slot-loaded tc9/tg9fd paralleled for higher sensitivity. Any experience/thoughts? - diyAudio
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Old 18th September 2015, 02:33 AM   #1
Quard is offline Quard  United States
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Join Date: Nov 2012
Default slot-loaded tc9/tg9fd in parallel for higher sensitivity. Any experience/thoughts?

1) purpose of this thread is just to hear about any past experiences people are willing to share about 2 of these drivers (or similar, price-wise) in a slot-loaded parallel arrangement for ~90dB sensitivity from 300-3000 Hz. Very interested in effects on speaker distortion, whether HD or intermod.
Might try 1 Audax HM100z0, perhaps, but functional low end of its FR seems somewhat high. Comments on HD or IM of such are greatly appreciated, also.

Yes, I have read and am rereading many old (and new) XRK threads and others already posted here. Thanks, X, for all of the hard work in 2-4 inch land.
These and lany other links that you may care to post and remind me of will be accepted with great thanks.
VERY interested in recommendations re: slot size (~2/3 of total Sd?) or 3D configuration (vertical slot assumed). Are butt-cheeks, half-circle B&Oish "horn", or any other details desirable, or just don't matter?

2) Goal is to have an ~90dB 1W/1M mid, covering roughly 300-3000 hz in a 3-way. 12" to 36" baffle/cab width TBD, woodworking skills to deal with whatever.
Final xover settings/cab width to be determined after playing with various woofs / tweets / minidsp settings determined by my ear / my songs / on-site data I can manage to gather myself later. Minor xover details are NOT the main point here.

This will be a long-term, time-consuming project for me to expend some energy on, over a months/years time scale.
OB/cardioid games to proceed only after functioning sealed cab is established.

3) overkill of room/house details, so as NOT to deal with ever again on this thread:

"room" is ~18' x 21', but half of one long side is air, half of "back wall" (a short side), is air. When windows are closed, 7+ linear feet of "wall" (8' high) on each side of 2 corners where "speakers" will be placed at some distance from wall, TBD, for good or ill.

Setting is old farmhouse, of many starts/stops/additions/air-filled "doorframes"/functional windows.
~1" wooden floors throughout, with old, spotty, plaster walls on timber/lath frame beneath glued-on 1/4" paneling.
Basically "open" ground floor is roughly 8x larger than loudspeaker room.
Upstairs plan is 2/3 as large as ground floor, above narrow but open stairway.

~150-year-old basement of laid stonework below it all. pretty dry most of the time. No, I don't give a damn what you think about room/house details, just setting the context.

Thank you for any thoughts/experiences on slot-loading 2 parallel-wired TC/TG9FD drivers or similar,

-Quard, the Ignorant Busybody,
located far from "listening rooms" for cheap loudspeaker drivers.

Last edited by Quard; 18th September 2015 at 03:40 AM. Reason: more accurate phrasing for my question
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Old 20th September 2015, 07:32 PM   #2
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Location: Dallas
I had similar project in mind w series pair of 3Fe22 4ohm.
But the question is: What kind of slot best extends
horizontal dispersion for least other compromise?

Simple slot, Dumbell slot, Kolster Brandes,
Karlson, DOSC, Paraline. I'm leaning toward
DOSC, though might not be the easiest way.

And do we need to offset the focus such that
all appears to come from one point? Or is the
comb misbehavior of two drivers acceptable?
Two drivers is hardly a line array...

I need to give the simple slot a chance first.
To have a baseline for comparison, might
find there is no need for anything fancier.


Both speakers you mention come with QTS
higher than 0.7, right out of the box. Any
enclosure is going to raise this above 1...

Might not be a problem if you intend to cross
above the Q hump, but that hump might be a
problem if you intend to play much below 250.

The lower impedance Faitals, even the cheap
ferrite ones, are usefully low in Q. +3 or +4dB
more sensitive than Vifa/Tymphany for about
the same price. Beware the higher impedance
Faitals, higher Q and not as efficient. Look to
the measured graphs and half space efficiency.
Pay no attention the "copy and paste" spec of
91dB 1W/1M, that just doesn't add up...

Last edited by kenpeter; 20th September 2015 at 07:57 PM.
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Old 20th September 2015, 08:07 PM   #3
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Location: Dallas
Proper loading design put in front of cones could
raise efficiency, or lower Fs, or widen dispersion,
but any of the above cost upper end bandwidth.

I say OK to burn some upper bandwidth down to
meet the point where horizontal dispersion begins
to narrow. Full range with narrow dispersion does
not interest me, I'd rather add a thin ribbon and
match same coverage angle as the midranges.

Not really a slot, but add perforated and wavy plate
lens to options listed above. And the JBL EON shape
slot, if that's not just a dogbone slot in disguise....

