Triple driver - sealed. Pros/cons, and is it too much for a newbie - diyAudio
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Old 11th November 2012, 03:41 PM   #1
MedPed is offline MedPed  United States
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Default Triple driver - sealed. Pros/cons, and is it too much for a newbie

Hi guys, I have been hanging out reading searching through and reading several of your posts and am completely blown away by the talent and enthusiasm here!!
I have not heard DIY subs, but want to give them a try. Disclaimer: I have never built speakers before!! I would appreciate any help/guidance you can offer.

By marketing materials/specs, hexagonal subs like Paradigms Sub1, Sub 2, and Martin Logan's Depth i and Descent i, look good - although the MLs are not very powerful.
I like the idea of sealed subs due to the smaller size, reputation of being more accurate/musical then slightly larger ported designs, but realize that there is probably more cost involved in way of power and drivers with these sealed units. From what I read on these forums other designs such as folded horns etc are also very accurate, without being sealed, and are far more efficient, but space may be an issue. And I am not familiar with the sound of folded horns, making me a little apprehensive. I might consider a folded horn design that is vertical, and folds over only once - placed in a corner (or two), to maintain a small foot print, if that is what you guys convince me to do.

Can someone tell me tell the pros and cons of this hexagonal triple (or six) driver design - is the vibration cancellation design hyperbole, or is it for real?
Am I a victim of marketing? or is there some merit to these designs.
Would this be too much of a task for a noob? I have a buddy who has a woodshop, and good with woodwork to help so hopefully the cabinetry will not be too much of a screwup.

I have macs, and don't have access to WinISD etc, and that totally sucks!

Of the top of my head, I was thinking of 3 x 10-12 inch drivers, and don't have the foggiest of the best way to power them, or which ones to consider.

BTW, I do not have a HT receiver, and have a 2.1 set up and therefore lack active base management - which is another area where I will probably run into trouble. I would like to budget up to $1000 for this - of course lesser the better, but am I being too stingy?

It seems on these forums, that DIY is quite addictive, so lets see if you guys get me hooked!

Thanks.
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Old 11th November 2012, 04:40 PM   #2
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Vibration cancellation is a good thing, but can be done with two speakers either side mounted or sharing a slot load.
That said, vibration as a cause of distortion would require a very light cabinet with a very heavy cone driven at very high power, the THD would far exceed any distortion attributable to cabinet movement.

Using three or six speakers in a hexagonal relationship is OK if the speakers are small enough to physically be located within 1/4 wavelength of each other. Enclosures with a diameter greater than 1/4 wavelength of the upper crossover point (34" at 100 Hz) will create peaks and dips.

A 12" speaker has some directionality at 100 Hz, personally I am not a fan of having that directionality bounced off a wall, but many like "direct/reflected" sound fields, the Bose 911 was quite popular.

Three speakers may be a bit more difficult to match to an amplifier than one or two.

$1000 is adequate to get 1-4 speakers and a plate amp with built in crossover.
Sealed speakers strictly rely on excursion for output level, longer excursion speakers cost more, and require more power to push them, your budget is ultimately determined by the SPL and low frequency extension you desire.
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Old 11th November 2012, 04:51 PM   #3
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Please post a link or image example of what this hexagonal box is?

As far as vibration cancellation? Perhaps in some regard, but not enough to write home about, imo.

The more surface area you have the higher the potential SPL. BUT, that means a smaller volume for the box, which in turn means a higher F3 point, which means you need more EQ to get a flat response below F3, which in turn means you need additional *power*, which in turn means you need greater power handling in the drivers, which then limits the max SPL. Etc...

Take a look at Bob Cordell's site, and look at the EBS woofer design, it might fit into what you are trying to do.

There is a somewhat immutable relationship between the driver's Fs, VAS and power handling WRT the box volume, then relating to the max SPL and lowest usable frequency... very little free lunch.

It's mostly a balancing act between competing aspects.

The advice I would give here is to search out a fully documented project and copy it.

The other thought is that "20Hz." is much lower than most people know or think. 32Hz. is plenty low, and more than sufficient for almost everything except for some special effects in movies, and low organ notes, etc...

