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Old 13th August 2015, 01:52 PM   #1
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Default Purely acoustic crossover?

Has anyone used a sealed enclosure as a high pass filter? I'm looking at maybe using 2 Dayton rs100-4 as extended range midranges in a 3-way. My goal is to cross low to a woofer where the crossover won't be too noticeable. I was thinking, what if I built a sealed enclosure that was about 1.5 liters for both drivers. This would lead to an fb of 144 hz, a total q of .9 and f3 of 120hz. So wouldnt the response essentially act like a second order 120hz high pass with a slightly higher q than a standard lr crossover?
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Old 13th August 2015, 02:15 PM   #2
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Without a crossover you'll run out of excursion on the midrange very quickly. Have a simulation with unibox.

Ralf
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Old 13th August 2015, 02:29 PM   #3
system7 is offline system7  United Kingdom
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This sort of small sealed back idea is actually used in some cone tweeters and mids:

Phenolic Ring Tweeter Replacement for AR-4X CTS Marantz and More 8 Ohm

M 10 - 8 Ohm

In practise you always use at least a capacitor to take out the low frequencies. And IMO, they sound better with a second or third order high pass electrical filter. Nothing wrong with a proper crossover!
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File Type: png Phenolic Ring Tweeter.PNG (29.1 KB, 283 views)
File Type: png Visaton M10.PNG (13.4 KB, 284 views)
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Old 13th August 2015, 02:34 PM   #4
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Ya I think what I may end up doing is the sealed back crossover idea with a first order cross
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Old 13th August 2015, 02:36 PM   #5
adason is offline adason  United States
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...or you can use active crossover and biamp it...you get flexibility of crossover frequency and slope
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Old 13th August 2015, 04:28 PM   #6
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I do have an active crossover but I was specifically trying to make a speaker that can be single amped with the option to bypass the crossover if biamping is what you wanna do
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Old 13th August 2015, 04:46 PM   #7
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Quote:
Originally Posted by maggiesnmacs View Post
Has anyone used a sealed enclosure as a high pass filter? I'm looking at maybe using 2 Dayton rs100-4 as extended range midranges in a 3-way. My goal is to cross low to a woofer where the crossover won't be too noticeable. I was thinking, what if I built a sealed enclosure that was about 1.5 liters for both drivers. This would lead to an fb of 144 hz, a total q of .9 and f3 of 120hz. So wouldnt the response essentially act like a second order 120hz high pass with a slightly higher q than a standard lr crossover?
You can do this as you describe. Some problems are:

If the mid and woofer are both level response, not hp/lp slopes, then you can get a highbass peak as both drivers sum ~ 120Hz

At bass you are driving both in parallel so the system is low ohms at bass.

Very low xovers sound like a good idea in theory [say when drivers are closer than 1/4 wavelength] but in a passive xover it can throw up problems, like having a messy upper bass, expensive parts, or not finding a sensitive enough low bass driver to match mid levels.
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Old 13th August 2015, 05:01 PM   #8
AllenB is offline AllenB  Australia
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You could use a capacitor to cross below fc, and a second order filter would improve power handling etc. Closer to fc second order is a little less sensitive to the impedance peak. Filtering the peak would help more, but a cap at the input to the amp would be just as good.
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Old 14th August 2015, 01:13 AM   #9
system7 is offline system7  United Kingdom
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This is one of those interesting, off-the-wall ideas that actually has something going for it.

Eminence build a sealed back midrange that does exactly what maggiesnmacs is thinking about.

Speaker Detail | Eminence Speaker

In practise you are going to end up with a sharp high Q knee at the bottom. The theory says you will hear that resonance. Once you filter it with a crossover you end up with a sharpish rolloff. This overall sharp bend is called a Chebyshev filter. TBH, it's not often employed in speakers, I think I prefer gentler smoother curves, but OTOH, until you build it and give it a listen, who's to knock it?

I show you the sim with a 5" midrange in 0.5L and 8L below. You'd obviously modify the filter for the smaller midrange enclosure.
Attached Images
File Type: png Eminence 6 inch closed back midrange.PNG (20.5 KB, 208 views)
File Type: png Acoustic Crossover 0.5L mid.PNG (21.4 KB, 210 views)

Last edited by system7; 14th August 2015 at 01:19 AM.
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Old 16th August 2015, 05:42 PM   #10
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Why do you want to use that size of midrange enclosure? What are the advantages of the peak at 144Hz? At the levels I listen at in my small UK rooms, excursion would not be a problem but a lot of forum members listen at high levels in big rooms. I think the point bigbottom makes of low impedance at bass frequencies is very valid.
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