Subwoofer Replacement Question

[kevin007]

Calling all subwoofer design gods...

I know from what I have read that the most important parameters for replacing a subwoofer are the following:

fs
vas
qts
xmax

I have been looking for a cool low cost subwoofer build that would give me some deep thumping bass and would reproduce LFE from movies without sounding like muddy crap like my current sub does. I am also somewhat limited in space. What I have been thinking about building was Paul Carmody’s Pony sub.

I like the look of the pony sub and I think it would fit nicely into my living room. The thing that is holding me back right now from the build is an expensive driver. If my hypothesis is correct I think I may have found a low cost replacement for the driver being used in the pony sub.

Below are the parameters for each driver. Do you think they would be interchangeable?

Dayton Audio RSS210HF-4 8" Reference HF Subwoofer 4 Ohm

THIELE-SMALL PARAMETERS
Resonant Frequency (Fs) 28 Hz
DC Resistance (Re) 3.3 ohms
Voice Coil Inductance (Le) 0.68 mH
Mechanical Q (Qms) 3.08
Electromagnetic Q (Qes) 0.60
Total Q (Qts) 0.50
Compliance Equivalent Volume (Vas) 1.14 ft.³
Mechanical Compliance of Suspension (Cms) 0.48 mm/N
BL Product (BL) 7.76 Tm
Diaphragm Mass Inc. Airload (Mms) 66.02g
Maximum Linear Excursion (Xmax) 9 mm
Surface Area of Cone (Sd) 219 cm²

MCM 55-2421

Power capacity: 120W/240W RMS/peak
Frequency response: 25Hz ~ 1KHz
Nominal impedance: 4Ω
Voice coil diameter: 2"
Magnet weight: 47oz.
Sensitivity: 87dB W/M
Fs: 25.7Hz
Re: 3.4Ω
Le: 2.47mH
Qms: 14.0
Qes: 0.22
Qts: 0.22
Vas: 30.43 liters
Mms: 59.78g
Xmax: 8mm (one-way)
Magnet gap height: 8mm
BL: 12.99
Piston diameter: 163mm

Let me know what ya al' think :D

Kevin

[billfitzmaurice]

Re: Subwoofer Replacement Question

Calling all subwoofer design gods...

I know from what I have read that the most important parameters for replacing a subwoofer are the following:

fs
vas
qts
xmax

That's a tad too simplistic. You need to use Qes and Qms for best results. Qts is derived from Qes and Qms, but the Qes and Qms of two drivers can be quite a bit different while Qts is still pretty close. That said, the hugely different Q figures of the drivers you're comparing makes it very unlikely that they would both work well in the same cab. As for choosing a driver, there's no substitute for modeling the response in the intended box with a modeling program.

[kevin007]

Re: Subwoofer Replacement Question

Bummer, I was hoping for a low cost alternative.

Thanks Bill!

Kevin

[evilskillit]

Re: Subwoofer Replacement Question

Take the time, spend a day and learn to model a woofer in Unibox or WinISD. Chances are you may find there is no magic cheaper driver that will work as well (or maybe you will). But the knowledge you gain will be priceless.

Bummer, I was hoping for a low cost alternative.

Thanks Bill!

Kevin

[Psycoacoustics]

Re: Subwoofer Replacement Question

Take the time, spend a day and learn to model a woofer in Unibox or WinISD. Chances are you may find there is no magic cheaper driver that will work as well (or maybe you will). But the knowledge you gain will be priceless.

Spend a day,,,, a DAY? For someone like me it's more like 5 days! Ok 10,,,, well maybe even more!

There may be no magic cheaper driver but,,,, listening to the people hear and building something that sounds really good,,,,, now THAT'S MAGIC! And PRICELESS is exactly the way I'd describe the knowledge I've gained here! Thanks all! Mark

[Thomas Brown]

Re: Subwoofer Replacement Question

Kevin,

I have been doing a lot more modeling in winisd lately as the laptop I use most doesn't have MS Office for Unibox or Jeff's WBCD, I think Unibox and WBCD is more friendly to me (just my opinion) but getting more comfortable using winisd.

I believe Johnny Richards has written a tutorial on winisd, and Chris Roemer has a post somewhere about a good practice of entering parameters.

If I can be any help, I will do what I can. Been playing lately with some 8's to go behind my spot on the couch and am continually getting more comfortable with the results.

I have a thread with some models in it, per Chris R recs.
The model attached is 2x 8" in a 2cuft vented box with a little boost applied right near tuning.


Just get in there, punch in some numbers and see what happens, It is cool to see how different drivers act - and for myself, just barely scratching the surface of difference in parameters = much different results.
Most if not all of the more experienced guys, can look at parameters and get a good estimate of what a sub will do before even modeling - most impressive.

[Chris Roemer]

Re: Subwoofer Replacement Question

I've seen the Infinity 1260w 12" sub going for less than $60, and sometime closer to $50 on the net.
Used in a 14"x14" x 26" long box, with a 4"PVC x 21" long vent, it can take all the power of an unboosted Dayton SA250 amp down into the low 20's, with an F3 of 27Hz, where it looks to be capable of 107dB.

Chris

[zhillsguy]

Re: Subwoofer Replacement Question

+1 for the Infinity......best bang for the buck right now. As an option, build a 1.5 cu. ft. sealed box before bracing and driver, power it with an amp of your choice, 300 watts. May get one myself to play with.

http://www.amazon.com/Infinity-Reference-1260w-1200-watt-High-Performance/dp/B0028AVGEO

[kevin007]

Re: Subwoofer Replacement Question

Thanks everyone for your input. I googled the infinity sub listed above and found a document from infinity. The PDF shows sealed, vented, and band pass cabinets and the volume needed for each including port sizes. I wanted to see what you guys thought.

Infinity Link

If indeed thier plans would work I would consider getting either a 1.25 cf sealed or a 2.0 cf vented cabinet from DIYsoundgroup.

What do you guys think?

Kevin

[zhillsguy]

Re: Subwoofer Replacement Question

All of Erich's cabinets are superb. The ideal sealed size box is around 1.3 cu. ft. according to WinISD (for a Q of 0.7). The 1.25 sealed would do, though the driver/amp volume would subtract a little from that. Since the DIY Soundgroup boxes are cubes, you would need to get creative if you want to tune it low (port placement/length). Either way, you would need to contact him directly to get the baffle cut special for the driver, or do it yourself. The simplest build is sealed, no worries about driver overexcursion below cabinet tuning.