July 20, 2019

Speaker Upgrade - Part 2

Front Speakers Upgrade for Gen 2 (2013) Mini Cooper S

Car Speaker
Car Speaker

Changing the Front Stock Speakers to aftermarket speakers ...

Overview ...

This project started with the desire to improve the sound quality in my Mini. As background, I have a 2013 Mini Cooper S without Harman Kardon sound system. So what I have is the stock base audio setup with the USB and Aux audio inputs, which I think may have been supplied under a 'Technology' package. This setup consists of the main head unit (Radio) with bluetooth connectivity for phones, a USB and Aux input plate located below the center dash console, a CD player, front speakers, and rear speakers.

From what I have researched, there are options to changing out the head unit with an aftermarket radio by replacing the trim kit for the entire center console and putting in a DIN form factor aftermarket radio where the current CD player is. Although this is a tempting option, mainly to get more amplifier power, and more options, especially a rear view back-up camera, I'm not opting to do this sort of major overhaul at this time.

History of Project ...

To improve the sound quality, I'm upgrading selective speakers on the Mini. Ideally, I would upgrade all speakers with higher quality aftermarket ones, but some of the speaker replacements are quite involved. I started out with the aim to upgrade the front speakers, which consist of four speakers, 2 per side of the car, which are located on the doors. I'm now modifying that project to upgrade just two of the four fronts at this time, and then proceed with the front four speakers upgrade later on. The reason for this is that, although I have started on the front four speaker upgrade, Winter is now approaching and I'd like to at least do some sort of upgrade before Winter sets in. I'll explain what is involved shortly; first I'll start off with some information on the existing sound system in the Mini.

As I said, I do not have the premium Harman Kardon sound system. For the speakers, there are a set of fronts, and the rears. I believe the rears are 6x9 coaxial speakers. The fronts consist of two independent speakers per door. There is a roughly 5-1/4 inch round speaker located in the lower part of the door that serves as the woofer for the front sound and a roughly 3 to 4 inch round speaker located mid-way up the door in line with the arm rest; this serves as the mid-range and high end. So my initial plan was to put in a two way component speaker set for the front. I got a component set made by Infinity which has a 5-1/4 inch woofer and a 1 inch soft dome tweeter. Model number of that set is Infinity REF-5020cx. These are an older model of their Reference line and were gotten from Crutchfield for 50% off around the holidays last year. They have gathered a little dust since then, but I did progress on the project and I'll share that information towards the bottom of this page.

The thing about this upgrade is that nothing is really straight forward and easy. The 5-1/4 inch woofers from Infinity should go in with the plastic adapter bracket that was supplied with the speakers by Crutchfield, but getting the door panels off is a whole thing so that is why I am changing course at this point. The midrange speaker located in the door at the armrest level is easy to access. One thing I would recommend is that you use the proper tools for this work, so for accessing the mid-range, that means a nylon pry tool. Although easy to access, the midrange speaker location does not directly accept any small tweeter. The tweeters the come with most component speaker systems are small in form factor and, although they come with a variety of mounting hardware and adapters, I do not know of any standard component tweeter that is not relatively small in diameter. So for this location, I fashioned up a mounting plate using plastic. Information about this mounting plate is located further down this page. I want to jump to the current scheme of what I will be doing for the interim at least until I get the time and desire to tackle taking off the door panels to access the woofer locations.

Issues to Consider ...

So, with not wanting to tackle taking off the door panels, I decided on getting a pair of small coaxial speakers that would go in the midrange location which is pretty easy to access. Before going this route, I did a little research on what is going on with the audio system as far as the head end amplifier to speakers. I had read a while ago that someone thought the head end equalized the audio on the speaker lines prior to going to the individual speakers. From what I have researched on the web, this is correct for the Harman Kardon system, but not for the stock speakers. What I read on a forum from a reputable and knowledgeable source (link at bottom of page) was that the frequency range sent to the two pairs of front speakers was relatively flat and that sent to the rears was flat except for a notch filter in the bass section. So just dealing with the front speakers, I could put a different speaker in the midrange location and be able to receive the full frequency range. This being said, there are a number of points to consider and address:

  • To accomodate the existing headend unit amplifier, which I understand to have not a high power output, we need to consider, among other factors, the impedance of the speaker as well as the efficiency of the speaker.
  • The new speakers need to handle the output in wattage of the existing headend unit amplifier.
  • An understanding of the frequency response of the new speaker has to be gotten.
  • The physical space and arrangment for the mounting of the speaker has to make it possible to mount the new speaker.
Speaker - Infinity REF-4022cfx - Angled View Stock Image

Picture of Infinity REF-4022cfx (The speaker being used).

