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Discussion Starter #1
So this post will be my build log for adding a subwoofer amplifier as well as a subwoofer to my Kia Niro LX hybrid.


My primary goal is to add a subwoofer to the stock stereo. However, I have a few requirements that are going to make this build different.

Requirement #1

The subwoofer MUST NOT take away ANY cargo space.


Requirement #2

The amplifier MUST NOT exceed 315 watts which is equal to the Harmon Kardon premium audio amplifier size.


Requirement or Preference #3

A 10” subwoofer is used.



So how in the world am I going to have a 10” subwoofer not take up any cargo area? Well, I could put it in the spare tire well, but then I would have to put my spare tire and/or the tire tools in the cargo area. So that place is out. After looking and measuring closely, it looks like I can build a custom subwoofer box for a 10” sub to go UNDER the driver seat! Yes, that’s right. A 10” subwoofer under the driver seat.

Since my LX model does not have power seats, there is 6” of height there. Front to back is about 10” and width under the seat rails is a whopping 20”!! So that will leave me with a box of only, about 0.35 cubic feet. That’s not much to work with, but I found a shallow mount 10” sub that has a minimum sealed air space requirement of 0.35 cubic feet. Perfect!

The amp I will be getting has the capability of putting out nearly 700 watts so I’ll have to put my meter on it and turn the gain down so the maximum RMS wattage will be 300 watts, which is more than enough to drive this particular sub.


But before I order the sub online, I want to build the box. After the box is built I will be able to accurately measure the air space and will then confirm that this sub will work. If the box ends up being less air space than what I originally anticipated then I’ll have to downgrade to a single 8” sub that will work in the available air space.


So as progress is made, I will update this thread and will be taking pics along the way.
 

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Discussion Starter #2
What about the air vent under the driver and passenger seats that sends air to the back passengers?


In the back seat on the drivers side is my daughters car seat. That car seat is always in place so I can remove that vent.

That’s all fine and dandy, but how do you remove it?

You simply grab it and pull to the back of the car. It will pop out, and can be easily popped back into place at a later date if needed. Attached is a picture of the vent that has been removed.
 

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Discussion Starter #3
So why only 300 watts?


I wanted to have more power but I was unsure of the capability of the factory DC-DC converter. After numerous phone calls and a few online searches I could not find the rating.

So what I did is I looked at the factory premium audio amplifier and it’s ratings. There is a fuse under the dash for that amplifier and it is a 30 amp fuse. Attached is a picture of where that 30 amp fuse is located.

With that fuse removed, the factory radio still works. So, only the premium audio systems use that fuse. A simple, and typically pretty accurate, way of determining a Class D car audio amplifiers maximum RMS wattage is multiplying the fuse size times 10 (10 represents the voltage used which is higher but no car audio amp is 100% efficienct. So multiplying the fuse size by 10 gives you a more accurate wattage rating instead of multiplying fuse size by 13 or 14.). So this limits maximum amperage to 30 amps and maximum wattage to 300.


I want to stay within the factory wattage so as to be 100% sure that I will not be causing other problems due to excessive power consumption. This way, if there ever is an electrical problem in the car, it helps to minimize the possibility the warranty will be voided.
 

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You should end up with a good flat bass curve with the setup you've got planned. Probably wont get as much in the 20-40hz (really deep bass) range due to the starved enclosure volume, but you'll still get some bass in that range, and 40-100hz ought to be pretty good, and definitely should keep up with the factory speakers.

I'm not a fan of boomy bass, and I like bass that is the same level as the mids and highs. In other words, I like my "curve" to be flat. I don't like bass that's louder than what the recording meant for it to be. So I think your setup is going to get you as close to that goal as you can possibly get without sacrificing cargo space. What subwoofer did you pick?
 

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Discussion Starter #5
Exactly. It should be a decent sound quality setup vs an spl setup. The system in my last car was over the top and was metered at 137.6 dB at 80% of the tuned volume and was loud enough to crack the windshield in half. I’ll attach a picture of the crack on the windshield and how far the crack would progress each day that I cranked the volume. It was nice on occasion but I rarely cranked it that loud, so this time I’m going back to a modest system.


