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3ll3d00d

Should I go ported?

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I currently have a dual sealed UXL-18s powered by a speakerpower sp1-6000 amp up front with a pair of 12s nearfield behind me. This works well so I wouldn't be changing it except for the fact I want to make a change to the layout up front, this means I need to build a new sub up front and that got me thinking about options.

 

The new space available is ~4' tall x ~15" deep by ~2' wide (probably a few inches extra is ok in this dimension), i.e. something like 200-220L total internal volume. 

 

I can see 2 approaches, thought I'd post them here and see if anyone has any thoughts on which way to go.

 

The first one is basically the status quo option, i.e. leave the nearfield as is + build another box of the appropriate dimensions to hold the 2 UXL.

 

The 2nd one is;

 

- move the 2 UXL to nearfield, power these by the speakerpower

- build a single ~180-200L ported box tuned to ~18Hz using something like a FaitalPro 18XL1800 or B&C 18sw115

 

The thinking here is that the ULF wobble might be delivered more effectively by a pair of UXLs nearfield and I can get drivers like the faitalpro or B&C easily (whereas HT sub drivers like the UXL are non existent in the UK).

 

Thoughts?

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Ported pros:

  * more output at 15 Hz and up

  * possibly better tactile feel from ULF

 

Ported cons:

  * higher distortion of ULF frequencies with near-field placement probable

  * possible difficulty integrating sealed + ported responses (though your FIR filter capability will surely help here)

 

The distortion on ULF is likely to go up with the near-field placements because the distortion harmonics are not affected by room gain nearly as much as the ULF.  Moving the sealed subs closer will have negligible effect on ULF output but will increase the output of the distortion harmonics to the listening area.  The increase in tactile ULF is very debatable in my opinion.  In fact, given research suggesting that tactile thresholds for ULF are well above audibility thresholds in a room with rigid boundaries, I would guess that the close placement won't matter one bit for tactile feel because anything you feel in the ULF range will be due to the movement of the floor rather than any sound field effects.

 

So I'm at least down for keeping with sealed up front unless believe you will benefit from the additional output capability.

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The increase in tactility from NF placement is not remotely debatable in my experience, move more air in close proximity to the listening position and perceived intensity goes up. Achieving an equivalent effect from subs further away requires *much* more output, is a different sensation and requires SPL a fair way above my usual levels to get there. Note that I am talking from practical experience of adding/dialling in NF subs in my room. 

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Didn't @Madaeel do some experiments moving his bosso system NF, only to find that the <20Hz stuff was better when it was stacked in the corners?

 

(Where is he, by the way??)

 

 

Do you feel you're lacking in output at the moment?  I recall the various 'discussions' ;) on here regarding whether having massive 15Hz headroom is really worth the trade-off against the lower-end capability.  You're on a wooden-framed floor, aren't you?  So the <15Hz stuff should be much better on it, therefore Sealed would be better? :)

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Near-field is just a fad   :D   :P

haha nf is the only place I have space for more subs!

 

 

Do you feel you're lacking in output at the moment?  I recall the various 'discussions' ;) on here regarding whether having massive 15Hz headroom is really worth the trade-off against the lower-end capability.  You're on a wooden-framed floor, aren't you?  So the <15Hz stuff should be much better on it, therefore Sealed would be better? :)

 

I don't feel the need for more output. I think a ported sub vs the dual I have now will have v similar output capability from ~15-16Hz up. The current sealed makes it to ~9Hz before giving up. I don't think my wooden floor behaves in the way that people in the US describe a slab vs suspended floor, IME a suspended floor in a Victorian house in England is a v different thing (solid but leaky if that makes sense).

 

overall it seems to boil down to;

 

1) is more output from subs at the front from ~9-16Hz more important than more output from ~10-30Hz NF?

2) are there negative effects from ported in the 15-30Hz range?

3) will a pro style woofer be materially better than a UXL in the 60-100Hz range?

 

my guess is this reduces down to option 1 as the main point of difference

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What is it that you are trying to improve most with the change? More headroom overall? More tactile sensation in the deepest bass? More impact in the upper bass? Just bored and can't leave well enough alone?

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What is it that you are trying to improve most with the change? More headroom overall? More tactile sensation in the deepest bass? More impact in the upper bass? Just bored and can't leave well enough alone?

It's not headroom and it's not really "just bored..." though there is an element of that for sure. Basically I want to get my L and R a bit wider apart and also a bit more symmetrical with respect to adjacent room boundaries, I think this will bring some, relatively marginal, improvement to the system but it's not enough to warrant rebuilding a bunch of speakers. Nevertheless I still want to do that (there is another, also fairly marginal, non audio reason to do so) so then it's a question of what other changes could be made to make it worthwhile.

