Been dealing with an annoying rattling rear deck in my 97 LS400 resulting in somewhat subdued output when trying to play my tunes, After years of putting up with it I decided to take a leap of faith into something that is relatively old, but not often practiced with small subs or rear decks for that matter. I call it the birdhouse due to it's shape, but it is nothing more than a mere dual opposed manifold to house two 8" subs. The main idea is to reduce, if not eliminate vibrations transferred to the rear deck which should result in higher listening levels without the associated rattles most get when upgrading the rear deck sub. This practice is most often found in home audio where infinite baffle is used and the owner wants plenty of output without rattling the attached wall. Sometimes used in competition vehicles, but some older manufactured designs were produced by Linear Power & Coustic (Bass Pump).

How it works is by having the subs opposing, but still firing in phase, the movement of the cones cancel out each other's vibration. A big plus is the increase of cone area that will surely maximize output capability which will allow you to use less than stellar woofers that normally wouldn't cut it if using only one. The subs fire through the manifold which in turn fires into the cabin while still using the trunk as the enclosure, thus it is still infinite baffle, or trunk baffle rather. There should be no large variations in response and if so it should be out of the pass band of the woofer's main use...

The manifold is built of 1/2" mdf to help save on weight since it will be hanging from the deck along with the subs attached. I suspect it will be bit bulbous though I've built it as small as possible while still allowing the largest opening to the hole in the rear deck. Choice of subs are Cerwin Vega Vega series dual 2 ohm (which can be found rather cheap) that will wire in series/parallel to the 5th channel of a JL XD700/5. By the way, if anyone is looking for options for the rear deck, I found the Vega series to be worth looking at after doing some extensive modeling and testing. The amount of suspension stiffness/control beats out the usually suggested ID8 which I almost hated in the deck. Just remember to reduce power to about half. It may appear a bit big, but once the holes are cut for the subs, you will see that it really isn't that big at all. For now, here's a quick pic of the almost finished "birdhouse" sans woofer holes cut and top plate attached. It is upside down while some filler dries as well as I did some sanding to give a bit better finish.

 

The structure doesn't have to be vacuum seal air tight in itself, though a bit of compulsive behavior applied isn't going to do harm. A good quality wood glue and brad nails from an air gun was used. After cutting the woofer holes, the manifold is extremely light though the top plate isn't attached yet. Thicker wood is unnecessary since you don't need two heavy duty woofers (remember the advantage of doubling cone area), plus the benefit of vibration cancellation. It is purposely built lightweight to keep stress down on the rear deck. The top plate is of 1/2" mdf as well.

Here you can see the traced line for the sub cutout exposes how little the woofer mounts are. Just barely enough to mount the woofers. The magnet will be mounted on the outside. You could place the magnet assembly on the inside, but that will require a larger manifold.

Now as to why the birdhouse shape which I should have included in the first post, anyone driving one knows of the issue.... the bane & blessing (fuel pump replacement ease) of the LS400. The dang gas tank. After careful measuring, the angled sides was required to clear the tank. Though one side only needs to clear the tank, I did both for slight aesthetics. I must include that this is going to require a good amount of trimming of the trunk liner piece that hides the gas tank, but it should only be in the immediate area of the sub. I will carpet the manifold later on to match the OEM carpet as best as possible, but for now, testing will be done without the liner. That way I will know for sure how permanent it will be.

 

Top plate is attached. I can't speak for my work since I glue, clamp, and brad nail most of my enclosures, but I highly suggest that the top plate is securely attached since it will be load bearing. The heavier the sub, the more secure you want to make it. The top pic gives a clue to the actual size of the manifold in relation to the tank. Not too bad.

 

Decided to paint it so it sort of at least disappears into the trunk. Pics aren't too great and probably will be some of the last posted since I'm trying to finish up before it gets too hot outside, but if you can make out how it sits you will get the gist of what I'm doing.

