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Help with New Sub

Discussion in 'Home Theater Projects' started by Mark_B, Feb 14, 2006.

  1. Brent_S

    Brent_S Second Unit

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    Mark,

    if it helps. HD also has 24"x48"x.75" MDF panels. One or the other of Lowes or HD also carries Baltic Birch and Oak veneered plywood in 2'x2'x.75" and 2'x4'x.75" panels. Keep the dream alive and keep drawing those pictures! :)

    Just because the output capability is there, doesn't mean you have to use it all of the time. Not a great analogy, but nearly every car on the road can go much faster than the posted speed limit, but we'd all be in a world of hurt if we did. :)

    A single 3" flared port should be better than a straight 3" port. If you're absolutely dead set against bending your ports, the only choice is a 3" port, flared or not.

    The 3" port hits .1 Mach (recommended limit) at 150 watts at 20hz. That's still good for 103db @ 20hz. From your current performance goals, you'd probably be happy with only a 3" port. But, remember what they say about power corrupting...before long you'll find yourself thinking about one of those 500 watt amps to get every last available db out of the [email protected], but you'll definitely want a 4" port to match...two would be better.


    wbs
     
  2. Mark_B

    Mark_B Second Unit

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    An update on my progress and a question. Got the parts last week and started construction yesterday. Unfortunately, HD did not have the 16" shelving. Ending up getting 24X48 sheets. They cut it to specs, but unfortunately, were off a little. I originally wasn't going to let them cut it, but it sured seemed faster. Nothing a belt sander can't cure. Got 3 sides glued and waiting for them to dry. Will cut the hole for the driver tonight and get that glued on. I doubled up on the front baffle, so that is now 1 1/2" thick. It's progressing nicely. With luck I can test drive it this weekend. Will wait to do the final finish until its warmer and I can get outside.

    The question I have is on bass boost. The amp has a table on the PE web site at http://www.partsexpress.com/pdf/300-804boost.pdf . I'm not sure what I'm looking at or if I should even care. Can anyone explain how to read the table and what I can use this information for? Can I use a boost to raise the Db on the low level response?

    Thanks.
     
  3. Chris!R

    Chris!R Auditioning

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    My local HD does have the 16' shelving. One thing anyone should be aware of is that one edge is rounded over - they call it bullnose. If you want to trim that edge back to full thickness you may lose 1/4 - 1/2 inch.
     
  4. Brent_S

    Brent_S Second Unit

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    As the chart implies, by changing the resistor values, you can add a bit of boost at the specified frequency (actually across a small range above and below that frequency). Kind of like turning up the bass knob on your receiver or car stereo.

    The vented DVC12 is already going to be pretty much flat to 20hz with a little room gain. No real need for boost there, IMO.

    The sealed DVC12 is pretty close to max power and excursion in the 20-30hz range with the 240 watt amp. 3db of boost requires twice the amp power and roughly 50% more excursion, neither of which you have available. Any way you slice it, you'll max out around 98db @ 20hz, you'll just need a smaller turn of the volume knob to get there.

    Using the boost settings can get you a flatter response curve, at the expense of overall output. A sealed DVC12 example: your current volume setting yields [email protected], which needs 120 watts. A [email protected] boost would get you [email protected] instead of 94.5 w/o boost. But, you need 240 watts for that 20hz tone and only 120 watts for the 30hz. Now, you're listening along and want to turn it up a little more..say enough to hit [email protected] because you've still got 120 watts of output capability left. A 20hz note comes along and the amp tries to keep up, but it clips b/c now you're asking for 480 watts due to the 3db boost. Depending on how conservative the 240 watt rating is...if the amp can briefly deliver 280 watts, you just bottomed your driver before the amp clipped. It's an exaggerated example, but hopefully it helps clarify.

    You didn't say which alignment you decided on. Either way, I'd leave the bass boost stock to start with. At least until you've tried the sub in room. You can always experiment later.


    wbs
     
  5. Brent_S

    Brent_S Second Unit

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    My local HD has the mdf shelving with the bull nose. But, they also have 16"x48"x.75" and 24"x48"x.75" panels with square edges...may be referred to as project boards or project panels, something like that. I'll try to remember to get the exact name the next time I'm in there.

    wbs
     
  6. Mark_B

    Mark_B Second Unit

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    I went with the sealed model. 1.7ft^3. This amp has some sort of feature that prevents clipping, or so the review on PE's site says. I was planning to leave the boost alone for now, was just curious how it worked. The sub will be in a corner of the room and I'm sure that will help.



    I'm curious, how can you tell from the WinSD program when you have reached full excursion and bottomed your driver?
     
  7. Brent_S

    Brent_S Second Unit

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    On the signal tab, set your power to the desired level...in your case, I've been using 240 watts. Then, flip to the cone excursion graph and trace it. The graph shows peak-to-peak excursion. Xmax on the DVC12 is 15.1 so peak-to-peak excursion limits are 30.2mm. You've exceeded excursion when the WinISD graph is > 30.2. Technically, you may not be bottoming at this point, but you've exceeded the useful range of your driver and bottoming and possible damage are in the very near future.

    The max power graph shows you how much power a driver can take at a given frequency to reach Xmax.