I narrowed a list of possible subwoofers down to 10. From there I kept narrowing the field until there was only one clear option. They ranged in price from $50 all the way to $200. I took a lot of notes and compared their sensitivity, minimum sealed enclosure volume, Xmax, voice coil size, and bl specifications. Shockingly, in the end the $50 subwoofer had a better overall fit for what I was looking for. That subwoofer is a Cadence SLW10S2 which is a shallow mount 2 ohm 10” sub. I wanted a JL Audio sub, but the only one they had that was going to be anywhere close to meeting my needs was going to run over $300, and with the rest of the system being stock I just could not justify that.



This is not my first attempt at an under seat subwoofer. I had a 2014 Mitsubishi Mirage that I made a custom sealed enclosure for under the passenger seat. It was only 0.25 cubic foot and had an MB Quart 8” powered by a 250 watt JL Audio monoblock subwoofer amp. It sounded very good and despite the small box it had really good low end. Primarily because a sealed box has a smoother roll off on the bottom end over any other kind of box(except for a transmission line) and the amp was pushing 200 watts rms to that little 8”.
 

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Discussion Starter #6
After leaving work this morning I stopped by a local home improvement store and picked up a few things so the build can start soon. Picked up a single sheet of 3/4”X2’X4’ MDF, 2 cans of black spray paint, some new sanding pads for my sander, some wood putty, and a little wood glue.

I should be able to get started on the box next week. This week I’m too busy today and tomorrow, then my wife is taking my Niro out of town for work from Wednesday through Friday, then late Friday we are heading out of town all weekend for my daughters birthday party. So hopefully the weather will cooperate next week.
 

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Not to downplay the awesomeness of OP building his own custom box, but wouldn't a couple pre-fabbed units under both seats bump louder and with less effort and even less cost?

https://www.ebay.com/itm/Crunch-8-Inch-400-Watt-Compact-Under-Seat-Powered-Subwoofer-Enclosure-2-Pack-/352475746704


I've used under-seat subs before, and they work well for filling out the low-end. Further, having two would prevent the bass from feeling like it's coming from one place (under just your seat) and keep it more omni-directional. There are dozens of other options/brands that would fit as well. Eg, I like how the Pioneer TS-WX130DA has a multi-option remote, rather than just gain. There are others with similar multi-option remotes as well.
 

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Those pre-fab boxes will sound worse. Probably much worse. OP is making his box with 3/4" mdf, the prefab box is probably plastic or sheet metal, which causes distorted, muddy bass because most of the output will be coming from enclosure flex/vibration rather than from the cone. Also it's only an 8" sub in your example, so it won't produce much low-bass, regardless of what the mfgr specs say (as an engineer in the speaker manufacturing industry, I can attest that 99% of manufacturer claims are usually unrealistic at best, or downright lies at worst). For low bass, you need a bigger cone, it's physics. A pre-fab sub is better than nothing, but since OP can make his own, he made the right decision.
 

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Discussion Starter #9
Not to mention a very large majority of those pre-fabbed setups have VERY poor amplification. Most of them claim 200-500 watts, but they only have a 5 amp fuse! Take the fuse rating and multiply that by 10 and that will be a realistic amount of power that it would make.


Yes, I did spend some time researching them. Since I know how to properly build a box and do all of the wiring myself, the cost is very close between a pre-fabbed box/amp/sub and me putting everything together. As of right now, the total cost will be less than $200 for everything.

As to directional sound from the sub, the only time that becomes a factor is with midbass frequencies. Hearing where the sub is at is typically caused from poor crossover frequency selection which most of the time is due to a lack of midbass response from the other speakers. With how well the stock speakers produce midbass in the Niro, that will allow a lower crossover frequency to be used which will reduce or eliminate the directional sound coming from the subwoofer.


Having been in car audio since the early 90’s, I have seen many new technologies come about which have helped to improve the performance of car audio. One of the best increases in technology has come by the means of better subwoofers. In 1995, Alma Gates held the world record for the loudest car audio system in the world. It was a little over 153 dB. Fast forward 20 years and you can now have this same volume in a vehicle that you drive everyday. Another big gain has come from required enclosure size. In the early 90’s it was common for a 12” sub to require a 2 cubic foot sealed box. Then Kicker came along with their Solobaric line and dropped that requirement in half. Short of an isobaric setup(which is where the Solobaric sub got its name) there was no other way to get good bass from a small enclosure. So here we are today and I am looking at spending merely $50 for a 10” sub that will work in a 0.35 cubic foot sealed box. That just blows my mind!!
 

