Introduction

After moving back into my parents house, I had no space to place my large mtm speakers. But I still wanted to listen to speakers that I had designed and built myself. That's why I decided to use the parts of my mtm's and build smaller speakers. I still had 2 woofers and two tweeters, namely: the Scan Speak 18w/8546 and the Raven R1. The choice for a small bookshelfsized speaker was easily made. These speakers were to be placed on my desk, where I do most of my studying (That's the reason I moved back to my parents, if I hadn't, I doubt that I would ever finish).

I made a quicklist of whishes (small, able to be placed against a wall and in a corner, bass). About the only way of accomplishing this that I could think of, was making a sealed enclosure and using a linkwitz transform to extend the bass. Allthough the linkwitz transform would make the woofers run out of excursion pretty quickly, I decided that that wouldn't be a problem, since my listening distance would be around 80cm anyway.

I measured the T/S parameters of the woofers, with the setup described in the loudspeaker cookbook. This gave some surprising results. Every parameter differed substantially from Scan Speaks specs. I posted a question about his on the basslist and several people confirmed that this was also the case with their woofers of the same model. So in the simulations, I used my own measured parameters, instead of Scan Speaks.

I modelled the enclosure in LspCad. I already had a target volume, and would like to see how much a Linkwitz transform could add to the bottom end of the response. Without the Linkwitz Transform, the speaker's F3 point was at 62Hz. After some simulating, I decided to bring that down to 45Hz with the transform (which adds about 6dB in the low end)

Group delay and impulse respons were still pretty acceptable, the only thing that worried me a little was the increased excursion demands. But since I have no need to play really loud, I can live with that. Besides: the linkwitz transform is an external component, so I can modify it if needed. So I decided to draw a cabinet and start construction.

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The design

The cabinet is pretty simple. It is made out of standard 18mm MDF and has no bracing. The only feature, is that is has a seperate chamber for the tweeter.

These are the drawings of the cabinet(all sizes in mm) (lick to enlarge)

I asked a friend of mine, who has experience with 3dsMax, to make a 3d image of the speaker to be. It turned out pretty goodlooking.

The speaker itself

one speaker, placed on (a photograph of!) my desk

Two speakers, placed on a drawing of my desk:

Well, this seems to fit just nicely, so I made a start with the construction.

The Construction

The first thing to do was to make the stack of boards, that make up the speaker. With my previous speakers, I had sawn each board individually with a circual saw. Although this works and even produced accurate results, I'm glad that this time I could use the new table saw. And I was done in about 45 minutes, compared to the two and a half days for the other speakers (I admit: they were bigger and had more parts, but still!)

Instead of standard butt-joints, I decided to go for something a little more fancy. And it proved to work excellent: A perfect fit, and square corners, right out of the box :) It is a little more sawing work, but it saved a lot of work later on

I first planned on using the router for this job, but then thought of an other way. I removed the protective cover from the blade. Moved the fence real close to the blade (width of saw is 3 mm, 9mm needs to be removed, so the fence was 6mm from the blade). Precisely adjusted the height of the blade to 9mm and cut some testpieces. After some final adjustments, the settings were correct and I could cut the corners out of the boards. In this image you can see that the original blade is still on the machine. I didn't fit the new blade (which is more suitable for cutting mdf) because that one is very expensive and I'm still not completely good with the table saw. I didn't want to ruin it.

Next stop: The template for the baffle. Routing a circular hole is easy: Drill pilot hole, mount circle jig, set radius, route, done. So I won't bother you with that. No, what I find really difficult, is routing square holes! I already found that out with my previous speakers and now I have to make a square hole again. I already worried about this weeks before the actual construction. One day my wandered off, and I thought of a contraption that would be just perfect: Take 4 square pieces of mdf, mount them in such a way that the space between them always forms a square (or rectangle). Preferable sliding so you can easily set-up different sizes. Sure enough, the first Klang+Ton magazine that followed had such a thing featured in it! Only made out of aluminium, and costing 850 Dmark (around 425 euro).

