posted
Get a medium sized sealed box in the car (facing whichever way you plan on facing the box), then take a measurement of every freq, 40Hz, 41Hz, 42Hz, 43Hz, etc. Then what you want to do is take the same box out of the car, and place the mic the same distance from the box, (if you faced it back in the car, then make sure that you take the measurement from the cone, to the back, then back to where the mic was) and take the measurements again, then you will take the biggest difference in peaks and that will be your res freq.
I think that I have said too much....................I must go now................the SPL Ninja's are upon me Need more power? UP YOURS!! with Excessive Amperage! Posts: 6067 | From: Northern California | Registered: Nov 1999
| IP: Logged |
quote:Originally posted by shizzzon: hey, thanks for the info as well, but after taking measurement in car from trunk, you say take the box out.
Can you re-say what you said after taking the box out of the car cuz u kinda lost me at that point, hehe thanks.
Take the sealed box out of the car, then set the mic, the same distance from the box, as it would be in the car, and take the measurements again, and record what you get. Then you take the siggest difference between the two and that is your Res freq.
I think that I have said too much....................I must go now................the SPL Ninja's are upon me Need more power? UP YOURS!! with Excessive Amperage! Posts: 6067 | From: Northern California | Registered: Nov 1999
| IP: Logged |
posted
ok, just to clarify cuz i have to be picky so i understand this right-
The illustration u were making with theoretical SPL, when u take the box out, the illustration was sayin peakin at 132.2 Db. By taking the box out of the car and metering it, your new Db numbers should be a lot less due to no cabin gain, correct?
So the illustration u were sayin is like 130, 132.2, 132.2 and so on, if cabin gain is 18 db, most of the new Db numbers being shown on the meter would be like 112Db, 113 Db 114 Db, correct?
posted
You got it. The only reason you have to take the box out and measure it is because it will not have completely flat response, and the difference between the two readings is your cabin gain.
-------------------- 1995 Grand Am GT Nakamichi CD-45z Pair of Audiocontrol EQT's Audiocontrol 4XS Crossfire TEK100.2 Illusion Audio ND-6 Crossfire VR142 Image Dynamics CD1E V.2
Looking for the following: Image Dynamics IDMAX 12" Crossfire BMF1000d or VR1000d Posts: 48 | From: Buffalo | Registered: Oct 2002
| IP: Logged |
posted
When measuring the box outside the car, you should point it up in the air and put it on a table that isn't much bigger than the box, because reflections in the region of 40-60hz will partially mask the right car peak, OR, use a ground-plane method (which is possibly the better option but you have to know how to do it, read Vance Dickason's Loudspeaker cookbook, basically you put the box on the ground, point it at the ground a little bit (like a few degrees) and then put the microphone on the ground a couple feet away, make sure that there is about 25 feet of space all the way around the box to prevent reflections).
Also, take your measurements from the micing location with the box in roughly the right location for the final install.. That way, when you normalize the two curves (more on that later,) you will get ALL the car effects correct.
Normalization will give you the real "response effects" of the car. That is, if the box response is the same in both sets of data, when you divide the car response by the out-of-car response, you'll get a graph of just the car effects.. The upper peak of this around 50-80 hz is the one you want to shoot for in SPL
ShadowStar
-------------------- You can't build a reputation for what you're GOING to do.. But you can build one for TALKING about it!
It's all about knowledge, love and respect. Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
| IP: Logged |
What sealed box I should make? I have Alpine Type R. Alpine recommend 0.7-1cu.ft. sealed box. So ~0.85cu.ft box will be good?
For SPL competition I will use two Type R's, but to findout car resonant frequency I can use only one Type R subwoofer? Right?
ShadowStar said that there should be about 25 feet of space all the way around the box when measuring the box outside the car. If my garage is 10ft.width and 16ft. length, so can I expect accurate results? Because I don't have so much space
Thanks.
-------------------- Team Adassa Audio -------------------- Head Unit: Alpine CDA-9815RB Front: 2 x Alpine SPR-17LS Subwoofer: 2 x Alpine SWR-1222d Amplifier: Alpine MRV-F545 for components Amplifier: The Warlord for subs Posts: 24 | From: Europe | Registered: May 2007
| IP: Logged |
-------------------- Team Xtreme Loud Audio. Street B North East Stetsom Sales Rep Posts: 1431 | From: springfield | Registered: Apr 2004
| IP: Logged |
posted
Thanks. I found out my car resonant freq already. Tryed with few sealed boxes and result was almost the same.
-------------------- Team Adassa Audio -------------------- Head Unit: Alpine CDA-9815RB Front: 2 x Alpine SPR-17LS Subwoofer: 2 x Alpine SWR-1222d Amplifier: Alpine MRV-F545 for components Amplifier: The Warlord for subs Posts: 24 | From: Europe | Registered: May 2007
| IP: Logged |
![[Smile]](smile.gif)
Printer-friendly view of this topic