perform better in terms of lower distortion, extended response, more headroom, etc. The ideal dispersion pattern for a speaker is not something that has been settled, and may vary depending on tastes, the characteristics of the room being played in, and perhaps the type of music being played. What does seem to hold true though is that whatever the dispersion pattern, narrow or wide, or somewhere in between, or perhaps various combinations of wide up to a certain frequency before narrowing at various rates, the measured response from any angle off the speaker should ideally be smooth across the frequency band, with no stand out peaks or dips. If there are some peaks and dips, ideally they should be random at different angles, and not the same at all angles. However, if they are the same at all angles and you have access to a good EQ, you may be able to improve that speaker quite a bit with EQ.

I think there’s a limit to how smooth and flat the response needs to be, at least for me. I’ve recently compared speakers that measured better in every respect to what I’m using now. I even think they sounded better as a result, but they weren’t really solving anything that my ears couldn’t easily adjust to. My ear is forgiving of certain flaws, and I may even find some subtle colorations charming, so I was not persuaded to move up. My imperfect speakers are close enough, and I think I prefer their slightly wider dispersion in the upper frequencies, even if it isn’t as smooth and even.

Of the various speakers I’ve built, I’ve found that I really liked a minimum baffle design that used a 3/4" tweeter and a 4" woofer. I never tested the response on these, just set the electronic crossover by ear and found them captivating. My girlfriend did too. I’ve also built narrow dispersion horns that could hold a fairly tight pattern down to 600 Hz. I liked those a lot too, played in the same room as the high dispersion speakers. What I think I don’t like are speakers that are narrow up top but don’t hold pattern low enough. If you can’t hold it down to 600 Hz, then keep it wide as high as possible.

Speakers exist optimally and really in room which are tuned by one owner for his own ears...Otherwise it is only a well measured abstract design because not living yet in a room and  not yet working for some ears...😊


I probably just missed  it, but when you refer to flat frequency response are you referring to the sound level at the listeners position, or say 3 ft from the speaker? If you measure the FR at the listening position, depending on the speaker design, the sound could have rolled off enuf to to ease the FR linearity of a speaker with a flat (+/- 2db) measured a few feet in front of the speaker. FWIW.

Duke is 100% correct. Downward sloping in room which could still be flat/pretty flat at the speaker is perfect. 

@cdc Wrote:

Flat frequency response

JBL engineers speak about flat frequency response in monitor speakers. They believe it should have uniform on and off axis frequency response both horizontally and vertically at all angles. 😎 See article below:




Really excellent, thought provoking ideas.


1. The in-room response at the listening position dominates perceived tonal balance, and the most natural-sounding in-room response has a gently downward-sloping trend as we go up in frequency.


Yes. I remember Thiel wanted to keep flat and while some people liked them, I thought too bright. I suppose room and components could come into play.


It really is difficult to get a speaker to simultaneously have a flat, smooth on-axis response while also having a smooth but downward tilted response off axis at all angles.

Hhmmm, that is a good point.



They believe it should have uniform on and off axis frequency response both horizontally and vertically at all angles.

Hhmmm, that is a good point too.



when you refer to flat frequency response are you referring to the sound level at the listeners position, or say 3 ft from the speaker?

Haha, good observation. I have been measuring from 3 ft away and also 9 feet away listening. The 3 feet is an attempt a what the speaker really does. 9 feet is the speaker + room. My personal taste is the speakers measures flat through most of the treble so it will have the downward slope at the listening position since the HF rolls off fast.

I’ve had the opportunity to listen to some speakers lately and what I have taken away is the variety in how speakers are voiced. Maybe the designer will voice the speaker to 1) his taste or 2) what he thinks is most popular and will sell the most. It’s a tough balancing act. While the basic sound quality is often excellent, it’s frustrating to hear some frequency variations that don’t suit my taste.

What I see as obviously wrong, and maybe(?) we can all agree on, I made a speaker and was playing with EQ. Depending on EQ, I was shocked to find the singer didn’t even sound like the same person. They both can’t be right.


where would like. to measure the "flat" response? In your room in an acoustical chamber, in a large/small room. 

I can hardly imagine all speakers sounding the same if equalized to flat.  It's how a speaker releases its notes that gives it its own distinctive sound, whether you enjoy it or not.  Room reflections and acoustics are, of course, important.

But speakers in rooms are usually far far from perfect. The first thing to musical bliss is taming the bad bass nodes and room issues, and if the speaker is contributing to that it gets corrected as part of the process. With a tiny bit of lowering excessive spots in the upper bass and some high treble my goal is the very flattest response in room in my chair from 31Hz up to 12Khz (usually +-2dB). And that's no sub. Taking the irritating bass bump 80-160 from the Raidho D2s is a very good thing. After that it's liquid music in your ears, and a flat response.

Taming the room and speaker into a nice flat response allows the true beauty of the sound to come through. The additional clarity and tight bass is a no brainer. Those who still disrespect any room correction may never have tried with the right unit. I'd never go back.  DSP gives me far better sound, always.

@cdc Wrote:

Flat frequency response

''There is another aspect of the spatial domain that is important. This is that the frequency response should be the same in all the directions in which sound is radiated. That is the same as saying the directivity pattern is independent of frequency. If this is not the case, the speaker may fail to excite reverberation that can be identified as such by the ear because it will be coloured.''

This article just came to me, see below:



where would like. to measure the "flat" response?

I would like speaker to measure flat through the midrange for sure. i do not see anomalies there serving any worthwhile purpose - tastes notwithstanding.

I would like a speaker which could do that, within reason, in a room and do it with a combination of proper direct and off-axis response. Some designers do this with high order x-over, some with room placement. Maybe that is only a dream.

A dipole is the only radiator that is directional down to the lowest frequency.

I am convinced that a properly designed sound system can perform well in a great variety of rooms and requires only a minimum of room treatment if any at all.