So, I thought of a different way. I needed a square, 94mmx94mm hole. So I used the table saw to make a strip of MDF 94mm wide. Positioned them correctly on the template. (By simply placing one piece between two others. So the spacing between them was exactly 94mm, and the width of the two opposing pieces is also 94mm). Screwed two strips along these two, cut out most with the jigsaw, and finished it of with the template bit in the router. Tadaa, perfect square. What? My explanation is incomprehensible? Just look at the pictures, They explain everything.

The routing of one of the baffles. Now that the template (and thus the hard work) is done, a 5 minute job.

Driver holes routed and countersunk. T-nuts mounted. I couldn't resist fitting it together to see how well it fits. And it does fit! Whoohoo...

Since everything fits, why not start glueing the thing together? And so I did, and first I glued the small seperate enclosure for the tweeter in place. I routed small countersinks for the panels, so they are kept securely in place.

And the rest of the box (except for the back) in clamps.

The sides are rounded with a round-over bit. And the surfaces are smoothed with painters putty, to obtain an even surface for the veneer. On the next page, you can read how I applied the veneer.

In the meanwhile the speakers are fitted with the drivers, have been measured and a first attempt at designing a crossover is made.

Veneering

For veneering, you first need a sheet of veneer. I used paperbacked veneer, because it is possible to bend this around tighter corners than conventional veneer. The brand I got is Decoflex, and the type is "American walnut". Luckily, it is springtime, so I could use the gardentable to cut the veneer on (yes yes I have used a cuttingboard), which about the only table around that is large enough to hold the sheet of veneer (which comes in a standard size of 125x250cm)

This piece is removed from the large sheet. It is important to notice the grain when applying the veneer to the speaker. Simply because it is nice when left and right speaker are somewhat equal.

This is the speaker with the contactglue applied. What a pain! Somebody could have warned me in advance that contactglue has the tendency to dry in 3 seconds. This makes spreading the stuff out with a brush virtually impossible. Note to self: start looking out for sprayable contactglue!

Now that the glue has dried for about 30 minutes, it is time to make the preperations for applying the veneer on the speaker. One of the properties of contactglue is that it sticks on contact, hence the name. But this sheet of veneer is a. fragile and b. difficult to handle. All the ingredients are in place for errors. So I masked a large part of the glue with plastic foil, which I will remove when needed.

Yes, it worked! Indeed no pics of the actual applying of the veneer, because at the time, I had something better to do! The edges are easily removed with a SHARP knife (insert new blade in a stanley knife and change it every 50cm!) or a router, and some light sanding.

All the veneer applied, and the edges removed. I have also lightly sanded the veneer (using the recommended 220 grit paper). Click on the image for a close-up of a corner. You can hardly see the thin paperbacking of the veneer. And that will completely disappear after painting.

Caution, WET!! First coat of paint is applied, two to follow. This is the first and also the last time I'm painting something myself! My mtm speakers were spraypainted and that looks much, much better! So when I have a new set of speakers, I will also have someone spraypaint those. My painting skills simply suck.

In the end, it didn't turn out too shabby. But still: my next speakers will be (spray) painted by someone else.

e're getting there. I've mounted the speakerunits and installed the spikes. On the backside, the 4 speakerposts are in place (so I can easily connect the test crossover, nifty ey?).

Since the speakers are to be placed on a desk, they need some form of protection. And that's why I made a grille for them. And on this image, you can see the mounting holes for the grilles in place. Since there was too little room next to the tweeter, that mounting hole is placed below the tweeter.

This is the backside of the grille. It is a simple mdf frame, which is a little wider where the nippies are to be mounted. The front of the grille is rounded over with a 9.5mm roundover bit, for my viewing pleasure. For installing the cloth, I used the instructions I found on Audiofriends, which in short come down to this: Cut the cloth to size. Apply contact glue (yuk) to both the frame and the edges of the cloth. Wait, and press the cloth onto the frame, stretching it out a bit. Be carefull in the corners, because there is double the amount of cloth there.