 

so this leaves us with "More tactile sensation in the deepest bass? More impact in the upper bass?" . I would like to achieve the former for sure, particularly more tactile sensation per dB spl. I am unsure about the latter, of course that would be great to achieve but I can't say the system is lacking as is so it is not something I need to "fix" per se. I've never tried a pro style (sub)woofer though so I am curious as to whether I would hear/feel a marked difference in SQ in that range when compared to my UXL. That alone makes it an interesting one thing to try out (even if it means I end up changing again next year).

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The increase in tactility from NF placement is not remotely debatable in my experience, move more air in close proximity to the listening position and perceived intensity goes up. Achieving an equivalent effect from subs further away requires *much* more output, is a different sensation and requires SPL a fair way above my usual levels to get there. Note that I am talking from practical experience of adding/dialling in NF subs in my room. 

 

Is this true for the entire subwoofer range, including ULF?  Or is it only true for a particular part of the range?  If you believe this is true for ULF, is it possible that you are just feeling the relatively higher levels of harmonic distortion?  Also, unless your NF subs are dual-opposed, how do you know you aren't just feeling vibration transmitted directly from the subs to your seat through the floor?

 

I have my own experience in this area.  I got better tactile sensation by using near-field MBMs that handle 50 Hz and up together with subs placed at the front of the room to handle 50 Hz and below than I did using the same subs run full-range either up front or near-field alone.  The subs are tuned to 18 Hz or so, and I've heard/felt output from them down to 12 Hz at the lowest.  My impression is that the tactile feeling in the 12-20 Hz range was better with the subs up front than with them near-field.  However, the improvement was more pronounced in the 20-45 Hz range where they gained a lot of headroom over the near-field placement.

 

overall it seems to boil down to;

 

1) is more output from subs at the front from ~9-16Hz more important than more output from ~10-30Hz NF?

2) are there negative effects from ported in the 15-30Hz range?

3) will a pro style woofer be materially better than a UXL in the 60-100Hz range?

 

my guess is this reduces down to option 1 as the main point of difference

 

I think the answers to all of these are "it depends".

 

If for whatever reason you feel more tactile sensation from the same SPL over the 10-30 Hz region with a sub placed NF   than up front and if you want to feel more of that sensation, then I think you'll want more capability back there.  Why not?

 

An 18 Hz ported sub will be prone to power compression close to the tune but will probably offer lower distortion at levels approaching the saturation point.  Is that better or worse?  It depends on a lot of details.

 

Will a pro sub sound better in the 60-100 Hz range?  Hypothetically, a pro style driver benefits from higher efficiency over that range and possibly lower and/or more linear inductance.  The higher efficiency will only help if you are pushing the sub to levels where power compression comes into play.  Inductance is a stickier issue.  Undoubtedly, inductance can cause distortion and harm transient response at high power levels and/or high excursion levels.  But does inductance affect linearity at lower levels?  I haven't seen definite proof of this, but if this is the case then a sub driver with lower and/or more linear inductance could definitely make a difference.

 

As another idea.  What if you invest in Crowson transducers before making the decision about which way to go with the subs?  If the Crowsons gave you all the tactile sensation you were after, how would that affect your decision here?

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Is this true for the entire subwoofer range, including ULF?  Or is it only true for a particular part of the range?  If you believe this is true for ULF, is it possible that you are just feeling the relatively higher levels of harmonic distortion?  Also, unless your NF subs are dual-opposed, how do you know you aren't just feeling vibration transmitted directly from the subs to your seat through the floor?

 
the NF dominates below 40Hz in my room & my measurements do not indicate harmonic distortion is an issue. The delivery mechanism is via the seat, it's not via the floor (as far as I can tell at least, my floor seems really quite inert no matter how hard you pound it).
 
I think crowsons would be tricky and/or expensive to accommodate in my room (I have a quite large bespoke L shaped sofa) unfortunately.

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the NF dominates below 40Hz in my room & my measurements do not indicate harmonic distortion is an issue. The delivery mechanism is via the seat, it's not via the floor (as far as I can tell at least, my floor seems really quite inert no matter how hard you pound it).

 
I think crowsons would be tricky and/or expensive to accommodate in my room (I have a quite large bespoke L shaped sofa) unfortunately.

 

 

If you have your acceleration measurement system working, maybe you can compare acceleration measurements between your floor and furniture separately.  I don't know that pounding on the floor will tell you much about how inert it is unless you are pounding it with something real heavy.

