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Finally built a new sub (now whelmed)

Discussion in 'Home Theater Projects' started by Dennis_H, Jul 25, 2007.

  1. Dennis_H

    Dennis_H Well-Known Member

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    I bought a Tempest several years back along with a PE 250 W plate amp (the one with the remote) with the intentions of building a great new sub. Didn't get to it until this weekend. Used WinISD and built a vented box that is close to 13.5 cu ft after driver and ports. I tuned it to around 18hz with 4" diameter 13.5" length flared ports. I tried it out last night and it did not seem to have near the punch I thought it would. I played Toy Story 2 several times and it doesn't sound great or give any real punch. I have a huge volume room because it is vaulted to the second story and open everywhere. The sub was sitting out in the middle on it's side, driver facing me.

    I know it will give some more impact in a corner, but I wanted to fire it up and make sure it worked before putting it there. I get a terrible noise that sounds distorted when I hit it with with TS2 where Buzz blows up all the robots in the beginning. I'm pretty sure that I have leads or speaker wire slapping the driver also. I'll find a way to get those out of the way. It may sound a little better when I stuff the ports, but not a lot. I play my old 4.4 cu ft blaupunkt based sub I built a long time ago tuned to about 27 and it rattles the house. I really expected more out of it.

    WinISD says it should be flat to about 17 Hz, but I included some numbers measuring it vented, stuffed, and the old sub. Used RS digital SPL meter C weighted about 3 foot from the drivers facing them. I used the NCH tone generator program to drive the subs. It looks like it should be loud, but it doesn't seem even half as loud as the old sub even though it measures higher. I did change volume between tests, but not during.

    Freq vented sealed old
    60 110 113 109
    56.6 109 112 107
    53.4 110 111 107
    50.4 112 112 107
    47.6 111 113 107
    44.5 110 112 105
    42.4 109 110 102
    40.0 108 109 100
    37.8 109 108 100
    35.6 106 107 103
    33.7 107 107 104
    31.8 105 105 102
    30.0 104 104 101
    28.3 105 105 104
    26.7 105 104 102
    25.2 104 103 102
    23.8 102 101 99
    22.4 100 98 97
    21.2 97 96 94
    20.0 95 93 91
    18.9 92 90 86
    17.8 90 86 82
    16.8 87 84 78

    Any ideas? Does the sub need some break in time? Is the through the roof group delay killing me? I know fixing the leads to get rid of the slapping sound and putting it into a corner will help, but I measured the little on a couple feet from the walls too.

    Thanks,
    Dennis_H

    BTW, should I ask this on a different forum since the DIY section here seems to have died?
     
  2. Robert_J

    Robert_J Well-Known Member

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    The plate amps have gone through numerous changes over the years. Did yours come with bass boost or no boost? What's the SSF? Did you apply the correction to your SPL meter numbers?

    Did you measure your Blau sub? It may have an hump in the frequency response since it is tuned higher? You may be used to listening to "bad bass" and not used to a flat frequency response.

    -Robert
     
  3. Dennis_H

    Dennis_H Well-Known Member

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    The instruction sheet says it comes with no boost and has the values to change if you want some boost.

    I guess I don't know what SSF is...

    I did not apply any correction to the meter reading, so I know that the values should be somewhat higher on the low end. Used C-weighted, but that is only so good. That's why I compared to the old sub to see what the levels were on it also.

    The 3 columns are Tempest vented, Tempest sealed ports, and the old Blau. I know that the amp in the old sub has some bass boost on the low end and it seems to work out OK for that sub. It has a dip around 40, but it doesn't seem too noticeable. The bass boost kicks in where it really starts rolling off and keeps it flat enough to about 24Hz where it starts dropping.

    I know I didn't have a great sub, but I never had any bad distortion that I hear in this one when it hits the mid 40s. The rattle or slap is really bad, so that is job 1. I'll tie wrap the wires to the frame to see if that helps.

    Thanks,
    Dennis_H
     
  4. Robert_J

    Robert_J Well-Known Member

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    It may also be tinsel lead slap. Glue a small felt or foam pad to the cone so if the leads are touching it, you won't hear anything.

    You measured the subs at 3 feet but are your listening impressions taken from the same location? Try measuring the sub from the listening position. That will let you know if you are sitting in a null in your room's response.

    -Robert
     
  5. Dennis_H

    Dennis_H Well-Known Member

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    Yes, my initial listening was done 5 or 6 feet in front of the driver. Once I get the slap fixed, I'll move it to where it's supposed to sit and put it back with the driver on the bottom. I think I have about about 4500 cu ft volume in that room with big vaulted ceilings, so I know I am not going to pressurize the room with this sub, just want it to be better than the one I already have.

