2x f112 for 1xF212

[Warpdrv]

If you mix and match subs, the overall system f3 point will be limited to the sub with the highest 3dB point. This is discussed in the article I referenced earlier in this thread.

Could you elaborate on this a bit further...

My room is laid out like a diamond, with the screen in the corner, 1 of the subs is behind the screen, 2 others are in the left and right corner, which would basically be mid wall, but corner loaded. In the corner behind the seating is a 15" single sealed which is highpassed at 15hz.

I'm running my 3 x Dual Opposed 18" subs in the front, left and right - no HP filter.
DCX2496 for eq on each sub, MIC2200 for HP on the 15" driver.

Are you saying that my 18" subs will not play below what my 15" sub will do...?

 

[Franin]

Just like to say thank you for all your help.

 

[Warpdrv]

Kinda nice to have a thought inspiring thread on subs

 

[Franin]

Kinda nice to have a thought inspiring thread on subs

To be honest when it comes to subs you guys I personally believe have much more knowledge than most.

 

[gene]

Could you elaborate on this a bit further...

My room is laid out like a diamond, with the screen in the corner, 1 of the subs is behind the screen, 2 others are in the left and right corner, which would basically be mid wall, but corner loaded. In the corner behind the seating is a 15" single sealed which is highpassed at 15hz.

I'm running my 3 x Dual Opposed 18" subs in the front, left and right - no HP filter.
DCX2496 for eq on each sub, MIC2200 for HP on the 15" driver.

Are you saying that my 18" subs will not play below what my 15" sub will do...?

Nope not saying that at all. The other subs won't influence what your 18" sub is playing but they may influence the combined overall output at the listening area.


Excerpt from my article:
Ideally you should use identical subwoofers for the best overall performance, but it is possible to mix and match subwoofer brands and types if you're willing to do the extra work. If using mismatched subs, bear in mind that systems with different low frequency cutoffs may well be in phase and additive over most of their band, but at or below system resonance may well be out of phase. This can put us in the position of having the sub with a higher cut-off frequency reducing overall system output below its cutoff frequency. This is why we usually recommend using identical subs all around.

 

[AJinFLA]

Excerpt from my article:
Ideally you should use identical subwoofers for the best overall performance, but it is possible to mix and match subwoofer brands and types if you're willing to do the extra work. If using mismatched subs, bear in mind that systems with different low frequency cutoffs may well be in phase and additive over most of their band, but at or below system resonance may well be out of phase. This can put us in the position of having the sub with a higher cut-off frequency reducing overall system output below its cutoff frequency. This is why we usually recommend using identical subs all around.

Hi Gene,

I'm not disagreeing with that per se, but "below system resonance" would be indicative of very low frequency, in all but (some of) the smallest subwoofers. Even at say 30hz (and below), I can't see the phase differences being significant enough (<180 deg) to cause significant cancellation if they are relatively in phase throughout their passband. Add on top of that the different modal interactions due to spatial position and I would say you would have to be fairly unlucky for this to be true. It certainly won't hurt to have identical subs, but I would love to see a measured example of non-identical subs causing phase cancellation due to different LF roll off, when spaced apart in a living room.
Typical ported powered subs have a sharp highpass (subsonic filter) on their amplifiers below system resonance to prevent unloading/overexcursion/destroying the driver, so there is not much output there to be phase mismatched with say a sealed sub that may still have some output in these regions (though they typically also have an amplifier highpass as well).
Not saying it's not possible, but IMHO, somewhat unlikely.

cheers,

AJ

 

[Warpdrv]

Agree AJ.....

I think if Frank was looking to add a couple subs to what he had this would be the way to go... He would increase his low end performance and add headroom he's looking to achieve.

Of coarse this will not just be a plug and play operation. 4 subs in room can take some effort to get right and EQ is important, but worth it...

