[Duke]

A couple of months ago I started a thread asking people to tell me what they'd like to see in a loudspeaker:

http://www.audiocircle.com/index.php?topic=45525.0

Several interesting suggestions emerged - one of which still haunts me, namely Weez's tube-friendly sealed-box speaker.  Weez is no longer with us, as many of you know. 

http://www.audiocircle.com/index.php?topic=46518.0

I have decided to attempt a variation on Boris's augmented fullrange driver suggestion.  Briefly, I'm shooting for a tube-friendly impedance curve and an efficiency in the 94 dB ballpark.  I'll augment the bass with a built-in powered woofer section, and augment the highs with a supertweeter.   

One questions remains:  Would you rather see this speaker as a stand-mount, or as a floorstander?  I can think of arguments in favor of either one.

If it's a stand-mount, dimensions will be roughly 21" tall by 10" wide by 14" deep, with bass extension to about 36 Hz.  Ballpark price estimate $1500 a pair plus stands (I do not intend to manufacture stands). 

If it's a floorstander, dimensions will be roughly 36" tall by 10" wide by 11" deep with bass extension to about 25 Hz.  Ballpark price estimate $2200 a pair (calls for more expensive woofer and plate amp to get that deep bass).  I kinda like the floorstander's bass extension - looks impressive on paper even if relatively few recordings could take advantage of it. 

Let me know what ya'll think.

Duke

[Russell Dawkins]

I'd go for the latter. It would be nice to kill two birds - eliminate the need for a sub and also for a stand.

Plus I am a believer in the Bell Labs rule of 400,000 (product of upper and lower -3 dB points) being the ideal window into the sound.

[Carl V]

A couple of years ago you had a Cheetah (sp?)
speaker...it kinda sorta fit those 'ideals'...are you
revisiting that?

And I'd second Russell's idea.

Size does can you a bit of extension & sensitivity.

Good luck ...sounds nice.

[Duke]

Russell, thanks for joining in!  Your experienced opinion is the sort of thing I'm looking for, as I'm liable to go off on some impractical tangent.

Carl V, you remember the Cheetah?  Wow, you made my day!  That was my first commercial effort.  Yes, I am revisiting the Cheetah concept (so named because using a built-in powered woofer section is "cheating").

When the woofer I used in the first version of the Cheetah was discontinued I had to switch to a more expensive woofer, which unfortunately drove the price up considerably.  My enclosure cost also went up, and by then I felt that the speaker had become too expensive to really be competitive. 

In general concept this project is quite similar, though at this point I'm not planning on it being a bipolar like the Cheetah was.  I still like the bipolar format, and use it in my top-of-the-line Dream Maker.  As far as the woofer-augmented high efficiency wideband driver format goes, obviously I think it still has promise.  The problems that arose with the Cheetah were supply-related and didn't indicate deficiencies in the basic concept, assuming one accepts the somewhat limited macrodynamic capability typical of wideband drivers. 

One thing that will be different is this:  I will be limiting my wideband driver search to units that have a linear motor topology, probably using Faraday rings (shorting rings) in the magnetic circuit.  I did some experimenting in the development of another model that led me to believe magnetic flux modulation causes loss of articulation on complex passages especially at fairly high volume levels, and a fullrange or wideband driver is the type most likely to suffer from flux modulation effects.  The fix is either an alnico magnet or a ceramic magnet with well-designed shorting rings, the latter being the less expensive solution.

Well now it's off to the workshop to make some sawdust...

Duke

[bluemike]

Duke
I'm alway's looking forward to hearing what other new designs you have up your sleeve

I'm familiar with most of your speaker designs they tend to be on the large side
This new initiative looks to be addressing this point

[Duke]

Hi Bluemike,

I didn't realize anyone out there was paying attention to what might be up my sleeve!  I'm flattered that your interest in loudspeaker design and development includes my projects.

Yeah you're right about my speakers usually being pretty big.  I was assembling the prototype Boris speaker cabinet in my basement this evening, and had to double-check the dimensions because it looks so small in comparison! 

There is something else up my sleeve, but it's not ready for prime time yet.  I have a custom woofer under development that will give me an additional degree of freedom in juggling box size vs bass extension vs efficiency.  I have two or three speakers planned around this driver.

Duke

[Audiovista]

Duke,

This is great! If not too much trouble keep us posted about your progress....few pics would be interesting (anything that is not trade secret, of course). I agree with Russel, floorstanders would be my pick too.

And if you need an amp to test the speakers, I'll be happy to lend you one....we can even tweak it for different things (no feedback/low feedback, or SE amp) to give you an opportunity to evaluate different amp configurations your speakers may meet.

What is the expected sensitivity?

Best,
Boris

[Duke]

Hi Boris,

Thanks for your vote of approval. 

I will gladly take you up on your amplifier offer, provided I have the option to buy it!

It may be a while before I'm ready for your amp (tweaked or not), as first I have to test drivers & make my selection, then work on the crossover so that I will know what the impedance curve is going to look like.  I won't build stereo prototypes - the first stereo pair will be in enclosures made by my woodworker.  Well maybe those should be called the pre-production prototypes - he and I typically designate the first set of enclosures of a new design as "prototypes", which means I'll show him whatever's not right but won't give him a bad time about it because I know he'll correct it on the next set.  Sometimes it's my screw-up anyway.

