[Duke]

Recently I built a custom pair of speakers based on the Planetarium Alpha system.  My customer couldn't spare the floor space that the multisub system demands, so I built them as floorstanders with the bottom half of each speaker being a built-in downfiring subwoofer.   

The subwoofers are driven by a single external shelf-mount amplifier that puts out about 500 watts into the 8-ohm load that the subs present (they are 4-ohm subs, wired in series because the amp isn't rated for 2-ohm operation; this configuration doubles the effective damping factor).  The amp has a single band of parametric EQ and a switchable bass boost feature, so extension into the mid 20's is quite feasible.  The sub is a 10" unit with enough excursion to handle the full output of the amp down to 20 Hz, in a Qtc = .5 sealed box.  So it's nice and tight, with very solid impact on kickdrum.

The finish is a custom black stain that allows the woodgrain to show through, and then there's a hard clearcoat on top of the stain.  I think I'll call this finish Black Oak.  This is the first time I've had my woodworker do this type of finish (which was at my customer's request), and it came out really nice.  The front is solid 3/4" oak backed by 3/4" MDF, and the other surfaces are veneered MDF.  There are solid oak "skis" on the bottom for protection. 

Here's a shot of the front:



And, here's a shot of the rear:



The bottom set of binding posts is the input for the subs.  The set just above that is the input for the main speaker section.  The top set of binding posts is for the external level-setting resistor for the compression driver (which can be seen in the picture).  The port is for the midwoofer, and is tuned very low so it actually increases the power handling by reducing cone motion from bottom-octave signals.  It also decreases backpressure on the cone in the midrange region.

The 45-degree angled rear/corner panels make it easy to visually line the speakers up at  the 45-degree toe-in angle that I recommend.  This gives a very wide sweet spot, and very good tonal balance throughout the room. 

I haven't decided whether this will become a regular part of my lineup, but at least it's something I can do on a semi-custom basis since the design work has already been done.

*  *  *  *

Specifications:

Type:   Controlled-pattern monopole with built-in subwoofer

Woofer:  12" prosound type with treated paper cone and high quality motor

Tweeter:  1" compression driver, neodymium magnet, polyester diaphragm

Subwoofers:  10" long-throw, Qtc = .5 sealed box

Subwoofer amp: 500 watts into 8 ohms, 4th order filter (30-200 Hz variable), 1-band parametric EQ, switchable bass boost, continuously-variable phase control

Waveguide:   Low-coloration 90 degree constant directivity

Crossover:   1.5 kHz, asymmetrical transfer function

Impedance:   Between 8 and 12 ohms, aside from bass impedance peaks

Efficiency:   96 dB/1 watt at 1 meter

Typical System Bandwidth:   25 Hz to 17.5 kHz in-room

Power Compression:   Less than 1 dB of compression at up to 112 dB/1 meter SPL

Recommended Amplifier Power:   3-100 watts (unclipped peaks up to 200 watts acceptable)

Dimensions:   44" tall by 14.25" wide by 14" deep

Weight:  110 pounds each + 30 pound subwoofer amplifier

System Price:  $6000 in Oak finish; Black Oak (shown) slightly more

[Russell Dawkins]

Very nice! I am curious as to the sub arrangement. Are you saying the 10s in each box are in series with each other and driven by a mono amp? What is the crossover frequency to the subs? Are the 12s run full range at the low end or are they high passed?
Fascinating - I'll bet they sound sweet. They look good.

[poseidonsvoice]

Are you saying the 10s in each box are in series with each other and driven by a mono amp?

I think you got that right.

Anand.

[Duke]

Hi Russell and Anand,

Thanks for dropping in!

Yup, the two subs are connected in series with one another, driven by a "1000 watt" shelf-mount mono amp.  Into the 8 ohm load that they present when wired in series like that, the amp puts out about 500 watts. 

The crossover frequency is in the 70 Hz ballpark; I say "ballpark" because that's the theoretical -3 dB frequency of the midwoofer, but I can't say for sure that the amplifier's crossover frequency control is set at that exact frequency.  The setting I use is about 10:00 on the dial.  Depending on room acoustics and amplifier damping factor, the ideal setting could be lower or higher. 

The 12" midwoofer is indeed running fullrange (or should I say, all the way down); in other words, there's no highpass filter.   A filter isn't needed from a power handling standpoint, so there's no point in having the additional circuitry (whether active or passive).  The continuously-variable phase control on the amp can theoretically be used to fine-tune the blend in the crossover region, but I didn't use it while I had the speakers in my living room as the blend came out quite well just playing with the frequency and level controls.

