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How low can you go in active speakers?

Posted 11th December 2010 at 11:54 PM by abraxalito
Updated 5th March 2012 at 02:57 AM by abraxalito

On one of my regular pilgrimages to the computer plaza a couple of days ago, I noticed these little puppies. The price apparently was a shade over $80 the pair so I was indeed very curious. A quick peek around the back showed they were not using a standard speaker cable, rather a custom 4-way umbilical between the two boxes. Whenever I see this, my heart misses a beat because what floats my boat is genuine active speakers, not just powered ones which still sport passive crossovers.

Click the image to open in full size.

Not wishing to ask to disassemble the powered unit on the spot (and doubtless be turned down) I went back home to do some online research. I was pleased to discover these were indeed true actives, and what's more they're powered by TDA8947 chip amps. I'd not come across this part before but its cool at least on paper because its 4 channels in one package - they're using two...
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Posted 11th December 2010 at 07:53 PM by chris661

Well, here we are again (unless, of course, you're here by mistake).

After much contemplation, I've decided that my subwoofer needs upgrading. Currently, it's a pair of MCM DVC woofers (you will probably have seen me going on and on about them), which, while good for the price, aren't that good compared to my Fostexes (which, now fully broken in, are fantastic). They're given ~100w between them, with a Linkwitz Transform to get them down low. Good for normal listening levels, but quickly run out of displacement below 40Hz at anything about normal listening levels.

So, a new bass system is in order. I've always wanted to try a Tapped Horn, so I've chosen a design originally intended for an Exodus 6.5" midbass, that's shown to work pretty well with the Tang Band 6.5" subwoofer... All the way down to 25Hz. Those will be fed by an amp1-b from 41Hz, with a +/-34V supply. Should be more than 100w per side. Ca suffice, especially for a bedroom system ...
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First test post to blog - general audio gear

Posted 11th December 2010 at 01:48 AM by googlyone

Couple of projects of mine - not sure if the photos will load OK.

First is a pair of 25Hz horn subs I used to have - used 18inch drivers, placed facing one another along a wall to form part of the horn and achieve adequate mouth area for the 25Hz cutoff.

Efficiency was well over 100dB/w/m.

Second photo is one of my digital crossovers I built, 4 way AD1940 based audio DSP with an AD1939 CODEC as A/D and D/A. Works a treat, and makes setting speakers up a snip, as can program in delays, HPF / LPF, parametric etc.

Also included my subwoofer couch - I built this as a challenge from a colleague of mine. The carcass of the couch forms an 800 litre enclosure, the ports exit at the back of the headrest three of them, and I used four fifteen inch drivers. It is tuned to 19Hz, and achieves a -3dB point below 20Hz.
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Posted 6th December 2010 at 03:10 AM by ihaveKRELLparts

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Posted 29th November 2010 at 07:36 PM by klewis
Updated 5th January 2011 at 10:25 PM by klewis

Pcb software


Audio analysis software;

Virtins MI
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Opamps for dc servo

Posted 29th November 2010 at 02:57 PM by klewis

For servo duty, there are some newer TI offerings which look worthy. That is assuming that lowish noise and bias currents are desirable (they would be to me if I were seeking out a servo amp). OPAX141, OPAX376 and OPAX209. The latter is bipolar but has lower noise than any JFET I've seen coupled with commendably low input bias current for a bipolar.
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Squeezebox SB3 update 3

Posted 26th November 2010 at 09:54 AM by audi0

Hi guy's I haven't added to this blog for a couple of weeks as progress has been a little slow.

I have however had the front and back plates cnc milled and I have drilled and cut the connector holes in the back plate. The plates will now be cleaned up, acid etched and clear anodized.
The timber sides are cut and the threaded bushes are in, I still need to rabbet the top and bottom edges for the covers, but the enclosure is taking shape. I'm not sure about the perforated ally for a top? What do you guy's reckon?

A redesign has slowed the power supply board a little, I now have the board (thanks to Neville @ Sesame who etched and drilled it for me) all the components are ready to stuff, so the next blog will update how the power supply performs
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Teac TD-X250i Service Manual

Posted 25th November 2010 at 09:18 AM by Andrew Burn

Please can anyone give information about where to obtain a service manual or schematic diagram for a Teac TD-X250i CD/iPod micro hifi. Information seems to be un-available as this model was apparently made solely for the Currys/Dixons retail chain.

Any help would be greatly appriciated.
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New scope - update

Posted 25th November 2010 at 01:36 AM by abraxalito

The Tekway is still working well and survived the 35oC temperatures of Hangzhou's summer despite having no internal fan. That is, apart from its CMOS store of the date/time, which for some reason now thinks the year is 2011.

Someone on the EEVBlog just posted this - I haven't read it thoroughly yet but I intend to find out if I can upgrade to 200MHz. Looks promising

Upgrading DST1102B to 200MHz bandwidth
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JBL L100 Homage

Posted 20th November 2010 at 04:55 AM by DougL
Updated 11th February 2011 at 04:50 AM by DougL

I got into audio my freshman year of collage in 1973. While I hated the "West coast sound",
The JBL L100 looked great, and had a great woofer. It is also higher efficiency than most.
HTGuide did a Thread on redesigning the XO and made a very appealing speaker.
I looked up the woofer and its 88 db efficient. So much for perception of efficiency.

My thought was to design a 3 way speaker that is ultra low distortion, 50Hz F6, and 93db efficiency. Borrowing the L100 concept, Driver compliment 12" woofer, 4" mid-range and OS compression driver.

There are at least 3 drivers in the 4" class with 93db Audax HM100Z0 4" Aerogel Mid-range ,
Fostex FE126En 4" Full Range
I already have and love MP14RCY/P in ob, but they are only 90db sensitivity.

The B&C 3/4" or 1/2" CD look like they might be a perfect match. Sure beats a 2" paper tweeter.
Even a B&C...
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