Interior/Exterior Rear Seat Delete Cabinet Project
#1
10-19-2007, 08:42 PM
Rear Seat Delete Cabinet Project
I'm mostly done with a rear seat delete cabinet. So, I thought I'd post some photos of the finished cabinet and some taken in process.
The main point of this was that I rarely carry more than one passenger and the rear seats in my Integra have bugged me for many years. So, with the MINI, I thought I'd get rid of them and put up a barrier to keep cargo from coming forward in a quick stop or accident. I also wanted to make the cargo area concealed so people couldn't see what was in there.
Since the back would be sealed off, I thought I should move the 6x9 speakers. The wiring is not finished. It will be better hidden at some point. The speakers are Infinity Kappa 693.7i. I think I'm going to have to go with a full audio upgrade using a clean sweep and new amp. The crossovers in the HIFI don't seem suited for the Kappas. No bass comes through.
The front of the cabinet is painted metalic black. The fuzzy material is "Subwoofer Box Carpet" from Crutchfield and looks very much like the interior of the MINI. The trim is Ziricote hardwood.
The main point of this was that I rarely carry more than one passenger and the rear seats in my Integra have bugged me for many years. So, with the MINI, I thought I'd get rid of them and put up a barrier to keep cargo from coming forward in a quick stop or accident. I also wanted to make the cargo area concealed so people couldn't see what was in there.
Since the back would be sealed off, I thought I should move the 6x9 speakers. The wiring is not finished. It will be better hidden at some point. The speakers are Infinity Kappa 693.7i. I think I'm going to have to go with a full audio upgrade using a clean sweep and new amp. The crossovers in the HIFI don't seem suited for the Kappas. No bass comes through.
The front of the cabinet is painted metalic black. The fuzzy material is "Subwoofer Box Carpet" from Crutchfield and looks very much like the interior of the MINI. The trim is Ziricote hardwood.
The cargo areas in the back were painted with a textured "Stone" paint and then oversprayed with metalic black. Black pile carpet covers the floor.
Here is how it began:
This is the area where the rear seats were. The wooden pieces are attached to existing elements in the MINI without drilling any holes in the car. The rear part uses two boards that are clamped to brackets similar to those used for hooking cargo nets in the boot.
The front piece uses wooden pins going through loops that the seats snapped onto.
The front piece uses wooden pins going through loops that the seats snapped onto.
The seat cavity was filled with acoustic batting.
A floor of 1/2" Finnish Birch plywood was attached to the boards with T-nuts and machine screws in the front and wood screws in the back.
The floor was removed and a cabinet attached to it. Here are photos of the cabinet being built. It is made of 3/8" Finnish Birch plywood.
The difficult part about this cabinet is that very few joints are right angles. Typically there are two angles involved in each edge. Getting it all to fit was a mind twister and required a lot of care. I had to re-cut more than one piece when I got one of the angels backwards on the saw.
#4
10-20-2007, 08:52 AM
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Not to take glory away from your cool little project... But aren't you the one who was giving me a hard time about the weight of my wife's OEM rims and run flats (which is trivial compared to this behemoth)??? Talk about adding a substantial amount of weight to your car! 
That box has to weigh close to 200 pounds (or more when you account for speakers, amps, etc.). 
And to think... Some folks complain about the weight of a silly sun roof. :impatient Nothing like having a fat guy sitting in your back seat permanently eh. 
Really nice job though.
That box has to weigh close to 200 pounds (or more when you account for speakers, amps, etc.). And to think... Some folks complain about the weight of a silly sun roof. :impatient Nothing like having a fat guy sitting in your back seat permanently eh. Really nice job though.
Last edited by TheOfficeMaven; 10-20-2007 at 08:54 AM.
#5
10-20-2007, 11:00 AM
Not to take glory away from your cool little project... But aren't you the one who was giving me a hard time about the weight of my wife's OEM rims and run flats (which is trivial compared to this behemoth)??? Talk about adding a substantial amount of weight to your car! That box has to weigh close to 200 pounds (or more when you account for speakers, amps, etc.). And to think... Some folks complain about the weight of a silly sun roof. :impatient Nothing like having a fat guy sitting in your back seat permanently eh.
