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

[lsiberian]

I have made up my mind that I will not get the Sony driver. Although it has slightly better specs, I don't think it is worth the extra £30. Also from reading reviews of Sony drivers, they don't seem too good.

This is my first sub anyway, so I can always build a better one somewhen in the future (Not quite so sure how my parents will react to having this shaking my bedroom, may have to turn it down a lot!)

O.k, so I am going to make a 150W RMS amp by bridging three TDA2050 IC amps and I am going to make a 4th order active butterworth high pass filter at 25Hz with a stage gain of 10.

The sub will use the driver mentioned and have an internal volume of 5.154 cubic feet and using a tuning frequency of 25hz and as so a square port, with length calculated at 9.91" long and 3.97" wide.

I will use 18mm (0.75") MDF for the box.

Lastly theres the rumble generator itself.

Do you think I should put the port at the front or the rear of the sub enclosure?

Also, one thing I did think of, my reciever for some reason only does down to 27Hz, is there any way I could get the full range through the sub when watching DVD's?

No don't plug the port that will ruin the rumble.

You have some great idea. Have you modeled the sub in WinISD yet? Do so and then use Box notes to get your cuts.

Make sure to account for dampening and bracing. Look at the DIY Kappa I suggest using 4" rockwool on the backwall and using dense oak rib braces on every axis for ever 6" to 8". You will want to cloth wrap the rockwool. Then I suggest doing a top wall and a side wall with rockwool if possible.

This should be a lot of fun. Remember a flush trim router bit is your friend.

 

[TLS Guy]

I have made up my mind that I will not get the Sony driver. Although it has slightly better specs, I don't think it is worth the extra £30. Also from reading reviews of Sony drivers, they don't seem too good.

This is my first sub anyway, so I can always build a better one somewhen in the future (Not quite so sure how my parents will react to having this shaking my bedroom, may have to turn it down a lot!)

O.k, so I am going to make a 150W RMS amp by bridging three TDA2050 IC amps and I am going to make a 4th order active butterworth high pass filter at 25Hz with a stage gain of 10.

The sub will use the driver mentioned and have an internal volume of 5.154 cubic feet and using a tuning frequency of 25hz and as so a square port, with length calculated at 9.91" long and 3.97" wide.

I will use 18mm (0.75") MDF for the box.

Lastly theres the rumble generator itself.

Do you think I should put the port at the front or the rear of the sub enclosure?

Also, one thing I did think of, my reciever for some reason only does down to 27Hz, is there any way I could get the full range through the sub when watching DVD's?

How on earth are you going to bridge three amps?

When you bridge amps, it is like a push pull output stage, with one amp handling the the +ve wave for and the other the -ve. So you can only bridge two amps, and they have to be closely balanced at that, and need to see twice the output impedance of a single amp. If you parallel amps you will blow the output transistors instantly.

Also not all output stages are bridgeable. Bridging is almost never a solution I recommend. There are too many opportunities for damage and spoiling quality.

Peter Walker of Quad would bridge amps on request, but he supervised it himself, to make sure the amps were perfectly balanced. If they are not, and this is often the case, non linear distortion rises.

You will be far better off with a 150 watt amp.

 

[s162216]

o.k thinking about it know I don't know why I thought I could bridge 3 amps.

Found this though, could order PCB and heatsink then get the components and build it; build a 70V supply and put it in a very well ventilated case.

http://www.sound.westhost.com/project68.htm

Not sure if power is peak or RMS though. Think its peak (Don't think you would be able to build an amp that powerful too easily)

I will model the driver later in that program and produce some 3d concept images

Just finished watching Back to the Future Part II over my new speakers My Tannoy Mercury F1 and FC Customs are excellent for first HT IMO, remebered to remove the foam port plugs and now the bass is really thumping

 

[lsiberian]

o.k thinking about it know I don't know why I thought I could bridge 3 amps.