 

The manifold is installed with the Cerwin Vega subs. It took a bit of trimming the underside panel to get it to fit as some of the panel is in the way of the woofers and part of the manifold, but if trimmed right (my skills aren't that great) it looks very natural. You have to get down to see where it's been trimmed, but from the view when normally standing while opening the trunk you don't see anything but the subs and manifold which is tucked up under the deck quite neatly. It was a slight pain getting the manifold bolted to the deck since I was by myself, but I used a small bottle jack and stacks of scrap wood to get it to where I needed it. I then secured it from the top with multiple screws. And yes, the stray piece of weatherstripping in the pic from above the rear deck was tucked back in before finishing. LOL








As for performance? HECK YEAHHHHH!!! Not a hint of rattles with plenty of output even on a meager 300 watts total. Extension is great and of course depends on the subs you choose. The CV's does a fine job of articulation, control, extension, and overall output, Plenty of kick, and.when it gets low you feel it like there's a bigger sub in the trunk. This is for a SQ setup so don't think it's all boom. Guitar thrusts, drum hits, etc.. are clear. Far more output available than a single 8" and no box on the floor. And can I say it again??? NO RATTLES!!! Anyways..... it's done and it's staying!

Hope this helps someone as this can be applied to any vehicle with rear deck subs.

 

So it's been a week now since the manifold was installed and so far I've been entirely impressed with the results. Can't say for sure if the Vega subs are fully broken in, but the response is absolutely satisfying! Although I run a Helix DSP in the setup, the EQ on the sub is pretty much flat in the DSP and headunit. I may have a slight cut of -3db around 50-60hz, but I tend to do that in all of my setups regardless of vehicle. The xover is around 120hz with a -6db Butterworth slope to mate up with the stock Nakamichi fronts which will soon be replaced with a set of JBL P560c. After that are a few minor areas (crossover point, level, and some EQ) that will be improved on the subs and mains to get that last bit of sound desired, but we're talking about very fine tuning that most could do without or might not even notice. The level of output could be equated to maybe a set of low to medium power 10" buried in the trunk except there still are no rattles and the sound is more direct with very little to no phase issues. The low end is very impressive (it gets lowww) with very good dynamics and accuracy. I experience no issue with extension and overall smoothness in the response. Kick, punch, and thrust are all present with more than enough to fill in what the small door drivers can't present without struggling. And yes, we're talking about bass you can feel even in the lowest registers.

 

I've almost started another thread detailing what I will be doing for the next step, then decided it would be best if I kept it all in one thread despite having an odd title that may throw some off in what I'm doing. I've noticed a few of my pics from the sub setup are gone. Not sure if there is a limit, I've somehow deleted them, or whatever, but this way I can also replace pics where needed if I see it was an error on my part.

As a warning: I am not attempting to be condescending or determine what others should do with their stereo. I've read over and over on the stereo forums with very little confirmation in what will fit in a 2nd Gen LS400. So some investigation was in order since it was time to replace a bad driver in the door. I don't care to cut or do much custom work in this vehicle than I already have with the subs that can be seen in my earlier posts. I do most of my custom work in another vehicle which still has limits set on what I will do. In the LS400, I will be attempting to use the stock door enclosures without cutting them up. This will include some measurements that may aid others if they attempt to do the same or need to know. Rather than concentrate on exactly what the 97 LS400 w/ Nak appears to have, I've chosen to take measurements to see what will fit by removing the front driver's side enclosure, mid, & tweet which is quite simple. Measurements were taken of the woofer's mounting flange width which is 5-1/8" with a half inch lip. Now I see where the confusion comes in as a common 5.25" may appear to fit, but without actual frame measurements of the replacement, you could wind up having to trim quite a bit of the enclosure just to be able to do a top mount. May work for some and I'm sure it has, but I'm desiring to make full use of the enclosures internal airspace for the correct driver that will achieve an ideal sealed or ported alignment.


I did a water displacement measurement (using distilled water of course) and wound up taking right at 2.7 liters before almost overflowing the cabinet. This also included water in the port so that will have to be subtracted if the port is used. So basically there is about .097 cubic foot of airspace or a tiny bit more in the front enclosures excluding driver displacement which shouldn't be very much to make a big difference. The rear wall of the enclosure is slightly angled leaving a reduced measurement of 2-5/8", from the back wall to front mounting surface so to give the least amount of room I've set limits in my own speaker driver hunt to a maximum mounting depth of 2.5" (63.5mm). The enclosure baffle has a cutout diameter of right at 4-1/16" or 103.18mm. Anything right at or above that number could require sanding to outright cutting of the enclosure to fit. Also, you have to keep in mind that the stock grill has raised ribs and the stock woofer has a raised flange end and port that extends about .5" outward with about a 1/8" foam gasket sandwiched between to help seal the driver to the door which helps direct sound out past the door panel. Pretty common with some stock speakers to help aid in sound dispersion. With that said, using any sort of added baffle to extend mounting depth could cause issues with the woofer contacting the grille while playing the system. For that reason I am avoiding that option and will also pay attention to driver mounting flange thickness.