I'll re-examine the crossover once I have the pre-production boxes, as the fit 'n' finish will be better so little anomalies like from drivers not being properly flush-mounted will go away.

Expected efficiency is 93-94 dB/1 watt, and I'll try to keep the impedance around 6-8 ohms.  As I recall, you said your amps work well with a 6 ohm load.

I think I want to do some measuring before going public with what drivers I'm working with, just because chances are I'll go through several drivers before picking the final ones.  I don't want to have posted about "reject" drivers, as that's not doing any favors for a driver manufacturer whose product might work great in another application, and whose services and good graces I may need in the future! 

If all goes well, an image of two test boxes appears below. 



The one on the left is being scavanged from another project (that's an improvised tweeter-holder on top, and I can make others as needed), and the one on the right was built for this project.  At first all I'll be doing is measuring various individual drivers to see which ones look promising for this application.  I should have included something to give a sense of scale... hmm.... okay, the box on the right is 36 inches tall.  (The scavanged box on the left is a mere 30 inches tall - see bluemike, I TRIED to make some small speakers once!)

At the moment I've had to put away all my measurement stuff because we have company coming for Thanksgiving and we have to turn the basement back into a people-friendly place (relatively speaking). 

Duke

[Audiovista]

I'll show him whatever's not right but won't give him a bad time about it because I know he'll correct it on the next set. 

Hi Duke,

Having met you I can hardly imagine you giving a hard time to anyone. I'm sure your woodworker is thankful for the opportunity to work with such a great guy!

Happy Thanksgiving!
Boris

[Duke]

Just wanted to give an update on where the Boris project is...

Main driver diameters that I've looked at go from 6.5" to 10".   I measure driver parameters including impedance, and measure the frequency response not only on-axis but at 7.5 degree increments all the way out to 90 degrees off-axis.  I use 1/3 octave smoothing so that I can clearly see overall trends.  This gives me a comprehensive overview of what the driver is doing.  I'm not fixated on the on-axis response; in fact, I'm more interested in what's happening off-axis. 

For the main driver, I have found two that I like.  One is a 94 dB wideband driver by Hemptone, and the other is a 93 dB prosound woofer by B&C  I'll build prototypes with each and listen to them once I've selected a tweeter.  The prosound woofer has greater macrodynamic capability, and that might be the deciding factor - but I don't know how audible this theoretical difference will be practice.  The prosound woofer is also more expensive. 

The tweeter choice is likewise unresolved at the moment, but the road ahead is pretty clear.  I've eliminated quite a few tweeters (some of which are very good in some areas).  The only ones that do what I want use some type of horn or waveguide.  I will probably use a little B&C compression driver, but haven't decided which horn lense to use.  So far I've found two that work well, and I'm waiting on a third that would be a less expensive option that still does what I want if the published curves are accurate.

On the powered subwoofer section, I've done some modelling but that's all.  Until I've made the main driver choice I won't know how loud the subwoofer will have to play to keep up, so no point in building a prototype sub until then.

Duke

[Audiovista]

Thanks for the update Duke!

[Audiovista]

Hi Duke,

It's been a while - hope everything is well. How is the project coming along?

Best,
Boris

[Duke]

Hi Boris,

Well the multi-driver concept was getting too expensive and complex so I'm going back to examining a single full-range driver augmented by a woofer section (which is what you originally suggested, if I recall correctly).  At present I'm waiting to try out a particular fullrange driver that looks fairly promising, as it has a very good motor.   

I went ahead and worked on several possible bass sections.  I presume this speaker will most likely be used in small rooms, so that figures into my juggling of trade-offs.  You see, a small room will typically have significant low frequency room gain.  For instance if the room gain is +3 dB per octave below 100 Hz, then the ideal would be a speaker whose anechoic bass rolls off at 3 dB per octave below 100 Hz.  This can be done with an appropriate low-tuned vented box but isn't practical with an unequalized sealed box.  A Qtc = .5 sealed box has a bit better impact on kickdrum, but the low-tuned vented box has better tone on a wide variety of bass instruments.   

Duke

[Audiovista]

Hey Duke,

Just checking....what did jury decide - vented or sealed enclosure?

Boris

[Duke]

Hi Boris,

On the bass thing, another factor proved to be significant:  Power handling.  The 10" woofer in the low-Q sealed box would go into gross distortion long before the half-the-cost 6.5" woofer in the low-tuned vented box.  A sufficiently long-throw sealed box woofer would avoid the power handling issue, but that would probably at least double the woofer cost.  In this case, the low-tuned vented box makes more sense to me. 

Duke

[Audiovista]

Hi Boris,

On the bass thing, another factor proved to be significant:  Power handling.  The 10" woofer in the low-Q sealed box would go into gross distortion long before the half-the-cost 6.5" woofer in the low-tuned vented box.  A sufficiently long-throw sealed box woofer would avoid the power handling issue, but that would probably at least double the woofer cost.  In this case, the low-tuned vented box makes more sense to me. 

Duke

Well, vented boxes are more difficult to do right (based on my very, very limited DIY experience) but, judging by your other products, you definitely know how to do it! 

Keep us posted....would love to see some pics when you're ready! 

Boris