The Project Pad

I know I'm a little behind the curve on this one, but I was looking at my avant door cards and I'm contemplating building a little speaker box to sit in the forward pocket where the bose enclosures go in the sedan. Wouldn't be as large, but would probably sound better than just cutting a hole and mounting to the door... I have to do something about the stereo in mine ASAP.

Too bad we could all meet up at Drew's, have a nice little avant party...

loxxrider wrote:Will do Dave!


Ed, do you have the caps with the correct color code and everything? They should say 7ZC somewhere on them to indicate that. They're painted right? Got an up-close picture?

**edit** nevermind, I found a good picture on ebay finally. Looks like the 7ZC is not cast into the part, only on the package they came in (makes sense from a manufacturing standpoint). That is definitely the correct color code though.

I'll check in a few, busy day. Sounds like you have it figured out though!

loxxrider wrote:Will do Dave!


Ed, do you have the caps with the correct color code and everything? They should say 7ZC somewhere on them to indicate that. They're painted right? Got an up-close picture?

**edit** nevermind, I found a good picture on ebay finally. Looks like the 7ZC is not cast into the part, only on the package they came in (makes sense from a manufacturing standpoint). That is definitely the correct color code though.

I'll check in a few, busy day. Sounds like you have it figured out though!

I measure 63.5. The color is not an exact match but really close.

paradox11235 wrote:I know I'm a little behind the curve on this one, but I was looking at my avant door cards and I'm contemplating building a little speaker box to sit in the forward pocket where the bose enclosures go in the sedan. Wouldn't be as large, but would probably sound better than just cutting a hole and mounting to the door... I have to do something about the stereo in mine ASAP.

Too bad we could all meet up at Drew's, have a nice little avant party...

Man, that would have been awesome! I wish I could have had more time to plan it.

I think your idea for an enclosure is a good one, BUT ONLY IF the speakers you have are made for a sealed enclosure, and one that is very small. That space is probably only going to give you a liter or two of enclosure space. It might be enough to get some midbass out of a 5 1/4, but ideally you want a 6.5 up there and that will require more space than the front pocket will give you unfortunately. I'd love to see what you end up with though. Maybe acoustic engineer Alex can help

Mcstiff wrote:I measure 63.5. The color is not an exact match but really close.

Thanks Ed! That's about what I expected. Now I have to make a decision. To get caps like these and have them machined for customization purposes or go with resin covered "stickers" for Ronal style plastic center caps.

Something marginally interesting, but definitely a concern for me if I go the machined metal cap route is that there seem to be some slight differences between these little caps over the years. Likely due to manufacturing efficiency changes. Check it out... one is not like the others, and none are quite like yours!





The differences are slight, but they will bother me! I like the smooth edges of the middle one (and yours), but if I have something engraved into it, the tool will leave a more square edge around the lettering like in the two caps to either side. Bah! So stupid lol

Waoh great story about the pick up of this avant ! Thanks for sharing it Chris !

The wagon is looking really good man!
Let me know if you need a VEMS setup, I have one available that I got from Marc and wont be using.
Question about the exhaust cutout, Does it seal 100% when its closed? Its a really cool idea.

Going to answer a few of your points now, but ultimately I think I want to make a resonator design guide sort of like what Jeff has done with engine building. That'll be slow to make, but hopefully I can help you out for the time being.

loxxrider wrote:1) Does the angle of entry into the tube matter? I would think that some wave energy would be lost if it hits a 90 first before entering the tube. However, having a bend shouldn't be as big of a deal at all. Probably not much energy gets lost there at all.

I need to research more on this and the performance affects on angle, but in a standard no-flow environment, a side-branch resonator is generally placed perpendicular to the 'duct' (exhaust pipe). You'll most likely want to make a smooth transition from perpendicular to parallel with a mandrel 90. When you start placing the resonator at an angle, I would imagine it gets trickier to determine the effective length since it varies depending on the position in the cross-section.

loxxrider wrote:2) When calculating the length, only arc length matters right?

For the most part yes. There are length corrections depending on the interface between the resonator and the duct, but those can most likely be ignored.

loxxrider wrote:3) Does location in the exhaust matter? Before/after cat, muffler, etc.? I would think the sooner the better really.

For packaging purposes, near the muffler probably makes the most sense. Since the drone is most likely a resonance of the duct, you can place it nearly anywhere. However, you'll not want to place it exactly in the middle of the exhaust in case that's where a resonance node is (assuming the drone is the fundamental). But the exhaust system is not a very steady state problem with the variation of temperature/flow/rpm, so the optimum placement of the resonator would vary. I would place it anywhere between the muffler and cats.

loxxrider wrote:4) The bigger the diameter of the pipe I use, the more energy will be able to be used for destructive interference right?

