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

[s162216]

Hi,

I have designed a few subwoofers in the past, but never actually made one.
A couple of days ago, I was looking at Sensurround on the internet that rumbled the cinema in the film 'Earthquake' and I actually found the circuit diagram for the rumble generator. Its not actually that complex and I should be able to build it.

However the next day at school (actually 6th form but located at an Upper School) when I was talking to my Physics teacher about finding it and how good it would be to be able to actually 'rumble the room, he suggested I could make a smaller, less powerful version of it that could rumble a table as we will be doing about Earthquakes somewhen next year and it would be a good demonstration, I began to think about how I could build a sub to do that.

I have been looking at drivers, but I have not been able to find a cheap(i.e under £100) driver with a frequency range that extends to 17Hz. From previous research I know that a ported enclosure would be the best way to achieve that sort of frequency and I have read up on the design of ported enclosures.

To power this, I am going to make several cheap IC amps and bridge them. How many amps can you safely bridge together as I estimate about 600 to 800W should be sufficient as the sensurround version used a 1500W amplifier.

This idea may seem stupid and a prehaps too complex but I am willing to have a go at doing it as on the plus side it will also give me a sub afterwards to go in my HT

Any suggestions on drivers that I could use and an internal volume?

 

[lsiberian]

Hi,

I have designed a few subwoofers in the past, but never actually made one.
A couple of days ago, I was looking at Sensurround on the internet that rumbled the cinema in the film 'Earthquake' and I actually found the circuit diagram for the rumble generator. Its not actually that complex and I should be able to build it.

However the next day at school (actually 6th form but located at an Upper School) when I was talking to my Physics teacher about finding it and how good it would be to be able to actually 'rumble the room, he suggested I could make a smaller, less powerful version of it that could rumble a table as we will be doing about Earthquakes somewhen next year and it would be a good demonstration, I began to think about how I could build a sub to do that.

I have been looking at drivers, but I have not been able to find a cheap(i.e under £100) driver with a frequency range that extends to 17Hz. From previous research I know that a ported enclosure would be the best way to achieve that sort of frequency and I have read up on the design of ported enclosures.

To power this, I am going to make several cheap IC amps and bridge them. How many amps can you safely bridge together as I estimate about 600 to 800W should be sufficient as the sensurround version used a 1500W amplifier.

This idea may seem stupid and a prehaps too complex but I am willing to have a go at doing it as on the plus side it will also give me a sub afterwards to go in my HT

Any suggestions on drivers that I could use and an internal volume?

You won't find a sub 100 dollar sub going to 17hz. LOL. But you can get a room shaking with Infinity Perfect 12.1 drivers. Usually go used for under 100 dollars.

 

[s162216]

To shake the room depend on the size, but a pair of ported Audiopulse builds could shake a class room probably.

I said £100 (British Pounds) not $100. £100 is equal to about $162. That any improvement?

 

[s162216]

I can't seem to find any of those drivers you mentioned, used in the UK. I don't really want to import from US because of hihh postage costs

 

[lsiberian]

I can't seem to find any of those drivers you mentioned, used in the UK. I don't really want to import from US because of hihh postage costs

http://cgi.ebay.co.uk/Infinity-Kappa-Perfect-12-Car-Subwoofer_W0QQitemZ220432717889QQcmdZViewItemQQptZUK_Audio_TV_Electronics_In_Car_Entertainment_GPS_Car_Speakers_PP?hash=item3352d05841&_trksid=p3286.c0.m14&_trkparms=65:12|66:2|39:6|72:1689|240:1318|301:1|293:1|294:24
(You would want it removed from the box)

http://www.amazon.co.uk/Infinity-Kappa-Perfect-subwoofer-Watts/dp/B00009V3SA/ref=sr_1_5?ie=UTF8&m=A3L6BX3BPCMFWA&s=electronics&qid=1245094216&sr=1-5

Seems options are limited. I will need to do more research to see if I can find anything in your area.

You want the lowest Fs you can get, but you also want a good excursion
limit because you will be driving it hard.

I'll see what I can dig up.

 

[s162216]

I may have found a suitable one for, would you believe it? £79.99 inc VAT
See here http://www.incarexpress.co.uk/view_product.php?partno=XSL154P5

I know its a Sony and their speakers are not rated too well, but it has reasonable looking specs. Will go down to 18 Hz but also claims 15 so not sure which one to use.

I calculated with a 4.6 cubic feet internal volume and a square port 3.27", the port would need to be 16.64" long. I used a tuning frequency of 18Hz

Hows that look?

 

[jamie2112]

I may have found a suitable one for, would you believe it? £79.99 inc VAT
See here http://www.incarexpress.co.uk/view_product.php?partno=XSL154P5

I know its a Sony and their speakers are not rated too well, but it has reasonable looking specs. Will go down to 18 Hz but also claims 15 so not sure which one to use.