The first item in the above list is one of the most important as far as mechanical-electrical criteria. The impedance of the existing midrange speaker that is to be replaced I measured to be approximately 3.8 ohms. This is fairly standard, and the new coaxial speakers that I was considering should be around that same value. This is because I do not have a lot of information on the existing headend unit's amplifier. So with the Infinity's that I ended up getting, the impedance is touted as a true 4 ohm load given the about 3 ohm resistance (impedance) of the drivers and the high resistive value of the small gauge wire in the car to amount to 4 ohms of impendance in total. This is fine, even considering that the existing midrange is on the same wire as the new ones will be, so a 3 ohm speaker driver to a 4 ohm speaker driver comparison is good. The efficiency of the new speaker drivers is sometimes overlooked when selecting an appropriate replacement driver(s). In an ideal world, we would know the efficiency of the existing speaker drivers, and/ or more information about the capabilities of the existing headend unit amplifier that is currently powering the existing speakers and will be used for the new speakers.

For the efficiency of the speaker, the specification that is often published is the "Sensitivity". This is usually given in a dB value at 2.83V or 1 watt per meter. What this means is the volume of the audio that is produced by the speaker when measured at 1 meter from the speaker with either 2.83V into 8 ohms or 1 watt of power. The higher the dB value of this sensitivity rating the more efficient the speaker; that is, the higher the sensitivity rating, the more sound volume is produced from the same amount of power. The Infinity speakers that I a bought (REF-4022cfx) have the following published specifications:

  • Impedance: 3 ohms
  • Frequency Response: 75 to 21k Hz
  • Max RMS Wattage: 35 watts
  • Peak Power Handling Wattage: 105 watts
  • Sensitivity (at 2.83V): 92 dB

So, to continue the discussion of sensitivity, for this particular installation, the sensitivity is important, because I am going on the basis, based on what little information I have about the head end unit amplifier, that there is not a lot of avilable power per channel from the amp. So as a comparison, I was considering the Morel 4 inch coaxials (Morel Maximo Coax 4) which may be a better speaker, but the sensitivity of these are 87.5 dB at 2.83V which is considerably less efficiency, and I think they may require more power than available from the stock head end amplifier. If you were upgrading the whole audio system including head end, amplifiers, speakers, then you would have the ability to select various speakers without the restrictions of the stock equipment. You would size the replacement amplifier(s) appropriately to the speaker requirements.

Speaker - Morel Maximo 4 Coax - Angled Rear View Stock Image

Picture of Morel Maximo 4" Coax (not the speaker being used).

Just as an aside, the reasons I feel the Morels may be a better speaker is based on three basic things for me (not having heard the actual speakers themselves): Name Brand, Tweeter size, and the crossover component. I'll use the last item to segue into a relevant item to this project, that is the single crossover component on the Infinity speakers that I got and by comparison, the Morels. The Infinity speakers have a crossover component that produces a filter for the tweeter only. Not having information on the individual drivers of the coaxial speaker, I can only go on the basis that the small woofer doesn't require a filter because it will be handling a large portion of the midrange frequencies. As a side note, to save money, crossovers sometimes do not have filters for the woofer since the notion is that the woofer will just not respond to the high frequencies that are sent to it and therefore a filter to filter out these highs is not necessarily required. There are a lot of different viewpoints on this topic, I'll just leave it with the mention of the topic. So with this speaker, the crossover consists of a lonely capacitor which functions to block a portion of the lower frequncies from reaching the tweeter. Most people agree that this is a must for most tweeters. Comparing the Morel to the Infinity speakers, based on the photograph of the Morel's, it looks like they are using a certain capacitor type which is a higher quality than that being used on the Infinity's. It looks like the Morel's have a film and foil or metalized polypropylene capacitor and based on my examination of the Infinty's that I got, the Infinity's have a non-polarized electrolytic capacitor. All electrolytic capacitors used in a speaker level crossover need to be non-polarized since they are subject to the alternating current of the speaker audio signal that drives the speaker cones and membranes. It is commonly agreed that electrolytic capacitors are of inferior quality audio wise to other type of capacitors such as film and foil or polypropylenes. The reasons for this are outside the scope of my current discussion, but perhaps in the future I will add some relevant information to this post. So, long story short, the only upgrade/ customization I am going to do to the electronics portion of this speaker is address the crossover capacitor. Based on the value printed on the existing capacitor, which is 3.3 uF, I'm looking to replace that electrolytic with a metalized polypropylene capacitor of the same value of 3.3 uF. The other option is the go with a film and foil capacitor, but those are just too crazy expensive with possibly limited benefit given the listening conditions. This brings me to the topic of bypass capacitors. There are a lot of individuals who are under the belief that you can take an electrolytic capacitor, and correct the audio degradation characteristics of the electrolytic by using a small value, higher quality capacitor such as a film or polypropylene cap. My understanding is that this is not correct. I'll leave it at that for now, just if you want to know more about that topic, there are a lot of discussions on the topic and you can gather your own information and base your own understanding on that.

Close up of Crossover Capacitor - Existing

Close Up Picture of Infinty Speaker's Crossover Stock Capacitor.

