I typically use my POC3 TH along with my Blastoramas as part of a mobile "PA" system that can be powered off of the car audio amplifiers installed in my car. The setup usually works pretty well for background and loud (but not conversation-threatening) playback. Depending on what time the "gig" finishes, I sometimes just toss them back in the car and use them as the car's system until I get home, and then reconnect the car audio speakers there while I'm packing away the POC3 TH and Blastoramas.
The POC3 TH sounds way better than I had expected it to sound when used in-car (particularly considering that its mouth is maybe about two inches away from the back of the trunk), and it was noticeably able to take more power before the driver started complaining.
I was curious as to the reasons why it sounded better than I expected, so hooked up my DATS and measured the POC3's impedance curve when located on the ground, and then again in-car with the trunk closed (see attached image). Along with a slight reduction in the resonance frequency, it looks like the car's cabin significantly changes the impedance right around where the middle impedance peak starts, which is around where the driver's excursion peaks in its pass-band. In fact, leaning against the trunk resulted in even further reduction in the peak, to the point that the impedance curve started resembling that of vented alignment with its two peaks.
The reduction in impedance suggests that the driver's excursion is being reduced a bit, which would explain the impression that the volume could be turned up a bit more before the driver ran into excursion problems. Now I'm curious about if this effect can be emulated and modeled. Simple boundary loading changes in HornResp (specifically going from 2*PI to 0.5PI loading) explains quite a bit of the change in impedance. However there's something additional going on around 60 Hz, some sort of resonance that's dropping the impedance even further than expected. That's what I'm curious about modelling. A 60 Hz resonant chamber or horn perhaps?
The POC3 TH sounds way better than I had expected it to sound when used in-car (particularly considering that its mouth is maybe about two inches away from the back of the trunk), and it was noticeably able to take more power before the driver started complaining.
I was curious as to the reasons why it sounded better than I expected, so hooked up my DATS and measured the POC3's impedance curve when located on the ground, and then again in-car with the trunk closed (see attached image). Along with a slight reduction in the resonance frequency, it looks like the car's cabin significantly changes the impedance right around where the middle impedance peak starts, which is around where the driver's excursion peaks in its pass-band. In fact, leaning against the trunk resulted in even further reduction in the peak, to the point that the impedance curve started resembling that of vented alignment with its two peaks.
The reduction in impedance suggests that the driver's excursion is being reduced a bit, which would explain the impression that the volume could be turned up a bit more before the driver ran into excursion problems. Now I'm curious about if this effect can be emulated and modeled. Simple boundary loading changes in HornResp (specifically going from 2*PI to 0.5PI loading) explains quite a bit of the change in impedance. However there's something additional going on around 60 Hz, some sort of resonance that's dropping the impedance even further than expected. That's what I'm curious about modelling. A 60 Hz resonant chamber or horn perhaps?
