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Old 27th September 2014, 12:46 PM   #1
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Default two subwoofers + plate amplifier + FF85wk FAST

Hello everybody,

first of all, please forgive me for just putting questions and not much contributions into the forum bowl! I am a "frequent reader" but too many hobbies and not enough time prevent me from being an expert in all of them ...

I would like to put an (temporary? after other attempts in different configurations, not always really satisfying ) end to my quest and after a lot of reading I was thinking of something like:

2 subwoofers, active, with suitable plate amplifier, acting also as stand for mid-high units (full range - FF85wk?) in a FAST config. I would like to have them all in sealed cabinets.

1. I have a good valve integrated ampli (50w PP) and don't want to go the active xover route. Is it a blasphemy to use high level inputs on the plate ampli (bridging them IOT to feed each with only 1 channel from the ampli) and then pass the signal to the full range loudspeakers using plate amp speaker output and its high pass (again only 1 channel each)? Any issues? is it possible to use only one channel (bridged) in/out of the plate amps (in theory I would say yes but ...)
2. what could be a reasonable xover frequency (120hz 12db/oct my guess) between sub and full range?
3. which sub would suit best this project (I would say capable of decent output up to 1000hz?)?
4. and ... can a pair of FF85wk fill adequately the room (5x6 m - 17x20 ft) in this configuration?
5. can I go sealed for both? I really do like sealed cabinets.

Many thanks in advance for any help. Contributions really appreciated!

Cheers,

CR

Last edited by cyberlancer; 27th September 2014 at 12:49 PM.
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Old 27th September 2014, 07:36 PM   #2
zman01 is offline zman01  Bangladesh
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CR,

No experience with the FF85wk, but did a FAST experiment with Alpair 7.3 XO'ed at between 110-150 Hz with 2 smallish TB W6-1139 subs - worked pretty well. The XO was active (5.1 sounds card and Foobar plug-in). Room was around 25 sq meter.

I don't know of any true subwoofer driver which can go up to 1000Hz... rather 150 would be the upper limit; Bob Brines speaks of a Dayton sub he has which works well till 150 HZ IIRC. If you are looking for higher XO points then ¨helper woofers¨ would be more suitable. Planet10 really likes the SDX7 mid-woofer for FAST, but they are unobtanium now...

There's a also a new bass-wide driver from Mark Audio - design on post #51:

ALPAIR 7P & ALPAIR 12PW combination.
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Old 27th September 2014, 08:11 PM   #3
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Zman01,

thanx for your suggestions. Everything's useful to shed some light before any decision.

However, I am really trying to avoid active crossover (I use SB Touch as source, connected to an integrated ampli and I'd like to keep this unchanged).

So what I really need is clarification on the questions posed in my initial post (hoping they are understandable ... ) Especially #1,3 and 4. I couldn't find any clear answer digging the forum .

As far as the subwoofer going up to 1000 Hz, I meant capable of coping with the supposed xover and slope, not that I think of any useful output up there (assuming a 12db/oct slope, at that freq the output is attenuated by circa 36db).

Many thanks again and ... anoyone else?

CR
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Old 27th September 2014, 08:20 PM   #4
zman01 is offline zman01  Bangladesh
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CR,

Did you take a look at the MA 7P+12PW design? It has a passive XO design which you will probably need to experiment with. Your PP amp should be able to drive the combo easily, but YMMV.

Do you already have the FF85WK?
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Old 27th September 2014, 08:28 PM   #5
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Yes, indeed, I was reading that thread right now. And yes it's quite similar to what I was thinking, thanks.

But: it has a regular passive xover instead of a dedicated plate ampli for each of the woofer, which is something I really would like to experiment (Q#1).

And it's a ported design.

I don't have the FF85 yet but Dave (planet10) seems recommending it over anything else for this specific application. I also would like to know if a decent sound level is achievable in a farfield application, med-sized room.

CR
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Old 28th September 2014, 03:16 PM   #6
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Hello,
Anybody willing to answering my questions? Sorry if they appear silly but I really couldn't find clear answers in other threads.
Many thanks.
CR
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Old 28th September 2014, 04:44 PM   #7
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There will be a bandwidth gap between the subs and the sealed FF85wk. Subs usually go up to a max of about 120Hz (or a bit higher). The sealed FF85wk will roll off much higher, thus there's a gap.

So you either have to (a) put the FF85wk in ported cabs, near corners (or at least against the wall) in order to mate with the subs. It won't play really loud.

Or (b) use the FF85wk in sealed boxes, but use woofers (not subs and plate amps) so that you can run up to wherever the FF85wk's bass rolls off (for crossover, you can use a simple first-order series crossover which is just a cap and coil). This will play louder than (a) but because of the nature of sealed cabs, it will roll off gently in the bass, which some people love.

If you don't like those options, and you want "the simplest possible setup" then I would say use a 4-6" driver in a BiB, in corners. No crossover, no plate amps, plentiful bass depending on your room and positioning. There's no perfect solution, but there are many good options.
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Old 28th September 2014, 06:51 PM   #8
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In a sealed box, Q=0.7 FF85wk rolls off naturally at 150 Hz. Due to the big resonance hump any passive XO will be next to useless. A woofer could be brought in to fill below the natural roll-off. You will be exceursion limited.

We typically XO FF85wk higher than that. They worked bi-amped at 160 Hz 1st order, but were better at 240. Passive XOs usually end up higher.

With the plate amp, you are bi-amping, just now a question of what XOs you are going to use, the plate amp will have one built-in, a cap in front of the tube amp will allow you to get more level out of the FF85.

dave
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Old 28th September 2014, 07:32 PM   #9
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Many thanks rjbond and dave, it makes all sense.

Then:
1.I am talking sub but I probably mean good woofer so I assume rjbond concerns are addressed?
2. As far as the enclosure for the ff85, I get the point. I just like the old school sealed sound. But if it's a no-no, I can afford any build (not really good at designong LS but good woodworking skills!). So what is the recommended enclosure? ufonken perhaps?
3. then, as you point dave, with plate amp I am basically bi-amping. But is it feasible what I write in my first post? Bridging inputs and sending only one channel from the amplifier to each of the two plate amp? And then doing the same for thespeaker out to the satellites? Or It's better to just use one channel of each plate amp and leave the othe unused?
4. Last ... any suggestion for a good woofer? (F10 40hz sealed possible?)

Sorry for being so verbose ...

Thanks a lot.

CR
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Old 28th September 2014, 07:45 PM   #10
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Quote:
Originally Posted by cyberlancer View Post
1.I am talking sub but I probably mean good woofer so I assume rjbond concerns are addressed?
We use woofers with quite extended response. EL166, Peerless 830870, Silver Flure W14. Nonework sealed.

Quote:
2. As far as the enclosure for the ff85, I get the point. I just like the old school sealed sound.
Not a no-no, just that the sealed roll-off determines your XO point. Plate amps i have seen go up to 150 Hz

Quote:
3. then, as you point dave, with plate amp I am basically bi-amping. But is it feasible what I write in my first post?
You will need to have 2 pre-amp outputs (whether that is with a Y-adaptor is immaterial) and use one set to drive the plate amp and the other the tube amp.

dave
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