'Tandems'- an InDIYana 2018 theme driven build process...

[Wolf]

Since Bill is spilling about his 'Keeping up with the Jones' build, I thought I would as well...

I looked around for awhile for a coax that I thought would be a great candidate for this, and finally settled on the B&C 5FCX44. I had looked at it about 6 months prior for a compact 3-way, even doing a prelim simulation to test the waters, and it seemed viable for that now defunct idea. Then this theme came up and rejuvenated my interest in it. Then I found a review in Voice Coil November 2012, Volume 27, Issue 1. The linearity of the suspension, the better than spec Bl range allowing an Xmax of 5.0mm, and the high enough sensitivities lend well to smoothing out the not so flat responses. To top it off, Vance measured HD at 125dB. The compression driver is under 2% at that output above 3.5k. The woofer is (I think, it's hard to read in PDF form) 6% at the same output from 400Hz and up, except for a blip just below 1k. Since I'm not going to be using them at those levels, and the xover deals with the issues, HD will be greatly reduced.

The woofers I'm using are a quad of the KB 55-5665 series, running a pair in each cabinet in isobaric mode. Since I got them when they were for sale and not yet on closeout, per the rules, this is okay. I have been told that they may remain on sale from another company for an extended period of time, but I don't know for how long or if they will even renew the stock when depleted.

I'll elaborate more later in detail, but suffice to say that this combo lends itself well to a solid F3 of 28Hz, and the volume does not exceed a cubic foot in total. Volumes are 5 ltrs sealed, and 22 ltrs vented. Preliminary simulations dictate a reference sensitivity of just over 80dB. Unfortunately you can't get very much above that level unless you go with a larger more sensitive woofer in most cases. 88dB - 6dB BSC = 82dB reference and then DCR losses or frequency response manipulation.

So- about the name...
The coax works in tandem.
The woofers work in tandem
...and the masochistic (hint) xover also works in tandem.

This made the name aptly stated, and it stuck!

More later,
Wolf

[jhollander]

Sounds interesting. Are you doing clamshell or nested iso/ compound?

[ani_101]

Wouldn't isobaric cut the sensitivity further?

This should be a pretty sweet build.

[ani_101]

The woofers don't say they are on close out yet. Not even on sale...

[Paul K.]

Two isobaric-configured drivers wired in parallel will have the same sensitivity as a single woofer, but twice the power will be required from the power amp for the isobaric pair compared to a single driver. Thus, the primary benefit of the isobaric setup is requiring only half the cabinet volume of that for a single driver.
Paul

Wouldn't isobaric cut the sensitivity further?

This should be a pretty sweet build.

[bcodemz]

Very interesting. I've been curious about the B&C 5FCX44 for some time and thought of using it in a speaker. I'm curious how this will sound.

[jhollander]

Two isobaric-configured drivers wired in parallel will have the same sensitivity as a single woofer, but twice the power will be required from the power amp for the isobaric pair compared to a single driver. Thus, the primary benefit of the isobaric setup is requiring only half the cabinet volume of that for a single driver.
Paul

My experience was If you calm shell the drivers you take a 1-2 dB SPL hit due to the basket.

[Paul K.]

You may be correct. I built two isobaric setups long ago, one with the pair magnet-to-magnet, and the other with them aimed in the same direction, magnet-to-cone, but I've never built a clam-shell isobaric. My comment was theoretically based, not from personal experience.

My experience was If you calm shell the drivers you take a 1-2 dB SPL hit due to the basket.

[ani_101]

Thanks for the clarification - the sim I had done was for a 4 ohm in series, where the sensitivity had dropped 6 db (they were 4 ohm subwoofers). these are 8ohm for a final 4 ohm

[davidB]

What was the measuring distance when you did the clamshell?

[jhollander]

What was the measuring distance when you did the clamshell?