And an image of the speaker with the grille in place. Looks almost real :-)

Crossover

I got the chance to have my speakers measured at BD-Design, needless to say, I grabbed that chance. Here are the resulting Frequency response graphs, on axis:

Tweeter

Woofer

I chose a crossover point at around 2500Hz. Low enough for the woofer to avoid the troubles at 4k, and high enough for the tweeter to be safe. After a few hours of tweaking, designing and simulating in LspCad, this is the first filter and the filter I'm currently testing by listening to it:

Tweeter

Woofer

As you can see, I did a baffle step correction for the woofer and did some serious padding on the tweeter, since it's almost 6db more efficient than the woofer. It gives me this on axis frequency response:

There's a high and narrow peak at around 600Hz. I suppose it's from standing waves inside the box (it was tested without dampening material). I stuffed the box lightly with wool, and a new measurement will have to show if this worked. The dip in the tweeter's response is there, but I don't know why. I did not correct for it in the crossover. The phase response is promising, around 2500Hz, the tweeters phase tracks the woofer's phase almost exactly. (visible in the indiviual phase response plots, not shown here)

I first listened to it in mono, to do a first quick check if there were big noticable mistakes.

The mono test revealed no big errors, so I purchased the parts to build a second crossover, so I could listen in stereo. I confiscated my sister's bed, to make a quick stereo setup, hooked up an amp and a cdplayer and started listening.

Now that I could listen in stereo, I immedately found two things wrong with the speakers, luckily they were quite positive.
First, the speakers sound really good. They shouldn't. They are my first own built stereo pair of speakers, containing my first self made crossover. They can't sound this good. I'm not really qualified to give an objective opinion, so I hope that in the near future, I can have some friends over to give their opinions on the speaker. Also, I want to have them measured again, with the crossover in place, so I can check if the peaks and dips in the response are gone, and if the FR looks anywhere near the simulation.
Second, they produce bass. The Linkwitz isn't even in place yet, and already some of my bass test tracks sound just fine. But these are 12L closed boxes, with an F3 at around 60Hz. This must be becouse of the small room they're placed in, or just my imagination playing tricks on me. I'm not saying that these speakers produce chest-thumping bass, just that the low notes in my favourite music can be heard just as good as on the larger speakers I have listened to. I will still finish the Linkwitz transform, but I'm not convinced anymore that I'm going to use it. (remember:these speakers are to be placed on a desk, with me 80cm in front of them. They're not meant to fill a livingroom with music)

They past this test with flying colours, so I placed them on the desk and will try them out for the next few weeks, to check if I keep liking them.

In the next few weeks I will keep updating this page, with updated crossovers, and new measurements. Some tests of my own, showed that the measurements on these pages are not fully correct. And I have also designed some new crossovers, which I plan to try out some time soon. Or maybe it's time to start saving up for LspCad pro!

Crossover 2

I've been listening to the speakers with the test crossovers quite some time now, and they are really quite good. That's why I wasn't in a real hurry to finish these speakers. Which is a good thing, since that gave me the time to learn how to measure speakers myself and also acquire the right equipment and software to do so. Now that I have a nice speaker measurement jig and measurement software (Sample Champion) I went ahead and measured one speaker. Here are the individual on axis responses:

Tweeter

The scale is a little different than on the previous page, but the resemblance is quite obvious. The two main differences are the Y-scale (I need to find out how to get absolute SPL on the Y-axis) and the phase. The measurements taken at BD-Design were not compensated for the distance between speaker and microphone, these are.

woofer

Same goes for the woofer: The resemblance is clearly visible. The small "jump" in phase around 600Hz is due to the merging of near and farfield measurements.

I stuck to my original choice for a crossover point at 2500Hz, only this time, I would make sure that it actually stayed at 2500Hz. When you inspect the summed frequency response on the previous page closely, you can see that the XO point has shifted up to around 4KHz (!!). I also wanted less components in the signal path for the woofer. For two reasons: Soundquality and cost. High quality inductors are pretty expensive and if they're avoidable you can gain sound quality and save cost.
In the individual responses, there are several things that I noticed. Two peaks in the response of the woofer. The peak at around 600 Hz is due to a standing wave in the enclosure. It seems that the wool I put in the box to damp this standing wave, isn't totally up to it's task. The woofer also has a peak at around 4000Hz. This is the cone breakup, which was to be expected. The tweeter has a large dip around 10KHz. This really surprised me, because it shouldn't have this. But it's real. The dip is visible in the BD-design measurements (taken on the other speaker) and in my own. I also have some trouble explaining this dip, because the wavelength of this frequency is really small. The only reason I can think of for this dip is the gap in which the ribbon is mounted. But if this is so, this dip should also be visible on measurements taken by others.

