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Multi-Way Conventional loudspeakers with crossovers

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Old 4th February 2009, 08:50 AM   #4981
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Congratulations on getting the 604's up and running. Here's a little souvenir from the 1954 Altec catalog - a mere 55 years ago. I'm sure you'll recognize the speaker at the top left.
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Old 4th February 2009, 09:11 AM   #4982
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From the same catalog ...

Actually, I've been talking to Gary Dahl about a simplified system using a pair of 414-16's in separate closed boxes for the bass, the 288+AH425 for the mid/treble, and a 2.5 way crossover (the upper 414 covers 50~800 Hz, the lower 414 covers 50~300 Hz, with a multi-tapped lowpass inductor for the lower driver so the system can be matched to the room).

Although a box gets us back to the bad old world of box colorations again, it's simpler at the conceptual and physical level, since there's no need for bi-amplification and twiddling with room/dipole EQ to get it flat at the listening position. I'm still going ahead with the dipole, but the twin-414 approach has the merits of simplicity, tunability, high efficiency, and only requiring one amplifier per channel.
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Old 5th February 2009, 09:32 PM   #4983
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Default big big thanks to Lynn and all you guys!

Dear Lynn! And hello to all others posting so much valuable information here!

I've found this thread just a few weeks ago, and I'm still struggling to catch up. I'm approaching late 2007 now, unable to increase my reading speed while I'm busy to extract and soak up all the knowledge that's to be found here.

You've managed to answer a ton of my questions before I was only ready to verbalize them.

Thank you!

Now, why am I posting now, without a real connection to what's going on right now? Well, my decision to follow Lynn's plan in building an ultimate speaker is made for quite some time now. And as I understand an esteem his listening experience and based on that his design approach, I'm preparing to follow this path.

These days I've started collecting candidates for the wide range transducer. I'll start auditioning them as soon as I manage to install a pair of open baffles with replaceable boards in my living room. (Remember, I'm behind more than one year, so I do not know anything about midrange horns yet. )

The candidates I have or will receive soon are very different, but hopefully interesting:

Beyma 122Nd (my top three favourite, based on specs and paper, with insane driving force and the claim of a beautiful roll-off at very high frequencies)

B&C 8PL21-16 (I wonder how different an 8" may sound)

Tang Band WQ1005D (4 pcs, maybe better as low-mids)

Coral 12L27B (vintage low-mids)

I've been promised some guitar amp 12"s that are replaced, too.

18sound 12NDA520 and Precision Devices PDM.12MBH25 are still sitting the top places of my list.


I'll try to catch up with you and keep you updated about my experience at the same time.

Thanks again for all your great support!

Cheers,
Axel
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Old 8th February 2009, 01:51 AM   #4984
JoMoCo is offline JoMoCo  United States
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Default Beware of swimming w/ Giant Mantarays

Like a much improved version of this old school leviathan...
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Old 8th February 2009, 01:57 AM   #4985
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Whoa. This thread is up to 200 pages of posting now. Don't know if I'll ever find time to scroll thru them all.

I noticed there's some discussion of alnico Altec drivers. It's great if GPA offers them, because to my ears, alnico is clearly superior to mud magnets sonically.

Which sort of leads up to my Iron Lawbreakers which I have finally, after three years, 'completed'.

They use Altec 288G 16 ohm drivers with Pascalite diaphragms that GPA installed. But for the LF, I went with JBL 2220A's reconed and rezapped by GPA for the following reasons:

They have underhung VCs
They appear to be at least, if not more efficient than the most efficient Altec LF drivers.
Their VC's are 4" diameter, so have less thermal compression than 3" VCs.
They have somewhat higher power handling ratings than Altec LF drivers.
Their mounting flanges are almost an inch smaller in diameter than Altec drivers (not very important).

Of course, if the 2220A's don't sound as good as the Altec drivers, I guess the above wouldn't be that important, but without a direct comparison, they sound pretty good to me.

