Notes
18 August, 2004: Unfortunately, I noticed severe variation in two MDT-20 tweeters I received recently.
I'm wondering if Morel might be having manufacturing issues (which has been rumored in the past). It's
something to consider before building this design.
30 June 2003: Added a parts list.
Intro
This is only the second time I've worked with an aluminum cone. The first was
the MCM 55-1855 in my Mini 2-way It's also
only the second time I've worked with a Seas driver. Seas woofers are known
for their linear motors, high build quality and wide range of materials. In fact, the only
credible cone material not somewhere in the Seas line is wood pulp, and that
should show up in the Excel line sometime this year.
The L15RLY/P (a.k.a. H1141) is one of their new generation aluminum cone drivers. It has a higher Xmax than is common for prior Seas drivers (5mm!) which makes it a strong contender despite its petite size. Most 5.5" woofers only come with 2-3mm of Xmax, making them sutiable only as midranges or for low-output systems.
I chose the MDT-20 tweeter for this project because of its outstanding reputation. Also, having worked with the MDT-30, I've seen what Morel can do, and I like their tweeters. I'll have to say, the MDT-20 is an excellent tweeter, and unless I need shielding, I can't think of any other tweeter in this price range I'd rather use.
The resulting speaker is fine for general use, but should only be used with a subwoofer in any situation where respectable bass levels are expected (i.e., home theater). The F3 is in the mid-80's so an 80Hz crossover to the sub is acceptable, although an 85Hz crossover should be used if your pre/pro or receiver gives you the option.
Here is a near-complete parts list. (Right click on the link and select "Save Target As...".) It is formatted to send to Madisound and contains prices as of 30 June 2003. It can also be used as a reference when ordering from another vendor. Total cost is just over $200, not including cabinets.
The L15RLY/P (a.k.a. H1141) is one of their new generation aluminum cone drivers. It has a higher Xmax than is common for prior Seas drivers (5mm!) which makes it a strong contender despite its petite size. Most 5.5" woofers only come with 2-3mm of Xmax, making them sutiable only as midranges or for low-output systems.
I chose the MDT-20 tweeter for this project because of its outstanding reputation. Also, having worked with the MDT-30, I've seen what Morel can do, and I like their tweeters. I'll have to say, the MDT-20 is an excellent tweeter, and unless I need shielding, I can't think of any other tweeter in this price range I'd rather use.
The resulting speaker is fine for general use, but should only be used with a subwoofer in any situation where respectable bass levels are expected (i.e., home theater). The F3 is in the mid-80's so an 80Hz crossover to the sub is acceptable, although an 85Hz crossover should be used if your pre/pro or receiver gives you the option.
Here is a near-complete parts list. (Right click on the link and select "Save Target As...".) It is formatted to send to Madisound and contains prices as of 30 June 2003. It can also be used as a reference when ordering from another vendor. Total cost is just over $200, not including cabinets.
Box Design
I chose to go for a sealed box design with Butterworth response, which
led me to about 6L internal volume. The box is 11.25"x6.75"x7.5" (HWD) and made
of 3/4" MDF. A small amount of stuffing should be added, about a handful. There is
no bracing.
In a blatant thumb-of-the-nose to the diffraction crowd, both drivers are centered on the baffle. Despite this, the final design shows very little diffraction-induced ripple. The tweeter is 2.75" from the top of the box, the woofer at 8" from the top.
In a blatant thumb-of-the-nose to the diffraction crowd, both drivers are centered on the baffle. Despite this, the final design shows very little diffraction-induced ripple. The tweeter is 2.75" from the top of the box, the woofer at 8" from the top.
Crossover Design
Once again, the standard 4th order Linkwitz-Riley is employed. There is about 5.5dB
of baffle step compensation on the woofer.
First, the low-pass (woofer) circuit.
The high-pass (tweeter) circuit is the standard topology attached to most tweeters in a 4th-order LR. Once again, the resistor next to the coil is the DCR of the coil. An 18-gauge coil should be used.
If this speaker sounds too "bright" to you, decrease the 30 Ohm resistor to 20 Ohm. Likewise, if you think it sounds too dull, increase it to 40 Ohm, 50 Ohm, or leave it out altogether.
Here is a TurboCAD file of the crossover layout. You can get a free version of TurboCAD that you can use to print it out. It is a full-scale drawing which you can use to drill holes in your crossover boards.
Here is what the completed crossover looks like.
Any way, my listening impressions are that this is a fine little speaker. The Seas L15 and Morel MDT-20 are both stand-out drivers. Smooth and bouncy, with plenty of energy. It's a pitty neither of these driver are available shielded in the US. Morel makes a shielded MDT-20, be nobody sells it here (Mafidound has ordered some, and I'm on the list to get one!). Seas has commented that if a distributor places an order for it, they would be happy to build the L15 shielded. (Hint: Seas are sold by Madisound and Zalytron. Maybe if enough people ask...)
Depending in component selection, this speaker should cost about $225 to build, including everything but the veneer.
First, the low-pass (woofer) circuit.
The high-pass (tweeter) circuit is the standard topology attached to most tweeters in a 4th-order LR. Once again, the resistor next to the coil is the DCR of the coil. An 18-gauge coil should be used.
If this speaker sounds too "bright" to you, decrease the 30 Ohm resistor to 20 Ohm. Likewise, if you think it sounds too dull, increase it to 40 Ohm, 50 Ohm, or leave it out altogether.
Here is a TurboCAD file of the crossover layout. You can get a free version of TurboCAD that you can use to print it out. It is a full-scale drawing which you can use to drill holes in your crossover boards.
Here is what the completed crossover looks like.
Final Results
Any way, my listening impressions are that this is a fine little speaker. The Seas L15 and Morel MDT-20 are both stand-out drivers. Smooth and bouncy, with plenty of energy. It's a pitty neither of these driver are available shielded in the US. Morel makes a shielded MDT-20, be nobody sells it here (Mafidound has ordered some, and I'm on the list to get one!). Seas has commented that if a distributor places an order for it, they would be happy to build the L15 shielded. (Hint: Seas are sold by Madisound and Zalytron. Maybe if enough people ask...)
Depending in component selection, this speaker should cost about $225 to build, including everything but the veneer.