My sub is talking through the vent

Russell R · 09-14-2003, 07:45 PM

Hello,
I have recently built a 142.5L, 21hz tune. I ran spl's today without any other speaker playing and noticed that the lower octave has serious vent noise. Somewhere around 40hz and below. The levels are only at an average of 89db from 40hz to 16hz. What can I do to remedy this? Larger port? Multiple ports?

Thanks,
Russell

Jake K · 09-14-2003, 07:59 PM

What size ports are in there now? And what driver is it?

Russell R · 09-14-2003, 08:48 PM

I have a Shiva MKIII with a 4" i.d. flare. I followed the Adire EBS alignment but raised the tune from 18.1 to 21hz. After re-running the numbers with WINIsd, both tunes in a 142.5L enclosure will have high velocity through a 4" port. Why did I not notice this beforehand? Oh well, the sub is not cosmetically finished; I guess the upper end cap will come off to house multiple ports. Looking at 3 - 3" i.d. straight tubes roughly 23" long each. How does this sound? The mach with the single 4 is .19, but the mach with the 3 -3" is .04. Should be better. Any thoughts or other ideas?

Thanks,
Russell

Jake K · 09-14-2003, 08:50 PM

A 4" flared port should be more than good enough for a shiva, should it not?

Russell R · 09-14-2003, 10:03 PM

Well, that was my understanding before I built this. It was my fault. I should have looked closure at the velocity. Just thought that there could be nothing wrong with a CANNED recipe. Should a 4" flare be enough? Maybe I did something wrong. I calculated the internal volume of 142.5L and added end caps to this. The tune was higher, but it did not affect the velocity that much. Will try the 3-3.

Thanks,
Russell

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Jack Gilvey · 09-14-2003, 10:19 PM

You're getting "port noise" at 40Hz with a 21Hz Fb? Never had a noise issue with my Shiva 141L 18Hz EBS, same 4" port.

Russell R · 09-14-2003, 10:43 PM

Yes, it is a chuffing sound through the port. Only on the lower freq's. What could cause this? If everything was perfect, according to WINisd; the calculations indicate a high velocity. What should be my next logical step?

I played around with sinewaves today up to 90 Hz. I have some room modes that I want to address, but without adjusting my gain; there were freq's in the upper range around 120db and at the lower end of the spectrum around 87db. Room needs work.

I will post some in-room curves soon. The sub does put out, just needs a tweak.

Thanks,
Russell

Jack Gilvey · 09-14-2003, 10:53 PM

Is it audible at all during actual use (assuming you don't listen to sine waves for fun)? You can still get some noise with a good design. That's the same port SVS uses, and it's the one used in the $3500 Ariel SW12.

Russell R · 09-14-2003, 11:12 PM

During playback of HT and 2 channel, I do not hear the noise. If I am playing sweeps or sines then I can hear it at certain freqs. Should I change anything? It makes me nervous to think that I can hear chuffing on a 20-40 Hz tone @ ~90-95db. I placed a pillow over the port during tests and it stopped the sound. The pillow shook with the pulses.

Russ

Dan Hine · 09-14-2003, 11:46 PM

Quote:

During playback of HT and 2 channel, I do not hear the noise.

Then don't worry about it.

Jack Gilvey · 09-15-2003, 07:46 AM

Yeah. If it really bothers you, buy some PR's.

Russell R · 09-15-2003, 08:49 AM

Ok, maybe I am making a big deal about it. You are right. Who sits around the house listening to sinewaves anyway. The only time that I hear the noise is when I am pushing the sub hard anyway to reproduce the lower freqs. PR's and sealed are in the future. I have the DIY bug.

If I were to change out the port to multiple 3", would there be a difference? According to software, there should be slower air speed through the ports. If I had to do it all over again, would I use multiple ports; that is the question at hand.

Will continue to tweak room and listen/enjoy the boom.

Thanks,

Russell