Finding gaps and filling them with useful products is one of the main tasks of loudspeaker building, and we have made that our mission from the very beginning. At first it was easy, but after what feels like 150 or more assembly suggestions, you would think there aren’t too many openings left. You’d be wrong! We get new suggestions every day, and our ears are always open as long as it’s not just a request from one person. “I can’t take it anymore!” is something we’ve been hearing so often lately that we were almost forced to provide some spontaneous help.
The problem, of course, was the sound – if it even deserves to be called that – that comes with today’s flat-screen TVs. Hollow, tinny and like the inside of a watering can were some of the more positive descriptions, and any installed equalizers only made it worse. Earlier, because of the picture tubes and the necessary cooling system, large cabinets were needed, which left enough room for even multi-path speakers. Today, the sound is projected by mini-squeakers that would never be accepted even in a cell phone. Clarity of speech, which is the most important thing when watching the news, is nonexistent; the background music is annoying, sometimes even off-putting. If we recommended running the television through an AVR, we often heard the reasonable response, “I just want to watch TV – I don’t want surround sound all the time.” So we listened to the voice of reason and quickly invented the “Seas CoaxTV.”
The incentive, almost not worth mentioning, came from the recent demise of a friend’s old tube television. At the mercy of the market, he replaced it with one of those often-criticized flat-screen TVs, in this case a small one due to space considerations. He stuck it out for three months because TV played a fairly small role in his life, just a way to unwind after the end of the day. But when you’re channel-surfing and all of the voices more or less remind you of Mickey Mouse, and even the biggest gangster cars sound like they have a Yugo engine, it’s time for even the least picky loudspeaker builder to take action. Things turned especially dire when one of the channels broadcast a “Pink Martini” concert. Compressed to the bandwidth of a bad telephone, it was impossible to watch the efforts of the musicians for very long while waiting for the results to match up. The discrepancy from the CD – which we officially want to thank Holger for giving us – was just too obvious.
It probably would have been enough if we had plunked two FT 9s or RS 100PCs down lengthwise under the television, but then we wouldn’t have had much of a report for the magazine. So it was a good thing that an assembly suggestion using the 12-cm cm Coax L12RE/XFC from Seas had already been in the works for a while. A home theater or a PC speaker would have made sense, but we could easily imagine using it for a stereo-TV board to ease the nightly torment. To start with, here are the data and measurement results for the two chassis components.
Data sheet, L12RE/ XFC
Item No.: 1381721
|Membrane:||aluminium||air gap height:||6 mm|
|Surround material:||rubber||winding height:||12 mm|
|Pole piece hole:||yes||mounting holes:||6|
|Centering:||raised spider||outide diameter:||120 mm|
|Magnetig shielding:||no||installation opening:||96 mm|
|Voice coil:||39 mm||milling depth:||5 mm|
|Voice coil former:||aluminium||installation depth:||74 mm|
|Frequency under 0/ 30/ 60°|
|Distortion for 90 dB||Step response||Waterfall|
|Membrane:||textile||Effective membrane surface:||7 mm²|
|Voice coil:||26 mm||Polepiece hole:||yes|
|Winding height:||1,5 mm||Ferrofluide:||yes|
|Poleplate thickness:||2 mm||Magnet:||Neodym|
|Resonance frequency||1200 Hz||Moving mass:||0,3 g|
|Frequency under 0/ 30/ 60°|
|Distortion for für 90 dB||Step response||Waterfall|
Once we had entered the data for the bass component into LSPCad and done simulations for a couple of our own ideas for reasonable cabinet sizes, the result was a capacity of 5 liters for the L12RE/ XFC. For the TV board, we put two smaller cabinets into a continuous box; with a width of 70 cm, we even had room left over for the DTA-2 or the TA 215, which is used to power the two Coaxes. Those who prefer to put the amplifier on top of, behind or in front of the board should go with the DTA-1. In both cases, the amp is connected to the TV via the headphone jack, and then the volume can also be adjusted using a remote. Naturally, you can once again download a drawing in SketchUp format.
