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April 26, 2013

Building an M80 Floorstanding Speaker: A Look at What’s Inside

Filed under: Audio Knowledge — Tags: , , — Amie C @ 7:19 am

Most people only ever see the outside of their loudspeakers, and that’s probably a good thing!  But if you’ve ever wondered what goes into building a loudspeaker, then this video will walk you through the inner workings of an M80 Floorstanding Speaker.  Axiom Engineer Andrew Welker explains the parts inside and Axiom’s innovations in the loudspeaker building process.

Andrew Welker:  I thought it would be quite interesting today to show you a view of either a speaker you own, if it happens to be an Axiom Product, or actually what goes into building a speaker box.  Obviously most of the time we only see what’s going on on the outside of the speaker, not what’s inside.

Let’s start with the sleeve of the speaker, which is actually one piece that comprises the front, back, and the sides of the speaker cabinet.  This is actually CNC machined out of a single, solid complete piece of MDF.  This is a piece of our standard finish Boston Cherry vinyl.  If I flip this up you can see that the vinyl is already laminated onto the MDF (or Medium Density Fiberboard), which is the wood that provides the strength and the good acoustic properties we want.

In this case the vinyl is actually providing the hinge to allow us to fold the front, back and sides together to make the cabinet.  Then all we have to do is add the top and bottom pieces.

You can see we’ve got a number of different components here.  We’ve got ports, already mounted.  There’s two on the back of an M80 and one on the front at the bottom.

The crossover network which divides the frequencies between the different drive units – the tweeters, midranges and woofers – is mounted here.

We’ve got braces, and in the M80 there are four window braces.  Those braces are actually locked into these grooves called dados so that when the entire cabinet is glued together and the glue sets,  it provides a very very rigid, very solid, vibration-free cabinet.

Another interesting thing that’s inside any of our products that have a dedicated midrange are these black boxes: an independent sealed enclosure for each midrange.  Because you don’t want the midranges interacting with the air pressure  from the woofers inside of the cabinet, they have to be isolated.  To do that, we have these plastic injection-molded chambers that are air-sealed to the cabinet.  There’s a gasket that fits into a groove in the wood so that when the box actually meets up with this flat rib and it’s screwed down, now we have an air-tight seal.

The box itself is quite interesting in its construction and is another example of the level of detail we go to at Axiom to get the best performance we can.  More on that later.

Essentially, once the box is mounted, glue is put in all of the grooves and all of the openings in the back of the cabinet, it’s folded around the top and bottom, and it’s clamped together until the glue dries.

The Parts

The crossover network is responsible for dividing up the various frequency sections that are going to be  reproduced by the tweeter, the midrange and the woofer sections.  The reasons that this is critically important are:

  1.  It’s the most important part of the integration between the drive units so that when you listen to the sound it sounds seamless: there’s a seamless blend between each of the components
  2. From a practical standpoint, if we tried to put bass signals into something like a tweeter, we’d burn it out instantly because it’s not designed to produce those low frequency sounds.

Axiom’s proprietary corrugated Vortex Port

Next are our Vortex Ports.  Unlike many conventional ports that are simply circular in shape and are a complete cylinder on the inside, ours have these flared edges.

One of the things that happens is that when you play your speakers at high levels with lots of low frequency information, there is a lot of air moving through the ports.  And the air can actually create turbulence at high velocities, which will cause noises.  We call it chuffing.  And it sounds like what you normally hear when wind is rushing through a door that’s not closed properly.

By putting these little fluted areas into the port itself, both the inside edge and the outside flare, we reduce the air turbulence and hence get a much quieter port.

The other thing that happens is that we increase the effective surface area, or the cross-sectional area of that so that we have the ability to more tightly control the tuning frequencies.

Next, let’s take a look at the  backside of where the woofers mount in an M80.  The brass-colored metal discs that you can see are T-nuts: metal-threaded inserts that mount from the backside with a little flange that keeps them secure against the inside edge of the front baffle.  With a normal wood screw there is a risk: if you over-tighten it, it will spin and allow the screw to back off slightly, so you can actually get air leaks and other bad effects happening because now your woofer is not tightly tied to the cabinet.  The T-nut allows us to put quite a bit more torque on the bolts that hold the driver in, which prevents that bolt from backing off in the future.

These T-nuts are on all of the drive units from the tweeters, the midranges and the woofers.

Injection Molding and Custom Design

Let’s talk a little bit about this unassuming-looking piece of plastic which we call our midbox.  Think of it as its own cabinet for the midrange drivers in products like our M60 Floorstanding Speaker and M80 Floorstanding Speaker.  It’s a fairly complex and involved piece of tooling that was required to make this.

Like any speaker cabinet, we don’t want any sort of vibrations.  We want a very solid, very rigid enclosure for the midrange.  Being plastic, if this was simply a straight-sided, straight-walled part, it would be very flexible.  We designed the ridges to create strength in the part.  So what we are doing is reducing the effects of any sort of vibrations that can be created from the frequencies that the midrange is reproducing.

One of the other things that we’re concerned about is the back wave of the midrange interfering with the signal that’s coming from the cone of the midrange.  We know that the sound comes off the front of the cone, of course, but sound also comes off the back of the cone.  That sound – even with the damping material that’s inside the box – will reflect off of the interior surface.  That’s why this surface has a convex shape to it.  Between that and the ridges that are in the midbox, we can break up those reflections and smooth out the frequency response.

