Triticum Agricolam Posted January 11, 2015 Report Share Posted January 11, 2015 So I just got my AMM-1 the other day and someone mentioned to me that I might be able to test for port compression and power compression with it. This is a totally awesome idea that I would have never thought of so I wanted to give it a try with my test sub. I played a tone through my sub at the box's tuning frequency and used my hand to block the port and sure enough the impedance would spike as I did so. Then I watched the impedance as I turned the power up and once I started hearing some port noise the impedance would rise again. I need to do some more testing to make sure what I'm seeing is port compression and not power compression, but I'm pretty sure this is working like I want it to. Testing for power compression should be easily enough to do too. Just test at a frequency well above tuning and look for the impedance to rise. Does what I'm doing sound like it makes sense to anyone else? "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: Link to comment Share on other sites More sharing options...
Wicks Posted January 13, 2015 Report Share Posted January 13, 2015 Here's an impedance sweep I did on one of my Hertz 8"s By blocking the port you're changing the box from ported to sealed and the impedance would change accordingly which is probly what you're seeing. Port compression could play a similar factor I suppose. This post sent with 100% recycled electrons. 2004 BMW M3Mechman 280A 2 - XS Power XP30001 - XS Power D375 500F of Maxwell SuperCaps (soon to be 1000F) iPadMini2Dash mounted O-scopeAudison bitOne (Remote DRC MP) Highs Amp - PPI Art A404 Hertz HSK130 (HSK165 waiting...) DC Audio DC9.0K 2- DC Audio XL12m2LEGAL - 147.3dB @ 41Hz OUTLAW - 150.2dB @ 45Hz OUTLAW - 145.7dB @ 30Hz JUNE 2014 SOTM WINNER 2014 COLORADO PEOPLE'S CHOICE WINNER SOTM BUILD:http://www.stevemeadedesigns.com/board/topic/141656-wicks-e46-m3-build-bass-turbo-button-and-a-big-new-addition/page-68#entry2802026 Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted January 13, 2015 Author Report Share Posted January 13, 2015 When I said I was blocking the port with my hand, I was only partially blocking it off and it took very little restriction before you would notice a change in impedance. "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: Link to comment Share on other sites More sharing options...
Wicks Posted January 13, 2015 Report Share Posted January 13, 2015 Sure, makes sense. Completely blocking the port will change the impedance characteristics to look like a sealed box. But partially blocking it will only affect the impedance slightly. I saw the same thing when measuring my impedance in my car with the cabin sealed (Legal) vs the door open (Outlaw). Same thing with lowering my window little by little from a sealed configuration. Every tiny change will affect the impedance. I would suspect compressing the port to have a similar effect. Would be cool to see some tests graphed out on what you find! This post sent with 100% recycled electrons. 2004 BMW M3Mechman 280A 2 - XS Power XP30001 - XS Power D375 500F of Maxwell SuperCaps (soon to be 1000F) iPadMini2Dash mounted O-scopeAudison bitOne (Remote DRC MP) Highs Amp - PPI Art A404 Hertz HSK130 (HSK165 waiting...) DC Audio DC9.0K 2- DC Audio XL12m2LEGAL - 147.3dB @ 41Hz OUTLAW - 150.2dB @ 45Hz OUTLAW - 145.7dB @ 30Hz JUNE 2014 SOTM WINNER 2014 COLORADO PEOPLE'S CHOICE WINNER SOTM BUILD:http://www.stevemeadedesigns.com/board/topic/141656-wicks-e46-m3-build-bass-turbo-button-and-a-big-new-addition/page-68#entry2802026 Link to comment Share on other sites More sharing options...
hoit Posted January 13, 2015 Report Share Posted January 13, 2015 feel free to play around with my subs with the amm1! im curious to see how they perform! tuned in! 2007 Chevy Aveo Ls sedan 2 Sundown Xv2 on scv4k @ .5 ohm 2 pair RE XXX 6.5 components on sax200.4 @ 2 ohm Big Three, Three runs 1/0 power from front to back, 1 ground front to back Two runs ground from rear bank to chassis XS power d3100 upfront, 3 Odyssey 2150s in bank Singer 220 amp alt Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted January 14, 2015 Author Report Share Posted January 14, 2015 feel free to play around with my subs with the amm1! im curious to see how they perform! tuned in! Oh man I may do that a bit, but I only have a 1,000 watt amp on hand which would only give those things a tickle. I doubt I even get 1000 watts out of my amp, at least I can find that out for sure. Oh and to Wicks, I've got a test box I've used for some other port experiments. When it get time I'll probably play around with it some more with the AMM-1 to see what happens. Its too bad there wasn't an easy way to measure port velocity. "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: Link to comment Share on other sites More sharing options...
Wicks Posted January 14, 2015 Report Share Posted January 14, 2015 Cool. I'm always down for some out of the box experiments. So an anemometer is used for measuring wind speed. A normal cup or fan anemometer measures air flow in one direction which wouldn't work. But how about a hot-wire anemometer. http://en.wikipedia.org/wiki/Anemometer#Hot-wire_anemometers They use a heated wire which cools as air flow passes over it. The temperature drop is used to calculate the amount of air flow. Seems non-directional so it may work with port velocity as the speaker moves back and forth......? http://www.extech.com/instruments/product.asp?catid=1&prodid=676 Not the cheapest tool around, but eBay has a lot of various options with prices that aren't tooooo bad. Depending on how serious you are with the testing. This post sent with 100% recycled electrons. 2004 BMW M3Mechman 280A 2 - XS Power XP30001 - XS Power D375 500F of Maxwell SuperCaps (soon to be 1000F) iPadMini2Dash mounted O-scopeAudison bitOne (Remote DRC MP) Highs Amp - PPI Art A404 Hertz HSK130 (HSK165 waiting...) DC Audio DC9.0K 2- DC Audio XL12m2LEGAL - 147.3dB @ 41Hz OUTLAW - 150.2dB @ 45Hz OUTLAW - 145.7dB @ 30Hz JUNE 2014 SOTM WINNER 2014 COLORADO PEOPLE'S CHOICE WINNER SOTM BUILD:http://www.stevemeadedesigns.com/board/topic/141656-wicks-e46-m3-build-bass-turbo-button-and-a-big-new-addition/page-68#entry2802026 Link to comment Share on other sites More sharing options...
Triticum Agricolam Posted January 14, 2015 Author Report Share Posted January 14, 2015 Yeah I've heard of folks using hot-wire anemometers to measure port speed. There was a paper put out by Polk I believe on optimizing ports and I think that's what they used. I'd love to have one for testing, but I have a hard time justifying a several hundred dollar tool that really only does one thing. I just need to make friends with some HVAC engineers, those folks use hot-wire anemometers all the time from what I hear. Anyway, I'll test what I can and report back with my findings. "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: Link to comment Share on other sites More sharing options...
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