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Resonant freq vs tuning freq


Bret

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Just built some old 15” punch subs and am breaking them in. I designed/built an enclosure for a 30hz tuning and testing shows it ended up 29hz. I determined this by playing test tones and at 29hz the subs don’t move. 

I’m playing sweeps and graphing the sound pressure level and it’s about 2db higher at 40hz than it is at 30hz. I’m really happy with the sound and will use a dsp to lower the 40hz a little, so I’m not asking for help to solve a problem. I’m just curious if any of you could speculate why the enclosure would be louder at 40hz when it’s tuned to 30hz? I suppose the resonant frequency of the car must be the reason. Does that sound reasonable?

 

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Joe x,

im using an app called SPL graph on my iPhone. I’m using the built in microphone. Maybe not a reliable test.

I ran the sweep from 25hz to 100hz and the subs do move quite a bit at 25hz. I just turned down the subsonic filter and ran the test again to see if it was cutting in to my 30hz output and it measured the same. I have no idea what my filter is set at, the lowest it goes is 17hz.

 

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Like others have said, you are probably getting a lot of cabin gain at 40 Hz.  Just because you are tuned to 30 Hz does mean you will get peak output there though, regardless of cabin gain. Depending on the specs of the sub and the box it is in it’s not uncommon for subs to have peak output in 40 Hz range despite being tuned to the low 30s, especially subs with a higher QTS. 

"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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Interesting feedback. This is exactly the info I was looking for. Like I said, I'm very happy with how this enclosure sounds. Its the best sounding setup ive had to date and ive been at this a long time. I had always been told sealed enclosures were best for sound quality and after a long lifetime of using sealed ones, I have to strongly disagree. I guess some people think a flat response means perfection. I really prefer this tuning where the upper-low frequencies  start to roll off pretty dramatically above 40hz while the 25 - 35 hz frequencies are boosted way the hell up. To me it sounds much more balanced even though it certainly is not. To each his own I guess.

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8 hours ago, Bret said:

Interesting feedback. This is exactly the info I was looking for. Like I said, I'm very happy with how this enclosure sounds. Its the best sounding setup ive had to date and ive been at this a long time. I had always been told sealed enclosures were best for sound quality and after a long lifetime of using sealed ones, I have to strongly disagree. I guess some people think a flat response means perfection. I really prefer this tuning where the upper-low frequencies  start to roll off pretty dramatically above 40hz while the 25 - 35 hz frequencies are boosted way the hell up. To me it sounds much more balanced even though it certainly is not. To each his own I guess.

Glad I could help!

While it is true that sealed enclosure USUALLY have flatter frequency response in a vehicle compared to a ported box, it is always the case and there is a LOT more to sound quality then just frequency response.  Like you, I prefer ported enclosures and sound quality is very important to me.  

"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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