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Old 24th November 2006, 08:07 PM   #1
Oborous is offline Oborous  Canada
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Default Need Advice on Sub Testing Box rig and Options for Rig

Hi All,

So I've been busily reading and asking questions on Subwoofers, and I'm thinking I need some real-life experience with subwoofers that I've built.

I've got an idea for a variable volume test box and would like to hear opinions and ideas to make it better.

I -won't- be making this cabinet myself, I don't have enough experience to make this with enough precision to make it work. There is an excellent cabinet-maker in the building that I currently work in; if I give him good drawings, he's willing to do pretty much anything with wood.

What I"m thinking is a heavily reinforced, thick walled box, probably 24" x 24" x 60" internal dimensions would be ~ 20" x20" x 56" (yes, I'm thinking this is walls of about 2" thick) Meaning, I could get an internal volume of upto 11 cubic feet. It would lay flat, as the 24"x24" face would be where the subwoofer mounts

I would have multiple slots where I could put a baffle in, say every twelve inches and the have a slightly smaller, but movable baffle attached with this to move the smaller baffle in and out, then I can really tune the enclosure size.

I would have the top of enclosure removable so I can move the baffles to different spots, and really try different things in cavity.

The front face (24"x24") would be removable also. I would have different front faces made up with cut-outs for different sized subwoofers.

I'm thinking I could use Blu-tack to seal the baffles in air-tight.

I think closed cell foam along the front face, and the top of the enclosure would make that air-tight.


For options, I'm thinking...

High quality binding posts
Flush Mounting carrying handles
an 8"x8" panel that I can remove (again with multiple panels made up) that I can attach different configurations of ports, if I want.

A smaller panel that I can remove. I'm thinking this one, I'll drill holes through, feed wire into, and then caulk the wires to be air tight. The wires can be things like accelerometer leads, temp probe leads, etc.


I'll try drawing up a scetch, but wanted to start hearing ideas.

Is this a good idea?
Does any one have advice on this project?
Does any one have ideas for other options to put in? (I've been wondering about some sort of T-nut in the bottom to test the effectiveness of various feet/spikes)
Any comments on my explaination? I will be explaining this (and diagrams) to the cabinet maker, and if anyone has alternative wording or suggestions...

Thx
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Old 25th November 2006, 05:26 AM   #2
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sounds like alot of trouble if you ask me......


I mean what exactly are you trying to figure out here? What Q factor you prefer for listening to a sealed box with a certian driver? Or how effective spikes are...

Personally I think slapping a few test boxes together out of 3/4 inch MDF would be sufficient for figuring out what Q sounds goood to your ears, and as far as enclosure vibration isolation goes, if you want complete isolation you need not any spikes whatsoever... simply use a push-push design and you're done....
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Old 25th November 2006, 11:56 AM   #3
Collo is offline Collo  Australia
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I did some testing a while back that required a few different sizes boxes.

I had a 100 litre box and a 50 litre box that could be bolted on top with a spacer. I also had a 30 litre reducing cylinder.

This gave me sizes of 50, 70, 100 and 160 litres.

Various external test ports were added to the front, and up to four drivers were externally mounted firing in through the sides.

In earlier tests, I used screws to hold everything together but these flogged out quickly.

The later tests used bolts and nuts with gaskets made from closed cell foam. This arrangement survived extensive testing without any further problems..

Here's the 70 litre arrangement....

Click the image to open in full size.

More info and a few more photos here
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Old 25th November 2006, 04:48 PM   #4
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I too like a box with a variable volume as I can't always trust the books to get where I'm going. Some woofers just seem seem to sound better with the Q higher or lower than the 0.707 standard.

I use a box with a removeable panel and simply insert 2X4's of known volume into the cabinet to adjust.
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Old 25th November 2006, 05:58 PM   #5
TerryO is offline TerryO  United States
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Cal & All,
A variable volume box is probably the best solution "if" you do, or intend on doing, a lot of this sort of thing. The absolutely neatest application of the variable volume box I've ever seen is Dave Rosgaard's box. It is simply a box within a box, within a box, etc., that he designed. I'd like to have one, if for no other reason than to show other people.
Basically he designed tight tolerance boxes that fit within each other using a seal around each one. To use, you merely pull out one of the boxes until it aligns with the correct registration mark for the desired volume. Obviously, he has a assortment of removable baffles for mounting the driver, and IIRC, also has a plate the allows you to add vents of various diameters/ lengths to actually do some preliminary "tuning". All in all, an extremely elegant solution.
I'll have to see if he's around, maybe he'd be able to elaborate on, or correct any of my above statements.
Best Regards,
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Old 26th November 2006, 01:04 AM   #6
Dave R is offline Dave R  United States
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Default continuously variable test box

The variable volume box that TerryO is referring to is one I made several years ago for demonstrations, but still use it occasionally.

The box I made is continuously variable from 30 Liters to 100 Liters. (At one time, I had planned to make one that would go from about 7-25 liters, but never got around to it.) It's kind of like a box in a box in a box. The middle "box" is more or less a sleeve. There are stops built on the edges of each compartment to limit how far they can be pulled apart. I simply used particle board, and a fairly durable weather-stripping bulb seal. The tricky part was to miter the seal and silicone them together to maintain a good air seal in the corners.

