Will adding more subs really improve bass response in a properly calibrated setup? (1 Viewer)

[steve nn]

>>>Currently running two SVS Cylinders a PC+ 16-46 and a PC Ultra in a room 12'x11' and I immediately noticed an improvement in the intensity of the bass.

 

[Rutgar]

Sorry, but that's simply not true. A second sub DOES help improve frequency response. If you do a Google search on multiple subs, you'll find lots of data to support this. Here's an interesting review/article on the Velodyne DD-15, where the reviewer discovers this as well:

http://www.hometheaterhifi.com/volum...03-part-1.html

- Rutgar

 

[Kevin C Brown]

Nope, sorry. Think about it this way: You have one sub. -3 dB limit is let's say 20 Hz. You add another one. That one is also -3 dB at 20 Hz. Now, you simply have 2 subs with the -3 dB point of 20 Hz. The two can certainly play louder, but there is no improvement in low end extension if a single sub by itself wasn't reaching the limits of its performance in the first place.

The only way you get lower extension with 2 subs is if you have some eq going on to purposefully depress the output of the two drivers while allowing for deeper low end extension.

This is exactly why for low end extension alone, a PB2-ISD is better than two PB1-ISD's, for example.

 

[Rutgar]

What you're saying would be true, if you could "super impose" a 2nd sub onto another at the exact same spot. And in that case, there would be no effect in response. Fortunately, a second sub sits in a different place in the room, and therefore it will excite different room modes. Thus, helping the frequency response. This isn't up for debate, it's a fact. Another benefit of adding a second sub (of equal size and power), is that you also get a 6dB boost. Read the article I a gave a link for in my previous post, and do a Google search on "multiple subwoofers". You will find that multiple subs do in fact help frequency response. Moreover, I've had two Velodyne ULD-15's for ten years, and there's absolutely no question that there is a major difference in my low-end response, when I'm running both of them as opposed to just one of them. And believe me, I've done tons of experimenting, and measuring over the years.

- Rutgar

 

[Robert Cowan]

i agree with rutgar. even in a poorly setup situation, you should almost always benefit...

 

[Jonathan Dagmar]

not to hijack the thread, but i think my question fits here rather than starting a new one.

Because sub have their own amp, adding a second sub is as simple as splitting the output from the LFE out jack on my receiever? Or am I mistaken?

 

[Robert Cowan]

jonathan:

yes. however, you could also do it as a pre-out (if using two subs, you could use the pre-outs of your mains and go into the subs), and then pass through to the amp, or use speaker level as wel. but, if just using lfe, you can just split it.

 

[Arthur S]

You guys are giving me a bad case of subwoofer envy

I wonder if you can get them cheaper by the dozen?

Maybe we can organize a group buy and just meet the tractor trailer at a mutually convenient location.

Anyone have a pickup truck I could borrow?

Can you camoflage subs?

 

[frank manrique]

quote:

"Can you camoflage subs?"

Why......yes! It is the easiest thing to do in the world, but why hide such works of art?!!...

-THTS

"...hi, my name is Frank...and am an SVS bassaholic..."

 

[Kevin C Brown]

Not in my world.

Different modes are excited in the room, yes. But aside from the potential problems you can have with uncontrolled deconstructive and constructive interference around the room with trying to integrate two or more subs, and the resulting peaks and valleys in response, those nodes cannot be excited below a freq at which a sub can output. Multiples higher, yes, that's what room nodes are all about. But not lower.

I have had this discussion with Tom at SVS already. And this is also exactly what he told me. Maybe I'll see if he can pop in here.

I did look at the Secret's review of the DD-18. No where in there did I see him mention any extension of low end response by using two subs. Just that he could get a flatter response by correct placement of two subs. And if you notice, the best apparent low end extension he got, which was also the flattest, was when he had the EQ engaged with the DD-18 while he also had the HGS-18 running.

 

[SteveCallas]

You get higher output at lower frequencies. The point at which a single sub begins to dropout at your reference level is strengthened with two.

As I explained earlier in this thread, let's say your sub goes -3db at 20hz at your reference level of 85db. Now add a second sub collocated and calibrate both subs to 80db. Now at 80db, a single sub will do better than -3db at 20hz, it will be able to play it fine. So now if you have two subs each playing 20hz at 80db, you get around a 6db gain, so you are now playing 20hz at 86db with two subs, whereas with one sub, you were at 82db.

In this respect, you do get an extension of low end response. However, if the subs are not collocated, you probably don't get this benefit.

