Setup of dual subs

[Buckle-meister]

All,

I remember another poster once asking about how to correctly set up a second sub in his room. If memory serves, he was advised to setup the first as good as he could before moving onto the second. Fair enough.

My question relates to the volume the subs should be set at. If the above advice is correct and followed, isn't it likely that I'll end up with my two subs at substantially different volumes? In other words, it's possible that the best setup of the first sub requires the sub's volume set reasonably high, but only a little of the second sub's volume to smooth out the frequency response of my room that bit more.

If true, wouldn't this be a disadvantage? I mean, isn't one of the advantages of multiple subs the fact that with twice the available output, both subs can be driven half as hard as one sub only?

 

[tbewick]

I'm a bit wary of making any suggestions, these two papers might be of some use to you:

http://www.icad.org/websiteV2.0/Conferences/ICAD2002/proceedings/71_Martens.pdf
http://www.aes.org/technical/documents/AESTD1001.pdf

I admit I haven't heard that advice before but I've only got one subwoofer. Based on one suggestion in the AES document, where you put the subwoofers near the wall of the front loudspeakers, it would strike me to set the volumes of each unit so they were level. You would do this by turning one unit off and then setting its volume. Then you would turn that unit off and then set the volume of the other. Following this, I'd turn both units on and check the phase settings, then set overall volume with both units turned on.

The AES papers puts forward several possible set ups, so I guess it might be worthwhile experimenting. Certainly I would have thought that you'd want both units working equally hard and at the same time aiming for a smooth bass response. The other paper might be handy. It discusses spatial imaging with two subwoofers. I haven't read this paper.

Good luck

 

[Buckle-meister]

...these two papers might be of some use to you...

Thanks for those. They are interesting, but I'm afraid of limited help with respect to my specific question.

...set the volumes of each unit so they were level. You would do this by turning one unit off and then setting its volume. Then you would turn that unit off and then set the volume of the other. Following this, I'd turn both units on and check the phase settings, then set overall volume with both units turned on.

Presumably you suggest turning the volume of both subs down by an identical amount?

The AES papers puts forward several possible set ups, so I guess it might be worthwhile experimenting...

Experimenting is what I'm trying to avoid! I went through a lot of iterations of (my single) sub placement and volume before achieving a response I was happy with. I'd like to try and avoid twice the work (I'm moving flat soon) if possible with two subs - though I suspect I'll still end up having to experiment a fair bit if I want to get the best results possible.

The other paper might be handy. It discusses spatial imaging with two subwoofers. I haven't read this paper.

Yes, it concludes that even though low frequency information isn't particularly localizable, two, or rather more than one sub, does actually help increase spacial imaging.

 

[tbewick]

Yes, I would put them down equal amounts. I'm trying with great difficulty to imagine how the subwoofers will interact acoustically. I'd think if the subwoofers are in quite similar environments relative to each other, as in near to walls and are symmetrically positioned, then it would make sense to have them set at similar volumes.

In my subwoofer's manual, one arrangement suggested for two subwoofers is to put them as close as possible to each other. If you have them arranged like this then you'd probably want them set at the same volume (SPL). If the subwoofers are in quite different environments, ie. one near a wall and the other not, then you might want to set one louder than the other.

 

[Buckle-meister]

...if the subwoofers are in quite similar environments relative to each other, as in near to walls and are symmetrically positioned, then it would make sense to have them set at similar volumes.

Not only that, you've made me realise, but one would have to conclude, logically, that with a symmetrical room and setup relative to the listening position, it may be desireable to setup both subs simultaneously (though I suspect there still exists the possibility of achieving a better frequency response with dissimilar sub settings).

...one arrangement suggested for two subwoofers is to put them as close as possible to each other.

This would virtually be the same as setting up a single sub. As above, one would, presumably, setup both subs at the same time with identical volume of the two maintained. This time, however, dissimilar settings wouldn't be advantageous as, ignoring phase, only volume could be dissimilar and since the two subs would effectively share the same position, the net (realistic) output of both subs could be achieved from one alone.

Gosh this acoustics stuff messes with the head!

 

[Jack Hammer]

When I did mine, I set both subs volume at the reference mark. Then I used a few test tones and a sound level meter to adjust both to the same volume (at the subs). Then I used my Avia disc to set up the first sub, 2nd one off, and adjusted the volume from the reciever. Turned 1st sub off and 2nd on. Checked volume at listening position against the 1st with a sound level meter. The were both still the same. Then I turned both on and level matched them to the rest of the system at the reciever level.

I don't bother to re-level match or adjust the LF volume if I only use one for late night. I find the volume of just one sub to be perfect for late night usage and two subs perfect for daytime usage. I just reach behind me and turn the bigger one off for that.

Jack

 

[Buckle-meister]

Sorry Jack Hammer, but I can't quite follow your post.