I calculated with a 4.6 cubic feet internal volume and a square port 3.27", the port would need to be 16.64" long. I used a tuning frequency of 18Hz

Hows that look?

I don't see anything...... your post didn't come up

 

[s162216]

Left the link out - look at the edit

 

[lsiberian]

I may have found a suitable one for, would you believe it? £79.99 inc VAT
See here http://www.incarexpress.co.uk/view_product.php?partno=XSL154P5

I know its a Sony and their speakers are not rated too well, but it has reasonable looking specs. Will go down to 18 Hz but also claims 15 so not sure which one to use.

I calculated with a 4.6 cubic feet internal volume and a square port 3.27", the port would need to be 16.64" long. I used a tuning frequency of 18Hz

Hows that look?

Fs (Hz) 20.2 Good
Qts 0.46
Qes 0.49
Qms 7.25
Vas (l) 175.2
Vas (cubic ft) 6.19
Mms (g) 325.2
Lvc (mH) 1.1
Xmax (mm) 5.7 Bad. Very Bad. You can't push this thing at all.
The Kappa has twice the xmax.

Xmax (inch) 0.22

This sub isn't suitable for anything but a car.

 

[lsiberian]

Try modeling this one.

http://www.infinitysystems.com/car/products/product_detail.aspx?prod=REF1250W&CheckProduct=Y&Language=ENG&Country=US&Region=USA

http://www.incarexpress.co.uk/view_product.php?partno=1250w

I've modeled it and you can get around 105db+ at 20hz. A jack hammer is 100db at 1m. This can get a bit louder than a jack hammer.

The next question is how big do you want this to be. The larger the greater your extension.

For your box size I suggest a 25 hz tune.

 

[s162216]

O.K] I have modelled it on the calculator I am using.

Picture 1 shows what volume and tuning freq it reccomends, if you can't read it it says:

• Vb = 5.154 cubic feet
• F3 = 19.01 Hz
• Fb = 21.05

I was not sure whether to tune it to 25Hz like you reccomended or to 21.05 like it calculated. So I did both.

21.05 Hz:

• Vent length 25.59"

25hz

• Vent length = 20.52"

Which would you go with? Theres not much difference and I have decided to go with the slightly larger volume of 5.154 cubic feet (god knows where I will put this sub afterwards - my HT is in my bedroom, but lifes a challenge)

Also, what actually is the tuning frequency?

What sort of amp power would you use for this? I have found an IC amp I can easily build that will sink about 70W RMS into a 4 ohm load and I could easily build two or three of them and bridge them.

 

[lsiberian]

O.K] I have modelled it on the calculator I am using.

Picture 1 shows what volume and tuning freq it reccomends, if you can't read it it says:

• Vb = 5.154 cubic feet
• F3 = 19.01 Hz
• Fb = 21.05

I was not sure whether to tune it to 25Hz like you reccomended or to 21.05 like it calculated. So I did both.

21.05 Hz:

• Vent length 25.59"

25hz

• Vent length = 20.52"

Which would you go with? Theres not much difference and I have decided to go with the slightly larger volume of 5.154 cubic feet (god knows where I will put this sub afterwards - my HT is in my bedroom, but lifes a challenge)

Also, what actually is the tuning frequency?

What sort of amp power would you use for this? I have found an IC amp I can easily build that will sink about 70W RMS into a 4 ohm load and I could easily build two or three of them and bridge them.

It's a rookie mistake to tune the sub much lower than the Fs.

The tuning frequency is the frequency at which the speaker system is boosted. However the drawback is port resonance. But in a sub this is rarely a concern.

I could model a smaller box you could use for home use after.

I suggest it be powered with a 300w amp. Make sure to use a high pass filter or you'll blow it.

I'll show you a comparison graph in WinISD when I get the chance.

 

[Loren42]

It's a rookie mistake to tune the sub much lower than the Fs.

The tuning frequency is the frequency at which the speaker system is boosted. However the drawback is port resonance. But in a sub this is rarely a concern.

I could model a smaller box you could use for home use after.

I suggest it be powered with a 300w amp. Make sure to use a high pass filter or you'll blow it.

I'll show you a comparison graph in WinISD when I get the chance.

Isiberian,

What about this idea?

For this system he would need to find an instrument speaker with a high Xmax and high power handling, put it into a sealed enclosure tuned to 30 or 35 Hz, and electronically assist the speaker. 500 watts should be enough to create plenty of low frequency sound out of a 15" or even an 18" driver. The circuit is simple to make, too.

The nice thing about this approach is the cabinet is very, very compact and the driver can be had at a price that meets budget. The trade off is some phase shift at the lower frequencies, but if you are just interested in shaking a room, then it matters not.

What do you think?

 

[TLS Guy]

Isiberian,

What about this idea?

