In an audio forum, the question arose as to whether a high SPL, low distortion two way was possible. No mention was made of cost, so, negating cost, it surely sounds possible. Also, high SPL and low distortion weren't quantified. Examples of some that were designed by an audio engineer were frowned upon due to their size, which measured between 26" and 35" in height, the width and depth being around 10" to 12". That being said, size is one strike against the design shown here, which measures 36"Hx14.5"Wx11"D at the top and 15"deep at the bottom. It has a 10 degree slanted front. Internal volume is 3 ft^3.

Another topic of negative discussion among that group was the performance of a 12" woofer up to about 1khz. Apparently, these folks seem to have considered using a tweeter instead of a full range or high quality midrange of about 5" to 6" in diameter. They were aware that large woofer cone excursions would increase modulation distortion but no data was presented to quantify that nor had anyone claimed to have noticed it under a listening test.

While I do have the means to make such a test, the point is moot. Distortion of any kind, THD and IM are easily heard when one tone is played for THD or two tones for IM but how does it affect a band or full symphony orchestra? Then, there is no way other than recording a live performance and comparing the playback with the live performance. Another detriment to such a test is our short acoustical memory. By the time a few minutes of recording is done of a live performance to the playback, a couple of minutes would have passed and our memory of such subtle details will have vanished like a dream. 

It should also be noted that a tweeter will give a better transient response than a 5" or 6" unit, but how much better is again, subjective.

The contention is that one who listens for such subtleties is focusing too much attention to their system and missing the music.

The upper register in this design uses a MarkAudio Pluvia 11, a full range with a 5dB peak centered at 10khz and beginning at about 7khz. This may not be a problem but a wide band notch filter was designed to flatten that band.

This speaker (two) was bought for study purposes at a cost of about $85 and is currently priced at $101 and the GRS SFPC-B is currently priced at $33.

The MarkAudio Pluvia 11 with its aluminum cone is fairly linear to about 17khz and exhibits very low THD, about 0.3% above 200hz

  Madisound has many more that will work, especially if cost is not considered.

FIGURE 1

1w1m MarkAudio / GRS xover at 300hz     BLACK with N2    RED without N2

Grey curve is THD (~0.3%) >200hz

FIGURE 2

The first order network showing the location of the N2 filter.

The bypass switch, SW1 is optional.

The components of the N2 notch filter are shown and are critical. The 9k, 11k and 13k are the lower knee (-3dB below the center frequency), the center frequency and the upper knee, ( -3dB above the center frequency), resp., resulting in an effective bandwidth of 0.5 octave.  During its design, the resistor used was a 25W variable. It was used to adjust the required resistance which would compensate for the resistance of the coils and the ESR of the capacitor rather than rely on filter calculations which assume a perfect inductor and capacitor. It also gives the opportunity to adjust the attenuation. In this case, 9.4W a  maximum attenuation, above which no further attenuation is obtained. Therefore, any resistance between about 8W and 10W would work.   

The inductor was made using four inductors in a series-parallel configuration. Two 0.01mh inductors were wired in parallel to get 0.005mh. This parallel pair was wired in series with another 0.01mh inductor along with a 0.05mh inductor. Total inductance as measured with CLIO 0.065mh.

The capacitor is a precision audio capacitor of 2.7uf 1% which resulted in the required value. All components in this design with exception of the MarkAudio were purchased from Parts-Express  The MarkAudio was purchased from Madisound

FIGURE 3

Impedance of the system with and without the N2 filter. 

The black and orange peaks (superimposed) at the left is at the resonance of the woofer in the closed box. The lower center peaks are those of the crossover point, 300hz. The orange large right peak is that of the notch filter, N2 in series with the MarkAudio and its associated high pass filter. The lower black right peak is that of the MarkAudio only with its associated high pass filter. The nominal impedance of the system is 7W 

A look at the woofer

The left (blue) is the one used; the other is an option. While it has a lower fs and slightly higher power handling capacity, it's sensitivity is 6dB lower, meaning it would need 4 times the power to equal the output of the other.

