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Old 5th December 2005, 05:41 AM   #11
simon5 is offline simon5  Canada
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troyhenson don't forget to check the excursion after you added the filter, excursion will increase alot.

I think you made a nice choice there. Good woofer for your application.
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Old 13th December 2005, 04:54 PM   #12
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Thanks to everyone for your input. Excursion is now tamed, in WinISD at least. As I'm looking at WinISD's graphs the one entitled "Amplifier Apparent Load (VA)" is rasing some concerns. I've decided to use a 300W BASH amplifier from Parts Express. When I enter 300W into WinISD's signal box it shows that the amplifier will see almost 460W of a load. Please note that this includes 5dB of boost (awful, I know) to get the response a little more flat in room from such a small enclosure.

Is this something to be concerned about? Most of the excessive load shows up below the 30Hz I would expect the subwoofer to reach, so will this just result in a higher effective rolloff? The amp has a soft clipping feature so I'm hoping that will help somewhat, and I've read that there is not usually a lot of energy down that low. Any words of experience in dealing with this would be appreciated.

-Troy
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Old 13th December 2005, 04:54 PM   #13
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Sorry, by rolloff in my post above I meant rolloff rate. Does this just effectively increase the slope (like a virtual rumble filter) by limiting the amp's output to 300W (via the amp's soft clipping feature) below about 30 Hz? What other effects are there? I don't intend to push the amp this hard very often, but it might happen occasionally.

If I lower the overall output by 4-5dB to match my mains (very likely needed) does this give me back the headroom and keep the amp from going into clipping? Thanks in advance for the responses.

-Troy
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Old 13th December 2005, 10:32 PM   #14
simon5 is offline simon5  Canada
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You'll need to lower the output by 2 dB so your amp can play across the range under 300VA or so.

It's not a big problem, just don't push the amplifier too far for too long or it will start clipping around 30 Hz.

So excursion with 460VA is still under Xmax? Then it's a good project, good for it.
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Old 3rd January 2006, 09:13 PM   #15
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So, after coming back from vacation I built this. It's a fairly compact unit, only 14.8 liters internal volume with a 300W BASH plate amp. It has enough oomph to shake my listening room very well and still sound pretty good, but it definitely needs to be dialed in. I modified the plate amp with an external board for the resistors that determine bass boost. My initial model in WinISD assumed that I would get 3dB of boost from the room centered around 23 Hz. In order to get flat in-room response to 25 Hz from such a small sub enclosure WinISD said I'd need about 5dB of boost at 28Hz. This turned out to be quite a bit high. I did a sweep on the sub and it got significantly louder from around 25 to 30 Hz. So I guess my room response estimations were a bit conservative. Having the boost reistors outside of the enclosure makes it easy to adjust, so I'm playing with that now. When I get it all dialed in I'll post the results.

-Troy
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Old 8th January 2006, 06:41 AM   #16
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Results and a pic of the sub would be nice
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Old 9th January 2006, 11:36 PM   #17
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This is a long post, so I’ll apologize in advance. I had the sub all tuned in and it sounded pretty good. I took it apart to veneer it, and did a pretty poor job on the veneer. javascript:smilie('')
xeye So I was unhappy with the veneer and decided to just put it back together and fix the veneer job at a later date. As I was putting it back I accidentally put the driver in with the binding posts in the one spot I couldn't get to them, so as I was pulling the driver out, the one T-nut that I couldn't reach with pliers from the inside tore loose. javascript:smilie('')
hot

Apparently I cross threaded it while putting it back together. The driver was stuck in the box with no way to hook up the leads and no way to get the driver out. This 10" driver in a 14 liter box has almost no room to get my hands in. I tried for an hour to figure out how to get the driver out without destroying the box, but to no avail. In the end, the box was worth less than the driver to me (especially after the crappy veneer job). I tried to do as little damage as possible to the box, but it was destroyed in the extraction. javascript:smilie('')
smash

I had another box on hand (this one 30 liters in size instead of 14) so I've put the driver and amp in that for the time being. The larger box doesn't need nearly the power that the smaller one did, so the 300W BASH amplifier now has very easy duty, though I do appreciate it's 4th order low pass and rumble filter. When I'm less frustrated about the whole incident I might build another box for it. One benefit of this situation is that I was able to measure how the driver did in my listening room in two different boxes. javascript:smilie('')
wink The driver was somewhat happier (at least with test tones) in the larger box being driven with less power. It also plays a bit louder, though either configuration could play loud enough to make me want to turn down the sound. (My 10 year old wanted to know how I could stand to have my head vibrated at 45 Hz and 103+ dB. He's right, I can't.)

In both cases I'm only using the sub below about 50 Hz as my mains have a nice roll-off that fits in well with that. The plate amp has 5dB of boost dialed in at around 27 or 28 Hz for both sets of measurements. Here are the results. They have been normalized to show Keep in mind that these are in my listening room so won't be what everyone else would expect. The 14 liter box was heavily stuffed with AcoustaStuff, the 30 liter box (at this point) has no stuffing. Also, the 30 liter box is front firing and the 14 liter box was down-firing. (I know, this isn't the greatest comparison, but I wasn't planning to break the 14 liter box. At least they are both in sealed boxes!)

Hz......14 l. (dB)....30 l. (dB)
21.........-26............-15
23.........-10............-4
25.........-3...............0
27..........0...............0

29.........-3...............0
31.........-1..............-1
33.........-2...............0
35.........-3..............-2

40.........-2..............-1
45.........-8...............0
50.........-8..............-1
55.........-5..............-3
60.........-10............-12

I have a nasty room resonance right at 55 Hz (vibrating duct work...javascript:smilie('')
mad ... how do I fix that?) so the numbers at 55 Hz are a bit higher than they would be in another room. There is also an odd room mode around 65 to 75 Hz at the listening position. It's not phase induced (checked that first thing) and is outside of the sub's main operating range. I probably wouldn't have noticed it if I hadn't been doing sine wave sweeps, but now that I know it's there I'll try to tame it with speaker placement. It's amazing how much stuff can rattle when excited with a sine wave. It seems every frequency has it's own sympathetic little (or big) rattle somewhere in the room. I quit trying to kill them all when stopping one induced several more. Oh well, if this were easy everyone would be doing it.

No pictures as the 14 liter box is splintered (lousy veneer job anyway) and the new one is just an MDF box at this point, but I thought the measurements were interesting. I wanted to have a smaller box so I could unobtrusively fit two subs in the room, I think that would have evened out response of the smaller sub a bit, but I'm happy with the response of one 30 l. sub (still small, I know, but not what I had originally envisioned) so I'll live with it for a while before I decide if I really need two. While I don't begrudge anyone who wants more bass, this sub (literally) rattles the windows, doors and walls more than I need. Two would likely be overkill for me.

I couldn’t tell much difference between the two by listening, though they were a few days apart in existence so it’s hard to make direct comparisons. The 30 liter sub seems to disappear a bit more when playing with my mains (just some inexpensive Paradigm Titans, though music sounds quite nice through them, especially with a good SACD), though the 14 liter version was by no means objectionable.

So are these figures about what everyone else gets in room? This was my first sub and I’m pretty pleased with it as a first effort, despite the frustrations. How does this compare to subs you have listened to and used?
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