    What do you think about break in? Will it loosen up a little after using it?
     
  6. Robert_J

    Robert_J Well-Known Member

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    After break-in the measured parameters may change but there will be very little change in output.

    The Tempest has been around for years and I've never once read the description of "underwhelming" in the same sentence. Do you have another amp to check the sub with? Maybe an old receiver?

    -Robert
     
  7. Robert_J

    Robert_J Well-Known Member

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    What are you plate amp settings? Is the cross-over knob turned up to the max? What's the level setting on the amp? Do you have the remote module connected?

    I just ran a sim in Unibox and this thing should be blowing your roof off.

    -Robert
     
  8. Dennis_H

    Dennis_H Well-Known Member

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    I have a small sub amp that I may be able to hook up, but it's only about 40W or so at 4Ohm. I may be able to dig my son's receiver out of his room and give it a shot.

    It is wired with the voice coils in parallel. Actually they both go to a dual binding post block with the bridging bars in place. The amp has the crossover all the way up and the remote module works fine. The volume and frequency controls have lights and are operational. The box is not stuffed at all. The ports definitely put out a lot of air near the tuning point. The driver isn't moving a lot at that point, so all that seems to be correct. When the ports are stuffed, the driver moves quite a bit.

    I also tried disconnecting the shorting bars and running a single VC to make sure I didn't really screw up and wire them out of phase. Wasn't the issue.

    I did get the amp to shut down once when I was running 16hz sine wave through it. I was watching the driver and it was nowhere near it's excursion limits.

    Dennis_H
     
  9. Dennis_H

    Dennis_H Well-Known Member

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    OK, I'm a little bit of an idiot. I knew everything went too smoothly. I used 3" diameter ports instead of 4". Looks like the tuning drops to about 13.5 or so, but it rolls off much earlier. I'm not home, but thinking back, the circumference was under 11" since I wrapped a piece of paper around it, so I used 3" ports instead of 4" that I thought I had when I modeled it. Doesn't explain everything, but it's a start. I'll find a way to cut those down to 7.3" with the flair and join them back together. I'll get this and the leads done tonight and see how I feel about it.
     
  10. Ryan Schnacke

    Ryan Schnacke Well-Known Member

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    "The sub was sitting out in the middle"
    "I know it will give some more impact in a corner"

    Its also a good idea to eliminate the obvious problems before you ask for help troubleshooting. Take 5 minutes to drag it to the corner.
     
  11. Robert_J

    Robert_J Well-Known Member

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    You asked earlier about SSF. Subsonic filter. The majority of the PE amps come with an SSF set at 20hz. It starts rolling off the lows at that frequency at a rate of about 12db/octave. So playing a 16hz tone through it won't ever get you close to max excursion.

    Was there any particular reason you went with such a large enclosure? Most of Adire's published designs for the Tempest are much smaller.

    -Robert
     
  12. Dennis_H

    Dennis_H Well-Known Member

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    The reason it is so large is that it will be replacing an endtable that is the same size. I don't think that amp rolls off at 20 with the default resister values set to no bass boost. They list the values and I kind of interpolated that it should be a roll off under (what I thought was) the 18 Hz tuning frequency, close to 15 or 16.

    The reason I didn't put it in the "correct" position is that I have to move a bunch of stuff to get it there and I don't want to try to move it in and out till I am sure I have it working correctly. When I measured the old sub, I did pull it out of it's corner to near the position that the new one was sitting.
     
  13. Robert_J

    Robert_J Well-Known Member

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    What's the part number of the amp? PE keeps their old pages up for research but you need a number to find it

    And based on your new tuning, you can push the sub pased xmax at around 25hz to 30hz. You should still be hitting 110db based on Unibox modeling.

    -Robert
     
  14. Dennis_H

    Dennis_H Well-Known Member

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    Part number is 300-793. Here is a link to the PDF file.

    http://www.partsexpress.com/pdf/300-793.pdf

    It is straight from the factory with no boost, but they don't say what the frequency cutoff is. I'm not sure how to tell from this. I guessed any rumble filter would be low enough when configured with no boost, but after looking at this again, I may need to change the R24 value. Don't know what to change it to though. Guess I could give it a 1 dB boost at 20-24 which changes the Fc to 14Hz.
     
  15. Patrick Sun

    Patrick Sun Moderator
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    You'll be getting plenty of chuffing from using 3" ports. How many ports are in the enclosure?

    It still seems like something's wired out of phase.
     
