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FAST system design advice
FAST system design advice
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Old 19th September 2013, 08:52 AM   #1
JourneymanFr is offline JourneymanFr  France
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Default FAST system design advice

I started a project to build my own speakers mid august.
I'm currently in my last year of a Bachelors degree in acoustics and I thought it would be a good way to see the practical side of what I'm doing in the lectures.I also love DIY projects.

I am going for an active design using the TDA 2002 for the amps and I'm thinking maybe a tube preamp section but that will be extra. My current setup: B&W 686, Stormaudio V35, Micromega CD player (was my dads).

Now, I have a problem. I have no idea where to start. I originally started with the active crossovers with a LR4 design. I then realised I really need the speaker caracteristics for the crossover point, but the speaker depends on the design of the encolsure.

After much searching and reading, I'm hesitating between two:
-FAST design. I was thinking of using Fostex FF85WK for the mids/upper but not too sure on what to use for the bass, a Visatron W200 maybe?

-Using a Fostex FF165WK in a TQWT design

These are the artists I listen to most: (Bonobo, Thievery corporation, Amon tobin, Trentemoller, UB40, Angus & Julia Stone, The flashbulb) to name a few.

I live in an apartment so massive spl is not imoportant. Budget, maybe 300-400e max

Can anyone give advice or a pointer in the right direction?
I'm going to continue my research.

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Old 19th September 2013, 12:36 PM   #2
xrk971 is offline xrk971  United States
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FAST system design advice
Are you opposed to bi-amping and passive line level XO's? How much bass extension do you need or like? 30 Hz vs 50 Hz makes a big difference in design. The FF85WK with a bunch of Peerless 8 in woofers seems to be a popular and great sounding combo from what I hear. I have actually not heard anything but raves for the FF85WK as a full range/tweeter with bass off-loaded to helper woofers. However, the simplicity of a single driver aided by a good MLTL to get bass extension down to circa 40 or 50 Hz is also a very good way to go if you are in a small apartment where high SPL's are not needed.

If you look around, there are plenty of MLTL designs for drivers like the Fostex FE's, FF's, Tang Band W3's and W4's, etc. The TABAQ is a great design for an apartment.

If you are short on floor space for speakers, you may want to look at wall mounted Cornu's which are easy to build and sound great - and sound much bigger than they are. http://www.diyaudio.com/forums/full-...w-you-can.html

If you are into having great dispersion, nice bass extension, and ability to place close to walls - look at a scaled down Karlsonator with dual 4 or 5 in full range drivers (the dual smaller drivers give you enhanced sensitivity and great HF's with sufficient bass). These sound really natural and can get loud if you want them to. Karlsonator

If you have not looked into the TI TPA3116D2 amp already, have another look because it is one of the best sounding 50 w/ch amps out there, and at $17 (shipping included no P/S) is a no brainer for powering a small full range system. At this price can also be used to bi-amp with line level passive crossovers. Feedback for this amp indicates that it sounds better than many much more expensive amps out there. TPA3116D2 Amp

Good luck!
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Old 19th September 2013, 02:37 PM   #3
Octavia is offline Octavia  United States
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Visatron W200 looks like it might make a good bottom end for a FAST
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Old 19th September 2013, 03:34 PM   #4
chrisb is online now chrisb
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Count me in as one of those big fans of the FF85WK in exactly the type of application you describe.

How constrained are you to footprint and/or space around enclosure? A floorstanding MTM with something like a pair of Peerless 830657 per side could come in at a reasonable price ( approx $170 USD for drivers before taxes & shipping).

As xrk and others have noted and elsewhere, this is one of those cases where $20 in parts for a Passive Line Level and any of the abundance of great value low powered digital amps have a lot to offer in terms of performance and flexibility of dialing in the XO. If you target the turnover frequencies much below 500Hz, the total value in parts for a higher order of speaker level XO can easily exceed that of a second small amp.

I've built several FAST systems with both series passive and simple 1st order PLLXO, and find the latter much easier to calculate and build ( if I can sort out the math with only a little help - anyone can) .
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Old 19th September 2013, 04:19 PM   #5
Peter Menting is offline Peter Menting  United States
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Default FAST?

Sorry to interupt but what does FAST stand for and where can I read more about it?
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Old 19th September 2013, 04:29 PM   #6
Cal Weldon is offline Cal Weldon  Canada
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FAST system design advice
Fullrange And Subwoofer Technology.