FIGURE 4

FIGURE 5

This set of curves may lead one to believe that the orange speaker is the better choice due to its bass output. However, there is no such thing as free bass any more than there is a free lunch. See fig.6

FIGURE 6

Here's the same two speakers with the same power delivered. The high frequency rolloff of the orange speaker is due primarily to its system mass, Mms being slightly more than twice the blue one and its voice coil inductance, Le being a little more than three times the blue one.

Given the availability of high power amps, this may not be a problem.

Please bear with me on that one as I come from an era when anything more than 30 watts was considered an arc welder. 

FIGURE 7

Again, the maximum acoustic power delivered at 1 meter with 50 watts. Keep in mind, both diaphragms' area. Sd are within 10% of each other, the blue being 10% larger as well as having a 12% longer diaphragm excursion.

FIGURE 8

In 3 ft^3 closed, the orange unit will handle more power at lower frequencies.

FIGURE 9

With an input of 50 watts, both will approach and possibly exceed Xmax. Under this condition, the orange unit fares better but look at fig.10

FIGURE 10

By lowering the power to 37 watts, the blue now fares better but only by 1.3dB

FIGURE 11

The delay between the input signal and the speaker's acoustical output, the latter lagging behind the former.  The acoustical difference, if any, is unknown to me. However, consider a single speaker. Now, connect this speaker to an amplifier through a DPDT switch which, when toggled, will reverse the connection of the speaker to the amplifier. If you can hear a difference, you're a better man than I am, Gunga Din. (Rudyard Kipling, 1890)

FIGURE 12

Ahh, group delay, which is phase response expressed in time. For one thing, the more linear the graph, the better the transient response.  At low frequencies, this may be perceived as a tighter bass.  It will usually go unnoticed unless the delay is long or the listener doesn't care. However, if the speaker system is being used with video, this can become quite noticeable. With a camera zoomed close to a bass guitarist, the note will be heard after the string is plucked. This I've seen to be quite noticeable with classical music and the camera zoomed to the kettle drums. The drumstick hits the drum and the note is heard when the drumstick is elevated back up.  This is quite noticeable with a single strike to the drum. A glass dropped to the floor will shatter before the sound is heard. With a person talking in a low register, the lips will appear out of sync with the sound.

The following is here for purely academic reasons. It attempts to show how critical microphone placement can be with regard to frequencies above 10khz, where the wavelength is 1.3" and shorter. Note the angle of the mic beam, its sensor end being tilted down. It's tilted down at 11^o. This makes its line of sight, or sound, if you prefer to be perpendicular to the front baffle.

A few days earlier, measurements were made on another 6" midrange which had a peak around 12khz. (fig.14, green trace above the red dot)  A subsequent sweep showed no such peak. (fig.15, green trace above the red dot) Investigation led to the above described observation. Details are shown in fig.13

PHOTO 3

FIGURE 13

FIGURE 14   Mic at A in fig.13

FIGURE 15   Mic at B in fig.13

Near field response of the woofer through its low pass filter. Mic distance, about 0.25 inch (6mm) from dust cap. Relevant below 400hz, ignore the rest.

Comparing the part of this curve below 400hz with the two above, the effect of the room becomes quite evident.

Here's a comparison of the near field responses. BLUE-GRS   ORANGE-Eminence

Both are taken with the woofers' 300hz low pass filter

FIGURE 15

A listening test corroborated the above, the GRS seemed to have a slightly better low frequency response. The listening tests were performed prior to taking these response curves so as not to influence that which was heard. 

Comparison of the bass below about 300hz with the near field responses of fig.15 shows the effect of the room.

This shows the 1w1m response, with the N2 filter (orange)

Then, this was generated with bass Box Pro; same color references, Blue-GRS and Orange-Eminence.

Both look identical in the bass above 40hz. This doesn't coincide with the above near field responses but, to quote Albert Einstein, 

"In theory, there's no difference between theory and practice; in practice, there is."