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My nearly-4-year 4-way speaker project has reached a plateau. A little Tassie GTG today made me reflect that it's all been worth (some of) the struggle.

 

The design and build thread is:

 

 

The most recent photo:

 

182193155_Brians4-waysand3-waycentre.jpg.2b80ef4e70594cde8d9e7b5697f6b545.jpg

 

But this is a hobby, and this is SNA. Things must proceed. The words "so, it's basically the same as last time" really touched a nerve today (just kidding, you-know-who ?). This must never happen again!

 

I've played a few low tones and walked around the space - 10 x 6 m, with 3.2 m concrete ceiling, and noticed nulls, halfway along room, at the sides. Not huge, but a bit of a sag around 50-55 Hz.

 

It's a passive system. No DSP. The design aimed to maximize bass extension by doing what few seem to do: use a large vented box. These are 240 litres, with twin 102mm diameter vents.

 

So the new intention is to build 2 subs (stereo of course) to augment the bass, and place them in the "null" areas. This can hopefully coincide with the same distance from the listening position, so there are no time-delay issues.

 

The best option would seem to be in the joint of wall/ceiling, behind the listening position, a bit more than half-way back into the room. How to get them there was an unresolved discussion today. They will be around 320 litres internally, and likely approach 100 kg each; securing them is the easy part, getting them there is another thing. A "sub-crawl" would necessitate a reversal of gravity.

 

I initially thought the best driver would be the same as my 15" SBA woofers, but I was recently tempted by some gorgeous Acoustic Elegance TD15H drivers, so decided to model them in WinISD.

 

It was all settled for a couple of days, then I simmed the SBA's more recent "long-throw" version of my woofer. It's a bit confusing, as the TS parameters are very similar, including X-max.

 

The 3 drivers in this graph are:

 

SB42FHC75-6      black (mine)

SB42FHCL75-6     red (new long-throw)

Acoustic Elegance TD15H   blue

 

These all have LP (hi-cut) filters applied. The black one is the same as my 4-way woofer, cutting off at 100 Hz, as with its present passive 4th-order filter.

The blue trace, the AE driver, was very appealing, but both are completely blitzed by the (red) FHCL, so I've ordered 2 of these. Also, the 3" voice coil and greater power handling* (*Edit: wrong - see later posts) appealed.

The red and blue traces have a 60 Hz 2nd order filter applied. Of course, this can be adjusted in real life to match the 4-ways and the room.

 

203294586_3x15inchwooferWinISDsims.JPG.fed52d31e722d08de578b82c63d2dae9.JPG

 

The box sizes are 300 to 320 litres, all vented.

 

So I can't be saved from the spend, but maybe your comments can help me with the next stage - designing the boxes for the wall-ceiling corners? As a cube, internally they could be around 700mm each way, but I anticipate angled baffles, from 45 degrees to whatever into the room. Looks like they'll need to be about 1.6m "wide".

 

Edited by BioBrian
wrong link, error re power handling
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Just a quick announcement that twins were painlessly born today, to a badly-presented but relieved BioBrian and his wonderful StereoNetter cohorts. I'd really like to gratuitously thank all staff, but

It's an odd experience when I find someone referring to something I wrote that I can't remember.   When you compare different kinds of subs, there are two experiences. The first is the easy

Spurred on by hearing @deblur's lovely sealed 15" AE subs yesterday, it's good to get another step closer to finishing these (here comes another one) big birthers.   The baffle flares worked

Thanks Brian for having us to visit at such short notice.

 

Thoroughly enjoyed the company and the music, definitely better sounding with the door open.

 

This is the latest photo I have of your system, apples and herbs.

BioBrian_270419_SNA.jpg.eda7c6aa63b4815bb832b89b4bd2e2c0.jpg

 

Will eagerly await the new sub configuration whatever it is.

 

Sphere calculator?

https://www.calculatorsoup.com/calculators/geometry-solids/sphere.php

 

These links may help with positioning? 

https://amcoustics.com/tools/amroc

https://www.bobgolds.com/Mode/RoomModes.htm

http://www.sengpielaudio.com/calculator-roommodes.htm

 

Best of luck with them, to quote @Upfront "don't be shy", yell if I can assist.

 

 

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6 hours ago, Wozza_Lee said:

sub built long and thin, almost like a pillar mid wall

This would certainly help with finding the best spot, and could be an interesting feature, as you say. I've sort of been led to believe that box shape (hence internal reflections) is almost irrelevant at these frequencies (bottom 2 octaves: 20-80 Hz). This would allow freedom not to be found in the upper octaves, where baffle step is also an issue.

