Melded piezo array switching - Full/Half/Off

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Bill Fitzmaurice
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Re: Melded piezo array switching - Full/Half/Off

#31 Post by Bill Fitzmaurice »

Clef's of Bass wrote: Fri Jan 15, 2021 7:35 pm I presume that the piezo crossover would be at 8 ohm as well, wired in parallel with the 15 making the cab's impedance @ 4 ohm?
The piezo array is a high impedance capacitive load, so it's not 8 ohms. The high and low frequency sections are not wired in parallel. Part of the reason for using a crossover is that it provides separate low frequency and high frequency impedance loads to the amp.

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Clef's of Bass
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Re: Melded piezo array switching - Full/Half/Off

#32 Post by Clef's of Bass »

Bill Fitzmaurice wrote: Fri Jan 15, 2021 10:45 pm
Clef's of Bass wrote: Fri Jan 15, 2021 7:35 pm I presume that the piezo crossover would be at 8 ohm as well, wired in parallel with the 15 making the cab's impedance @ 4 ohm?
The piezo array is a high impedance capacitive load, so it's not 8 ohms. The high and low frequency sections are not wired in parallel. Part of the reason for using a crossover is that it provides separate low frequency and high frequency impedance loads to the amp.
Hello Bill and Grant, thank you for your quick responses.

First time cabinet builder, long time woodworker, and long time bass player here.

From the illustrations in the instructions and the sketch up model, it appears that the 2 speakon jacks are wired in parallel with one crossover on each.

If both crossovers are 8 ohms each, would the amp see and put out a 4 ohm load?

Follow up, would the the load by dynamic or static with the tweeter switch?

Sorry for all of the newb questions, I'm still researching an amp head to pair it with.

Do you guys have any suggestions for amp heads...Tube/ SS?

Regards

Justin

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Bill Fitzmaurice
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Re: Melded piezo array switching - Full/Half/Off

#33 Post by Bill Fitzmaurice »

I'll try again.

The high and low frequency sections are not wired in parallel. Part of the reason for using a crossover is that it provides separate low frequency and high frequency impedance loads to the amp.

If anyone else can think of a better way to explain why an eight ohm low frequency section and an eight ohm high frequency section do not result in a four ohm load please have at it.

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Re: Melded piezo array switching - Full/Half/Off

#34 Post by Bruce Weldy »

Bill Fitzmaurice wrote: Sat Jan 16, 2021 9:51 am I'll try again.

The high and low frequency sections are not wired in parallel. Part of the reason for using a crossover is that it provides separate low frequency and high frequency impedance loads to the amp.

If anyone else can think of a better way to explain why an eight ohm low frequency section and an eight ohm high frequency section do not result in a four ohm load please have at it.

I had the same head-scratching moment years ago about this subject.....until I finally figured out that because the woofer and the tweeters were not in the same frequency spectrum the loads don't become parallel. Only when two drivers are producing the same content does the resistance change. As long as they aren't operating in the frequency range - the load doesn't change. The crossover is what keeps these two drivers separated and on their own side of the frequency fence - that's why the impedance doesn't change.

Maybe that makes sense.....it did to me.

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Re: Melded piezo array switching - Full/Half/Off

#35 Post by Dale Hammer »

Tubes.

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Seth
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Re: Melded piezo array switching - Full/Half/Off

#36 Post by Seth »

I didn't understand for a long time either. Basically, adding a passive crossover in a driver circuit adds impedance to roll off the response. The load depends on the frequency.

The black line in the bottom graph illustrates the net effect of combined high-pass (red) and low-pass (green) filters.

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Re: Melded piezo array switching - Full/Half/Off

#37 Post by Clef's of Bass »

Bill Fitzmaurice wrote: Sat Jan 16, 2021 9:51 am I'll try again.

The high and low frequency sections are not wired in parallel. Part of the reason for using a crossover is that it provides separate low frequency and high frequency impedance loads to the amp.

If anyone else can think of a better way to explain why an eight ohm low frequency section and an eight ohm high frequency section do not result in a four ohm load please have at it.
I'll try this question again. I understand that the crossovers keep the frequencies separate, but at some point the amp see a total load or impedance from the cabinet. What is the total load the for the amp? 4ohm? 8 ohm? 16 ohm?

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Re: Melded piezo array switching - Full/Half/Off

#38 Post by Clef's of Bass »

Dale Hammer wrote: Sat Jan 16, 2021 1:55 pmTubes.
Thanks Dale, I was leaning towards that too!

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Re: Melded piezo array switching - Full/Half/Off

#39 Post by Seth »

Clef's of Bass wrote: Sat Jan 16, 2021 4:52 pm
Bill Fitzmaurice wrote: Sat Jan 16, 2021 9:51 am I'll try again.

The high and low frequency sections are not wired in parallel. Part of the reason for using a crossover is that it provides separate low frequency and high frequency impedance loads to the amp.

If anyone else can think of a better way to explain why an eight ohm low frequency section and an eight ohm high frequency section do not result in a four ohm load please have at it.
I'll try this question again. I understand that the crossovers keep the frequencies separate, but at some point the amp see a total load or impedance from the cabinet. What is the total load the for the amp? 4ohm? 8 ohm? 16 ohm?
8
Last edited by Seth on Sat Jan 16, 2021 5:03 pm, edited 2 times in total.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Re: Melded piezo array switching - Full/Half/Off

#40 Post by Clef's of Bass »

Seth wrote: Sat Jan 16, 2021 5:00 pm
Clef's of Bass wrote: Sat Jan 16, 2021 4:52 pm
Bill Fitzmaurice wrote: Sat Jan 16, 2021 9:51 am I'll try again.

The high and low frequency sections are not wired in parallel. Part of the reason for using a crossover is that it provides separate low frequency and high frequency impedance loads to the amp.

If anyone else can think of a better way to explain why an eight ohm low frequency section and an eight ohm high frequency section do not result in a four ohm load please have at it.
I'll try this question again. I understand that the crossovers keep the frequencies separate, but at some point the amp see a total load or impedance from the cabinet. What is the total load the for the amp? 4ohm? 8 ohm? 16 ohm?
8
Thank you Seth

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Re: Melded piezo array switching - Full/Half/Off

#41 Post by Seth »

Clef's of Bass wrote: Sat Jan 16, 2021 5:02 pm
Seth wrote: Sat Jan 16, 2021 5:00 pm
Clef's of Bass wrote: Sat Jan 16, 2021 4:52 pm

I'll try this question again. I understand that the crossovers keep the frequencies separate, but at some point the amp see a total load or impedance from the cabinet. What is the total load the for the amp? 4ohm? 8 ohm? 16 ohm?
8
Thank you Seth
No problem. :thumbsup:

8ohms, nominal. In actuality, it varies significantly throughout a drivers frequency range. But, the nominal rating would remain 8ohms.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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