# Two subwoofers, what's best: Mono amp or stereo amp?



## aaron7 (Feb 5, 2012)

I've got a pair of 4ohm single voice coil subs and wondering what's best to power them... a mono amp or a 2ch in stereo? Or the 2ch bridged? 

What's a better setup? 

I've heard from some that the mono amp would be better... but why?


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## miniSQ (Aug 4, 2009)

I cant see any reason NOT to buy a mono amp. But to be sure what are the subs in question?


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## sirbOOm (Jan 24, 2013)

Mono - because they're built to be subwoofer amplifiers through and through (assuming you buy a quality amplifier). If you are not going into SQ competitions and know advanced phase and time tuning, you do not need separate channels for a subwoofer. Debate over.


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## aaron7 (Feb 5, 2012)

That's what I needed to know!

Figured there was no need for 'stereo' subs, but wasn't sure if bridging a 2ch was better than running two off a mono amp!

This is more theory than for a specific sub to be honest.


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## Alrojoca (Oct 5, 2012)

Mono amps give you more flexibility to upgrade subs and have different configurations, besides having more power available. The issue with some sub amps is that the xovers can not be defeated while a 4 ch or 2 channel amplifier has the option do an all pass signal and let a DSP or HU handle the rest.

A good sub amp even without the option of not being able to defeat the crossover, it offers a subsonic filter, it could be a good option if using small subs in ported enclosures.


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## wisnulie (May 24, 2015)

nice information
thanks all


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## gstokes (Apr 20, 2014)

2-channel bridged to mono Vs Monoblock, hmm..
both are equally proficient at amplifying signals, whichever one has the features you need and makes the power you want is the best choice..


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## Alrojoca (Oct 5, 2012)

Not quite a 2 ch bridged vs mono with a single sub.

More like with 2 subs, meaning 2 ch amp in stereo with 2 subs since 2 single 4 ohm voice colis present a 2 ohm load and a bridged amp could not handle the 2 ohm load unless the subs are wired in series for an 8 ohm load not being an ideal option, I think.

Then the issue about a box sharing the volume for 2 subs versus 2 separate boxes or a box separated and each sub having its own separate space volume.

Something that brings another subject or question, subs in stereo or subs in mono? I don't see an issue with driving subs in stereo, the 5th and 6th ch are meant to be mono, even if that is not the case, I know others may not choose that option, but why not? when some tracks may have a stereo sub signal and it may be more noticeable, bass runs always in mono and the sub phase polarity or a steeper slope may fix an issue if the bass can be localized in the rear.


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## Instaburn (Aug 22, 2013)

It may just be hocus pocus.. but given that the amp has the same features and tuning options regardless of "stereo" mode or "mono" mode... i would be inclined to run 2 subs from a 2ch amp.. using the stereo mode.

I am not an EE or an amp expert, but thinking logically one would figure from electronics standpoint.. having 2 current paths -vs- one is better, right?
In one scenario I have to land 2 wires per terminal... the other , each terminal gets 1 wire and its own dedicated current source path.

I guess you would really have to measure it with a multi-meter and verify...

I guess It could also would depend on the resistance impedance and whether there is any benefit or detriment to running a dual 4 ohm load or a single 2 ohm load...

I would just think that the amp wouldn't have to work as hard pushing 1000w through 2 terminals -vs- 1000w through 4 terminals.

My logic could be completely incorrect of course...


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## Weigel21 (Sep 8, 2014)

Never seen a model for the subs or the amplifier. 

Running a pair of SVC 4 ohms subs off a 2-channel that has the desired power and crossover features would be no better/worse than a mono with desired power and crossover features. 

Some 2-channel amps are 2 ohm stable bridged, some are not, but if you can get the power you need for each sub when wired to it's own channel, there's no real reason one can't do just that. 

And given I "believe" bass is actually recorded in mono, there'd be no L/R channel separation for the bass to produce increased cancellation between the drivers.


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## gstokes (Apr 20, 2014)

I try not to look at how many subs their are but rather the total load impedance of all the subs combined and there is no advantage to running subs in stereo but there could be some disadvantages such as phasing issues..
The monoblock is designed ground up for sub application and a lot of of them are 1 ohm stable, not very many 2-channel amps that can be bridged to mono are 1 ohm stable so it makes no sense to use a 2-channel amp for a sub when a monoblock is better suited..


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## gstokes (Apr 20, 2014)

Weigel21 said:


> Never seen a model for the subs or the amplifier.
> 
> Running a pair of SVC 4 ohms subs off a 2-channel that has the desired power and crossover features would be no better/worse than a mono with desired power and crossover features.
> 
> ...


x 2, subs are recorded in mono so there is no channel separation..


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## seafish (Aug 1, 2012)

gstokes said:


> x 2, subs are recorded in mono so there is no channel separation..


Not really sure that this is true anymore.