My wife was sorry to see 'em leave.  That's usually a sign that a speaker has a really nice bottom end.

By the way, Anand, great avatar! [GedLee Abbeys as I recall]  Not quite as colorful as your other one, but it's a picture that's worth 1.0k words.

[poseidonsvoice]

By the way, Anand, great avatar!  Not quite as colorful as your other one, but it's a picture that's worth 1.0k words.

Yes, I quite agree. Indeed, like your speakers, they are difficult to completely describe cause you end up sounding like a little kid that just opened the cookie jar. So everybody thinks you are some freak or fanatic. It's because there is actually something fanatical to talk about finally in audio. Night and day difference compared to competing designs. Not a tweak.

Anand.

[Norris Wilson]

These look great Duke,

I am glad that you successfully integrated a subwoofer into a tower speaker design.

I am curious to know where the midbass drivers bottom frequency ends, and what type of overlap you have with it and the subwoofer?

I love the small footprint design that will help in a small room that many music lovers have to work with.

Bravo

Norris

[Duke]

Thank you, Norris.

The settings for the lowpass filter and level of the subwoofer amp are somewhat intertwined.   Suppose you want a very solid bass foundation.  You might set the level a few dB high, but then to avoid a peak in the crossover region you'd lower the lowpass filter setting a bit.  Later you decide that was a tad more bass than you really want, or you make a component change upstream, or you reposition the speakers closer to the wall.  Anyway, now you turn down the subs a bit, and to avoid a dip in the crossover region you correspondingly raise the lowpass filter setting a bit. 

In theory the continuously-variable phase control on the subwoofer amp can help dial in the transition in the crossover region, but I didn't use it when I was listening to the system.

[jsaliga]

Holy smokes these speakers are a thing of beauty!

Duke...I may be talking to you about these and how they compare to the Jazz Modules.  The more I think about it the more your approach to bass intrigues me.  I may be willing to let go my Omega Deep Hemp sub.

Could you give me the dimensions of the subwoofer amp?  If I go this route I would need to manufacture some rack space for it.

--Jerome

[jsaliga]

So everybody thinks you are some freak or fanatic.

Gee, aren't we all? 

--Jerome

[Duke]

Hi Jerome,

The subwoofer amp measures 17.5" wide by 13" deep by 4" tall.  Some ventilation space above the amp is recommended, but it doesn't seem to run hot to me.

Now if we got into something semi-custom, it might be possible to use a single plate amp in each enclosure.  That wasn't possible with the enclosure shape you see in this thread, as this geometry doesn't leave any flat surfaces large enough for a plate amp. 

[jsaliga]

Hi Jerome,

The subwoofer amp measures 17.5" wide by 13" deep by 4" tall.  Some ventilation space above the amp is recommended, but it doesn't seem to run hot to me.

I checked my rack and would have to move out one component to make room.  I don't think it will be a problem to put the amp on a shelf all by itself  with a couple of inches of space above to spare.

Now if we got into something semi-custom, it might be possible to use a single plate amp in each enclosure.  That wasn't possible with the enclosure shape you see in this thread, as this geometry doesn't leave any flat surfaces large enough for a plate amp.

I don't think that will be necessary.  Thanks for the time on the phone today.  Let me think about it for a while.  I am quite certain that I will putting an order in very soon.  I just need to make up my mind between the custom Planetarium Alpha and the Jazz modules (while keeping my existing sub).  I am leaning heavily towards the former but want to kick the idea around for a few days before making a commitment to it.

--Jerome

[jsaliga]

Well I just made my decision.  I am going to buy the custom two-piece Planetarium Alpha system finished in Natural Walnut.  I just got off the phone with Duke and finalized the order and arrangements.

Duke, many thanks!!   I'm really excited and am looking forward to hearing these speakers.  I will get a deposit out to you right away.

--Jerome 

[Duke]

Thank you very much, Jerome!

The set Jerome is getting will be Walnut, and assuming it's okay with him I'll take some pictures and post them before his pair is shipped out.

Duke

[alan m. kafton]

Hi, Duke!  How would you compare the sonics of this new speaker with the Jazz Modules that I love?  I wish I had room for either of these beauties.

Then again, I could be persuaded....how many Cable Cookers can I trade you for a pair??    

[Larkston Zinaspic]

Jerome,

Congrats and best of luck with your new acquisition. I'm hoping that you'll post a review once those speakers have settled in...hopefully you'll have some time to share your thoughts about them after you've had ample listening time.