Found this though, could order PCB and heatsink then get the components and build it; build a 70V supply and put it in a very well ventilated case.

http://www.sound.westhost.com/project68.htm

Not sure if power is peak or RMS though. Think its peak (Don't think you would be able to build an amp that powerful too easily)

I will model the driver later in that program and produce some 3d concept images

Just finished watching Back to the Future Part II over my new speakers My Tannoy Mercury F1 and FC Customs are excellent for first HT IMO, remebered to remove the foam port plugs and now the bass is really thumping

http://www.hometheatershack.com/forums/diy-subwoofers/19305-i-would-like-build-large-av-subwoofer-but-need-some-advice.html#post172237

Lot's of UK based drivers mentioned here. Worth a look for sure.

 

[s162216]

Looked around but all a bit expensive for me.

Have found some cheap 2 channel bridgable 250W per channel car amps that I could power off an old Pc power supply I have. Don't know about quality though

 

[s162216]

I have just tried modelling the driver - stupid program won't let me enter the TS data, says there are inconsistancies even though I have entered it exactly like on the data sheet, I could not find it in the preset drivers.

 

[TLS Guy]

o.k thinking about it know I don't know why I thought I could bridge 3 amps.

Found this though, could order PCB and heatsink then get the components and build it; build a 70V supply and put it in a very well ventilated case.

http://www.sound.westhost.com/project68.htm

Not sure if power is peak or RMS though. Think its peak (Don't think you would be able to build an amp that powerful too easily)

I will model the driver later in that program and produce some 3d concept images

Just finished watching Back to the Future Part II over my new speakers My Tannoy Mercury F1 and FC Customs are excellent for first HT IMO, remebered to remove the foam port plugs and now the bass is really thumping

You are limited in the UK for choice of drivers. Back when I was your age, I used Wilmslow Audio. The only half decent sub they have is that Peerless. Here are the TS parameters.

This outfit used to stock Dayton, but now does not. They do not have anything impressive.

For your situation I think this JL audio unit is your best bet.

This will give you 103 db in a box 2.5 cu.ft. With the slot vent I have modeled, the vent air velocity is 14 M/sec and will not cause port compression. F3 is 22.24 Hz. Here is the model.

Type: Standard one-way driver
No. of Drivers = 1
Fs = 25.24 Hz
Qms = 6.36
Vas = 50.6 liters
Cms = 0.337 mm/N
Mms = 117.9 g
Rms = 2.939 kg/s
Xmax = 9.5 mm
Xmech = 14.25 mm
P-Dia = 203.4 mm
Sd = 325 sq.cm
P-Vd = 0.71 liters
Qes = 0.432
Re = 4.086 ohms
Z = 4 ohms
BL = 13.3 Tm
Pe = 150 watts
Qts = 0.405
no = 0.182 %
1-W SPL = 84.53 dB
2.83-V SPL = 87.66 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box
Shape: Prism, square (optimum)
Vb = 2.415 cu.ft
Fb = 20.8 Hz
QL = 6.695
F3 = 22.24 Hz
Fill = minimal
No. of Vents = 1
Vent shape = rectangle
Vent ends = one flared
Hv = 2.5 in
Wv = 5 in
Lv = 30.69 in

One of the reasons sub selection is poor in the UK, is that a very large proportion of the population live in terraced and semidetached houses. Subs cause police complaints and the penalties draconian, with the police allowed to confiscate all your equipment for causing noise disturbance to neighbors.

The amp circuit you have picked is interesting. However you will not build it for the cost of a plate amp from Winslow Audio, or another vendor. Building your own electronic equipment never saves money, but you learn a lot. Building speakers is an entirely different proposition.

One word of warning, using home made equipment with homemade power supplies invalidates the house insurance policy, so you need to be upfront with your parents about this.

 

[s162216]

O.K, now I am not sure which driver to use. The Xmas is slightly less on the one you selected, but the enclosure is way smaller. Why have you chosen a tuning freq below the Fs? Won't that cause problems with the design?

What one do all you guys think I should use? At the moment I am thinking of using the one Isiberian chose as it is cheap, but fairly good.

Found this amp here, 400W peak. 4 100W channels or 1 400W channel. Not sure if this is for use in a car though as otherwise it will draw too much current and I will ahve to use the old PC power supply I mentioned.

http://cgi.ebay.co.uk/CHROME-400W-AMP-AMPLIFIER-4-CHANNEL-BRIDGEABLE-NEW!!_W0QQitemZ260359441272QQcmdZViewItem#ebayphotohosting

Only £29.00 plus postage - excellent deal if taken at face value and its alright to use.

