Fostex FT17H with Audax PR170M0 - will this work?

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Hi,

I can't find any frequency response information on the PR170M0. The Fostex tweeter says it goes down to 5kHz - can the Audax midrange be used up to that frequency? Does anyone have a frequency response plot for this midrange driver? Has anyone used these two in the same speaker? Can anyone suggest crossover frequencies/slopes for these two?

I'm trying to build a speaker by keeping my current Eminence Beta 12, and adding a midrange and probably a new tweeter to it. Active XO between the woofer and mid+tweeter, passive between the mid and tweeter. Run the top two of my 2A3 SET, run the woofer off a Gainclone, keep my sub for the low bass.

Any other drivers that you would recommend? I'd like to keep this relatvely inexpensive but still sound good, which is why I thought I'd try the FT17H instead of the T90. Other driver suggestions are most welcome too. Since the driving amp will be a 2A3, I need around 97dB or higher overall efficiency.

And mounting questions - what size enclosure would be good for the Audax mid? I've also read that it can be mounted onto just a baffle. How wide does the baffle need to be? Does the height of the baffle matter? Could I just make an L-bracket and put that on top of my woofer cabinet and mount the mid (and maybe even the tweeter) to it?

Thanks in advance for any help.

Saurav
 
I measured this driver last night; I should warn you that I have an OEM model, but it supposed to be the same.

From looking at the response graphs, the actual numbers were about what I expected. Roughly flat to 6300Hz, usable to ~7000Hz, and way downhill after that.

Apparantly this driver is used in the Pass Rushmore with the tweeter crossed at 8kHz. I can't really reconcile that with the published specs or my measurements, but I am curious about it.

In summary, yes, I think it would work. ;)
 
Thanks. Sounds like it's worth trying.

Do you just have this driver lying around, or are you using it in a speaker? If you are, what XO points and slopes did you select, and what woofer/tweeter have you paired this with? If you don't mind my asking, that is.
 
I am afraid I can't be of much help, they are quite literally "lying around." I should note that this driver is massively constructed...5.5 pounds!

On the low end, anything from 300-400Hz looks good. I'll try 1st and 2nd order cutoff. There should be a lot of candidates for this range (50-300Hz or so).

I have the same questions as you about the high end. Mostly due to the Rushmore inspiration, I plan on starting at 3kHz (1st/2nd order) and moving up to as high as 7kHz (essentially no filter) for the -6dB cutoff. I have a feeling this is going to require endless listening and measurement. :( I will use Aurum Cantus G2 on top.

My main concern with using this at a high xover point is that the FR looks like cone breakup from 3kHz on up, and this seems to be backed up by the waterfall. Yet the Rushmore must be using it full out on top! :confused:
 
My main concern with using this at a high xover point is that the FR looks like cone breakup from 3kHz on up

I was wondering if that's what those ripples represented, but since this is my absolute first attempt at 'designing' a speaker, I kept my mouth shut :)

On the low end, anything from 300-400Hz looks good. I'll try 1st and 2nd order cutoff. There should be a lot of candidates for this range (50-300Hz or so).

I already have a 12" woofer in its cabinet (my current speaker) that I plan to use. It's a 'full-range' driver (Eminence Beta 12CX), so I'll probbaly run it up to somewhere between 300 and 500Hz. I have an NHT1259 handling sub-100Hz frequencies. My room modes are really bad, so the only way to get smooth bass was to high-pass the mains, send the bass to the sub, and EQ it.

I have the same questions as you about the high end.

I guess I'll be experimenting here as well. I can't go below 5kHz because of my tweeter, and I'm not sure I can do a 1st order since the overlap between the drivers probably isn't good enough.

The next book on my reading list - Vance Dickason's cookbook :)
 
Audax Mid

There is a difference in efficiency with the Audax mid being more efficient than either the Fostex or the AC ribbon. You usually want to avoid padding the mids, but it can be done.

The other problems I see are the ripples in response at the end of the bandwidth, and the potential for beaming when you run a mid way high. Beaming is the dispersion angle growing smaller as frequency goes up. The off axis response begins to suffer and the sweet spot diminishes in size and may be confined to just a narrow spot at the listening position.

It may sound OK as long as the speaker is firing directly at you.
I would use the ribbon crossed in at just above its lower limits with the 3rd order slope they recommend.

Saurav - Use another Fostex as a mid with the FT 17H super tweeter rolled in at 12 or 14 KHz with a single capacitor in series with the tweeter terminal, like a 1uf (one microfarad). They don't handle much power but with your 2A3 amp it should work well.

Also, Fountek offers the JP2 ribbon thru Madisound that matches a little better with the Audax in efficiency at 98 dB, can be crossed lower, and with a lower price.
I have heard the AC G2, own the 2Si and think they sound very good.