Looking at my stock of poly caps, I do not have a 3.3 uF, but do have three caps which would add up to that value when placed in parallel wiring (2.2, 1.0, and 0.1 uF). The problem with utilizing these three caps is the physical size of the capacitors. Poly's and Film caps are much bulkier than aluminum electrolytic ones and working with three seperate ones is going to be very difficult in terms of finding room on the speaker frame to secure them. So I set to shopping around for a 3.3 uF poly cap and checked out both Parts Express and Madisound. Both have suitable options. I'm finalizing on the Solen PB Series Poly Cap at 3.3 uF value. These are 33 mm long x 18 mm in diameter. This translates to 1.3 inches long x 0.71 inches in diameter, so it's fairly bulky, but I'm only dealing with one cap per speaker. So where to put it ties in with the next aspect of this project, how to mount the speaker.

Installation - Door Panel Removal ...

Side by Side Comparison of Existing and Replacement Speaker

Left speaker is the Stock (existing) speaker.
Right speaker is the new speaker to be installed.
Red Circles represent overlay of mount points on car door frame.

What I will opt to do is use a piece of plastic sheet that I have left over from the custom mounts made for the initial speaker project, which is discussed below, and cut that to span between the two quad mounting tabs and the required third mounting point. Another, probably better, option is to do the same bracket in metal, either flat steel sheet or a thicker aluminum bar, which would yield a more rigid bracket. I'm going to try to over come the flexibility of the ABS plastic sheet that I have with some reinforcements placed perpendicular to the flat surface of the bracket; this should stiffen it up considerably. To do this, I will be glueing the bracket stiffeners to the bracket flat sheet with glue specifically made for ABS plastic. You'll be amazed at the variety of glues there are for plastics and all I can say is that some work with certain plastics, and others work with other plastics. I strongly recommend using the glue designed for the plastic that you are working with. Here I am using ABS plastic. As an aside, this little bracket manufacturing would be an ideal project for a 3D printer, but I do not have one and it's not worth outsourcing for the printing of these two required brackets.

The tabs of the new speakers are flat metal, just basically part of the stamped steel basket, cut to shape. The plastic bracket will have the thickness of the plastic sheet, which is 1/8" (or 0.125"). So to keep the three final mounting tabs in the same plane, the plastic bracket will be mounted to the face of the speaker frame along the perimeter of the speaker circle. I'll cut it to shape and drill the holes for the screws, and glue on the stiffeners. The idea is to secure the bracket to the two free tabs which are located on the quad points and allow for a mounting point at the third location that matches with the car door frame.

Illustration of Speaker Bracket

Illustration of Speaker Bracket to be Made for Mounting Speaker.

Preparation ...

In addition to making the bracket as described above, the existing speaker 'cups' had to be readied to house the new speakers. Basically, the styrofoam rings and adhered foam stripping had to be remove from the cups as they would interfere with the new speakers.

Installation and Test Fit ...

So, I made the brackets and installed one of the speakers, all went pretty well. The only thing to check on at this point is whether the housing/ cover will fit back on. Prior to this, I removed the round ring of styrofoam and the glued on foam ring from the inside of the cup (cover/ housing), because it was apparent that this would press on the new speaker, definately not something you want to happen. There's a few pointers I can mention here for anyone doing a similiar installation. The bracket will be close to the end of the arm rest when it is installed so you'll need to make sure it is narrow enough to clear that. Also, in terms of bracket size and shape, my first pass at a bracket needed a little adjustment. At the third mounting point that the bracket produces, the bracket can be too big and protrude too far into the circumferance of the circle and bind up on the cup when you go to install the cup after installing the new speaker. It took a few passes reducing the size of the speaker bracket to avoid binding up on the cup to be re-installed. I ended up lining the cup with painters' tape to see where the binding was occurring exactly. You can see the scuff marks on the tape after you go to install the speaker cup and can not because it binds up. For me, the last point to cut back was at the screw hole that is at the point where the speaker bracket is attached to the door frame.

View of Installed Speaker

Picture of Installed Speaker with Bracket - First Pass. A: Point at which bracket is close to door armrest.
B: Part of bracket to be modified because it hits speaker cover 'Cup'.

Illustration of Speaker Bracket after Modifications

Illustration of Speaker Bracket After Modifications.

Preliminary Listening Results ...

So, I ended up having one installed for quite a while which allowed me to compare the two speaker setups (stock and new) by adjusting the balance on the receiver to play either right or left side. The after market upgrade is a big improvement over the stock 'tweeter'. For this particular coaxial speaker, it gives some punch to the mid bass and extends the high range considerably. Definately worth doing, and really not a huge undertaking.


    Relevant Links:
  • https://theminithatroared.info/post_speaker-upgrade.html
  • https://www.northamericanmotoring.com/forums/navigation-and-audio/216180-mini-audio-basics-specs-details-and-upgrades.html

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