Need help designing Sub - Need to go down to 17Hz for 'Earthquake' Project

[TLS Guy]

If you look on the graph though, the line has drifted to -3db by the time it reaches 23Hz, and the needed highpass filter worstens that even more as the rumble generator gives frequencies as low as 17Hz which could destroy the driver.

You won't blow a driver if you don't add Eq. 22 to 23 Hz is the 3db point, and it will roll off 24 db per octave below that. So it will be about 15 db down at 15 Hz. That is very good performance.

 

[s162216]

So do I actually need a high pass filter or not?

 

[TLS Guy]

So do I actually need a high pass filter or not?

Here is the complete design on the JL audio 10w1V24 in an enclosure of just under 2.5 cu.ft.

As far as a high pass filter, with a 100 watt amp and that driver, I don't think you need one. If you do build one, it will have to be centered around 10 Hz and be at least 24 db per octave. The higher the order the greater the phase shift and time delay.

Personally I would just go ahead and build the speaker. Don't rush it and use obsessional bracing. The length of the slot vent is on the center line at the turns. A 45 degree angle piece will need to be inserted at the turn in the vent to keep the cross sectional area constant, or nearly so.

You can see form the graphs you have decent output to the 17 to 18 Hz range were the sub is down only 6 db. After that the driver completely decouples from the box, as you can see in the cone displacement graph.

JL Audio drivers are superior robust drivers. That outfit has it at a good price. In the UK you do not have a large selection of sub drivers available.

Where do live in the UK by the way?

 

[s162216]

In Bedfordshire, about 5 miles from the town of Bedford. Bedford is basically not exactly the greatest place as it is a magnet for immigrants, theres lots of Polish and Middle Eastern people especially.
Milton Keynes is only about 8 miles away though and it has a much better selection of shops - I got those speakers in my signiture from Richer Sounds in MK two weeks ago, managed to get the centre and fronts for just £129 when I was expecting to pay £160, so I got a really good deal.

This what the port sort of should look like?

 

[TLS Guy]

In Bedfordshire, about 5 miles from the town of Bedford. Bedford is basically not exactly the greatest place as it is a magnet for immigrants, theres lots of Polish and Middle Eastern people especially.
Milton Keynes is only about 8 miles away though and it has a much better selection of shops - I got those speakers in my signiture from Richer Sounds in MK two weeks ago, managed to get the centre and fronts for just £129 when I was expecting to pay £160, so I got a really good deal.

This what the port sort of should look like?

Yes you have the idea of the slot port. I would open the port on the front below the driver so port and driver reinforce each other. Since vent velocity is low, there will be no chuffs or chiffs to hide.

You can run the port along the back and turn 90 degrees up the back, or turn 180 like you show. You still need 45 degree pieces to ease the turns and stop turbulence at the turns. One piece for 90 degrees and two for 180.

This is a TL speaker, not a port, but the design of the turns is the same.

I have been to Bedford a few times. I grew up at Rochester, Kent. In fact my brother Paul, is chairman of the Kent County Council, at Maidstone.

The family still has the holiday home, at Eastern Bavance, about a mile up the coast of Southwold Suffolk. I spent many summers there.

After the war my father started an earth moving business with yards at Cheshunt, Hertfordshire, and Greenhithe, Kent. Bedford was just in the territory of the Cheshunt site.

 

[s162216]

This like what it should be? I have chosen not to fold it as it is more complex.
Tomorrow when I have some time off, I will create a 3D model in pro desktop to give the idea of what it will look like.

With the bracing, should I put a piece of 0.75" MDF like I am making the case out of from one side the other and cut some holes in it so its like a cross?

If you don't see what I mean you will tomorrow when I make the model.

Still looking at amps - found these two interesting kits at Rapid, ones 200W and the others 400W (not sure if RMS or total).