I have made a few different front baffles for it, for different sized woofers, vents, etc. The air seal seems to work fairly well. When the vents are capped off, the cap (or the woofer) needs to be removed to allow the box to collapse.

Unfortunately, the plans for it are "secured" electronically on a hard drive that crashed on me a couple of years back.

I think some photos would be better than trying to describe it anyway, but I don't have a digital camera, so it may take a week or so to get some electronic pics. If anyone is interested, send me an email.

drosgaard_AT_cedarcomm.com.
(replace the _AT_ with the @ symbol)


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Old 27th November 2006, 05:17 PM   #7
Oborous is offline Oborous  Canada
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Default Re: continuously variable test box

Quote:
Originally posted by Dave R


I think some photos would be better than trying to describe it anyway, but I don't have a digital camera, so it may take a week or so to get some electronic pics. If anyone is interested, send me an email.
Hi Dave,

Yes, I'm interested in photos, have sent you a private mail.

Thanks
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Old 27th November 2006, 05:49 PM   #8
Oborous is offline Oborous  Canada
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Quote:
Originally posted by BassAwdyO
sounds like alot of trouble if you ask me......


I mean what exactly are you trying to figure out here? What Q factor you prefer for listening to a sealed box with a certian driver? Or how effective spikes are...

Personally I think slapping a few test boxes together out of 3/4 inch MDF would be sufficient for figuring out what Q sounds goood to your ears, and as far as enclosure vibration isolation goes, if you want complete isolation you need not any spikes whatsoever... simply use a push-push design and you're done....
Hi BassAwdyO,

Yes, could be a fair amount of trouble. But I'm a tweaker/tinker/tester. Plus, well... your signature tag of Build nice or Build twice. I want a setup that I can test multiple different subwoofers

I was reading this by TerryO about building and testing, rather than just reading books... this is making alot of sense to me.

I'm looking at the Build Nice or Build Twice... well, what about the testing phase... so I figure something like this will allow me to tune the volume of the enclosure, so I can build a single cabinet that does look nice.

Besides myself, I have six other friends that are very interesting in building speakers (I'm the only one to so far have something actually listenable)... they all have different requirements.


WAF factor is significant for two of the guys (I'm -so very very lucky-, my fiancee has less WAF issues with enclosures than I do.... ), so we'll have to do some experiments with virtual volume increases due to stuffing.

So, I figure something like this will be the 'build twice... but only for the first time' And, one of the guys with the WAF issues... wife is a chiropracter... so he has a budget for trying different woofers... such as Adire Tumults. I want in on that. I can afford a Tumult or TCSounds woofer... but that needs to be the final choice, if that's what I choose. And, if a Mach5Sounds sub works for me... I want to know that, cause I can then build -more-; so need to be able to test and evaluate quickly.

Thanks
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Old 30th November 2006, 12:14 AM   #9
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hey, Orborous

Here's my opinion

I think you're on the right path... sometimes I forget that not all of us have been DIYing very long and they just havent explored many of the avenues as I have(not saying I'm a diy master by any means, just saying I've done a fair bit of testing and experimentation myself and some people havent gotten there yet even).

I visited Sigfried Linkwitz over the summer at his home in california. I had the pleasure of listening to his Orion and Pluto, and let me say they were some awesome speakers.... But on the other hand, I realized that even the great Linkwitz hasnt gotten audio reproduction to a exact science... I doubt anyone ever will. It's just too subjective

I do however think that there are certian advantages to SOME expensive drivers and electronic components that only proper implementation can reveal. So yes, spending more money can get you places that going el cheapo just cant....

Now on the flipside its very subjective, so you will realize after a while that its not a great idea to spend $200 on a tweeter or $400 on a midbass. The subjective clarity that those more expensive drivers will add is minimal even with proper implementation compared to say a $100 midbass driver and a $30 tweeter.

The least subjective area of audio I've found however is in the lower bass register. Sure some people prefer dipoles, horns, or sealed subs down to about 50hz... but below that, there just isnt as much detail to the sound to even detect. Spending more money here gets you things like... higher output in a smaller size(at the cost of efficency), or just higher output period.

I do not reccomend Tumult unless you're aiming for infrasonic bass or want high output in a small enclosure. If you can fit a 10 cubic foot enclosure in your listening room somewhere go for a couple cheaper 15's or even 18's(you can get the same swept volume and higher efficiency for LESS!!!). Your wallet will thank you on the cost of the drivers and amplification!!!


As far as your test box goes......


If I were you I'd build something like a 10 cubic ft enclosure(big enough to put 2 drivers in comfortably). Make a couple 18" cutouts(opposing sides to test push-push) and then a few sets of rings for mounting smaller sized drivers(and a single 19" circle to mount over one of the holes if using a single driver). Just use some foam tape to seal the rings when you mount them.... Then you could reduce the box volume by using retaining wall blocks(if you have a retaining wall) or something of the like which you could insert into the enclosure to reduce internal volume by a know amount... Making something that slides apart sounds complicated(well it wouldnt be extremely complicated to make, but just to make air tight). Test ports are also a good idea
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