DPDT Switches for Electrical Phase Reversals from a Crossover into Various Drivers - diyAudio
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Old 30th July 2012, 04:13 AM   #1
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Question DPDT Switches for Electrical Phase Reversals from a Crossover into Various Drivers

I'm wondering if using a DPDT switch mounted on the front baffle (the two position rocker style) to change a tweeter's phase from 0 (normal) to 180 (reversed) would be wise? The switch would be electrically inserted into the pathway from the 3-way crossover's tweeter output terminals to the tweeter's input terminals. I am not an electrical engineer but can assemble the drivers and crossover (and solder too, ooh, wow). The 3-way crossover, for clarity's sake, is tweeter, midrange, woofer. Max RMS wattage of 275W.

But, I have noticed that when I turn on/off any household electrical switch, my over-the-air (OTA) ATSC HD signal gets interrupted for a second or so (kind of depending on the distance of the switch to the antenna atop the HD TV). Therefore, there must be a nice electrical arc (square-wave type arc with lots of ripple/noise???) happening when those switches are 'energized' and 'de-energized' (aka 'thrown').

Would the 'physical switching' cause a power spike that would injure the tweeter? And, would the switch itself represent a 'poor electrical pathway' for the audio signal and therefore degrade the signal?

My overall goal would be to not only allow the tweeter to be phase reversed but also the enclosure's midrange and woofer too. My thinking is why not allow for each to be phase reversed? But, as the latter two (2) drivers use much more wattage, I would assume that reversing the phase of them in this manner using DPDT switches would be more difficult/dangerous?

Please let me know if this is possible and if so, which DPDT switches the DIY experts have successfullly used (brand, model, distributor)?

Thank you very much!
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Old 30th July 2012, 09:26 AM   #2
tvrgeek is offline tvrgeek  United States
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If you try it, be sure it is a break before make switch. Not all are.
I really don't know why you would want to do this. Do you want a switch that when thrown, sucks out everything at the crossover point? I could see wanting to build a test rig where you could so it from a listening position, but once the crossover is designed, I can't think of any reason.

Yes, if there is any difference in potential when a switch is thrown, it will arc. How much depends on how much the load is. I doubt it would blot the tweeter unless you were pushing it to the limits of it's life when you switch.

Switch quality. You are trolling for arguments there. People will fight about $70 binding posts and this weeks magic speaker wire, forgetting what is inside the speaker.
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Old 30th July 2012, 12:47 PM   #3
DrDyna is offline DrDyna  United States
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Make before break switches are pretty expensive if I remember right, but in any case, I'm with tvr on this one, I can't think of a reason to do this, as the phase is going to be "correct" in one orientation and "incorrect" in the other.

To go after the question directly though, speaker switch boxes usually use DPDT relays and switches anyway. I've got an A/B selector here that uses a 12v DPDT relay with a push button that doesn't seem to have any ill effects.
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Old 31st July 2012, 02:30 PM   #4
AllenB is offline AllenB  Australia
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When you have a sudden switching, the energy will manifest itself as a broadband spike and find an easy path, sometimes with bad results. In reality you'll probably be OK. There are a number of reasons why this is OK but there are no guarantees. You ought to turn off the equipment between switches, but then I ought never to solder a crossover while music is playing

Anyway, you may find that neither way gives you great results and this is not the ideal way to match phase.
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Old 31st July 2012, 02:34 PM   #5
DrDyna is offline DrDyna  United States
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Quote:
Originally Posted by AllenB View Post
..but then I ought never to solder a crossover while music is playing
At first I was like but then I realized that I and do the same thing sometimes.
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Old 31st July 2012, 03:10 PM   #6
AllenB is offline AllenB  Australia
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Fortunately I had a hard taskmaster in my early years and subsequently I cringe when I touch a live circuit with a conductor which isn't isolated, even after a quiet drink. Mind you I also made him cringe a few times. Experimenting 'on the fly' is just my style but it's not without personal risk.
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Old 31st July 2012, 04:01 PM   #7
DrDyna is offline DrDyna  United States
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Quote:
Originally Posted by AllenB View Post
Fortunately I had a hard taskmaster in my early years and subsequently I cringe when I touch a live circuit with a conductor which isn't isolated, even after a quiet drink. Mind you I also made him cringe a few times. Experimenting 'on the fly' is just my style but it's not without personal risk.
No crossover toolbox is complete without a heaping handful of aligator clips