Thanks for saying about insurance - if I buy an amp does what you said not apply? With the noise I will likely never turn it up too very much in my room anyway as our house is semi-detached. (Leave the Earthquake for other places and when I have my own house in about 5 or 6 years, must get a detached house so I can play it as loud as I like!)

 

[TLS Guy]

O.K, now I am not sure which driver to use. The Xmas is slightly less on the one you selected, but the enclosure is way smaller. Why have you chosen a tuning freq below the Fs? Won't that cause problems with the design?

What one do all you guys think I should use? At the moment I am thinking of using the one Isiberian chose as it is cheap, but fairly good.

Found this amp here, 400W peak. 4 100W channels or 1 400W channel. Not sure if this is for use in a car though as otherwise it will draw too much current and I will ahve to use the old PC power supply I mentioned.

http://cgi.ebay.co.uk/CHROME-400W-AMP-AMPLIFIER-4-CHANNEL-BRIDGEABLE-NEW!!_W0QQitemZ260359441272QQcmdZViewItem#ebayphotohosting

Only £29.00 plus postage - excellent deal if taken at face value and its alright to use.

Thanks for saying about insurance - if I buy an amp does what you said not apply? With the noise I will likely never turn it up too very much in my room anyway as our house is semi-detached. (Leave the Earthquake for other places and when I have my own house in about 5 or 6 years, must get a detached house so I can play it as loud as I like!)

I would use the JL unit, they are superbly built units and highly regarded and have excellent reliability. Also for the performance the box is relatively small, which save money and makes it easier to build. That outfit has a very good price on them.

Sub plate amps are also in short supply in the UK.

Here is one from Wilmslow Audio

You may be able to find others, however my quick search led me to believe they are not plentiful in the UK.

 

[WmAx]

Note: many cheaply made plate amps have been known to fail in the PS, even causing fires. I recommend not using any cheap ones. O Audio makes highly revered plate amps of very high build quality and solid measured performance, and they are available to Europe....

300 Watt basic version...
http://www.oaudio.com/300W_SUBAMP.html

500 Watt version with parametic filter and subsonic filter options...
http://www.oaudio.com/500W_SUBAMP.html

As for the driver... if you would up the budget a tiny bit you could use an Infnity Kappa Perfect VQ driver. These are comparable to the JL W6v2 drivers. Bass drivers really do not get any better than these at any price, but you can pay more to get drivers with higher SPL output ability(even though these already have very high output capability). Very high level of performance. Absolute transparent bass if you design/build the cabinet properly.

-Chris

 

[s162216]

As for the driver... if you would up the budget a tiny bit you could use an Infnity Kappa Perfect VQ driver. These are comparable to the JL W6v2 drivers. Bass drivers really do not get any better than these at any price, but you can pay more to get drivers with higher SPL output ability(even though these already have very high output capability). Very high level of performance. Absolute transparent bass if you design/build the cabinet properly.

-Chris

Can't find the Kappa driver anywhere in the Uk and the JL driver does not seem to appear for less than £300, way too much. I only want to spend about £150 or so max total on the driver, enclosure and amp.

I am leaning towards the driver Isiberian found at the moment as it is cheap and has fair performance. I will proberly never use all 500W very much (just for special times) anyway as otherwise I will get noise complaints.

TLS Guy, do you know what the freq ramge of that driver you found was? I have been trying to find it for ages and if it is below 23Hz then I may change my mind, but the actual Fs is almost identical so I will still be tuning it to the same freq anyway just in a smaller box.
At the moment though I have the enclosure for the driver at 5.145 cubic feet, what impact on performace will decreasing that to 4.5 cubic feet have?

The price breakdown I have now is (including P&P):

• £80 Driver
• £40 - £50 for enclosure wood
• £60 for amp

Thats £200, a bit much than I really want but its the best so far

 

[lsiberian]

Can't find the Kappa driver anywhere in the Uk and the JL driver does not seem to appear for less than £300, way too much. I only want to spend about £150 or so max total on the driver, enclosure and amp.

I am leaning towards the driver Isiberian found at the moment as it is cheap and has fair performance. I will proberly never use all 500W very much (just for special times) anyway as otherwise I will get noise complaints.

