Frequency Response

Thomasjclark45

I understand about a speakers overall frequency response, but can anyone tell me what this means?
Lower -3dB Limit 63Hz
Upper -3dB Limit 24kHz

kuntasensei

That's an indication of the speaker's natural rolloff, typically in an anechoic environment. It means that at 63Hz, the speaker's expected output level is down by 3dB, etc. Because your room itself will extend frequency response slightly below that, expect to get roughly another 20Hz of response in-room as a general rule. That said, if you're looking at these specs to determine proper crossover points for your system, it's typically better to set the crossovers in your AVR to a number ABOVE the lower -3dB spec so that you give enough room for the transition from speaker to sub. 80Hz is typically a good crossover point to use for a speaker with about a 60Hz -3dB point. Ideally, I would give about a half-octave above a speaker's lower -3dB point for a smooth transition, but any setting above 80Hz edges you closer to the point where bass frequencies become directional (which you don't want getting to your subwoofer if possible).

Auto-cal methods read the in-room response and set crossovers based on this, but this isn't necessarily the best setting to leave it at. Asking the AVR to push a speaker down near its natural rolloff increases the power requirements of the amp and can muddy up the sound. In the case of Audyssey, that's why they recommend that you can set crossover points UP from the detected number but not DOWN (as the point detected during calibration is the lowest point equalized during the process).

SDA1C

Isn't that the measurement for how fast a speaker can move? Once a frequency goes beyond that the driver it's self cannot return fast enough to start another cycle.

I think

Thomasjclark45

Thanks for the Info, that put it into terms that I can understand, I think. Just to recap to make sure I understand what your saying is that at 63hz the speaker/channel is going to lose 3db of volume. is that correct? Also that room accoustics will naturally lower the frequency that I am hearing, so if I set the frequency at 80hz room accoustics will actually produce a frequency around 60hz?
Next in my questioning is, is the -3db point effective throughout the volume range or does it grow as volume increases?

Tour2ma

^ Yes and no...

Yes, the spec means that at 63 Hz your main speakers output sound pressure level (SPL) will be down 3 dB from flat. If you've calibrated to 75 dB, then the 63 Hz level will be 72 dB unless targeted compensation is provided. Compensation could come in a couple forms: equalization, a secondary source for that frequency or room gain.

Equalization involves the boosting of that frequency (or a grouping of frequencies around a target frequency) at the Pre-amp stage. The boosted frequency is then amplified resulting in an increased 63 Hz signal going to the speaker. The result is you'd hear a flat, 75 dB 63 Hz tone rather than one that is down to 72 dB.

A secondary source would be your sub. Where your mains low frequency output "rolls off" your sub's output steps in, complementing your mains' output and as above you'd hear a 75 dB 63 Hz tone. This is commonly referred to as blending in a sub. Blending is possible only because 63 Hz is below the threshold of human ability to localize a sound source (as kun-sen touched upon). Prior to automatic EQ programs sub blending could be a painstaking process involving sub placement, x-over frequency selection, and sub phase setting.

Room gain is what kun-sen alluded to earlier. Whereas high and mid-range frequencies are easily absorbed and quickly lose their energy, bass is persistent, reflecting off objects. And deep bass is very persistent, reflecting multiple times in a typical room prior to dissipating.

When a reflection of a low frequency arrives at the listening position essentially in phase with the source's direct output of that frequency, "gain" is the result. Sub's are placed in corners to seek maximum gain. With two walls and a floor all very near the speaker cone, 1st reflections are almost guaranteed to arrive substantially in phase. The cool thing is, room gain is free... but then nothing is really free, is it?

Sometimes all of the above, well-timed reflections add up to too much of a good thing and result in unnatural, boomy bass. That's why many times subs that start in the corner are ultimately moved away from it and along one wall or another... at least they did in the old days with manual set ups.

Then there are out-of-phase reflections (nulls), secondary and tertiary reflections, and harmonics to consider. But we'll save all that for another time... besides you have Audyssey. So like Tom Rush sang,

Kids these days ain't like we used to be....

From the above you can see also that rooms don't produce frequencies, they merely reflect frequencies your speakers produce. So the answer to your second question was no...

SDA1C wrote: »

Isn't that the measurement for how fast a speaker can move? Once a frequency goes beyond that the driver it's self cannot return fast enough to start another cycle.
I think

Sort of... A driver's surface (cone) must vibrate (move) at the frequency it reproduces. Frequency is measured in cycles per second. But there is another component... amplitude.

Amplitude is the distance traveled per cycle. It is what determines the SPL of a given frequency from a given driver. The FR limits of a given driver is a matter of that driver's inability to travel the full distance per cycle, not its ability to complete the cycle.

Cone mass is the major factor that determines at what point a driver gives up reproducing sound at the upper end. The higher the mass, the higher the cone's momentum and inertia, and the more difficult it becomes, the more power is required, to change the cone's direction of travel. At the same time that the cone's need for more power to produce ever higher frequencies, the amount of energy associated with increasing frequencies is falling. Ultimately there comes a point where by the time the cone starts to move, it's time to reverse direction. But long before this point the amount of movement is sufficiently reduced that the output is inaudible.

Cone area is the limitation at the lower end. A small cone simply cannot deliver enough energy to air to audibly reproduce low frequencies, i.e., "move enough air". Bob Carver's True Subwoofer design illustrates this. He was able to shrink cone area by utilizing a "bladder" design with unheard of "throw" (travel) to get the required volume displacement. The design also called for unheard of amp power for sub duty. That he had the Sunfire amp design is what allowed him to pursue the sub design.

For most modern-day tweeters... simply substitute "dome" for "cone". Their very low mass is why they can produce frequencies well beyond the limit of human hearing. Which is 20 kHz-ish...

Syndil

Here is an excellent article that should help you understand the various terms regarding frequency response and what they mean.

http://www.ecoustics.com/electronics/products/articles/131062.html

steveinaz

It is widely accepted that an increase or decrease of 3dB is needed to be perceptable to the human ear. So the +/-3dB specification is letting you know when FR is deviating from linearity in a significant manner. This doesn't mean that frequencies don't exist below (or above) this point, it just means that they will be lower in level.