Yes, use the largest that provides feasible packaging. I'd use the same size as the main exhaust (3"?). There are limits to the size in theory since a quarter-wave resonator assume plane waves, but for 120 Hz you aren't anywhere near those limitations. A 3" diameter pipe has plane wave propagation below ~2600Hz at room temperature (and increases with temperature). So you'd need a really large pipe to have to worry about non plane-wave propagation at 120Hz.

loxxrider wrote:So the math isn't too bad. 120 Hz is the frequency I want to cancel, so I need to build a chamber which will make sound waves destructively interfere with other sound waves in the exhaust. To be most effective, the sound waves should arrive 1/2 wavelength out of phase. The pipe will have to be 1/4 the length of one wavelength in order to to arrive at 1/2 a wavelength out of phase since it has to travel the distance of the pipe twice.

SO, what's the wavelength of a 125 Hz sound wave in my exhaust? Well, that depends what the temperature is going to be inside that pipe. That's REALLY hard to make an assumption on because it is highly dependent on the airflow and heat transfer while cruising at highway speeds (since that's where I want the drone cancelled).

I am going to do the math now to see how much X degrees affects X length of pipe. It may not even be worth worrying about. It'd be really cool to get it right though and have the max attenuation at the target frequency!

Ignoring flow and static pressure (from muffler), temperature is a huge variable. I've seen vastly varying exhaust temp gases in mufflers, so I'm not sure what the right range is to assume. I need to do some more studying, probably in SAE papers. I simulated a 2-meter standing wave tube and varied the temperature to see it's effect on resonance frequency. From 300K to 800K, you get a shift of about 55Hz.

Temp_vs_ResFreq by Vex Art, on Flickr

So it is pretty important to get the exhaust temperature right. 1/4 wave resonators have a very narrow effective bandwidth.

So, that leads me to my recommendation...don't use a quarter-wave resonator! I'd use a Helmholtz resonator as they have a much broader effective bandwith and aren't too difficult to fabricate with a welder (you just need two different diameters of pipe and some flat sheet of the same gauge). They can be designed to take up less physical volume too.

Another idea for either, is to use v-bands on the resonator tube length or helmholtz volume to allow you to fine tune the lenth/volume.

And then you could also tune some helmholtz for enhanced scavenging...the rabbit hole goes deeper

Thanks Alex!

I could care less about scavenging to be honest. That's an NA thing. Plus, if I need power, I'll open my dump

But I guess I need to do more research into the Helmholtz resonator. I hadn't even considered that because I wasn't aware of the narrow bandwidth of the 1/4 wave. What is it? 10 Hz or so at 120 Hz target attenuation frequency? I think that's enough actually, but it would be even better to have more obviously.

I also agree that the temp makes a huge difference. The math shows that (as I briefly discussed earlier) and your test shows it too. To that end, I will probably end up making something which is adjustable and which also has a thermocouple port so I can experiment a bit and watch the math meet up with the testing.

I think mine look a lot like the "middle" version in your pic.

So not sure if this helps at all, but the exhaust we just fabbed on my 5k has zero drone with only one muffler.
rs2 knockoff manifold, 3 inch turbo back, one flow-thru box magnaflow muffler right at the rear diff. DP is header wrapped. Nice under load, quiet under cruise.

just my 2cents

loxxrider wrote:Thanks Alex!

I could care less about scavenging to be honest. That's an NA thing. Plus, if I need power, I'll open my dump

But I guess I need to do more research into the Helmholtz resonator. I hadn't even considered that because I wasn't aware of the narrow bandwidth of the 1/4 wave. What is it? 10 Hz or so at 120 Hz target attenuation frequency? I think that's enough actually, but it would be even better to have more obviously.

I also agree that the temp makes a huge difference. The math shows that (as I briefly discussed earlier) and your test shows it too. To that end, I will probably end up making something which is adjustable and which also has a thermocouple port so I can experiment a bit and watch the math meet up with the testing.

Here's a good read (click 'Download PDF' at the top) on how quarter-wave compares to Helmholtz: http://www.sciencedirect.com/science/ar ... 810001598#

Not only does a Helmholtz have a broader bandwidth, it also has a greater absorption potential.

Fig.7 from the paper above:

You just need to make it adjustable with a PWM stepper driven by VEMS.

Mcstiff wrote:You just need to make it adjustable with a PWM stepper driven by VEMS.

Easy!

http://en.wikibooks.org/wiki/Engineerin ... resonators

The tunable Helmholtz resonator is a variable volume resonator, which allows the natural frequency to be adjusted.As shown in Figure 5, a variable volume Helmholtz resonator can be achieved by rotating an internal radial wall inside the resonator cavity with respect to an internal fixed wall. The movable wall is fixed to the bottom end plate which is attached to a DC motor to provides the motion to change the volume.

