Intertechnik Family12 loudspeaker kit
The Family12 is the successor to the successful Family 6, which we were constantly asked about. Unfortunately, for a long time we could only answer: "Yes, once upon a time ...". In the meantime, there were no adequate chassis available for a new design. The problem was construction-related: Not every chassis runs in a bandpass design, including the W 148-4, which would have been the most obvious replacement. Computer simulation with other inexpensive 15s from the extensive product range did not promise much success either; bandpass chassis are usually a bit more expensive.
Chassis:
Now the tide has turned for the better and we can finally respond to the many enquiries about the Family 6 un with a successor model: Instead of the 15-inch chassis used in the Family6, there is now a suitable 18-inch chassis, the W 176-4, which does not even require a larger cabinet. With its ideal Thiele Small parameters, it is excellently suited for the successor in the handy bandpass cabinet.
This was the starting signal to completely redesign the Family 6, i.e. to choose a new driver for the mid-high range as well. So the question arose as to which mid-high range would be suitable, especially since the tweeters and mid-range drivers had also been discontinued in the meantime. Experience has shown that a set-up with drivers of one brand is more promising than a mixed set-up, if only because the technical data of one manufacturer can be reliably compared.
So we designed the Family12 completely with the Gradient Select range, which simplified the choice of tweeter: the GDT 104 N already cuts a good figure in some construction proposals and is virtually unrivalled as far as use in inexpensive speakers is concerned. Choosing the right midrange driver was a bit more difficult: W 148 and W 115 promised to be the best choice, especially since both have 4 ohms.
Even though the W 115 doesn't need a much smaller cabinet, we decided to use the W 115 for optical reasons alone - the surprise effect when a speaker with such a small driver produces decent bass orgies is simply overwhelming - and the tweeter and midrange have almost the same diameter, which looks quite good. So the only decision left was whether to use the W 115 in 4 or in 8 ohms. The four-ohm speaker is 3 dB louder, but leads to a critical impedance drop below 3 ohms in the crossover area, which is not tolerated by every power amplifier. So we opted for the safer eight-ohm driver and ended our choice of drivers with this.
Cabinet:
Now to the construction itself: In the computer simulation of the bandpass cabinet, LspCAD determined 5 litres for the closed chamber and 5 litres for the ventilated chamber, in which a full-length HP 50 BR bass reflex tube is already taken into account. The W 115-8 requires an additional 2.5 litres of enclosed volume. With this information it was easy to calculate a reasonable cabinet with Sketchup, which looks a bit more convoluted than a normal nest- pardon - box.
With a bandpass construction, however, you have to make sure that the inner boards do not get in the way of either the drivers or themselves. So we allowed the midrange driver its place in front of the closed bandpass chamber and placed the vented chamber below it - which works out quite well, as the bass reflex tube can then also radiate to the front, just like the midrange driver.
The internal subwoofer driver (or what should we call a bass driver with such a low crossover frequency?) of course needs a mounting hole, which should be placed in the relevant inner board before assembly. And if you don't want to glue the bass in, you also need a mounting frame with a removable base plate, which also pays off if the driver has to be replaced - otherwise you'd have to buy a new cabinet.
Since the assembly is quite simple despite the multi-chamber construction, we have not documented the assembly further photographically; the construction plan should clarify all the steps necessary for the assembly.
After cutting the MDF boards to size, we glued them together and, after drying, sanded the casings. In addition, for design reasons, we traced the cut edges with the shadow gap cutter. Finally, blue stain provides the final finish.
After the stain had dried, a total of two bags of Sonofil ended up in each box. Then it was time to install the loudspeaker chassis and the associated cables, which had to be soldered on first.
Frequency Switch
Then we could start developing the passive crossover, which is not so trivial with a bandpass construction, since the bandpass acts as a mechanical filter. The closed chamber limits the frequency response with 12 dB/oct. downwards and the reflex chamber with the same slope upwards. Theoretically, only a narrow frequency band should come out of the reflex tube - but in practice this doesn't work, especially as the impedance curve would then also pose a problem. So we tackled the mid-range, which whines too loudly without a crossover, with a core coil and a rough audio frequency electrolytic capacitor, which works well with a bandpass without having to choose higher-quality components. Due to this measure, the noise level was a good 20 dB below the useful level.
Since the closed cabinet of the W 115-8 is also a mechanical high-pass filter with 12 dB/oct. and thus already limits the excursion, only a large electrolytic capacitor for an additional 6 dB slope is necessary to not only further limit the excursion, but also to keep the impedance curve uncritical for the amplifier. Towards the top we added a low pass filter with 12 dB/oct. for the midrange driver so that the tweeter can take over cleanly. The tweeter also received a network with 12 dB/Oct. The GDT 104 N needs an additional voltage divider for level adjustment due to its high efficiency, which as a side effect increases the power handling.
The sum of the individual branches add up to an ideal frequency response curve as long as the woofer is connected out of phase with the mid-high range, which is explained by the driver being inside.
Sound Test
Then came the most interesting part of the construction report: The sound test in the listening room. There, the Family12 also had to face the test with different music material. First, Katie Melua landed in the CD player. Her soft, well-balanced voice was accompanied by a good spatial resolution and lacked any sharpness that even expensive domes sometimes lack.
Nevertheless, we didn't miss any details, they were definitely discernible, just not so superficially. Compared to the predecessor version, the Family12 low bass even reached a little further down into the frequency cellar, which makes a subwoofer superfluous even in rooms of 30 m² and more, at least when playing music. The bass guitar sounded clearly tapped behind the singer and the drums next to her struck short and surprisingly dry - despite the bandpass construction.
Quiet music with vocals by singer-songwriters, however, is no real challenge for properly developed speakers with serious drivers. So we fired up the newcomers with rocking sounds, or, following Katie Melua, we had Rammstein blasted into our ears, a band that, as we all know, can only be heard loud. It was pleasant during the sound test that even with Rammstein the ears don't have to hurt - although the little ones were very committed and spectacular. In rooms that are not too big, amplifier outputs of less than 100 watts are easily sufficient. Peter Fox is a little more restrained with our ears. The Pussycat Dolls, who followed the bard's footsteps, also provided sufficient stomping bass. Madcon also let us hear through that the bass was recorded a little loudly during the recording. At the end of the sound session, we simply caught music from the airwaves with the tuner - or wanted to, because the news was promptly read out. Clear announcements by the speaker documented world events - there were comprehension problems at most with the world events, less with the articulation.
The first buyer of the Family12 was amazed when the tiny Yello's "Baby" thundered into his ears. In any case, he was unable to describe the sound other than with "want to have".