  16. Robert_J

    Robert_J Well-Known Member

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    That's the standard resistor configuration that gives you no boost and an Fc of 20hz. With your current setup, you want to change the resistor values to give you a 1db boost and an Fc of 14hz. If you change tuning, shoot for a 1db boost and an Fc a few hz below the tuning frequency.

    -Robert
     
  17. Brent_S

    Brent_S Well-Known Member

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    According to a rumble filter calculator I picked up somewhere, your Fc is 16hz with a Q of .72...essentially no boost.

    The slapping sound you're hearing may also be the amp clipping. I used to have my sub amp misconfigured for 8/4 ohm operation and on more agressive soundtracks, it sounded like my grills were rattling against the driver...fixed impedance setting and could drive the subs harder without any noise at all. Point being, amp clipping creates "unusual" sounds that can be mistaken for something else being wrong in the chain.

    Your perception in loudness difference between the Blau and the Tempest, with nearly equal db measurements is most likely due to the Blau producing way more harmonic distortion. "Good bass" versus "bad bass", as Robert put it. This used to be a common response when people upgraded from a CC/BB sub to an SVS/Hsu...some would wonder what all of the fuss was about. Additionally, unless the subs were measured at the same gain, same physical placement for meter and sub, an inroom comparison is nearly pointless...sorry, even a few inches difference can mean big dips/peaks.

    From your measurements, I'd say the sub/amp are probably working fine given the tuning mistake. The amp may also be running out of steam before the SSF effects things causing a droop in your SPL readings. Looks like you're getting it pretty close to the 250 watt sims Robert mentioned, though. Also, even measuring at only 3 feet in room, you'll be subject to room effects.

    I've got a DVC15 (fraternal twin to theTempest) in 5.9 ft^3 tuned to 17ish hz, corner loaded. My room is about 3500 ft^3; with room gain, I easily get 100db down to 10hz (no SSF) without the driver breaking a sweat.

    I think you're underwhelmed mostly from the good bass/bad bass comparision, possibly some room placement issues, and maybe a sagging power supply in the 250 watt plate amp. Otherwise, rock on! [​IMG]

    -Brent
     
  18. Dennis_H

    Dennis_H Well-Known Member

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    OK, the mods can change the thread title... I am now plenty whelmed [​IMG]

    I got home and changed the ports. Not too bad to cut them down, just had to find a way to join them again. A trip to Home Depot and that was fixed.

    Removed the driver and tie wrapped the wires. Put on new rope caulk to reseal it, and noticed back in the corner something didn't look right. Found the cutout from my binding posts floating around in there. I thought I had everything cleaned out and vacuumed before I mounted everything, but somehow that was still there.

    I left the driver on top and ran a 45 hz tone through it which is where it was really making noise yesterday. I wanted to make sure there was no tinsel lead slaps, so I increased the volume till the driver was moving enough to know that there was no issue.

    Reinstalled everything still in the middle of the room and the difference was incredible. Definitely a huge improvement at the same location. I don't know if the noise was that piece of wood bouncing around, or the wires slapping, but that was gone. Everything seemed to be great. Maybe the driver didn't seal well? It should have been fine with the rope caulk, but who knows? I moved all the furniture and got it to it's new location and fired up Toy Story 2 opening scene, Incredibles opening scenes, and then Blue Man Group DVDA. It all sounded great. Haven't taken measurements yet, but there was a huge improvement.

    I cranked it all pretty good and didn't hear any amp clipping. I thought maybe I just didn't know good bass, but now that it's working, I know nice clean bass...
     
  19. Robert_J

    Robert_J Well-Known Member

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  20. Dennis_H

    Dennis_H Well-Known Member

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    Think I'll work at outgrowing this one first, but $650 for a retrofit... May have to think about that in a couple years when my wife and family are gone again.

    I didn't tell my wife I changed this. I replaced an endtable that is kept covered up with a large tablecloth. I'll see how long it takes for her to notice that the seat vibrates. She'll probably think I put shakers in the couch at first.

    I did put a set of shakers on the bed frame while she was gone on this trip too. We watch a lot of movies in our bedroom, but can't turn the sub up too loud in there since that's usually when the kids are asleep. It gives a nice little reminder that there should be more low end in the movie. So there is a lot more bass in the house when she gets back.

    And all this started because I needed to clean out the garage while the family was visiting in-laws. I was not going to put those projects back in the garage after organizing it...

    So I guess the moral is, hide your upgrades in the garage till they're old and you can say you've had it for years and it didn't 'cost' anything to upgrade.
     

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