Okay, so I'm super late to this party, but what an great story! I'm constantly amazed at how friendly and welcoming members of this community can be - and that goes for yourself, too, Chris. Seriously, major props to Drew for his hospitality. I'm glad everything went well (aside from missing Carlisle, but we'll see you next year!).

Having driven that flat stretch of highway in west KS/east CO several times in both a minivan and the 200, it's amazing how well the 200 will settle into a high cruise and just eat up the miles. Just gotta keep a sharp eye on the horizon for any hiding officers of the law.

I'll definitely keep tabs on this thread to see what you'll do to make me more jealous of this car, and I'm sure I'll learn about a lot on the way - like Heimholz resonators (thanks Alex!). I'll be lurking in the background to see what ideas I can steal for myself. Now you just have to dump the Poorsche and get this show on the road!

Alex, what do you think the bandwidth of the 1/4 wave is at 115 Hz? If it's +- 10 Hz, I think that'd be more than enough to be very helpful. I still need to read more about the design of the Helmholtz. I only shy away from it because I fear it may need to be too large in diameter and is a bit more complex than a very simple 1/4 wave. It might be an exercise in diminishing returns.

Phil, I don't know how you're achieving that. I haven't been in a 5 cyl car that hasn't had drone except for stock or very quiet setups. Is your muffler straight thru?

Kevin, thanks! I appreciate that. Of course, the same goes for you. I do wish I could have gone faster at times on that stretch, but where the speed limit is 75 is pretty good. 85 is a nice cruising speed. It does make me long for a 6th gear though! I'll get rid of the Porsche as soon as I can. It isn't currently holding anything up though It might end up that we sell Jessica's X3 instead as that'll be an easier sale. I'll give it my best shot this year to get the Cayenne sold though. I have to admit, I'll be a little sad to see it go!

I'd have to model the absorption, but I believe the pressure reflected was around 5Hz or so bandwidth (+/-2.5). However, lots of people get them to work with some pretty crude math so it might not need much to make drop the drone out of perception. I'll try and do a model next week, on vacation now

I don't really have a logical answer as to why. My old setup droned like a bitch with a resonator and same kind of style muffler. The bends are all very smooth which i think helps. When we were fabbing it up I was skeptical of it sounding good and still being bearable under cruise, and I was heavily surprised. I'll try to get an interior vid of sorts.

This may be amateur hour compared to what you're trying to do...but people are getting rid of drone with j-tubes -

http://www.performancetrucks.net/forums/gm-engine-exhaust-performance-21/how-build-exhaust-resonator-tube-eliminate-drone-489463/

http://forums.corral.net/forums/general-mustang-tech/496793-exhaust-drone-completely-gone.html

NewFlesh wrote:This may be amateur hour compared to what you're trying to do...but people are getting rid of drone with j-tubes -

http://www.performancetrucks.net/forums/gm-engine-exhaust-performance-21/how-build-exhaust-resonator-tube-eliminate-drone-489463/

http://forums.corral.net/forums/general-mustang-tech/496793-exhaust-drone-completely-gone.html

'J-tubes' are quarter-wave resonators like we're discussing

Yep, they are indeed. Some people just get more technical with it than others

I still haven't been able to register this car yet, but I'm having my cousin who is a major in the Air National Guard verify the VIN for me finally. What a hassle! Hopefully I'll be able to drive it for work soon.

In the meantime, I ordered a bunch of stuff. The first piece in solving the audio puzzle is a pair of JL Audio 5 1/4" midwoofers to fit in the rear doors.



They are the only decent 5 1/4" midwoofers I could find which don't need an enclosure, but based on what paradox11235 did, it looks like I could have saved myself a lot of time and just gotten a 6" or 6.5" woofer to fit in the rear doors. This is what he did:



I guess I'll take a look next time I'm with the car and see what I can come up with. These should sound fairly good though and I'll have them crossed over actively at some point so that they only produce midbass. I may even build a little enclosure for the door there if there is enough space! Otherwise, I'll try to seal and deaden the rear doors.

I may go back in and seal my doors up, don't want to add a ton of weight to them so I'll see how these sound. A solid wood mount I imagine will sound much better than mounted to the flimsy plastic doors. I'll report back tomorrow when I get the amp connected...

I managed to make some time (half a day) to work on the car. It still isn't registered, but we're one step closer to that so at least progress is being made

I had a fair list of things to get done, and didn't really have a plan of attack... so I just went at it! The first thing to be done was to unbox all the new parts I ordered.

From Hersh Performance...





Custom center cap decals in 64 mm from 3Dcarstickers.com / 3DTechlogies (sic?) in Ukraine!

I liked their little letter. The shipping was actually fast!



Here it is mounted on an Audi/Ronal center cap. The size is perfect. I think they look pretty good. The only way they could look better would be with actual metallic Audi rings like the OEM Audi ones. I figured it wasn't worth it this go around though. No pics on the car yet because I need to order three more center caps (this was a trial) and clean the wheels!




