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Multi-Way Conventional loudspeakers with crossovers

"Upgrading" SEAS Idunn to Bragi
"Upgrading" SEAS Idunn to Bragi
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Old 1st February 2020, 03:08 PM   #1
powderfinger is offline powderfinger
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Join Date: Dec 2010
Default "Upgrading" SEAS Idunn to Bragi

Quite a few years ago I built three SEAS Idunns using kits and pre-finished cabinets from Madisound. Originally they were uses as LRC in my apartment's home theater setup. Now that I'm in a house, I use two of them in my PC soundsystem while continuing to use one of them as a center channel.

I'm in the process of building some DIYSG Volt coaxials for surrounds and a center channel, which will leave me with a spare Idunn that I can use to experiment with.

My experience with the Idunns has been that I like the sound of the drivers, but the overall tonal balance is a bit bright (especially sitting close to them) and the bass has always been anemic. I never loved them on their own running full range. In my current setup, I have them crossed at 100Hz to a very powerful array of eight 12" sealed subs. I have a high shelf to tame the treble by a few dB. This setup sounds amazing, but the Idunns start to run out of steam a bit earlier than I'd like. They also lack punchiness in the midbass. I'm also just ready to try something a bit different.

The design goal of this system is to be hi-fi for daily listening but with the ability to crank up the bass and get loud when I practice DJing. Trying to have it both ways. The room is small at 11'x11' but treated with some bass traps and absorption panels.

One option is starting over and building entirely new and different speakers from a kit or from scratch. Put that aside. The other option is buying an additional SEAS woofer and going MTM.

My skill level: I've got a measurement mic and Dayton Audio DSP but have only done basic in-room response measurements of my finished system for EQ purposes. I've never done cabinet building or crossover design. I may be willing to dabble in both for this project, but wouldn't mind keeping it simple.

Which leads me to my questions about the SEAS Bragi design.

1. These woofers say they are designed for ported enclosures, but given my subwoofers I have no need for bass extension. Would they perform well as MTMs in a sealed 24L box if I were to reuse the Idunn cabinets with a new baffle (the Idunns being front-ported)? Would the crossover need to be redesigned for this?

2. Assuming I built new 30L cabinets for the Bragi, should I use the SEAS crossover design given my opinions on the Idunn voicing? Are there any issues with the crossover in general that jump out at the experienced designer? I figure if the crossover point and overall topology are good, I can probably tune the tonal balance to taste with my DSP rather than messing around with padding the tweeter or whatever, but if there are bigger issues then perhaps I'd take a stab at a different crossover or run them active (I'd need to purchase an additional amp, but that's ok). Keep in mind that my listening distance is about 5 feet, so driver integration is very important.

Thanks in advance.
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Old 3rd February 2020, 05:26 PM   #2
system7 is offline system7  United Kingdom
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Join Date: Aug 2008
Location: Portsmouth UK
The H1571-08 U18RNX/P is a reflex driver. The Qts of 0.37 tells you that. And bigger boxes have more bass. The Vas is 22L, so that is what you would use in an ideal world with a Qts 0.38 driver. With twin drivers, you'd use 44L and two ports. Simple as.

The SEAS Idunn has no bass! Everybody says that!

The SEAS Bragi might be a bit better. Seems to have more bafflestep with a proportionately bigger bass coil and smaller cap.

MTM works better than MT IMO. 6dB lower excursion from the bass drivers, so lower distortion. Must be better for loudness.

SEAS promote MTM as a good solution for overly lively rooms too: ACOUSTIC SPECIAL SOLUTIONS

Truth is, a 6" plus 1" speaker is not really loud party material in a big room. You'd need to spare the 6" driver all the low frequency work to keep it happy. Which would lead to a three-way for real loudness:


It can be done, IMO. But a 6" mid is not the easiest thing to do, requiring a lowish 2-2.5kHz cross to the tweeter to keep breakup under control.
Best Regards from Steve in Portsmouth, UK.

Last edited by system7; 3rd February 2020 at 05:45 PM.
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