Just a little fun sub for the bedroom

[b_force]

I have enough projects to build. One of these is to make a little surround system in the bedroom.
Just simple and not to expensive (advanced and expensive is for the living room 8) )

The plan is to make surrounds with the B3S in a MTM setup (with a Dayton tweeter) and make a little subwoofer.

So the goal was, how can I make a subwoofer that can deliver enough power and deepness without being very big?
My girlfriend and I also like to watch a lot of music concerts, so a BR subwoofer isn't good enough.

I was lucky that a broken Detonation DT300 sub-amp came onto my path. I got it free from a guy from another forum.
A looked and tested the amp and soon I discovered that only the 300VA transformer was broken. So for 40 euro I had a nice new 300W subamp (with a 500VA transformer because it was cheaper ! )

After that I got back to the drawing-board. I first want to use Linkwitz Transform, but result of that was that I had to modify the Detonation amp.
So I looked for another solution and that was a Closed High Pass filter.

With a CHP you can boost on a passive (and cheap) way, because it's just a cap in series with the woofer.

The driver I wanted to use was the Mivoc AWM104, but I found on the market a second hand Raveland AXX1010. The Mivoc is just a newer upgraded version of the Raveland. It has almost the same parameters, but is not as ugly as the Raveland :lol:
But when you can buy almost the same driver (but a little bit more ugly) for just the half of the price, it was an easy choice.

So it was the Raveland AXX1010 in a 11 litre closed box boosted with CHP.

first the simulation without the boost:


with boost (that's 3x470uF and 220uF = 1630uF in series with the woofer)


Maybe I will use a higher cap value to make a lower Q, but I will decide that after some listening tests.

And here some building pics:


the filter:


Isn't he cute and little?




inside view:


Almost finished.
The finishing would be just white with rounded corners to make it look even smaller.
There will be also a black grill to hide the woofer, normally I don't like grills, but this woofer is just to ugly.

(I have some drawings of the project, but I have to translate it from Dutch to English if someone is interested in)

[ThomasW]

That's rather clever, I've never heard of a CHP before. Do you have any actual frequency response measurements? It would be interesting to see those comparing w/wo the CHP.

[b_force]

There is an article in the German magazine where they describe hoe CHP work.
Maybe there can be found some English articles with google?

I will do some measurement later this week or I think next week, because I'm in an exam week right now (or how do you call that in English? :P )

[ThomasW]

Maybe there can be found some English articles with google?

Tried that and found nothing

I'm in an exam week right now (or how do you call that in English? :P )

Finals.....

[Bent]

wouldn't caps in series just limit the woofer's low frequency extension?

[b_force]

Bent, that's the whole trick

You can see that also on the simulations, but it's only at the very low frequencies (20Hz or lower or so), so nothing to worry about.
Together you manipulate the total Q of the system, so you can use it as a boost, or as a sort of Linkwitz Transform (when you use even a smaller volume whit a higher total Q)

@Thomas, I thought that finals where more for ehm (I think it's) high school.
I'm studying bachelor of physics, so that's something else, but maybe my interpretation is a bit wrong.
(Exam about laser physics, totally different then just sound that's completely understandable with the classic physics, instead of quantum physics 8) )

I will try to explain the whole trick with CHP later, but I have to translate the German piece to English.
(funny when your native language is something else )

[Amphiprion]

Mike Durzko of ACI used to have a page on his website about a '3rd order sealed' alignment with a series cap for the old SV12 woofer. I think it was the same thing being called a Closed High Pass here. Just thought I'd mention it if it helps anyone researching this.

Here's one link about it from back in 2001 over at another forum (hope no one minds the forum linking):

http://www.diysubwoofers.org/talkshop/messages/15134.htm

Edited to add: I did a search for the program mentioned in that thread (WinSpeakerz) and apparently Durzko made a deal with TrueAudio to have free demo versions released with his drivers. 3rd ordered sealed (sealed box with series cap) is an option in the drop-down 'Box' menu.

http://www.trueaudio.com/win_demo.htm

[ThomasW]

@Thomas, I thought that finals where more for ehm (I think it's) high school.

I'm old enough that on occasion we referred to them as finals/final exams when I was in graduate school....

[Dennis H]

Daryl, who posts a lot over at TechTalk, posted some small third order sealed alignments for the Dayton RS series. They all use a resistor and cap in series with the driver. I thought it was interesting and saved the pages. I'm glad I did because the graphs are still there but the description is missing.

http://www.villagephotos.com/viewpub...p?id_=16648948 and the next 4 images.

