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studiomaster 16th June 2012 11:33 AM

query about phase
 
Hi guys
Firstly, am new to the forum and from what I`ve resd so far looks very interesting. Have dabbled around with budget audiophile hifi for the last 30 years or so with good results, and consider myself myself to be fairly critical,with a keen ear.
I am assembling a pa from second hand gear for mine and my sons rock bands and so far have managed to get a very good/hifi type sound.
Really my first question is that i have purchased some used subs and believe you would call them 15" scoop bins.The drive units actually face INTO the chamber that then exits thru its full width port/vent at the bottom rear inside the open fronted cab to fire forwards.I have actually experimented with installing the driver the other way rouund ie cone facing out.It was SLIGHTLY less effective overall but did seem to exhibit slightly better tone and response at certain low freq` ie 30-40 hz ish when specified known low freq` were generated and played through. I have since re-mounted the driver the original way round.
The drivers are wired the conventional way ie + to + from amp but was wondering if that is actually correct as the driver faces backwards but the output from the front of the cone fires into the internal chamber and out thru the vent, will the phase still be correct?

Sorry to ramble but i thought i might describe better that way.

Any thought would be very welcome.

Regards
Kev. :)

NEO Dan 16th June 2012 04:55 PM

I'd go with + to + as the vast majority of the sound should be generated by the horn, think of it as if you were to remove the back cover on a compression driver to expose the diaphragm.

And welcome to the forum. :)

studiomaster 16th June 2012 05:30 PM

Hi Dan
Thanks for your reply. I did think that would be the case but wasn`t totally sure.

Kev.

weltersys 18th June 2012 01:54 AM

Quote:

Originally Posted by studiomaster (Post 3061896)
Hi Dan
Thanks for your reply. I did think that would be the case but wasn`t totally sure.

Kev.

Kev,

Old JBL cones were wired opposite of normal convention.
Check your cones with a battery to determine if "+" is positive cone (away from magnet) displacement.

Art

studiomaster 18th June 2012 08:27 PM

Hi weltersys
Thanks for your thoughts. Yes, the coils are wired conventionally in the drivers.
As a relative layman, as regards electronics and phase charicaturistics i was not sure what, if any, influence the rearward facing driver + venting may have on the sound/ + phasing probs with mid/top speakers.

All the best

Kev.

chris661 18th June 2012 08:56 PM

Hi Kev,

Its difficult to answer without knowing more about the whole set-up, however...

If you're using a crossover (hope you are!) to split between the woofers and mids, read off the crossover frequency, and play that frequency through the system (preferably with only one channel wired up, in a nice big space, or in a field).
If the phases are perfectly aligned, you'll get zero output with the wiring one way, and full output with the woofer wired backwards.
The phases are rarely perfectly aligned, so go with whichever comes out louder: this indicates the sound waves are combining together to give more output instead of cancelling out.

Chris

studiomaster 19th June 2012 02:13 AM

Hi Chris
Thanks mate. At the moment i am only able to use an elec` xover with a fixed freq` of 150hz splitting bass to mid. however I`m sure that this will give me better quality than the crummy in-built passives (now removed, will box up to use as external passives in emergency!) I am able to store pa at work and will soon test in a very large conference room, with all possible wiring permutations. Lets see what happens! ( its great to talk to you guys as the wife just doesn`t understand! although very supportive. I`m blessed.

Cheers

Kev.

chris661 19th June 2012 06:19 AM

Not a problem. There are frequency generator apps available for Android and iOS phones, or you could use a computer with winISD Pro.

Here's the crossover I use in my home stereo: Behringer: SUPER-X PRO CX2310
Sounds good there so should be fine for PA stuff.
Then again, I doubt you'll need to change the crossover much from where it is. Only one way to find out: sit down and have a listen.

Chris

PS - you're quite correct. Particularly at lower frequencies, active crossovers are generally superior.


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