[Poultrygeist]

I've read the MJK papers but can't find exact dimensions?

Also is there a preferred material and recommended thickness?

Thanks guys.

[JCS]

Martin didn't do anything exotic here.  The enclosure was 15" deep (7.5" in front and 7.5" back) and however big it needed to be for the driver to fit; maybe 16"?  He uses standard 3/4" ply with decent veneer surface. 

My opinion (based on absolutely NO experimentation) is that a bit thicker & heavier would yield some improvement--mostly because it would weigh more to hold the enclosure in place when the driver 'kicks'.  If I were building one, I might consider a marble or granite top for additional weight.

Cheers,  Jim

[Ric Schultz]

Time alignment is really important.  So, if you mount the drivers in an H frame then the mids and highs have to be set back a lot to time align with the woofs (assuming you are using passive or active, non digitial xovers.  If you are using digital xovers then you can time align using the xover.  So, that is why I like the idea of an U frame over an H frame.  The driver (s) would be on the front baffle for better looks and then the sound is not coming out a square tube and you can time align the drivers relative to the front baffle.  Make all you enclosures and dead and solid as possible.  I recommend two piece of .75 inch double refinded MDF as minimum.  Damping glue in between.  See Studiotechs speaker to see something done very serious.  The more dead and massive the enclosure/panels the more tight and clean all frequencies become.  Please damp the back of the Alpha woofs with constrained layer damping material and also brace the magnets to the base.  See pics under "funky brace". 

[maxro]

If you are using digital xovers then you can time align using the xover. 

Not with open baffles. Any "correction" to the time alignment at the front will double the original timing error at the back side. Acoustic alignment is essential.

[Russell Dawkins]

Not with open baffles. Any "correction" to the time alignment at the front will double the original timing error at the back side. Acoustic alignment is essential.

Good point! 

[Ric Schultz]

My only experience with digital delays for time aligning open baffle speakers were with two ways speakers crossed over at either 700hz or 1000 hz.  The guy with the modded CS-2s crosses his compression driver at 900hz.  All of this was done with modded Behringer DCX24/96s.  All three of these speakers used open baffle woofs with waveguides using either a compression driver or dome tweenter.  Never tried it on an open baffle speaker where the woofs and midranges were both open baffle.  We both found that changing the delay the tweeter even one millimeter makes a noticeable difference to the sound.  And one place and one place only works best.  And if you look at the physical correlation to the time it puts the drivers theoretically physically where you would think be the best setback.  So, time aligning using the digital xover was totally necessary.  If you do not delay the compresstion driver/tweeter the sound will not be good at all.  And finding the very critical amount of delay results in spectacular sound.  So, from what I and he did I would say that physical time aligning could work too but using the digital xover by itself is super, super important if you do not physically set back.  The person with the modded CS-2s did not delay the tweeter for a long time and I kept after him and when he finally did it he realized that he had never really heard the potential of the speaker at all before.  The trouble with physical time aligning is that you have to listen to every one sixteenth of an inch.  You cannot assume that physically aligning the voice coils or where you think the center of the radiadiated sound will give the best sound.  Usually the faster driver has to be put back even further.  You have to listen.  With the Behringer it is realy easy to set the delay on both channels and listen and within one minute change the delay and listen again.

[Rudolf]

We both found that changing the delay the tweeter even one millimeter makes a noticeable difference to the sound.  And one place and one place only works best.

I really feel with you, if such small differences in delay make such large difference in quality for you. Because - the geometric delay between woofer and tweeter will also change, if you move your head up or down, or forward and backward. Changing the chair you are sitting on, will probably need a new delay adjustment to arrive at the new optimum.

Sometimes it really pays that my ears are too deaf to hear changes that are less than 1 % of the considered wavelength.

Rudolf

[JohnR]

There's only one way to find out if a delay on some drivers causes a problem, which is to try it and measure it. I don't think getting a perfect response at the rear of the baffle is hyper-critical, it's not like you are going to turn it around 180 degrees and listen to it. Also, there was mention of compression drivers, so if that's the case they aren't radiating out the back anyway.

[Davey]

Ric,

You talk about these topics (time alignment, open-baffles, etc) like you're just learning about them.  'Probably better to kick back and read/learn from fellas like Rudolf who know what they're talking about.

Cheers,

Dave.

[Luigi]

My 1c worth, for this opinion isnt even good for 2c. I've made an H frame for the Alphas using MJK's dimensions, and sit my twin B200s in another separate baffle on top of these.

In my room, time aligning the Visatons by moving them back behind the plane of the woofers makes them sound dull and unlistenable. Move them right forward again, and the balance is much better, so go figure. Perhaps the reflections off the top of the H frame are causing issues, whereas up front no such problems.

Secondly, I made the H frames out of 19mm (3/4 inch) MDF, and when they're running there is very little in the way of palpable vibration on the tops of the H frames where the B200 baffle sits. I still try to isolate the baffle that holds the B200s but just dont think taking heroic steps is going to make that much of a difference.

