Ricci

 

The article suggests that larger diameter ports with greater flares can tolerate higher flow velocity before chuffing sets in.  Unfortunately, they don't address what happens with slot ports at all.  Presumably, it's not good, but maybe not so bad as to render them useless.

 

Best of luck on your design.  Unfortunately, I think port chuffing and compression are almost inevitable with ULF tuned ported and/or bandpass systems that don't have huge boxes.  The chuffing itself will very likely be more audible in the near-field, too.

Agreed. Near field does seem to be more problematic as far as port noise goes. Ports are always one form of compromise or another. It's almost impossible to get enough vent area without impractically long ports or enclosures that are gigantic.

The first comment based on Collo's work does seem to hold true in my experience. The M.A.U.L. cab models with nearly 100m/s airspeeds with full K20 signal and that's a 12" port. I knew that going in but there's only so much port you can fit and the port calculator seems to indicate that it should be reasonable performing up to perhaps 40 or maybe 50m/s. I'd say it did ok based on the testing.

Actually there was a guy who posted over at AVS awhile back who seemed to have information indicating that perhaps a large group of small vents perform better than a single large one ultimately. Think of a port like pack of straws vs a single 4" vent as would be normal. I'd always heard that you want minimal surface area inside of the port for air friction purposes but this would be the exact opposite of that. I can't remember what thread or who the poster was but I do remember that the information he linked to did seem to be legit, but I got busy and didn't really have a chance to give it much of a look.

Are you concerned about cancellation of the main subwoofers output at the seats from the nearfield subs at / near the high pass?

Thanks!

 

I have a curved sectional sofa where each seat is approximately angled toward the center of the screen.  It has a total of 7 back seat cushions and is about 10 feet wide at the extremes.  The center of the sofa is up against a wall that extends with openings on both ends.  I need to post a picture.  The near-field subs (a total of four) will be distributed behind the sofa.  They will be the same height as the back of the sofa so that they function as end-tables.  Each will consist of a dual-opposed pair of 10" drivers in side-firing configuration and a 6" down-firing port tuned in the 30-45 Hz range.  I haven't yet decided on the exact tune, and I plan to finalize the choice after they are mostly built.

What's the thought process behind tuning to 30-45Hz and not lower?

I don't think 1/8" thickness will be satisfactory if you are using ply or MDF.  It will most likely be very lossy.  Even hardboard is quite floppy at 1/8" thick.  I'd be concerned about 1/4" being to be too thin, but it depends on the length and width of the unbraced spans.  IIRC, stiffness roughly increases by 8X every time you double thickness, so you give up a lot when you reduce thickness.

Agreed. Not to mention it will also become quite fragile to shocks or other unintended incidents. Getting enough material to seal all of the joints well could be tough also.

Yah killing me Jeff. LOL

Yes, I actually did look at them, specifically the AC120, and the specs are unreal. However, when I asked opinions of them, multiple people chimed in to say the woofers measure *extremely* off spec, like Qts of 0.55 instead of 0.18. 

 

   The value factor on this project is a solid 0, but the fun factor is 12/10.

That's the exact driver I was thinking of and the first I've heard of that. I guess those specs are too good to be true.

Do you have any links to measurements or discussion? I was thinking about using the AC165 in a compact bookshelf design but not if its a fairy tale driver.

Discussion of the Cap S2 and its measurements should go here.

Hey LowerFe...Have you looked at any of the Aurum Cantus drivers? They have a couple which may work better than the SEAS for this type of project.

Any chance you would increase the enclosure size to 6.5x6.5 or maybe 7x7? That opens up a lot of more driver choices with a bit more SD. Also can you really fit the 3.5" mid and tweet in between the two drivers on a 14x6 baffle?

Someone bought the IPALs?  Nice.

Yep. Guy from Australia. I still have a pair for developing new designs and fooling around.

28HZ is the lowest loud note

Hmmm...That cannot be right on the version I listened to. Lowest note seemed to be lower in volume but is way below 28Hz or I'm losing my judgment. I'll see if I can run the version off of Spotify that I heard.

Has anyone done a spectrogram of the song "Put On" by Young Jeezy?

Not my type of music but it's popular for bass heads. Was wondering what the low note on this is. I've heard 25Hz but that is not the lowest note.

