Driver Options for Gainclone powered Sub

[raromachine]

Hi all,

I've spent a few nights looking and looking at the sorts of drivers I can get in New Zealand that might suits a Gainclone (LM4780) powered sub.

See this thread: http://www.diyaudio.com/forums/showthread.php?s=&threadid=94173&highlight=

I want to build a sealed enclosure around 40-50l in size as:
- I want to be able to hide it under a table, behind a couch etc
- I care about the quality of the sound more than the loudness
- I'm not planning on building a lot of speakers and have limited tools

I've been looking for drivers and 10" seems like a manageable size.

My choices so far have been targeting < NZ$150 so I've only been looking at what I can get locally (no nice/expensive Peerless drivers).

I've come up with the following:

Jaycar 10" - 4ohm 'double magnet'
- good looking db/w
- small xmax and higher fs.
- $80NZ

Jaycar 10" 2+2ohm Metal Coated Cone Subwoofer (car sub)
- okay db/w
- bigger xmax and low fs
- $150NZ

JBL GT4-10
- good db/w
- bigger xmax and fs is between the other two drivers
- $90NZ + national shipping

Are there other options I've not found?

Am I right in leaning toward the JBL driver as being right for my needs?

Help

 

[ocool_15]

In a sealed box of that size I find none of those drivers will hit even 50Hz You may want to try using a vented box. Try downloading win Isd to model some designs.

When providing specs of the " 10" Profile Metal Coated Cone Subwoofer" they only drove one VC of a DVC driver so if you drove both coils the specs would be different.

 

[arjscott]

Hi there,

I gave up trying to find subwoofer drivers (or anything related to speaker building) locally in New Zealand.

I recently purchased a Dayton DVC 8" from www.partsexpress.com. It's fantastic for what I wanted - a small sealed box with in room extension in high 30hz - low 40hz.

Shipping is a bit expensive, but it's still worth the money. I ordered a few other parts to exceed the US$ 50 minimum international order.

In my opinion this US$ 23 driver is better than drivers from Jaycar, or car subwoofers available here.

You might be able to get a Dayton 10" and a few other parts for NZ $150 including shipping. Maybe a little more than that...

I'm also planning on using an LM4780 for my sub. Plate amps from Jaycar are so expensive!

Andrew.

 

[raromachine]

Hrm - interesting, was the shipping fast? or slowwwwwww?

 

[arjscott]

Really fast. Ordered on Wednesday, shipped that night, arrived on Monday morning. I expected nothing less considering the shipping cost! But still like I say, reasonable cost in my opinion.

 

[raromachine]

Thanks for the link - I have to say the range looks great esp with the NZ$ so high at the moment.

http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=295-550

 

[arjscott]

No worries. Let us know how your project works out.

One more thing - if you register on partsexpress you can find out exact shipping costs. If you add items to your cart and click "checkout", confirm your address and do a few other things, it will tell you the total cost without having to confirm payment.

 

[raromachine]

I'm not sure if the data I have is 100% or if I setup WinISD properly - but it's interesting to look at.

I plugged in all of the values I could find and skipped the ones I couldn't.

I set the box to sealed, and 42Litres (400mm^3 made from 18mm MDF).

Am I nuts - or does the JBL driver look pretty good?

 

[richie00boy]

Depends if you think that a 50Hz -3dB point is good or not. I would say not really. Some EQ will be needed.

I suggest you try modelling the second Jaycar driver in a vented box. It's low Qts means it's designed for a vented box. Usually a vented box is the best way to get good results on a budget.

Also bear in mind you are only looking at relative frequency response there. Achievable SPL is equally if not more important.

 

[raromachine]

What does achieveable SPL mean? (I've googled but came up with junk).

And does the SPL plot in WINISD mean anything in relation to this?

 

[raromachine]

Some new plots...

 

[raromachine]

I ended up going with a Jaycar CS2362 Sub - its an ugly affair, 12" diameter, but they were on sale for $60NZ at my local store and the specs looked better than the other models there for the price.

The magnet is pretty strong - at .5m from a CRT display there are all sorts of lovely colours and effects going on.

Unfortunately, I didn't take a copy of the specs with me, and they are old-stock (i.e. no longer on their website or in their mags). Can anyone help me?? :\

 

[raromachine]

I found an older Jaycar catalogue, for the internet record the data for the CS2362 ( or CS-2362 ) is:

Nominal Impedance: 4ohms
Power Handling: 250W RMS
SPL: 90.2db 1 Watt @ 1m
Voice Coil Resistance: 3.8ohms
Fs: 32.5Hz
QMS: 6.338
QES: .36
QTS: .34
Vas: 59.13litres
Voice Coil Diameter: 59mm BASV
Xmax: 7.5mm
Speaker Dimensions:
A 319, B 298, C 285

 

[ocool_15]

I found an older Jaycar catalogue, for the internet record the data for the CS2362 ( or CS-2362 ) is:

Nominal Impedance: 4ohms
Power Handling: 250W RMS
SPL: 90.2db 1 Watt @ 1m
Voice Coil Resistance: 3.8ohms
Fs: 32.5Hz
QMS: 6.338
QES: .36
QTS: .34
Vas: 59.13litres
Voice Coil Diameter: 59mm BASV
Xmax: 7.5mm
Speaker Dimensions:
A 319, B 298, C 285

That woofer is not very well suited to your intended enclosure at all. You can provide some equalization or go vented but your initial recommendations look better.

