[gooberdude]

1 sub is ok for HT, 2 subs are needed for stereo.     just my opinion, but 2 is more fun...

[1000a]

I have been thinking  about this alittle while, I can get an extra sub (a member would like to sell his) to match mine exactly and have 2 subs that can reach to 25 Hz. and pretty flat IMS according to past readings with my db meter.

For a little more money about 150.00 I can go to 1 sub that can reach 18 Hz. but I can not afford 2 anytime soon.

So:
Its 1 that does 18Hz. / 12" woofer / 250 watts
or
2 that do 25 Hz. /10" woofers / 150 watts

I read 50 watts on the amp only accont for 1/2 db louder, so I would gain 1 db in volume with the 12".  1 db is not much I was thinking more in terms of the amp's head room and abilities to controll the driver better?

I have not had any detecting of bass direction issues using just one sub for the last 5 yrs. used in 2 different locations.  I have read lots on 2 vs 1 sub but it seems divided among most people.  So I know jack about the benifits of 2 subs except correcting the issues I do not have.  Since I do not have directional issues I am leaning towards going for 18Hz. / 250 watt / 12" woofer sub, using my old one for movies or maybe selling it.  Any options, insights welcome.  I know little of the bennies of 2 subs. Thanks.

[Daryl]

I've got a subs either side of my mains, but before these two I had only one, centered between the mains. To be honest I cant tell much difference.

The Harmaon Kardon papers seem to deal only with the FR benefits of dual subs, i.e less pronounced excitation of room modes. But if one is EQ'ing for flat I dont see much theoretical benefit of having 2 subs (other than more output, if that is needed)

If a single sub excites room modes then frequency response will be dramaticly different at every point in the room (standing waves) and you will be able to EQ only one position within the room and if nulls exist at your sweet spot you won't be able to EQ them far enough to be flat.

If you then installed four subs methodicly to minimize room modes then frequency response will be relatively constant throughout the room so you can EQ your sweetspot flat and the rest of your room will also have a fairly flat response and you likely wont have nulls.

[doug s.]

i'd go for the two smaller subs.  you would gain ~50% less distortion for the same spl.  and, you would get better room loading, & better soundstaging.  unless, you can do the one larger one now, & then get a second larger one later.   

doug s.

I have been thinking  about this alittle while, I can get an extra sub (a member would like to sell his) to match mine exactly and have 2 subs that can reach to 25 Hz. and pretty flat IMS according to past readings with my db meter.

For a little more money about 150.00 I can go to 1 sub that can reach 18 Hz. but I can not afford 2 anytime soon.

So:
Its 1 that does 18Hz. / 12" woofer / 250 watts
or
2 that do 25 Hz. /10" woofers / 150 watts

I read 50 watts on the amp only accont for 1/2 db louder, so I would gain 1 db in volume with the 12".  1 db is not much I was thinking more in terms of the amp's head room and abilities to controll the driver better?

I have not had any detecting of bass direction issues using just one sub for the last 5 yrs. used in 2 different locations.  I have read lots on 2 vs 1 sub but it seems divided among most people.  So I know jack about the benifits of 2 subs except correcting the issues I do not have.  Since I do not have directional issues I am leaning towards going for 18Hz. / 250 watt / 12" woofer sub, using my old one for movies or maybe selling it.  Any options, insights welcome.  I know little of the bennies of 2 subs. Thanks.

[1000a]

Thanks Doug, really 50% less distortion really interests me, in mono or in stereo wouldn't that effect the outputs being different.  How or why does that happen I'm clueless, I just read conflicting reports on running em mono vs stereo?
I guess since I'm mostly a 2 channel guy, I would be runing them in stereo by default,
one wire rt chn info, 1 wire left chn info?

I am not disagreeing with you just trying to get a better handle on this 2 sub deal.
Better soundstaging definitly gets me excited, everytime. 

thanks,

[dewar]

True, more subs benefit people not in the sweetspot if that matters.

Doug, I'm trying to understand the theory behind why 2 subs(playing the same signal) would sound better than one(from the sweetspot). I'm imaging it being like the difference between having dialogue coming from L&R vs centre i.e none really.(in fact most people prefer one speaker here dont they?)

1000a, an option, if you dont have one already, is to spend $150 dollars on a Behringer DSP1124. You can then use the extra headroom offered by 2 subs to flatten the FR to 18hz. Best $150 one can spend imho, infact I would not use subwoofers at all if I could eq them and draw my own roll-off slopes.

cheers,

B.

I dont own a TV either and must agree it is reason to be happy

[Daryl]

i'd go for the two smaller subs.  you would gain ~50% less distortion for the same spl.  and, you would get better room loading, & better soundstaging.  unless, you can do the one larger one now, & then get a second larger one later.  

Well using two subs does cause each one to have to move half as much air if they are both being fed the same signal and that would result in less distortion.

Your ears are only 7" apart so you cannot hear sub bass information in stereo despite people claims to the contrary.

Their is a difference with stereo subwoofers though but it is created in the playback system and not a part of the intended program.