 

I should say that there's fairly aggressive competition for wall-space though, and forget the floor!

 

The wall-ceiling junction looks most likely at the moment, as there are grooves in the Bondek ceiling for "Bon-nuts", which take heavy weight, and can be slid along the grooves if needed, to find the right placement.

 

I'm kind of hoping that the triangular box shape could match future room treatments, such as a continuation of the box-shape along the corners, but made of fluffy stuff with adjustable reflectivity surfaces. This could be material, holy plywood, metal, slats, etc, on their front surfaces. It may be too shallow for effective bass traps, but it's a thought at the moment.

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Russell, it was very refreshing to have you and Linc down yesterday. Thank you (both) for all your advice and discussion. Nice pic from your phone, too.

 

Your post above has given me quite a lot of food for study! It's the first time I've come across these mode calculators, etc. And I thought I was just building a couple of subs ?.

 

Still wondering about the spherical enclosures - that would surely test the notion of box-shape-being-irrelevant. They could be stunning, especially if made of concrete and dangling from the ceiling (and you walk into one in the dark). New meaning to the phrase "balls in the air"? To get the 330 litres, with bracing, vent, and reasonable wall thickness, they'd need to be about 1m diameter. That's a statement.

 

It was kind of disturbing that the speakers sounded better with the Rolladoor open. That's not going to work well in winter. Or spring/summer, with all the bird noise. I'll try to get around to organizing all the mattresses and insulation into more correct places at some stage. The last 2  queen mattresses, that are currently leaning in one side of the room, seem to have swallowed some life out of the mid-range, but that's really hard to be sure about. I think they need to move to hanging vertically, somewhere out from the back corners.

 

If the door is acting as a limp mass membrane, maybe it needs tuning. It should be doing something towards diffusion, with all those horizontal folds. I've tried hanging batts in the middle there, but need to do some more serious tests.

 

One day we should have a REW party, with somebody who knows how to do it (not me).

 

I think the new subs need to happen first. They might have a future in somebody's home one day. Form will follow function, but I'll try to keep the shape a bit useable, hopefully.

 

 

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Does anybody have experience using Green Glue to laminate speaker box panels?

 

I used to think its benefits would be negated by having to have joins at the edges, but even in the middle of panels it may help.

 

And I used to think it stayed sloppy forever, but someone recently said it sets hard.

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Does anybody have experience using Green Glue to laminate speaker box panels?
 
I used to think its benefits would be negated by having to have joins at the edges, but even in the middle of panels it may help.
 
And I used to think it stayed sloppy forever, but someone recently said it sets hard.
I use rubberised adhesive (most contact adhesive is rubber based and will stay flexible).

Although wall thickness really isn't that important with a sub (as you said frequencys down that low are 15-18 meters long).

Its all about braces, for a sub that size I would have a skeleton with 2 vertical and 2 horizontal braces full size of the inside of the cabinet interlacing
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17 hours ago, BioBrian said:

but both are completely blitzed by the (red) FHCL

Your chart doesn't show that.

 

17 hours ago, BioBrian said:

designing the boxes for the wall-ceiling corners?

What frequency range do you intend the boxes to cover up to.  If it's ~100Hz or lower with a relatively steep cutoff (eg. 24db/octave) - then the shape and angle of the bafle is of much less (if not zero) relevance.

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2 hours ago, BioBrian said:

Does anybody have experience using Green Glue to laminate speaker box panels?

Yes - don't bother trying to laminate two boards together with an "elastic" material if the purpose is to achieve some type of damping or vibration resistance.... and the frequency of operation is <400Hz.

 

Use extensive bracing to "lock the walls in place".     Like "B&W matrix" bracing .... but you don't need to quite go that extreme IMHO.

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17 hours ago, BioBrian said:

Also, the 3" voice coil and greater power handling appealed.

"greater power handling"?

 

The AE TD15H-8 - 500W (cont).

AE_TD15H-8_spec.jpg.9f6f6e83fc81589683200256fc0034c1.jpg

 

The SB42FHCL75-6 - 300W.

SB42FHCL75-6_spec.jpg.c923a18c24fa0d905b32fc9a249cd3fc.jpg

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3 hours ago, BioBrian said:

Does anybody have experience using Green Glue to laminate speaker box panels?

I got better results using significant bracing. Think B&W Matrix.

