A bargain DIY sub project... ?

[Deleted]

The Eltax 'Rumble' sub-woofer

OK - I'm stuck for something to do and haven't contributed to the Audio side of this forum in ages.. got a few minutes? It'll make a change from photographing nachos and burgers.



These little and inexpensive subs are around 80 GBP from Richers. They are cuboid, measuring just about 11.5" each side, which is a similar size to my MJ Acoustics Reference 100. The cabinet is reflex-loaded with a HUGE port; about 8-9" long and 4" diameter which tunes the cab to c. 40Hz-ish.

The amplifier section is described as "60 Watts" but this is not qualified in any way. The 8" bass driver is labelled 4 Ohm so this could mean the amplifier is 30 Watts into a more normal 8 Ohm load. And if that 30 W is 30 W peak, then it's a 15 W RMS job. Right?. There is continuously adjustable phase plus low pass filtering from a usefully low 40Hz upwards.



I have just won one of these for 20 quid on Ebay with the intention that the electronics will make a fine basis for a home-built sub. But seriously this little babe is cool. Even at full price this is a tasty little chap. It does a good job and I could see it working very well with our old favourite, the JBL Control One. I've tested it with my new Spendors and it is bl@@dy surprising how well this works!

OK - problem one. The Ebay vendor said this was in "good" condition. It was not. Scratches all over the top of the cabinet (dog claws?) with something pink and sticky on the baffle.

Problem two.. the driver has obviously been faulty since new. Somewhere inside the magnet/spider area there is a foreign body loose. Blob of rogue solder maybe; impossible to remove. It buzzes and bounces around when you turn up the power.

Anyhow that's fortunately unimportant as I bought this for the electronics. And I ain't driving a second 90 mile round trip to get my 20 quid back; it was a 'local pickup only' deal you see.

So what I have here is a pretty cheap but competent-enough 'plate amp' for a sub-woofer project.

The best sub I've ever had was a Maplin-published DIY design years back. It was based around a KEF B200 driver in a reflex box and powered by just a 10 Watt-ish amp. This rather low power was justified by saying that you're only dealing with the bottom octave or two so you don't need tons of power. And in practice it worked just fine.

I didn't make the speaker it was intended for; instead I built a massive 100l box and stuck in a 10" Audax bass driver. It was fab and worked for ages until the amp went faulty. I got around this by using a car-audio low-pass filter with a spare amp.. again this worked well... until the Audax's foam surround went the way of all foam surrounds. By then we have moved house and the 100 litre sub just couldn't be fitted in. I eventually bought my MJ Acoustics sub - but I still hanker after something with a bit more welly.

So just for fun, and definitely without the hi-est of fi in mind I'm going to put something together.

Speaker driver options will be

1. A pair of 10" Eminence / Shark subwoofers - I could connect these in parallel to give the amp the 4 Ohms it's expecting to see.

or..

2. Something to make use of a pair of B200s plus ABRs rescued from an otherwise useless pair of KEF Cadenzas.


Regards,


Derek

[mrarroyo]

Good luck with the project, good bass is both hard to do and could be quite expensive. A few years ago I was looking for a sub and ended up with a Klipsch LF-10 unit that has performed flawlessly over the last 9-10 years.

[rowuk]

Times have changed. Rumble used to be the last thing that you wanted in your hi fi system.

I still think that you need a bigger box for realistic THUMP and SLAM. Little subs just tickle.

[Deleted]

Jun 4, 2011 16:30:31 GMT rowuk said:

Times have changed. Rumble used to be the last thing that you wanted in your hi fi system.

I still think that you need a bigger box for realistic THUMP and SLAM. Little subs just tickle.

I agree - I am aiming to build a box of at least 40 litres. Bigger would be very good but I need to compromise on size.

D.

[XTRProf]

Seriously for deep satisfying bass, 60W and 10" is not enough. Should aim for 300W and 12" to 15" instead.

[mrarroyo]

Well the Klipsch has a forward firing 10" with two side mounted passive radiators. The amp can output 700 watts continuously with 1,200 watt peaks (if I recall correctly). It is very satisfying bass!

[Deleted]

Jul 15, 2011 2:59:02 GMT XTRProf said:

Seriously for deep satisfying bass, 60W and 10" is not enough. Should aim for 300W and 12" to 15" instead.

I do agree entirley but that's not in keeping with my aim of LOW COST. I have found a local timber merchant who will cut boards to size. I will stick to c. 40 litres (about 2 cubic feet?) and use driver(s) I have lying around.

The amp in the plate subwoofer amp I took from the Eltax in the photo is based around an TDA 7294 which gives 50W into 8 Ohms so there will be enough output for what I have in mind.

Derek

[PinkFloyd]

Derrick, have you worked out the VAS / Q etc. or are you just going to whack a woofer into a random cabinet and hope for the best?