Really nice job though.
That box has to weigh close to 200 pounds (or more when you account for speakers, amps, etc.). And to think... Some folks complain about the weight of a silly sun roof. :impatient Nothing like having a fat guy sitting in your back seat permanently eh. Really nice job though.
I didn't weigh it because I don't have an accurate scale that would handle something like that. My guess, based on the the specific gravity of Baltic Birch, is that with the Dynamat it added about 60 lbs. Subtract from that the weight of the rear seats. Oh, and the Kappa speakers are a little lighter than the stock speakers they replaced. They have special magnets that allow them to be lighter.
Also, there is a big difference between sprung weight and unsprung weight. Unsprung weight (wheels, tires, brakes, etc.) has a more profound effect on ride comfort, braking, handling, and acceleration.
In comparison to a sunroof, the weight of this mod is much lower. The Dynamat (about 20 lbs) is mostly on the bottom of the interior. The floor at about 14 lbs is also very low. The material to make the cabinet would have weighed about 22 lbs., but there was a lot of scrap. The sunroof weights more than my mod added to the car (after subtracting the weight of the seats), and is at the very top of the car, raising its center of gravity.
Last edited by Robin Casady; 10-20-2007 at 11:02 AM. Reason: correction
#6
10-20-2007, 03:34 PM
Thanks. The Dynamat did make a big difference in sound coming from the back. However, there is still a lot of sound coming from the front. So, it needs to be done to the floor under the front seats and foot wells, and possibly the doors.
#7
10-20-2007, 05:40 PM
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#8
10-20-2007, 06:18 PM
#9
10-20-2007, 06:43 PM
Nice project.
Thanks for posting.
I would have thought a subwoofer would be a natural to include.
Maybe build it into the floor and hide the amp.
Even a sub in the place of the two 6x9s and run just component front speakers in the doors or similar.
If you like your results that's all that matters.
Any ideas for a rear cargo area security cover?
#10
10-20-2007, 08:33 PM
My original idea was just to replace the HIFI speakers and be done with the audio. Now...
I hope to get a chance to hear Unixgal's audio upgrade. That might persuade me of the value of a sub.
If you like your results that's all that matters.
Any ideas for a rear cargo area security cover?
#11
10-22-2007, 04:06 AM
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Very ambitious project, well done!
Does the relatively thin wood give you problems with resonance? I would expect the wood to add its own sound to the mix.
About the missing bass -- does the air volume of the enclosure match the compliance/free air resonance of the woofers? If it's too tight, less bass; too loose, distorted bass.
Again, congratulations on the project!
Does the relatively thin wood give you problems with resonance? I would expect the wood to add its own sound to the mix.
About the missing bass -- does the air volume of the enclosure match the compliance/free air resonance of the woofers? If it's too tight, less bass; too loose, distorted bass.
Again, congratulations on the project!
#12
10-22-2007, 10:51 AM
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#13
10-22-2007, 01:10 PM
Peace Keeper
#14
10-24-2007, 02:51 PM
About the missing bass -- does the air volume of the enclosure match the compliance/free air resonance of the woofers? If it's too tight, less bass; too loose, distorted bass.
Again, congratulations on the project!
Again, congratulations on the project!
A very rough calculation on my boxes is that they have > 220 cu. in. free air. Any thoughts on that?
#15
10-24-2007, 04:00 PM
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No resonance. The speaker box is a separate unit in the center. It is made of MDF. It attaches to the Birch ply cabinet with isolation pads.
A very rough calculation on my boxes is that they have > 220 cu. in. free air. Any thoughts on that?
A very rough calculation on my boxes is that they have > 220 cu. in. free air. Any thoughts on that?
Assuming that you have an airtight box, I would expect the needed volume to be twice to three times the 220 cubic inches you have. High-compliance 8" woofers I have used needed about a cubic foot of sealed air space.