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18 hours ago, BioBrian said:

The blue trace, the AE driver, was very appealing, but both are completely blitzed by the (red) FHCL

You and I have a very different idea of 'blitzed'. By the time it's in room, you won't be able to tell the difference based on those sims. Also remember, that the sims assume the drivers are completely linear throughout their excursion based on their T/S or small signal characteristics so cannot and do not take into consideration the surround, spider and motor linearity. A driver can have a specified Xmax, but only a fraction of that usable because of said non-linearity.

 

Do you actually have a measurement system?

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1 hour ago, soundbyte said:

"greater power handling"?

OK, this looks like I made a glaring error - thanks Russell. Brain overload.

 

I think either driver would suit the intended purpose in this case. I came away from the search thinking that because of the frequency performance of the AE drivers, they were less of a pure sub. This was supported by a post from Paul Spencer back in 2015 about the TD18H still needing a "sub" below.

Edited by BioBrian
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@davewantsmoore and @A9X, thanks for your posts re my comment "completely blitzed". I know I have a tendency for overstatement and cheap theatrics, but to me the SB42FHCL version looked better in WinISD.

 

As a passive driver sub, I want something that will produce 20 Hz with the least effort, and the least overshadowing by, say, 30 Hz.

 

The 3 traces were for drivers in the same sized vented enclosures, so include output from vents. Not sure about response using more than 2.83 V, but maybe you guys can see this.

 

In the same graph, the "L" says it puts out 3dB more at 20 Hz, and nearly 5 dB at 10 Hz (not that I'm bothered about 10 Hz).

 

Could you please explain what I'm not getting? Does it mean WinISD is not fit for purpose?

 

It may be not too late to cancel the SB order, as Wagner apparently didn't post them on Friday.

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Another issue that's come up since ordering is from reading a comment by @almikel, also I think from 2015, that has pointed to the SB "L" having an Le of 2.1 mH, and the AE 5 times lower, this having a significant effect on lower frequency response. My error here is that I had thought 2.1 was pretty low.  Not sure of the implications here.

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1 hour ago, A9X said:

I got better results using significant bracing.

2 hours ago, davewantsmoore said:

Use extensive bracing

 

2 hours ago, davewantsmoore said:

Use extensive bracing to "lock the walls in place".

 

I think this part is in hand - my previous builds didn't raise any doubts, from memory.

 

Awesome footage of the B+W building! Putting the hard-ish foam in the back is interesting.

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19 minutes ago, BioBrian said:

Awesome footage of the B+W building!

Link?   Would like to see that!

 

Still thinking on how to build spheres, just for fun.

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1 hour ago, A9X said:

based on those sims

... but the sims shown are only the "transfer function magnitude" tab .... which tells nothing .....  ie. we don't know that drivers higher/lower on there will be actually higher/lower in SPL.

 

That being said, I'd expect all drivers to hit zero on the  "transfer function magnitude" view .... so given they're not, then I don't know what is going on.    Perhaps the mentioned HPF and LPF have caused that.

 

Anyways... the proof in the pudding is on the SPL tab

 

.... and also the power handling tab ;)

 

... and if they have significantly different Xmax or construction, then perhaps the max power/SPL tabs.

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1 hour ago, BioBrian said:

but to me the SB42FHCL version looked better in WinISD.

 

My comment wasn't about the power handling.    It was that the picture you posted - doesn't (necessarily) show that one driver is better than the other.    You need to look on the SPL tab.     The transfer function magnitude screen isn't showing what it seems like you think it is  ;)

 

1 hour ago, BioBrian said:

In the same graph, the "L" says it puts out 3dB more at 20 Hz, and nearly 5 dB at 10 Hz (not that I'm bothered about 10 Hz).

No  (unless I've missed something, in which case, sorry).   Do this:

 

Set each driver to 2.83v 

Turn off all EQ/filters

Go to the SPL tab

 

Post pic.

 

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38 minutes ago, davewantsmoore said:

Set each driver to 2.83v 

Turn off all EQ/filters

Go to the SPL tab

 

Post pic.

Red - SB42FHCL (new toy)

Black - SBFHC (old toy)

Aqua - AE TD15H

All with no filters, set to 2.83V (thanks Dave, didn't know I could do this)

 

1769022569_3woofnf2.83VSPL.JPG.e37015b5b6b15672570606b161abc3ae.JPG

 

And "Max Power":

 

1599762147_3woofnf2.83VMaxPower.JPG.97a6af5a33c46824b14f9c3e460ac680.JPG

 

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OK.