With the low powered amp in your "Rumble" box make sure you get a VERY efficient woofer.... don't get one that needs 500 watts just to make a raspberry type sound

[XTRProf]

Jul 15, 2011 10:42:47 GMT mrarroyo said:

Well the Klipsch has a forward firing 10" with two side mounted passive radiators. The amp can output 700 watts continuously with 1,200 watt peaks (if I recall correctly). It is very satisfying bass!

Wow, the Americana free wheeling spirit!

[Deleted]

Jul 16, 2011 10:53:15 GMT XTRProf said:

Jul 15, 2011 10:42:47 GMT mrarroyo said:

Well the Klipsch has a forward firing 10" with two side mounted passive radiators. The amp can output 700 watts continuously with 1,200 watt peaks (if I recall correctly). It is very satisfying bass!

Wow, the Americana free wheeling spirit!

Yes. and that's only in his Canary yellow VW ! ;D

[Deleted]

Jul 15, 2011 20:00:44 GMT PinkFloyd said:

Derrick, have you worked out the VAS / Q etc. or are you just going to whack a woofer into a random cabinet and hope for the best?

With the low powered amp in your "Rumble" box make sure you get a VERY efficient woofer.... don't get one that needs 500 watts just to make a raspberry type sound

The short answer is "yes".

In more detail... I have the TS parameters for my drivers. Also I have a spreadsheet I created many years back to help design a sub. I used my copy of Martin Collom's "High Performance Loudspeakers" as the reference for the maths. And as far as I can see these particular dirvers will do fine in a c. 40 litre box. I have already used these drivers in a diy project project a while back and powered them IIRC with a 30W per channel Kenwood amp. PLENTY enough I found.

But as I keep saying, this is just for fun. It's not an excercsie to build the ultimate sub. It's just a bit of playing around on the cheap.

My speaker design spreadsheets worked well when I designed my own mini tower speakers.



Using a 4" Audax paper cone driver I managed to get some real bass out of them using a 10 litre box and reflexed (below the drivers resonant frequency) at 50Hz. They are so good and unbeliveable bass extension for such a small box / driver. Downside is they cannot and will not play very loudly but the whole project was built from 'found parts'. Crossover was very definitely a 'let's try these bits and see how it sounds' and a bit of intuitive fumbling resulted in a nice sounding speaker. I knew the values of all my caps and resistors but inductors? That was guesswork.

I know just enough about the maths and science. Not a lot, but just enough.

Derek

[mrarroyo]

Jul 16, 2011 10:56:38 GMT @sandyk said:

Jul 16, 2011 10:53:15 GMT XTRProf said:

Wow, the Americana free wheeling spirit!

Yes. and that's only in his Canary yellow VW ! ;D

It is yukon yellow you "senile old man"! You see for being an old fart I can learn, even from Merton.

[Deleted]

Jul 16, 2011 12:12:01 GMT mrarroyo said:

Jul 16, 2011 10:56:38 GMT @sandyk said:

Yes. and that's only in his Canary yellow VW ! ;D

It is yukon yellow you "senile old man"! You see for being an old fart I can learn, even from Merton.

Did you leave it parked down near the beach for too long ? ;D

Attachments:

[PinkFloyd]

Jul 16, 2011 11:24:17 GMT hifidez said:

Jul 15, 2011 20:00:44 GMT PinkFloyd said:

Derrick, have you worked out the VAS / Q etc. or are you just going to whack a woofer into a random cabinet and hope for the best?

With the low powered amp in your "Rumble" box make sure you get a VERY efficient woofer.... don't get one that needs 500 watts just to make a raspberry type sound

The short answer is "yes".

In more detail... I have the TS parameters for my drivers. Also I have a spreadsheet I created many years back to help design a sub. I used my copy of Martin Collom's "High Performance Loudspeakers" as the reference for the maths. And as far as I can see these particular dirvers will do fine in a c. 40 litre box. I have already used these drivers in a diy project project a while back and powered them IIRC with a 30W per channel Kenwood amp. PLENTY enough I found.

But as I keep saying, this is just for fun. It's not an excercsie to build the ultimate sub. It's just a bit of playing around on the cheap.

My speaker design spreadsheets worked well when I designed my own mini tower speakers.



Using a 4" Audax paper cone driver I managed to get some real bass out of them using a 10 litre box and reflexed (below the drivers resonant frequency) at 50Hz. They are so good and unbeliveable bass extension for such a small box / driver. Downside is they cannot and will not play very loudly but the whole project was built from 'found parts'. Crossover was very definitely a 'let's try these bits and see how it sounds' and a bit of intuitive fumbling resulted in a nice sounding speaker. I knew the values of all my caps and resistors but inductors? That was guesswork.

I know just enough about the maths and science. Not a lot, but just enough.

Derek

Sorry Derek..... for some reason I called you "Derrick" last night

[XTRProf]

Jul 16, 2011 11:24:17 GMT hifidez said:

Don't tell me my eyes is seeing things. Is that box made from some sort of galvanised sheet metal? Looks like it.

[mrarroyo]

Jul 16, 2011 12:23:18 GMT @sandyk said:

Jul 16, 2011 12:12:01 GMT mrarroyo said:

It is yukon yellow you "senile old man"! You see for being an old fart I can learn, even from Merton.

