Hello! I'm new and working with a small 4" two-way speaker. With some help from the community I am hoping to add an active crossover with some frequency correction.
· Wired separately for bi-amplification and active crossovers
· Mid-tweeter has a protection capacitor
· Rated for 70 Watts of music input power
· Harmonic distortion typically under 0.3% in normal use
· Rear port creates a lift at 50Hz, in-room response.
· Good imaging behaviors
· Improve the overall response
· Active crossover
· Keep woofer and tweeter wired in phase for proper step response
· Design a bass boost similar to Panasonic’s Super Woofer bass mode.
I came across a pair of attractive Panasonic SB-PM28 speakers and thought of building a project around them. I know someone that could really use a sound system and these may fit the bill.
A problem (IMHO) is that small speakers often have limited bass output. Panasonic worked around this problem with bi-amplification and tailored bass boost. The Super Woofer bass boost was comprised of a steep peak centered where most musical fundamental bass notes reside, and it created the illusion of larger speakers having extended output. Below the peak was a high-pass filter to prevent infrasonic over excursion and distortion, and above the peak the response flattened quickly to prevent muddying the low midrange.
The bass response might be regarded as psychoacoustic, as the theory is that when loudspeakers are not permitted to extend deep (due to mechanical limitations) a narrow peak in the bass creates the illusion of extension. One implementation of this psychoacoustic perception is discussed in the paper, “Optimized Frequency Curves in the Bass Range” by Ingvar Ohman, published in Musik och Ljudtejnik, Sweden. Graphs can be referenced on page 9 of the paper.
Right at this point I’ve looked into DSP and analog frequency correction. I think I prefer analog with opamps for reduced cost, but suggestions are welcome.
· Measurements were taken outside 45.7cm/18" from the calibrated measurement microphone, 152cm/ 5 feet above the ground outside at high levels using a `vintage` receiver. The distortion impacted the results.
· The final 2 measurements in this post were taken indoors with the mic 3cm from the woofer’s dustcap. A Panasonic SA-AK27 (Class H) active mini system’s left Super Woofer channel was used for measurement. Ignore everything above 2kHz in these two graphs, as the channel contained signal processing.
· The harmonic distortion and low frequency response were impacted by ambient noise floor.
The speakers.
The frequency magnitude of both drivers at 45.7cm/18 inches from mic.
The tweeter's relative phase response versus frequency. Roughness in the response is partially due to the wave guide.
The woofer's relative phase response versus frequency.
The tweeter's relative harmonic distortion. Ref is 2kHz, 0.197% THD.
The woofer's relative harmonic distortion. 0.292%. Ref, 1.5kHz.
The tweeter's impulse and step response, 20ms.
The tweeter's impulse response , 2ms time window. Modeling with DSP software showed that this could largely be corrected through EQ.
The woofer's impulse and step response, 20ms time window.
Frequency Response and Phase with S.Woofer Bass boost on. 3cm from mic.
Harmonic distortion is .388% at 80Hz with S.Woofer Bass boost on.
The Speaker:
· 4” woofer and 2.25” mid-tweeter
· Wired separately for bi-amplification and active crossovers
· Mid-tweeter has a protection capacitor
· Rated for 70 Watts of music input power
· Harmonic distortion typically under 0.3% in normal use
· Rear port creates a lift at 50Hz, in-room response.
· Good imaging behaviors
The Goal:
· Minimal cost
· Improve the overall response
· Active crossover
· Keep woofer and tweeter wired in phase for proper step response
· Design a bass boost similar to Panasonic’s Super Woofer bass mode.
I came across a pair of attractive Panasonic SB-PM28 speakers and thought of building a project around them. I know someone that could really use a sound system and these may fit the bill.
A problem (IMHO) is that small speakers often have limited bass output. Panasonic worked around this problem with bi-amplification and tailored bass boost. The Super Woofer bass boost was comprised of a steep peak centered where most musical fundamental bass notes reside, and it created the illusion of larger speakers having extended output. Below the peak was a high-pass filter to prevent infrasonic over excursion and distortion, and above the peak the response flattened quickly to prevent muddying the low midrange.
The bass response might be regarded as psychoacoustic, as the theory is that when loudspeakers are not permitted to extend deep (due to mechanical limitations) a narrow peak in the bass creates the illusion of extension. One implementation of this psychoacoustic perception is discussed in the paper, “Optimized Frequency Curves in the Bass Range” by Ingvar Ohman, published in Musik och Ljudtejnik, Sweden. Graphs can be referenced on page 9 of the paper.
Right at this point I’ve looked into DSP and analog frequency correction. I think I prefer analog with opamps for reduced cost, but suggestions are welcome.
Measurements
Important Notes:
· Measurements were taken outside 45.7cm/18" from the calibrated measurement microphone, 152cm/ 5 feet above the ground outside at high levels using a `vintage` receiver. The distortion impacted the results.
· The final 2 measurements in this post were taken indoors with the mic 3cm from the woofer’s dustcap. A Panasonic SA-AK27 (Class H) active mini system’s left Super Woofer channel was used for measurement. Ignore everything above 2kHz in these two graphs, as the channel contained signal processing.
· The harmonic distortion and low frequency response were impacted by ambient noise floor.
The speakers.
The frequency magnitude of both drivers at 45.7cm/18 inches from mic.
The tweeter's relative phase response versus frequency. Roughness in the response is partially due to the wave guide.
The woofer's relative phase response versus frequency.
The tweeter's relative harmonic distortion. Ref is 2kHz, 0.197% THD.
The woofer's relative harmonic distortion. 0.292%. Ref, 1.5kHz.
The tweeter's impulse and step response, 20ms.
The tweeter's impulse response , 2ms time window. Modeling with DSP software showed that this could largely be corrected through EQ.
The woofer's impulse and step response, 20ms time window.
Frequency Response and Phase with S.Woofer Bass boost on. 3cm from mic.
Harmonic distortion is .388% at 80Hz with S.Woofer Bass boost on.