You're right though, there's always risks. I usually won't experiment with subwoofer circuits or single driver-per-channel while speakers are on, except for maybe zobels, but as far as l-pads or flipping a tweeter polarity as long as it's not the only component in the system, should be relatively safe. I've always been pretty comfortable with it considering how many speakers I've seen with selector switches and tone controls and I've not heard of someone nuking an amplifier playing with them.
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Old 31st July 2012, 09:05 PM   #8
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Quote:
Originally Posted by tvrgeek View Post
If you try it, be sure it is a break before make switch. Not all are.
I really don't know why you would want to do this. Do you want a switch that when thrown, sucks out everything at the crossover point? I could see wanting to build a test rig where you could so it from a listening position, but once the crossover is designed, I can't think of any reason.
Thanks everyone for the replies! It is good to be back.

I am considering doing this (DPDT switches to flip over driver phase) ONLY because I have a relative that wants his 20 year old 'college days' 3-way speakers rebuilt. The story gets better, trust me.

He powered them up after like 17 years of storage and the original 12" Pyle woofers' foam surrounds just puffed out and away into the air like powder! So, he chose a couple Dayton 12" replacements and had them drop-shipped to me. I also now have the speakers too.

I noticed and pointed-out that each cabinet is not anywhere near large enough for the vented type and it wasn't correct even when the original woofers were in there (T/S parameter speaking). But, it probably had that nice 50Hz 'college sound' hump and then a very quickly dying-off low-end.

He would like me to use those Dayton woofers, have me build a properly sized and ported cabinet and is now asking about which mids and tweets to buy even when the current ones are OK. He also heard that 4ohm drivers will sound louder than 8ohm ones but does not know the real reason as to why. That would mean returning the Dayton woofers at the very least! And, the 3-way Radio Shack crossovers are only rated for 100W continuous power...yeeesh. Model 40-1299a if I recall correctly. Yes, I know the electrical and mathematical problems this whole thing is presenting.

So, this simple project of just replacing two 12" woofers is becoming a monster in terms of physical, mathematical, and 'my best guess' at a sound blend that he will like.

With car audio (components of mids and tweets up front), sometimes reversing the polarity of the tweets will result in a better blend. Even with the subwoofer, that can be done for a smoother blend. And, with this kind of 'picky' relative, I thought I'd just bet on the safe side and make ALL of the drivers phase reversable!

Heck, if I could put adjusters for everything on its front face, I would! Sliders for -12dB to +12dB for each driver, sliders for what each driver would see frequency range wise, choosable slopes, you name it!

Yes, self-deprecating laughter at me as I am pretty much starting from scratch but with two 12" Daytons in hand.

I prefer extremely accurate sound and then loudness (and lastly, aesthetics, ha!). I bet he is kind of the opposite... So, I would be approaching this whole design from a completely different direction for ME. But, for him, I don't know. I don't even yet know if his receiver's amp can drive 4ohms. It is quite old so it likely can only drive 8ohms!!

So, who here has built speakers for someone when neither the builder nor the owner know what kind of sound the owner would like in the end?!?!?! Any generic plans out there?
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Old 31st July 2012, 09:14 PM   #9
DrDyna is offline DrDyna  United States
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Oh, there's tons of plans out there.

It sounds like you're in for a mess, especially using pre-fab crossovers, as crossovers really need to be designed part by part for the drivers they're controlling. If you're going at it from scratch, do something like this:

https://sites.google.com/site/undefinition/tarkus

Or, you might be able to google your way into a 3 way design that uses the woofers you already have on hand, something like "3 way design using dayton ____".

As far as the receiver goes, older is probably better. A lot of the older receivers are actually much better at driving lower impedance than newer ones. They don't make em like they used to. It's most likely safe driving a 4 ohm load.
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Old 31st July 2012, 09:16 PM   #10
sreten is offline sreten  United Kingdom
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Hi,

Driver polarity switches are a dumb idea, its either right or wrong.
What is right or wrong sometimes is not as obvious as it seems.

rgds, sretem.
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