After reading the various DIY Sub threads recently (and browsing some of the WWW sites linked from them) I have a few Q's. The general level of the threads was pitched slightly beyond my current technical knowledge particularly in respect to the electronics/hi-fi side of things. Conversely, my DIY skills are truly awesome and many a wonderous item has been borne from an 8' x 4' sheet of 18mm MDF, a hammer and few choice swear words.

With regard to making a sealed unit with onboard amp....

1. In a nutshell, is the whole DIY Sub thing the harmonious marriage of cabinet volume (in litres sq) + driver + amp?

2. Can anyone suggest a UK online retailer and part/catalogue no. for the input/amplifier/bit with the volume & cutoff knobs on. I'm not entirely sure of the true name for that particular component

3. What does 'flat' refer to in Subwoofer terms?

4. Does the output from the amp unit described in Q2 connect directly to the driver?

5. Once all the tech details are taken into account it all seems fairly straight forward. Is there something that I'm overlooking that would make such a project not so?

Thanks in advance.

[RichardH]

1. In a nutshell, is the whole DIY Sub thing the harmonious marriage of cabinet volume (in litres sq) + driver + amp?

Yup you got it! You would usually fill the cabinet with stuffing (not Sage and Onion) when building a sealed enclosure, which is easier than a vented one (i.e. it has a reflex port - this needs "tuning" in length and adds to the fiddling factor).

2. Can anyone suggest a UK online retailer and part/catalogue no. for the input/amplifier/bit with the volume & cutoff knobs on. I'm not entirely sure of the true name for that particular component

http://www.bkelec.com. Click on the "modules and hybrids" button. You want either one of the British Sub Bass (BSB) or Class D panels (DT 150/300). http://www.cpc.co.uk also stock one for around £120. I'd recommend BK though, as they can offer a bundle with those DT amps with a suitable bass driver.

3. What does 'flat' refer to in Subwoofer terms?
It's to do with frequency response. The idea with any speaker is for the output signal's amplitude (i.e. volume) to be the same at all frequencies, otherwise a particular frequency will be exaggerated. Obviously any speaker is limited by its physical design, and will only go so low. When someone says the speaker is "flat to 20Hz" for instance, they are saying that it is capable of outputting a decent sound level right down to 20Hz, which is quite low, and capable of flapping any teenager's flares. The image attached is "flat" to 30Hz.

4. Does the output from the amp unit described in Q2 connect directly to the driver?

Yes. You have a low level (i.e. unamplified) signal from the AV amp (the output from the subwoofer connector), which runs to the sub amp's input. The sub amp amplifies it, and this then goes to the driver.

5. Once all the tech details are taken into account it all seems fairly straight forward. Is there something that I'm overlooking that would make such a project not so?

Make sure the cabinet is airtight - might be worth buying the MDF from somewhere that will cut it for you - that way you get nice sharp square edges, and all the same size (hopefully). There are plenty of recommended designs to suit particular drivers out there - don't get hung up on "getting it flat to 20Hz", as this will require a large cabinet and beefy amp and driver. There's a bloke called Tom at BKElec who's fairly helpful and will guide you to a suitable combo - he's the guy who tends to answer the emails you send to BK.

Think about the space you have available for a sub, as well as the room size. Don't forget that the cabinet volume will be reduced by adding the amp and driver, so take that into account when working out your cabinet dimensions.

HTH!

Good post Richard.

I have found Adire's Shiva/Tempest 'White Paper' and 'Sealed Application' PDFs useful background reading, even if you don't intend to use their drivers.

Site is www.adireaudio.com. From memory, the PDFs are available to download from the respective driver pages, and also the Tech Central area.

Finally, the Home Theater Forum is worth a look as you will find loads of DIY sub piccies.

Regards

Thanks folks. All useful stuff.

With regard to setting up a 2 Sub system, how do people do it? Do they split the sub output signal from the source with a 'Y' splitter or do the plate amps have a 'thru' conncetion of some sort?

[RichardH]

Those DT modules (also known as RKAcoustik IIRC) have "High Level and Low Level In and Outs" - so yes, they have a "through" connection of the low level input, as well as the high level (i.e. already amplified - this is used if you want to use the sub to bolter the low level output of a "normal" speaker - you would run the speaker cable from amp to sub, then from sub to speaker. The sub would split the frequencies - it delivering the low level stuff, and passing on the higher frequency signal to the main speakers - i.e. it acts as a crossover).