 

I've had a nice brand new set of JBL Power Series P560c stored up for a while to be put in this car, but after taking those measurements and doing some box modeling, this just isn't going to work for me. The 5.25 components are too large to fit cutout diameter, plus the provided T/S parameters suggest that the box is wayyyy tooo small for a SQ setup. Qtc comes weighing in at 1.7 providing bit of peaking on the lower end so I've decided to scrap that option. I've searched through some sources for a 5" mid since that is what the stock Nak appears to be, but that is just about incorrect as well. There may be some car audio brands that have a 5" comp set, but I prefer raw drivers and the constraints on the enclosure suggest that a 4" driver is best suited. But it isn't that simple as most raw drivers just like car audio drivers vary quite a bit in frame measurements as well as airspace required.

So far, the main two options I've found that will not only fit without trimming, but will work well with the limited .09 cubic feet are the Dayton RS125-4 (marketed as a 5" but really a 4") and the SB Acoustics SB12NRX25-4. The RS125-4 has several options in it's lineup including impedance and cone material. It's a decent quality driver that has been tested to perform well for the money and even outperform some common brands, but the 125P-4 is being singled out due to it's improved upper end and paper cone to avoid the aluminum cone breakup. The SB12NRX25-4 is used in a home audio kit called The Sopranos and gets some good praise by the designer Jeff Bagby and users including his brother Randy. Both drivers can be used in the stock box as is though ported may require some EQ manipulation on the bottom end. In sealed applications, the SB extends down to 101hz while achieving an ideal Qtc around .7 or a hair lower unstuffed. The RS125P-4 is a bit over it's head with the enclosure as it's roll-off is 113hz which isn't bad at all, but Qtc is quite low at .49. The last thing needed here is dry midbass from a small driver. More on this later when I've found more contenders and/or have settled with a set to go with.

 

After much deliberation I decided to go with the SB Acoustics SB12NRX25-04 mostly due to the extra xmax (5mm) which a small mid could really use since it's already at a cone area disadvantage. It's a pretty stout driver for it's size. Obviously enough that Arc Audio bases it's Black 4.0 mids off of it, if it's not a simple rebadge. After receiving them, I took one and mounted temporarily in the stock enclosure. Depth is more than fine as measured. Enclosure cutout diameter is a bit oversize as the mid has a bit of room to slide around which can leave a small gap to be seen in one of the mounting holes of the frame. This will require some careful positioning before securing to the enclosure and perhaps some sealant or extra gasket material to insure there are no leaks.

I took the mid & enclosure and did some minor listening evaluation on a home stereo amplifier. Lower midrange sounds nice and rich. Plenty of excursion from the little driver that remains quiet through it's stroke. What I found rather offensive is the excessive port noise. Indicated by the modeling software, I knew there would be some, but this seems much worse than it should have been. I turned the volume up and down, but the port noise only decreased to a minor degree at the lowest volumes though still audible. Next, I stuffed the port to create a pseudo sealed enclosure as modeled and the results were much much better. Midbass was smoother with enough extension below 100-120hz that exhibited a controlled sound like that of some mini monitors. I went back and forth again & again listening to different tracks, while giving both sealed & ported a try on the same track before moving on to the next track. Ported got a tad lower, but the port noise just really gets in the way to the degree that any performance gains are negated. I finally decided to take the enclosure apart and do further examination although I had already determined at that moment that sealed was going to be the way it is installed. Ported could work if crossing high enough to eliminate noise, but then you lose the advantage of a higher throw mid and revert back to the neutered upper bass sound of stock mids.