There's a fairly complex relationship between coil impedance, surround compliance, free-air resonance, magnetic flux, and box volume -- and a formula to go with it. I don't have the data or the formula at hand, so this is a semi-educated guess.
The speaker specs I saw indicated a separate crossover. Are you feeding the amplifier's full spectrum to the speaker's crossover? If not, it may be that the bass is simply being filtered-out. I have no idea how the MINI's amplifier output is wired.
Reversed polarity on one of the speakers is another possibility. Right channel and left channel bass can cancel each other if they are out of phase.
If I am being obtuse or begging the obvious, please forgive. Just giving it a shot.
#16
10-24-2007, 05:54 PM
Thanks for your help.
What happens when someone puts a baffle behind the speaker? I would think that would kill it, but the guy at Crutchfield said it would help the bass.
The MINI HIFI has two sets of wires going to the 6x9 location. One for the woofer and one for the tweeter. I assume there is a crossover in the HIFI amp. One of the reasons I chose the Kappas was because they have two inputs (result of having a separate crossover).
I had assumed that the crossover to the 6x9s were what was limiting the bass, but other NAMers claim they are getting bass out of their HIFI 6x9s. On my setup, all the bass comes out of the larger speakers in the doors.
Is there a way to check the polarity of the feed wires. I don't want to gut the car again just to make sure I didn't switch wires on one side.
It would be useful to know exactly how much free air the Infinity Kappa 693.7i needs.
There are two designs for woofers: acoustic suspension (sealed box) and tuned port (box with a tube to the outside). The specs I found for this speaker indicate a rubber surround. Rubber surrounds are usually quite compliant, so this suggests that the designer expects the speaker to be used in a sealed box whose air would act like a spring, keeping the cone's motion under control.
Assuming that you have an airtight box, I would expect the needed volume to be twice to three times the 220 cubic inches you have. High-compliance 8" woofers I have used needed about a cubic foot of sealed air space.
There's a fairly complex relationship between coil impedance, surround compliance, free-air resonance, magnetic flux, and box volume -- and a formula to go with it. I don't have the data or the formula at hand, so this is a semi-educated guess.
Assuming that you have an airtight box, I would expect the needed volume to be twice to three times the 220 cubic inches you have. High-compliance 8" woofers I have used needed about a cubic foot of sealed air space.
There's a fairly complex relationship between coil impedance, surround compliance, free-air resonance, magnetic flux, and box volume -- and a formula to go with it. I don't have the data or the formula at hand, so this is a semi-educated guess.
The speaker specs I saw indicated a separate crossover. Are you feeding the amplifier's full spectrum to the speaker's crossover? If not, it may be that the bass is simply being filtered-out. I have no idea how the MINI's amplifier output is wired.
I had assumed that the crossover to the 6x9s were what was limiting the bass, but other NAMers claim they are getting bass out of their HIFI 6x9s. On my setup, all the bass comes out of the larger speakers in the doors.
Reversed polarity on one of the speakers is another possibility. Right channel and left channel bass can cancel each other if they are out of phase.
If I am being obtuse or begging the obvious, please forgive. Just giving it a shot.
#17
10-24-2007, 06:46 PM
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Thanks for your help.
What happens when someone puts a baffle behind the speaker? I would think that would kill it, but the guy at Crutchfield said it would help the bass.
I'm not sure what kind of baffle he would be talking about. In my language a baffle is something that isolates. At low frequencies a baffle is always used to separate the sound coming off the front of the speaker from the sound coming off the back. Since their phase is opposite, the front and back sound tend to cancel each other. This is the reason for having a box. It is the baffle that separates the front and back wave.
People who set a woofer on a shelf without mounting it in a baffle get far less bass because the front wave and back wave are neutralizing each other.
It's essentially the principle used in the Bose noise-cancelling headphones, but Bose has to actually generate a very complex inverse analog of the noise waveform to cancel it.
The MINI HIFI has two sets of wires going to the 6x9 location. One for the woofer and one for the tweeter. I assume there is a crossover in the HIFI amp. One of the reasons I chose the Kappas was because they have two inputs (result of having a separate crossover).