One more thing, you can buy from Parts Express a complete subwoofer with enclosure, amp and driver, assembled for ~$125 (less shipping). You could stack 4 of these on a side for $1000 and have pretty substantial low end... of course this depends on your physical space and any WAF that may be involved.

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Old 11th November 2012, 05:09 PM   #4
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... How about a pair of those new 18"ers?

You still get the vibration cancellation (if you so choose), but you can avoid the complicated cabinetry and build something simple.

Get one of those Behringer DSP amps and you're good to go, with a system potent enough to (I expect) cheerfully annihilate anything you'll find in a shop.

Chris

PS - how big can this subwoofer be?
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Old 11th November 2012, 05:18 PM   #5
tb46 is offline tb46  United States
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Hi,

Maybe something like this?

Regards,
Attached Files
File Type: pdf Hexagonal.pdf (16.4 KB, 97 views)
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Old 11th November 2012, 05:46 PM   #6
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WHOA! That's insane.

A whole lot of drivers in "isobaric" on a small volume... how many kw will it take to make it go low?

If you want that sort of thing, I guess it will make sound...

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Old 11th November 2012, 05:49 PM   #7
MedPed is offline MedPed  United States
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@tb46: The shape I was thinking of was a bit like the paradigms and MLs.
I hope it is ok to share pics from their websites:
Click the image to open in full size.
Click the image to open in full size.

@chriss661: The only problem I could imagine going with pair of 18" would be the potential size.

For my information - is there value in sound quality in going for larger number of smaller drivers, eg. physically lighter, and more nuanced in their music reproduction, as well as less load/heat at the voice coils of each driver, or is this not an issue with massive 15 or 18 inch drivers. Intuitively it seems that moving a large mass would be more difficult. Or is this where DSP comes into play to keep things nice and linear? Or do I have everything all wrong!

@weltersys: I plan on crossing them over no higher than 60 Hz, how far apart would the drivers have to be?

@bear: I'll check out bob cordells site, thanks for the tip.

FWIW, I really wanted to go deep beyond 30 hz. My current sub is till about 30 Hz, I find it lacking. You are right, I do miss it more in movies, than in music, but still miss it. Occasionally (twice a year?) it would have to provide double duty to provide some reasonable output in a room full of 30 people shaking their assess to some crap music, but usually for music (all genres), and movies.

I do want the ability to play loud, but want to keep the foot print as small as possible - the subwoofer dilemma every manufacturer has. If I can get the foot print of a vertical TH design small enough to have it tower in a corner that might be acceptable to the wife, but otherwise I am looking at side table size - (big side table maybe?).

Out of curiosity - how small can you make a sealed dual 15" or dual 18". And am I hung up on this sealed issue for nothing, or is there some science behind the fact that you can go with smaller cabinetry with sealed units?

Thanks a log guys.
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Old 11th November 2012, 05:51 PM   #8
tb46 is offline tb46  United States
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Hi,

Isn't it great what you can do in AutoCAD :-). Just scratch out the drivers you don't want to use.

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Old 11th November 2012, 05:54 PM   #9
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by tb46 View Post
Maybe something like this?
Oliver, didn't know you were into engine designing for propeller planes;
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Old 11th November 2012, 06:11 PM   #10
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These designs with the multiple drivers in the tiny enclosures *require* massive EQ. That means that an awful lot of power is used up, up into the kilowatt region in order to produce output and SPL. You do gain something with greater surface area, but there is a limitation none-the-less.

You're going to trade off between power, power handling, SPL and the lowest frequency to be reproduced.

In a box that small, it's all EQ to get bass...

As far as an advantage in using smaller cones for bass is usually not there because small drivers with low Fs simply don't exist. You have to equal the Sd (area) regardless. There may be less cone breakup, and better cone stiffness (more piston like motion).

As i mentioned earlier it's going to be a design equation for trade-offs WRT what is acceptable in your room.

If you own the house, your options open up somewhat, as you can consider IB and other "built-in" solutions...
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