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PostPosted: 18 Jan 2009, 18:17 
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Hello Folks, newbie question here: having read numerous reviews regarding the extraordinary bass extension of the dual-woofered (push-pull) Totem Acoustic's Mani-2, I wonder how easy it would be to modify a pre-existing speaker to something siimilar. A high current ampliifer that could cope with the halved impedance of twin main cones in parallel is likely a necessity, but the reason I ask is that I have a pair of full-range speakers whose sound, cabinetry and small size I positively adore (and have no intention of parting with), but I also have spare duplicate drivers for these speakers, and this dual-woofing could potentially alleviate the one issue I have with them -- bass extension.

I have read that there are electrical issues related not just to impedance with such a design but also the interaction with crossover (?back EMF) to consider; however, my speakers are the single cone full-range variety so this shouldn't be an issue. Presumably, there is no extra carpentry required as the push-pull aspect of the design (if I understand it correctly) implies a certain coupling of the air-mass between the drivers, which suggests that the drivers occupy the same internal free space. In effect, what I'm suggesting is simply grafting the back of the internal driver basket on to the back of the outward facing driver in a, well, 'push-pull' sense. Does this adequately capture what I'm gettintg at? Question: are the drivers connected out of phase to achieve the pushing and pulling in unison, or are they in-phase? Would the proximity of one magnet affect the other? How are the cones wired in parallel (as opposed to series)?

A far from well thought out approach to DIY to be sure, but if it could be made to work it might make a great pair of speakers perfect for someone. And, of course, it's largely reversible (hell, I could even A-B, as I have three pairs!). Any help much appreciated..

Incidentally (something to be added as a signature, but as I say I'm a noob), if I can help anyone in return with issues related to computer audio, i.e., software tools, codecs, and formats related to lossless red-book CD and DVD-A ripping and re-authoring, then please ask


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PostPosted: 18 Jan 2009, 21:09 
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Welcome davip,

You could set them up in a bipole configuration. Here is a Fostex FE127E bipole speaker that I made in a sealed enclosure. No reason why the enclosure needs to be sealed. The main advantage of a bipole configuration is that you won't need to compensate for the Baffle Step.

Which FR drivers will you be using?

Cheers,
Gio

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PostPosted: 18 Jan 2009, 21:44 
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gmilitano wrote:
You could set them up in a bipole configuration. Here is a Fostex FE127E bipole speaker that I made in a sealed enclosure. No reason why the enclosure needs to be sealed. The main advantage of a bipole configuration is that you won't need to compensate for the Baffle Step.

Which FR drivers will you be using?


Hi gmilitano, thanks for your response. I'd be working with JVC SP-UX2000 and SP-EXA1(wood cone) loudspeakers from the UX-2000 and EX-A1 micro-systems, respectively. The CD/DVD head units are nothing special, but the little speakers that come with them with their edge-wound 3.25" cones (the VGS0801-009 and CS-WD85) and solid cherry enclosures sound exceptional to my ears, bar the need for more bass. They need to be up against a wall (and need the reinforcement), so a dipole is out I'm afraid. I have heard interior-driver bass loading before and the extension achieved from even small cones is phenomenal, so this is what I'd be looking to achieve, and as I say -- if it sounds awful, I can just pull the drivers right out again. So how would I wire in parallel to achieve this?

One problem with these little speakers is their 4 ohm impedance -- doubling them up will push that down to an amplifier-unfriendly 2 ohms...

cheers,
D


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PostPosted: 19 Jan 2009, 11:11 
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Just connect them in series and get 8Ohms.
Ri

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PostPosted: 19 Jan 2009, 12:26 
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Series? Ok then, how about the phase? Would two cones back-to-back (firing in opposite directions) need to be in phase to augment output?

Actually, can someone explain how this interior driver loading (a la Totem Mani-2) actually extends bass rather than just increasing output across the board?
Attachment:
jvc_cswd85_woodcone.jpg
thanks,
Dave


