The Best Coaxial Loudspeakers

19th April 2024 Adam Rayner

Let’s start at the deep end to help you pick a coaxial speaker. Speakers and microphones do the same thing, just in different directions. They are my favourite things in all tech. Everything else is to me is just about making speakers work. The microphone takes a pressure wave of sound and uses a diaphragm to catch the air. The movement of that diaphragm makes a coil of wire fixed to its back, move within a magnet gap. That makes a signal go up the wire. Speakers take a wire with watts in it – way bigger than the microphone’s one, and turn it back into sound. It’s like magic to me and both are about a thing called ‘Fleming’s Left Hand Rule’. I won’t bore further, but you’re now an expert that can bandy words with speaker physicists and amaze your HiFi friends.

Back in the real world, you are sick to death of the medium quality sound in your car. You know it can be better. You really want to feel the need to sing along bloody awfully to your guilty-pleasure music. The stuff you won’t admit to your friends – I adore ‘cheese’, like Barbie Girl.

Better speakers are the immediate and best way to upgrade your audio in the car. But you need to take a few things into account. The budget is the first one of course, followed by if the speakers will fit in your car. There are standard sizes of all speakers for cars. They use centimetres but they are all sized from classic inches dimensions in diameter. Thing is, the high power handling ones have beefy magnets on their behinds. Some will fit only in bigger cars, so you need an expert to check for you. The crucial measurement is mounting depth.

What Are We Looking For?

These speakers are the coaxial type. That means there is a tweeter assembled with a mid-bass driver in the same chassis. It creates a single source – or ‘point source’ for your sound. This is inherently cool and is used by fancy HiFi brand Cabasse for their home stuff, for instance. Coaxial does not mean low quality, it just means compact. Your car will have it’s own locations but there will be speakers to fit. We have used the 6.5inch size of each for comparison of technical and musical ability. The bullet points list the sizes each speaker line can be had in. We range from entry-level to upper-midway to awesome. After each one, we name the favourite model from each line, if we were to pick one. You will choose by size, though.

MTX Terminator TR65C (seen at £45)

The most major issue with new coaxial speakers for your car is any eventual upgrade. Loudspeakers have various specifications and how many watts they take without dying is one. That’s the famous one. The ‘secret one’ is sensitivity or efficiency. Put just one watt (called 2.83V as signal level in the specifications) into a speaker. Then at one metre away, measure how loud it is in watts. You need an anechoic chamber or an outdoors lab to do this right. Anyway, some speakers can be MUCH louder on less watts than others. Sadly, super efficiency comes with lower power handling. It is a very rare and posh speaker that can do big power and yet be sensitive. It is all about the soft parts that move.

Speaker makers brag about their cone material being light and stiff and the suspensions being extra wibbly-wobbly. The brag about the material their tweeters are made of and their voice coils’ technology. In this case, these are an affordable speaker that MTX expect you not to use the grille with. Ideal as a drop-in replacement, the 92.5dB sensitivity means they will rock on stock power. The suspension is real rubber and the cone is a pretty electroplated polypropylene injection moulding. Fabulous value and those 22kHz tweeters will make the details sing.

Power Handling/Impedance: 65W RMS/4ohms
Sensitivity: 92.5dB @ 2.83V (1W)/1m
Frequency Range: 48Hz to 22kHz
Made as: 4in, 5.25in, 6.5in, 6x9in
Which one we like the best in the range: The 5.25in XTR50C is fabulous value

Alpine SPG-17C2 (seen at £60)

Features like square voice coil wire on heat-proof Kapton bobbins is tech from posh woofers. The square wire means more metal in the magnet gap and so more shove from Fleming’s left hand rule! Like a stack of square section carpenters’ pencils rather than round ones. Here, despite a lowish 60W RMS power rating, Alpine are saying that this is a high power design and can handle peaks of 240W. This is believable in the face of its way lower 88.5dB efficiency. That is 4dB less than the MTX. It means that while the MTX will be great on stock power, these may not be as loud. But if you’re using even a small amplifier, rather than OEM power, or a head unit, these will be awesome.

The tweeters are a soft silk dome type, the absolute best thing you want to see. Only a 20mm one though at the price. Their magnets are Neodymium and so despite looking quite small, have the thrust of a much bigger normal Ferrite. Neodymium is serious and cool to see at this price point. It makes the tweeters’ sound very high end and detailed. The main drivers have normal ferrite magnets as it is still just a 60W RMS speaker. Lovely coaxials, from a posh brand.

Power Handling/Impedance: 60W RMS/4ohms
Sensitivity: 88.5.5dB @ 2.83V (1W)/1m
Frequency Range: 68Hz to 20kHz
Made as: 4in, 5.25in, 6.5in, 6x9in two-way and three-way versions
Which one we like the best in the range: The 6×9 SPG-69C2 is worthy

Focal Auditor ACX165S (seen at £90)

This brand goes all the way to a home speaker called GRAND UTOPIA, at seven feet tall each. Focal know a lot about loudspeakers and are known for making really good affordable stuff as well. These are their entry level offering. The 6.5in size of Auditor ACX comes in two kinds, one regular, one shallow-mount. The other models are the regular basket and magnet. Focal offer the rare 5×7 oval in this line, too. The truly bonkers thing is that the ACX165S is not merely shallower of basket, it has higher power handling, too. The 70W RMS is also married to a 93dB sensitivity, somehow 1.5dB better than the chunkier one. The fatter ACX165 is a bit less in price, handles 10W less and has that 1.5dB lesser sensitivity. How the ACX165S has these specs is bonkers, and took checking via data sheets as it seemed hard to believe.

