Question about using Modula MT crossover design with RS28F instead of RS28A-4

[Alayers]

I was planning on building a 2-way speaker with the RS180 and RS28F drivers, and I came across the Modula MT crossover. I was wondering how much modification the crossover would need to accomodate the RS28F instead of the RS28A-4, the frequency responses is pretty similar. If someone could provide some insight it would be greatly appreciated!

[Alayers]

Right after I posted this, I came across a much simpler crossover for a MTM using the same drivers by Jeff Bagby, can anyone enlighten me as to what the advantages of the Modula crossover might be over the one by Jeff Bagby?

[jclin4]

Look at the parts count for both XO's. Jeff's is much simpler and still achieves outstanding results. And you'll get better bass performance from an MTM over an MT.

[2leftthumbs]

IIRC Jeff's uses the sheilded version--nla except the occassional clasified ad. The modula was pursuing steeper target slopes at the expense of parts count if I remember right. The natalie p, while also a very complex crossover was cheaper to build than the modula mt despite the extra rs 180 in each back when I looked at it.

[jclin4]

Also to consider...MT's and MTM's tend to exhibit different 'lobing' patterns on the vertical axis, that is regions of reinforcement and cancellation between the tweeter and midwoofer(s), depending on the crossover slopes employed. MTM's are typically more limited vertically, which can be an advantage, i.e. reduced floor and ceiling bounce / reflections.

In think there are other posts here indicating that the non-shielded RS180's are a drop in for the shielded's, but this may be subject to argument and differing opinions. My own opinion is that this is true for the larger RS drivers, including the RS180, but less so for the smaller ones like the RS100's.

[Jeff B.]

IIRC Jeff's uses the sheilded version--nla except the occassional clasified ad. The modula was pursuing steeper target slopes at the expense of parts count if I remember right. The natalie p, while also a very complex crossover was cheaper to build than the modula mt despite the extra rs 180 in each back when I looked at it.

Actually, I believe Paul Carmody showed overlaid plots of the shielded and nonshielded versions of the RS28 which were nearly identical, indicating that you could substitute one for the other in my design.

[czag]

Right after I posted this, I came across a much simpler crossover for a MTM using the same drivers by Jeff Bagby, can anyone enlighten me as to what the advantages of the Modula crossover might be over the one by Jeff Bagby?


The modifications to Jeff's xover are easy to get the RS28F to play nice. The RS180 should drop right in for the RS180S with no modification. You can read about it here (http://techtalk.parts-express.com/showthread.php?t=225603&highlight=rs28f&page=2) from someone that actually built it.

Chris

[Alayers]

@Czag, I couldn't seem to get your link to work, but I'm very interested to see it.

[Alayers]

Is there any reason that I couldn't put the crossover from the MTM's into a two-way design if I compensated for the change is impedance? I'm not sure I have the money right now to buy two more drivers...

[marvin]

I would recommend trying Jeff's xover with the MTM. I have the Modula MTs. For me, their weakest points are inefficiency, and too much bass in my room below 40hz.

Dual woofers in an MTM should address the efficiency, and possibly offer more control of room modes. The bass problem may be entirely my room--others may not have the same problem.

Marvin

[czag]

@Czag, I couldn't seem to get your link to work, but I'm very interested to see it.

Fixed, try it now.

Chris

[Alayers]

I'm sorry if some of my questions seem very basic, but I come at this from an electronics background and I don't understand all of the finer points of this yet... I bought 2 of the 4-oh rs180's before I saw the Bagby MTM design. I'm assuming that I shouldn't really expect a normal home-theater quality receiver to be able to drive a 2-ohm load? Can I simply put a 4-ohm resistor in series with each driver to simulate two 8-ohm drivers? Or does that have an adverse effect on the audio quality?

[Chris Roemer]

I'm sorry if some of my questions seem very basic, but I come at this from an electronics background and I don't understand all of the finer points of this yet... I bought 2 of the 4-oh rs180's before I saw the Bagby MTM design. I'm assuming that I shouldn't really expect a normal home-theater quality receiver to be able to drive a 2-ohm load? Can I simply put a 4-ohm resistor in series with each driver to simulate two 8-ohm drivers? Or does that have an adverse effect on the audio quality?

I'm assuming that JB's MTM uses 2 8n woofers in parallel for a 4n load (which also increases the sensitivity of the bass section by +6dB).

If you wanted to use a single 8n woofer, you could roughly get to a "starting point" (for voicing) by adjusting the LP filter components to the higher load impedance, AND by attenuating the tweeter by an additional 6dB.

NOW, assuming that the 4n and 8n RS woofers have the same FR curve (which they probably don't), AND that a single 4n woofer has exactly the same impedance profile as a pair of 8n woofers in parallel (which they also probably don't - BUT most likely will be fairly close) . . .

YOU'RE already at a 4 ohm load for the LP (low pass), the same as JB's LP (again, assuming a pair of 8n woofers in parallel). So, all other things being equal (which, again, they're probably not), there's no need to run a 4n resistor in series with your 4n woofers (which is not a good idea anyway, you're burning up half your amp's power heating up the resistor), BUT you'd have to account for a change in effciency between his pair of 8 ohmers (in ||) and your single 4 ohm driver. Most likely (once again, . . .) your 4n will be 3dB less efficient than his pair, so the tweeter would have to be cut an additional 3dB.

Chris