 

[raromachine]

Sure - but it was cheap

I had planned to do a bit of experimentation - mostly down the Linkwitz transform route (see attached pic). I've checked the driver with this and found that a -3db point of 25hz means aroudn 12db. The excursion only gets to 4.5mm too.

If it turns out that I can't live with what the driver is giving me then I'll pony up the extra $$$ go and find another (better/nicer) 12" driver to suit the enclosure.

Just for completeness sake the specs sheet lists a couple of enclosures:

Small Vented Box: 25L
Tuning Freq: 36Hz
-3db point: 28hz
Port size: 66mm x 236mm

or

Large Vented Box: 60L
Tuning Freq: 29.3Hz
-3db point: 33.63 Hz
Port Size 50mm x 69mm


----

Forgot to say - thanks for your input

 

[richie00boy]

I think you'll find a 50mm vent tuned to 29Hz will be too noisy. I think a 66mm vent tuned to 36Hz will be problematic as well.

 

[raromachine]

Thanks Richie - I didn't notice your post, but if I do go with the venting I'll make sure I run it through the various tools out there.

In the mean time here is the box taking shape:

 

[richie00boy]

Looks like a nice clean cut box.

 

[pjpoes]

If I may throw in my two cents, be careful with the Linkwitz circuit, its not something you can throw at any old woofer. Though it does work well to extend bass flat to whatever frequency, it has the problem of using essentially a lot of EQ down low. As a result of boosting bass as it does, the woofer will draw more and more power and the cone will move more and more, taxing the xmax and power handeling. A woofer with a high power handeling, huge amplifier, and a lot of xmax handles these cuircits fine, and you get great results. However the woofer you have has very limited xmax and the power handeling and power amp situation is limited. This isn't to say it won't work, you just will be limited as to how loud you can play it. You can modle this effect in WinISD to see just how limited.

Basicly, plug in the power you want, and check xmax, keep raising or lowering the power until you hit the xmax, or are close. Then go check the spl screen, and that will tell you how loud the sub will play before exceeding xmax. It will also tell you if your amp will be adequate to drive it to that level.

How many amp chips are you running, with that chip, a stereo chip, I assume you are just going to parallel it, which will about double-120 watts, the power into 4 ohms. When you modeled it, did you put in 120 watts as the amount of signal?

 

[raromachine]

If I may throw in my two cents, be careful with the Linkwitz circuit, its not something you can throw at any old woofer. Though it does work well to extend bass flat to whatever frequency, it has the problem of using essentially a lot of EQ down low. As a result of boosting bass as it does, the woofer will draw more and more power and the cone will move more and more, taxing the xmax and power handling. A woofer with a high power handling, huge amplifier, and a lot of xmax handles these circuits fine, and you get great results. However the woofer you have has very limited xmax and the power handling and power amp situation is limited. This isn't to say it won't work, you just will be limited as to how loud you can play it. You can model this effect in WinISD to see just how limited.

I had put the LW transform and the LP filter into WinISD - and it looked okay. I didn't quite grasp the input power thing.

At just under 12db gain and following the math on Rod Elliot's page I'm making a guess that the power the amp needs to drive the speaker to the levels for the low freqyencies doubles four times?

So 1W - > 2W -> 4W -> 8W -> 16W of power to give the same appreciable loudness at ~30hz at at ~55hz?

Basically, plug in the power you want, and check xmax, keep raising or lowering the power until you hit the xmax, or are close. Then go check the spl screen, and that will tell you how loud the sub will play before exceeding xmax. It will also tell you if your amp will be adequate to drive it to that level.

Thanks - that's really helpful

I'm not sure exactly how I plugin the input power - I have setup the speaker with the 250W RMS specified on the spec-sheet.

How many amp chips are you running, with that chip, a stereo chip, I assume you are just going to parallel it, which will about double-120 watts, the power into 4 ohms. When you modeled it, did you put in 120 watts as the amount of signal?

You're on the money there re: setup and output power - I've updated the thread under "ChipAmps" (linked to above somewhere) to show what I'm doing. The LM4780 is on a BIG heatsink, and at present I can't even make it warm to touch running at as much bass as I can handle - but if I need to up the supply (higher voltage + VA bigger transformer) then that's a possibility.

----

One additional q relating to matching the cross-over freq of this setup with my main speakers.

The specs on my main speakers are pretty thin on the ground - it says something like 55-20,000hz. At the moment my LP filters -3db point is 150hz - but I don't know enough about manufacturers specs to know if I should be aiming for 55hz, or slightly higher/lower?