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I'm also glad that people have started to realize that ported boxes are awful.

When I was in high school, they were all the rage, because they made your bass go boom. The only problem is the bass only went boom in a very narrow bandwidth (say 70-80hz), but at other frequencies the bass was almost non-existant because of 1) a complete lack of air suspension and 2) the bass coming out the port was invariably out-of-phase with (and thus cancelling out) the bass coming from the cone. The result was bass that was only audible in one or two very specific and very small low-frequency bandwidths, so it only sounded good when playing a song that had a bass track that happened to coincide with that bandwidth. In other words, they sounded really impressive as long as you only ever played one specific track on one specific cd :D
 

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Discussion Starter #11
I'm also glad that people have started to realize that ported boxes are awful.

When I was in high school, they were all the rage, because they made your bass go boom. The only problem is the bass only went boom in a very narrow bandwidth (say 70-80hz), but at other frequencies the bass was almost non-existant because of 1) a complete lack of air suspension and 2) the bass coming out the port was invariably out-of-phase with (and thus cancelling out) the bass coming from the cone. The result was bass that was only audible in one or two very specific and very small low-frequency bandwidths, so it only sounded good when playing a song that had a bass track that happened to coincide with that bandwidth. In other words, they sounded really impressive as long as you only ever played one specific track on one specific cd /forum/images/KiaNiroForum/smilies/tango_face_grin.png

That also describes bandpass enclosures when people first started building them. One note wonders if you will. Both ported and bandpass enclosures have gotten a lot better, but for their small size and smooth roll off you just can’t beat a sealed box. I prefer a sealed box.
 

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Great thread! Good luck with your build, really looking forward to your report of how it all turns out. Having better bass is the one thing I wish the non-premium sound system I have in my Niro featured. Unfortunately I do have the power seats so I couldn't go this route... and like the OP, am absolutely unwilling to sacrifice storage space, which is already pretty small.
 

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I have simply concluded that no matter what you do, a car will never sound at all good, so why bother. If I wanted to listen to music then I would just go to my dedicated media room in the basement where I've got propper designed accoustics. I do play music in the car sometimes while driving but it's just for passing distraction. no where near the same level.
 

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And no sound system will ever be as good as live music, so why bother? Kidding of course, but I suspect a drive in a well equipped car would change anyone's mind. I'm pretty much in the do not bother camp in a car too, and in the home now too.

More news on the lo-fi front, I picked up a new iPhone model to try yesterday (as a trial) and so far the most compelling feature is the audio speakers. Loud enough, and really nice sound.
 

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Discussion Starter #15
In my younger days, I helped out a friend of mine who competed professionally in sound quality competitions. This was 20 years ago when my hearing was much better. The competition car was a Honda Civic sedan that, due to the massive stereo system and sound deadening, weighed a whopping 5,000 pounds!

That car had perfect imaging thanks to custom mounted speakers in the foot well/fire wall area that faced directly to the occupants. The front seats were also relocated 6” back to diminish the length differences between the left and right speakers to the occupants.

From 20hz to 20k hz there was only about 3db difference which is about as good as can be done. It had a pair of 1/3 octave mono equalizers to fine tune it all. The factory trunk was also 100% useable as the subwoofer enclosure was below the trunk floor where three 12” subs were mounted. 5 1/2” midbass drivers were installed in custom enclosures into the bottom seat cushion of the front 2 seats! The car was over the top and, at that time, cost $50k to complete.

Rarely have I heard home audio systems that rivaled this car. Play well recorded classical music, close your eyes, and you could point out exactly where each instrument was located on the stage when the piece was recorded.


I said all of that to say this. Anything is possible with enough money. With my diminished hearing and with the increase in quality of factory car audio systems, about all that is lacking to me in the base stereo are the subwoofer frequencies of around 60 hz on down. With my musical taste, there is a lot missed in the factory stereo. Hence this build.


My apologies on the long winded posts.
 