    The SPL graph doesn't take Xmax into account...it essentially assumes the driver has unlimited Xmax and power handling.

    You need to look at Max SPL, Max Power, and driver excursion to understand the limits of a given design.

    For the sake of explaining the bass boost option, I didn't want to get into the soft-clipping circuit on your particular amp. Yes, it'll help avoid clipping the amp, but you may still have enough power to drive the DVC12 into bottoming below 25hz or so. And, you're still displacement limited to [email protected], regardless of boost level or power applied. Boost can get you a flatter response curve up to the point of max excursion.

    The most common use of the boost options for your design might be to extend flat response down to say 25hz using a couple of db boost somewhere between 25-30hz and write off everything below that. The boost setting usually acts as the rumble filter in most plate amps...response drops off a cliff a couple of hz below the center frequency of the "boost". You can see the rumble filter in the frequency curves in Darren's review of the amp, although his measured numbers don't quite agree with the stock setting in the bass boost table...could be explained by manufacturing tolerances.


    wbs
     
  8. Mark_B

    Mark_B Second Unit

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    I see why I didn't see it before. I was using the regular WinISD. This stuff is in the WinISD Pro. Maybe you can send me the parameters you are using for the DVC 12. I plugged in the stuff off of the PE website and show it not reaching max, but I don't have some of the information and had to let the program assume, which I hate to do. I also cannot find what the Pe is for this driver. I also added a high-pass filter for the rumble filter at 18.3hz. per information I found searching archives. With the filter in place, it isn't even close to max. It looks like the design will be fine, unless I have something in there wrong. I got all the bracing in and the top on last night. Going to round the corners and start filling in the screw holes this evening. Plan to try it out over the weekend. One other question. When I mount the driver, will I need to add more gasket material? It has a foam gasket now, just curious if I need to add weatherstripping or caulk as I have read on the forums here.
     
  9. Brent_S

    Brent_S Second Unit

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    Didn't realize there was more than one version of WinISD. Well, not counting version upgrades. Speaking of which, sounds like it's time for me to upgrade...I don't seem to have an option for adding a rumble filter.

    For the missing specs, check the Dumax report on the DVC12 specifications tab. Pe is 600 watts for the coils in parallel. I doubt the specs you missed will change your models signficantly, if at all.

    The attached foam gasket should be fine. Some may think it heresy, but I don't even have gasket material on my current subs. Never been able to detect any air leakage. Assuming you're using T-nuts to hold in the driver, you might want to consider some loc-tite on the threads during your final install. I've had bolts work loose a couple of turns now and then.

    I apologize if I made it sound like over excursion was a major concern with your design. As designed, per the published specs, you're absolutely right, you shouldn't have to worry about over excursion or clipping. But, if you get a slightly underspec driver or the amp has a little extra juice, you could get there. Darren's review said the amp could sustain 240 watts into 4 ohms without clipping, but he didn't say how much power it peaked or clipped at. Given it would maintain 292 watts into 2.6 ohms for a few minutes, I'd guess 270-280+ watt peaks into 4 ohms aren't out of the question. Until you just said you were aiming for 1.7 ft^3, I've been using 1.75 (my original suggestion). At 1.75 without the rumble filter, the DVC12 will hit Xmax with 266 watts at 20hz. You pick up almost 10 watts of headroom with your -.05 change.

    If you decide to experiment with stuffing, you'll increase the apparent size of the box, which will lower your power handling. Increasing the box size 12% to 1.9 via stuffing, lowers your max power at 20hz to 245 watts. Again, shouldn't be a major concern, just something to be aware of.

    wbs
     
  10. Bryan Michael

    Bryan Michael Supporting Actor

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    good luck with your project i am on my seccond sub and i moved from crazy to insane i went from 2 15 av to 4 aa 18 in a ib

    i would look in to a pro amp you will have room to upgrade in the futhure also dont skimp on the sub or amp i would save up a little more and get more than what you want so you dont have the bug bighting you to upgrade.
     
  11. Mark_B

    Mark_B Second Unit

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    There is an EQ/Filter tab. I added one from a post on the amp I read. It said to put it in as a Highpass Butterworth filter with an order of 2 and a cutoff of 18.2Hz. With this in place, the graph doesn't show me getting anywhere near full excursion with this amp.
     
  12. Mark_B

    Mark_B Second Unit

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    Well I got 'er done on Saturday and the results were beyond my expectations. The only thing left to do is put a final finish on the box. I put a rolled on a few coats of flat black in preperation for Truck Bed liner I have read about here. In all honesty, the flat black doesn't look half bad. The wife is pleased with the look. She even helped me make the grill for the front. I'll have to wait for the liner paint until we get some warmer weather. (BTW, don't try to use Bondo in the house.)

    As far as performence, it blows my previous subs away in special effects, yet works well with the music. No more of the booming I had with my first sub that was the source of all the complaints, but it still rattles the walls during the pod race in Star Wars. It seems a perfect balance.

    I want to thank all that provided input and guidance during this project. I learned a lot and it was sure fun!
     
  13. Brent_S

    Brent_S Second Unit

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    Way to go! Let's see some photos when you get a chance.


    wbs
     

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