I do suspect that in the case of the M.A.U.L., it is the higher mass that is helping to stabilize the drivers when used in the series horn-loaded configuration.  I could be wrong about that, but I lean toward higher mass because it agrees with my intuition somewhat and because the mass is the parameter that's most different between the IPAL-21 and RF T3 19, IIRC.

That's what my gut instinct is as well. That's the trait that is most different between the 2 drivers. Suspension stiffness also probably plays a role. Not in this exact comparison between drivers because it is very similar but in other cases it likely does.

Welcome Travis. Looks like you've assembled yourself a nice system.

Can I hear what you had in mind for your active studio monitor? I'm surprised it is only a little bit bigger than mine. 

 

This is definitely not gonna be a passive build. I will be using miniDSP(s) as an active crossover for this speaker. I've been thinking about the compressor a lot, and I can't think of a nice way to do it with the miniDSP. The miniDSP only has a single band compressor, which will kill a lot of upper bass output with real content given the amount of boost I will be applying. While it is possible to make a DIY multiband compressor by buying multiple miniDSP's and using a mixer to combine the signal back into one, that's a lot of additional hardware. 

 

Are you aware of any DSP's that natively implements a multiband compressor, or another type of compressor?

 

 

 

Challenge accepted! 

I didn't have anything set in stone for active monitors. Mostly some general ideas and goals. They would've been a bit larger than yours. Plate amps would've been built in etc. As far as compressors a lot of the pro audio stuff has advanced limiting features.

Glad to see you started a dedicated thread.

Josh, I'm not sure if this has been asked but how the heck does this thing beat out 18" and 21" woofers with even far more sensitivity even at the upper bass frequencies like 60Hz? Including the BC21SW152, Pro5100 and BMS18N862? It matches or bests all those at 60 and just obliterates them below 60 

 

And It embarrassed the LMS5400 from pretty much  20Hz on up and the RE XX only hangs from 20 to 30hz. This thing has set a new bar, damn...I never figured a moving mass of 1Kg could do that!

Good question...Couple of reasons.

#1. I switched from the K10 amp to the more powerful K20 amp. The K20 should have about 1 to 1.5dBW higher burst output.

#2. Some of the pro style drivers are failing for distortion or even bottoming out at 50-80Hz and this limits the SPL. 280volts+ is not a joke. No issue for this driver.

#3. There are things that start to happen at those types of very large signal input levels that are different from what the small signal data suggests might. Current induced distortion gets out of hand in some drivers, others lose linearity in the suspension and /or motor and the effective motor force and efficiency drops off greatly at higher output levels. All of this can cause compression of the output so that by the time you are hitting the driver with 250 volts its performance has shifted greatly from what it was at 2.5 volts. Once the power levels get high enough you're no longer getting a full dB from the speaker per dB of signal increase. It may be a half dB or even 0.3dB. This isn't only something related to thermal heating or excursion. I see this all the time with the burst tests where thermal heating is not a factor. The RF compresses less and exhibits less behavior change with strong input signals than most other drivers. Beastly strong motor helps with the huge MMS.

#4  Magical Super Woofer Dust (Trademark of Simonian's California Bass Blingers)

For example look at the 21SW152 sealed test burst graph under static images. It is distortion limited at 50Hz and then mechanical limited before the amp runs out of gas and that was with the old K10 amp with less burst potential. The driver is actually being run out of xmax at 50Hz. Check out the 21LW1400 also. That driver is way more sensitive and efficient than the 19 but it folds up shop way sooner as well.

Dig around as in find someone who is not charging full retail price. Might need to send some emails or pick up a phone and talk to a real person.

August 2016

Updated for sale list...

I'm in the Louisville  KY metro area. No international shipping.  All equipment is used and may have a few cosmetic blemishes, etc... but is otherwise in correct functional shape.

SOLD!!!! Aurasound NS18-994-A SOLD!!!

Bought last year. Tested. Needs a good home. Good condition.  $450 shipped or $400 local pickup. I will drive a bit to meet.

SOLD!!!

2 RE AudioXXX 18d2's

Two left. Both are the overhung version 2 which has much higher motor force and the RE logo. $475ea shipped or $375 each local pickup. I will drive a bit to meet. $700 takes both of them with a local pickup!  

BMS 18n862 18's.

1 pair. Low distortion with excellent all around performance. Little bit of oxidation on the motors. $450 each shipped. $400 each local pickup.

SOLD!!!!!

B&C 21 IPAL's.