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Classical or other music with a high dynamic range is quite the test of a car audio system with a typical noise floor of 70 dB at highway speeds. When I was very young, I flirted a bit with figuring out ways to compress the dynamic range (dbx had one system - analog back then) so you could hear the quiet bits without getting blasted in the loud bits. Same thing radio stations do (or did) for their largely car driving audience. Commercials also compressed audio even more so it would sound louder and pop better than the radio station content. Vinyl records and audio tapes do the same thing, for practical physics reasons and noise reduction, with the playback device decompressing the audio into something similar to what the recording engineer intended.

From what I read, noise reduction in cars is one of the better ways to get better sound. Of course, it is not easy or cheap and requires a lot of trial and error. Best is to do that during car manufacture, and so luxury cars automatically will have better sounding audio. High end audio brands also do better with new cars as they can more efficiently map the car's response curves for a production run rather than one car at a time. Still expensive, and they don't always get it right. Lots of choices for speaker placement and equalization curves in a very complex environment, several magnitudes more complex than home environments.
 

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Discussion Starter #17
Got some progress, but not much.


Total times the front seat has been unbolted to date; 2


So after some rough measurements, it appeared as though the bottom of the box had a 10” X 20” measurement. So I cut this out and did a test fit. It was not quit a perfect fit and there was extra room that could be utilized if I were to step up 3/4” from the base. So that is exactly what I did.

I also saw that the cut out in the carpet for the air bag wires on the seat looked nasty, and was getting in the way. So a simple cut on the carpet now allows the carpet to sit where it should be.



My next step is to find my pneumatic brad nailer, measure and cut out all of the sides, and then start the slow process of assembly. I’m also concerned about clearance issues with the air bag connectors under the seat. They hang down quit a bit. If I can rotate and resecure them, I might be able to gain another 1” of depth for the box, or an extra inch in clearance for the subwoofer.

In the meantime, here are some pictures from today’s activities;
 

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Discussion Starter #18
The weather has not been cooperative the last several days so no progress has been made. I did decide on what amplifier will be used and when I’ve got more time I’ll elaborate more about it. What I will say is it is Korean made, puts out a true 650 watts at 2 ohms, and can be had brand new for less than $100.
 

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Discussion Starter #19
More progress


Total number the seat has been removed since the beginning of this project;

3


The 2 pieces that make up the bottom of the box were glued and screwed together a couple of days ago. The weather and my allergies have not allowed much work at all over the last week till today.

So with the bottom of the box complete, now I can measure and start working on building the box up. Got the measurement on one side of the box, so I just made 2 of these cuts without thinking that the passenger side of the box is different than the drivers side. DOH!!! Oh well. No biggie. Got the drivers side of the box glued into position.

The first time I looked under the driver seat I noticed this large bracket. In my LX, all this bracket is doing is holding the seat belt sensor and air bag wires out of the way. This bracket appears to be a mount of some kind for the power seat models. Since this is such a large bracket, I am VERY tempted to remove it. Removing the bracket would allow a taller box to be built, and it would also give more clearance for the subwoofer when the system is cranked up. Both subwoofers that I am looking at(the shallow mount Cadence 10” or a Massive Audio 8”) have just over 1” of peak to peak excursion. This amount of excursion requires adequate room above the box so the sub does not hit anything. Removing this bracket would allow at least an additional 1”-2” of room. The bracket is only held in place with 2 small welds. So removing it would not be too hard. The main question is this;

Is removing the bracket going to help that much?

The answer to that question eludes me at the moment. So, it is time that I sit down with pen, paper, and a calculator to see the air space differences with and without the bracket. Once I have this information, then I will be able to make an informed decision.



One other item that is slowing progress on this is a recent move to a new house. During the move, I misplaced several tools. A pneumatic brad nailer, all of my C clamps, a counter sink drill bit, metal straight edge, and all of my screws. Once I find all of this, progress will improve greatly.
 

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Discussion Starter #20
Alright, after putting pencil to paper and taking some more measurements, it looks like my answer is pretty obvious.


With making the box 6” deep total between the seat frame rails, it would leave me with 0.315 cubic feet of air space. This is exactly 10% smaller than the minimum recommend air space and target minimum of 0.35 cubic feet.

If I remove the bracket, it looks like it would free up an additional 2” of total height to 8”. This would give an air space of 0.438 cubic feet. Once you take into account the air space lost due to the structure of the subwoofer inside the box, it would still be ok.


So, the bracket has to go.
 

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