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Old 1st October 2004, 01:16 AM   #21
djQUAN is offline djQUAN  Philippines
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Quote:
Hmmm... Within a good stone's throw of my office, I could buy a dozen car amplifiers of 500W or more. Many of these would actually cost me less to buy than it would cost me to build a P68 for home use.
well, I had all the parts needed to build the 500W SMPS at hand here in my room so I couldn't resist. besides, how many people have you seen that took their cars to a car show using DIY amps? (I'm just planning. and I'm going for SQ/SPL. not install )

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For my car, I can get to 130dB SPL, and that's with plain sealed enclosures, with the windows down, (It actually makes no difference in my car) but my car is a lot different from an SUV. I'm running 60W/channel to a pair of 10" subs (120W total)
well, your car is SMALLER than my truck. and the volume is much louder with the windows up. OR I might be guessing wrong and I'm getting more sound than I think I am.

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djquan,
how about some plans for the enclosure that u have built? Would i be able to get a hold of those. and there are plans for the horn for sale online at billfitzmaurice's website i cant remember it. please post for the others
the boxes are basically sealed dual chamber (one for each sub) type with the side walls extended to the front of the baffle by 2 inches. leaving one side open, you get a slot around 30.75" x2" for the sound to come out.

basic box dimensions extermally are 32"x 9"x12" (if I remember correctly.) all I know for sure is that the subs are getting 0.75cu ft of airspace each.

although if I get the time, id go around drawing the plans and putting it in my website.

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Old 1st October 2004, 03:55 AM   #22
eXn is offline eXn  United States
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The designs for the horn earlier stated in a reply can be found here
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Old 2nd October 2004, 12:10 PM   #23
tuneman is offline tuneman  Australia
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all this babble about one being superior to the other is nonsense!!

both boxes sealed or ported are excelent when tuned correctly and the same goes for the mentioned horn boxes but for someone building there own for the first time or just wanting decient sound in there car they can be to complicated, there usually huge anyway

the deciding factor is what type of music you listen to and the type of sound your after, its no good building a nice smooth response sealed box for someone who wants stupidly loud techo music or a high output ported for a classical listener!.

for all the people who say a sealed is far superior' what happens if i own a sub that suits a ported box only? say a soundstream spl series or a Digital designs sub of any sort, even a stroker!! they will sound pretty much like *** if you put any of them in a sealed box of any size! remember that some subs are designed to exibit there best in a ported and vice versa or both.

they both have advantages and disadvantages, the sealed is simple and is forgiving of inacuracies in the size and will generally sound smooth and good and offers a relativly flat impedience curve, but it lacks efficency.
the ported can handle more power above its tuned freq, has higher output for the same amount of power(they dont 'use' less power ) adding a port is like adding another sub! and you have the ability to change its sound by altering the port dimentions but they can sound boomy if not setup right and have nothing but the subs suspenstion for control if the freqs drop below the box's tuned freq.

in a ported setup te sub will always be better cooled as well, but dont get me wrong im a sealed fan and have had sealed boxed in my car for many years, i just like there simplicity, but haver changed to a ported homemade 15" sub reciently and im quite impressed
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Old 3rd October 2004, 03:48 AM   #24
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SupraGuy wrote:

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And the long and short of it is that a sealed box in a car audio environment is typically superior to a ported one.

I actually carefully measured cabin gain in my car before designing my box, then designed the parameters for the subwoofers to give me an inverse of the cabin gain curve
Obviously this is a highly debateable subject, but I agree with SupraGuy on the sealed box suggestion. By no means does that mean a very nice ported, bandpass, horn, or even TL can't be produced for a car. But with the number of variables in car audio, it's usually a good idea to hedge your bet with a more forgiving design.

If your goal is decent sound quality, that is. If you want lots of "bump", or want your woofers to "hit hard", that's another story...

I'm very curious about how you measure your cabin gain, SupraGuy. Your idea of measuring the environment first, and designing around it is indisputably superior. Are you talking general terms here, a symmetrical hump in response with a center frequency related to the length of the interior, or a more detailed analysis of the car's acoustic transfer function, or room response?

Though measurement equipment around here is nonexistant, a method would be most appreciated...

Tim
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Old 4th October 2004, 04:33 AM   #25
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I'm very curious about how you measure your cabin gain, SupraGuy. Your idea of measuring the environment first, and designing around it is indisputably superior. Are you talking general terms here, a symmetrical hump in response with a center frequency related to the length of the interior, or a more detailed analysis of the car's acoustic transfer function, or room response?
Look at me, I'm blushing.

Actually, measurement was a relatively simple process. I put a box with a known response curve and sat it in the back of the car, roughly where I intended to put my subs. Play pink noise, measure with an RTA, and subtract the known response curve of the box in the back. I now have a plot of cabin gain in my car. As it happens, it's a fairly linear gain, but with some inevitable bumps and dips.