TLS Guy, do you know what the freq ramge of that driver you found was? I have been trying to find it for ages and if it is below 23Hz then I may change my mind, but the actual Fs is almost identical so I will still be tuning it to the same freq anyway just in a smaller box.
At the moment though I have the enclosure for the driver at 5.145 cubic feet, what impact on performace will decreasing that to 4.5 cubic feet have?

The price breakdown I have now is (including P&P):

• £80 Driver
• £40 - £50 for enclosure wood
• £60 for amp

Thats £200, a bit much than I really want but its the best so far

Their suggestions are all excellent, however I agree with your course of action given the budget. In a perfect world you get a get a 12.1 driver and build the Kappa with a bash amp, but in your position compromise is required. Infinity makes very good subwoofer drivers so don't think your getting a bad brand.

A great enclosure can do wonders for quality so do that correctly. Look up Wmax's and TLS Guy's posts and read. You can learn a lot that way about good speaker and subwoofer building.

 

[s162216]

O.K heres the two graphs, the first in an enclosure almost exactly 5 cubic feet with a square port approx 2" x 2" (sorry about poor conversions - I am using cm as I live in the UK), 10.5" long and tuned to 25Hz.

The second shows the difference with an 8th order butterworth high pass filter. I can use a quad op amp to make this. The 30Hz is punched up a bit and the lower limit slightly lower due to the 23Hz cut off frequency.

I am not sure what the displacement of the driver is though as it does not say. Obviously I will need to factor in the driver, the bracing and the port into the volume.

Still no too sure what to do for an amp though at the moment. This could be a start though at Maplins (Our equal of Radio Shack). Does 100W RMS into 4 ohm. May only be £14 but the transformer costs £21 and the heatsink £10.

http://www.maplin.co.uk/Module.aspx?ModuleNo=46467

 

[WmAx]

O.K heres the two graphs, the first in an enclosure almost exactly 5 cubic feet with a square port approx 2" x 2" (sorry about poor conversions - I am using cm as I live in the UK), 10.5" long and tuned to 25Hz.

This port will not work. It will have severe compression around the tuning frequency making it useless at even moderate SPL levels.

You must use a far larger cross sectional area - more like a minimum of 25 square inches - not 4 square inches - and the port will be very long folded slot port.

-Chris

 

[TLS Guy]

O.K heres the two graphs, the first in an enclosure almost exactly 5 cubic feet with a square port approx 2" x 2" (sorry about poor conversions - I am using cm as I live in the UK), 10.5" long and tuned to 25Hz.

The second shows the difference with an 8th order butterworth high pass filter. I can use a quad op amp to make this. The 30Hz is punched up a bit and the lower limit slightly lower due to the 23Hz cut off frequency.

I am not sure what the displacement of the driver is though as it does not say. Obviously I will need to factor in the driver, the bracing and the port into the volume.

Still no too sure what to do for an amp though at the moment. This could be a start though at Maplins (Our equal of Radio Shack). Does 100W RMS into 4 ohm. May only be £14 but the transformer costs £21 and the heatsink £10.

http://www.maplin.co.uk/Module.aspx?ModuleNo=46467

The JL audio driver I found for you is 90 GBP including VAT. That is in your price range. If you build the enclosure I designed for you, with the slot vent, you will get 103 db with a 150 watt amp, an F3 of 22.24 Hz and a vent air velocity of 14 m/sec, all in an enclosure of 2.5 cu. ft. You can get everything you need in the UK, and you will be set and on budget. And yes, the sub will give the shaking you want. Please read my last night's post again carefully.

Generally a sub to be really useful needs a slot vent. If you keep vent velocities below about 18 m/sec you won't have port compression.

And by the way, Maplins is a lot more useful than Radio Shack.

 

[s162216]

This port will not work. It will have severe compression around the tuning frequency making it useless at even moderate SPL levels.

You must use a far larger cross sectional area - more like a minimum of 25 square inches - not 4 square inches - and the port will be very long folded slot port.

-Chris

Sorry, the port is actually 4" x 4", I misconverted Cm into In. Is that Any improvement?

