frequency range for instrument vs speaker

One of the things that bothered me most about early digital recordings (actually, until very recently) was not the harshness, brightness or grain, it was the very obvious (to me) sense that there was a frequency extension ceiling above the music; that the upper harmonic extension simply came to a screeching halt; technically speaking, around 21KHz. Some would argue that we can't hear above that range. Well we can argue that one forever, but wether it is the absence of harmonics above that range, or the effect that this absence has on lower audible frequencies doesn't matter, it is audible either way. I hear a similar effect at the bottom end of the spectrum. Wether it is the ambience cues that we hear/sense, or undertones, or whatever, when the speaker is incapable of reaching into the lowest octave there is an audible low frequency ceiling (floor?), where just as with the high frequency ceiling, things come to a halt and one hears/senses the absence of limitless extension even if there is no musical content in that frequency range. All this compared to the sound of live music, of course; not just in a hall, but also what one hears in a studio.

06-22-12: Onhwy61
>I think Frogman is correct, but it should be put into perspective. Suppose you were an audiophile with limited funds. Would you be better off pursuing bass response down to 20Hz, or compromise at 50Hz (with room reinforcement) and put more money into going for a better quality midrange and treble? Unless you're an absolute bass fanatic the answer is self-evident.

The answer is counter-intuitive and not at all self-evident without a far better understanding of acoustics and psychoacoustics than the average audiophile's. The combination of physics and consumer market expectations make getting quality midrange without last octave extension unlikely so seeking good high frequency performance means looking for the same things that give you lower bass.

Beyond a room's Schroeder frequency (100 - 200 Hz in typical domestic rooms) and assuming the speaker is correctly voiced for your chosen placement with respect to room boundaries how natural a speaker sounds comes almost entirely from

1. Its polar response with the ideal being flat on-axis with directivity increasing monotonically with frequency. Our brain determines timbre from the spectra of what it believes to be a direct sound and its delayed reflections. An increase in reflected high frequency energy isn't consistent with natural sources (directivity increases with frequency) and environments (natural materials like foliage absorb and diffuse more at high frequencies where they're becoming acoustically large) and doesn't sound right.

This comes predominantly from the driver/baffle sizes/shapes you use including options to increase directivity from an acoustically small driver with a wave guide or cancellation from acoustic dipoles and cardioids.

Untamed driver and cabinet resonances can also play a negative role, showing up as amplitude peaks at all angles.

2. The distortions which go with approaching and exceeding a driver's linear limits. Harmonic distortions change the timbre and IM distortion adds non-musical sounds that weren't in the recording and damage the midrange.

Unfortunately you can't build a flat baffle 2-way with conventional cone and dome drivers which does well in both areas. When you compromise with a smaller mid-range to get better polar response you lack the displacement needed for clean reproduction of lower frequencies (250Hz is probably a nice lower limit for a 4" driver, 150 Hz 5", 120Hz 6-7", 80Hz 8.5", 40Hz 10"). When you compromise with a larger midrange to get clean output at acceptable listening levels you end up with a noticeable harshness resulting from the significantly broader dispersion crossing to the tweeter at 2-4KHz or beyond. People work around that with some success using a drop in output in the range (the BBC dip) although the resulting speaker is more sensitive to the room (you'll notice the lack of energy in a large/absorbing room because there's less compensation for the on-axis dip) than a speaker built with more uniform directivity.

Sticking to flat-baffled vaguely box-shaped speakers that most consumers shop for the solution is at least a 3-way, whether in one cabinet or separate boxes. 120Hz and beyond can work well crossing to stereo "sub-woofers" which are better described as woofers, although if terms like "pole", "zero", and "biquad" aren't in your vocabulary that probably won't end well as a DIY exercise.

Once you do that the extra extension has negligible additional parts cost, although it costs you 9dB of efficiency for the same cabinet size or a box 8X as big at the same efficiency. Most consumer speaker company marketing departments compromise with lower bass to satisfy more listeners, smaller cabinets for spouses, and less efficiency.

The intuitive but incorrect counter-argument is that you're better off with fewer more expensive drivers. It fails because a pair of drivers in a conventional configuration have audible and measurable problems from their inherent physics that more appropriate sized less expensive drivers with lower total cost (and better sound) do not.

Whether you're spending $200, $2000, or $40,000 on drivers flatter on-axis and more monotonic polar response sound more similar than different. Deviating from that design goal is not good although the specific failings vary. It's like Tolstoy's comment "Happy families are all alike; every unhappy family is unhappy in its own way."

06-22-12: Onhwy61
>I think Frogman is correct, but it should be put into perspective. Suppose you were an audiophile with limited funds. Would you be better off pursuing bass response down to 20Hz, or compromise at 50Hz (with room reinforcement) and put more money into going for a better quality midrange and treble? Unless you're an absolute bass fanatic the answer is self-evident.

The answer is counter-intuitive and not at all self-evident without a far better understanding of acoustics and psychoacoustics than the average audiophile's. The combination of physics and consumer market expectations make getting quality midrange without last octave extension unlikely so seeking good high frequency performance means looking for the same things that give you lower bass.

Beyond a room's Schroeder frequency (100 - 200 Hz in typical domestic rooms) and assuming the speaker is correctly voiced for your chosen placement with respect to room boundaries how natural a speaker sounds comes almost entirely from

1. Its polar response with the ideal being flat on-axis with directivity increasing monotonically with frequency. Our brain determines timbre from the spectra of what it believes to be a direct sound and its delayed reflections. An increase in reflected high frequency energy isn't consistent with natural sources (directivity increases with frequency) and environments (natural materials like foliage absorb and diffuse more at high frequencies where they're becoming acoustically large) it doesn't sound right.