While the simple, practical square shape of our assembly suggestions has often been criticized in the past – fairly or not – our new computer-controlled router means we can now attempt more elegant designs. Given the relatively small dimensions of the television stand, we remembered the frame we had already created for the Duetta Top and BlueNote; a router file was quickly created for the individual boards.
Those who accuse us of wasting materials will soon see that they are wrong. We already have plans for using the scraps, but that’s another story. The router created precisely overlaid dowel holes according to our instructions – we never could have done it ourselves. And as long as we were doing so well, we also cut out a shadow gap on every board. The following pictures show the simple assembly without words.
We did not include a reinforcement area in our cutouts, but in exchange we had to stretch the width to 76 cm. Wider versions of the TV board would naturally work, too. Those who want to make a stereo set out of them can separate the two parts of the cabinet, and if the 17-cm cabinet is too tall, it can be reduced to 13 cm without any problems. The width is also arbitrary, because the non-functional middle section can be stretched out. And just to answer the inevitable question: instead of a tube, a reflex channel can be used to ventilate the box, as long as the starting surface and depth remain the same. Oh yes, and the opening can also be in the back if it isn’t blowing into a closed box. The assembly suggestion is not necessarily limited to TV sound – it would also be a very welcome partner for a PC, in the kitchen, the bedroom or even the greenhouse.
Except for the component values, the crossover does not hide any secrets or rare tricks – an easily modified 12 dB for the bass, 18 dB and volume reduction for the tweeter. The axis frequency curve shows an apparently ugly dent around 10 kHz. This is caused by reflections on the membrane of the bass component, and it is typical for the Coax chassis. But who sits so close to the speaker that he can hear both tweeters on the same axis? Even at a very small angle, the dip disappears.
The table shows the complete measurements:
|Distortion for 90 dB|
|Frequency edgeways 0/30/60°||Frequency middle 0/15/30°||Waterfall|
Now the round piece just had to fit into the square hole, even if the curved lines don’t exactly correspond to the ideal here. We took a picture anyway.
We dimensioned the crossover to make sure it could be glued in comfortably under the lid of the box, above the reflex tube. We cut off a third of a Sonofil mat; rolled up loosely, it fills in the area in front of the terminal.
The rest of the mat is stuffed into the box through the chassis cutout, making sure that the area around the reflex tube stays free. Then as long as you make sure to solder the right cables onto the tweeter and the bass, you won’t need to take out the chassis after the first listening session the way I did.
Once we had fixed that mistake, we took the CoaxTV into an apartment – contrary to our usual practice – and placed it in a drawer under the TV board. As described above, it was connected to the headphone jack via DTA-1, and now the sound finally matched the high-resolution image. Suddenly, the thin man and the nearly disembodied woman were no longer voicing all of the movie roles, and they no longer had that watering can with its strange echo in front of their mouths, either. The dialogue was no longer covered up by annoying background noises allegedly written by a composer. And when various concerts were broadcast on May 1 on arte, we were happy for the bass player and drummer, who were no longer just playing to look good. Unfortunately, just then my friend’s son came over for a visit, but as we mentioned earlier, the TV plays a very minor role in our friend’s life. So it doesn’t matter if the sound is now back to the way it was three months ago.
|Loudspeaker drivers||2 x Seas L12RE/ XFC||Wood list in 19 mm MDF|
|for one TV-board:|
|Sales||Intertechnik||70,0 x 17,0 (1x) front|
|Construction||70,0 x 13,0 (2x) lid/ floor|
|29,9 x 13,2 (2x) back wall|
|Function principle||bass reflex||13,0 x 13,2 (4x) sides/ inside|
|Nominal impedance||4 Ohm|
|Terminal||2 T98/98||milling depth: 4,5 mm|
|Insulation, damping||1 bag Sonofil|
|Reflex port||2 HP 35|
The Seas CoaxTV is available from Intertechnik.