 

[Rutgar]

Kevin, I went back and re-read what you wrote. I finally figured out that we're talking about two different things. You're talking about bass extension, and I'm talking about the subs frequency response, or overall flatness in a small room. What you're saying is correct in that a second sub will not give any better extension below either subs normal low end range. I guess I need to learn to read a little closer.

Dyslexia is a terrible thing.

- Rutgar

 

[steve nn]

Another thing to keep in mind is staying with the train of thought of (within the single subs limits) Go beyond it's limit, then of course dual will provide better performance.

 

[Kevin C Brown]

Rutgar- I keep wishing you were right about the low end extension, because then if I *want* more low end extension, I could just get another sub like what I have instead of having to box mine up and get it to UPS for when I sell it to get a bigger newer one. (My current one is 18" on a side and about 80 lbs, and I'm looking at the PB2+...)


Steve- I agree, except that I made sure to specify that the 2nd sub wouldn't help if you weren't overdriving the first one by itself in the first place. So in that case, -3 dB at 20 Hz is still just -3 dB at 20 Hz, one sub or two, don't matter none.

 

[steve nn]

I agree with you 100% Kevin. I get the same extension / same spl readings whether I run one or three 25-31CS+'s at my normal listening level colocated.

>>(My current one is 18" on a side and about 80 lbs, and I'm looking at the PB2+...)

 

[Kevin C Brown]

I've emailed some back and forth with SVS Tom thinking he can say the magic words to get me over the hump of how big the PB2+ is... I'm getting closer. Maybe I'll do a separate thread on it soon.

 

[frank manrique]

quote:

"Go beyond it's limit, then of course dual will provide better performance."

...yet EIGHT is even better than two!...

-THTS

"...hi, my name is Frank...and am SVS bassaholic..."

 

[Richard Greene]

In a rectangular room (and most common room shapes) using two subs on opposite sides of the room will prevent odd-order standing waves from forming between two opposing surfaces.

The common left-right subwoofer set-up places the two subwoofers out-of-polarity for the first-order axial room mode between the front walls.

Whether this is an improvement to the overall bass frequency response is the question.

The primary bass problem under 80Hz. (except in very large rooms) is too few room modes.

Our ears have a one-third-octave smoothing ability ... but they are usually unable to smooth out the erratic frequency response in the bass frequencies.

Two subwoofers can be used to cancel some room modes between opposing room surfaces.

That may sound like a good thing to do, but doing that results in even fewer room modes under 80Hz. ... which can make the remaining bass peaks caused by standing waves more audible (and more annoying) than before.

In general, for a person sitting half way between the side walls, which is a null for the first-order standing wave between the side walls, the bass usually sounds better with one (or two) subs placed on the same side of the room so they DO excite that standing wave.

In general, for a person sitting well off-center and away from the null of that standing wave, the bass usually sounds better with subwoofers on opposite sides of the room so they do NOT excite that standing wave.

For non-rectangular rooms it's impossible to generalize the effect of two subwoofers in different locations versus one subwoofer. Measurements work well.

In most rooms the bass frequency response is either uneven or VERY uneven ... unless you use many bass traps to reduce the reflections that cause standing waves and/or use a parametric EQ to reduce bass peaks at one listening position.

Using two subwoofers to improve the bass frequency response under 80Hz, is usually a gamble.

Measurements of a sine wave sweep at the listening position will usually shows no significant improvement from using two subs versus one (or even deterioration of the frequency response) because using two subs can only eliminate one out of the typical five or six axial room modes under 80Hz. = so many of the bass problems remain.

 

[BruceD]

My experience echoes Kevin's and Richard's, in that multiple subs (in different locations) makes the frequency response worse more often than it improves it. Plus it becomes a real nightmare to correctly balance 2+ subs in different locations vis-a-vis SPL, phase and room modal peaks.

 

[Mitch Stevens]

I always had this wrong in my head. I have ALWAYS thought that people added a 2nd sub just to get higher ouput, without over-doing their subs.

For example, most people (who have VE) calibrate their subs to 75 dB. Now normally, you could kick it up a few notches to 78 dB or so, but most subs would crumble under the pressure of super heavy bass tracks.

So, I thought that these people would add a second sub, also calibrate that to 75 dB so that together the subs would give you an output of 78-81 dB which would be much louder, and yet, the subs wouldn't be straining to do that output as much as a single sub would have to do in order to hit that kind of output.

I had no idea that people would lower both subs in order to get a reading of 75 when the two subs were played together.