12" & Horn 2-way build

Hi all,

I have some RCF HF94 90x40 horns which I'd like to use for a 2-way active speaker build. I'll be building 3 speakers (left, centre, right) for home theater.
Goal is for something which can play loud effortlessly with plenty of dynamic range. The will also be used for music and need to stand up to the occasional party when the volume gets turned up also! :)

Anyway, I'm currently seeking any tips or suggestions for a 12" woofer and 1-1.4" inch compression driver that would work in this scenario. Budget caters for higher end components if worthwhile (without going super expensive though).
What do people recommend?

As for compression drivers, the B&C DE250 seems to get good reviews. Would this be suitable and be able to crossover low enough, or should I perhaps aim for something different or a 1.4" driver?

As for woofers, I'm looking at a pro audio driver to meet the output needs.

Finally, is it worth considering using a sealed enclosure for the woofer to better integrate with subs?

Thanks for your help.
Benno
 
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The horn and woofer are going to be bout 300 mm minimum C2C spacing, this results in 1/4 wavelength been at 1147 Hz, ideally you want to crossover below this frequency to avoid irregular polar response in the vertical plane. For this low frequency you will want a driver with a larger diaphragm than the typical 1.75" dome found in 1" compression drivers, so I would tend towards 1.4" throat drivers. The sacrifice with larger throat drivers is sometimes the high frequency dispersion is constrained by the throat size. Saying that there are so many cravats on that actually happening (for example):
1. Plane wave condition at the throat, if the wavefront is bent into a circular cap the narrowing is at a higher frequency.
2. No diffraction
In your case the HF94 has a diffraction slot for the wider horizontal plane so I can see no disadvantage apart from cost to go with the larger throat. Another advantage of larger throat and diaphragm drivers is that the distortion in a compression driver is mainly due to air non linearity and so as they have a greater spacial volume they typically have lower THD at a given SPL. However larger diaphragm drivers can also have more problems with the dome breaking up, particularly Ti diaphragms due to the lack of damping, so I would recommend choosing a driver using a polymer diaphragm. Be diaphragms avoid breaking up in the audible band even for a 4" diaphragm but are not in the non super expensive category:

This Faital pro driver looks great, capable of very low crossover and smooth frequency response curve indicating well controlled breakup behaviour. Not sure if its actually available yet?
HF1440

There is also the DCX464 coaxial compression drive.
 
The B&C DE250 is a very good 1" compression driver.... smooth.... capable of 1.2 - 1.3kHz crossover.
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A few 12" midbass capable of smooth 1.1 - 1.3kHz crossover to 1" horn.
--Dayton paper Dayton 12" woofer DS315P-8 $80
--Eminence DeltaPro 12A $130
--Eminence Kappalite 3012HO $190
--Faital 12PR320 $230 (I have and like the Failtal 12PR300)
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A properly designed sealed 12" cabinet will produce better transients than a ported alignment, BUT sealed has a higher -F3 frequency so woofer selection and placement is more important. A single cabinet 3-way may be more difficult to design, but it both limits the scope of the challenge and forces the designer to create a complete CAD before spending money and cutting wood. Your center channel can still be a 1" CD + horn + sealed 12" midbass.

Mark Levinson has made BIG & TALL attractive with his Daniel Hertz M1 speaker. 1" horn + 12" midbass + 18" woofer

The Tweek Geek audio Boutique in Colorado uses a pair of counter-force 12" woofers to match the area one 18" woofer.
 

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As this is got HT I would omit those 18" drivers as the frequency range <80 Hz should be taken over by your subs. Bass reflex is very useful to control cone excursion when used with appropriate high pass filtering and aids driver cooling if operating at sustained high power (by selection of a high tuning frequency). Reducing cone excursion reduces the modulation of higher frequencies the midwoofer has to produce and reduces harmonic distortion so increases fidelity.

For me the downside to ported boxes are the inevitable pipe pipe modes and mid-range leakage. This can be reduced by careful application of damping material and keeping ports short such that any problems are pushed up in frequency where the damping is effective.

