2 ways with 11K7511 driver... worth trying ?

[Nemophyle]

Hello
i want to build a two way with an active crossover, wich don't (for me) necessarly need a sub. i was considering building it with a 6.5 incher bass reflex and the fountek JP3, but lurking at the focal drivers, and discovering this 11 incher with an (almost) flat response to 2Khz (but with a big resonance at 2Khz still), i wondered if i could pair it to the Fountek JP2 ribbon, with XO at 1.8... used in a closed enclosure it would give me a very nice bass i think, and moreover, i have more skills in electronics than in speaker designing, and a closed design is appealing by its simplicity.
as i have decent skills in electronics, i could consider building a very high order (36 or 48 db) crossover if needed,or using XO at 2 , and in any case i could consider making a notch filter to tame the 2khz resonance...
in any way i don't want to use a 'true' medium as i want to keep it 2 way .
so what do you think ?

[Steve M]

Hi There,

I also have a brand new pair of these Focal drivers, but have not used them just yet.

I wouldn't necessarily put them in a sealed box as Focal recommends a 75L Bass Reflex box to give excellent, tight accurate bass (their words not mine). Focal and WINISD modelling shows that in this box the bass response of the 7511 is flat to about 48Hz and rolls off to 33Hz at -3dB. These are good results.

I have modelled the 7511 on WINISD extensively and the program basically matches Focal's suggested results but in a slightly smaller 66L box. WINISD is said to be sometimes inaccurate, so I would stick to a minimum of 75L if you want to go down the path of accurate bass with a bit of extension.

It's also interesting to note the 7511 extends and models really well into a 130L BR box. In this larger box, WINISD shows a relatively flat line down to 35Hz (@ -1dB) and goes to a low 28 Hz at -3dB.

I am leaning towards putting my 7511's into the 130L box and later converting the box to a Transmission Line. The TL box can be configured to give about a 3.2m long line (not ideal, but 80% of the 4.2m that is required). I have had good results before with the smaller Focal 8K5412 driver in a TL box, it gave very quick and extended bass that 'breathes well' and suits the delicate soundfield of the electrosats and Fostex 206E drivers that I like to use...

Regards,


Steve M.

[morbo]

If you try to use these in a 2 way I think you will get bad power response, since the woofer will be beaming really badly at the crossover frequency... I'm sure the woofer has good on axis response above 1khz, but I would be surprised if it is still strong off axis at that point.

[Bose(o)]

Agreeing with morbo, if you listen to your speaker on-axis then I'll wish you luck and fun. Otherwise, if you're looking for a wide soundstage at all frequencies then do not go with such a large speaker.

I think the general rule is not to have the driver produce sound at the frequency which has a wavelength equal to that of the driver's diameter.

Since, it appears that you know your electronics I have a quick question. What software(s) do you use to design your active xos. What power supply circuits do you use?

I can get a hold of a regulated power supply and oscilliscope I just need to get my feet wet on the circuitry side of things.

[Greg B]

I don't think it's a good idea.

Ribbon drivers are notoriously difficult to integrate, and the lower end of their range tends to be higher than usually claimed. Add to this the idea of using a synthetic cone driver well past it's recommended range, and you have a major problem. The 11K looks well behaved, but I still would not cross it higher than 1khz.

There is also the power response issue previously noted.

My AC G3 ribbons work very well with 7 and 8" focal coated paper drivers. I had struggled quite a bit before trying these. Being that the G3 is a larger ribbon with more range, I'd think that a 6-7" driver would be the maximum size driver for a 2 way.

Personally, I would build 3 ways with the 11K7511 and dome midranges. I accidentally discovered that dome mids are a very good subjective match for ribbon tweeters, and will allow a higher crossover to ease the strain on the ribbons.

I recommend a BR or ML-TL for that woofer.