This comes predominantly from the driver/baffle sizes/shapes you use including options to increase directivity from an acoustically small driver with a wave guide or cancellation from acoustic dipoles and cardioids.

Untamed driver and cabinet resonances can also play a negative role, showing up as amplitude peaks at all angles.

2. The distortions which go with approaching and exceeding a driver's linear limits. Harmonic distortions change the timbre and IM distortion adds non-musical sounds that weren't in the recording and damage the midrange.

Unfortunately you can't build a flat baffle 2-way with conventional cone and dome drivers which does well in both areas. When you compromise with a smaller mid-range to get better polar response you lack the displacement needed for clean reproduction of lower frequencies (250Hz is probably a nice lower limit for a 4" driver, 150 Hz 5", 120Hz 6-7", 80Hz 8.5", 40Hz 10"). When you compromise with a larger midrange to get clean output at acceptable listening levels you end up with a noticeable harshness resulting from the significantly broader dispersion crossing to the tweeter at 2-4KHz or beyond. People work around that with some success using a drop in output in the range (the BBC dip) although the resulting speaker is more sensitive to the room (you'll notice the lack of energy in a large/absorbing room because there's less compensation for the on-axis dip) than a speaker built with more uniform directivity.

Sticking to flat-baffled vaguely box-shaped speakers that most consumers shop for the solution is at least a 3-way, whether in one cabinet or separate boxes. 100-120Hz works well crossing to stereo "sub-woofers" which are better described as woofers, although if terms like "pole", "zero", and "biquad" aren't in your vocabulary that probably won't end well as a DIY exercise.

Once you do that the extra extension has negligible additional parts cost, although it costs you 9dB of efficiency for the same cabinet size or a box 8X as big at the same efficiency. Most consumer speaker company marketing departments compromise with lower bass to satisfy more listeners, smaller cabinets for spouses, and less efficiency.

The intuitive but incorrect counter-argument is that you're better off with fewer more expensive drivers. It fails because a pair of drivers in a conventional configuration have audible and measurable problems from their inherent physics that more appropriate sized less expensive drivers with lower total cost (and better sound) do not.

Whether you're spending $200, $2000, or $40,000 on drivers flatter on-axis and more monotonic polar response sound more similar than different. Deviating from that design goal is not good although the specific failings vary. It's like Tolstoy's comment "Happy families are all alike; every unhappy family is unhappy in its own way."

06-23-12: Stringreen
>Richard himself helped me with my setup and told me that the goal was NOT to get a flat frequency response...just s pleasing one.

That's an over-simplification.

As an engineer I have built speakers with acoustically small drivers and baffle sizes decreasing with frequency for a flatter first derivative of amplitude with respect to frequency off-axis.

Richard does the same, spending more on labor than he would with rectangular cabinets and then wraps the result with a cosmetic grill-frame producing more conventional aesthetics he can sell.

I can't come up with technical reasons for him to do that apart from the same pursuit of measurable "flatness" whether he quantifies it like that or the result just sounds better.

>Flat frequency response is a-musical.

That's wrong.

Your brain is looking for flat response in the direct sound with less high frequency content in the reflections. That's what you get from live un-amplified performances in good venues which should be the reference for sound reproduction. Any more real would be surreal.

When you feed such ideal signals to a SPL meter it doesn't look at the time domain and just averages everything together. It will and should show a roll-off towards high frequencies. It also picks up wiggles from combing which are often not perceptually important.

Trying to correct what the meter sees can ruin the things the speaker is doing right.

Amplitude adjustments around directivity minima can make things subjectively more natural and flatter (the BBC dip), although simple measurements may not show that's what's happening.

I'd say that there is not a divergence of opinion here; but a divergence of preference. What frogman said yesterday triggered a memory. I was listening to a 70s vintage record a few months ago and remember thinking to myself that the reverb was not nearly as apparent as it was years ago on my old system with the speakers that had 20-20k response. This record is a studio recording and the reverb from the walls is very apparent. On my old system it was nearly at a level of distraction. I remember my brother listening to that record years ago and commenting on it and he didn't like it. I could still hear the reverb a bit but much more subtle on today's system. Another observation: In the services yesterday morning a musician was playing the drums. Not real drums, they were electronic. The loud low frequency thumping created a pressure in my head. I didn't really enjoy that part of the music.
I used to do NVH (Noise Vibration Harshness) work in automotive in the 90s. I remember back then a course instructor at an SAE seminar said that older people do not like low frequencies but young people do not mind them so much. When gas prices started rising and cars started shrinking, the stiffness of chassis went down. Late 70s to late 80s saw a trend away from body on frame moving towards unibody for weight savings and better fuel economy. The NVH of cars worsened. I think cars made in the 50s and 60s rode quieter than 70s and 80s cars if compared as new to new. Boom was prevalent in unibody cars. Remember one design solution? They added speed sensitive volume to radios. By the early 90s automakers started using better steels, weld joint designs and stamped in patterns to increase body stiffness. They also added constrained layer damping materials and e-coat to reduce Boom and rattles. But I remember what that instructor said and I think I have reached that point where I don't really want the low, low frequency material at the same comparative loudness as mid bass and mid tones.
That what I was saying before- many people love their Maggies and Quads for their mid range magic and don't mind not having the bottom register.