Daryl's missing description:

Third Order Sealed Alignments for Dayton RS Subs

The Dayton RS subs (High Fidelity versions) some of the finest available. Modelled here in 1ft^3, 2ft^3 and 3ft^3 for the 10", 12" and 15" respectively (net volumes...100% fiberglass fill...not dacron, not Acousta Stuff nor wool). Small enclosures for such subs considering the bass extension reaching 22hz@-6db for the 10" and 20hz@-6db for the 12" and 15" without active EQ and in a sealed enclosure! The third order sealed topology is the key, using an RC filter in conjuction with a sealed cabinet causing a bass emphasis BELOW system resonance. The network values are 1500uf and 2ohm (three PE#027-378 NPE caps and two PE#017-4 resistors) for the 10" system. The network values for the 12" system are 2000uf and 2 ohm (four PE#027-378 NPE caps and four PE#017-8 resistors). The network values for the 15" system are 2500uf and 1ohm (five PE#027378 NPE caps and four PE#017-4 resistors) The wiring diagram is coming up four images ahead. System sensistivities are 83db@2.83V (10"), 84.5db@2.83V (12") and 88.25db@2.83V (15").

[Mazeroth]

I know a few others on the PE forum have used a CHP on their subwoofers, and I remember Wolf using a 500 uF on an Aura NS3 (3" full-range) to achieve around a -3dB at 60 hz. in a small, sealed enclosure (I think 4 liters). I do recall someone using one on an RSS390HF as well.

Oh, and yes, we still call them finals in undergrad and graduate courses, at least in Ohio.

[b_force]

I found the CHP idea at an article in the Hobby-Hifi a German magazine.
I think the concept is very simple and cleaver.
So simple that it's amazing that there are just a few projects which use this concept.

I think the biggest issue is that there are (bipolar) caps in series with the loudspeakers and most people are very afraid of that.
There may be another point and that is that a small box volume will at some compression distortion. (according to linkwitz closed box sheet)
That point can be true if you use your subwoofer at very loud volumes, but for something like this minisub that's not really an issue.

It's just what goals you have

For a non-compromise system I would use Linkwitz Transform because it is much more flexible.
It's funny that this little fellow has a 300W class-d amp, but that's just because I could repair it for only 40 euro. :twisted:

[eyekode]

Neat idea and very clean implementation.
Why did you seal the amp off from the driver? Does the plate amp leak air?

[ThomasW]

Why did you seal the amp off from the driver? Does the plate amp leak air?

So the pressure wave off the driver doesn't pound the amp...

[eyekode]

So the pressure wave off the driver doesn't pound the amp...

Seems like it wastes a large amount of volume. And I am surprised amps would fail from this. I would think they would be more likely to fail from the vibration caused by the physical coupling to the cabinet.

[Amphiprion]

Actually, I think they are most likely to fail because they are usually cheaply made Chinese pieces of junk I've had one fail on me and sure enough it was a bad solder joint.

[JonP]

Well, makes sense to minimize the volume necesscary to seal off the amp.

It's not so much that the amp might be damaged by the pressure (not likely) but preventing the air leaking out sockets or other holes... or preventing the plate from vibration. We go to all that effort to make the wall thick, sturdy and braced, then to have a thinner wall might be a compromise.

[JonP]

Well, makes sense to minimize the volume necesscary to seal off the amp.

It's not so much that the amp might be damaged by the pressure (not likely) but preventing the air leaking out sockets or other holes... or preventing the plate from vibration. We go to all that effort to make the wall thick, sturdy and braced, then to have a thinner wall might be a compromise.

Kind of a last 10% thing, unless you actually have leaks thru the amp.

[b_force]

Normally the Detonation DT300 amp is already sealed off, so the total box can be even smaller, but because I have a 500VA transformer instead of the (original) 300VA the sealing cap didn't fit any more :lol: :lol: 8)
You can also see on the pictures that I had to file of some of the panel where the plate-amp is mounted in to make it fit.

The plate of the plate-amp is full with holes for ventilating the heat of the amp.

If you have a well sealed plate amp I think, if the goal is to make a little subwoofer, I would take out the middle piece of mdf.
On the other hand, that middle piece makes the box a little bit stiffer.

you can see on the attachment, the original sealing cap.

[b_force]

All right, it took a while, but we are back on track
I almost broke today (back, spine and arms hurts like mad), but finally some results,

The roundings are a quarter of a cirkel with a diameter of 35mm.







And special thanks to my little friend, without him I really had huge blisters on my hands. Thanks !! 8)