GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: The tapped horns: cons, pros and Sound

Post Subject: More tapped horn stuffPosted by JLH on: 5/5/2009

I have been doing some work with integration of tapped horns. I have discovered some interesting things that are not being discussed on any other forums. I’ll start at the beginning so a full picture will be clear.

At first I placed the tapped horn such that its woofer was time aligned with my large tractrix horn’s woofer. I found that this gave reasonable results. However, I felt that the pacing between the tractrix mid-bass horn and the tapped horn wasn’t quite right. I proceeded to make exact distance measurements so both horns were time aligned per the center section of their voice coils. The effect this had was interesting. The bass range from about 50Hz and down, was excellent. However, something was still off about the 70Hz to 100Hz range. There was a strange phasiness to the sound. What to do?

I stopped for a moment and started to think about what was actually happening. Reading back through my notes on tapped horns, I believed I found my answer. The main principle that allows the tapped horn to work involves its varying phase properties. In the low frequencies the phase relationship is such that the front and back side of the cone is in a phase additive mode. Therefore, both sides of the woofer are contributing to the horn. As frequency climbs, the back side of the cone progressively goes out of phase. This gradually reduces the cone’s back side contribution to the horn. What I believe was happening is the phase change of the tapped horn was having an unexpected interaction with my mid-bass horn. This is why I could only get perfect integration over a very short frequency range. Great, what am I going to do now?

Well, after thinking some more, I decided that I could still have proper time alignment, but change the phase relationship between the tapped horn and my mid-bass horn. I did this by keeping the time of flight distance along an arc in reference to the listening position. I then moved the tapped horn along this arc until the two horns stopped interfering with one another. This worked like a charm. Instead of being right next to the mid-bass horns, the tapped horns are now about 2 and ½ feet to the outside of each mid-bass horn. Sound location is not an issue because the tapped horns are only covering material below 80Hz, so they are very non-directional. Problem solved. So, far this is the best sound I have had in my system. I’ve got the dynamics I’ve always loved, but have better integration than before.

Rgs, John

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