Reference mark? At the subs = the sub's volume control? ...from the receiver = Speaker Level within the receiver's menu? ...at the receiver level?

 

[Jack Hammer]

Sorry Jack Hammer, but I can't quite follow your post.

Reference mark? At the subs = the sub's volume control? ...from the receiver = Speaker Level within the receiver's menu? ...at the receiver level?

Eh, yeah sorry about that. I haven't gotten much sleep this past week. My cognizant sentence structures may be begginning to fail. Here are a few pictures of my subs face plates. That may help. All adjustments at the sub were done using these. All adjustments at the reciever were done using the internal +/- levels in my reciever.

Hope that made more sense.

Jack

 

[Buckle-meister]

...I set both subs volume at the reference mark. Then I used a few test tones and a sound level meter to adjust both to the same volume (at the subs). Then I used my Avia disc to set up the first sub, 2nd one off, and adjusted the volume from the reciever. Turned 1st sub off and 2nd on. Checked volume at listening position against the 1st with a sound level meter. The were both still the same. Then I turned both on and level matched them to the rest of the system at the reciever level.

If I understand things rightly, you:

• Initially set both sub's volume at midway, i.e. reference mark, resulting in identical volume from both subs at the subs;
• Using test tones and an SPL meter, independantly set both subs' volume so that they were equally loud at the listening position (sub layout asymmetric with respect to the listening position?);
• Turned sub 2 off, left sub 1 on and adjusted the level of sub 1 through the receiver's menu to match your other speakers;
• Turned sub 1 off, sub 2 on, checked its level at the listening position and found it to be the same as sub 1 (pure luck given an asymmetrical sub layout relative to the listening position?);
• Turned both subs on and adjusted (reduced?) their levels by an identical amount to match your other speakers.

Is this at all correct?

 

[Jack Hammer]

If I understand things rightly, you:..

...Is this at all correct?

Pretty much. I had played with my sub position previously and already had two spots the gave me the best response within my placement limitations. So I plopped the 2nd sub in the 2nd best location.

• Initially set both sub's volume at midway, i.e. reference mark, resulting in identical volume from both subs at the subs; Yes
• Using test tones and an SPL meter, independantly set both subs' volume so that they were equally loud at the listening position Yes (sub layout asymmetric with respect to the listening position? No, but best I could do with room limitations);
• Turned sub 2 off, left sub 1 on and adjusted the level of sub 1 through the receiver's menu to match your other speakers; Yes, because this was my main sub.
• Turned sub 1 off, sub 2 on, checked its level at the listening position and found it to be the same as sub 1 (pure luck given an asymmetrical sub layout relative to the listening position?); Pure luck, though not even close to asymmetrical, they were within ~1db, which I evened out by turning the knob on the 2nd sub itself just a little. After this I didn't adjust the knobs on the sub anymore. except the phase control
• Turned both subs on and adjusted (reduced?) their levels by an identical amount to match your other speakers. No, At this point I turned both on and level matched as if they were one sub, with a spl meter using the recievers +/-db control. I didn't touch the volume (gain?) on the subs for this, only level adjustment in the reciever

There is a very good article somewhere on this site which explains how to use more than one sub. For the most part I got very lucky. I haven't had the opportunity to set up both subs with test tones of varying frequencies, I've only used pink noise. I'm very limited in where I can place my subs. There may be a spot that is better, but I live in a tiny apartment, so options are limited. I put my 2nd sub behind the middle of the couch in the drawing below. It is the size of a two drawer filing cabinet, it doesn't fit in two many places.
View attachment 4565
Jack

 

[mtrycrafts]

All,

I remember another poster once asking about how to correctly set up a second sub in his room. If memory serves, he was advised to setup the first as good as he could before moving onto the second. Fair enough.

My question relates to the volume the subs should be set at. If the above advice is correct and followed, isn't it likely that I'll end up with my two subs at substantially different volumes? In other words, it's possible that the best setup of the first sub requires the sub's volume set reasonably high, but only a little of the second sub's volume to smooth out the frequency response of my room that bit more.

If true, wouldn't this be a disadvantage? I mean, isn't one of the advantages of multiple subs the fact that with twice the available output, both subs can be driven half as hard as one sub only?

Two subs doesn't mean half the power on each, unless they are collocated, one on top of the other so they would have equal room reaction from the same position. But this advantage will be offset by the nulls as that would be just as bad if not worse.

If you have time to play with them, get a test disc with 1 Hz increments, measure and plot each sub individually and see how different the plots are

Then, you can repeat this with both subs on and see what effect that has on the overall response. An eye opener.

 

[Buckle-meister]

Got it now Jack. Cheers.

Two subs doesn't mean half the power on each, unless they are collocated, one on top of the other so they would have equal room reaction from the same position.

