Why did my subs get louder?

gp4jesus · May 2016

Years ago I had a pair of dual 12" driver isobaric subs. They shared a dedicated 2 channel amp, EXO'd 80hz, w/ a single 10' run of 10ga, one driver daisy chained (and soldered) to the other. Took several weeks, HOURS of listening, and a bunch of testing to dial them in. During this phase I had disassembled & reassembled the TWO unsoldered connections once or twice.

"Al-ri-ght, they're dialed in." Listening bliss, right? Nope. What does a single tweak-a-holic do now?

Well I noticed I didn't really need 10' to connect them, so for fun I cut the wire in half. Then "Hey! I'll give each driver their OWN connection," (BI-WIRED!), soldering them at the driver end.

Now I have a new problem because they're LOUDER*! And I don't mean a teeny weeny bit louder either. Some testing and (a few less hours than the 1st time) of listening, dialed in again.

I do NOT have a clue* and for years I've puzzled over why such a tiny change produced a big difference. What do I know:
1. they were nominally 4 ohms w/a 3 ohm low point in their impedance curve
2. the "bi-wire" connections have a calculated resistance of .0025 ohms, .0075ohms less than the single 10' run (.05 ohms)
3. each driver in an isobaric alignment presents a different load to the amp.

Recently I had an "ah-ha" moment.
1. Each of those drivers presents different back EMF "characteristics" to the amp.
2. I believe the respective "characteristics' interfered with the other driver.
3. Bi-wiring separated the "characteristics" leaving the amp w/which to cope.

I care deeply why you think they got louder and only that. If/why my theory is wrong/ flawed, doesn't answer the question.

And if you don't know why then we have something in common.

deucekazoo · May 2016

Not sure if I followed all that but here we go. So you had them daisy chained from a two channel amp? If in series, those two 4 ohm speakers were a single 8 ohm speaker. Now a two channel amp with one wire. Was it in mono mode? If not then you were just running it off a L or R channel which will give you the power that amp was rated at one channel. If in mono mode then that amp will put out more power with both channels connected. But anyway so when you hooked them up in stereo mode the amp sees them as 4 ohm speaker and not 8 ohm. Most amps will output more power into 4 ohm so that is why they are louder.

tonyb · May 2016

If I read that right, I agree....you had them daisy chained before, then you gave each driver their own connection. You pretty much answered your own question.

polrbehr · May 2016

Reminds me of when both of the drivers died in my SVS PB12-NSD/2.
They wire their drivers much the same way, ala Xmas lights of yore, in that if one driver was out the other wouldn't work either.
Turned out I only needed to replace the bad one.

JPete · May 2016

Wire them in parallel and get a 2ohm capable mono block.

gp4jesus · May 2016

To all:

1. I neglected to mention earlier these subs were quasi DIY - home made based upon on a tried & true commercial design - the source of the impedance curve info.
2. I hard wired the speaker wires resulting in each having a 10' "tail" before and two 5' tails after the bi-wire.
3. Right after I put these in service I discovered the (dedicated) 2 channel amp* ran significantly warmer** at lower volumes than w/any other speakers at high volumes. I kept it* on a milk crate to enhance convection cooling. That** didn't change after the bi-wire.
4. In 2004 added a second Belles*. That safely upped available power ~30-40% per driver. Impedance per channel changed to nominally 8ohms, low point 6 ohms, solving the WARM amp issue.
* no mono feature & in my system today

I'm certain the drivers were paralleled before the bi wire. Due to the isobaric alignment I was VERY careful soldering the drivers the first time. I would have noticed the series wiring "mistake" during the bi-wire mod. Further, I regret not following MY protocol - rewiring one, listening to each "solo," then deciding to either rewire the other or reverse the former.

Thanks for your thoughts. Kind regards. Tony

lightman1 · May 2016

Bi-wire is in essence a parallel set up. Just having different points of signal seperation. And if you look at the feeder tap rule of supplying current form a common source, the wire supplying that current (signal) should, at minimum, be able to carry the demand load of the speaker tap to each crossover network.

msg · May 2016

Russ, just reminded me of Will Ferrell's debate scene in Old School

gp4jesus · October 2019

I’m reviving this thread for several reasons:
partially on the behalf of the link below...

https://forum.polkaudio.com/discussion/comment/2543466#Comment_2543466

I noticed from some of the responses I did a lousy job explaining or describing some details

Way back when I had two sealed Isobaric subs. For the uninitiated, each sub had two drivers in the preferred isobaric configuration, facing each other.

Each driver nominally 8 ohms. Per the manufacturer, in this alignment, a 6.4 ohm low point in its impedance curve. I chose to wire them in parallel thus halving the above impedances. A few years later I provided them a second amp, same & model of course, giving each driver its own channel taking SQ to another level.

To connect them, using 10 ga wire throughout, I daisy chained the internal drivers to the external, being careful to observe correct polarity, soldering along the way. Then ran a 10’ piece from each sub to the amp, the left to the left channel; the right to the right. Using an EXO, I LP’d @ 80 Hz.

In the 2nd chapter, for each sub, I merely removed the driver daisy chain from the internal to the external. Then I soldered a 5’ piece of 10 ga cable to each driver. I finished by doing as I did before, running the left sub’s cables to the left channel, the right’s to the right, essentially bi-wiring them, but NO other changes.

I hope all see the only change was a 5’ double run versus a 10’ single. Using 10 gauge wire I began w/an extremely low resistance connection, an estimated 0.01 ohms. After I bi-wired them, the estimated resistance was 0.0025 ohms. Overkill? I think no but everyone is entitled to their opinion.

They came to an unfortunate demise due to flooding. I salvaged the drivers. Later, before I got around to rebuilding them, Ozone had its way w/the foam surrounds. In spite their size, I miss their “unassisted” anechoic 22hz* F3. W/a little assistance, 17hz* F3.
*I verified this in my back yard before I blew up my HP tube tone generator

SVS & HSU “eat your hearts out!”

Cheers

Why did my subs get louder?

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