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-   -   Feedback on low budget subwoofer (http://www.diyaudio.com/forums/subwoofers/93861-feedback-low-budget-subwoofer.html)

noodle_snacks 10th January 2007 08:54 AM

Feedback on low budget subwoofer
 
I am planning to help a mate build a low budget consisting of a peerless 10in csx woofer in a 100l cab tuned to 23hz (as suggested in their spec sheet), using a 200w, stones sound studio amp from WES Components. We chose to go with the 10in csx over say a 15in jaycar venom due to the smaller enclosure size and probable lower distortion.

We will be using 1x 4in pvc pipe for a port with a 25mm radius flare on either side (using a router bit and MDF. Under a power of 125w in win isd, and according to the program by the name of "flare-it" port noise does not become an issue until 27hz. This sub is for music mostly with some movies, group delay is very comparable to sealed until below 40hz. So I don't expect port noise to be an issue.

Box construction will be 18mm mdf with approximate external dimensions of 600x600x400, most probably with some shelf bracing to keep things rigid. the driver will be at one 400x600mm end with the amplifier at the other end.

I'm just wondering if anyone has any driver suggestions or any changes they'd make to the design before construction?

sreten 10th January 2007 02:36 PM

Hi,

Near 4 cuft is is very big for a 10 in driver and does not appear
to be the optimum choice for that sort of size cabinet to me.

:)/sreten.

joe carrow 10th January 2007 03:48 PM

I agree, this does seem to be a fairly large enclosure, although the manufacturer's sheet does indeed recommend 100 liters. What output level does port noise cause a problem for at 27 hz? With a 4 inch port with flares, I would expect it to be a very high output.

If you have to pick two attributes out of efficiency, bass, and size, then size is the cheapest to sacrifice. This looks like a fairly well considered design, just take a look at what your desired output and extension are, and decide if that's right for you and your application.

noodle_snacks 11th January 2007 02:49 AM

100l and 23hz tuning is very close to a QB3 alignment. Basically port noise only becomes a problem at 27hz with an output level of around 125w or so, I would suspect that if this were to happen then there would be plenty going on with the mains to mask it. This project is fairly budget limited, and we decided to go with the smaller, but higher quality peerless 10in, over other larger, but higher distortion drivers that are availible for a similar cost. The system is destined for a relatively small bedroom, and i think the additional output gained from say a cheap 12in driver is only minimal (less than 3db) is a fair trade for the higher quality of the csx motor design.


Unless someone can think of a another high quality, 10-12in driver to use, (How far away are peerless SLS subs?), within the price range suitable.

I suppose it really comes down to a question of port tuning. Some more experimentation in winISD led me to believe that perhaps a higher port tuning of 27hz, may be better, the shorter port length due to higher tuning means i can use an (optimum) 5in port, 6in would not really fit inside the enclosure design, which lowers air velocity a fair bit (See attachment), Flare-It shows that this enclosure with 1 5in port with a 25mm flare will only have minimal chuffing.

The attached picture has a 0.707 alignment sealed for reference, the 23hz tuning (red) and the 27hz tuning (blue). Which would you go for?http://img150.imageshack.us/img150/8...shot028bv2.gif

joe carrow 11th January 2007 04:38 AM

How large is the room? If it's a small enough room, I'd go with the 23 hz tuning, and if you're going to make any errors in construction try to make it a little higher than 23 hz.

The reason for my suggestion is that room gain will give you a boost down low, and a design that models flat anechoically will be too loud at the lowest frequencies.

Overall, though, the design looks great. I really can't offer much more than that because I don't know what drivers are available in Tasmania.

INM8 14th January 2007 02:37 PM

Hi, I'm the person who noodle_snacks is helping. The sub is going to go in my bedroom which is approximately 4.2 x 3.6 meters with a ceiling height of about 2.6 meters. All of the walls are brick and the room has raised timber floors.

joe carrow 14th January 2007 05:37 PM

Some googling on room gain yielded this: http://linearteam.proboards12.com/in...ead=1087022128

Looking at this, your room isn't so small. It looks like you'd have around 3 db of boost at 30 hz and 6 db at 20 hz... that's really not so much, since it's assuming that all of the doors and windows are closed with good airtight seals.

Still, I'd go with the 23 hz tuning, since that one was down 2 db at 30 hz, and 7 db at 20 hz. The one with higher tuning was down 10 db at 20 hz. The lower tuned one seems better all around, don't you think? In practice, I think it's safe to aim for a tuning between 23 and 27 hz. It's really probably the difference between a few centimeters of port length, and effective port length can be changed by things such as the flare and room placement.

It's OK to make adjustments after the thing is built. You can make the port a little longer or shorter to see how it sounds. I recommend moving the subwoofer around the room as much as you can to see if a particular position sounds best. Even 20 cm can make an audible difference, believe it or not.

AKN 14th January 2007 05:58 PM

Hi noodle_snacks,



Quote:

100l and 23hz tuning is very close to a QB3 alignment. Basically port noise only becomes a problem at 27hz with an output level of around 125w or so
Port noise may not be the limiting factor, that high power is only possible when there is sufficient loading of the cone.

Small drivers tuned low will have limited power capabilities when the driver has poor coupling to the air at low frequencies slightly above tuning. In this design at ~40Hz you will reach x-max at 60-70W input.

If given the choice I also vote for 23Hz tuning as it will probably cope with room gain better. Transient reponse will also be little better.

joe carrow 14th January 2007 06:36 PM

I think that's really the big tradeoff for "low budget".

This thing won't be breaking any windows, messing up your hair, or killing your pets- but it will provide very nice sound with good low frequency extension. Some day when you can afford more, the box is of a proper size that you should be able to find a better performing driver to deliver more volume. There are plenty of woofers out there with double the excursion, and the box is large enough that you can probably find a 12" with long excursion that will work well in it.

Another thing to keep in mind is that most commercial subwoofers below $300 really aren't worth very much. Large boxes just aren't commercially feasible due to people's prejudices about audio components (our wives, specifically), and due to shipping costs. Small subwoofers can be made to work well, but they need a LOT of power and some expensive driver construction. Most people just don't have the kind of bass that DIYers are capable of achieving, and they don't know what they're missing.

This project looks like good bang for the buck. Good luck to you.

AKN 14th January 2007 06:56 PM

Hi,

I might add that a minimun of 70W capability all the way down to 20Hz without exceeding x-max from a cheap (rather good x-max of 9mm peak) driver is not bad at all.


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