3-way mid-top for small venues.  12"+8"+1".

Getting the combined rear chamber and port design right took a bit of thought.

Drivers are all 18Sound.  12ND930, 8M400 and NSD1095 on XR1064.  Runs 2-way active with a custom passive crossover between the 8" and 1".

bet it sounds great. 

I haven't gigged them yet but testing so far is promising.  The 8" is covering ~400Hz to 2.4kHz and the TiN diaphragm on the 1" is quite nice.  The impedance lumps on the 1" around the crossover region caused a few issues with the passive crossover design but managed to make it work without adding lots of extra compensation components.  If you're wondering, 2.4kHz was settled on because it's a half wavelength of the 8"/1" driver offset so you can effectively get them in phase at the crossover point. Yes you get issues either side but it works well enough.

It's the first cab I've designed for myself for a long time, have had the drivers lying around for years.  Originally I was working on all kinds of complex horn loaded designs but realised for a lot of the jobs I do in small venues, something like this would be far more useful.

Next up is something new to do the bass underneath...

Nice work there, I still have a load of your old bits in the garage and one day I'll do a similar project. Sometimes trying tomake the best thing you can out of a pile of odd bits is an interesting challenge.

You don't go back once you've got a decent CNC though do you. I was thinking the other day that with the right workflow angled cuts wouldn't be too hard or take too long.

Love this new top btw

Did you ever get the chance to do measurements of the speakers? 

And what is the lower bass response like? I would be planning to cross over around 120hz but do you think I could achieve 100hz or even 90hz with a similar design (12, 8, 1”) ?

It will be my first attempt at building a speaker and I am just trying to learn the basics at the moment. I am finding the research fascinating and appreciate I have much to learn!

Thanks

The bass response is obviously determined by the choice of 12" driver and the cabinet.  It has a fairly gentle roll off from probably a bit above 100Hz and I think the tuning is around 60Hz.  I normally run them with a crossover around 120Hz depending on what I'm using for the bass.  The 12" driver I used has plenty of excursion available so there is some scope to apply some EQ to flatten out the low frequency response and you could cross over lower, especially running at lower volume levels.

I'm very happy with the design, it sounds really good, there's nothing that I can immediately think of that needs changing.

It definitely ticks all the boxes I am looking for. 

 

Have you looked at which drivers you want to use yet?  I happened to have some 18Sound drivers I'd bought years previously but there are e.g. B&C alternatives that would work as well.

Where are you located?

Would you mind sharing the box dimensions?

Also did you put the 8” driver in a sealed chamber?

I thought it would be nice to cross the 8” mid into the compression driver as high as possible (maybe 4K?), are there any drivers you know of that could do this while still maintaining 90 degree dispersion to match the horn?

I was only thinking this after hearing Tony Andrew’s speak of his dislike for comps in the midrange. Don’t know if this is possible with an 8” though and I may be just being suckered in by his biased opinion!?

Really appreciate your replies, thanks

I don't like the sound of Yamaha speakers. But I like RCF. 

Others will strongly disagree. It's all about taste 

I cross over just over 3kHz from memory, in my opinion that's still high enough to get it out of the critical range.  I'm using a 60deg wide horn so trying to match the dispersion of the 8" is less of an issue.

The overall dimension of the box is 800mm tall, baffle is 320mm wide and 355mm deep, including the curve on the front.  It's a 15deg trap angle.  I think the total volume available to the 12" once you take out the chamber for the 8" and the ports either side is probably around 45litres.

What mm ply did you build from?

I was thinking of maybe modifying the port to run horizontal below the 12” driver - purely for aesthetic reasons, but might add too much unnecessary height!

The top and bottom of the ports, which also form two sides of the rear chamber, are also rebated into the side panels and provide significant bracing to the cab without needing any extra parts.

I have a couple more thoughts and questions before I begin to finalise my plans.

Due to the small room these speakers will be placed in I was wondering whether I may be better off with a wider dispersion horn, in order to avoid dead spots in the room and maximise coverage. The listening zone will be near field and I am concerned there may be a gap in the coverage when stood between the speakers, unless further back where the horns’ output meet as it were.

Obviously a wider dispersion will also result in more reflections however the room is quite well treated so I am slightly less worried about this.

So my question is whether there are any other drawbacks to choosing a 90 degree horn that I may not have considered? Such as getting the directionality of the 8’ to match that of the horn around the crossover point for example. Or just general sonic qualities etc.

I can’t seem to find any directivity plots of the 8’ driver anywhere online so am completely unsure of its specs in this regard. Would it be safe to assume anything based on the driver specs/data of the 8M400?

I have also been simulating using a Fane 12MB for the low mid unit, it seems to give a better low end response for the ~45 litre box volume. However I am not sure whether gaps in my knowledge are making me blind to it’s suitability for this build, are there any reasons that are obvious to you as to why it would not work well for this build?

Apologies for all of my questions, I am aware I have a lot to learn but am getting excited now to begin this build.

Many thanks

The Fane Colossus 12MB was historically a very good driver, I don't know whether the modern production ones are as good but if it is, I see no reason why it would be a bad choice for the box.  You can of course make the box larger if you need more volume to get a better low frequency response.  If you leave the ports the same size, that will naturally reduce the tuning frequency.

This probably warrants a new post but I'm now working on another new design, this time a 2x10+1.4". Uses the same external panels as the 3-way 12+8+1.

How would you say it compares with the 12, 8, 1 design?

It's intended as more of a scalable design, I've used 16Ohm 10" drivers so that I can drive 2 or even 3 boxes off the same amp channels.  Initial thoughts are it's got amazing transient response, probably mostly due to the light coned 10" drivers.  Vocal presence is great (important because I mostly do live work) and the sound is very clean.  There's a massive overlap in terms of frequency range between the 10" and 1.4" drivers so plenty of scope to play with the crossover frequency to see what works best.

The compression driver currently is the 18Sound NSD1424BT as I had a couple left over from a project many years ago, they're a 2.5" diaphragm.  They're quite expensive nowadays so I've got a couple of alternatives shortlisted which are slightly more cost effective if I want to have more than one pair of them.