 

Do the NF subs fire into the sofa?  If so, how close are they?  I wonder if the strong ULF tactile effects you are witnessing require drivers that fire very close to the furniture?  FWIW, one of my original two subs had the driver firing into the sofa when it was situated near-field.  I often found it to too much, to the point of being distracting, in the mid-bass frequencies.  I still preferred having the deep bass and ULF frequencies reproduced at the front.

 

Indeed, with the full subs near-field, the SPL response at the seats was poor over the 30-45 Hz range and exhibited a deep null at 40 Hz.  I was using Audyssey MultEQ XT at the time, and it was applying a full +9 dB boost to much of that region.  Needless to say, my woofers were moving a lot of air when trying to reproduce that content, but apart feelings of shaking, the tactile stimulation from content in that range was pretty much non-existent.  I also recall running a 40 Hz tone where that null was and measuring lower SPL about 12-18" from the 15" driver than I measured in a distant corner.  That's just crazy, and it reveals how much a room can dominate the sound field in the bass even measuring/listening very close to the driver.  Only recently have I learned that room interactions actually change the in-room efficiency of a speaker/sub in terms of (acoustic watts output) / (electric watts consumed).

 

I have similar limitations with respect to crowsons.  I have a 5 piece sectional sofa, so I think I would need at least 5 transducers for full coverage.  I'll see how I like ULF bass-induced vibration (if I feel any) before I decide whether to go down that road.  Maybe my floor will turn out to be inert for the ULF.  As another anecdote, I was surprised by how much the UH-21v1 drivers I bought excited the floor during free air testing, but the weird part is what frequencies were affected.  Sine waves at around 30 Hz seemed to be the worst by far and made my house rattle like mad even with miniscule power inputs.  At 10 Hz and below, I felt almost nothing, even with the the driver near its excursion limits.  Maybe ULF bass will turn out to be a dud in here.  :)

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Well based on your replies and the fact it's your money I vote for trying the UXL's nearfield and trying a pro woofer up front. :D

 

How much is the 21DS115-4 compared to the 18SW115? It could work in that much space.

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If you have your acceleration measurement system working, maybe you can compare acceleration measurements between your floor and furniture separately.  I don't know that pounding on the floor will tell you much about how inert it is unless you are pounding it with something real heavy.

 

just for a quick test, I measured the floor while playing my white noise calibration signal at a fairly loud level & normalised the measurement against background noise (i.e. sensor on same floor but with no signal playing)

 

top graph is NF only at ~5cm away and ~20cm away

 

http://imgur.com/sdYk9vq

 

this is same but with both front and NF playing

 

http://imgur.com/Kb3G9Fy

 

 

scale is in dB La which puts 0dB at 1 µm/s2

 

so you can see there is some increase in vibration on the floor but more at higher frequencies than low. Not sure if this tells us anything but might as well use this app I've written!

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Well based on your replies and the fact it's your money I vote for trying the UXL's nearfield and trying a pro woofer up front. :D

 

How much is the 21DS115-4 compared to the 18SW115? It could work in that much space.

About £450 for the 21, £400 for the 18 (similar for the faitalpro). Net cost is less than zero though as i have a uxl-18 to sell as well as a dual infinity 1260.

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About £450 for the 21, £400 for the 18 (similar for the faitalpro). Net cost is less than zero though as i have a uxl-18 to sell as well as a dual infinity 1260.

 

In that case I'd spring for the new 21. It moves more air, is more sensitive and efficient. It would easily fit in a 24x48x15 cab. I'm really liking them so far. The reasonable 30lb weight is refreshing too. If you have not had hands on experience with the modern top end pro woofers I think you might be surprised. If nothing else I'd like to hear what you think of the subjective difference compared to the UXL.

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Do the NF subs fire into the sofa?  If so, how close are they?  I wonder if the strong ULF tactile effects you are witnessing require drivers that fire very close to the furniture?  FWIW, one of my original two subs had the driver firing into the sofa when it was situated near-field.  I often found it to too much, to the point of being distracting, in the mid-bass frequencies.  I still preferred having the deep bass and ULF frequencies reproduced at the front.

 

 yes they do, they are right up against the rear of the sofa. From what I've seen (on other threads), this is the standard position for such a sub. I don't have that much room behind the sub so I can't say how far away you have to be before the effect really tails off. I roll this sub off quite steeply (2nd order NT low pass) around 45-50Hz, mainly because I find it negatively impacts SQ when running higher (the notes get thicker/duller) though also because the measured vibration hands over to the main subs nicely around about this point. As measured, a relatively smooth (with a slightly upwards incline as you go up in frequency) measured acceleration curve seems to feel good to me, not distracting or unnatural at all. The current subs roll off around 15Hz though as they lack the excursion to go further safely so I can't crank that ULF end without thinking I'm going to destroy them :)

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here's a quick model of the b&c 21, set voltage to limit velocity to ~20m/s. I imagine the port would be bigger ideally but space constraints probably mean not possible (and actual SPL probably means I won't compress to much anyway)

 

http://imgur.com/oKDN1eY

 

seems like the 18 has same shape at the low end but results in less output higher up. What is the advantage of the 21 over the 18 in this situation?