See how at 200Hz, the AE driver is ~1dB lower than the others?  (which is about what you'd expect given their datasheet specs)

 

What this is telling me, is that your box for the AE driver is poorly designed.  (ie. it should be ~103dB @ 30Hz) .... and the same issue (but less impacting) for the "new toy" driver.

 

 

 

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Re: which driver is better?

 

I'd say the decider 100% comes down to how hard they will be driven.    There are reasons to think that the AE driver will perform a lot better under significant power and excursion.

 

https://www.audioxpress.com/article/test-bench-the-sb42fhcl75-6-15-subwoofer-from-sb-acoustics

 

 

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2 hours ago, davewantsmoore said:

your box for the AE driver is poorly designed.

Hi Dave, thank for your attention to this again.


My design criterion is to get max volume (efficiency) at 20 Hz, so the boxes/vents have been tuned to achieve this. Whether it's good or poor, that's what I've used WinISD to present.

 

I found a couple of driver data entry anomalies, which I've corrected - let's see if that sticks? Also, it kept changing the 2.83 V back to 2.8, so I've let it.

 

This new pic is just the 2 drivers of interest - red still the SB42FHCL, blue is AE TD15H. Does that look more like what you were expecting?

 

225331277_2woofcorr.JPG.26dca8a39b1f057f7066f5c4c7fe0c29.JPG

 

Also, not sure if you saw this, but they will be cut off around 60-80 Hz, just being augmenting subs.

 

I have no interest in them doing stage reinforcement - just clean quiet hi-fi noises, like bass drum and organ at easy listening levels.

 

Please let me know if "poor" is going to give bad or destructive results.

 

Still no word from Wagner re my order...

 

 

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Russell, it was very refreshing to have you and Linc down yesterday. Thank you (both) for all your advice and discussion. Nice pic from your phone, too.



Thanks for having us Brian. Always a pleasure listening to your system, although briefly! Really enjoyed just sitting and having a chat. My place next time. Will PM you when I work out a time and date.
Thanks again mate.
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4 hours ago, BioBrian said:

Also, it kept changing the 2.83 V back to 2.8, so I've let it.

I don't use this version of winisd (I'm stuck on the older one).... but I suspect it is just rounding what it is displaying to x.x

 

 

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On 28/04/2019 at 6:54 PM, BioBrian said:

Another issue that's come up since ordering is from reading a comment by @almikel, also I think from 2015, that has pointed to the SB "L" having an Le of 2.1 mH, and the AE 5 times lower, this having a significant effect on lower frequency response. My error here is that I had thought 2.1 was pretty low.  Not sure of the implications here.

It's complicated.

 

The inductance slows the change in current in the voice coil.    This means that the current can't change quickly .... this means the driver can't play high frequencies....  This is why an inductor, rolls off higher frequencies.

 

The other, and more problematic issues .... is that as the voice coil moves in and out ..... the amount of inductance (the Le parameter) in the driver varies.    If you looked at the impedance of the driver vs frequency .... while the driver was moving, the impedance curve would wobble around.

 

This created non-linear (harmonic and intermodulation) distortion .... which increases with increasing excursion.

 

It's one of the reasons why I said it's expected the AE driver would work better at high power (ie. high excursion)

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5 hours ago, BioBrian said:

My design criterion is to get max volume (efficiency) at 20 Hz, so the boxes/vents have been tuned to achieve this

"Poor" is perhaps being a bit of a doomsayer.

 

This issue you'll face is that:

 

The small vent (making it bigger will make it too long) causes turbulence and compression...  that winisd doesn't model.

 

You will need multiple filters to make the driver behave.

  • Perhaps - a high pass (otherwise there's a theoretical risk of damage at very LF, even at home levels)
  • A filter in band to cure the rolloff stating below ~200Hz.    In my sim I just did, I was able to get away with a simple 6dB/octave filter.
  • A low pass filter

All of them will require enormous values.... not to mention the bass is still uncorrected for any issues in room.

 

There are a lot of reasons to consider if a sealed box will work.   Typically you would only avoid a sealed box if you wanted to lower power and/or excursion for your desired max SPL....  but with drivers like these, they are within their comfort zone.

 

With the AE driver you only need 120w and half of xmax to get to 105dB@ ~20Hz

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OK what about this.