I also ordered a custom boost gauge from Speedhut.com I really like the way it came out.



Sadly, this is one of the only things I didn't have time to install.

Next was the speaker installation. I wanted at least a little midbass to hold me over until I do the front doors (if ever). I decided against the Focal Utopia 13ws because they need a sealed enclosure, and I didn't want to get into that just yet. Maybe I'll change my mind and try it later, but for now I decided on using some JL Audio C5-525cw woofers for rear midbass. Here are some pictures of them before installation. They are definitely nice and Made in Germany as a bonus!







Compared to the stock speakers... look at the difference in magnet size!



They drop right into the doors easily. There is practically a cavern back there. The focals would definitely fit right in there, but again, custom boxes would have to be made. Maybe later!

I have elected not to run tweeters in the rear as I don't feel it is necessary. I intend to run an 8 channel digital signal/sound processor to best integrate the speakers in the car and bring the soundstage front and center where it should be. Having tweets in the rear probably wont help with this, but I could experiment later. What works for a car without active processing is much different than one without and I've read that having rear fill is actually not detrimental when using one.

Anyway, for now the rear tweets are just disconnected. I kinda wish the grills were gray. Maybe I'll paint them! They don't look too bad though.





After I finished tuning everything with the relatively limited DSP in my head unit, the sound improved a LOT. However, I wouldn't say it improved too much over the stock speakers with the same tweaks in the DSP. Having them crossed over properly (with the DSP) has allowed me to maximize the upper midbass they are able to put out at volume without distortion. I compared when I had one JL installed and one stock still there. They seemed fairly comparable except I think the JL was able to handle a little more power and extend a little lower.

With both JLs installed, it seemed like the improvement was more apparent. The levels of midbass (especially upper) are acceptable now. It actually has a little bump to it if you go in with mediocre expectations!

Next up on this front will be a sub/box (maybe custom?), sub amp, speaker amp (6 channels or so), and the DSP. I think sub and amp are first on the list though.

Here's a picture because I don't have any pictures for the next part. Looks good right? Except for the dirtiness of course!



Next up was finding a final location for the exhaust dump switch. I thought about it for long time and finally came to the conclusion that placing it inside the steering column surround behind the steering wheel was the best solution. It is easy to reach, akin to the blinker/wiper stalks. It is also easy to run wires to that location, and it packages well within the confines of that space surprisingly! I will have to take a picture sometime, but I'm very happy with the result. I always get frustrated with wiring and while I always take care to make good connections, I don't always take the time to do proper wire routing and clean integration. This time I did!

Next, I wanted to check if I had some part. I forget what it was, but I ended up looking around in the box of spares the PO gave me. It was there that I discovered that he gave me another set of Euro lights! I remember him telling me the car came with the original radio, lights, and AC compressor, but I'm not sure he knew they were euro ones! HELLLLL YES!



The only problem is that the ones on the car have a small-ish crack in the passenger side lens. Too bad the spare ones have bad glass on the same side! I will try to find some good glass ASAP and I will be getting thick headlight film to cover whatever goes on the car.

I also recently ordered some nice pieces that go along with the euro lights. I think I got the last ones available! I'll take pics when they arrive.


Next, I started the boost gauge installation. By far my least favorite part of installing a boost gauge is running the tubing through the firewall. I thought about tapping off of the ECU's boost line, but after a bit I decided it would be nice to have the boost gauge coming off of the FPR tap so it will be easy to tell if these is a leak somewhere in the ECU's path (by watching in VEMS or by installing a cheapo mechanical gauge in the glove box). Two points of reference can't hurt right?

So I managed to pull the rubber hose for the gauge through the firewall, but then I gave up on the install for now because I was running out of time. I still have to do the wiring and figure out a mounting solution. So I have two questions/problems which need solutions.

-Where/how to mount the boost gauge
-What to tap into for dimming of the gauge (I guess any of the gauges/switches which also dim would work fine, eh?)

I may try to design a boost gauge pod to have 3D printed... That's for another day though.

By this time it was getting pretty dark, so I decided to see if this car would fit in the barn behind the M5. It barely does, but it fits!





One day I need to get my uncle to clean out his stuff on that side of the barn and let me take it over for more of my cars!

I attempted to measure some strut mount dimensions, but it's pretty hard to do that properly with them installed in the car, so I gave up and decided to stare at the glory that is a stock 3B for a bit Oh! You can see the new oil cap I bought too lol. The one on it before was really weird. Good riddance!



Then I remembered that I had parts to use for measuring! I will get on that soon. Here's a picture of that stuff and the contents of my pocket by the end of the day lol



and finally, I thought I'd share a picture of the reason I have so little free time

Lol, I love the little customized bits. Nice.