Lightest cones in 8", 10", 12"

[Bill F.]

I'm hoping to tap into the hive mind here for some suggestions of drivers in the 8"-12" range with the lightest moving mass. (I see lightweight 15" is being covered in another thread right now.)

I'm looking at acoustic bandpass alignments in Hornresp, and achievable bandwidth seems to be limited mostly by Mmd.

I'm not limiting my search with other parameters like motor strength, Fs, etc. right now, just looking for a selection of the lightest moving masses in drivers between 8" and 12".

Thanks in advance for any and all suggestions!

Bill

PS. Is there a large driver database somewhere that's sortable by parameter? That'd be slick.

 

[63781]

The Lowther 8-inchers are all 8.75 grams. Pretty light!

(thats just 1/3 of the Seas Excel W22EX001 !)

 

[Glowbug]

Seas Exotic F8...http://madisound.com/catalog/product_info.php?manufacturers_id=177&products_id=8320

Only 10g.

http://www.madisound.com/catalog/product_info.php?manufacturers_id=144&products_id=1474

23.1g for a 12" cone.

 

[Ron E]

PS. Is there a large driver database somewhere that's sortable by parameter? That'd be slick.

If you search on Thiele small, one of the sites that comes up has a database. You may have to calculate Mms...

 

[Bill F.]

Thanks for the suggestions.

I'll share some I'm looking at:

RCF MR8N301 8" -- 10.1g
Eighteen Sound 8M400 8" -- 14.1g

Electro Voice EVM-10M II 10" -- 20.7g
Electro Voice EVM-DL10X 10" -- 25g

Fane Studio 12B 12" -- 29g
JBL 2152H 12" -- 30g

Any more candidates in the neighborhood?

 

[tinitus]

Do you want bass, or just midbass/midrange

 

[Bill F.]

I'm looking at how production cone midbass/midrange drivers behave with acoustic lowpass filters, anywhere in a range from about 80Hz up to about 1kHz. In-box resonance usually sets the midpoint of the passband. 2 octaves isn't too hard to get without rear-chamber porting, but I'm aiming at three or better, and that seems to demand very low Mmd.

 

[tinitus]

Strange driver
10gr mms and very high sensitivity
But seems to have very limited BW
http://www.rcf.it/it_IT/c/document_library/get_file?p_l_id=251804&folderId=22488&name=DLFE-2228.pdf

Its no doubt intended, and other similar drivers seem to be the same
EMINENCE Beta-8A would seem like a better choise, and much cheaper, if 95db will do

I still have no idea what it is you talk about ?

 

[Bill F.]

Sorry for the unclear description.

If you imagine a 4th-order bandpass alignment for a subwoofer, that's the type of alignment I'm exploring in midbass and mid frequencies. Drivers are loaded by a sealed chamber in the rear and a ported "throat chamber" in the front. This front chamber of course creates a second-order acoustic lowpass filter function.

I simulated with the Beta 8A, and its useful bandwidth is pretty small in this application (Mmd/Sd is too high). But it gets much better when I arbitrarily lower the number in the Mmd field. 🙂\

That RCF MR8N301 simulates quite well in this alignment, with two octaves of useful bandwidth between 220 and 900Hz. Basically, it's intended as a mid horn driver, and I'm looking at it with the horn throat chamber but no horn flare. Call it a half-space horn. 🙂

 

[CLS]

RCF MR8N301 comes with its own 'backchamber', just like a seal-back midrange, just slightly larger volume.

 

[CLS]

Forgot to ask, other than acoustic low pass, what's the benefits of such design for a mid?

 

[Bill F.]

The acoustic lowpass filter has a lot going for it, I think. Electrical filtration does nothing to roll off harmonics and self noise originating in the driver, but acoustic filtration does. I suspect this may be a part of why horn bass and midrange often sounds so clean--their acoustic lowpass characteristic.

Also, the smaller diameter of the exit port means the effective radiating area remains acoustically small far into the stop band.

Basically, using room boundaries, I'm toying with the idea of a true half-space loudspeaker (constant directivity of 180 degrees).

 

[CLS]

Sounds terrific! 😀

But I think of something which might not be as good. It's a "compression chamber" (if in a horn), so there'd be compression. Aren't there some inferior effects like cancellations, unwanted resonances, longer group delay, some possible non-linearities in the air being compressed... etc? (I maybe wrong, of course.)

Besides, a wider range (extends higher) in such configuration needs lighter cone, but a ligher cone tends to be more fragile and (maybe) prone to breakup even earlier (happens in lower frequencies). I have no idea and kind of worry about the operation condition of a light & fragile cone in relative high pressure environment.

As I've been reading around, I found many people don't like horns because of the compression, which bring feels of congestion and, well, "compressed". It also happens in the comparisons of compression drivers with the same size diaphragm but different sizes of exits (different compression ratios).