Here is the kind of performance a 12" high end pro driver can get:
Test Bench: The PD.124NR1 High Power 12” Neodymium Midbass Driver from Precision Devices | audioXpress
You can observe that its above 120dB/1m down to 70 Hz which should be enough unless your home theatre is huge.
 
Goal is for something which can play loud effortlessly with plenty of dynamic range. They will also be used for music and need to stand up to the occasional party when the volume gets turned up also!

Geddes: “The mains should be designed for the best possible direct field with as flat a power response as possible. Room bass equalization using the mains could only make them worse.” Initially put your single subwoofer along the rear wall to help equalize room bass modes at the listener.
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There are benefits to building a pair of high quality 3-ways with -F3 ~30Hz to generate an optimal stereo soundstage.

1) Stereo bass down to 20Hz has been produced in low distortion, high SPL since 1982 on CDs, DVD-As, SACDs, and 5.1 movies.
2) Most people with normal hearing can identify the difference between stereo vs. mono bass. Stereo bass has phase for location.
3) At frequencies below 80Hz most people with normal hearing cannot isolate the physical location of the woofer.
-----Expert listeners can isolate location of woofers down to 60Hz by focusing on impact harmonics, port noise, upper harmonic distortion.
4) Not being able to locate the subwoofer is a good cost simplification, but summing low bass into mono degrades true stereo recordings.
5) With stereo woofers & subwoofers, any out-of-phase bass information in a true stereo (acoustic) recording is reproduced properly at full level, adding immensely to the perceived width and depth of the room in which the recording was made.
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Thanks for the input guys, much appreciated.

Based on comments and research so far, I'm leaning towards a 1.4" compression driver, as I feel this will give me more flexibility with crossover points and allow it to go lower if required. The Faital HF1440 sounds like a good choice (if available). Are there any other 1.4" drivers that get good reviews people would recommend?

As for woofers, I'm pretty sure I'll aim for a ported configuration.
As mentioned I'll have subs to fill in the <80Hz region so getting deep bass extension isn't a big priority. I consider it more of a nice to have if possible.

Kipman, I'm interested in your comment regarding pipe modes, mid-range leakage and keeping ports short. How short would you consider short?
I've been playing around with B&C 12NDL88 woofer numbers in WinISD where 2x 4" ports seem to be over 20cm in length for the manufacturer recommended box volume (40L) and tuning frequency (65Hz). Should I aim for smaller diameter ports to reduce their length, as any port chuffing is likely inaudible at high SPL's anyway?

I've also played around with the Faital 12PR320 numbers in WinISD which appears to have a little more bass extension than the B&C. Additionally it seems to extend higher in frequency also, so I'm thinking it may be a good choice and provide some added flexibility in the crossover again if required?
Are there any other popular driver people use with good results which are recommended?

Finally, from my understanding all 12" woofers seem to suffer off axis response (beaming) once they start getting up over 1-1.5kHz, so I'm running under the assumption if my target crossover frequency is around 1kHz or less, I should be fairly safe with it integrating with the horn ok? Assuming the woofer has adequate high frequency extension and doesn't start breaking up or show any irregular behaviour or off-axis response around the 1-2kHz region?
Is this a reasonably safe assumption?

Again, thanks for the comments guys.
I apologize for the noob questions :)
 
Geddes: “The mains should be designed for the best possible direct field with as flat a power response as possible. Room bass equalization using the mains could only make them worse.” Initially put your single subwoofer along the rear wall to help equalize room bass modes at the listener.
=====

There are benefits to building a pair of high quality 3-ways with -F3 ~30Hz to generate an optimal stereo soundstage.

1) Stereo bass down to 20Hz has been produced in low distortion, high SPL since 1982 on CDs, DVD-As, SACDs, and 5.1 movies.
2) Most people with normal hearing can identify the difference between stereo vs. mono bass. Stereo bass has phase for location.
3) At frequencies below 80Hz most people with normal hearing cannot isolate the physical location of the woofer.
-----Expert listeners can isolate location of woofers down to 60Hz by focusing on impact harmonics, port noise, upper harmonic distortion.
4) Not being able to locate the subwoofer is a good cost simplification, but summing low bass into mono degrades true stereo recordings.
5) With stereo woofers & subwoofers, any out-of-phase bass information in a true stereo (acoustic) recording is reproduced properly at full level, adding immensely to the perceived width and depth of the room in which the recording was made.
=====

This is something I'd like to consider or play around with by moving my subs next to or below my left/right speakers and running them stereo in future.
For the time being home theater is the primary goeal and I'm planning to stick with a 2-way setup. My only concern however is whether the 12" drivers being ported will cause issues when integrating with the subs?
 