I chose a third order electrical, 4th order acoustical filter. The third order electrical is to protect the tweeter from low frequency signals, because it is quite sensitive to this. I Left the dip alone, since there isn't much you can do about it.

Tweeter

For the woofer, I designed a first order electrical-4th order acoustical crossover. It has two notchfilters, to remove the two peaks mentioned above. I'm quite pleased with this, because this allows me to purchase a very high quality inductor to put in series with the woofer, because I only need one :)

Woofer

The resulting frequency response is quite good, if it weren't for the irregularities in the 10KHz and up region. Once the filter is finished and installed, I will do some further testing. I hope I will find out what's causing the tweeter to behave like this.

Total response

I tried this filter out, using the aural emulator built into LspCad (I borrowed a friend's pc, with this version of LspCad). It sounds pretty good (better than my current testcrossover), so I decided to go ahead and purchase the parts. The aural emulator, built into LspCad, also gave me an opportunity the listen to the speakers with a Linkwitz transform. Allthough the diagram, displaying both the target and achieved transfer functions showed a big discrepancy between these two bass improved markedly. A small boost turned out to be the best choice. Because of the way the speakers are positioned and my listening position, I get a lot off bass for free. Only a small amount of boost is sufficient to give them enough extension for my taste. After the passive filtering is done, I will finish the linkwitz transform filter (I already have all parts soldered onto the boards, but it needs a nice housing)

The parts arrived in just a few days, yippie. I used mkp capacitors throughout the filter, because they're relatively affordable. I thought about using a higher grade capacitor to put in series with the tweeter, but that would almost triple the cost for the total filter. (a 10µF mkp costs €4,70, a mkp-plus, costs €40.) I chose a tritec inductor to put in series with the woofer, because of their low resistance value and I used a foil inductor to use parallel to the tweeter.

First, I had to see if everything would fit onto the board (which had to be small enough to fit through the woofer mounting hole). Luckily, it did. I shifted everything around a little and this is the layout that seemed to work best. Because there are four inductors in each filter, it isn't possible to mount them in such a way that they won't influence each other. So, I placed the two inductors that are positioned the same as far away from eachother as possible.

I marked the position of each part on the board. After that, I drilled holes for the tie-wraps. I placed every component on the board, using hot glue and a tie-wrap. Everything sits in place very firmly.

There's just enough room to place the filter, but that's all that's needed. I glued the board in place using a n. Mconstruction glue that (according to the label) is solvent-free and resistant to vibrations (how usefull!)

After all was done, I took some measurements to check how it worked out and how the simulations compared to the real thing. The graph below is a comparison of the simulated FR and the measured FR on axis. I think the matching is good enough.

The graph below is a comparison of the FR with and without grille. The notch at 9Khz deepens a bit and the small hump at 20Khz is lowered a bit. Not really big issues. The protection of the grille is necessary, and luckily it doesn't harm the sound that much.

The graph below is the horizontal off axis frequency response.

and last but not least: a waterfall plot, form 500Hz and upwards:

I also measured intermodulation distortion at four points: 900Hz and 1Khz to measure the IMD of the woofer, this was a decent 0,4%. Also 2250Hz and 2500Hz, to measure IMD in the crossover region, this was at a less decent level of 2%. The !khz and 10Khz measurment was to measure IMD between woofer and tweeter and was 0,3%. The last measurement at 10Khz and 11Khz was to measure the IMD of the tweeter and was about 0,3%.

Well, how do they sound? Pretty darn good, actually. At first, I was little nervous if LspCad had simulated the level of the tweeters properly. But after a few minutes listening, I decided that the tweeters had the proper level. This filter sounds better that my testfilter, and the difference isn't subtle, but very audible. Also, the highs seem to have improved quite a bit. I'm hearing a lot more detail now, which scared me a little at first: I thought something was broken, but it appeared to be on the cd. All in all, I'm very proud of my first completely finished speakers and I'm convinced that more will follow!

Raymond van Weeghel