Ah yes, I see what you mean Mtrycrafts. I was superpositioning without even realising!

...get a test disc with 1 Hz increments, measure and plot each sub individually and see how different the plots are.

ETF is good to 1Hz resolution.

 

[STRONGBADF1]

All,

I remember another poster once asking about how to correctly set up a second sub in his room. If memory serves, he was advised to setup the first as good as he could before moving onto the second. Fair enough.

My question relates to the volume the subs should be set at. If the above advice is correct and followed, isn't it likely that I'll end up with my two subs at substantially different volumes? In other words, it's possible that the best setup of the first sub requires the sub's volume set reasonably high, but only a little of the second sub's volume to smooth out the frequency response of my room that bit more.

If true, wouldn't this be a disadvantage? I mean, isn't one of the advantages of multiple subs the fact that with twice the available output, both subs can be driven half as hard as one sub only?

Hi Buckle,

I would think that once you know where your going to position both subs that you level match sub #1 with sub #2 off and then vise versa (both with the subwoofers volume knob on the sub) then turn both on and level match with the receiver internal settings.

This all assumes you know where the best locations are to get a nice even bass response throughout the listening area without any cancelation...

am I all wet?
SBF1

 

[Buckle-meister]

Hey StrongbadF1,

...am I all wet?

Hahahaha! No, but you do realise you've compressed what will probably turn out to be a hell of a lot of work for me into just one paragraph of text?!

It's not as simple as simply determining where to place the subs as each position trialled will have to be adjusted in level to see how its influence 'fits'. Then, assuming sub 1 and 2 are set independantly, it seems to me that there's just as much likelyhood that the two subs acting together will be detrimental as beneficial to the overall frequency response of the room.

 

[Tomorrow]

Robbie,

I gave this issue some thought as I began to use two subs in my asymetrical room. As an aside, the two subs I use now are two slightly different animals (an Hsu STF-3 and an Hsu VTF-3). There are many complications to your question and without giving us the specifics of your room, sub types, treatment locations, positioning limitations, etc., replies are all speculative.

However, if it helps you, what I did was place the subs in the most desirable (Missus says!) locations, level match the subs at the main listening position, and using both subs 'on', run automatic parametric eq with the Yamaha AVR. Then using an AVIA disc, I repeatedly swept the spl's from 20-80 Hz while hand tuning the (continuous) phase controls of the subs until I achieved a reasonably flat FR across that frequency field. I then re-ran the YPAO, double-checked the FR field, and presto....flat response from two integrated subs at the main listening position. (I don't care what it does anywhere else in the room.)

I hope this helps. It may not be scientifically perfect methodology, but it sure worked for me.

 

[STRONGBADF1]

Hey StrongbadF1,



Hahahaha! No, but you do realise you've compressed what will probably turn out to be a hell of a lot of work for me into just one paragraph of text?!

It's not as simple as simply determining where to place the subs as each position trialled will have to be adjusted in level to see how its influence 'fits'. Then, assuming sub 1 and 2 are set independantly, it seems to me that there's just as much likelyhood that the two subs acting together will be detrimental as beneficial to the overall frequency response of the room.

Its' absolutly easier said than done but thats why you love this hobby so!

That and maybe the music and movies...
SBF1

 

[mtrycrafts]

...
Then, assuming sub 1 and 2 are set independantly, it seems to me that there's just as much likelyhood that the two subs acting together will be detrimental as beneficial to the overall frequency response of the room.

Likelihood? You better count on this being the case
It is no small task setting up two subs and EQ ing them as they WILL need it, no matter what.

 

[Buckle-meister]

...without giving us the specifics of your room, sub types, treatment locations, positioning limitations, etc., replies are all speculative.

Two weeks from now I begin looking for a flat in London and for this reason I'm unable at present to give room dimensions. However, I will be hoping to find a place with a decent sized, non-square plan-shaped living room.

As for the rest, that's easy. I now have two identical Mission Elegante e8as1 subs, RealTrap acoustic absorption which will be placed in the four corners of the room. There will be no limitation on positioning.

...using an AVIA disc, I repeatedly swept the spl's from 20-80 Hz while hand tuning the (continuous) phase controls of the subs until I achieved a reasonably flat FR across that frequency field.

My subs have only a 0/180 degree phase switch.

I hope this helps. It may not be scientifically perfect methodology, but it sure worked for me.

Thanks Tomorrow. I'd have no problem going with your methodology but for the fact that I'm probably just as quick using ETF to get results at each trialled sub position as YPAO, and since the former is accurate to 1Hz resolution down to 20Hz and the latter to 1/3rd octave down to 63Hz, it's a no-brainer which to use.

All; is there general consensus that both sub's phase will be identical (remembering that I have only a 0/180 degree switch) wherever they end up being positioned, or is that up in the air too?