For this system he would need to find an instrument speaker with a high Xmax and high power handling, put it into a sealed enclosure tuned to 30 or 35 Hz, and electronically assist the speaker. 500 watts should be enough to create plenty of low frequency sound out of a 15" or even an 18" driver. The circuit is simple to make, too.

The nice thing about this approach is the cabinet is very, very compact and the driver can be had at a price that meets budget. The trade off is some phase shift at the lower frequencies, but if you are just interested in shaking a room, then it matters not.

What do you think?

Most instrument speakers are low Qt with high Fs, and usually tune in a sealed box around 60 Hz. They have stiff suspensions (low Qt and suspension compliance) so they don't destruct at high power. These types of drivers do not usually respond well to Eq.

I would go with a ported box and a speaker with a Qt of 0.3 to 0.4 with an Fs in the mid twenties or less.

Don't try and tune the system much or at all below Fs. The power response is much better that way, and it is far more likely to produce your earthquake with high power response that going for ultra low F3.

 

[s162216]

It's a rookie mistake to tune the sub much lower than the Fs.

The tuning frequency is the frequency at which the speaker system is boosted. However the drawback is port resonance. But in a sub this is rarely a concern.

I could model a smaller box you could use for home use after.

I suggest it be powered with a 300w amp. Make sure to use a high pass filter or you'll blow it.

I'll show you a comparison graph in WinISD when I get the chance.

When you say 'blow it', do you mean the amp or the speaker?

Should the high pass filter should be about 24Hz and above as thats about the range of the speaker?

When you say 300W, do you mean peak or RMS?

Christ man, this is going to rumble the scout hut at the next party (my mum runs a Cub Scout group and I usually lend my reciever and speakers for the music whenever they do an event, I think they would like this if I could get it to rumble the scout hut)

One little interesting thing I found out though, on the 3.1 version of the Earthquake DVD, the 25 and 35 Hz control tones that actiavted the 'rumble generator' are actually present on the LFE track even though in the cinema you would never actually hear them. A pity I could not use those tones to actually activate the rumble generator circuit.
Now that would be good!!

 

[lsiberian]

When you say 'blow it', do you mean the amp or the speaker?

Should the high pass filter should be about 24Hz and above as thats about the range of the speaker?

When you say 300W, do you mean peak or RMS?

Christ man, this is going to rumble the scout hut at the next party (my mum runs a Cub Scout group and I usually lend my reciever and speakers for the music whenever they do an event, I think they would like this if I could get it to rumble the scout hut)

One little interesting thing I found out though, on the 3.1 version of the Earthquake DVD, the 25 and 35 Hz control tones that actiavted the 'rumble generator' are actually present on the LFE track even though in the cinema you would never actually hear them. A pity I could not use those tones to actually activate the rumble generator circuit.
Now that would be good!!

Put a highpass filter at the tuning frequency. Or you will blow the driver. Don't give this think more than 250watts to play with just to be safe.
This thing can produce jackhammer like sound. Think about how you can hear those from very far away.

hearing supposedly ends at 20hz. But you can certainly get test tones of 25 hz and 35hz. I don't suggest constant playing of them though.

Now I will offer you an idea. Parts-express sells 300w bash amps which are perfect for this type of project. Paired with a sub the shipping might be more reasonable. I think it's worth a look if you go the cash to do it.

 

[lsiberian]

Most instrument speakers are low Qt with high Fs, and usually tune in a sealed box around 60 Hz. They have stiff suspensions (low Qt and suspension compliance) so they don't destruct at high power. These types of drivers do not usually respond well to Eq.

I would go with a ported box and a speaker with a Qt of 0.3 to 0.4 with an Fs in the mid twenties or less.

Don't try and tune the system much or at all below Fs. The power response is much better that way, and it is far more likely to produce your earthquake with high power response that going for ultra low F3.

The biggest problem we have is he is in the UK. I know nothing about getting good drivers there. We got him the most suitable one at his store. I think it will work for his needs. I modeled all the ones in his store and it was the best. Still a higher Qts than I would like, but when you've got limited choices. :-(

Anyone heard of Fane Colossus drivers?

 

[s162216]

I decided to just have one last look around for drivers, when I discovered the Sony XS-LD125P5 which can go down to 18Hz and handle more power. It also has a smaller Qts value and the Xmax is roughly the same, 10mm.

See picture for TS data

Bit more expensive though where I found it, £94, but may find it cheaper. Do you think the price increase is worth it?

 

[lsiberian]

I decided to just have one last look around for drivers, when I discovered the Sony XS-LD125P5 which can go down to 18Hz and handle more power. It also has a smaller Qts value and the Xmax is roughly the same, 10mm.

See picture for TS data

I would be leary of anything sony, but that's my bias. Model it in WinISD.

http://www.hometheatershack.com/forums/diy-subwoofers/6330-winisd-pro-tutorial-download-detailed-guide-how-use-winisd-pro.html

 

[s162216]

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?