2 Way Horn System

Whitesunds National Park, NM USA Photo by Yuichi

This 2way system consists of a horn speaker for high range and a direct radiator speaker for low range as shown in the right photo. This configuration is widely adopted. The system configuration is as follows.

- Woofer system: TAD TL-1601 (38cm Dia.) with 170 liters Enclosure (E-170)
- Tweeter system: TAD TD-4001(5cm throat) with A-290 horn

Amplifiers and filters
- Accuphase C-200X Control Amplifier
- Accuphase P-300X Power Amplifier
- LC passive filter (12dB/oct and Fc=520Hz)

This sort of configuration always has issues and concerns. Which is caused by deferent diaphragm positions from the point of a listener. And it is difficult to adjust it due to physical limitations.
Also, we have to consider about the group delay of each diaphragm. Every speaker system has its own group delay property. Therefore, we have to consider about its value at the point of crossover frequency. Actually we can not feel the delay. However, the delay affects the phase difference. This will make serious problem on gain-frequency property

So, there are two factors to be considered. One is physical locations from the listener and the other is the group delay of each speaker at the crossover point. It includes all the components including crossover filters and speakers.

Below is simple model how sound arrive to the listener. There are three sound source exist. In this layout, mid range sound arrives first, and high range arrives next. Finally, vent output arrives. We do not care about vent output because there is no way to control at this moment. This model simply shows the arrival order caused by diaphragm locations. Below is the passive filter circuit diagram which also affect the delay and the phase of the system. So, we have to measure those two parameters in combination with speaker properties.
Following graphs are the group delay of the woofer. Red line shows the speaker property and black line includes the speaker plus the filter. The frequency range shown is higher than 100Hz. The diaphragm distance from the mic. position is compensated. Below is the phase graph. Red one is the speaker only properties and black one is the speaker plus the filter. We can see the phase shift in case of the speaker only as well as the delay property.
Below is the group delay graph for the horn speaker. We can see some delay at the crossover frequency point which is 520Hz. Below is the phase graph for the horn speaker. We can see some phase shift at the crossover frequency point, too.
When we consider about the group delay value measured above, virtual sound sources looks like the left illustration at the crossover frequency point.

Since we have to give up to align the arrival timing of the sound from two sources, our priority is to match the phase to obtain flattest frequency curve.
Above is the Wavelet analysis which shows frequency and time domain data on the same chart. Red colored shows the high gain zone. This is the example of two sound from different sources which do not match. This causes the phase mis-match. Hence, The gain is lost at the crossover point. Above is the improved property by adjustment of the diaphragm location, little bit, and the cable connection. Time alignment is still have problem but this is an optimum adjustment to gain good connection between High and Low range speakers.

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Whitesunds National Park NM, USA Photo by Yuichi