Third, biamping the Alphas made a huge impact in my system. Despite the average reviews for the unit, I bought a two-channel Gallo Ref3 subamp which is ideal for biamping and drives the Alphas perfectly. It has dual inputs which is handy, and neat adjustments too, like bass boost, phase for each channel, full range/low pass button. And of course adjustable low pass filter, up to 210Hz. The 9.5mH passive crossovers are gone-burgers.

Fourth, I picked up some AE15 dipoles recently and while these definitely sound a bit better in my H frames than the Alphas (and also work well with the Gallo subamp) they sound amazing in my cylinder enclosures which are essentially U frames, so have the Alphas back in the H frames and the AEs for the really low stuff. No lack of open baffle bass now, no siree.

[Ric Schultz]

Some people think they know everything.  Some do not want to learn.  I know I don't know much of anything (but more than many) and I want to learn.  I also share with others what I have learned by experience.  I only post things that I have actually heard or someone else has heard whom I trust. Someone will find some good information in what I share.  This is the only reason I share, to help others.

Biamping almost always is an advantage.

If you magnet mount and basket damp the Alphas in your H frame you might get sound that equals or beats a non tweaked AE15.  The only way to know is to try.  Does not cost much.  Takes very little time.

The only way to know if making a baffle more thick and dead makes a difference is to try it.  These multi-thousand dollar speakers don't make their baffles three inch thick or out of trick stuff for nothing.  This is one of the main reasons they get great sound.

The only way to know if time aligning (digitally or phsyically) makes a difference is to change the distance and measure but especially LISTEN!  I have made many speakers over the years (both box and open baffle) and always time aligning is super critical!  My first time aligned speaker was in 1980.  Just an 8 inch Audax woofer in a box with an Audax tweeter on top and set back, felt around both drivers.  Just a coil on the woofer and a cap and resistor on the tweeter.  No binding posts, of course....hard wired directly from the transistors on my home made amps.

Years ago (early 80s) a friend made a transmission line container for two 8 inch Audax woofers that weighed something like 180 lbs.   On top he had a home made midrange container out of concrete......he molded it himself.  It had a round straight shot hole to the rear and on the front he had an isolated baffle where his 4 inch midrange driver stood.  The back wave of the driver fired into this hole that was damped and filled with increasingly dense amounts of stuffing.  On top of the midrange cement thang was another cement thang that he molded that contained both of his tweeters.  His whole speaker weighed over 250 lbs.  All 6 db per octave xovers and all time aligned.  The acceleration factor on these speakers was amazing.  The clairity through the roof.  It made Watt/Puppies at the time sound like they were going backwords....he he.  This same guy later made a woofer box out of cement and mounted large woofers in it that were magnet mounted to the rear of the cement cabinet with some kind of rods (cannot remember exactly).  He told me the bass was to die for.  I believe him.  He is the first person I ever heard of that magnet mounted bass drivers (early 80s). 

So, no matter what you think, I am going to keep preaching thick dead and braced baffles with dead damped drivers and time aligning.  These things have been proven to work and they make sense scientifically.  Many DIYers are too lazy or too righteous to take something to the next level.  Look at Studiotech....this man is a GOD!

[Luigi]

Hi Ric

 You mentioned: "If you magnet mount and basket damp the Alphas in your H frame you might get sound that equals or beats a non tweaked AE15.  The only way to know is to try.  Does not cost much.  Takes very little time."

Over the weekend I did damp the baskets of the Alphas, but not sure exactly how to go about magnet mounting. Can you explain how this works please?

Does it mean essentially that i remove the screws from the front baffle after supporting the driver from the rear? Is it merely a case of making a circle that's a tight fit for the magnet, and a support stand?

I like the concept of this, for it physically isolates the full rangers from the bass drivers, though might be tricky with an H frame.

Like you, I simply try things and if they sound better to my ears I incorporate them. Regarding time aligning of tweeter and midrange units, mine (FT17H Fostex) are rear facing, on the back of the baffle, adjacent to and between the B200s. Never really tried placing them anywhere else on the baffle; any suggestions?
Cheers

[mcgsxr]

Is it merely a case of making a circle that's a tight fit for the magnet, and a support stand?

Yes, if you search threads from years ago, a member from Costa Rica built up several cool looking implementations of magnet mounting, and he was very positive about the experience.

Lots of information to share here folks, thanks to all that chime in with ideas and share their experiences - that is the only reason I am here - I have learned so much from the generosity of the group that visits here with frequency.

No need to start in on each other about it, thanks for keeping it pleasant to date, let's keep it that way.

[JohnR]

Fourth, I picked up some AE15 dipoles recently and while these definitely sound a bit better in my H frames than the Alphas (and also work well with the Gallo subamp) they sound amazing in my cylinder enclosures which are essentially U frames, so have the Alphas back in the H frames and the AEs for the really low stuff. No lack of open baffle bass now, no siree.