TLs guy, I noticed that driver you used only actually has a frequency range down to 25Hz when I looked it up. But that may be wrong as thats practically the Fs, so correct me if I am wrong.

Would that 100W RMS amp be enough to get the rumble as thats about 200W peak?

By the way, what is a slot vent exactly? Why is it better?

 

[TLS Guy]

Sorry, the port is actually 4" x 4", I misconverted Cm into In. Is that Any improvement?

TLs guy, I noticed that driver you used only actually has a frequency range down to 25Hz when I looked it up. But that may be wrong as thats practically the Fs, so correct me if I am wrong.

Would that 100W RMS amp be enough to get the rumble as thats about 200W peak?

By the way, what is a slot vent exactly? Why is it better?

Yes, that driver in the enclosure dimensions a I gave you has nice smooth output to 22 Hz.

Now to slot vents. If you make a vent with bigger cross sectional area, the velocity of air from the vent is slowed. You need a nice slow velocity, otherwise you will not rumble but just chuff. The problem is that the port gets too long to fit in the box, unless it is wound round the interior of the box.

This is the box I designed.

Box Properties
Name:
Type: Vented Box
Shape: Prism, square (optimum)
Vb = 2.415 cu.ft
Fb = 20.8 Hz
QL = 6.695
F3 = 22.24 Hz
Fill = minimal
No. of Vents = 1
Vent shape = rectangle
Vent ends = one flared
Hv = 2.5 in
Wv = 5 in
Lv = 30.69 in

Now the port is 30.69 inches long. So you make a tunnel staring at the bottom and going up the back. That vent big though it is just gets to the good range for vent velocity.

As far as power 100 watts will be fine. When you double amp power you only up spl by 3 db, so your 100 watt amp will still produce over 100 db with that driver in that box.

Don't forget to add volume of the bracing, the materials for the vent, and the plate amp to the internal volume. I already allowed for the driver volume Vd.

 

[s162216]

I have moddeled the driver suggested by TLS guy and the unmodified graph is shown below on the left with port size, length, enclosure volume etc exactly as he said. Is it just me or have I inputted something wrong??

The second graph shows the same, but with some filters added in. As can be seen it improves performance quite a bit. The static gain filter is not strictly needed as I can put it in a stage gain with the low pass filter, but this program, does not support that. Lowpass filter may not be 10th order as that is slightly overkill, but you get the picture. The EQ I can build as a simple op amp circuit that gives 6 db increase around 21.5Hz.
Not all centre freq values may be correct as I still can't find the frequency range of this driver, so I have guessed at about 21Hz.

What do you all think?

(After finishing this sub, theres only 2 more HT things that I one day have always dreamed of getting - next on the list a CRT RP TV, saw one in a shop when I was 6 and have always wanted one since)

 

[TLS Guy]

I have moddeled the driver suggested by TLS guy and the unmodified graph is shown below on the left with port size, length, enclosure volume etc exactly as he said. Is it just me or have I inputted something wrong??

The second graph shows the same, but with some filters added in. As can be seen it improves performance quite a bit. The static gain filter is not strictly needed as I can put it in a stage gain with the low pass filter, but this program, does not support that. Lowpass filter may not be 10th order as that is slightly overkill, but you get the picture. The EQ I can build as a simple op amp circuit that gives 6 db increase around 21.5Hz.
Not all centre freq values may be correct as I still can't find the frequency range of this driver, so I have guessed at about 21Hz.

What do you all think?

(After finishing this sub, theres only 2 more HT things that I one day have always dreamed of getting - next on the list a CRT RP TV, saw one in a shop when I was 6 and have always wanted one since)

Don't try and Eq the bass of a ported speaker. Leave it alone. If you do, all you get is violent cone movement and no extension of bass, only distortion. It is a good way to ruin a driver. Build the sub well, brace it and follow the suggestions.

don't over complicate it. I tried to keep the project clean and simple. It is and will work far better than most commercial subs if you build it right.

I have a busy weekend, and I'm awaiting the onslaught of visitors to arrive. When I get a chance I will publish you complete design on my web site.

Right now, I have to go and start my old John Deere 420 tractor and mow the lawn and the sides of the road. This place runs on vintage two cylinder power.

 

[s162216]

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.