 

SB42FHCL driver. 320 l box. 150 x 348mm vent (dare that to chuff!). 36W input. 60Hz LP filter (imagine around 18mH C-coil (rated to 2000W), and 100-300uF parallel cap as 2nd Order:

 

122631072_L36W60HzLP.JPG.20fdd2fd794cc1b9d0f8183b4fbe2717.JPG

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Personally, I'd want a steeper cutoff.    (It's too loud at 200Hz)

 

... but more so, the idea of putting 36w (perhaps even double that) through a huge inductor and a capacitor... on the way to my speaker driver - doesn't seem like a very good plan.

 

People argue about the distortion these components create even when they are much smaller, and the energy transfer is much lower.    If we accept the views (I'm not 100% sure) that there is something to these people claims  (for example, different components sound different) .... then using them at all - let along in this situation - seems like a bad strategy.

 

Quote

dare that to chuff!

It's only 6 and a bit litres.  ;) 

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On 28/04/2019 at 6:54 PM, BioBrian said:

Another issue that's come up since ordering is from reading a comment by @almikel, also I think from 2015, that has pointed to the SB "L" having an Le of 2.1 mH, and the AE 5 times lower, this having a significant effect on lower frequency response. My error here is that I had thought 2.1 was pretty low.  Not sure of the implications here.

Quite a while since I've been back here...other priorities...but I think @davewantsmoore has covered it - lower inductance affects the upper end, not the lower end...

 

...but on my previous investigations of the Acoustic Elegance range of drivers, if looking to produce down to 20Hz without DSP, and you can manage a large box, the IB15 was the only driver I ever found that could get to 20Hz in a sealed cabinet without EQ - it was a big box though (around 240litres) - not surprising for a driver designed for Infinite Baffle alignments.

 

Around the same time I went to the darkside and started using EQ with sealed cabinets, so I never tried the IB15s - I ended up with TD18s instead - tiny boxes and loads of EQ - but requiring a sub underneath.

The IB15s are proper sub territory, but need a big box or Infinite Baffle...

...in your scenario have you considered Infinite Baffle?

Just a thought...

 

cheers

Mike

 

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6 minutes ago, almikel said:

have you considered Infinite Baffle?

Thanks for your post, and welcome back! Hope those pesky distractions aren't too disruptive for too long.

 

Interesting about the IB15. I didn't follow through with the idea of this in a vented box. A little swayed by the presence of a pair of used TD15Hs for sale locally.

 

I was going to respond to one of Dave's posts about baffle shape, which would elicit much the same words as this:

 

My intended wall-ceiling box placement, with a 45 degree angled baffle, would effectively be an infinite baffle - ie no baffle step loss, in fact I'd expect a net gain over IB (on a flat wall) - approaching "corner placement" - huge room gain.

 

But IB implies a virtually infinite air space behind the baffle, doesn't it? It's all looking fairly similar though - my vented box size is 320 litres, so I'm guessing they won't get many Watts thrown at them.

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13 hours ago, davewantsmoore said:

Personally, I'd want a steeper cutoff.    (It's too loud at 200Hz)

 

... but more so, the idea of putting 36w (perhaps even double that) through a huge inductor and a capacitor... on the way to my speaker driver - doesn't seem like a very good plan.

 

People argue about the distortion these components create even when they are much smaller, and the energy transfer is much lower.    If we accept the views (I'm not 100% sure) that there is something to these people claims  (for example, different components sound different) .... then using them at all - let along in this situation - seems like a bad strategy.

 

It's only 6 and a bit litres.  ;) 

The 105 dB is also a little loud!!   But yes, I could do the same as my other SB42 woofers (vented 240 l) - use a 4th order passive. Easy. I'd call that fine-tuning, and I suspect room-tuning will predominate those decisions.

 

Not sure that the parallel capacitor sound 'thing' is an issue with large bass drivers - much more a tweeter issue. Happy to do some tests. There is a new generation of electrolytic caps, but Jantzen Cross-caps aren't that much dearer (I have a couple of 150 uF here).

 

Huge inductors?  No idea how they affect sound.  Not at all, from my listening. From all the emotive stuff on "damping factor" threads, I have sort of gleaned that R is the only relevant issue there, and these C-coils have almost none. Thick, short wire. Phase and group delay may be important, but that's unfortunately something I'll have to swallow with these design parameters.

 

I had modelled the vents using 2 lengths of 102 mm ID sewer pipe, as in my previous build. At the GTG on Saturday, we played a 24/192 version of "Hotel California" through them, appreciably louder than my normal tolerance, and I held a tissue over one of the vents. It only flapped about a centimetre. I have zilch worries about a 150 mm vent chuffing, as its area is larger than the 2 x 4" pipes (177 cm^2 vs 163 cm^2).