You take a fullrange driver and cross it over fairly low to a woofer, in a multi chambered cabinet. It can be made as a regular two way or you can bi-amp as Chris is explaining. The advantage of the biamp is that a passive line level XO is inexpensive and so are the little chip amps.

Affordable, not complicated, and hard to beat in that range. A very rewarding build.
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Old 19th September 2013, 04:46 PM   #7
JourneymanFr is offline JourneymanFr  France
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I'm not opposed to bi amping and passive XO's. Active seemed like a better way to implement a XO, in that you don't have to calculate impedance values while taking into account the variable impedance of a speaker depending on frequency.

I think 50Hz i enough as bass is what gets people complaining in apartment complexes.

Floor space isn't really a problem as i have two fairly large spaces on either sides of the Hifi/ TV table. Even though I like the idea of the Cornu's, drilling holes in the apartment walls to support them isn't going to please the estate agency much, so I think that's out of the window.

The Karlsonator sounds interesting, I'll look into that. Thanks

With regards to the T amp, I already have a stereo TDA 2002 somewhere, It was designed by the amp guru where I did my Internship, and it has the same effect whenever I take it into Hifi shops to listen to speakers, they can't believe that its coming from something that produces 3 W.

My Dad had an Arcam DiVa, the T amp blew it out of the water.

Whats the difference between a Passive crossover and a Passive Line level crossover?

An approximate footprint for the speaker; 30x30 to a max of around 45x45 (cm). Height wise:, a max of around 1m I think.
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Old 19th September 2013, 05:21 PM   #8
tuxedocivic is offline tuxedocivic  Canada
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If you're doing this as a learning experience, I suggest you don't worry very much about the woofer selection and just get something cheap and available. But something with some information on it so you can get feedback from more experienced builders. Spend the money on the mid/tweet driver you choose. The FF85wk is popular as others have noted. I'm picking up a pair of ChrisB's in an hour to play with and measure. I'm looking forward to it.

Once you have your driver selection, just start playing and learning. Start a thread and ask questions. Build a crappy box and see what happens. Build another crappy box and see what happens. Try a theoritical XO, try a proper XO, etc.
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Old 19th September 2013, 06:14 PM   #9
planet10 is online now planet10  Canada
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FAST system design advice
FAST is an order of magnitude more complicated than a single FR. Done well the extra effort is well worth it.

As Ryan says, concentrate on the mid-tweeter 1st. There are LOTs of good midbasses around (with most of their issues well above where you use them in a FAST), so sourcing a woofer should be no problem.

A passive XO uses big chokes & big caps & uses 1 amplifier before the XO. A PLLXO uses small resistors & capacitors and sits after the pre-amp & divides the signal into 2 to feed separate amps for the bass & mid-tweeter.

With the size you have suggested you should easily be able to hit 50 Hz.

Click the image to open in full size.

The MTM sitting on top is an example of an FF85wk FAST that reaches 50 Hz using a pair of silver flute W14 mid-bass. XO in this case is a simple passive series XOs (a choke + a cap per side). A passive XO restricts your woofer choice considerably.

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Old 19th September 2013, 07:23 PM   #10
chrisb is online now chrisb
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let's clarify one point at least - as the term "passive" has been used to describe filter networks on either side of the amplifier

In the case of line level i.e. before the amp, you have the option of "passive" ie. no gain, just simple R/C circuits, to "active XO" - i.e. with some degree of amplification or buffering via powered circuits as simple as an OP amp, something as elaborate as a Marchand tubed XO, or the current vogue of using semi-pro PA/ Stage gear such as Behringer etc. The advantages of Passive Line Level XO are their very low cost of entry and ease / flexibility of design, and their immunity to variable load impedance as encountered in speaker level XOs. The only disadvantage is that the calculations are based on the fixed load impedance of the power amps, which may not necessarily be the same ( .e.g. when using a tube amp for mid/tweets with 100K input, and solid state for the woofers that can vary from 22 to 47K at least)

The Passive XOs after the amp(s) of course operate at much higher signal levels, and the load impedances of drivers are fractions of those at amplifier's inputs. The math formulas are pretty much the same, but as any simple on-line calculator will reveal, the resulting component values will be considerably higher for the same XO frequency - and the last place I'd wanna use EL caps would be for a high-pass filter in a speaker system.

Not every DIYer has several unused amps to recruit to the cause of bi-amping with PLLXO, but as I and others noted before, the cost of zoom-zoom parts for speaker level XO at frequencies typical in FAST systems ( well below 500Hz), can easily exceed the cost of a small class T or chip amp.

but I'm probably repeating myself
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