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Old 15th January 2013, 03:24 PM   #11
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Quote:
Originally Posted by xrk971 View Post

I know you are looking for a FAST design

I'm not looking for a specific FAST design. I just notice a lot of threads saying, what woofer, or what driver, or where to cross over, or what type of cross over. I wanted to discuss woofers and cross overs generically.

For me, I once did a FAST using a pair of Silver Flute W17 because I had space restrictions. They were to small. It was a passive design. It had to be. If it was active it may have gone better.

Because the impedance spike from the woofer is so close to the cross over, I got a peak in the response just above the impedance peak.

Have a look at this example:

Click the image to open in full size.

I have quite a few examples of that. And from my silver flute FAST I have a measurement also here:

Click the image to open in full size.

You can see the peak at 150hz. I found this was quite audible and objectionable to me. Not as bad as the issues around 1.5 to 3khz that the Fostex FE83 gave me. But still.

For this reason, and for the lack of Vd with small woofers, I'm advocating for large, low Fs, high Sd woofers like those in my second post.

It is also for this reason I'm advocating for active. With active, I wouldn't have gotten that peak in the response at 150hz. Again, that's not just this Silver Flute woofer. I can show about a dozen examples from pro audio 8 and 15"ers to small low sensitivity 5 and 6"ers. It also applies to ported boxes. But different alignment that can suppress that impedance peak would not cause this issue, although I haven't done much box design so I'll leave those thoughts to others.
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Old 15th January 2013, 03:29 PM   #12
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Here is an active design I did using the 3" Tang Band buyout from parts express and a Silver Flute W20.

Click the image to open in full size.

Talking about the woofer section, this design sounds better. Unfortuneately the measurements are on my other computer. But the woofer measures smooth and flat across it's pass band, nearfield, farfield, and suprisingly even at the listening position.

It's active 4th order at 300hz. The previous one was passive 2nd order at 450hz. I just couldn't push the cross over down any further with passive.
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Old 15th January 2013, 07:35 PM   #13
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Hi tuxedocivic,

If the ~150hz bump is (in part) a function of the driver's position and baffle width / geometry, did you consider mounting to cure? Or perhaps I'm misunderstanding your graphs.
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Old 15th January 2013, 07:51 PM   #14
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It's not related to driver position at all. It's entirely related to the impedance profile. In my first graph, look on the right for the before and after impedance around 150hz. See how the impedance drops there. That's because of the filter interacting with the impedance of the driver.

A single inductor does this as well, but possibly less.

The active version doesn't do this.

And a woofer with a smoother impedance will do this less. Hence, my desire for a low Fs if going passive.
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Old 15th January 2013, 07:51 PM   #15
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I have successfully used SDX7 (EOL), EL166 (EOL) and Peerless 830870 as helper woofers. Next upfor trial is the Silver Flute W14, with a queue forming behind.

Active (usually PLLXO as i work the speaker design to be compatible with low order XOs) are easier to get right than passive, but we have been working on passive (so far all 1st ordr series) for these FASTs.

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Old 15th January 2013, 07:53 PM   #16
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Quote:
Originally Posted by tuxedocivic View Post
Hence, my desire for a low Fs if going passive.

Or low Qms?

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Old 15th January 2013, 07:55 PM   #17
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Quote:
Originally Posted by planet10 View Post
with a queue forming behind.
What is this? A brace? Or some other thing?

Glad you popped in to add your choices. Any info you can share about PLLXO would be helpful. Also your box choices to make bass from these small woofers. Something I have no experience with.
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Old 15th January 2013, 07:56 PM   #18
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Quote:
Originally Posted by planet10 View Post
Or low Qms?

dave
Ah, ya, that helps. But I have some examples that cause some peak despite being low q. It's a good observation though, if forced into a small woofer.
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Old 15th January 2013, 08:17 PM   #19
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Quote:
Originally Posted by tuxedocivic View Post
What is this? A brace? Or some other thing?
queue = line up. I have some cheap Peerless to try, as well as some 12" Foster, and am exploring other drivers all the time.


Quote:
Any info you can share about PLLXO would be helpful.
TLS.org | Passive Line-Level Crossover

Quote:
Also your box choices to make bass from these small woofers. Something I have no experience with.
SDX7 invariablt sealed. EL166 in a variation on Scott's ML-TL (the taller one has better performace -- as in the MTMs you heard), the little Peerless in another of Scott's ML-TLs, the SF in a miniOnken style box. These last are built and still waiting for an XO i can use, but fit into a startlingly (is that a word) small box.

Series XO, requires broad overlap, some reduction acoustically of the mid-tweeter resonance peak (ie lowering of Qms), and needs to be far enuff from the driver peaks (wheras a 160 Hz PLLXO worked well with the uFonkenSET + its woofT, the passive is still too low at 200 Hz). Note that ignoring the extra amp, the PLLXO cost less than a single component in these 6 part series XOs.

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Old 15th January 2013, 08:19 PM   #20
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Quote:
Originally Posted by tuxedocivic View Post
It's entirely related to the impedance profile...the filter interacting with the impedance of the driver.
Ah, of course. Thank you for explaining. I had a similar problem trying to passively high-pass a widebander right around its Fs (of course it didn't work).

Can you elaborate on what the FE83 is doing ~2k-3k? Is that simply the driver? That seems wildly chaotic for a small, whizzerless wideband. Thank you again.

EDIT: Added factory graph, which if stretched out, may be showing something roughly similar.
Attached Images
File Type: png FE83En-curve.png (21.7 KB, 234 views)

Last edited by rjbond3rd; 15th January 2013 at 08:23 PM.
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