The difference is due to distortion of the subwoofers and objects in the room which vibrate depeding upon how strongly each subwoofer energizes them, even though the stereo low bass signal is not audible in stereo the distortion products of your subwoofers and objects they energize are and will be in stereo since the signal that caused them is stereo.

Also the acoustic loading/frequency response for each of your subs will be different due to different locations within the room causing a stereo feed to produce a different mono bass signal at the listening position than a dual mono feed would.

A dual mono feed would maximize the output capability of your subs and minimize their distortion.

[1000a]

Daryl

My amp is an audio only amp 2 channel, so how do I run a mono feed to 2 subs?

Presently I run a y adpt off (the amp's sub out) the RT & LT RCAs fems and one cable to my only sub, at that point I do another Y to the Rt and Lt RCAs on the sub.

With 2 subs if I run 2 wires is that stereo info being feed to ea. sub?

Thanks a mil

[Daryl]

Daryl

My amp is an audio only amp 2 channel, so how do I run a mono feed to 2 subs?

Presently I run a y adpt off (the amp's sub out) the RT & LT RCAs fems and one cable to my only sub, at that point I do another Y to the Rt and Lt RCAs on the sub.

With 2 subs if I run 2 wires is that stereo info being feed to ea. sub?

Thanks a mil

You are saying that your two channel reciever/preamp has a stereo subwoofer output is that correct?

Would that be with a built in subwoofer crossover in the reciever/preamp or is it just a full range preamp output meaning that you are running your main speakers full range?

At any rate I would not recomend using a 'Y' adapter for the purpose of combining R and L channels as this may cause distortion in the output stage depending upon it's design (if it is discreet class 'A' it should be okay but if it uses a feedback loop like an opamp buffer you could have trouble).

Of course using a 'Y' adaptor to send one output to two componets is fine so long as you don't overload the output section.

Most equipment featuring a subwoofer output has the option of a mono subwoofer output in which case you would use a 'Y' adaptor to create two mono subwoofer outputs and use one long RCA cable to each subwoofer (use the L input on the subwoofer).

If you only have the option of stereo subwoofer outputs or you are simply using a full range stereo preamp output you can use two 'Y' adaptors to create two L outputs and two R outputs and use two long RCA cables to each subwoofer (one L and one R to each) and let you subwoofers combine them to mono.

[JimJ]

Once I get a bigger listening space, I'm going to have to try dual subs. My current room just isn't big enough to justify it now

[1000a]

Thanks Daryl

My amp is an Integrated tube amp, push-pull design, Ultra Linear Class AB, Low Feedback Design, Only 5 dB.  Negative feedback is less than 5%.  Pulled these stats from maker of amp.

The internal pre amp is essentailly a passive design.  The unit did not have a sub out so I had the amp maker put one in.  There were 4 total imputs, so we scraficed 1 of them for him to do the sub out, hence the Rt and Lt RCAs.  This is specifically an audio amp, but I do not understand if he made the output stereo or mono?

[Daryl]

With a passive preamp section your subwoofer output would have to be stereo, either that or the output impedance would be much higher than the already too high output impedance of passive preamps (unless the builder put in a buffer amp for the sub out).

Also if there is no buffer amp for the sub out then using a 'Y' adapter to sum it to mono will also sum your main channels to mono since your main channels and your subwoofer outs would both be connected directly to the volume pot.

[doug s.]

Your ears are only 7" apart so you cannot hear sub bass information in stereo despite people claims to the contrary.

the only problem with this statement is people can hear subwoofer bass info in stereo.  ask psychicanimal what happened to his soundstaging when he accidentally bumped the "sum" switch of his marchand x-over to the "on" position, when he was dusting his rig?  he couldn't figure out what happened to the soundstaging, & spent a coupla hours troubleshooting before he discovered the x-over bass switch had been set on "sum".  i have also heard stereo bass  in my dual-subwoofer system.  maybe you cannot hear stereo bass, but you shouldn't speak for others...

Their is a difference with stereo subwoofers though but it is created in the playback system and not a part of the intended program.

The difference is due to distortion of the subwoofers and objects in the room which vibrate depeding upon how strongly each subwoofer energizes them, even though the stereo low bass signal is not audible in stereo the distortion products of your subwoofers and objects they energize are and will be in stereo since the signal that caused them is stereo.

Also the acoustic loading/frequency response for each of your subs will be different due to different locations within the room causing a stereo feed to produce a different mono bass signal at the listening position than a dual mono feed would.

huh?  i am not sure what this even means.  first of all, the signal at the listening position w/stereo subs is stereo, not mono.  and, any differences between signals of each sub, due to differences in their signals - being stereo, not mono - will *improve* acoustic loading/frequency response characteristics.  this is because the room loading will be more averaged, with different signals being presented to it. 

A dual mono feed would maximize the output capability of your subs and minimize their distortion.

a dual mono feed would certainly be better than a single sub, due to more even room loading, but it is not as good as stereo subs.  stereo subs are better, due to a bit *more* even room loading than running them in mono.   but the main benefit to running stereo subs is better soundstaging.  also there is loss of phasing info when you sum two stereo l/r signals, which could actually result in unintended frequency response changes, due to inadvertent reinforcement or cancellation of sound at some frequencies.

doug s.

