[QUOTE]Originally posted by Squeezer
[B]

the S2000 is a body on frame, not unibody.

 

Your idea is great but dont you think you should have used a better woofer and some MDF wood instead.

 

Looks awesome!! Great option if you don't want to give up trunk space.

 

I'll assume you are addressing me? (there are two of us that have posted in this thread).

First - I'm curious why you think I should use mdf? And don't say "because that's what you use to make speaker cabinets", give me a good reason why it matters. I'm not busting your stones, just wondering what your reasoning is.

Second - I'd love to use a "better" woofer. If you can help me find one I'd appreciate it. It must:

• be a 10" driver (obviously)
  
• must not be deeper than 5 1/4 inches (mounting flange to fartherst point)
  
• must not have a magnet structure bigger in diameter than 5"
  
• must work well in a 15 liter box

The dimensions are critical, because it will hit the frame if it's any bigger - I had to grind off part of the magnet structure as it was to keep from hitting. The "work well" part is described in my previous post.

Even though it's a big pain in the rear to change the driver, I would do it if I found one that was significantly better than what I've got.

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Unbelievable!

 

MDF is a traditional choice for the following reasons (reasons I have observed and otherwise), and others I am unaware of:
* MDF has better damping than solid wood and plywood. I don't know if this is an unban legend or not. I think I might have observed this behavior, but I wouldn't swear to it. Wouldn't be hard to prove with a little instrumentation.
*MDF is more uniform (within a single sheet or piece and ignoring small scale uniformity) than solid wood and plywood. I haven't proven this one, either, but I can take this one on faith.
*MDF is denser than solid wood or plywood. Go to Home Depot and pick up some sheets. Denser just moves resonances around, it doesn't kill them, so I don't know why people get all bent about this one.
*It is easy to hold tight tolerances in compared to most solid woods and plywoods. This is short term as it is subject to some real swelling with humidity.
*Crap plywood has voids, solid wood, knots, MDF, neither.

Having said all than, I have used high grade plywood with very good success in speakers. High grade plywood and BCX plywood (and the sort) have only a passing resemblance.

After all that, I used BCX in my sub because I was cheap and didn't care. I figured that I was using an unknown sheet metal piece for the rear so why get high and mighty on the baffle (especially since most of the baffle was the driver.

 

Ok, I admit it. I didn't use my head in this project. Yet.

So when Modifry puts up a simulation of my sub and it has a low end of 75 Hz, I'm wondering to myself, "Why the hell did I make this thing?" and "Why does it sound like it goes lower than 75 Hz?" and "Thank God someone around here is thinking when I am just drooling on myself."

So off I go to measure this pig and figure out what it does (and doesn't). Here is the frequency response (I have an 80 Hz 12 dB/oct low pass on that is included in this data):



I measured it in the near field with the carpet and floor mat all in the normal position. I didn't calibrate to any particular amplitude, so the amplitude is in dB, but the numbers are relative. It is 1/8 octave smoothed.

What are the 5 dB peaks and dips? Beats me, but I found that it was difficult to get a smooth measurement no matter what I did. Outdoor acoustic measurement can be a challenge, too. I think those peaks are real because I can make measurements of my home system and it is nice and smooth. I'm going to chalk it up to a cheap sub and a sh!itty enclosure and reflections in a car (I know it is nearfield, don't remind me!).

So this answers what it does by itself, but what does it do in the whole system?

 

Let me start off by saying that I have an Alpine head unit that lets me compensate for each speaker's distance and make all speakers have an equivalent arrival time. That means that I don't expect a tough time getting the sub to integrate in with the other speakers.

I took some data with my subwoofer gain on the head unit at no sub (turned off), +4 dB, and +11 dB (sounded the best to me). Let's look at the data:



It appears that the 60Hz peak I have is all 60 Hz interference at the peak. I didn't think of 60 Hz interference when I measured because I was using battery powered equipment. Oh well. I don't think that the whole 60 Hz peak is ficticious because the subwoofer shows a change on either side. I don't think it is door woofer / subwoofer interaction because it is basically the same amplitude despite widely varying subwoofer volume. I think that the nearfield measurements I made below are more valid (but still subject to 60 Hz trash) because the volume is higher at the mike in the nearfield, helping the signal to noise ratio.

The +4 dB setting looks the flattest, but sounds a little thin in the car. Go figure.

The mike was in line with my head, but above the hand brake. I had an 80 Hz low pass on the sub and an 80 Hz highpass on the door speakers. I only had the right speakers on in these measurements.

And holy smokes, what is up with the sharp dips and peaks above 400 Hz? It's no wonder nobody likes the stock speakers. That is close to a 20 dB delta from 700 Hz to 1150 Hz.

There is no appreciable difference above 300 Hz for the different subwoofer settings, which is expected.

I suppose I should go measure the door speakers without the highpass and figure out how low they go...

 

Gee, you got serious about this huh?

First, I agree about the mdf/plywood thing, and in my "cabinet" there were no panels more than 5" wide, so I wasn't worried too much about the panels vibrating or dampening problems. I thought about sticking a few strips of dynamat on the inside of wood panels or maybe the floor, but decided it wasn't worth it - the wood area was so small and the floor metal is structurally pretty solid.

I was not implying that your sub would have no output below 75 hz, just that it would sound different than mine. With some equalization you can probably get them to sound about the same, but your lower Xmax will not allow for as much bass boost as you'll need to match my reponse at 50 hz.

My comment about "I dont' know why they recommended a .5 cu ft box" was because your driver performs much better if you quadruple the size of the cabinet. The response curve flattens out, loses the 100hz peak, and has much better low end. It also indicates you should completely stuff the cabinet with fiber-fill. Partly-stuffed makes the peak/rolloff more pronounced.

The spreadsheet I used assumes an optimal infinitely large listening room (anechoic chamber). I've read that auto interiors have a significant gain in the bass region, probably because of the small volume and the fact that almost any woofer design will be "corner-loaded" which improves efficiency in the low end. This is probably why it sounds much better than it looks on paper.

I also assume your peaks and dips are pretty typical of any stereo system, and are partly due to the drivers response but mostly due to reflections and standing waves. Moving the mic will reveal standing waves, but if you figure 50hz is a 22 foot wave you gotta move it a lot to see a difference. And I bet that even doing near-field measurements the standing waves are significant in such a closed-in "room".

I wonder what it would look like with the top down and the doors open?

I have a PC-scope that has a spectrum analyser mode but I've never used it. Maybe I'll play with it sometime, but it won't be too soon. And since it's going to be totally different equipment (especially the mic) it won't necessarily be a good comparison.

 

Hey modifry, great work! How about a template for the wood work. I am seriously considering doing this!