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DIY Home theater sub project help


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#21 of 30 schan1269

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Posted March 03 2014 - 02:29 PM

Based on your dimensions, I calcualted that your enclosure is tuned to 41.5 hz.  Give or take 1/10hz. 

 

That is way, way, way too high unless you are listening to 80's rock (they didn't record any bass in it).  For that sub, you need to tune 25hz or lower.

 

You aren't listening to the right 80s rock ( ;) )

 

I wonder what would happen if the ports were plugged(the box too big for that?)



#22 of 30 VanillaRice

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Posted March 03 2014 - 06:51 PM

 

I wonder what would happen if the ports were plugged(the box too big for that?)

 

I haven't tried this but I'm interested to see what happens, I have very dense packing foam at work that I could cut to shape and try.

 

Robert, could you suggest modifications to my enclosure to achieve 25hz tuning ?



#23 of 30 VanillaRice

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Posted March 03 2014 - 09:06 PM

Here's the foam I was talking about. Almost resembles the same density that HSU uses with their subs

 

WP_20140304_005.jpg



#24 of 30 Robert_J

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Posted March 04 2014 - 08:01 AM

Plug the port.  That's the easiest thing to do.

 

Your other option is to lengthen the ports.  How long?  60"  That's right each port would need to be 5 feet long to get your tuning down to 25hz.



#25 of 30 VanillaRice

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Posted March 04 2014 - 08:56 PM

Plug the port.  That's the easiest thing to do.

 

Your other option is to lengthen the ports.  How long?  60"  That's right each port would need to be 5 feet long to get your tuning down to 25hz.

 

I'd sooner make a new box.

 

Today I plugged the ports with the foam and gave it a test run. I'm quite sure the frequency response is better than it was. I've reconnected my ep2500 and giving it much more power now.

 

I'm very confused about what I'm supposed to hear between 20-25hz. I get lots of structural vibration in the house from 20-24hz. Practically everything that isn't tied down is rattling and it's not until about 25hz that the tone is much more audible. 26,27 begins to get exponentially louder and 28hz is like a sweet spot. Are room accoustics / low room gain playing a part here ? Are subs with lower Fs and higher xmax parameters very audiable at these frequencies or do they just shake the house panels apart like mine does and the tone is only barely audiable ?

 

My previous living room had hard wood floors and low ceilings. I recall playing a few favourite tracks with low 20hz tones that even my 10" mission m6as sub could pull off. Now that same song, same sub in a different room and it's completely missing from the song. 

 

I also have some serious peaks and nulls in my living room. I'd be interested to graph the frequency response of the sub at my seating position. Is there a cost effective way to do this ? I don't own an expensive calibrated microphone.



#26 of 30 Robert_J

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Posted March 05 2014 - 12:10 PM

Do you have an SPL meter? The Radio Shack analog model is best. That paired with Excel and a free spreadsheet or a free Java applicaton will allow you to plot the in-room frequency response. You can also make sure your panels aren't vibrating. That enclosure should be heavily braced. And you are correct, as you start to get to 20hz it is more of a tactile feel. If you don't have small items secured, they will move and vibrate. There is a lot of energy produced by these large drivers. I have one 21", five 18" and eleven 15" drivers to play around with.

#27 of 30 Robert_J

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Posted March 05 2014 - 12:10 PM

Do you have an SPL meter? The Radio Shack analog model is best. That paired with Excel and a free spreadsheet or a free Java applicaton will allow you to plot the in-room frequency response. You can also make sure your panels aren't vibrating. That enclosure should be heavily braced. And you are correct, as you start to get to 20hz it is more of a tactile feel. If you don't have small items secured, they will move and vibrate. There is a lot of energy produced by these large drivers. I have one 21", five 18" and eleven 15" drivers to play around with.

#28 of 30 VanillaRice

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Posted March 06 2014 - 12:04 AM

No I don't have an spl meter. I've been looking at a few spl meters available online locally and they all have frequency ranges from 31.5hz - 8khz are these some magic numbers ?. Why don't they go up to 20khz ? Would they most likely measure sound outside those parameters but need a correction factor like I can see with the Radio shack model ?



#29 of 30 Robert_J

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Posted March 06 2014 - 07:05 AM

This mic http://www.minidsp.c...surement/umik-1 along with the Room EQ Wizard is all you need to start measuring.  You can use their DSP modules if you want to make changes.  REW will also interface with a Behringer Feedback Destroyer.

 

Very few SPL meters are designed for tuning an audio system.  They are for industrial sites that need to comply with OSHA (Occupational Safety & Health Administration for you non-US based folks) regulations on noise.  We got really lucky on the Rat Shack models and could make them work.



#30 of 30 scot9055

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Posted March 11 2014 - 11:29 AM

This forum is full of details, my brain is easily overloaded on here




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