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Discussion Starter · #1 ·
I’m beginning to plan out a Home Theater subwoofer.

I have a Dayton Audio SA1000 amp that puts out 500rms @8ohms, 1000rms @4ohms.

My original plan was to use a pair of Audiomobile MASS 12’s series/parallel to 4ohms mono.

Now I’m thinking I may add a third MASS into the mix.

I would series (1) 4ohm coil from each driver for a total of 12ohms, then parallel the 12ohm “pair” down to 6ohms. I’m pretty sure the added cone area of a third driver will compensate for a small reduction in power going from 4ohms to 6ohms.

I think this should work out fine.
 

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I am not convinced…
Putting them is series is probably not as good as using 2x 8-ohm DVC subs, all in parallel and ending up at 2-ohms.
or even using the 2 ohm DVC in series and then the pair of subs in parallel.

You will end up at 1000W at 2-ohms, and at 6-ohms you end up at 333W

That is 4-5 dB, whereas the extra sub may only give you 1-2 dB.
So the extra sub sets you back 3dB.

I would probably also consider going to a pair of 15s.

Lastly… Are the subs in a single box?
(You probably would be better off with 2 boxes and 2 amplifiers.)
 

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Discussion Starter · #3 ·
This is for a home theater subwoofer setup. The amp does 1000rms @ 4ohms…I cannot drive the amp into 2ohms. I already own the drivers…I’m not asking about alternative setups…I’m just comparing the idea of (2) subs vs (3) subs.

The enclosure will likely be a single box…ported tuned between 20hz-25hz.
 

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Due to Back EMF, avoid wiring two or more subs in series.

.... It is far less desirable to make subwoofer to subwoofer connections in series. Due to slight and unavoidable differences between speakers and the high likelihood of uneven loading between different speakers in a car, there will be slight differences in the mechanical behavior of the two speakers in series. These differences in movement result in the creation of induced voltage (called back EMF) by the speakers across the series connection. This effect causes a problem when two speakers that behave differently are connected in series because the speakers can modulate each other (cause each other to move), resulting in distortion. The problem becomes more serious as more speakers are connected in series.

The following is a good experiment to show the effect of back EMF: connect four speakers in series and short the positive and negative input leads of the series circuit. Push down on one cone with your hand; you will notice that the three other speakers will move in the opposite direction of the one you are pushing. Now, reconnect the speakers in parallel, short the inputs and push down on one cone. The speakers will not modulate each other because each one is shorted directly.

Back EMF modulation is not a concern when the voice coils of a dual voice coil speaker are wired in series to each other because the coils are physically coupled on one moving mass. Therefore, they cannot possibly modulate each other because they cannot move independently. ....


https://jlaudio.zendesk.com/hc/en-us/articles/204374150-Speaker-Wiring-Tutorial?mobile_site=true
 

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Discussion Starter · #5 ·
Looks like the point may be moot…

WinISD shows that (3) 12’s getting 750rms is pretty much the same as (2) 12’s getting 1000rms.

307269
 

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This is for a home theater subwoofer setup. The amp does 1000rms @ 4ohms…I cannot drive the amp into 2ohms. I already own the drivers…I’m not asking about alternative setups…I’m just comparing the idea of (2) subs vs (3) subs.

The enclosure will likely be a single box…ported tuned between 20hz-25hz.
I would investigate the use of multiple subs.
You will have room modes and more subs in a single box does nothing but provide and extra 3dB. whereas another box, in a different location of the room can provide 10 dB or more to a room null.

Which means, “do not get a third sub, just get a second amp.”

It is common to get the wrong gear, and yoru 1 ohm speakers do not appear to be suited to the aforementioned scheme.
IMO sell or trade them, and get 2x of 8–ohm DVC (to be wired in parallel) or single 4-ohm VC.

Even though you already own the gear… the gear is incomparable with each other,… and the whole scheme is sub optimal as single box compared to 2 boxes..

However you should probably run it all by someone more knowledgeable.
 

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Discussion Starter · #8 ·
While I appreciate the advice I think you’re still a bit off about what I’m doing.

I have a single stand-alone 1000 rms @ 4ohm amp.

My original thought is to run a pair of 4ohm doc subs at 4ohms mono. How exactly is this incompatible? I also have what some would argue to be some of the cleanest subs ever designed…the Audiomobile MASS is a legend for SQ and output. So how is that choosing the wrong equipment?

I will be building the enclosure myself and can just as easily build a pair of boxes as opposed to one…I am aware that multiple subs in different locations in a room can make up for variations in frequency response due to room size/shape/reflections.

