Side Project: The LM-1 Center Channel

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I thought I would share with you this project. Prototype crossovers were just finished. It uses the same drivers as the LM-1.

IMG_20160305_145932.jpg




It's pretty simple, though definitely not done. Need to do something about it's physical location before I can finish voicing it.


Schematic.jpg


And the predicted response. Keep in mind I have yet to finish tuning the ports or the crossover:

FR_Predicted.jpg



For more please visit my blog, here.
 
The LM-1C was made because I needed a center channel, but it's the same design I would have made if making MTM for a stereo pair. The timbral balance is made to match my main speakers.

Overall I really like it but at times older pop music may sound like it's too far in the back of the hall. Jazz, Classical, movies and more modern recordings don't seem to suffer from this. If you feel that's an issue I suggest bumping up the treble by reducing R3 to 3.9 Ohms or so.

The far-field measurements on a cabinet are really great and if you plan to use them with a subwoofer you should have no problems at all. By themselves, stand mounted they could sound a little too light-weight and need adjustments.

The last thing is they sound good off angle, but they really do have a sweet spot due to the relatively narrow dispersion of the XT25 tweeters. I personally love this about the XT25 as the tweeter sounds much the same at 9' as they do at 2'. Not what you can say about most wide-dispersion drivers in a typical room.

The tweeter is also great for movies, as they give the illusion that your room can disappear and you are in the movie at the cost of not having the same level of detail everywhere in the room.

Best,

Erik
 
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Hi Erik,
Went down this road a few years ago with Peerless 4ohm drivers (from the early 90s). So wanted to build a updated version for stereo listening.
A few questions:
What do you think about a narrow baffle, with front slot ports, similar to the attached pic?
A quick look at Madisound's website, the spec sheet calls for .3 - .4 f3 box, any thoughts about going with a .8 box?
Any concerns about stacking the drivers in a straight line?
What was your xo point?
Posting the xo from the project from a few years ago, we started with a 6.8uf series cap (tweeter), then moved down to 3.9uf which does sound really nice.
I believe the general consensus is the xt25 is a fine tweeter, if crossed over high.


Attached crossover on right by Dissi

woofer link: https://www.madisoundspeakerstore.com/approx-5-woofers/peerless-830991-5.25-fiberglass-cone-woofer/

Doug
 

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A simulation of the LM-1 Center shows a crossover at 2 kHz and a distinctly falling frequency response. I don't know whether the double magnet tweeter allows a lower crossover frequency. A guy in Germany even did an MTM with the XT25 TG30-04 crossed at 1.65 kHz (Bausatz Samuel HQ – Heißmann Acoustics). The opinions are divided. :)
 

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A simulation of the LM-1 Center shows a crossover at 2 kHz and a distinctly falling frequency response. I don't know whether the double magnet tweeter allows a lower crossover frequency. A guy in Germany even did an MTM with the XT25 TG30-04 crossed at 1.65 kHz (Bausatz Samuel HQ – Heißmann Acoustics). The opinions are divided. :)

Thanks Dissi!

Yes, the frequency resposne is more or less as you say but the difference between the tweeter and bass hum is not quite as exaggerated, please see the measured graphs from the blog. Also, the tweeter is smoother than predicted by your cool charts, especially below 20 kHz.

Final_FR.jpg




The larger, dual magnet XT25 can be crossed over lower, but I didn't feel the need. Zaph claims that the small XT25 has a lot of distortion below 2 kHz but I did not find this to be true at least with the dual magnet.

Best,

Erik
 
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Hi Erik,
Went down this road a few years ago with Peerless 4ohm drivers (from the early 90s). So wanted to build a updated version for stereo listening.
A few questions:
What do you think about a narrow baffle, with front slot ports, similar to the attached pic?
A quick look at Madisound's website, the spec sheet calls for .3 - .4 f3 box, any thoughts about going with a .8 box?
Any concerns about stacking the drivers in a straight line?
What was your xo point?
Posting the xo from the project from a few years ago, we started with a 6.8uf series cap (tweeter), then moved down to 3.9uf which does sound really nice.
I believe the general consensus is the xt25 is a fine tweeter, if crossed over high.


Attached crossover on right by Dissi

woofer link: https://www.madisoundspeakerstore.com/approx-5-woofers/peerless-830991-5.25-fiberglass-cone-woofer/

Doug

I'm not very experienced with slot loading, so you'll be on your own there. :) Having the 2 8 ohm woofers allows them to attach directly to the amplifier, for best damping. Look at the final impedance plots, the speaker is really easy to drive so no reason to try 4. Also the sensitivity matters. Having the 2 8 Ohm drivers gives 3 dB more than 2 series 4 Ohms. Makes it match the tweeter more easily.

The tweeter is deliberately offset, allowing smaller distance between all 3 drivers, plus minimizes diffraction effects.

Try WinISD for box simulations if you'd like to compare cabinet sizes.

Best,

Erik
 
Dissi,

The low pass filter 1.6mH coil actually is high impedance, around 1.2 Ohms since I used two small coils I had lying around. :) It actually helps smooth out the FR as well as keeps the minimum impedance above 4 Ohms and damps down the bass a wee bit.

Best,

Erik
 
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Just wanted to let everyone know I have posted the far-field measurements and didsortion results as well as the process I used on my blog here.

One cool thing is that I measured the woofers together but created separate drivers in XSim by hacking the measurement files.

Thanks for the measurement hack hints and for the blog. Here another2 articles how to sum together woofer near field and farfield levels:

https://www.google.fi/?gws_rd=ssl#q=Measure+Loudspeaker-at-low-Frequencies

http://www.audiomatica.com/wp/wp-co...Loudspeakers-at-low-Frequencies-with-CLIO.pdf

https://www.klippel.de/fileadmin/kl...39_Merging_Near_and_Farfield_Measurements.pdf

might be good links to your blog.
 
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