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here's a quick model of the b&c 21, set voltage to limit velocity to ~20m/s. I imagine the port would be bigger ideally but space constraints probably mean not possible (and actual SPL probably means I won't compress to much anyway)

 

http://imgur.com/oKDN1eY

 

seems like the 18 has same shape at the low end but results in less output higher up. What is the advantage of the 21 over the 18 in this situation?

 

Less power required, less excursion used, higher potential headroom = driver being driven less hard and all of the improvements in the reproduction of the signal that brings. Plus maybe later on you get into a situation where you can build a bigger cab, want to go sealed with it or actually need all the headroom you can get.

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came up with this so far

 

http://imgur.com/a/maWLT

 

~205L net with a 304cm2 by 110cm port, 1kW and a 15Hz LR4 puts excursion at ~10mm and velocity at 20m/s. Going longer doesn't seem to add much in this size enclosure so this seems a reasonable balance to me, port resonance is ~135Hz so outside the realm of my LPF.

 

My main doubt is whether having the port that far away from the driver makes bad things happen, adding the centre to centre distance to the path difference in hornresp properly trashes the combined output. Any idea if this is an issue in reality (in a room)?

 

btw, is there a reason to go with the 4 or 8ohm option other than the load presented to the amp? they seem to model pretty similarly.

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came up with this so far

 

http://imgur.com/a/maWLT

 

~205L net with a 304cm2 by 110cm port, 1kW and a 15Hz LR4 puts excursion at ~10mm and velocity at 20m/s. Going longer doesn't seem to add much in this size enclosure so this seems a reasonable balance to me, port resonance is ~135Hz so outside the realm of my LPF.

 

My main doubt is whether having the port that far away from the driver makes bad things happen, adding the centre to centre distance to the path difference in hornresp properly trashes the combined output. Any idea if this is an issue in reality (in a room)?

 

I don't know what you are doing in Hornresp, but for the frequencies that you are interested in, that port is definitely not "far away" from the driver.  It's less than 1/4 wavelength at the port resonance, which is what will give you trouble if anything.  Depending on how strong it is, you might want to try to knock down the port resonance with a PEQ.

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I don't know what you are doing in Hornresp, but for the frequencies that you are interested in, that port is definitely not "far away" from the driver.  It's less than 1/4 wavelength at the port resonance, which is what will give you trouble if anything.  Depending on how strong it is, you might want to try to knock down the port resonance with a PEQ.

that's what I thought (that the port is not far away in wavelength terms) but it seems like that setting has a relatively strong effect (in terms of making the port dominate output if you move the port closer to the listener). This makes me think that that setting doesn't do what I think it does (wouldn't be the first time in hornresp), It's described pretty plainly as

 

The distance from the port outlet to the listener can be adjusted if necessary using the length difference parameter. A positive value for path length difference increases the listener distance.

The path length difference is the distance from the port outlet to the listener minus the distance from the direct radiator diaphragm to the listener. The difference is positive when the distance from the port outlet to the listener is greater than the distance from the direct radiator diaphragm to the listener.

 

Example of the effect - http://imgur.com/s3IwddN

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I have no idea what's going on there.  Assuming the driver is front-firing toward the listener, the distance difference to the listener from the port vs. driver is like 20 cm at most.  You definitely shouldn't be losing 3 dB at the 15 Hz tuning frequency with that distance.  Is there an issue with the units used in the field?  Even if there was, I would expect to see a ripple across the response, so I really have no clue what that setting is doing.

 

I've used Hornresp for some ported models before, and I don't recall seeing that behavior either.  I can't recall whether I filled in that parameter or not.  Maybe someone else with Hornresp experience can chime in.

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I don't know what you are doing in Hornresp, but for the frequencies that you are interested in, that port is definitely not "far away" from the driver.  

 it seems like that feature adjusts spl of one source by an inverse square law sized amount which I suppose is where the "surprising" result comes from as I'm thinking of "what will happen in a room" and the model is not. 

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My 21DS115 turned up today, seems like a nicely built driver and I can definitely feel the benefit of the lighter magnet (vs lugging around my UXL)

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Have you started on your cab?

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