Disassembled and well, well.... what I've found, the port of the enclosure is a poor design! A flattened area midway of the port means that vent area is severely compromised which accounts for the excessive port noise. The equivalent of running a smaller port which may have been okay on low power and a shorter xmax mid, but trying to make improvements in output and response won't work like this. Perhaps it is to accommodate the shallow enclosure and could be improved with some pvc replacement, but at this point I'm not sure I will bother since modeling shows vent noise is still going to ramp up some. I also noticed the passive crossover. A simple cap for the tweet and inductor for the mid. Didn't seem too bad with stock speakers, but it would be safe to assume that any upgrades that use existing wiring without considering crossover improvement will not be optimal for performance. I will be going active for better control of both mid & tweet so that circuit will bypassed. Later on any of that, but for now here's pics of what I've detailed:

 

Finally getting needed parts in I have further prepped the enclosure and sail panel to accept the new mid & tweet. A little bit of sanding with a 150 grit disc rolled up got the tweeter to fit superbly. I soldered a protection cap inline should the processor ever fail or glitch. The tweeter was secured with a few dabs of hot glue on the backside of the panel. I then soldered and heat shrinked xt60 connectors on both mid (In the enclosure) and on tweeter pigtails for easy plug & play should either one need replacing or if i decide to upgrade. The original plug for the enclosure will remain in use for the mid while the internal xt60 connector will make leaving the enclosure installed possible during replacement. The tweeter will use new wiring and xt60 likewise.

 

The next step before tearing into the passenger side to repeat the process is to go ahead and run the necessary wiring. Since I'm employing a fully active system, using the existing wiring won't work as each mid and tweeter will require its own. However, this is much simpler than most think or what I've read on here. There's only two grommets to be concerned with. One on the inner door skin where the wiring comes through and the usual one that most dread snaking wire through. The last piece to be concerned with is a plastic cover that easily snaps off or on that the wiring passes through the lower pillar. A large zip tie wrapped with electrical tape to hold the wire works well and won't damage or scratch anything in the process. I also chose to use 4 conductor speaker cable for ease of install and less bulk which makes snaking and pulling a heck of a lot easier. I'm using 18 gauge which is more than adequate for the level of power I have (75×4), but 16 gauge is available in the same Monoprice Accesss series should anyone be interested. One run per side makes quick work of wiring. Some quick pics before I continue on back to work.

 

Got the stock enclosures back in the vehicle with the SB Acoustics mids & Peerless tweets in place. Having to rewire everything is somewhat of a pain, but it pays off in the end. Now I have full control of each one's level & response separately. I haven't done a full tune using a mic & RTA yet, but did a preliminary setup to get things up and running while checking for any issues. The sealed mids are high passed at 140hz with a -6db Butterworth slope, then low passed with a Linkwitz/Riley -24db slope at 4khz. The tweeters were crossed at the same with a 4khz LR @ -24db.. I'm sure this won't be the final setting once the mic is brought out to spot & improve issues in the response, but I can say for now that the mids have more usable bottom end now that the enclosures are sealed. I've actually been able to run them down to 100hz on a -6db Butterworth slope without much issue, but when blending in with the sub you would have to cross it lower than what is optimal (around 50hz or so) which gives up a bit of midbass from the sub. I brought the mids up a bit to 140 which allows the sub to cross at about 70hz still with a shallow slope of -6db. The reason for the shallow slopes and staggered response seems trivial, but I did this for phase reasons and summed response in the crossover area. Leveled just right you get a seamless blend where the sub sort of disappears and the bass is up front with you. The system is time aligned through the processor so keep that in mind as well. The mid's crossover point may seem a bit low with a shallow slope or maybe even high to some, but you still have the inherent slope from being sealed so audibly it sounds about right where it's at, and handles power very well. Much more than the stock Nakamichi mids. Once the mic & RTA are put to use I should be able to clean things up quite a bit more.

Altogether, the system sounds pretty good even compared to my truck which uses an active 4-way setup (.75" tweeter, 2.5" midrange, 8" midbass, & 10" sub) utilizing two amps & same exact Helix DSP. No, the midbass impact isn't as good in the LS400, but it's still a much better rattle-free improvement compared to what it used to be in response & volume. Aesthetically, nothing looks different other than the grill cloth has been replaced using the beige cloth from Speakerworks which happens to match very nicely and cleans up the doors well if you have tattered or stained cloth. A hot glue gun and scissors are all that you need to fix them.

In all, an upgrade like this is pretty simple & fairly inexpensive though improvement is big, so no need to drag on with more updates and writings. Forgot to take pics of the enclosures in the doors, but really not that important as we all know what that looks like. So here's what's left of the pics I did take of the enclosure before installing, and with the door panels back in place with the new grill cloth. Still have some panels to put back in later on so excuse whatever mess you may see. Enjoy the pics and thanks for reading.


New mid in place. Port removed and hole sealed.