If I had the extra space and extra cash that Planetarium Custom would've been my choice as well...truly one of Duke's more intriguing designs, IMO.

[jsaliga]

Thank you very much, Jerome!

The set Jerome is getting will be Walnut, and assuming it's okay with him I'll take some pictures and post them before his pair is shipped out.

Duke

Thanks Duke.  Feel free to take and post as many pictures as you like.

That way I can drool over them before they arrive at my door. 

--Jerome

[jsaliga]

Jerome,

Congrats and best of luck with your new acquisition. I'm hoping that you'll post a review once those speakers have settled in...hopefully you'll have some time to share your thoughts about them after you've had ample listening time.

If I had the extra space and extra cash that Planetarium Custom would've been my choice as well...truly one of Duke's more intriguing designs, IMO.

Thanks.  I'm sure I'll have plenty to say about them once they're here and settled in.

--Jerome

[Duke]

Thanks, Jerome.

Alan, the overall sound is similar, with the custom Alphas combining higher efficiency with deeper bass extension (the latter due to the built-in subwoofer section).   The Jazz Modules start out with a smoother-sounding woofer in the alnico-magnet TAD, but because I use a somewhat different crossover approach in the Alphas the net system smoothness is comparable.  The Alphas are a bit more dynamic and lively.  Maximum SPL will be mechanically rather than thermally limited in both models, and on that score the Jazz Modules probably have a bit more headroom, but either one will play quite loud in a domestic setting.  The "voicing" of either one can be adjusted by changing an external resistor that's in a cup on the back of the cabinet, which functions as a combination tilt/shelf control (it has more effect at 10 kHz than at 2 kHz).

Unless you need the higher efficiency and/or deeper bass extension and/or greater bass adjustability and/or somewhat smaller footprint of the Alphas, the Jazz Modules make more sense because they're 1.5 grand less expensive.  However if I run out of TAD woofers and am unable to get any more, I'll have to redesign the Jazz Modules to work with a different woofer.  That TAD really does offer a very nice combination of qualities, including quite deep bass extension without needing a sub.  I do have a medium-sized floorstander that will be coming online soon, but the parameters of its woofer don't allow it to go as deep as the TAD.  I frankly don't know of any woofer that has the combination of smoothness, bandwidth, and efficiency as the TAD.  Designing the low-pass section of the Jazz Modules was a real breeze.

So far I don't think I've had anyone say the bass is lacking on the Jazz Modules, but I have had people say the bass was too much at least initially.  So several customers are using extra-long port tubes (which lowers the tuning frequency, resulting in a higher but shallower bass cutoff).   I have one customer who has stuffed the ports of his Jazz Modules so they're now sealed boxes, but he has an unorthodox setup (speakers against one wall, listening couch against the other).

One advantage of the Jazz Modules is potentially smoother in-room bass due to the locations of woofer and port relative to one another.  When toed-in as recommended, the woofer and port are displaced relative to one another in three dimensions, so they interact with the room differently, and the net result will probably be smoother than bass from a single source (per speaker).   On the other hand, the subwoofer amp that comes with the custom Alphas has one band of parametric EQ, so if there's a nasty in-room bump you can do something about it.

A couple of months ago I delivered a pair of Jazz Modules to a customer who was replacing some transmission-line speakers.  He told me that it had taken him a while to get their bass to sound good, and he expected to spend a while moving the Jazz Modules around.  We plopped them down and toed them in, and right off the bat he said that their bass was smoother than the speakers they replaced.  I think the reason was the three dimensional displacement of woofer and port; his transmission-line speakers had the line terminus on the front baffle so they were only displaced in one dimension. 

Sorry for the ramble.... but hey it's my forum, right??

;o)

Duke

[jsaliga]

Hey Duke, I enjoy reading your rambling.  So ramble on!

Thanks for the PM update on my speakers.  I was very excited to hear that they will be ready to ship the week after next.  Don't forget to take some pictures and post them.  I want to have something to drool over while they are in transit. 

--Jerome

[jsaliga]

Speakerless...



My Omegas have been sold.  They are boxed up and ready to start the journey to their new owner tomorrow.  My new speakers from Duke should be here in a week or two, but in the meantime I am speakerless.  I have a nice headphone rig to fall back on so between now and when my Audiokinesis speakers arrive I will be using my AKG K1000 setup.  Still, there is no substitute for a good loudspeaker.

Duke, a check for the balance due will go out to you in the next day or two...as soon as I can get to the post office.

--Jerome