Nth Audio

Type: Size: Usable range: Sensitivity: Continuous max SPL: Est. build cost:

Three-way, modular, partly active, high output design Huge floor stander 25 Hz-20 KHz (in-room) 95 dB / 2.83 V / 1 meter 120+ dB (pair, 1 meter, from 30 Hz) 800€ excl. amplification.

Updated 2009-09-14: Added some more information and cleaned things up a bit.

Introduction

When people find out that I build loudspeakers I often get asked if I can build them some. I usually say no, because most people don't realize how much work there is and how many things can go wrong in the process, but this time I said yes because I'd get to do something I hadn't done before.

So this guy likes his music right. We're talking mostly modern, main-stream music. But he likes it really loud. I mean really, really loud. This meant they'd have to be big. I couldn't resist the challenge.

So Tempest was born.

Drivers

I started out looking for suitable woofers, taking extra notice of efficiency, low Vas, low Qts and decent Xmax. I wanted a small box with a high tuning frequency without boominess, but I didn't want to use professional drivers. I eventually found the perfect driver in the cheap German brand, Mivoc.


It is a twelve inch woofer with a painted paper cone built on an extremely solid cast frame and with a strong motor. The excursion was plenty for the job, as there would be a total of four of them, and they could be fitted in small enclosures with their high Fs and low Vas. They are more woofers than sub woofers, but that was exactly what I needed, sacrificing the very lowest bass for raw efficiency.


The next thing on the list was the tweeter. As I wanted these speakers to produce well over 115 dB continuously, a standard 1" dome wouldn't work. I knew from before that Monacor made a 30 mm dome tweeter that could also be had with a large waveguide, so I started simulating around this tweeter and pretty soon I settled with it because apart from using large ribbons or compression drivers, it was the only alternative. Not only does the tweeter have a lot of gain in the lower treble from the waveguide (meaning less distortion), it also has a significantly larger surface area compared to a standard dome.


It took a while before I choose the mid woofers and I can't say there was a lot of research behind the choice. They looked cool, seemed well-built, could play the frequencies I wanted and they were not expensive. That's loudspeaker design on a high level right there.

Cabinets

I decided pretty early on that the speakers would be modular and consist of a middle part with the mid ranges and the tweeter, placed between two equally sized woofer modules. I did this because building a big ass speaker as one piece is so much of a hassle it's not even funny. Not only transporting the huge MDF sheets to build the enclosure, transporting the actual final speaker box up and down stairs several times as you sand them, paint them, measure them and what not... It's just a pain in the ass.

So, externally, per speaker, three identical sized boxes, two of them with a woofer each, one of them with two mids and the tweeter.
After deciding on the woofers I settled with the dimensions of 400x400x600 mm (width, depth, height) meaning the whole tower, excluding any feet, would be 1.8 meters high. The woofers would each get about 55 liters.


I didn't go all the way with material thickness this time. The boxes were built with only one layer of 19 mm MDF, but fairly effectively braced. I tried to save some money here and the end result doesn't suffer from it.


For the woofers, I planned a tuning frequency of a bit above 34 Hz, but it ended up at 29 Hz because I didn't double check the ports I ordered. But 29 works without any issues. You can tune at 33-34 and get a wee bit of extra gain at 30 Hz, but anywhere around 30 is fine. If you use a 90 mm inner-diameter port of 25 cm length, you will get the correct tuning. Mine were a bit conical so the inner diameter was more around 80 mm, thus the lower tuning. But no harm done.

The mid woofers has about 15 liters and in this application it doesn't really matter as they are crossed above any potential enclosure gain. Just stuff their enclosures with some heavy insulation to absorb the back wave as much as possible. The chamber behind the tweeter can house the passive crossover, or a kitten.

Line all the walls of the woofer boxes with about one inch thick acoustical foam dampening material. I used some heavy stuff I got from work but anything decent from ie. Parts express will do, as long as it is fairly dense and heavy.
If you glue it against the walls (use lots of glue) the added mass will help reduce vibrations in the cabinet.

Woofer enclosure in PDF format

Mid enclosure in PDF format

Also, one more thing regarding the woofer enclosure. The frame of the woofer and the positioning of the screw holes make it hard to use T-nuts on the rear of the baffle. I skipped this and instead glued/screwed blocks of plywood to the rear of the baffle to allow the usage of long wood screws to hold the driver. Here's a pic that explains it better. (It worked out great.)

Filter

The only way to squeeze all the power out of these speakers is to cross them by active means between the woofers and the mids. I did build an entirely passive filter but it soaked up a lot of power and that is kind of counter productive when you want to play loud. So I will not present it here.

So, first of all you need an active 4th order LR HP/LP at 100-150 Hz. I recommend the affordable Behringer CX2310 unless you have something better already. The built in bass management in a surround receiver would work, as well, but it might be hard to predict the end result as manufacturers use different slopes and orders.


Secondly, you need the amplifier for the woofers. If you don't have one already, I recommend - on a budget - the Behringer Europower EP1500 (or EP2000) which will provide each woofer driver with a comfortable 350 watts or so. Ludicrous bass? No problem.

I assume here that your main amplifier will drive the mid/tweeters. But for that you need a passive crossover:


This simulation assumes an bass/mid XO at 120 Hz but anywhere between 100-150 is fine, depending on what sounds best in your setup and in your room. The wide baffles support the mids down to around 150 Hz, meaning it is a good place to crossover.  The construction with the woofers near the floor AND ceiling gives you quite a bit of gain, and placed near a corner, the woofers will produce well over 100 dB from 2.83 V. Adjust levels appropriately via your spanking CX2310.

Additional notes The way I set them up was with a main amp (a Harman/Hardon 3490 stereo receiver) with pre-out and main-in. So I hooked up the pre-out to the CX2310, the low-pass on to the Behringer Europower 1500, and the high-pass back to the main-in. If you have a dedicated pre-amp you could get an additional Europower 2500 and use that for the bass, and the 1500 for the mid/highs. They are very affordable amplifiers and great value. These amps also come with a variable subsonic filter. You can choose too have it off, at 30 Hz or at 50 Hz. If you intend to play really loud for long periods I recommend to have it at 30 Hz. You'll not loose much at all but the woofers will thank you for it. Below the tuning point they have no air spring to help them from over excursion, so they can be damaged from subsonic frequencies at high levels. You'll also need something to put between the boxes and against the floor. I recommend soft feet, some sort of rubber pads or something more specialized for audio. No spikes as they will make sure every beat will reach straight into the floor with authority, and trust me, you don't want that.

Conclusion

Insane bass output, much more than I'd ever need and clean, strong and effortless mids and highs. If you have ever been to a nightclub you might have thought "Damn it's loud but the quality is horrible!". Well, with these speakers you have the "loud" part but not the "horrible" part. And I know I haven't been to any nightclub that could play 30 Hz at 120 dB.


They are not the kind of speakers I would use in my home, but if you have a larger house, and have a room to spare, and no neighbors that hate you, these are for you. Since they are modular, you could easily use them for a serious home-theater system as well. Add more woofer modules if you need them. Use the mid/tweeter module as center and surrounds. THX reference levels? Not a problem. I assure you. Use the mid/tweeter module in-wall? No problem either, don't even have to modify the crossover!

I can honestly say that I had really fun trying these things out and the raw force they can put out is just hard to imagine. At peak SPLs, I actually almost fell over a few times when the bass notes hit. Without exaggerating, you will loose your balance.

Feel free to contact me if you are interested in building a HT setup based around this project, or if you have any other questions!