I do not need a second amp nor do I need to rethink my subwoofer selection. The point of this thread was to get options and considerations about adding a third sub (really just for ****z and giggles).

Given that when both setups are modeled there is very little difference in output. That being said, a pair of subs will take up less room and accomplish the same thing, and as noted by another member, going with a pair helps me avoid the back EMF produced by coils from different drivers in series.
 

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My original thought is to run a pair of 4ohm doc subs at 4ohms mono. How exactly is this incompatible?
Ok so they are 4-ohm DVC and you‘ll just run a single coil?



I have a single stand-alone 1000 rms @ 4ohm amp.
OK, and then just ignore any separate EQ and TA, and just run them off of the single amplifier?



… and as noted by another member, going with a pair helps me avoid the back EMF produced by coils from different drivers in series.
If you run the 2x 4-ohm subs in parallel, then wouldn’t the amplifier would be seeing ~2-0ohm load?
 

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Discussion Starter · #10 ·
I will be using (2) 4ohm dvc drivers…each driver has (2) 4ohm coils. I will run each drivers’ coils in series (so each driver is now 8ohms), then parallel the (2) drivers bringing the impedance down to a single 4ohm mono load.

I will be running most likely in separate enclosures and yes they will be driven by a single amp. Time delay is handled by my A/V receiver and the amp has a basic set of tuning tools(not extensive but enough for me).
 
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I will be using (2) 4ohm dvc drivers…each driver has (2) 4ohm coils. I will run each drivers’ coils in series (so each driver is now 8ohms), then parallel the (2) drivers bringing the impedance down to a single 4ohm mono load.

I will be running most likely in separate enclosures and yes they will be driven by a single amp. Time delay is handled by my A/V receiver and the amp has a basic set of tuning tools(not extensive but enough for me).
Should be perfect
 

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@ Holmz - take off your car audio ball cap and put on your home theater slippers :) You make some valid points, but they aren't really relevant to the OP's question/situation. Sometimes taking a third route is good, but he's asking between two only.

@nstain - good on you for using WinISD to find the answer. Indeed, in this situation, from an SPL, space saving, and cost situation, it appears you are better off to use all of the available power to you by wiring your two subs as described for the amplifier to see a nominal 4 ohm load.

What you would gain from using three subs for a total impedance of 6 ohms would (and could) be lower distortion at SPL and more over-excursion protection. These may or may not be important to you. IMO, at 118 db in a room, 1% THD in the low bass region isn't going to be any more discernible than .5% THD or even 10% for that matter. My walls and lights and couch and soda can and fillings in my teeth are usually making more noise and distortion at those levels. But splitting 750 watts three ways vs 1000 watts two ways pushes half the input power to each sub which, assuming the drivers are operating in their linear pistonic range (this is an assumption we all make and WinISD makes, but is almost never true), means the excursion of each driver is halved. Thus - lower distortion (which grows with excursion) and more protection for the drivers.

As for running two separate subwoofers on two separate channels as has been suggested - this is true that it can correct room nulls and create a more even bass response throughout the room. But it isn't always necessary with proper placement of the single sub to begin with. Right now, I am fighting this in my basement; we rearranged some things to improve other aspects of the room and it put a giant hole in my room response from 100-200 hz at the main listening position. A hole over 12 db deep. EEk. But by moving the sub 1 foot to the side, tweaking the delay on the receiver, then clocking the sub 20 degrees back the other direction, I was able to add 8 db back in to the response. Still not perfect but I'm still working on it. And I'm prolly going overboard on the solution but it will be fun :)

Interestingly, nothing really changed from 20 to 70 hz with those tweaks. I took the brute force approach and ran 30 different iterations of placement, box clocking, and delay and crossover settings on the AVR and that region remained pretty constant. This also tells me that much of my problem is actually coming from the interaction between the sub and the mains. But that's another story.
 

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Nothing wrong with that..
Just confirming that the OP means to run the subs off of the same channel, many to different boxes, and then are they ignoring TA/FR or would that work out fine-n-dandy?
(Your example of 20 degrees, moving it a foot over, and adding delay… sort of suggests that a separate amp channel may be better than a third subwoofer in a single large box?

And then DVC 4 ohm coils could be series on a sub to get tp 8 ohms, and then parallel the subs to get to 4 ohms.
but I saw mono and ”1x” suggesting that maybe a single VC might be used?

As I just got a preamp AV processor, it is relevant to what need to consider on moving fwd.
 

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As stated above...stick to running the pair. There is no need to complicate this with 3 boxes and less power.
 
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