Fostex FT17H with Audax PR170M0 - will this work?

[Saurav]

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

[Bill Fitzpatrick]

Info on the mid is at:

http://www.audax.fr/main8.html

click on the diskette icon to view.

[claudio]

Hi,
here the FR of the Audax: http://www.audax.fr/reponse/pr170m0.jpg
All the info are found in www.audax.fr

Claudio

[Saurav]

Thanks a lot. I looked through the Audax site, but since I don't know any French, all I managed to find was the page with the T/S parameters for the driver.

So... do you think this would work with the FT17H?

[tiroth]

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.

[Saurav]

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.

[tiroth]

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!

[Saurav]

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

[tiroth]

Good luck! Will be interested to hear your results. I'll certainly post anything I discover.

[Tim Moorman]

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