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Triticum Agricolam

6th Order Port Area Experiment

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On 8/6/2017 at 1:32 PM, WalledSonic said:

But it seems that near the tuning frequency, the large port prevents impedance rise.

Looking forward to more data!  Cool stuff man

That's what I'm seeing.

Ditto! 


2001 Ford F150 XLT SuperCrew 5.4L 2wd, Mechman 240A, Jensen VX7020, Boston Acoustic GT-42, Kicker KS68's, Power Acoustik BAMF 5500/1D, 2 Polk Audio MM1540DVC's in 3.25ft Sealed.

2000 Toyota Solara SEV6, Jensen VX7020, factory JBL amp and speakers.

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Now, post up in-car response graphs of each. That's what really matters ;)


1996 GMC Sonoma
Four Fi BTL Neo 18's In 2:1 6th Order Bandpass
2 Ampere 5k's @ .5

TEAM FI
TEAM #LITHIUMCANTDEMO

 

On 10/20/2013 at 0:37 AM, KillaCam said:

Fucking with a Prius driver is like making fun of a disabled kid. Pussies.

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34 minutes ago, Raptorman said:

Now, post up in-car response graphs of each. That's what really matters ;)

Although I'm down with any and all data, I dont know if in-car response curve is necessary to illustrate the point of this thread.  If the in-car response somehow affects the way the driver loads/unloads at or below tuning, then I could see how that may be helpful. 


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It's completely necessary. It's the most necessary thing to test IMO. Unless this isn't a mobile audio forum and our ears don't perceive pressure-levels and only perceive impedances lol.


1996 GMC Sonoma
Four Fi BTL Neo 18's In 2:1 6th Order Bandpass
2 Ampere 5k's @ .5

TEAM FI
TEAM #LITHIUMCANTDEMO

 

On 10/20/2013 at 0:37 AM, KillaCam said:

Fucking with a Prius driver is like making fun of a disabled kid. Pussies.

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Other points to be made are "how much power you can put to a speaker" and "how low it can actually play before it launches".  I think all are valid points, really, so fair enough sir.

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Chevy Sonic Wall (4) 15's on 10k Build Log

https://www.stevemeadedesigns.com/board/topic/209412-2015-chevy-sonicwall4-15s10klithiumlarge-case-hairpin-us-alts/

(4) Fi SP4 15's | (2) Ampere 5Ks | Active! | Arc KS600.2 & KS125.2mini | CDT Silk Domes | Silver Flute 8s | 240Ah JY | US Alts

Jeep Wrangler JK (4) 8's in a 4th Order Build Log

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1 hour ago, Raptorman said:

Now, post up in-car response graphs of each. That's what really matters ;)

I intend to. I think both in-vehicle and halfspace measurements are useful so plan on doing both as soon as I get time. 

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"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

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I got some time today to take some SPL/frequency response measurements.  I was hoping to test everything all at one, but I screwed up when I was making the lower tuned, large port configuration so it wasn't included in today's testing.  I'll get to it eventually.  For today I tested the large and small rear port, higher tuned configuration, the sealed rear chamber config, and the lower tuned small rear port config.  I was able to take measurements both outdoors and in-vehicle.  Over all I tested 48 different port configurations and power levels.  Its a lot of data but I'll try to organize it and present it as best as I can over several posts.  

So first off, here is my outdoor testing apparatus:

5994d019eef89_2017-08-1614_05_23.jpg.a0f3f7c34e9368c1763a1de018726dd1.jpg

Mic is one meter from the port opening.  I measured at 38 volts (about 360 watts at 4 ohms) and then decreased the input signal in 4 dB increments down to -20 dB.  This should show how the frequency response changes (if any) over different power levels.  I picked 38 volts for my max power level since that's about all I dare put into my SA-12 at 15 Hz.  That should be pushing it right up to Xmax.  For the in-vehicle measurements is pretty much the same setup in my Durango.  I put the box against the tailgate with the port firing up, mic was on the passenger side dash. 

