Home-Made IEMs
Sep 29, 2009 at 3:33 AM Post #211 of 16,258
Quote:

Originally Posted by meraj.salek /img/forum/go_quote.gif
But then as you keep paralleling drivers, aren't you lowering the impedance?


Yes. Assuming they are wired properly, it's easier for two speakers to handle the same load as one speaker. One graph often used in connection with speaker performance is the impedence graph showing the point at which the driver's impedence spikes at the load presented it. If you double the speakers, you effectively half that load, allowing the two speakers to handle up to twice the load short of producing that same impedence spike.

Quote:

Wouldn't driveability become an issue with 6 drivers in parallel? Or are they wired in a series/parallel arrangement? Or am I just missing something?


I'm not an engineer, nor is my position based on number crunching. I suppose an argument could be made that multiple drivers multiply issues, including impedence. I don't, however, have any experience that would lead me to that conclusion. On the contrary, as long as the wiring and the placement didn't produce phase issues, I've always found that several drivers sound better than one, even when those drivers were simply duplicating the same frequency band.

To be perfectly candid, I won't be able to speak from experience until I've done what I'm talking about doing. I have, however, noticed that when I wired up the CI-22955 and the TWFK together, I got a lot more SPL. This accords to a big difference in output I'd noticed between my UM3Xs and my PFEs. While the PFEs sounded great, the UM3Xs naturally blew the doors off - in terms of output at the same level of current. The PFE has a sensitivity of 107 dB at 1 mW, with an impedence of 32 ohms. The UM3X has a sensitivity of 124 dB at 1 mW, with an impedence of 56 ohms. What's the deal??

Given its use of a crossover circuit involving an SMD crossover cap and inductor combo, I'm not surprised that the UM3X has a greater impedence. It's also possible that multiple drivers add to the impedence issues. But the UM3X clearly has a much greater sensitivity (124 dB vs. 107 dB for the PFE). Running A/B tests between the two, I found the difference overwhelming, so much so that I'm inclined to think that doubling drivers improves sound, even if the drivers are covering the same frequency band.

With respect to the six-driver issue, it should be kept in mind that the TWFK is a "dual driver" in a somewhat nuanced way. There's only one soundport and only one set of pads can be wired up at a time (The second set are merely there for convenience in wiring). When you pair up a CI-22955 with a TWFK, you're really pairing two drivers but getting credit for three. By the same measure, a "super six" using these drivers is really made up of four actual drivers. Even though it's probably the largest of the KA drivers, the CI-22955 is still so much that you could pack a pair into an eartip. In the meantime, the TWFK's, which are much smaller than the CI-22955, can be packed in a pair without really making the package that much larger.
 
Sep 30, 2009 at 1:29 AM Post #212 of 16,258
I might suggest some sort of measurement jig?

I'm told that a reasonably effective "ear" can be built using a Panasonic WM60AY capsule and a bit of rubber tube, which will in turn give useful measurements on frequency and phase response. Combine this with a measurement of impedance over frequency, and you have all the information you need for an old-fashioned crossover.

Also, has anyone considered mounting the crossovers in a separate "puck", similar to the integrated volume controls on many cheap headphones? This would allow for the use of an easy-to-design LRC crossover similar to that found in speakers and easy prototyping. Alternately, an active crossover makes for easy design, though it makes amplification rather more complicated.

Heck, I'd be willing to loan someone my DCX2496 if I was guaranteed a cheap set of kickass headphones out of the deal. I've yet to find any IEMs I actually like, including my Triple-Fis. (Then again, I don't really like headphones in general. If only Scan-Speak started making them...)
 
Oct 9, 2009 at 7:17 AM Post #214 of 16,258
Quote:

Originally Posted by Midnighttown /img/forum/go_quote.gif
im looking to do 3mids 3 highs 2 lows any sugesstion drivers?


i prefer the ED/FED series from Knowles as mid drivers, just like the warmth and signature. For highs, i'm still with the smaller TWFK series. Lows, Knowles CI series, or Sonion's 2000 series.
 
Oct 10, 2009 at 6:10 AM Post #216 of 16,258
I popped open my UM3X case to modify it with filters only to discover the same CI-22955 and TWFK combo I've been talking about, which costs $78 per channel for the drivers, quite a discount from the $350 it would cost to buy one new. For that price you could double the drivers and build a super six.

After comparing the hearing aid style shell with a simpler arrangement involving an in the ear earpiece, I found no advantage to the hearing aid shell, apart from making a fashion statement.

I'm going to go shell free. My drivers will have a housing but not an outer ear shell.
 
Oct 10, 2009 at 7:01 PM Post #217 of 16,258
UM3X IMPROVEMENT

Westone puts a single filter into its UM3X, a white 680 ohm filter, which is enough to attenuate the HF a little without darkening things up too much. A stronger bass could be obtained, with a different colored filter, but you'd lose HF in the process.

This week, I tried several new methods for getting extra bass without robbing HF. I originally popped open the UM3X shell so I could wire the drivers separately. One complication I found was in placing the filter within the housing. There is a fairly tight fit between the housing and its components. This may be one reason Westone chooses to place the filter into the outside sound tube. Because the tube assembly is designed to feed directly into the sound tube, with no space for a filter, I tried mounting separate filters in the cushions. This has the benefit of making filter swapping easier.

One strategy I employed (with pictures to come) was to create a hat (using a combination of stethoscopic tubing and standard hearing-aid tubing) to place two filters side by side: a white filter for HF and a red (or brown, green, red, orange or yellow) filter next to it, for LF. This is not as good an arrangement as placing the filter next to each driver but it's an easier fix and it works. The stronger filters, the bass is much lower and more ominous.

You can use a darker filter by itself, but without an EQ correction, the sound signature is muddier and less lively. Placing high and low filters next to each other does a little less for the LF than it would if the filter were placed directly in front of its matching driver (with no pre-mix signals to sort through) but you still get throbbing bass and great HF - without the need for an EQ correction.
 
Oct 10, 2009 at 11:15 PM Post #219 of 16,258
Quote:

Originally Posted by Midnighttown /img/forum/go_quote.gif
so how many of each is good mao di? thanks


One of each is enough. But 2 Ci, 1 Mid, and 1 TWFK is better, but rather an expensive combo without having ever made DIY's.
 
Oct 11, 2009 at 7:42 AM Post #221 of 16,258
Just 1 TWFK as high, 2 CI22955 as lows, and 1 ED29689 as mid. This is my choice of drivers based on my own listening and testing of the drivers, and it's what i think sounds nice to me. May be from one person to another though
 
Oct 11, 2009 at 7:51 AM Post #222 of 16,258
what can you recommend if i want foward vocals? more mid? btw can we configure TWFK as mids?
 
Oct 11, 2009 at 8:10 AM Post #223 of 16,258
Quote:

Originally Posted by Midnighttown /img/forum/go_quote.gif
what can you recommend if i want foward vocals? more mid? btw can we configure TWFK as mids?


That would have to be up to tuning. A simple way is to use strong resistors for the high and low driver. The TWFK won't be that nice of a mid driver, where as the ED is. The CI is also a nice mid driver.
 
Oct 11, 2009 at 1:03 PM Post #225 of 16,258
Hey, it might have been addressed, but where are you getting the cables and what kind? I saw one post with Westone's cable, but wondered about alternatives. I'm really interested in a project like this, and perhaps scavenging cases and other parts to load with custom internals to tweak, and maybe to replace the cables on my e3 one day.

Thanks!
 

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