Last edited by kenpeter; 20th September 2015 at 08:13 PM.
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Old 20th September 2015, 08:14 PM   #4
sreten is offline sreten  United Kingdom
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Slot loading has no effect on sensitivity / efficiency.

rgds, sreten.
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Old 20th September 2015, 09:13 PM   #5
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Location: Dallas
Ridiculous! Take the extreme example of 4th order bandpass...
Efficiency at cost of bandwidth. Put any kind of cavity with any
kind of port or slot or horn in front of a driver, same thing will
happen to some extent. Look up "efficiency bandwidth product"
as it applies to the entire system.

We can also cup the back and kill low end bandwidth to push
up efficiency, not in this case that we need to. Could raise Q
peak to a level that would be unreasonable to operate near.
A slotted (tuned) front cavity would kill both high and low end
bandwidth as it raises Q. Offering a narrower band of higher

Would not be to our midrange benefit to push luck with that,
as we want as much bandwidth as we can evenly disperse.
Choice of narrow slot for exit is mostly to do with dispersion,
but we cannot ignore that it also entraps a tuned cavity.

Slot loading is only absurd if we are talking abut ripole or
other nonsense that fails for serious lack of connection to
reality. And of course must have excessive bandwidth and
low Q to burn as prerequisite for having options on how to
spend it.

There are other threads and context where I might have
agreed with such a statement. You are not crazy to say
you have experienced something like that...

Last edited by kenpeter; 20th September 2015 at 09:18 PM.
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Old 20th September 2015, 09:26 PM   #6
Quard is offline Quard  United States
diyAudio Member
Join Date: Nov 2012
I may have presented this poorly,
the idea is that 2 mids in parallel does have a practical effect on "sensitivity",
mainly due to doubled cone area/halved resistance (as long as my amp can supply the resulting amperage increase)

slot-loading is just my way of keeping the c-to-c distance of the 2-cone mid system
as close as possible, hopefully extending the desired "point source" behavior to as high a frequency as possible.

that said, I'm going to xover to a tweeter at 3-5 kHz anyway.
rough rule-of-thumb beaming calculations (13,740/total diameter of dual-cone mid as actually implemented, in inches)
may just be way too approximate to be of any use here, even as a "something to keep in mind."

Thanks for any and all thoughts on the matter!
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Old 20th September 2015, 09:48 PM   #7
Sonce is offline Sonce  Macedonia
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Two TC9/TG9 in parallel will have 90 dB/2.83V/1m sensitivity and good horizontal dispersion at 3000 Hz, so design goals are already achieved without any slot.
C-to-C distance will not be closer with a simple slot - it needs an elaborate double-driver to single-exit waveguide to achieve that.

@kenpeter There is no bandpass action to increase the sensitivity at such a wide bandwidth from 300 to 3000 Hz, so slot will not increase the sensitivity.

Last edited by Sonce; 20th September 2015 at 10:00 PM.
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Old 20th September 2015, 10:03 PM   #8
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Location: Dallas
@Sonce Baloney.
Cavity and slot is bandpass. Pinch 100-20K down to 300-5K, efficiency increases.

Of course, a slot will spread high frequency energy over a wider angle. Expect on-
axis highs to measure very attenuated, may require CD equalization. But increase
is there if you account for energy spread to the sides. Notice I said 5K, not 3K, but
again, that's what the slot is for...

Proven example that meets the OP's requirements:
Mini Karlsonator (0.53X) with Dual TC9FD's

Last edited by kenpeter; 20th September 2015 at 10:06 PM.
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Old 20th September 2015, 10:09 PM   #9
Quard is offline Quard  United States
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Join Date: Nov 2012
Thanks, Sonce!

I was thinking a simple face-to-face arrangement,
as close to front surface of baffle as physically possible (and structurally wise),
with a simple slot opening on the baffle itself,
roughly 3.3-4" high (driver width, give or take) x about 1.5-2" wide,
as little depth as possible to accommodate full width of driver cones
(on the front-to-back axis of this arrangement)

any pictures you may have of more elaborate double-driver to single-exit waveguides
greatly appreciated.

Thanks for the input!
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Old 20th September 2015, 10:15 PM   #10
xrk971 is offline xrk971  United States
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Slot loading will kill the HF's that you are trying to get to combine with a shorter CTC distance. For a TC9 or TG9 the frame is about 3.5in wide - thus, that is the shortest slot depth and that determines the first null. 3.5in is equivalent to a 960Hz 1/4-wave cutoff. So you can slot load, but think of it as a woofer that only goes up to 1kHz.

You may be able to reduce CTC distance by mounting them at a V and open - no slot. That will still have some 1/4-wave null effect.

However, if you put two TC9's behind an acoustic lens like a K aperture you will get the increased sensitivity, better polar dispersion, and some band pass cone loading at the expense of a little coloration. However, it sounds great still. Look at dual driver Karlsonator. Lots of happy builds.
Mini Karlsonator (0.53X) with Dual TC9FD's

Last edited by xrk971; 20th September 2015 at 10:18 PM.
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