GB

[Nemophyle]

Nah ok it was not a good idea i'm a pretty newbie into speaker designing so it's good i didn't bought the drivers before asking here
now i'm not renouncing and if somebody knows of a not too expensive midrange that i can couple with the ribbon with no or very simple crossover (6db) it would be cool.
about the box ...
why is this so a bad idea to use it into a closed box ?
simulating it in Winisd give me a ~30 liter Box with a 60hz at -3db. i was planning, as i'm going active, to use a linkwitz transform on it to extend the bass response to, say 40-45 Hz, not more. i will power them with a dual homecook ESP 100 watts amplifier.the size is important and a 30 liter cabinet is very appealing to me,also, i don't need 35 Hz or 28 Hz (to be honest i live by my parents and my mother dont WANT 35 Hz ) but i want very good bass.
has this solution any advantage compared to a 6.5 incher (Focal 6K4411 that i got) into the bass region, as my newbie instinct is saying me, or is this a completely stoopid idea ?

[Nemophyle]

Bose(o): i'm not using any program to design my Xo's . but there are lots of ressources on the net for making the job of designing an active DIY XO very simple.
The ESP site had very convenient information and calculators for each kind of crossover he offers... also he is saying that his design is 'revolutionnary' (not exactly his words) but after lurking on the net i saw that this kind of XO's were pretty common with theses formulas.
here is the link http://sound.westhost.com/
its into the preojetcs/crossover/
i remember the linkwitz site is pretty good too and there are lots of others on the net.
i know that some program can model active XO's (leap for example) but i don't found any that was free, and as i told you, i'm a pretty newbie into speaker designing.
What is positive into the active Xo principle is that you don't have to care of impedance interference with the drivers, wich make the design more simpler. in most cases you just have to know what slope you want and what frequency XO and you're done.
besides, if i said that i had more skills into electronics than into speaker designing, it was because it is true, but consider that i have almost no experience into speaker designing
... i have good practical skills into electronics, but am still a newbie into the theoretical side... well not as much that in accoustics also the woodwork and designing of a bassreflex frightens me, although i love my iron ... you seem to have the opposite syndrom

[EngelholmAudio]

I don't doubt it would be possible to get a descent freq response with ribbon + focal driver (of that size). But that's only on axis. Large speaker units have a natural tendancy to have bad of axis response (at higher frequencies, where high is high for that particular driver).

Bad of axis response results in, if not bad at least, strange sound.

For example - the reflex from the side wall will not have the same tonal balance as the direct sound.

[Greg B]

now i'm not renouncing and if somebody knows of a not too expensive midrange that i can couple with the ribbon with no or very simple crossover (6db) it would be cool.

A true 6db crossover requires two octaves of overlap on both sides of the crossover point, which means a very wide range driver must be used. This limits the choice to full range drivers, or a few of the wider bandwidth midranges. The focal access 5A looks like a contender. The impulse response is nearly perfect, and frequency response is extremely flat and wide.

Now, if you just want to use 6 db of electrical crossover, combined with the natural roll off of the mid driver, the morel MDM55 may be a very good choice. This is a well regarded midrange dome that is known to work well with the Fountek ribbons.

Of course, a 6 db acoustic high pass crossover is not possible with the ribbons anyway. This is the achilles heel of ribbons.

Now, as far as sealed boxes, IME many focal drivers simply do not sound good in them. They are designed for vented, and several I've used sounded congested and 'shut in' when I tried them sealed. That isn't to say it is not possible. The 10W6452 sounded very good sealed, but of course this driver was recommended for sealed or vented enclosures.

Regardless, I think that getting good integration between the drivers from the crossover will present much more of a challenge than the box. If you are not confident in your abilities to design one, I would simply follow Focal's recommendation: 75l @30hz. If you don't like it, plug the port. I do recommend that golden ratios be employed!

[DickM22]

Not too much to add for whats been said, but I can tell you that the Focal 11K is a truly superb woofer, and the one I use in my reference setup at home. It likes to be ported. If you are a sealed woofer guy, sell the Focals and use a Scan 25W instead......my other favorite woofer.

The 11K plays beautifully up to about 500-600 Hz, then starts to sound very "woody" or "mealy". Integrating it with a cone mid is not rocket science, but choose wisely....the cone to the ribbon IS rocket science. My preference is the Focal 5W, also a nice driver if you can lay your hands on some. Ribbons will work with little woofers if you prefer two-ways, but really perform best in a three way crossed over above 2500.

Dick