 

[gene]

Typical ported powered subs have a sharp highpass (subsonic filter) on their amplifiers below system resonance to prevent unloading/overexcursion/destroying the driver, so there is not much output there to be phase mismatched with say a sealed sub that may still have some output in these regions (though they typically also have an amplifier highpass as well).
Not saying it's not possible, but IMHO, somewhat unlikely.

It's more likely than you think and I have measured it in my own system which features two ported subs and 2 sealed subs. You can see a drop off below 20Hz that doesn't exist when the subs with the lower f3 are being played alone. Also a phase shift at low F also affects frequencies above the 3dB point. I asked Paul Apollonio to comment on this point later today.

Luckily I was able to adjust the f3 point of the sealed subs to reduce this effect but I could imagine it being more dramatic on subs that don't have such flexibility. This is one of many reasons why Dr. Toole / Sean Olive, etc recommend using identical subs all around. Of course I don't practice what I preach but it makes the job of blending all the subs that much more difficult.

 

[AJinFLA]

It's more likely than you think and I have measured it in my own system which features two ported subs and 2 sealed subs. You can see a drop off below 20Hz that doesn't exist when the subs with the lower f3 are being played alone.

Interesting. Did you move the mic around the listening area and observe this <20hz cancellation everywhere?

Also a phase shift at low F also affects frequencies above the 3dB point.

Correct, since frequency and phase are inter-related.

Luckily I was able to adjust the f3 point of the sealed subs to reduce this effect but I could imagine it being more dramatic on subs that don't have such flexibility. This is one of many reasons why Dr. Toole / Sean Olive, etc recommend using identical subs all around. Of course I don't practice what I preach but it makes the job of blending all the subs that much more difficult.

With eq I assume? The thing about commercial subs is that there can be a large amount of variability, i.e., neither observing classic 2nd or 4th order rolloffs due to the use of hi pass and biquad filters in their active circuits, the ported typically having the sharp hi-passes I mentioned previously and the sealed using Linkwitz transforms (and a high pass) to extend f3. They can have more similar than dissimilar roll-offs. All depends on the model I suppose.
You've piqued my interest. I'll have to scrounge up some ported subs (I use only sealed) and do a couple measurements in my room.

cheers,

AJ

 

[Paul_Apollonio]

Phase Matters

Dear All,

If the subs in the same room have different rolloff frequencies, different Qts, or different order (2nd or sealed vs ported or 4th - vs ported w/high-pass circuit which could be anything from 5th to 8th order), the phase shift of a minimum phase system(which most loudspeakers are) is tied to and predicted from its frequency response. This phase shift will have significant effects on the way the subs add (As will their distance to large reflective surfaces) OR the RELATIVE distance between them to the listener. While it is a given that you will NEVER get mid and high frequency devices which are far apart to add in anything other than a completely random way (distances between them are great relative to the size of the wavelengths), at very LOW frequencies, the wavelengths can easily be greater than the entire room dimensions, so it is HERE where it is most important that phase and polarity are observed. NO ONE would question that two subs (identical) run out of phase (180 degrees apart) is a problem. Why then is it not as clear that two subs, one a sealed box with a 50hz cutoff, and the other a vented box with the same 50 hz cutoff and a second order high pass WILL NOT be in phase even when the polarity is right? The sealed box will have 90 degrees of phase shift at Fc (cutoff or -3db pt) while the vented with the 2nd order HP will have 270 degrees phase shift. (180 from the vented box, and another 90 from the second order HP filter. Just so happens, now these two units are 180 degrees out of phase AT the cutoff frequency, NOT below it....

It may be that our rooms are so awful that this effect is secondary to all the destructive interference from walls and ceiling and floor. That does not mean this advice (USE THE SAME SUBS) is not well founded. That is my two cents worth.... I HAVE measured this in fact, just one week ago.

 

[Franin]

Mixing the ported and the sealed subs together how does it sound and how would you place them?

2 ported at front and 2 sealed at back

Or

2 sealed at front and 2 potted at back.