 

Further on "passive" inductors - did you see what I think I saw, of the mH values on @acg's line-level filters?? I seriously want to know more about this approach.

 

Edited by BioBrian
GTG on Sat, not Sunday. Wish sun'd been there.
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3 minutes ago, BioBrian said:

Thanks for your post, and welcome back! Hope those pesky distractions aren't too disruptive for too long.

I've been learning how to play harmonica - a fantastic distraction!

6 minutes ago, BioBrian said:

But IB implies a virtually infinite air space behind the baffle, doesn't it?

correct - but drivers designed for IB alignments can work in sealed boxes if the box is big enough - when you sim a driver meant for IB in a sealed box you'll see it peak before roll off - the bigger the box the lesser the peak...

...if you're considering a 320 litre vented box and haven't purchased a driver yet, then consider the AE IB range, and run them in a large sealed box...or proper IB - they don't have to be on a flat wall to be IB...most IBs have a manifold (that the drivers mount on), with the manifold exiting outside.

 

IMHO I would avoid ported alignments if sound quality is the goal - too many things go awry as SPL changes - much less so with sealed or IB subs.

 

cheers

Mike

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9 hours ago, BioBrian said:

The 105 dB is also a little loud!!

Not in a max SPL sense.

 

If you think about what you measure on a SPL meter with music .... You need to add the crest factor of your content on top.    Is that 4dB?  10dB?  30dB????  ;) 

 

Otherwise what happens, is that on the "short, sharp, loud" bass tones ....  You get some sort of linear or non-linear distortion....  which typically results in either a raised noise floor (from non-linear), or a reduced level (from linear) .... both results in "indistinct" bass.

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9 hours ago, BioBrian said:

Huge inductors?  No idea how they affect sound.  Not at all, from my listening. From all the emotive stuff on "damping factor" threads, I have sort of gleaned that R is the only relevant issue there, and these C-coils have almost none.

No, it isn't a "damping factor" thing.

9 hours ago, BioBrian said:

Phase and group delay may be important

They're directly related to the frequency response in this instance ..... so, just the FR is important.

 

9 hours ago, BioBrian said:

but that's unfortunately something I'll have to swallow with these design parameters.

Yes, I guess that's my point.  :) 

 

9 hours ago, BioBrian said:

I have zilch worries about a 150 mm vent chuffing

I didn't mean to imply that was the primary problem.    It's more a "compression" issue, when you look at how the driver responds at LF vs time.

 

9 hours ago, BioBrian said:

did you see what I think I saw, of the mH values on @acg's line-level filters??

Yes.    You'll see some comments from me in his thread  ;) 

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10 hours ago, BioBrian said:

My intended wall-ceiling box placement, with a 45 degree angled baffle, would effectively be an infinite baffle - ie no baffle step loss, in fact I'd expect a net gain over IB (on a flat wall) - approaching "corner placement" - huge room gain.

At the frequencies you are talking about, the concept "of baffle step loss" is kinda nonsensical.    At LF essentially anywhere in the room you place the subwoofer it is approaching being "in the corner".

 

10 hours ago, BioBrian said:

But IB implies a virtually infinite air space behind the baffle, doesn't it?

Yes.

The practical effect of doing that is reduced power requirements vs SPL at LF.

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Looking at the drivers frequency response in a box, before you have shaped the response to your needs - is not the right way to evaluate a driver.

 

Need to mould their response to be the same (whatever your target is), then look.    A lot of the differences will go away, others will become more obvious.

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13 hours ago, BioBrian said:

Further on "passive" inductors - did you see what I think I saw, of the mH values on @acg's line-level filters?? I seriously want to know more about this approach.

It's pretty simple Brian, you jam the filter at the input of the amplifier where the voltages are much smaller, let's say 2V max (4V in my case) and use the input impedance of the amplifier as the load for the filter rather than the reactive impedance of a speaker level crossover network and transducers.  Then you direct connect your transducer to the amplifier.  It keeps the filter component values much smaller, so tiny caps and inductors.

 

In some circumstances you may even be able to build part of the filter into the amplifier itself.  For example an interstage coupling capacitor can be sized such that it creates a first order high pass filter at the desired frequency.  Couple that with a low pass filter  before the amplifier and you have a bandpass filter.

 

I've not yet read your thread Brian but the speaker photos on the front page look excellent.

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