Did you leave it parked down near the beach for too long ? ;D

Perhaps ...

Attachments:

[Deleted]

Jul 16, 2011 14:35:51 GMT XTRProf said:

Jul 16, 2011 11:24:17 GMT hifidez said:

Don't tell me my eyes is seeing things. Is that box made from some sort of galvanised sheet metal? Looks like it.

No it's not metal. The cabinets are made from standard 15mm MFC (melamine faced chipboard). The board was rescued from one of my customer's (at that time) unwanted, because damaged, bookshop display cabinets. All glued and screwed together with softwood battens on all corners.

Then, to finish them, I used a 'veneer' of a kind of rugged sticky backed plastic; designed for refurbishing old kitchen worktops. I had bought a roll in a sale previously in case it came in handy; which it did.. ..

These cabinets are about 6" square and something like 33" tall. Tweeters are Audax HD100D25 pulled form an old pair of Tangent SPL1s. Bass drivers were left over from a previous project (Audax AP100MO). All crossover components came from my spares box. I think I did actually have to buy glues and screws - but apart from that these were assembled from junk/spare parts.

Somewhere I have some binaural recordings of them 'in room' along with a similar recording of my LS3/5a monitors for reference.

Derek

[pete]

I thought they were Audax tweeters, I used to have a similar pair of those many years ago.

I love to see DIY speakers, its more fun than buying a pair of ready done ones.

[Deleted]

I now have the boards cut to size (maybe more on that topic later) and I have cut the apertures for driver, amp and port. Made from 18mm veneered MDF.

My final choice is to use a single Shark (by Eminence) 10" driver in a 86 litre box and reflex-tuned to around 25Hz. The driver is fairly efficient so 'just' the 50W amp should be fine.

Derek

[Deleted]

The IOTA sub-woofer project.

Progress! :

Ok - cabinets are built and the glue is drying. I plan to fit the driver, reflex tube and plate amp tomorrow and try it out. Final dimensions chosen means that internal cabinet volume (allowing for a few battens) is 80.5 litres. Large enough to give the bass driver enough volume to work with, small enough to be practical in the room for which it is intended. After guessing the space taken up by the driver and the amp circuitry let's call it 79 litres.

I will fix a reflex port of average diameter 7.25cm and the length is fixed to tune the box / port system to c. 25Hz and, if predictions are correct I could then get some useful response down to around 17Hz... driver limitations permitting that is.


Design and construction philosophy:

Cabinet sides are all 18mm thick - except for the face on which the plate amp is mounted. This is double thickness; two boards sandwiched together and fixed with plenty of Evostik 'Resin W' plus a number of screws randomly placed.

Cabinet sides are a selected mix of MDF, soft timber and high density chipboard, veneered inside and out of course - attention to detail is paramount here. The philosophy behind the board material mixture, and the previously mentioned random screw placement technique, is to spread any dominant resonance modes that develop in each board - the mixture of board materials, liberal glue applications and non-regular screw positioning should promote a more chaotic resonant behaviour. I.E. all cabinet sides should have non-equal ringing frequencies and be of different Q too. To aid the dissipation of such random resonances the top and bottom faces overhang by around 60mm for and aft; an idea borrowed form the 'tray' back panel idea promoted by Wharfedale some years back. This means that, in side view, the sub resembles the capital letter "i"; it's the Greek letter 'Iota' therefore which gives the sub its name.

The speaker baffle is both glued to the main carcass AND fixed and tensioned by 10 x 2" long coach screws that drill deeply into the cabinet sides. This intimate bond between baffle and cabinet sides means that any energy created by the driver, while in action, is transmitted as quickly as possible into the surrounding cabinet walls where the random board materials dissipate and absorb any unwanted vibrations before giving them the chance to colour and smear the wanted sounds.

To avoid any remaining low-level resonances affecting the amplifer and filter circuitry in a microphonic way, this is where the sandwiched boards upon which the plate amp is mounted come into their own. This technique is known as 'constrained-layer damping' and is typically where a viscoelastic, or other damping material, is sandwiched between two sheets of stiff materials that lack sufficient damping by themselves. In this case the (generous) glue that lies between a layer of MDF and the other of chipboard is acting as the damping layer.

An alternative view:

My wife has been watching the build with amused interest. Watching me select the materials, I am sure she thought that just because I had six or seven odd 600 x 400mm kitchen cabinet door samples lying around that I just decided to use them up because I wouldn't have to cut anything. I reckon she thought that I had just put any old box together, with some left over glue, screws and bolts. I reckon she thought that I had to screw two panels together to mount the plate amp on because I had made a big mistake in cutting a hole and had to hide it in some way. I reckon she thought I was just lucky that the plastic bass port I already had was good enough for a try-out. Little did she know that it was all part of an elaborate plan to build a very effective sub-woofer.


Regards ,

Derek

P.S. pictures will follow when it's fully assembled.