THs in cars...

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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?
 

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  • 2016-04-19 (1).png
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Sure, here is the hornresp input:

ID=39.00
Ang=2.0 x Pi
Eg=2.00
Rg=0.00
Fta=1.02
S1=82.36
S2=91.02
Par=10.23
F12=0.00
S2=91.02
S3=252.44
Par=191.23
F23=0.00
S3=252.44
S4=514.98
Par=153.78
F34=0.00
S4=514.98
S5=533.16
Par=12.50
F45=0.00
Sd=333.30
Bl=16.32
Cms=1.88E-04
Rms=4.63
Mmd=118.73
Le=1.55
Re=3.80
TH=1
Vrc=0.00
Lrc=0.00
Ap1=0.00
Lp=0.00
Vtc=415.00
Atc=350.00
Pmax=100
Xmax=5.0
Path=0.0
Fr1=0.00
Fr2=0.00
Fr3=0.00
Fr4=0.00
Tal1=100
Tal2=100
Tal3=100
Tal4=100
Comment=Mobile T-5 - Sundown E-10v2 D2 (10.75" Internal)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
FILTER
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
0 0 0 0
0.50.50.50.5
0.50.50.50.5
SSSS
1111
1111
2222
1111
111
000
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Just to give credit where credit is due, this is not my original design. I modified the Cinema T-6 home theater horn designed by lilmike on AVSforum.com
 

just a guy

Member
2006-05-12 6:59 pm
The problem was on my end. I have no idea why but I did resolve it.

I saved the record that gave the results as posted in post 6. Then I imported this one, which is exactly the same except for Eg. https://dl.dropboxusercontent.com/u/1642665/E-10Horn.txt

Then I ran the sim and got the results you and Patrick were getting. Then I went back to the first import and ran that again and it was now giving same results you were getting. So I have no idea what happened.

Originally Hornresp said it was an invalid file but it loaded it anyway, and gave the results as shown in post 6. But now it's all better for some reason.
 
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