200W http://www.rapidonline.com/productinfo.aspx?tier1=Electrical+%26+Power&tier2=PA+%26+Audio+%2f+Video&tier3=PA+%26+Audio+Kits&tier4=200W+Mono%2fstereo+amplifier&moduleno=74657

400W http://www.rapidonline.com/productinfo.aspx?tier1=Electrical+%26+Power&tier2=PA+%26+Audio+%2f+Video&tier3=PA+%26+Audio+Kits&tier4=400W+Mono%2fstereo+amplifier&moduleno=74658

If you click on the little pdf symbol next to the description you get the data sheet which gives quite good specs for only £55 for 200W and £71 for the 400W

 

[s162216]

Just noticed - the 400W/200W is only into mono bridged 8 ohm.
I could use an impedence matching transformer to use the 4 ohm speaker as an 8 ohm though could'nt I?

I worked out the ratio would need to be 1:0.7 but unfortunately I cannot find one like this, could I get one and rewind it to have extra/less turns?

 

[TLS Guy]

Just noticed - the 400W/200W is only into mono bridged 8 ohm.
I could use an impedence matching transformer to use the 4 ohm speaker as an 8 ohm though could'nt I?

I worked out the ratio would need to be 1:0.7 but unfortunately I cannot find one like this, could I get one and rewind it to have extra/less turns?

One of the advantages of transistor amps is that they are direct coupled. Unless you have a transformer that costs a small fortune, you will severely limit the bass. By the way those Velman kits are not much bottle. I would find a plate amp. When you bridge you need twice the load impedance versus unbridged, as I explained before.

 

[MidnightSensi]

I didn't read through the whole thread, but, has anyone suggested using a transducer without a voice coil instead? Bass shaker type of thing.

 

[s162216]

Just noticed this - 2 ohms 100W max x2, 50W continuous. Bridgable to 200W 4 ohm, 400W max???.
B grade one at just £29, think its worth it?
I know its for a car but I have an old PC 350W power supply I can use that should work although my calculation have worked out it only draws 7A in bridged mode so I could easily make a small dc power supply.

I.e, Square root of 200W/4ohms = 7.07A

http://www.maplin.co.uk/module.aspx?ModuleNo=45185&C=RMCybernetics&U=DIYCymatics

 

[TLS Guy]

This like what it should be? I have chosen not to fold it as it is more complex.
Tomorrow when I have some time off, I will create a 3D model in pro desktop to give the idea of what it will look like.

With the bracing, should I put a piece of 0.75" MDF like I am making the case out of from one side the other and cut some holes in it so its like a cross?

If you don't see what I mean you will tomorrow when I make the model.

Still looking at amps - found these two interesting kits at Rapid, ones 200W and the others 400W (not sure if RMS or total).

200W http://www.rapidonline.com/productinfo.aspx?tier1=Electrical+%26+Power&tier2=PA+%26+Audio+%2f+Video&tier3=PA+%26+Audio+Kits&tier4=200W+Mono%2fstereo+amplifier&moduleno=74657

400W http://www.rapidonline.com/productinfo.aspx?tier1=Electrical+%26+Power&tier2=PA+%26+Audio+%2f+Video&tier3=PA+%26+Audio+Kits&tier4=400W+Mono%2fstereo+amplifier&moduleno=74658

If you click on the little pdf symbol next to the description you get the data sheet which gives quite good specs for only £55 for 200W and £71 for the 400W

That looks perfect.

 

[TLS Guy]

Just noticed this - 2 ohms 100W max x2, 50W continuous. Bridgable to 200W 4 ohm, 400W max???.
B grade one at just £29, think its worth it?
I know its for a car but I have an old PC 350W power supply I can use that should work although my calculation have worked out it only draws 7A in bridged mode so I could easily make a small dc power supply.

I.e, Square root of 200W/4ohms = 7.07A

http://www.maplin.co.uk/module.aspx?ModuleNo=45185&C=RMCybernetics&U=DIYCymatics

That is really only a 100 watt amp bridged, and I bet that is pushing it. I would avoid using car gear. You then have two power supplies, as the amp has to convert DC to Ac and then back to DC, as 12 volts is not a high enough rail voltage for that power. If it is running on 12 volt on the rails then the specs are optimistic.

May be you should look at eBay and see if you can find a second hand amp. Even a big old receiver would do the trick.

Take a look at this.

 

[s162216]

Thanks for that, I may seriously consider detting that - only £60 at the moment including P&P, but its bound to go go up.
It ends in 7 hours - so I have some time to think.

