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Multi-Way Conventional loudspeakers with crossovers

SB Acoustics reference 3-way by Audio Society of Minnesota
SB Acoustics reference 3-way by Audio Society of Minnesota
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Old 15th February 2014, 09:11 AM   #1
Ron E is offline Ron E  United States
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Default SB Acoustics reference 3-way by Audio Society of Minnesota

New SB Acoustics Reference design published (writeup is still a work in progress)
Design was started (and drivers obtained) before Zaph's SB 12.3 design was published, but once we saw Zaph's design it was obvious that comparisons would be inevitable.

At one point we had a full passive crossover, but the 7.5mH/400uF capacitor in the resonant peak filter for the SB15 "midranges" can get really expensive if high quality components are used. We decided active is a better way to go.

Some of the details of this design are specific to the club environment (40" tweeter height and larger cabinets to compensate for the relatively high output impedance of our clubs' Tube amps.)

Evolving writeup here at the Audio Society of Minnesota:
https://sites.google.com/site/audios...tics-reference

Feel free to share any opinions or questions.
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Old 15th February 2014, 09:21 AM   #2
Lojzek is offline Lojzek  Croatia
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Ron E,

you are right, 400 uF looks like a bad idea, not because of parts quality,
rather causing a near dead short on the impedance graph, if I understood
correctly. You were referring to the passive low pass filter of the woofers?
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Old 15th February 2014, 09:29 AM   #3
Ron E is offline Ron E  United States
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Quote:
Originally Posted by Lojzek View Post
you are right, 400 uF looks like a bad idea, not because of parts quality,
rather causing a near dead short on the impedance graph, if I understood
correctly. You were referring to the passive low pass filter of the woofers?
The resonant peak filter was a series notch 7.5mH. 400uF and 4 ohms (minus inductor DCR) in parallel with the SB15 woofers - so not a dead short by any means. I was speaking of passive "highpass" of the SB15 5" midwoofers, which have very tall impedance peaks - shown are measurements with socks loosely plugging ports, so more of a quasi- aperiodic than strictly sealed, which should actually reduce the impedance peaks a bit.
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Old 15th February 2014, 09:35 AM   #4
Lojzek is offline Lojzek  Croatia
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So, you were trying to null the impedance resonant
frequency peak of the midwoofers in the box ?
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Old 15th February 2014, 09:44 AM   #5
Ron E is offline Ron E  United States
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Quote:
Originally Posted by Lojzek View Post
So, you were trying to null the impedance resonant
frequency peak of the midwoofers in the box ?
Yes. If you don't use a peak filter, a passive highpass doesn't work very well Measured impedance was quite flat using only the peak filter, so it was designed properly It is a COMPLETELY moot point since the final design didn't use it...
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Old 15th February 2014, 09:54 AM   #6
Lojzek is offline Lojzek  Croatia
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Ron E,

I am affraid you are not right about nulling impedance peak as
a necessity. You can do whatever passive high pass filter you desire
without building RLC circuit for nulling impedance peaks. I have
been there and done that. RLC has this unwanted effect that it makes
amplifier waste more power for nothing. This kind of circuits are
normally placed in parallel to amplifier output and there they alter
impedance as wanted but do not change FR response.

Wish you success !
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Old 15th February 2014, 08:30 PM   #7
PeteMcK is online now PeteMcK
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Ron, nice work, look forward to the write-up on the 8" bass cab, those woofers are appealing...
Lojzek, re:"nulling impedance peak" - I see Joe's doing this on the Elsinore now, white paper promised... I sense a debate on this coming up....
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 15th February 2014, 09:36 PM   #8
5th element is offline 5th element  United Kingdom
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Zaph also does it in his SB big three way and shows what nulling the impedance peak does to the frequency response.

In general nulling an impedance peak will have no effect on the frequency response, if and only if, there is no filter trying to act on the driver in the frequency range that the impedance nuller is going to have its effect on. If there is a filter, such as a high pass, then it has a considerable effect and it is absolutely necessary for the correct function of said filter.
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Old 15th February 2014, 10:03 PM   #9
PeteMcK is online now PeteMcK
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5Th, re:"Zaphs SB big three way" - got a link to that? I can't find it on his site
cheers
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Old 15th February 2014, 10:11 PM   #10
_henry_ is offline _henry_  Australia
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pete, its on madisound page and link to zaph's

The Madisound Speaker Store

Zaph|Audio - SB12.3 3-Way Tower
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