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PostPosted: 19 Jan 2009, 13:00 
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By Bass Extension I am assuming you mean how low of a frequency they can reproduce at a decent SPL.
I dont know how that speaker is achieving it. Ways to do so with the same speaker would be to add stuffing to the box. It makes the speaker think there is more room in the box. Or add more room to the box. If its bass reflex you can mess with the length of the port. You could add a volume control for bass under a certain level and increase the bass that way.
Two drivers will not reach a lower frequency but the SPL of the frequency you are getting will be higher. You will have more square inches of driver and it will be easier to hit those low notes harder so you should see an increase in SPL on low notes.
BiPole/DiPole Phases: This guy over at ecoustics addresses your question
"A bipole speaker projects in two directions, equally. A Magnepan planar speaker is a mylar driver stretched over a wooden frame. Since there is no box, the mylar panel vibrates and projects its sound in two different directions at once. In a more typical bipole arrangement, you might have a box with mirror sets of drivers pointed into different directions, usually in opposite directions, or at least close to opposite. An excellent example of a bipole speakers is the PSB Image 10S, in which a matched pair of drivers are mounted on identical baffles, and angled at approximately 90 degrees from one another. Using two panels provides a much wider soundfield.

Dipole speakers are just like a bipole, with two sets of drivers, but the different driver panels are wired out of phase from one another. The purpose of wiring them out of phase is to create an even wider soundfield than bipoles provide. Wired out of phase creates a null field around the speaker where the sound cancels out, but the overall soundfield is even wider, and the cancelled out area around the speaker itself makes pinpointing the speaker difficult. I think the best example of a dipole are the surround speakers from Paradigm, the ADP line of speakers."
http://forum.ecoustics.com/bbs/messages/3/318047.html

You asked about series/parallel wiring. Parallel would be wiring the - to the - and the + to the + giving you 2ohms. Series is wiring the + of one speaker to the - of another and then the amp to the remaining + and - giving 8Ohms.
Ri

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PostPosted: 19 Jan 2009, 13:21 
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Those are great looking drivers.

As noted already, bipole speakers are in phase and dipole speakers are out of phase.

In a bipole configuration, the bass is reinforced to the point where where the baffle step takes over. Note that this will not give you deeper bass, but it will eliminate the need for a BSC.

I'm not familiar with the Totem Mani-2 and a quick search did not revel much about the design. They may be using a compound dipole:
http://www.linkwitzlab.com/x-models.htm#B1

Hope this helps!

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PostPosted: 19 Jan 2009, 15:52 
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Many thanks all, a great help. Below is a link to the speakers that rekindled my interest in such things (and the $4K price tag that makes a home-made solution desirable).

http://www.stereophile.com/standloudspeakers/462/

I'm not sure about the distinction between higher SPLs at low frequencies and increased bass extension, frequency-wise, but the figures in the review speak for themselves: this is a bookshelf speaker with a 7" cone that is flat to the mid 20s -- this has to be a product of the interior push-pull bass loading, and as I say I have heard this type of loading before and the bass is truly phenomenal (extension, rather than just volume at higher freq's).

I remain intrigued by the concept and will try this out with the JVC micro's I currently have. I don't know if one hefty magnet stuck on the back of another will affect their operation, but I shall find out. Compound dipole might be right -- I think the Totem's are isobarik-like in their arrangement.

Incidentally, if you like the cones, the wood variety and the regular poly-paper mix varieties (which JVC calls 'Hyper Neo-Olefin'), all with solid cherry enclosures, are found in the systems which I described (UX-1000, 2000, 5000 and 7000 [speakers alone are SP-UXn000]) which can all be found cheaply on Ebay -- I paid < $200 for four pairs -- which included two CD / DVD / DVD-A playing head units as well. All the cones have butyl surrounds, so don't rot. My oldest pair is 11 years old and still perfectly on-song.

cheers,

Attachment:
UX-2000 copy.jpg


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PostPosted: 19 Jan 2009, 16:33 
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How about just wiring up two of the ones that you have that are not in a cab yet. Allow them to couple magnetically and then play them. Then remove them from each other and play. See if it sounds different. It probably will. I dont think it would be best to have them actually interfering with each others magnetic fields as this is what controls the speaker. Who knows, it may change the resistance. I am unsure, but I am pretty sure it will affect there performance.
So your cabs allow for no room between the two?
Maybe they could be offset. One higher than the other. How tall are your speakers now? Maybe Gio can chime in on this. Not sure if BiPole will act weird if they are higher/lower than each other.
WOW 4 grand for speakers with about the cheapest interconnects possible. Thats a suprising price and an odd choice for them to use as interconnects.
Makes you wonder where the value comes into the price.
Ri

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PostPosted: 19 Jan 2009, 19:08 
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Some isobaric info: http://www.audiogearreviews.com/tech/th ... obaric.asp

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