Now the Iron Lawbreakers are a nominal 16 ohm system, but I chose 8 ohm LF drivers because I realized that my xover circuit approach (such as using 600uF of input polypropylene series capacitance to block DC & maximize the utility of the 2220A's limited Xmax) could easily increase the LF impedance minima to be close to 16 ohm, and in the final version of the speaker, that's exactly what happened. The LF minimum is about 12 ohms at 30 hz (the port tuning), but between 16 and 20 ohms all the way from 40 hz to over 200 hz. IOW, I was able to nearly eliminate the typical BR impedance peaks which surprised me.

This is because 1) I chose the 8 ohm LF driver which cut the impedance peak amplitude by half right off the bat. 2) I added about 10 lb of activated charcoal (in gas tight bags with desiccant) to each enclosure which further cut the impedance maxima to about 30 ohms) and 3) I created an air core transformer/series filter choke for the LF xover that I could tune to both flatten the baffle step/driver LF rolloff and incidentally almost remove the remaining upper BR impedance peak.

The result is really detailed, tight bass and lower midrange in a 3.5cu ft cabinet that still sounds good backed up against a wall (natural for the 'world's largest bookshelf speaker') and with a nominal efficiency of 100db/w/m. The bass and lower midrange sound like what might be expected from an 'aperiodic' loading.

Btw, the activated charcoal was added to increase the acoustic compliance of the box air, which seems to work. Modeling shows that the cabinet behaves as if it were more like 5 cu ft, which means a couple more db of response around the 30 hz tuning, on top of the 3db extra by going to an 8 ohm driver, so there's some useable response down to this range.
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Old 8th February 2009, 01:13 PM   #4986
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Update for those patiently waiting for 425 horns: Flanges now mostly cast and drilled. Remains to finish, then pack and post.

This is a batch of 7 pairs. Normally I only do an occasional pair at a time - but this has led me to make some nice new tooling..

Drilling mounting holes accurately in the flanges has always been difficult - the bit always seems to wander however carefully one marks out, and drills the pilot hole. What works in metal just doesnt apply in calcine loaded resin. So I made a brass template using mini mill and rotary table. A spigot locates in the horn throat. A pin prevents the template from turning. A central clamp locks it down. Drilling flanges is now 10 x as quick, and accurate every time.

martin
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Old 8th February 2009, 01:33 PM   #4987
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Hand rubbing 14 horns is no joke - but I love the alabaster like finish it gives. So I modified a cheap wood lathe to make a spinner - note skate board wheel....

martin
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Old 8th February 2009, 08:43 PM   #4988
mige0 is offline mige0  Austria
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Quote:
Originally posted by thoriated
Whoa.
Btw, the activated charcoal was added to increase the acoustic compliance of the box air, which seems to work. Modeling shows that the cabinet behaves as if it were more like 5 cu ft, which means a couple more db of response around the 30 hz tuning, on top of the 3db extra by going to an 8 ohm driver, so there's some useable response down to this range.

Great - I'm gonna put some coal at the OB to minimize edge diffraction...



Lucky you - my own experiments in that direction way back didn't show any effect at all.

But if *KEF* is telling us .... Mabe the same bogus as the "inverse horn" from B&W Nautilus ?

Any verification by tough measurements ?

Michael
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Old 9th February 2009, 01:58 AM   #4989
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KEF wrote a white paper describing their implementation, and included it in some of their speakers. I also discussed with individuals in the industry my application, and saw no reason after this to doubt the efficacy of this approach. I also measured a dramatic drop in the BR upper peak magnitude from about 50 to 25 ohms after introducing the activated charcoal into the enclosure, and also a drop in the BR tuning frequency of several hz from about 35hz to 31hz. Now, I took care that the charcoal I used never adsorbed ambient atmospheric water vapor, which is supposed to seriously diminish its gaseous adsorptive capacity. Also, if the activated charcoal were totally ineffective wrt adsorption, I would have expected a rise in the box tuning frequency because of the significant volume that the added charcoal occupied, but, in fact, the opposite occurred.

Can you elaborate on your experiences with activated charcoal?
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Old 9th February 2009, 04:41 AM   #4990
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Default Pearl lite is so much cleaner to use...

the white agricultural pearl lite about the size of rice crispy works extreemly well. You must insure that the dust is remover and that particles cannot enter the driver (vents or open spiders etc.). I think the best way to use it is installed in a sealed thin wall plastic bag. This is the best most wide range acoustic damping material I have ever used. Give it a try and see what you think.
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