 

[s162216]

I've been thinking about about when I should build this sub, because I brought those speakers earlier this month, I decided to not spend any more money for 4 months to make up the difference.
If I build this sub next year, like in January, do you think that I will still be able to get the driver at that price?

Found this - looks like a plate amp to me, 215W RMS, £74 and in UK!! I never thought I would actually findsomething like that!! Just hooks up to mains

http://www.bkelec.com/Modules/mf200.htm

 

[TLS Guy]

Thanks for that, I may seriously consider detting that - only £60 at the moment including P&P, but its bound to go go up.
It ends in 7 hours - so I have some time to think.

I would try and get it. If you can get it for around 100 GBP it will be a good deal. Plate amps just are not around in the UK The only source I can find is Wilmslow audio. It might be worth calling them and see if they no of any sources, or see if they can get you a cheaper plate amp around 200 watts

 

[TLS Guy]

I've been thinking about about when I should build this sub, because I brought those speakers earlier this month, I decided to not spend any more money for 4 months to make up the difference.
If I build this sub next year, like in January, do you think that I will still be able to get the driver at that price?
Also, with the amp, I have been looking at that 500W amp project again, I have worked out that for about £120 I can build it, including the PCB and heatsink as cheap, old amps that support 4 ohm seem to be in short supply on ebay.
However I could build the 300W version for less at only about £90. Which one do you think is worth it more, the 300W or the 500W. Or if in fact any of them are worth it at all?
If you see any cheap (i.e under £100), 250W RMS plate amps, then tell me. Although that one on ebay, I have found where I can get one exactly the same in the US for $139 (£84) although I would have to get a power adaptor to step it up to 240V

I would at least pick up the woofer while it is on offer. These days gear comes and goes and is in uncertain supply.

Looking round the net, it seems UK sub builders buy their amps from the US, so they must use a step down transformer.

You could buy this amp, and this converter, and still be ahead.

Due to the high efficiency of class D amps and the nature of audio signals, I think that unit would power it.

This would do it for certain.

Strange as it seems buying a US amp and buying a transformer will be your best and cheapest solution, unless you can get that eBay unit for less.

 

[s162216]

Just as you replied I edited my last post - I have found something that looks like a plate amp, look at the post

 

[TLS Guy]

Just as you replied I edited my last post - I have found something that looks like a plate amp, look at the post

That should do the trick, but you will have to find a case to mount it in, or fabricate a mounting plate, so you can turn it into a plate amp. You will need some metal working facilities to turn it safely into a plate amp, that you can mount on the back of the sub, with the heat sink facing out.

 

[s162216]

I could get a cheap aluminium box, bolt it in that with some holes for ventillation and put it in the top compartment of the sub.
Just pure luck I found that amp, was looking for another one of that one on ebay and found that instead. Apparently BK Elec are one of only 2 UK plate amp sellers, the other being Wimslow Audio, although I have looked on their site and cannot find any amps apart from a guitar one.

I checked for other places that do that driver, several others do for about the same price +-£5.

Until I make it I can get the design perfect, so that when I buy the wood I already have a clear plan.

This has ended up even longer than that argument that I had with you about if SCART was good or bad TLS guy. Remember when I was asking about a SCART to S-Video adaptor?

 

[TLS Guy]

I could get a cheap aluminium box, bolt it in that with some holes for ventillation and put it in the top compartment of the sub.
Just pure luck I found that amp, was looking for another one of that one on ebay and found that instead. Apparently BK Elec are one of only 2 UK plate amp sellers, the other being Wimslow Audio, although I have looked on their site and cannot find any amps apart from a guitar one.

I checked for other places that do that driver, several others do for about the same price +-£5.

Until I make it I can get the design perfect, so that when I buy the wood I already have a clear plan.

This has ended up even longer than that argument that I had with you about if SCART was good or bad TLS guy. Remember when I was asking about a SCART to S-Video adaptor?

I remember that! Don't bury the amp inside the speaker box, that would be very unwise and dangerous It will be quite a lot of work to make that module into a proper plate amp. The easiest would be to find an external box, where the heat sink will be on the outside. You will need a volume control, and don't forget that amp has no phasing circuit. I have a feeling you will come out cheaper and better with the Dayton and a transformer.