I noticed the Kappas are rated at 2 ohm impedance. What is the impedance of the stock woofers? 4 ohm and 8 ohm are more common values. Speculating: maybe the 2 ohm speakers are trying to draw more power than the amp can tolerate, and it's protecting itself by attenuating the signal?
I had assumed that the crossover to the 6x9s were what was limiting the bass, but other NAMers claim they are getting bass out of their HIFI 6x9s. On my setup, all the bass comes out of the larger speakers in the doors.
Have you tried connecting the amp's output to regular home-style speakers to see what they sound like? This is a relatively easy test, to see what is actually coming out of the amplifier.
Is there a way to check the polarity of the feed wires. I don't want to gut the car again just to make sure I didn't switch wires on one side.
The simplest way is to reverse the wires going to one of the speakers. This is as easy as cutting one pair in half at a convenient spot and then splicing them back together, but not the same. Meaning, if you had a red and a black going to one of the woofers, you would cut them and then splice the black to the red and the red to the black. Polarity is thereby reversed. If you hear improved bass, then polarity is at least part of the problem. If the bass is worse, then you just put black on black and red on red again. No harm done except that it won't be quite as neat-looking.
It would be useful to know exactly how much free air the Infinity Kappa 693.7i needs.
What happens when someone puts a baffle behind the speaker? I would think that would kill it, but the guy at Crutchfield said it would help the bass.
I'm not sure what kind of baffle he would be talking about. In my language a baffle is something that isolates. At low frequencies a baffle is always used to separate the sound coming off the front of the speaker from the sound coming off the back. Since their phase is opposite, the front and back sound tend to cancel each other. This is the reason for having a box. It is the baffle that separates the front and back wave.
People who set a woofer on a shelf without mounting it in a baffle get far less bass because the front wave and back wave are neutralizing each other.
It's essentially the principle used in the Bose noise-cancelling headphones, but Bose has to actually generate a very complex inverse analog of the noise waveform to cancel it.
The MINI HIFI has two sets of wires going to the 6x9 location. One for the woofer and one for the tweeter. I assume there is a crossover in the HIFI amp. One of the reasons I chose the Kappas was because they have two inputs (result of having a separate crossover).
I noticed the Kappas are rated at 2 ohm impedance. What is the impedance of the stock woofers? 4 ohm and 8 ohm are more common values. Speculating: maybe the 2 ohm speakers are trying to draw more power than the amp can tolerate, and it's protecting itself by attenuating the signal?
I had assumed that the crossover to the 6x9s were what was limiting the bass, but other NAMers claim they are getting bass out of their HIFI 6x9s. On my setup, all the bass comes out of the larger speakers in the doors.
Have you tried connecting the amp's output to regular home-style speakers to see what they sound like? This is a relatively easy test, to see what is actually coming out of the amplifier.
Is there a way to check the polarity of the feed wires. I don't want to gut the car again just to make sure I didn't switch wires on one side.
The simplest way is to reverse the wires going to one of the speakers. This is as easy as cutting one pair in half at a convenient spot and then splicing them back together, but not the same. Meaning, if you had a red and a black going to one of the woofers, you would cut them and then splice the black to the red and the red to the black. Polarity is thereby reversed. If you hear improved bass, then polarity is at least part of the problem. If the bass is worse, then you just put black on black and red on red again. No harm done except that it won't be quite as neat-looking.
It would be useful to know exactly how much free air the Infinity Kappa 693.7i needs.
#18
10-24-2007, 06:53 PM
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Thanks for your help.
What happens when someone puts a baffle behind the speaker? I would think that would kill it, but the guy at Crutchfield said it would help the bass.
693.7i needs.
What happens when someone puts a baffle behind the speaker? I would think that would kill it, but the guy at Crutchfield said it would help the bass.
693.7i needs.
#19
10-24-2007, 08:17 PM
#20
10-25-2007, 04:05 AM
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I would try the two relatively easy checks, as described above:
1. Hook-up the MINI HiFi amplifier to a pair of good living-room speakers you are familiar with, and see how it sounds. Despite any difference in impedance between home and auto speakers, that would give you an idea of what sound to expect, and whether there's a problem in the amp.