 

So, on to the first test results.  Here is the the plugged port configuration (effectively a 4th order):

5994d17a0c860_PluggedPortHalfspace.png.fb89ceb23224ef5a76f150f5ff2e4cf2.png

The frequency response looks pretty consistent across different power levels (which is what we want).  To highlight differences, in the measurement software I can offset the measurements, so what I do is I offset the lower power levels so they are equal to the max output (-0 dB) measurement.  Ideally the lines will then be all stacked on top of each other.  If we are getting any compression (either port compression or power compression) that will show up as the higher power measurements being lower than the lower power ones.  Here is what we get:

5994d1760941c_PluggedPortHalfspaceEqualized.png.0158ae426c4189a2bc9375c58c8548d2.png

All the lines are stacked up on top of each other well, this is good.  

Now the large rear port configuration:

5994d284252f5_LargePortHalfspace.png.fe00d24fc6d5db79a2c154a97c2d8cf7.png

And here they are with the measurements offset:

5994d28070a98_LargePortHalfspaceEqualized.png.737c0d2fdc863e1138029505f33862ba.png

Overall this looks pretty good, we can start to see the effects of a little port compression between 30 - 40 Hz.  You will notice the yellow line (higher power measurement) is a bit below the lower power lines.  Probably loosing a little over a dB to port compression at that highest power level.  

Here is the small rear port config:

5994d3807d35b_SmallPortHalfspace.png.f903c7ca9dd523ae4c303049574db18f.png

The offset measurements:

5994d37cdd6a1_SmallPortHalfspaceEqualized.png.85ec5d255ea3854bf4c71facc64e719b.png

With the configuration we can see much more significant losses to port compression.  Here is a more zoomed in view:

Zoomed.png.5f217166acd5444495d472ac76edb047.png

Below 45 Hz you can see at each increasing power level there is a further reduced increase in output.  Comparing the highest power level measurement (the red line) to the lowest (the yellow line) there is about 2.5 dB of output that is lost to compression between 30-40 hz.  

Here is the lower tuned, small port config:

5994d50d18667_SmallPortLTHalfspaceEqualized.png.c4b4330baf8e816f4e874d750cacd351.png

The results here are similar to the higher tuned small port config, the port compression doesn't become apparent until a lower frequency due to the lower tuning.  

 

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"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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How do those four configurations compare to each other?  Here is the output of all four at the highest power level:

5994d5d290f45_Halfspace0dB.png.893179c9bc3f732d7e2dc130108968a9.png

The yellow line is the large port config, the pink line is the plugged port (4th order) config, the red line is the small port config, and the blue-green line is the small port lower tuned config. 

So the whole reason I performed this experiment was to see how a series-tuned box will small rear port area performs compared to one with large rear port area.  Does the small rear port area config get louder?  The answer is yes, and no.  It depends on the situation.  Between about 42 - 64 hz it does get louder, above and especially below the large rear port area config beats it though.  What I find interesting is the config with the highest peak output is the plugged rear port (4th order) configuration.  It has the highest peak output of everything by a fairly significant margin.  You can also see that the large rear port config has the widest bandwidth (significantly). 

Based on what is shown here with the SPL measurements what I theorize is happening is at higher power levels the small rear port configuration gets so much port compression that it begins to perform somewhat like a 4th order bandpass.  The peak output increases, but at the expense of higher & lower frequency output (and reduced bandwidth).  Since the rear chamber still leaks into the front chamber, you don't get quite the peak in output of the 4th order config, overall the performance ends up being somewhere in between the large rear port config and the 4th order config.  If you go back and look at the impedance plots, they show pretty much the same thing with the small rear port config measuring between the large rear port and plugged rear port configs.  

Next up will be the in-vehicle measurements.  I'll try to get those up later tonight. 

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"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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what was the difference in rise between the 3 styles?
 

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