I suppose that you could do the same thing with an SPL meter and a CD with test tones at 20, 25, 31.5, 40, 50, 63, 80 and 100Hz Measure the SPL levels in open air, then again in the car at the same distance fromt he mic. The difference will be your car's acoustic response.

By doing this, I determined that I could get pretty close with the 10" subs that I have by squeezing them into a slightly smaller box than the "minimum recommended" manufacturer's size, as long as I was willing to cross them over at a low frequency. (In this case 50Hz) This allowed me to use the hump on the response curve (For having "too small" a box) to increase apparent sensitivity and ride the cabin gain down to the low end. I still get a drop right at the bottom of the scale, but overall it works great. Consruction errors (slight miscalculation of the volume of the curved section of the sub enclosures) actually moved that response hump down the scale a bit, so if I cross over the subs at a higher frequency (say, 80 Hz) they sound terrible, but since I always use a 50Hz crossover, that's not a problem. (The original design was supposed to allow me to choose 50 or 80Hz as a crossover point, but in retrospect, I like it better this way. )
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well, your car is SMALLER than my truck. and the volume is much louder with the windows up. OR I might be guessing wrong and I'm getting more sound than I think I am.
In most cases, you would be absolutely correct, and the SPL levels would be higher with the windows up. This is not the case in my car. With the windows all the way down or all the way up I hit the same SPL scores in my car. It's a freak this way. Actually, with one window open about ¾" or so I sometimes get a 1-2dB increase at the driver's seat mic. Best guess is that the car acts as a bandpass box with the windows down, though it gives me a headache just thinking about trying to calculate the "port" characteristics, let alone trying to determine the "chamber" volume. One of these days it might be interesting to put a mic just outside the open windows and try to reverse engineer the system. For what it's worth, SPL drops a LOT with the hatchback open. And yes. My Supra's interior is much smaller than an SUV. This is what I was talking about by saying that it's very different.

What I did, worked for me, and in my car. I'd expect that if I took those sub boxes out of the Supra and dumped them into a minivan they'd sound bad. Worse if I put them in a listening room. (Well I suppose I could use a Linkwitz transform circuit, but that's another subject. ) As it is, I'm just finishing up a subwoofer 1/3 octave equaliser project for the car to try fixing some of the remaining bumps and dips...
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Old 5th October 2004, 11:15 AM   #26
tuneman is offline tuneman  Australia
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you can do the measument with LEAP/LMS sofware but carn't say i have the money for that but its the most acurate and effective method

using a RTA does work but the problem is, depending on the sort you have but most a 1/3 octave measuments so you only have 25,31.5,40,50,60,80,100hz or there abouts to play with for your subs which is sort of ok but for really good sub bass freq measument for a cabin gain curve you need heaps more.
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Old 5th October 2004, 03:28 PM   #27
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Originally posted by tuneman
using a RTA does work but the problem is, depending on the sort you have but most a 1/3 octave measuments
That's correct, I had 1/3 octave mesurements. While I know that this isn't 100% accurate, it's certainly more than I'd have been able to compensate for with box design. It gave me a general "shape" of the response curve, which I was able to use to design my enclosure with and get reasonable response. I simply did a point-to-point of the cabin gain plot (Which was actually measured 20-250Hz) and added that to the predicted response of my sealed enclosures. When I had a response curve that looked reasonably flat, I built that box.

Certainly further refinement is possible, as I still have a slight response hump from 30-40Hz, and a dip at the bottom (20Hz) of the scale. But that's why I'm building a 1/3 octave subwoofer equaliser. The one I'm using is Rodd Elliot's Project 84 which I will adapt a power supply to suit. Even here, I only have control in 1/3 octave increments, so measurements beyond that point are not practically usable.
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Old 7th October 2004, 02:40 AM   #28
eXn is offline eXn  United States
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This kind of got off topic but not in a bad way because I have learned other valuble info because I have to admit I am a newb. Thank you all soo much!!
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Old 11th October 2004, 11:05 PM   #29
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sorry it took so long to back to posting.know you can go with a single 12 in a small sealded box good bottom end.then you could go with the same in a ported box alot more boom.
But since space is not a problem here is a link to a site with the plans for a folded horn box.now the box is designed for 2-10`s but as you see in the insturctions it can be modified to fit 8`s 10`s our 12`s.I`ve seen a similar box used in a s10 with the cab and bed cut to fire into the cab,it had 2 jlw3`s and hcca amps but it hit a certified 160.
That would be the extreme,but I`m thinking a good setup like this would be to go with some jlwo 12`s and a good 75 watt amp wired 2ohm mono.that would be kinda cheap and have some killer bass.
the site does have a form for this set of plans so read through them before starting,and remeber the plans are FREE!
Good luck let me know how it comes out or which way you go.
http://www.decware.com/newsite/mainmenu.htm

these guys got so far over my head and made go to a software program for the first time.but I`m going to build box just to see if their way is better.But that`ll get cover inother post.
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