2. Reverse the polarity on one of the speaker wires leading to the bass side of the Kappas, as described above.
#21
10-25-2007, 04:19 AM
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#22
10-25-2007, 08:12 AM
Okay on that. Without any data to work from, I would guess that 400 - 600 cu. in. per speaker would be better, but that is major surgery and a last resort.
I would try the two relatively easy checks, as described above:
1. Hook-up the MINI HiFi amplifier to a pair of good living-room speakers you are familiar with, and see how it sounds. Despite any difference in impedance between home and auto speakers, that would give you an idea of what sound to expect, and whether there's a problem in the amp.
I would try the two relatively easy checks, as described above:
1. Hook-up the MINI HiFi amplifier to a pair of good living-room speakers you are familiar with, and see how it sounds. Despite any difference in impedance between home and auto speakers, that would give you an idea of what sound to expect, and whether there's a problem in the amp.
2. Reverse the polarity on one of the speaker wires leading to the bass side of the Kappas, as described above.
Something I don't understand; how could a car speaker be successful if it was dependent on an air-tight enclosure of a specific size? Different cars are going to have different spaces, and few would be air tight. For example, the MINI 6x9 location is quite large. It goes over the wheel well and is open at the rear where the amp is.
I wonder if porting my cabinet would help?
FWIW, the stock speakers don't produce bass when they are put in my cabinet.
#23
10-25-2007, 11:00 AM
I just received this message from Infinity:
"Although all of our multi element mobile loudspeakers were designed for free air installation, in order to obtain optimal base performance of the speaker we recommend that you use a sealed enclosure with a volume of 1 - 1.5 ft^3 per speaker to maintain proper bass performance."
I've sent a message asking if I could use a ported enclosure to good effect. It seems like it is that, or tear the whole cabinet apart.
"Although all of our multi element mobile loudspeakers were designed for free air installation, in order to obtain optimal base performance of the speaker we recommend that you use a sealed enclosure with a volume of 1 - 1.5 ft^3 per speaker to maintain proper bass performance."
I've sent a message asking if I could use a ported enclosure to good effect. It seems like it is that, or tear the whole cabinet apart.
#24
10-25-2007, 04:09 PM
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What I have are NHT speakers. A 1.5 would be easiest to get into the car. However, it is 8 ohms and the system is designed for 2 ohm. Any problem there? I know it is bad to go the other way (using a lower ohm speaker), but will an 8 ohm sound OK?
You could get a good idea of what's going on by just setting a speaker beside the car and running jumpers to it. A piece of lamp cord would be fine. Using an 8-ohm speaker won't hurt anything. It will just demand less from the amplifier, and might need a little volume boost. I suppose the response curve would be different, but complete accuracy isn't important here -- just whether the bass is getting through.
Something I don't understand; how could a car speaker be successful if it was dependent on an air-tight enclosure of a specific size? Different cars are going to have different spaces, and few would be air tight. For example, the MINI 6x9 location is quite large. It goes over the wheel well and is open at the rear where the amp is.
True: every car will have a different volume of air behind the cone, and in most installations the air would not be in a sealed box. It would even leak around the baffle at some point. Therefore, the surround and spider must not be too compliant, else the uncontrolled movement could shoot the voice coil right out of the voice coil gap when a user cranked the volume way up.
To the speaker manufacturer's advantage, few people will listen critically enough to tell the difference. Most have never heard a good loudspeaker, and listening to any loudspeaker in a car is dicey if you're a perfectionist. Room boundaries have a huge effect on perceived audio, and the boundaries in a car are all over the place!
I wonder if porting my cabinet would help?