Oh, one last thing. A driver with strong motor and light cone usually mean pro sound stuff. Ultra light cones usually mean exotic high price fullrangers. I believe very few would bury it within a little hole instead of showing it off 😆

Again, I maybe wrong. What's your opinions on these?

🙂

 

[Bill F.]

But I think of something which might not be as good. It's a "compression chamber" (if in a horn), so there'd be compression. Aren't there some inferior effects like cancellations, unwanted resonances, longer group delay, some possible non-linearities in the air being compressed... etc?

Don't see much to worry about in the simulations. In the example output below, there's a port resonance a little more than an octave into the stop band, peaking at about -17dB (other driver simulations often place the port resonance amplitude much lower). The only other blip is a throat chamber axial mode at nearly 8kHz that probably disappears completely with real-world cone damping. Group delay is well below the Blauert/Laws audibility threshold and probably pretty similar to what you'd see with electrical crossovers.

Besides, a wider range (extends higher) in such configuration needs lighter cone, but a ligher cone tends to be more fragile and (maybe) prone to breakup even earlier (happens in lower frequencies). I have no idea and kind of worry about the operation condition of a light & fragile cone in relative high pressure environment.

Valid points. This is where real-world testing is needed to determine the outer limits.

I found many people don't like horns because of the compression, which bring feels of congestion and, well, "compressed". It also happens in the comparisons of compression drivers with the same size diaphragm but different sizes of exits (different compression ratios).

To put it gently, the above conclusions are problematic. People grope for explanations of differences they hear, and they often misapply intuitive reasoning to reach their conclusions.

Using your example, let's look at two compression drivers from the same manufacturer: one has a 1.5" throat, and the other has a 2" throat. They are otherwise identical, using the same motor, diaphragm, etc. Assuming a 4" diaphragm, the average audiophile will calculate the compression ratios thusly using square inches: 12.56/1.77= 7.1:1 compression ratio for the 1.5" and 12.56/3.14= 4:1 compression ratio for the 2". Since throat size is the only difference between these two drivers, any sonic difference must be directly related to compression ratio. It couldn't be more obvious, right?

Well, wrong. The fact is that a compression driver's compression ratio isn't set by the throat area at the driver's exit, it's set by the area of the slits on the back of the phasing plug immediately in front of the diaphragm. In the two example drivers, these were likely about the same, probably upward of a 12:1 true compression ratio.

I suppose it would be possible to do a useful listening comparison of compression ratios using identical cone drivers loaded by two different-sized throats, but you would have to exactly match frequency responses, amplitudes, etc. over a full hemisphere to eliminate other variables. Otherwise it would not be a valid comparison.

Anyway, the alignments I'm looking at have at most a 7:1 compression ratio, so I'm really not worried about running afoul of air's linearity curve in even the loudest scenario in a home or studio. I'll be keeping an ear out for boundary turbulence in the port, too.

Ultra light cones usually mean exotic high price fullrangers. I believe very few would bury it within a little hole instead of showing it off 😆

Again, you're very perceptive. This is probably the paramount reason why only wonks like me would even consider this. In high-end audio, a fight between acoustic performance and sexy looks is no fight at all.

 

[Bill F.]

Forgot to attach sim...🙄

 

[tinitus]

Have you tried a vertical slot "port" ?

Though with a round "port hole" it could be interresting to try a long center plug
Ofcourse it should be mounted on pole piece

How many db is rolloff slope ?
Looks much like the closed rearchamber rolloff, so I suppose its 12db

Maybe also a vertical center "baffle" going inwards towards the cone could be interesting, with only enough distance to leave the cone space to move

 

[Bill F.]

Strictly speaking, I haven't tried anything yet, but, yes, I do have slot ports in mind when I start making sawdust. Hornresp only does axisymmetric, though.

 

[Bill F.]

I'm okay with a few OT digressions, but I'm still hoping for more suggestions of low-moving-mass drivers 12" and under.

I know some of you guys probably have whole manufacturer catalogs virtually memorized and mumble driver specs in your sleep. Pretty please? 🙂

 

[Bill F.]

Though with a round "port hole" it could be interresting to try a long center plug. Of course it should be mounted on pole piece

Something like this phasing plug contraption RCF makes for the MR10N301. Looks like it would juice oranges pretty well, too.

Or maybe a helmholz resonator mounted on the pole, tuned to cancel the exit port resonance...

Yes, rolloff is ~12dB/octave.

 

[CLS]

Thanks for the insight and clarification 🙂

It seems you are going to build a big compression driver out of a cone driver and use it without horn. Wow!

I once gathered some drivers' data and put them into a list, you may see it in this post:
http://www.diyaudio.com/forums/showthread.php?p=1649537&highlight=listmania#post1649537

The attached file more or less covers the driver sizes you need, and Mms is included. Maybe not directly helpful, but a reference.

And this is another reference I found on the web about phase plugs:
http://www.centauriaudio.com.au/diy/plugs.html