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Old 8th April 2007, 08:32 PM   #131
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Quote:
am enjoying the thread, tho I will readily admit that the majority of it goes WAY over my head ha ha.
-me too

Thanks to this thread I am starting to visualize my next loudspeakers. Most of what I intend to use I either already own, or will fit within a meager budget.

I own a set of Eminence Beta 12CX and psd2002 compression drivers. I personally don't like the way they sound (surprise) but maybe there is hope. I think I've picked up a couple of things along the way here.

The 12CX woofer has a terrible peak at 2k -it's major flaw I think - maybe I could notch that out. I could cover the rear of the 'horn' with felt to lower reflection. Also, I could perf near the edge or put a ring of felt on the very edge of the horn, or both. I could damp the 'room side' of the compression drivers' phase plug with some type of coating. The tweeter and 12cx horn combo simply isn't very good, but efficiency is very good - too good. The curve takes a dive out to 20k. I would have to somehow create a rising response and attenuating lower frequencies would be OK due to the 105dB efficiency.

I can see this driver in a modest dipole baffle on top with a W dipole down below using a pair of the Pyle PPA15 15" per side. I am thinking of doing what Infinity did on the old RS series using wood slats to reduce diffraction and make it look good.


The 15" drivers run by an Adcom 555II actively crossed to the Eminence. The top either active or passive (??) run by a Pass or Krell clone.

Am I on a good track?
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Old 8th April 2007, 11:52 PM   #132
terry j is offline terry j  Australia
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vital states, yes, that was exactly what I meant ie I couldn't find the vifa mids used in the ariels after maybe not exhaustive but nonetheless considerable use of the google search function on the computer. Boy that came out all contorted didn't it! ha ha.

Thanks for the link, will reconsider my options now.
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Old 9th April 2007, 12:00 AM   #133
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Smile WMTMW with 21" woofers

I'm a builder that uses dipoles with pro drivers. This WMTMW uses two 21" woofers, two JBL 2123J mids and a Heil Air Motion Transformer - it was tri-amped plus a horn loaded sub. These have been retired.

WMTMW Open Baffles

Click the image to open in full size.

Now I'm using 3-way dipole line arrays with six pro ten inch woofers, twelve 5.25" mids, and thirty neodome tweeters a side plus a horn sub. Multi-amped. 120 db no problem - low compression and simply fantastic imaging with my latest 'mods'

The large line-array open baffles are the best overall speaker I have built or heard to date. crossover is at 180 and 4k with a wideband 'notch filter on the mid (ypu need to play with a line array a bit) and configured to keep cross talk cancellation at a minimum from the midbass up. Kinda like large headphones but bigger, better and more natural from a listeners perspective.
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Old 9th April 2007, 12:16 AM   #134
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Default Re: WMTMW with 21" woofers

Quote:
Originally posted by Magnetar
I'm a builder that uses dipoles with pro drivers. This WMTMW uses two 21" woofers, two JBL 2123J mids and a Heil Air Motion Transformer -
Now I'm using 3-way dipole line arrays with six pro ten inch woofers, twelve 5.25" mids, and thirty neodome tweeters a side plus a horn sub.


Magnetar,

How bad was/is dipole baffle vibration from the front radiating woofers? W-baffles with mirrored moving mass compensation are often considered necessary, as you can see from this thread. So, how much rock and roll is generated in your baffles? Over the years I've become a big fan of WMTMW topology when the room allows the size.
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Old 9th April 2007, 12:22 AM   #135
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Default Re: Re: WMTMW with 21" woofers

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Originally posted by LineSource



Magnetar,

How bad was/is dipole baffle vibration from the front radiating woofers? W-baffles with mirrored moving mass compensation are often considered necessary, as you can see from this thread. So, how much rock and roll is generated in your baffles? Over the years I've become a big fan of WMTMW topology when the room allows the size.
They were heavily braced and made froma layer of birch ply, plus underlayment backer board plus marine ply. Then braced and reinforced with pine and MDF. I started out with just the birch and kept adding layers to quiet the beasts down.

The new open back line arrays are better in all respects.

I haven't read the whole thread yet -
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Old 9th April 2007, 02:07 AM   #136
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I can't believe I almost missed this thread about my 2 favorites OB's and OB line arrays.

Some interesting possible solutions to edge diffraction, which I think is the most ignored subject in speaker design. I'm not from the camp believing that diffraction is a moot point with dipoles, since it's caused by the pressure change at the edge which is double compared to a monopole. An infinitely thin baffle may help the front and rear components cancel, but I believe they are in large part directional so diffraction can't be ignored.

I was disappointed to see in the last few pages the idea to turn the bass section into a monopole through heavy absorption of the rear wave. Just build an aperiodic box if you want that.

Instead let's have discussion about how to eliminate the TL resonance via construction shapes. It's my understanding that the fundamental resonance is caused by the air mass behaving as a lumped mass at very low frequency, then transitioning to more normal behavior higher in frequency. The tangled mass of damping material breaks up the lumped air mass behavior, thus eliminating the resonance (this is why damping is required to make U-baffles function properly according to JohnK). I've had some success with using staggered cross bracing and expanding CSA's to break up the lumped mass behavior and reduce resonance.

Magnetar, it's good to finally get some feedback about your OB arrays. I'm glad they're working out for you. How well damped is the area behind your speakers? At high SPL's I prefer the rear wave to roll off early, because too much HF in the rear wave sounds congested to me.