Hi Luigi, interesting to hear. How long are the cylinders? Are they stuffed?

[scorpion]

Luigi,

you certainly got this right. Look at Mr Content's, Nigel in Newcastle NSW, B200 baffles: http://www.audiocircle.com/index.php?topic=57919.msg515665#msg515665 . Nigel was an early pioneer but there has been many discussions over the years here: http://www.audiocircle.com/index.php?topic=33408.0 .

Beside that it can be a good thing to hold something where the greatest mass is, the whole point of magnet mount is to decouple the speaker from the baffle or to get rid of the baffle altogether.

What are your crossover frequencies for the U- , H- and B200 baffles ?

/Erling

[Davey]

Poultry,

In MJK's paper he mentions the exact dimensions on page 3.  16" high X 16" wide X 7.5" cavity depth (each side.)  So, you have an almost perfect cube.

http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

Is that not the info you're looking for?

Cheers,

Dave.

[Ric Schultz]

I will repeat what I said (boring, yes) on another thread:  Magnet mounting and baffle isolating a midrange makes really good sense (yes, please do this...along with separate baffles for the midrange/tweets (of course, they still have to be seriously thick, dead and braced along with bracing/damping the midrange driver magnets, if you do not magnet mount). 

Not so with most woofers.  A big woofer will flex the whole front of itself when playing loud and low if it is mounted just by its magnet.  Best is to super hard mount both the basket to a super dead and thick and braced baffle and also damp the magnet by bracing it to the base or sides of the H or U frame.  Look at the pics on the thread on the "funky brace" thread.  If you have an H frame you make a piece of plywood as wide as the magnet and as long as tightly fits into the H frame.  (Make sure you have a hole in your brace if the speaker has a vent in the rear).  Put epoxy on the magnet and on the area inside where the brace will be and slide the brace into the H frame till it hits up against the magnet.  Turn the H frame on its face and put some weight on the brace till it dries.  Now the woofer magnet is braced to the H frame and the H frame is stiffened by it as well.  You can also run another brace at right angles to this first brace or use several right angle pieces glued together.  You will see a new thread later this week where he will add a right angle piece to the first funky piece. 

By bracing the magnet the small movements of the magnet/speaker frame are stopped and the transient response and clarity should be better.

[Poultrygeist]

Thanks Davey

[Luigi]

Dang, it so annoying taking the time to post, previewing, hitting the wrong button and losing the lot so to recap briefly.

John R: The PVC cylinders I have are around 40 inches tall, 16 inches in diameter and fully stuffed with dacron. People say not to use PVC but is is waaaay sturdier than Sonotube (no way you can compress it at all) and in my experience I have never heard a box sound as rigid as a cylinder. As an OB device, it is really something else.
Anyway it sits upright on three feet, each about half an inch tall, and on carpet. If you push the driver it moves easily so is definitely OB. If you sit it on the floor directly it is hard to move the driver, like sealed sub.
Have another sub almost identical, but not carpeted on the outside (so looks pretty hideous) in which I intend to stuff teh other AE15 this weekend. Hell, it's a pretty driver. I know, this is seriously sick stuff, but what I mean is that it makes the Alpha look like a thing an amateur cobbled together.

Scorpion: I now exclusively use the Gallo subamp crossover for the Alphas. By ear, they sound best when the Xover is set around 160Hz, which is round about where the passive was, so guess MJK got it right again to begin with. As he seems to have done with the H frame dimensions. The Kiega 5230 subamp is set at 50Hz for the AE15.

The B200s are driven by my Aksa 50wpc amp full range. Ive tried all sorts of circuits to tame these, but I reckon, like others, it robs them of vitality, so I just ensure there's a tube somewhere in the chain before them, and this seems to have a real calming effect on these drivers (in this case JJ 6922s in the output stage of the CD player). I dont find them fatiguing in the slightest with this set up, but stick a solid state CDP back in the system and I cant handle the B200s for long at all. Strange, but in my system the tubes are undoubtedly what tames the B200s!

Ric: Thx very much for your most useful advice. Have lots of spare wood so will have a crack at a magnet mount sometime soon. Will also play around with different rear tweeter mounting positions.

Finally, Poultrygeist, sorry for highjacking your post. I have the exact same H frames for my Alphas and they work a treat, especially if they are biamped. That's when you hear what they're really capable of.

[scorpion]

Thanks for the answer Luigi.

I suppose your sub really is some kind of Transmission Line, sort of MLTL. But of course concepts are gliding into each other. Let's say we start with an U-baffle, then move the baffle to the middle of the U-part and we would have an H-baffle, if instead we would add lenght to the U-part and also stuffing it we would be in the TL realm. Your chosen crossovers I think are just fine.

/Erling