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I like to run 4 subs at home that are approximately equi distant to the listening position in the corners of the room as this gives a very even bass throughout the room. My personal preference that I like a surrounded by sound sensation. I am also unsure of how stereo bass is compatible with room equalisation which I consider to be essential. I crossover at 120 Hz (acoustic): I can't localise the bass but I run very large subs far below their maximum output so don't have the higher frequency noise ques other people may have. I think a lot audibility of 'high' sub crossover points may be because its common to set the sub crossover electrically and assume the sub crossover is at that point acoustically. If the sub is louder than the tops then the actual acoustic crossover point is higher in frequency than the electrical. But after all try various things and see if they work, after all its not like there is a standard mastering studio.

If you model your ported box in Hornresp and correctly put in your box dimensions and port lengths you see the undesirable resonances in the frequency response graph, this will be very accurate. Hornresp also predicts vent air velocity which you should keep <17m/s. Here is some data on stuffing subs:
dB v2
Here are the calcuations you need for an open pipe (port):
Acoustic resonance - Wikipedia
I would use a single port just large enough to keep the velocity under 17m/s at maximum output with your intended high pass filter.

Crossover to your horn around 800 Hz (90 degree directivity point of the 12" driver - see audioxpress review above) however I'm not sure the horn able to control directivity this low or if distortion will rapidly increase below this point. Realistically a two way is a bit of a fudge and the crossover point is going to have to be a compromise. Perhaps you could use 48dB/octave slopes? or even steeper FIR? these can have group delay implications though.

*another unusual thing I like to do is have my speakers above sitting height and aim downwards as this produces a larger in room listening window and minimises ceiling bounce. This is a bit tricky if you speaker can't be pole mounted because its got an 18" bass driver.
 
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This is something I'd like to consider or play around with by moving my subs next to or below my left/right speakers and running them stereo in future.

My only concern however is whether the 12" drivers being ported will cause issues when integrating with the subs?

If you plan to put the (sub)woofers below or next to the 12" midrange, a sealed cabinet will give you better transients and still integrate with the adjacent (sub)woofer.

If plan to put the (sub)woofers around the room, the lower frequency bass from ported midrange cabinets typically allows better room integration.
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How deep of a speaker cabinet will fit your room / goals?

You want the center of the compression driver at a height of 36" - 39" for ear level. For breathing room around a 12" midrange you want a 15" - 18" wide cabinet.

So, consider building a cabinet of similar size like the Tweek Geek BMF-1 43”high x 16”wide x 20”deep
-OR-
A wider cabinet for larger radius edge cuts to reduce distortion, and less depth might come in about H46" W18" D17" This wider cabinet matches the 14.5" width of the popular PRV WG35 waveguide which I use (now Parts Express B-52 PHRN-1014) .

This will allow you to add a pair of counter-force 12" woofers in the future.
 
It's been my understanding that with a 2way horn system matching directivity at xo was fundamentally good practice. A 12" woofer should exhibit 90 degree pattern around 1.4 - 1.5khz. This is a function of cone diameter. A xo at 800hz would introduce mid frequency waistbanding off axis, while putting undo strain on the compression driver. IMO, this would be a poor design move. If you're after flat omnidirectional frequency response, other driver choices are in order. If not, xo that 12" driver around 1.5khz.
 
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It's been my understanding that with a 2way horn system matching directivity at xo was fundamentally good practice. A 12" woofer should exhibit 90 degree pattern around 1.4 - 1.5khz. This is a function of cone diameter. A xo at 800hz would introduce mid frequency waistbanding off axis, while putting undo strain on the compression driver. IMO, this would be a poor design move. If you're after flat omnidirectional frequency response, other driver choices are in order. If not, xo that 12" driver around 1.5khz.