In my own research in trying to decide dual subs in mono or stereo,. I found this quote from here--

Stereo Subwoofers: Why Every Man Needs Two


"Digital recording changed everything.

Digital cheerfully can record straight down to DC, and the new digital "Compact Discs" (CDs) allowed anyone who could afford a CD player to have perfect sound forever.

In practice, if the analog path is up to it, actual digital recorders and home CD players usually have distortion-free and flat response down to 2 Hz or less.

For the first time in 100 years of electronic sound reproduction, consumers have access to recordings with unlimited deep bass. Since there is no point in mixing or summing the bass to mono, bass has been in stereo in our homes since the introduction of the CD."


The entire link is also pretty interesting read, though of course it is very important to realize that he is talking about SQ home theatre, not SQ car stereo.

I think that the most problematic issue of running dual subs in stereo is simply that since the vehicle is simply NOT large enough for low frequencies to fully form, then the reflections of dual subs playing different frequencies at slightly different levels will result in cancellations, nulls and boosts that will likely color the sound we hear.

Personally I am still thinking of running dual IDQ10v2 subs in stereo from 80 to 150 and then a single center mounted BMmkIV playing 80 down to 20.


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## Instaburn (Aug 22, 2013)

seafish said:


> Not really sure that this is true anymore.
> 
> In my own research in trying to decide dual subs in mono or stereo,. I found this quote from here--
> 
> ...


I digress...

Typically, the "sub" channel is split into 2 rca jacks...

Even though it's a mono signal.. it gets split into 2 mono signals occupying the L and R inputs...

I wasn't trying to infer that the "sub" source was a stereo source.

Interesting to read what you have here though.


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## 1styearsi (Aug 13, 2012)

i was told sub bass freq are mono anyway?????
please correct that info if it is wrong.


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## seafish (Aug 1, 2012)

1styearsi said:


> i was told sub bass freq are mono anyway?????
> please correct that info if it is wrong.


Again, not necessarily true. It IS true that human hearing has trouble localizing frequencies below 125 hz, but that does not mean that frequencies recorded below that do not contain stereo information..it totally depends on the recording engineers preferences and goals.

Here are a couple links to threads on recording forums that pertain to this--

https://www.gearslutz.com/board/so-...requency-should-you-keep-everything-mono.html

mono bass frequencies below 260hz | Studio & Recording Forums

In short, it seems that recording below 125 hz in mono leads to a more "centered, punchier" bass/drum line.
But that does;t mean it can't; be recorded in stereo. However, when recordings were being done for LP/vinyl, low frequencies were in fact recorded in mono due to the limitations of the medium.


Now whether recordings with low frequency stereo information can be made to sound good in a car is a different story given the various limitations of the car environment. I, for one, I am HOPING that it can be done well, but have yet to experiment with it at all, only doing some research.


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## seafish (Aug 1, 2012)

Below is my favorite quote from there gearlsutz link above--

"Zero Hz. There is no frequency below which everything should be mono. It's a creative choice that can have some practical consequences. Mono'd low end can give more power and punch to low frequency sounds, but there's no law that says you have to do that. Mono'd low end is helpful when cutting vinyl in that the record can be made louder, but even on vinyl there are many examples of hit records with panned kick drums, basses and floor toms."

Here is another relevant quote regarding the utility of recording low frequencies in mono rather then stereo.

"When Mono is More Appropriate than Stereo"

While stereo recording applied in the right situations can improve the quality and interest of your mixes by leaps and bounds, there are some situations when it is simply not appropriate. Certain instruments that you record will sound better in mono almost 100 percent of the time.

And here are the most common 4:

Lead Vocals – The lead vocal is simply expected to be located at center stage. For that reason, it is typically recorded in mono.
Snare Drum – The snare drum is also expected to be at center stage. It would sound quite odd if it was located off to one side of the stereo image.
Kick Drum – A kick drum should be recorded in mono because its heavy low frequency content requires a lot of power to reproduce on speakers. In order to get the maximum output from the mix, it’s best that the work be shared equally by both the left and right channels.
Bass – The bass guitar is also made up mainly of low frequencies so it generally works better in mono as well. Another reason for this rule is that our ears are not good at obtaining directional information from low frequencies, so it makes little sense to create a stereo image for any low frequency instrument.

This is from--

Stereo Recording Methods: The 5 Useful Techniques


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## 1styearsi (Aug 13, 2012)

thanks for clearing that up i see what you are saying...that would or could make a difference in a home stereo, but in a car you will not get or hear stereo sound crossed over in a enclosure with 2 woofers side by side.
that said i would never do stereo woofers in my car unless my woofer/amp combo limited me to that choice.


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## aaron7 (Feb 5, 2012)

Wow, cool to see all this info being posted!

In a home audio setup it's totally different; I run two separate subs as most movies have stereo subwoofer tracks. 

But yes, just talking about car audio here. And I like the theory better than posting model numbers as that can sway opinions haha


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