First speaker project, need advice (xover concerns, etc)

[pres589]

Hey, I'm wondering if there are some kind souls that would like to help critique a speaker design I've been putting together. I've run through old posts and done some searching and the driver combination I'm thinking about using doesn't seem to be out there so I think this is somewhat fresh and should keep me out of trouble for asking.

The particulars of this design;
I'm wanting a 2-way system using a pair of drivers to control costs and keep it a little more simple (first timer and all). The design goal is to act as the only drivers for computer / small room use without the aid of a separate subwoofer. For power I've got an older Sony that is rated at 75 watts per channel to the mains. I'd like a smaller sized enclosure as I don't have tons of space. And to make this even more complicated, I'd like to use some Morel MDT-20's I already have from a previous project idea that never happened so they're sitting new in box. I know that's not the way to start a project but my hope is that this design restriction doesn't pose much of a problem.

To start, here's a link to the MDT-20 on Parts Express for those not familiar and want to check out the graphs and other specs;
Morel MDT-20

The driver I've been looking at to match with this tweet for this project is the Dayton RS180S-8. It seems like a good compromise and can reach up to near the MDT-20 without breaking up too badly. But that's what my eyes on the graph tell me; what do those with more experience think?
Dayton Audio RS180S-8

I'm not married to this driver by any means, although I do really like the shielding (even if it's not the best shielding ever, for this application I appreciate it) and the price of $35 each is good. I'm open to suggestions, for sure.

What I've come to on my xover is a want for steep roll off to keep these drivers from breaking up, while trying to get as much useful range out of them as possible. To that end, I configured a 24db/octave Linkwitz Riley as they seem fairly straightforward and don't carry with them an overly large number of required components. I figured on having the rolloff for the woofer start at 1700Hz and the tweet should come in at 2300Hz. I figured if the power is a little weak in that notch, I'm still in better shape than having the drivers overlap too strongly with a resultant peak. Thoughts?

The crossover layout as drawn up is here;


To keep this from getting too long as a thread starting post I'll skip my selected xover component values, although I've gone through with a couple online calculators and tried to work out some values. I then went through the Parts Express online catalog of Jantzen components and, using their 18 ga. air core inductors and their line of CrossCap capacitors, found the nearest available commercial values. I think it best to go that route instead of making approximated equal values to the computed values to keep thinks more simple for both construction and signal path.

The box I have in mind, based again on some calculated volumes, is a ported box using a slot port (not sure what the best term is here, I don't want a tube type port, but rather use the box walls plus an internal wall ending in a slot to the front of the box baffle). Volume is about ~.6 cu. ft, but I'm not nearly as concerned about this right now as driver selection and xover design.


If this post itself needs rework or I missed anything (or I need to do more homework, et cetera) please let me know, I'm pretty excited about this project.

[Jed]

Online calculators won't work for your crossover design because they don't take into account the driver's actual response, and notching out the high Q peak for one. Take a look at the crossover for the Modula MT to get an idea what I'm talking about. I don't think your selected tweeter will go low enough to work well with the RS180 as well. Might as well build one of the accomplished designs and work you way to designing your first speaker after you get some more experience.

Jed

[pres589]

My concern with using the Modula MT's crossover was proper matching of the impedance of that crossover to the MDT-20's I already have. Otherwise, yeah, I'd just copy that design.

Can the MDT-20 be swapped for the tweeters mentioned with that design? Offhand I believe that was something from SEAS, correct?

[ThomasW]

Can the MDT-20 be swapped for the tweeters mentioned with that design? Offhand I believe that was something from SEAS, correct?

Given the MDT-20's T/S parameters, the Modula MT should be used as an example of how to match a tweeter with the RS180. The crossover itself can't be copied for use with the Morel tweeter.

Following up on what Jed said....if you don't understand crossover design, and have the tools to measure the in box response of the drivers, you'd be better off paying someone like Meniscus to design one for you.

[Dennis H]

Like Jed said, your tweeters probably won't play low enough to cross to the RS180. Maybe you can sell them and buy the Seas or Dayton tweeters that Jon designed crossovers for?

http://www.htguide.com/forum/showthread.php4?t=13154

http://www.madisound.com/catalog/product_info.php?products_id=792

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=275-130

[ThomasW]

The other option is forget about using the RS180 and buy a Peerless or other driver that's more forgiving.

[pres589]

The other option is forget about using the RS180 and buy a Peerless or other driver that's more forgiving.

Been looking around for Peerless drivers and not sure if there's anything out there right now that fits the bill, although I may be missing something.