Tim
 
Saurav - Use another Fostex as a mid

Do you have any specific recommendations? In the same price range as the Audax, if possible? :) Or is there a different tweeter I could use that would allow me to cross over from the Audax at a lower frequency?

I don't think it'll be too much of a problem if the speaker beams a little, I can point them straight at the listening position. But obviously it would be better if it had better off-axis behavior.
 
Fostex 207E

The Fostex 207E has a natural roll off at around 10K Hz and would benefit from the super tweeter.

Both could be mounted open baffle if you cross to the Eminence
at 250 Hz or more.

I would use a baffle of perhaps 300 mm (or the width of the bass enclosure) and run extensions of 200 mm back on either side. Some experimenting may be needed here (cardboard), if measurements can't be had.

I've heard Fostex on an open baffle and the sound is very good.

I don't have the specs handy, but you will probably need to bi-amp the system to allow the 2A3 to work where it sounds best - the midrange. I know this is a complication, but a 2A3 doesn't respond well to the load the bass unit puts on it.

Perhaps a gainclone chip amp with volume control for bass?

May be more than you want to bite off, but believe me... the sound will be vastly improved if you relieve the 2A3 of the bass duties.

I own a Fi 2A3 X amp.

Tim
 
Thanks. I'll read up on those drivers. I just built a Gainclone for the 12" woofer, so I've got that part covered. I will have to adjust gain levels, my Gainclone has much more gain than my 2A3 amp. I'll probably start out with a stereo pot, and then put in fixed resistors once Ive found the correct attenuation level, or adjust the gain directly in the circuit.
 
S., I am using the Audax Pr17MOs with a JBL 2235 (15") on the bottom and a Vifa tweeter. After extensive experimentation with the Behringer DCX active digital crossover I have come to the conclusion that it is best to keep the Audax under 4K XO on the top, however they will work well with a minimum slope crossover at the top (1st order Butterworth) and, surprisingly, on the bottom. I keep coming back to around 280Hz on the bottom with a 4th order Linkwitz-Riley. I have taken them down even further into the low 200Hz. I know everyone will discourage this because of the minimal X-Max of the speaker, but for one reason or another I dislike taking the 15" up beyond 300Hz. To make a long story short: anywhere between 1.5K and 4K would be appropriate for the upper crossover frequency, well within the limits of some of the smaller ribbons. Strangely enough, the cone breakup ripples LOOK terrible on paper, but are not that dramatic in reality. I have listened to the PRs XO at 3.5 kHz with a 6dB/octave slope. No nasty surprises. If you are not going active, however, their enormous efficiency might be of concern. 100dB 1W/1M :bigeyes: I don't like padding down my system, so I recommend going active. Next I will try an open baffle configuration with the Audax mid. Tiroth, I also have been thinking about the AC G2 for the top of this system. Would you say the Fountek is an adequate contestant? I am more worried about the power handling and was thinking along the lines of an Dynaudio ESOTAR (hard to come by these days, and very expensive) or the MOREL MDT 33s (large power handling, decent sensitivity). I would appreciate your insight.


:D
 
Russianblue,

Strangely enough, the cone breakup ripples LOOK terrible on paper, but are not that dramatic in reality.

Interesting. I was on a French website that had a FR graph of PR170M0 that did not go up nearly as high as the Audax measurements, but was missing all of the HF resonances. That also jives more with what I've seen, but I haven't had a chance to setup a waterfall measurement yet. Thanks for the info.

I was interested in the Founteks but have been turned off due to questions about the expensiveness of repairs and how long replacement ribbons may be available. Check out mythread in loudspeakers for more info; we can discuss there to avoid threadjacking. ;)

MDT33 certainly comes up often as a quality driver, but I don't have any experience I am afraid.
 
Do you have a link to this website?

I think I'll try the Audax midrange for now and see how it works out. If it doesn't, the next thing to try is a Fostex fullranger.

RussianBlue, so you don't think I can push it to 5kHz. I'll keep that in mind. My tweeter says 5kHz minimum, but maybe that could be played with. Or if I keep the filter slopes shallow, I could do 5kHz for the tweeter and 3.5-4kHz for the midrange and get them to blend well?

This is definitely going to be a trial-and-error design process :)

Thanks everyone for all the help.
 
S.,
as I indicated 5kHz is not a problem if you start rolling the Audax off at a gentle slope before that. The driver sizzles out seriously once you hit 7-8kHz, but there might be some more noticeable issues with cone breakup before that. Let me take the mids up , give it another listen and report back to you. My preferred XO point right now for the PRs appears to be between 2.5 and 4.5 kHz. BTW, I bought two pair of PR17MOs and I ended up using only one pair. If you wish I could make you a good price on the other (unused) pair.
Cheers
 
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