Porting could be a good way to cope. I have experimented with ported speakers and found that the diameter and length of the port is crucial. The port tube maintains a controlled pressure within the box, while allowing more cone excursion than a sealed box would. The pressure has to be tuned to the speaker and volume of the box. Again, there is a formula, but I have lost track of it. If you are a patient and persistent man, as I suspect you are, you could start with a hole of perhaps one inch diameter, and a piece of PVC pipe to fit, and almost the depth of the box. Then you could slide it in and out and try different lengths. If there was some improvement, you might venture a slightly larger hole. But, with a cone only 6 x 9, and a small box, you wouldn't want to jump right to 2 inches. When you found the right port, you could simply seal it in place with silicone rubber caulk.
You could work on just one side, using the previous speaker as a reference for comparison, then duplicate the configuration on the other.
FWIW, the stock speakers don't produce bass when they are put in my cabinet.
This leads me to think that the test using household speakers is a very important "first" step. It may be that the amp simply isn't producing any bass. (Is the bass side of the amp fused? Someone may have cranked the bass and volume past their tolerance, and blew the voice coils and/or a fuse in the amp -- hopefully, not the bass side of the amp, as well.)
You could get a good idea of what's going on by just setting a speaker beside the car and running jumpers to it. A piece of lamp cord would be fine. Using an 8-ohm speaker won't hurt anything. It will just demand less from the amplifier, and might need a little volume boost. I suppose the response curve would be different, but complete accuracy isn't important here -- just whether the bass is getting through.
Something I don't understand; how could a car speaker be successful if it was dependent on an air-tight enclosure of a specific size? Different cars are going to have different spaces, and few would be air tight. For example, the MINI 6x9 location is quite large. It goes over the wheel well and is open at the rear where the amp is.
True: every car will have a different volume of air behind the cone, and in most installations the air would not be in a sealed box. It would even leak around the baffle at some point. Therefore, the surround and spider must not be too compliant, else the uncontrolled movement could shoot the voice coil right out of the voice coil gap when a user cranked the volume way up.
To the speaker manufacturer's advantage, few people will listen critically enough to tell the difference. Most have never heard a good loudspeaker, and listening to any loudspeaker in a car is dicey if you're a perfectionist. Room boundaries have a huge effect on perceived audio, and the boundaries in a car are all over the place!
I wonder if porting my cabinet would help?
Porting could be a good way to cope. I have experimented with ported speakers and found that the diameter and length of the port is crucial. The port tube maintains a controlled pressure within the box, while allowing more cone excursion than a sealed box would. The pressure has to be tuned to the speaker and volume of the box. Again, there is a formula, but I have lost track of it. If you are a patient and persistent man, as I suspect you are, you could start with a hole of perhaps one inch diameter, and a piece of PVC pipe to fit, and almost the depth of the box. Then you could slide it in and out and try different lengths. If there was some improvement, you might venture a slightly larger hole. But, with a cone only 6 x 9, and a small box, you wouldn't want to jump right to 2 inches. When you found the right port, you could simply seal it in place with silicone rubber caulk.
You could work on just one side, using the previous speaker as a reference for comparison, then duplicate the configuration on the other.
FWIW, the stock speakers don't produce bass when they are put in my cabinet.
This leads me to think that the test using household speakers is a very important "first" step. It may be that the amp simply isn't producing any bass. (Is the bass side of the amp fused? Someone may have cranked the bass and volume past their tolerance, and blew the voice coils and/or a fuse in the amp -- hopefully, not the bass side of the amp, as well.)
#25
10-25-2007, 04:16 PM
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I just received this message from Infinity:
"Although all of our multi element mobile loudspeakers were designed for free air installation, in order to obtain optimal base performance of the speaker we recommend that you use a sealed enclosure with a volume of 1 - 1.5 ft^3 per speaker to maintain proper bass performance."
I've sent a message asking if I could use a ported enclosure to good effect. It seems like it is that, or tear the whole cabinet apart.
"Although all of our multi element mobile loudspeakers were designed for free air installation, in order to obtain optimal base performance of the speaker we recommend that you use a sealed enclosure with a volume of 1 - 1.5 ft^3 per speaker to maintain proper bass performance."
I've sent a message asking if I could use a ported enclosure to good effect. It seems like it is that, or tear the whole cabinet apart.
Infinity would certainly have the resources to tell you the proper port configuration. I hope they come through for you.