HELP! Completed sub is bad! - diyAudio
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Old 16th February 2004, 05:38 AM   #1
pne123 is offline pne123  United States
diyAudio Member
Join Date: Jan 2004
Location: bay area
Default HELP! Completed sub is bad!

I built my sub.
It is a ported 118L box. port is 4" and 17" long (uncut flared port kit) so it should be tuned to approx. 20.5 hz.
Driver is a SHiva Mk IV powered by a PE250w amp.

It is bad! My yamaha 8" sealed sub plays louder.

It sounds really distorted like it is blown at low levels. If I can get it to go louder it sounds like it is bottoming out hard but what appears to be very little travel. Nothing is hitting the back of the woofer.
I have tested the amp by powering an old center speaker I have. It seemed to go ok. I had to turn the crossover all the up of course. I tested the driver by hooking up to my main speaker wire. SOunded bad cuz it was not in a box but seemed to function fine.

I have played w/ the phase, gain level, and the crossover. I have turned the crossover all the way down to the 40hzs and the gain to about 1/3 and still it sounds bad.

My receiver is couple yrs old. Has a sub pre-out (rca) but no menu to for settings.

The box is stout. No leaks. The bracing is good unless I have to much. You can see pix here in this thread

a thanks & HT sub UPDATE

or here at this website.

it is a 14x12 room centered in the middle of the 12' wall.

any ideas? please help. my wife is really starting to look at me funny. I really thought I had this nailed.

thank you in advance.
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Old 16th February 2004, 07:17 AM   #2
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Join Date: Oct 2002
Location: san jose,ca
Default bad sub

If You would like some help, I am in san jose, you can e-mail me for my number(no $). I have a full suite of test equip. I do speaker design for my company. john
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Old 16th February 2004, 12:34 PM   #3
JeremyD is offline JeremyD  United States
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Join Date: Mar 2003
Location: New Bedford, MA
All that shelf bracing is probably causing unheard of ammouns of turbulence....But at the low power and output level of an in-home sub, the effect shouldnt be as great as what you are experiencing...
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Old 16th February 2004, 12:37 PM   #4
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Location: Midland, Michigan
Does the driver have dual voice coils?
Make sure they are not connected out of phase with each other.
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Old 16th February 2004, 02:06 PM   #5
pne123 is offline pne123  United States
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Join Date: Jan 2004
Location: bay area
wow thanks. I am in south san jose. blossom hill and 85 area.

If I do not get this figured out in a couple of days, I just might take you up on your offer.

Has for wiring, yes dvc and yes they are right. black to neg. red to pos. ...neg to neg and pos to pos. the wires cross going from on voice coil to the next.
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Old 16th February 2004, 02:23 PM   #6
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Location: Duluth, Georgia
Try just using one of the voice coils. The amp may not like the low impedance of both voice coils in parallel.

Also, I suppose it would be possible for one of the voice coils to be mis-marked out of phase?

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Old 16th February 2004, 03:04 PM   #7
pne123 is offline pne123  United States
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The speaker is dvc @ 8ohms each so I am at 4ohms in parallel.
The amp is rated at 250w at 4ohms and used alot in the same configuration. unless i just got a bad one.

I tried just one vc and it still sounded bad. I forgot to check the other one alone. I might have just one vc bad....
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Old 16th February 2004, 05:47 PM   #8
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Default love solving problems but

I don't do well over the phone or e-mail. I have a day planned at home, cherry and hillsdale, doing speaker work if you are interested.
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Old 16th February 2004, 06:26 PM   #9
JohnSz is offline JohnSz  United States
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Location: Rural NY
I have a first gen Shiva, along with a PE 12DVC, and two of the PE amps. I have the Shiva in a 12x16 room with two open doorways and lots of glass. It produces plenty of bass for HT and too much for some music. I currently have the port plugged, for a low Q sealed. It sounds like something is wrong with yours, or your set-up.

Here are some things you may want to check:

Is your PE amp one with boost or without? For ported, you should have no boost. It is a couple of resistor change, on one of the boards.

How long is the port, not counting the flared ends? I haven't looked at port calcs for this, in a long time, but I get the impression yours might be too short to get 20.5Hz tuning. Are you able to do frequency sweeps? If so, you should get no cone movement at 20.5Hz, if tuned there.

How does it sound with the port plugged?

How hot is your amp getting? Can you still hold your hand on the heat sink?

Also, try other room locations, including the nearest corners.

I assume the new Shivas are still stamped frames. Make sure they are drawn down evenly and the edge is not hitting on a recess, and the frame didn't get twisted.

Some early Shivas had an issue with lead slap on the back of the cone. I doubt that is an issue with yours, but I added some foam at the leads.

I imagine that the Yamaha 8" over produced in the upper mid-bass. Do you have a SPL meter and test tones, to varify? What is lowest freq your mains put out?

BTW, very nice cabinet work.
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Old 16th February 2004, 07:01 PM   #10
pne123 is offline pne123  United States
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Join Date: Jan 2004
Location: bay area
the amp is w/o boost.

I ran my front main speaker wire thru the port and to the speaker. I still have the same problem. It played better do to the higher frequency (i am guessing) but still made the bad metalic noise.

The port is 17" w/o flares

sounds the same w/ the plug port.

did not specifically feel amp but never noticed any heat. not on very long to notice it was bad wrong

i have not moved it around trying to get it to sound better. it does not play at all so....did not see any reason to lub it around the room.

still stamped.

Is it possible that my cut out and recess cutout are to tight and this would cause the problem? The flange is very close (1/32-1/64) to the recess flange. The 11" cutout is also tight.

I am close to my bracing but not touching. The magnet is about 1/2 from the center brace. The braces from center to exterior walls is very close at the opening. If it was touching would it make bad noises? should I get my saw out and cut those back?

thank you
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