I want to build Mark K's Rs225 and RS28a

[///M5]

After much perusing and reading I am going to tackle my first major DIY home speaker project. I have built a few subwoofers and done a number of active installs in vehicles, but want a new set of speakers for my office. I am thinking of doing Mark's since I won't ever run a sub, I want to do a 2-way as a first project, and am interested in hearing the RS drivers.

Here is a link to Mark's build up on his speakers:

http://206.13.113.199/ncdiyaudio/mark/RS225_RS28A_updates/dayton_reference_rs225.htm

Part of the challenge and desire for me is that I like the idea of using the more advanced CE crossover to allow the use of an 8" driver, but am having a bit of a hard time understanding its layout completely. Since he recommends changing the approxiamate crossover to closer to 1.4kHz instead of 1.3kHz I was wondering what might be involved in doing this.

I also notice I large deviation from the published RS225 t/s specifications and the ones that Mark measured. Can I assume that I can follow his crossover? I have access to an acoustic analyzer and a B&K mic so I can definetely make measurements, but want to make sure that I am not biting off more than I can chew with the whole project.

[Dennis H]

I'd build it like Mark designed it. Quoting Mark's final conclusion on page 2: "First off, let's get it out of the way. There really is not any significant distortion from the low tweeter crossover point that I can tell." Just test the tweeters first as there have been some quality control issues in the past. I don't know if that's still true but it doesn't hurt to test them since you have the gear. About the TS parameters, Mark measured them in the box. The published specs are in free air so that explains the difference.

[///M5]

Thank you for the reply Dennis, I missed the "in the box" comment on the measurements.

As for testing the RS28A when it arrives, I assume that I should break it in and then just measure the FS to make sure that I didn't receive a "bad" unit.

[Dennis H]

Play a 1200 Hz tone and listen/measure looking for any obvious distortion or noise.

[///M5]

That is obvious enough I shouldn't have had to ask, thank you though.

Here is my parts list. Generically using all Poly/Metallized caps, Perfect layer inductors, and Mills resistors. Are there any areas that I should be using Film/Foil caps or Foil inductors?

The key is yellow is from Madisound, gray is for non-exact values where I need to parallel two parts, and the rest of the parts are from PE.



My questions are:
Should upgrade/downgrade any of the components.

If it is logical to unwind a 1.8mH to a 1.75mH.

If I should be adding a resistor to get the resistance of my inductors to what they were listed at on Mark's plans -- the pink values show the real and requested resistance of the inductors.

To get 3.4uF I used a 3.3uF and a .1uF, I have read it makes sense to use a foil for the .1 in this case but also that the two values should be closer together when running in parallel. What should I do?

Is there anything better than the Mills for a t/s measurement resistor?

Thanks again for all the help.

Sean

[ThomasW]

Film caps or film bypass caps are usually helpful on tweeter circuits.

Despite the hype we're not fans of foil inductors. Here's a link explaining why......

http://www.htguide.com/forum/showthread.php4?t=3533

[///M5]

Thanks for the link, I thought I had searched well enough but missed it. Are you saying to use foil for all the tweeter caps?

[ThomasW]

There's a link to reference threads in the Missions Accomplished section.

Use F&F for the entire value or at least 1/2 the value of the cap.

Our experince is that using tiny value bypass caps isn't all that beneficial.

[///M5]

Okay, I switched my order list to include FF on the tweeter section ignoring the zobel and the 60uF cap. It upped the x-over price by over $250, ouch, but probably expected?

[Mark K]

Hi Sean,

The resistances aren't at all important, except L2. Lowering the DCR by .2 leads to a fairly small, just under 1/2 dB increase just below the xover frequency. I doubt it would be very audible. I also agree with the other's comments. I wouldn't spend a ton of money on foil etc.

My only real concern with these, as I've mentioned, is the tweeter issue. Not all the RS28A's can go as low as you need to. You can build it; I can always check the tweeter for you later, if there is a problem.

mark

[///M5]

Mark,

Thanks for the reply, to get a little closer I will switch the L2 inductor to a Jantzen 15ga air core with a DCR of 0.29. As for the tweeters, I will test them when they get here if they can't play a 1200Hz sine tone clearly I would imagine that the FS is shifted and I should have no problem returning the tweet for one that meets spec.

Is the spacing of the drivers on the baffle critical? I will use the same size baffle and at least eyeball it to make sure they are close to what you used, but if there is a specific layout I'd love to follow it.

Sean