With my latest project, I've decided to go with Dr. Geddes' approach but in dipole form for constant directivity from top to bottom. Dipole radiation controlling things up to 500hz or so, which transitions to waveguided control above that. I really like the results so far, because I find that typical dipoles have toostrong an emphasis well off axis.

My upper section will accomodate up to an 8" driver as pictured below, with a 15" planned for the bottom. I plan to fill voids with a lot of sand to eliminate my only problem, which is significant vibration in the 4" diameter solid wood roundovers (a testament to the energy causing edge diffraction). The foam and material lining is absolutely required to eliminate colorations resulting from HOM's despite the minimal horn loading of the waveguides.

Here's a pic of my CDDWG's, Constant Directivity Dipole WaveGuides.
Click the image to open in full size.
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Old 9th April 2007, 04:06 AM   #137
BudP is offline BudP  United States
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JoninCR,

You might want to re-read the last few pages. They aren't actually about bass monopoles at all. Some cardioid bass was mentioned by Lynn, Gary Pimm's flat to 16 Hz system specifically, and then some slight discussion of how to use a specialized, infinite edge simulation pattern, with multiple, in this case likely hundreds, of ports in an attempt to make a perfectly terminated rear bass chamber for possible bipolar operation, as an alternate to the cardioid bass was also mentioned. I am not at all sure why more bass might be needed, Gary Pimm appears to have shown a clear path for integrating bass and bipolar mid and upper drivers.

Your point on the amount of power that is available at the null zone of a driver is important to note. There are some edge terminations that remove reflected energy from the cone edge, being experimented with in another thread here, the Walsh thread after page 6.

I can report that the EnABL process narrows the null zone at the periphery of a driver to just a handful of degrees. Would that help or hinder your damping procedure as shown in your pictures? This process will also eliminate edge diffraction from a baffle, regardless of it's shape, and even large radius edge contours can benefit from a less lossy termination.

The Mamboni process spoken of in earlier pages in this thread, will also remove edge diffraction by making the terminus infinite. The use of both of these tools to control driver and baffle plane reflections and energy storage, without significantly damping any of the active or passive surfaces with further energy storage mechanisms, might interest you in your future experiments.

Bud
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Old 9th April 2007, 09:41 AM   #138
peufeu is online now peufeu  France
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The Gary Pimm concept seems interesting, anyone has a link ? Google doesn't seem to know the man...
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Old 9th April 2007, 03:13 PM   #139
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EnABL and Mamboni are interesting indeed, and there may be something I can use there, though I'm really liking the 80-90deg wide null I've created at each side of my WG's. Added presence like a horn but without the coloration, a bit more sensitivity too, while they seem to retain much of the sense of space of a wide open dipole.

Re monopole, I have to disagree. If you start attenuating the rear wave at low frequencies in the bass section, there's a shift toward monopole. My room construction is primarily concrete, so I'm very sensitive to things that get away from a net pressure of zero introduced in the time domain below 200hz or so. Dispersion patterns whether dipole or hybrid with a shift toward cardiod both work for me with proper placement.

If you want more bass in an open alignment, I see only 2 choices, more drivers making EQ a requirement or lengthen the rear wave path. Before you cry foul "that's just a TL", if you use a TL only well below it's fundamental then isn't it just a U-baffle? My solution is to send the lowest frequencies on a longer path by using a Helmholtz slot to separate a portion from the rest of the rear output.

I've built 2 of these. One uses the Hawthorn coax 15, but the Qts is probably too high because cone control is lost too quickly for really high SPL. The other uses a cheap Selenium coax 15, and is in daily use at a friend's beach hotel outdoors. The 2m pathlength differential of the portion of the rear wave that enters the slot means that it actually helps reinforce the front wave down to below 30hz instead of cancelling it. The slot size and shape determine what frequencies enter the longer path. I use only 5 staggered cross braces, a little damping, and a tapered terminus with a Kslot shape in the shortest panel to prevent resonce in the 16" short pipe....nothing in the longer pathway.

Click the image to open in full size.
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Old 9th April 2007, 05:05 PM   #140
AJinFLA is offline AJinFLA  United States
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Originally posted by johninCR
With my latest project, I've decided to go with Dr. Geddes' approach but in dipole form for constant directivity from top to bottom. Dipole radiation controlling things up to 500hz or so, which transitions to waveguided control above that. I really like the results so far, because I find that typical dipoles have toostrong an emphasis well off axis.
John, can you post the measurements to show proof of concept?
Please post the measurements at varying angles so we can see that this is really taking place, instead of, perhaps mere speculation?

Quote:
Originally posted by johninCR
The foam and material lining is absolutely required to eliminate colorations resulting from HOM's despite the minimal horn loading of the waveguides.
So you have evidence of reduced HOM's here. Can you present it in the form of measured data please? Thanks.

Quote:
Originally posted by johninCR
Here's a pic of my CDDWG's, Constant Directivity Dipole WaveGuides.
That looks an awful lot like a midrange in an H-baffle, where the TL's are simply tapered, instead of constant cross section, as one would have in a typical H-baffle subwoofer.
Can you post your measurements where you confirmed this to have constant directivity? What frequencies are being wave guided? Why are high frequencies from different parts of the cone simply not reflecting around in this horn?
I guess I'll have to wait for the post of your measurements to see what might really be going on here.
Thanks in advance.

BTW, I've been following the thread from the beginning. Lots of good information - along with some good 'ol golden earred fantasy, all mixed into one. Quite entertaining so far .

cheers,

AJ
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