One of the things that we pride ourselves in is that we do all of our plastic injection molding and tooling in-house.  The core and the cavity are two pieces: one creating the shape of the outside of the part and one creating the inside.  All of the tooling was done in-house and we’ll also mold this plastic part with our own molding machinery.  We use something called ABS for molding parts in our 480-tonne press.

I hope you enjoyed this look at some of the design and engineering that goes into the inside of an Axiom loudspeaker.

 

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15 comments on “Building an M80 Floorstanding Speaker: A Look at What’s Inside

  1. Michael Pompey on said:

    Thanks for posting this. Makes me love my Axiom speakers even more!

  2. Brandon on said:

    Looks like Axiom as stepped up their build quality quite a bit from the original and v2 M80’s that I have owned. Not that those speakers were poorly built. Far from it infact. But what you are currently producing is clearly better. Well done!

  3. nice informative , nice to see what’s going on in developing the newer v speakers.

    My M80 ti did not have this much detail the flanged nuts were not there it was screws. The boxes were not there

  4. Richard on said:

    It is very exciting to witness new quality upgrades, such as: metal flanged nuts and midrange isolation boxes.

    The instructional video(s) from Andrew/Axiom, is very, very helpful. It brings that ‘Axiom fever’ to a higher level, wanting to buy a new V version.

    What would be highly appreciated would be some clear details on the crossover, plus any detail/explanation on the long awaited DSP crossover box. Finally how about an explanation on ‘speaker compression’ what it is, when (db level/power) it occurs, how say the M60 and M80 deal with this issue.

    Love Axiom Audio!

    • Hi Richard,

      We will have the DSP box ready for June. If you are going to be using it in conjunction with one of our amplifiers we can get quite sophisticated with what the code will be able to control. I like this idea of explaining compression. I think either Andrew or I should do a video on this topic for an upcoming newsletter.

      • Richard Martel on said:

        Today is June 6 :)

        Looking forward to the June release of the DSP box and V4.

        Yes a video explaining:
        – audio compression what it is?
        – a crossover does or does not determine audio compression?
        – possibly explain the logic design of the standard crossover (always fun :)
        – how the new (digital) DSP mates with the standard M60 & M80 analog crossover?
        – or will the new DSP supersede/by-pass the standard analog crossover?
        – 1080P video and Hi-Def Audio :)

        • Richard Martel on said:

          - The new (digital) DSP box for the M60 & M80, can they be matched/fine-tuned for any specific Bryston amplifier, considering the partnership between Axiom and Bryston :) Maybe James Tanner/Bryston might be agreeable to share the necessary specifications (win/win)?

  5. Leonard Hunter on said:

    It seems apparent that performing a procedure like injection molding of plastic parts in-house is what results in the complete control of materials and design that results in a product that can be tweaked and evolved into the fine speakers sitting in my living room. Thank you for the effort.

  6. Ken.C on said:

    Fairly sure that the earlier M80s also had isolation boxes, but I think they were cylinders of MDF or other wood based product. I seem to recall seeing that awhile back. I’m not tearing apart my M80s to verify.

    It would be nice, however, to have the video in the correct aspect ratio… ;-)

    • Hi Ken,
      I will save you the need to start pulling drivers out. The older models did have midrange boxes, they were a very thick cardboard tube with an MDF back on it.

  7. Awesome video. My appreciation for the design just went even higher.

  8. Ron Colvin on said:

    Thank you very much for doing this video. I have a pair of M80s that are
    the last V2 version, which as I understand from my serial numbers, have the
    V3 crossovers. I am extremely happy with these speakers, and I appreciate them
    even more now that I know more about their construction. Keep being good to
    your customers, and we’ll keep being good to you!

  9. Richard on said:

    Hi Ian & Andrew,

    Just a few suggestion for the next video(s):

    Use only a higher resolution camera ie: 1080P with a CMOS sensor for a low light environment, plus sharper contrast, would really make for a more pro look, plus the video will be visually a whole lot more clear. These videos are seen worldwide.

    A ‘wireless lavalier or lapel microphone’ would do wonders for the audio voice quality, instead of sounding like Darth Vader, due to being far from the microphone causing a hollow and sometimes a phasing effect. As a sound company, audio is supreme, should not its’ product videos feature very good audible sound?

    Plus would you explain what is the difference, between Maximum SPL anachoic power handling and Maximum SPL outside of the anachoic chamber. Is the difference between 1 watt, 1 meter SPL and the Maximum SPL, does the difference equal the Speakers’ Dynamic Output Compression limit ?

    Thanks gents,

    Regards to all the Axiom Family of Audio Professionals!

    • There is no difference in the Maximum SPL capability of the loudspeaker itself whether you are inside the chamber or not. We usually measure loudspeakers at a level of 2.83V/1W /1meter as that is a long time standard for acoustic measurements and does not appreciably stress a loudspeaker. That is useful when you want to get an accurate measurement of the amplitude response. The Maximum SPL measurement is, as you correctly point out, a measure of the compression limit of the loudspeaker. There are a number of ways to make this measurement, but we typically use an ever increasing level swept-sine wave signal until we see a non-uniform increase in the level at some frequencies. This gives us a good idea of which driver is beginning to compress first (usually the tweeter) and at what frequency.

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