I clamshelled two of the Aura NS3's and as I recall measured at something less than 1 meter. It was a varient of this project. http://techtalk.parts-express.com/fo...affle-150-pair

[davidB]

First, apologies to Ben for the threadjack. Now(or then)- in the early eighties a couple who were church organists became empty-nesters and moved. It fell to me to down-size their system while keeping those bottom notes(hey-that's a good name for a sub). They had 12" Peerless woofers paired in about 6cuft boxes, ported. Vas about 10cuft. We tried face-to-face, tandem, and back-to-back. We had a measurement dip with face-to-face at my normal(then)2ft distance(about 0.8db), but in the room at 10ft it disappeared. So we went closer and further. Still there at 3ft, almost gone at 4ft. They ended up choosing tandem for looks, as it was a wash for them, performance-wise. I'm thinking the relatively larger magnet on the little guys made it worse close up.
I'll have to set up an experiment some time and do a separate thread so people can find the data.

[Wolf]

To answer a few queries-
There is a net loss of 3dB in power efficiency, but the Voltage Sensitivity remains the same. I will be doing a 3" x 7" x 10" x sub-chamber that both magnets will be inside. Cone to cabinet volume, and cone to the outside world. This should prevent a change in the FR of the inherent single driver.

Oh, and ani- I meant 'for sale', not 'on sale', They are still currently available, but the extended shelf-life is questionable.

This should explain a bit...

The mid chamber will be triangular in nature, with the short side on the front. This will reduce reflections. The width of the chamber will be the same as the ISO-chamber, and then the sides will be attached atop of them. The bottom of the mid-chamber will be the top of the port, and the top of the vented volume is the bottom of the port, so this is a slotted port; 0.75" x 7" wide, and just over 13" long. The xover will likely go on the back external, because it will likely not be a simple filter according to the sim I did yesterday (more on that later), and the sides will flank to beyond the back panel to 'cover' the installation. The picture below is still a work in progress....

Let me also say this has been a very DIFFICULT simulation. I first used the spec sheet the initial go around. It was fairly simple for what I would deem plausible. The midbass had a single LP coil and about 3 conjugate shunts of varying nature, and the tweeter was a simple 12dB with small values, and a conjugate LCR to tame the impedance as most horn xovers would utilize. High-ish parts count, but still doable.

Then I found Vance's review which were measured on a 15" x 16" baffle., and I don't know if it was flush mounted or not or in the center or not, so I will be taking measurements to verify. I used the measured impedances and T/S for the box design and xover simulations, and adapted Vance's FR plots to my baffle dims. (I did it this same way for the Nephila that used his AMT FR plots, and I didn't have to change the xover, so I'm hoping this works this time around as well.) I guess we could call the BSC an average of 2 options in this particular case.

The woofer has a breakup at ~3.8k, and there is also a rise centered at 1.2k. The horn has a large bump in the middle, a generally decreasing FR, a small peak before rolloff at 2k, and a narrow deep dip at about 17k. I left the dip alone, but I hopefully remedied the rest. I won't post the FR plots he took, as that is likely personal property. The 5665 woofers were fairly easy to blend at 350Hz where the lower xover fell into place.

If you want to play, I've attached the files I created. The pllLCR files already have a 0.9mH/15uF/15ohm parallel notch placed in series to tame the bump at 1.2k.
More later,
Wolf


BC 5FCX44_horn_Meas_Tandems.zma
BC 5FCX44_horn_Vance_Tandems.frd
BC 5FCX44_woofer_Vance_pllLCR_Tandems.frd
BC 5FCX44_woofer_pllLCR_Tandems.zma

[Wolf]

And the woofer files... All of these files are already adapted to my baffle sizes. The Z Offsets are -0.090m for the horn, -0.020m for the mid, and -0.018m for the front woofer. The CTC from horn to woofer is -0.203m. Side to side delta is nothing as they are aligned vertically.

Enjoy!
Wolf

MCMselect 55-5665 KB-ISO-Tandems.frd
MCMselect 55-5665 KB-ISO-Tandems.zma

[ani_101]

Do you have the box model / simulation for the ISO?