Cheers

 

[Franin]

Warp is gonna hate this but ditch the JL all together. Believe me, I have been through this. You can sell the JL for what you paid for it on AG and get a much better sub. DIY will blow it away but if you don't want to do that(I sold my DIY because I wanted a simple plug and play) look at Submersive or SVS. I went with a SVS and get 90% of the performance of my DIY with 0 hassle. Both step all over the JL F113 much less the 112 unless you are dealing with a very small room.

Here is a small taste of 3rd party data. I have the data if you need to see it.

Freq PB13U F113 PB13U Advantage Acoustic Output

20 108.5 101.3 2.3X

25 112.4 105.5 2.2X

32 115.8 109.8 2.0X

40 116.9 114.0 1.4X

50 115.8 116.5 NA

Wrap, who is a good friend of mine will tell you the SQ is much better with the JL but I call BS...it is not...

Can I buy 2 SVS Ultra and keep my Fathoms will there be a problem?

 

[ParadigmDawg]

From 32 hz down the SVS has twice the output so you would likely be better off getting rid of the JL vs. trying to get a limited sealed sub matched to an aggresive ported sub.

Can I buy 2 SVS Ultra and keep my Fathoms will there be a problem?

 

[gene]

From 32 hz down the SVS has twice the output so you would likely be better off getting rid of the JL vs. trying to get a limited sealed sub matched to an aggresive ported sub.

Maybe true if all you care about is sheer SPL output below 32Hz.

I suggest reading this article that discusses SPL tradeoffs for extension:
http://www.audioholics.com/education/loudspeaker-basics/subwoofer-extension

 

[ParadigmDawg]

Maybe true if all you care about is sheer SPL output below 32Hz.

I suggest reading this article that discusses SPL tradeoffs for extension:
http://www.audioholics.com/education/loudspeaker-basics/subwoofer-extension

We already know how the Ultra-13 objectively stacks up against the F113 and there is a very strong correlation between objective data and subjective opinion. We don’t believe in “music subs” or “HT subs” – rather we believe simply in “accurate subs”, which faithfully reproduce the source material.



Here is the power response and the distortion levels of the PB13U in the 20 Hz tune.

And here is the power response and the distortion levels for the F113.

Notice the flattening of the power response at the deeper frequencies at higher drive levels. This is output compression, where the subwoofer is either running out of woofer stroke or amp power (or both). Output compression robs the presentation of deep bass dynamics at higher playback levels, leaving only the mid/upper bass intact. Notice there is almost a 15 dB discrepancy between max output at 40 Hz and at 20 Hz.

Also notice the high levels of distortion at higher drive levels over the common bass pass band. High distortion levels add false harmonics which make the bass sound muddy and complex instead of clear and distinct.

I’m not bagging on the F113 either – it’s a very good performer for a sealed subwoofer of that size. The SVS is flatter, deeper, cleaner, and more linear with no compression and those objective parameters are definitley audible to the trained and experienced ear.

I am uncertain what you are saying here. The question is "can he run a sealed with a ported" and I am pretty sure that your stance is that it is a bad idea, if I remember correctly.



.

 

[Franin]

Well I bought my 4th sub which hopefully should be arriving this Thursday. I took some of your advice I decided to go with the 4 Fathoms F112.

 

[lsiberian]

Notice the flattening of the power response at the deeper frequencies at higher drive levels. This is output compression, where the subwoofer is either running out of woofer stroke or amp power (or both).
.

In addition to the above quote.
It's also been demonstrated that the smaller the sealed boxes the greater compression from the limited air itself. In almost every case I'd suggest a ported sub over a sealed unless you have limited area for the sub. Even for music subs a port with the proper driver will outperform a sealed one.

If you want a sub for the theater the SVS Ultra is the way to go commercially. If you want to build your own I'd suggest a ported sub as well.

I plan to replace my current sealed sub with a ported sub soon.