What are you thoughts on the design shown here? http://murphyblaster.com/content.php?f=MB20.html

The woofer used is a GR Research M130... is this more in line with what you're thinking? Should be a fairly inexpensive speaker to build if this thing goes together like the narrator tells us it did, although I wish he posted response curves down to 50Hz instead of 200Hz.

[ThomasW]

If you want to build Dennis' design that's up to you.

Per our "New Rules" sticky post, we don't discuss GR-Research products on this forum.

[pres589]

Noted on the product which will from here on remain un-mentioned.

Telling me I can build something and it's up to me isn't exactly the feedback I was looking for. Or is commenting on another's published designs also verboten? (and it may well be, which is why I ask, not to be rude)

[augerpro]

Discussing commercial designs is typically not allowed is all. Here are some easy to work with drivers worth considering:

http://www.madisound.com/catalog/product_info.php?manufacturers_id=143&products_id=1613

http://www.madisound.com/catalog/product_info.php?manufacturers_id=149&products_id=789

http://www.madisound.com/catalog/product_info.php?manufacturers_id=149&products_id=823

Here is another cheaper driver that is easier to work with (and cheaper) but smaller:http://www.partsexpress.com/pe/showd...number=264-850

The big question is whether or not you feel up to designing a crossover your self. And the level of perfection you want. So you could learn speaker design and do your own (much longer and harder than you think), build one of the fine designs in the Mission Accomplished forum.

[pres589]

Discussing commercial designs is typically not allowed is all. Here are some easy to work with drivers worth considering:

http://www.madisound.com/catalog/product_info.php?manufacturers_id=143&products_id=1613

http://www.madisound.com/catalog/product_info.php?manufacturers_id=149&products_id=789

http://www.madisound.com/catalog/product_info.php?manufacturers_id=149&products_id=823

Here is another cheaper driver that is easier to work with (and cheaper) but smaller:http://www.partsexpress.com/pe/showd...number=264-850

The big question is whether or not you feel up to designing a crossover your self. And the level of perfection you want. So you could learn speaker design and do your own (much longer and harder than you think), build one of the fine designs in the Mission Accomplished forum.

Thank you for the driver ideas, I'll take a long hard look at them.

If I hadn't already screwed myself into a corner with the MDT-20's I wouldn't be so strung out over all of this. However, I could always put them aside for another time, I've another project I'd like to do but it's more complex and I saw a "simple" 2-way as a good starter project.

The MDT-20's would seem to work better in a 3-way design (which is what they were originally purchased for) anyway so I'll take a look at the drivers you've listed but I'm coming closer to hanging up on that and moving to Mission Accomplished or other sites. This forum, aside from my somewhat rocky start here today, still seems to be one of the better out there for this subject.

And I do have some filter experience, but it's in active filters using op-amps, and that experience is somewhat limited. Plus it was in a college setting where we had such niceties as function generators and o-scopes to check our work and tweak as needed. Which I now lack for my own projects.

[Turn2]

If I were in your shoes I'd build the Murphy design. Dennis is a respected designer so the project won't be a bust. The design meets your goals and you will have used those Morels in an appropriate way. Your end product won't match the Modula MT's, but you're at the learning stage, right? You've already referred to your "next project". You can go for more gusto and take a step up after you get a proven project under your belt.

Good luck! :T

[pres589]

If I were in your shoes I'd build the Murphy design. Dennis is a respected designer so the project won't be a bust. The design meets your goals and you will have used those Morels in an appropriate way. Your end product won't match the Modula MT's, but you're at the learning stage, right? You've already referred to your "next project". You can go for more gusto and take a step up after you get a proven project under your belt.

Good luck! :T

This is me trying to write a reply that won't get me in dutch for mentioning the wrong things...

I think you may be on to something. This setup is going to cost less than the Modula MT, which would probably allow me to (at a later date) try my hand at assembling a small subwoofer to match with the Murphy pair. Plus the Modula MT's, while not massive, are awfully big for a set of computer speakers.

I think the next project might be a set of "garage speakers" that let me try my hand at 2-way crossover design and driver selection that matches each other, instead of trying to wedge an odd set of parts together for a task they're not really up for. Plus if they come out not completely perfect that's fine for the task at hand, and I can save a little in crossover components without sweating things to the utmost detail vs. just trying for a simple yet competent crossover. We'll see.

[Dennis H]

This is me trying to write a reply that won't get me in dutch for mentioning the wrong things...

I know the rules seem a bit odd. Just to clarify, Dennis Murphy is one of the good guys and there's no problem at all discussing his designs. He even posts here once in a while and has a few crossover designs in Missions Accomplished for the Dayton 3-way series. However, this forum and some other online sites like Zaph's have had bad experiences trying to calmly discuss the relative merits of the drivers from a certain reseller (cough gr ) so we just don't do it any more to avoid flame wars.