I was basing that off the PD124NR measurements here:
An externally hosted image should be here but it was not working when we last tested it.

You can see that the lower 45 degree trace is at -6dB at 800 - 900 Hz. There seems to be considerable deviation from ideal piston directivity for real drivers. This emphasises that the decision should be made from measurements of the real system.

There is also the other criteria to keep acoustic sources within 1/4 wavelength so they constructively superposition throughout all positions which i calculated to result in a crossover <1147Hz.
 
I use Altec 414-8c 12" woofers in ported boxes with Altec 902 compression drivers on Edgarhorn wooden horns. 1200 hz crossover frequency using a Marchand 24db/oct crossover. I don't have any experience with other compression driver and horn combinations, but this pairing sounds very good IMHO.
 
Puppet has it right, you want to XO the woofer in it's narrowing directivity zone (where it matches the horn) but before it's breakup. That would be somewhere 1.2 - 1.5 khz depending on the horn. This also allows for a 1" compression driver for better dispersion. I think these new 1.4" super CDs are overkill for the application. B&C DE250 is a good choice. Check out Faital CDs as well, they are very nice. I happen to like the sound of polymer diaphragms.

The Faital 12PR320 would be good here if you wanted to use it in a sealed enclosure and XO to subs at 80-100hz, it has 7+mm of Xmax and a very well-behaved breakup in the upper XO zone.

Below is an interesting article on integrating horns in a domestic setting, especially the part about using the crossover lobing between the woofer and horn to "punctuate" the vertical directivity pattern. In this case the C-to-C distance between woofer and horn is chosen deliberately, not just minimized...

http://www.pispeakers.com/Pi_Speakers_Info.pdf
 
As you use them with a sub, replace the 12" for 2x6" (or 8"); you get better (more detailed) mids and you can cross at 2kHz with good off axis response to a cheaper/ smaller CD that plays higher and more detailed.

IMO sealed sounds best and is most easy to integrate with a sub.
 
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As you use them with a sub, replace the 12" for 2x6" (or 8"); you get better (more detailed) mids and you can cross at 2kHz with good off axis response to a cheaper/ smaller CD that plays higher and more detailed.

IMO sealed sounds best and is most easy to integrate with a sub.

Thanks guys.

Current speaker I have are 2x 8" and just don't have the kick I'm after.

Hard bounds for this design are as follows.
1. This is to be a 2-way design.
2. Horns are to be RCF HF94's.
3. Woofers are to be 12".
4. Cabinet width is to be around 15-16".

I'm leaning towards the following.

A ported design as most pro audio woofers seem to be more suited to this alignment and have much more output in the 100-200Hz region. My only concern was whether the extra group delay would cause issue when integrating with my subs. FYI my subs are sealed and will be placed throughout the room to give best frequency response in main listening positions.

A 1.4" compression driver as this will give me greater flexibility in the crossover and allow lower frequencies if needed. I'm thinking the HF1440 would be suitable and shouldn't restrict me higher in the frequency range.

I'm also looking at keeping the center to center spacing between woofer and horn as close as possible for better polar response. I can get this down to about 275mm.

Basic design I'm considering for now is shown in the attached picture.
 

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MTM will give +6dB more output, double the cost, more narrow vertical directivity. Vertical directivity could be too narrow though if crossover point to the tweeter is high. You could always go 3 way which would lower modulation distortion.

Have you considered coaxial? this looks pretty great if your not set on the horn:
FaitalPRO | Coaxial Loudspeakers | 10HX230

The problem with going over 1/4 wavelength spacing is not on axis, this can be corrected with appropriate phase shift for each driver not matter how far they are apart. The problem is the narrowing of vertical directivity and that there will be points illuminated off the listening axis. The reflected sound field is important and if the speaker puts out loads of energy into the room in off axis beams this is going to have a strong variance with frequency. A lot of effort has been expended by Danley, Genlec, EAW etc. producing novel designs focused on getting driver spacing as low as possible.