The tweeter is an exotic Mylar inverted dome, a classic bit of Focal smarts, under a really cool ‘F’ grille. The polypropylene main woofer cone has a rubber surround suspension, for durability and a good clean sound. The whole mounting depth issue is a big thing and Focal have really addressed this with the ACX165S. Get the regular ones if money is tighter and space allows. Get the shallower ones if you can afford the extra, even if space is not snug. Great for using on OEM power, even better on a Focal amplifier.

Power Handling/Impedance: 70W RMS/4ohms
Sensitivity: 93B @ 2.83V (1W)/1m
Frequency Range: 60Hz to 21kHz
Made as: 4in, 5.25in, 6.5in, 5x7in, 6x9in
Which one we like the best in the range: This ACX165S is amazing

JBL Stadium GTO620 (seen at £200)

JBL will never stop letting you know they are the fathers of live sound. Their ranges of car speakers are called after venues. Stage, then Club and then this Stadium range. Not cheap, Stadium are only available in the big ol’ 6.5in coax and mighty 6×9 oval. No messing about with smaller ones. These have a totally huge feature. They are not a standard 4ohm speaker but rather show just 2ohms to an amp. Look at how amplifiers’ specifications are rated. Most amps are able to drop more watts into a 2ohm load than a 4ohm. The specs show that 2ohm loads run at way higher wattages. Normally you get special 2ohm subwoofers or more than one and wire them up right, to show low impedance. Unheard-of rare amongst coaxials, this 2ohm impedance thing makes them bonkers loud on normal amps. The glass fibre woofer is light and stiff and is a Plus One™ design. With 25% more surface area crammed into any given chassis size. It works and makes bigger bass.

Part of what you are paying for is the absurd high efficiency along with high power. These offer 95dB for one watt, so if you shove 75W RMS up them, it makes mayhem. The bass is stupefying. Look at their frequency passband. This speaker runs happily down to 45Hz, the very frequency cited on most amps as the ‘Bass Boost’ centre. Lower than any referenced in this article. It means richer, fatter tones. A set of these, the 6x9s and a 4ch amp, and you’ll be an audio hooligan with that classic rich, fat rocking JBL sound.

Power Handling/Impedance: 75W RMS/2ohms
Sensitivity: 95dB @ 2.83V (1W)/1m
Frequency Range: 45Hz to 25kHz
Made as: 6.5in, 6x9in
Which one we like the best in the range: The mad GTO693 6×9 is crazy

Morel Maximo Ultra 602 (seen at £190)

Morel make some mind bendingly expensive car speakers and are more hardcore in automotive than HiFi I think. Their home speaker called the Fat Lady is a carbon fibre wonder, though. Morel’s idea of entry-level is over four times the price of the MTX Terminator. Evidence of a high-end approach. Absolutely meant as a very high quality (but in Morel terms) affordable speaker set to replace your stock ones. Proper high power handling at 90W RMS yet a serious 91dB sensitivity, means really posh engineering. Now in MKII version, Maximo Ultra’s tweeter features Morel’s EVC™ External Voice Coil tech for absurd high frequency control. They say it sets new standards for high power handling and low distortion for the price. Computer modelling was used to make the suspension of the mid woofer more linear under low midrange frequencies. That makes for better bass dynamics with less distortion.

It adds up to a ridiculous slice of performance with a rich bass that is faster than most. A particularly Morel thing, the leading edges of bass notes are carried in a tighter way that makes the whole sound just a level up from normal. The single most accurate woofer I ever heard was a Morel. They care about dynamics and snap. Also, this speaker system was designed to sound good off-axis, deliberately. They know that stock speaker locations will be used for these and they are often in bad locations, sound-wise. Not cheap but really good.

Power Handling/Impedance: 90W RMS/4ohms
Sensitivity: 91dB @ 2.83V (1W)/1m
Frequency Range: 55Hz to 20kHz
Made as: 4in, 5.25in, 6.5in, 6x9in
Which one we like the best in the range: This very Ultra 602

JL Audio C2-650x (seen at £220)

JL Audio started as the brand of pressed steel chassis woofer that simply won every sound off about sound quality. Suddenly, across all the car audio SQ contests, unless you had JL subs, you didn’t have the best sounding lows. That was along time ago. To this day my overall ‘best woofer ever’ remains the JL W7. Just a hairsbreadth less snug than the Morel one I was so impressed with, theirs can do incredible rich bass. It has both control and awesome goose-bumpiness! In the years since, their full range speakers have also evolved massively. JL make some lovely entry level stuff and they make some that are up there with the finest that exist. These ones are from their C2 range, with technology filtered-down from the fancier C5 range. High quality 19mm silk dome tweeters are married to mineral filled polypropylene bass cones. You can get C2 speakers as coaxials as well as components with fancier off-board passive crossovers.

Like so many of these, the coaxials’ frames have multiple sets of mounting holes. Although it looks like Swiss cheese along the edge as so many different ‘standard’ sets of mounting screw position exist, it works well and means easy installation in stock locations.

Power Handling/Impedance: 60W RMS/4ohms
Sensitivity: 91dB @ 2.83V (1W)/1m
Frequency Range: 59Hz to 22kHz
Made as: 3.5in, 4in, 5.25in, 6in, 6.5in, 6x9in
Which one we like the best in the range: C2-350X cute THREE inch!