[mcgsxr]

If you don't understand if the 2nd output is stereo or mono, could you connect your mains to it, just to check?

I use dual mono subs at present, but would consider stereo bass, if I had 2 plate amps...

[doug s.]

If you don't understand if the 2nd output is stereo or mono, could you connect your mains to it, just to check?

I use dual mono subs at present, but would consider stereo bass, if I had 2 plate amps...

i am not sure i can help much here, as i just run a separate outboard stereo x-over.  preamp runs its stereo outs directly to the x-over...

i am not really familiar w/home-theatre gear, w/all their built-in features...  but, couldn't you contact the mfr of your equipment for an answer?

doug s.

[Daryl]

i am not sure what this even means.

That says a lot Doug.

I just explained not only why it is impossible to hear low bass frequencies in stereo but also why you think you can.

If you don't understand it shouldn't you try to learn something before you comment?

You just skipped over all the important information and then went into your delusional rant.

Do we need a Paris Hilton of the audio world?

[doug s.]

i am not sure what this even means.

That says a lot Doug.

I just explained not only why it is impossible to hear low bass frequencies in stereo but also why you think you do.

If you don't understand it shouldn't you try to learn something before you comment?

You just skipped over all the important information and then went into your delusional rant.

Do we need a Paris Hilton of the audio world?

i hear it, i don't think i hear it.  so do others.  'nuff said.  you can't explain something is impossible if it is possible - what you said is gobbledygook.  the paris hilton comment?  talk about the pot calling the kettle black!!!     there was no ranting, & nothing delusional about what i said.  however, i can see how you might think otherwise.

doug s.

[ctviggen]

Your ears are only 7" apart so you cannot hear sub bass information in stereo despite people claims to the contrary.

Is this theory based on wavelength?  The wavelength at 20Hz is about 56.5 feet.  The wavelength at 80Hz is about 14.1 feet.  If you want to get something in the neighborhood of a foot, you'd need to get to around 1130 Hz (assuming the speed of sound is 1130ft/second).  What's so special about 20Hz that you can't hear it in stereo, yet can hear say 200 Hz in stereo even though the wavelength of stereo at 200 Hz i(5.65 feet, approx.) is still much larger than the width between the ears? 

[Daryl]

Your ears are only 7" apart so you cannot hear sub bass information in stereo despite people claims to the contrary.

Is this theory based on wavelength?  The wavelength at 20Hz is about 56.5 feet.  The wavelength at 80Hz is about 14.1 feet.  If you want to get something in the neighborhood of a foot, you'd need to get to around 1130 Hz (assuming the speed of sound is 1130ft/second).  What's so special about 20Hz that you can't hear it in stereo, yet can hear say 200 Hz in stereo even though the wavelength of stereo at 200 Hz i(5.65 feet, approx.) is still much larger than the width between the ears? 

Your ears localize by both amplitude and phase differentials ear to ear.

Amplitude can be different ear to ear because your head sheilds the far ear from the sound source but as it's frequency gets lower your head simply is not big enough compared to a wavelength to sheild the far ear and pressure has plenty of time to equalize on both sides of your head before changing.

Phase can be different ear to ear because of the 7" space between your ears.

Ordinarily phase is of virtually no meaning regarding your hearing but relative R/L  phase is used and a directional indicator.

Off center sound sources arriving at your ears will be phase shifted due to the delay caused by the distance ear to ear.

As the frequency of the sound source gets lower though the distance ear to ear represents less and less phase differential until finally both ears are always in phase regardles of direction.

At 315hz a wavelength is about 42", the 7" distance between your ears represents 1/6 wavelength or 60 degrees at this frequency.

Here is an oscilloscope type view of a 315hz tone burst plotted along with another delayed by the distance between your ears representing a source that is a full 90 degrees off center.

The delay and spectral density of the burst are shown also in the other two charts.



In a standard equilatteral triangle stereo speaker setup each speaker is only 30 degrees off center and the phase differential between your ears will be half of what is shown (30 degrees) at the most.

At 31.5 hz a wavelength is ten times greater and the phase differential between your ears can only be 6 degrees at most for sound sources a full 90 degrees off center.

Look at those charts again for 31.5hz



The two bursts now are right on top of each other and the delay is meaningless.

Again a stereo speaker setup would have a maximum of half the phase shift shown (3 degrees).

Also consider that looking at an oscilloscope type picture makes judging the phase differential far easier than the method and instrumentation your ears use.

[Rob Babcock]

Just because you can localize a bass instrument or sub doesn't mean you can localize bass- that's the crucial thing that some people are overlooking or misunderstanding.  Instruments like kettle drums and acoustic bass have overtones and harmonics at higher frequencies that give away their location.  Likewise, the crossover of to the sub may be steep but some higher frequencies are still present (eg 12 dB/octave, 24 dB/octave slope means it's that many dB down).  Lastly, they can rattle and/or produce spurious distortion tones that allow them to be localized by ear. 

So I guess I'm saying you're both right and both wrong.