1 pair. Barely used at all. $850 each shipped. $750 each local pickup. Will drive to meet.

I got the number from here :-P

http://www.rockfordfosgate.com/products/details/t3s1-19

Right at specs. :-) easy to miss if one doesn't look.

There is a video on youtube with a better drawing but it is not a clear 3d model.

That didn't used to be in the specs from what I can remember. They seem to keep revising and adding to the information released. Some of the videos they've posted I don't remember either. That is an absolute huge amount of neo. 7+ lbs???

By the way if you dig around you can find these for under $1500 shipped. Still super expensive but over $1000 under MSRP is a significant savings.

I've thought about doing something similar before except as a slightly bigger, active studio monitor type deal. Now I can experience it through your build.

As Contrasseur said you won't have any cancellation issues until up above 250Hz with those dimensions so if something was cancelling the bass it was likely a wiring issue or something else.  What frequency are you planning to cross the woofers to the mid range? Have you decided on a midrange and tweeter?

You will need dsp to increase the low end extension like SME mentioned. Really no way around it with a cab that tiny. On the other hand it might be a good opportunity to get your hands dirty with limiter and compressor use. 30Hz extension is probably a bridge too far for something so small.

LowerFe,

If you are building an ultra small bass module and trying to squeeze as much output as possible there are a few things to keep in mind in general. You have mentioned drivers in the 2.5-5" range. These are small drivers. Displacement is limited as is the power handling of the voice coil/s and the sensitivity. You also seem to be very limited on the size of the enclosure. Even to reach normal acceptable play back levels these tiny drivers will be being pushed quite hard, so it would be best to assume that they will be operating in the upper half of the performance envelope much of the time.

45Hz extension from a 14x6x6" enclosure means it will be very inefficient. Is this your desired enclosure size? You want useful output to at least 50Hz correct? What about the budget? Where would you like to be on cost? What will the amplification be?

"Ricci style" isn't terribly concerned with efficiency, and sensitivity even less so. It's more about putting a crap-ton of power into the low corner where box size determines sensitivity, and using components with enough displacement and thermal durability to handle the juice.

 

Hey now...I'd say that's not entirely accurate.

I definitely consider efficiency and sensitivity. However if the system runs out of displacement or thermal handling very early it's sort of pointless in this day and age of extremely cheap high output amplifiers. Also once things start to heat up and behave in a less than linear manner, those small signal efficiency advantages start to disappear. The less efficient design on paper may actually become the more efficient one once operating at realistic levels seen in use. Depending upon the application of course.

Pole placed mags are usually unable to produce as much magnetic flux due to limited surface area. Clearly you can still do a lot with them but you can get more from the outer surfaces due to more area being available. However that = more cost and space. Where did you get the 3kgs of neo magnet information? I've not heard or read that. That is a LOT of NdFeb. Possibly they have pole material and outer mag material in the pillars? However the guy in the video said a single huge NdFeb slug in the pole area. I would love to see the 3D models of this driver but I doubt they'll be sharing those if I ask for them.

The motor appears to bolt on to the top assembly but the screw placement is difficult to get to and seems like an odd size as well. I think I know what's going on in there but I'm still a bit leery about taking one apart. I did figure out that the surround clamp ring has the screws hidden under the gasket.

Thanks for the video. I was just assuming the motor used magnets in the pillars rather than the pole. Seems I was wrong. I'm glad he showed the surround attachment method a bit. I'm thinking about taking one of these apart but I also don't want to screw up a $1250 driver.

The best advice I can give is to use a simulation program and use it to look at the way the system design changes the impedance curve. Start by settling on a tuning. Change the enclosure volume while keeping tuning the same and watch how the response and impedance change. Then look at how the tuning will change the impedance curve while keeping the rest constant. Lastly you can look at various drivers in the same alignment and see how that changes the curve. This is the best way to learn the tradeoffs and how the impedance curve reflects the performance.

IPAL system is powerful but it still has the limitations of any other setup. The amplifier voltage and current limits, the driver excursion limits and thermal handling etc. The driver simulation circuit can only work up to the point that some limitation is met. In that way you want the highest power handling most efficient driver possible. True efficiency of the system cannot be changed. In that way the driver modeling is interesting to me but I would concentrate more on using a very high performance driver and match the cab to the driver as much as possible so as to use very limited signal shaping. To me the DPC feedback system is the real item of note with the system.