Advice on drivers for Sub-woofer

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darrylis

Member
Joined 2016
#1
I need low end to compliment a pair of speakers I made.

How do I go about looking at Thiele-Small parameters to determine the right choice. I'm interested in a bass range from 30-70 hz approximately. I'll be driving it with this amp.

Dayton Audio DTA-2.1BT2 100W 2.1 Class D Bluetooth Amplifier with Sub Frequency Adjustment

I'd like the speaker driver/box to be as small as possible.

Could someone please advise on how to go about just using Thiele-Small parameters.

Any advise is welcome.

Regards,
d.

In the meantime, I've just come across a driver (that is very large) used for bass guitar and on sale. Even though this goes against the size constraint, could it be used i.e. Celestion BL15-300X. Here are the parameters.

Celestion BL15-300X (8) - 15 inch Bass Guitar Speaker

General Specifications

Nominal diameter 381mm/15in
Power rating 300Wrms
Nominal impedance 8Ω
Sensitivity 96dB
Magnet type Ferrite
Voice coil diameter 63.5mm/2.5in
Coil material Copper
Cone material Kevlar loaded paper
Former material Polyimide
Surround material Cloth-sealed
Frequency range 42-3500Hz
Xmax 4.25mm/0.16in
Gap depth 8mm/0.31in
Voice coil winding width 16.5mm/0.64in

Small Signal Parameters

D=0.33m/12.99in
Fs=48.1Hz
Mair=14.15g/0.499oz
Qms=2.989
Qes=1.004
Mmd=68.24g/2.41oz
Qts=0.751
Re=3.15Ω
Vas=137.69lt/4.86ft3
BI=8.83Tm
Cms=0.133mm/N
Rms=8.327kg/s
Le (at 1kHz)0.47mH
 
#2
Big question there.
Quick answer, i wouldn't use that driver.

Hmm,
Fs 48hz
Qts .75
It won't go low enough without a bunch of eq.

How big of a driver ?
How much do you want to spend ?
How small of a box ?
2ft3 ?

Do you want a sealed box or a ported (usually lower f3 but bigger box) ?

Are you making your own box ?


If you have your heart set on that driver, possibly a bandpass, might be big though.
There are online calculators tht crunch numbers for you.

We enjoy questions like this.
 
#3
Greets!

Fs much too high for worthwhile 30 Hz capability; Qts much too high for a small box, though nowadays could be digitally EQ'd to meet your criteria, but with a way too tiny Xmax for such an acoustically inefficient cab alignment equates to a very low output, so would probably only be suitable for a near-field/computer desktop type system or maybe tiny room attached home/apt. system where the sub is at the listening position.

Search for highest Xmax, ~21-30 Hz Fs, < ~0.42 Qts you can find in 12-15", then compute [Vd] swept volume = Sd*Xmax to find which one moves the most air.

The Vas spec ideally needs to be high for the acoustic efficiency required for only 100 W, but then 'small as possible' will be quite large.

GM
 
#4
Thanks Norman and GM, really appreciate!

In regards to your questions:

How big of a driver ?
12" and smaller

How much do you want to spend ?
$100 at most on the driver, don't know whether that's possible

How small of a box ?
Smaller than 2 cubic feet, if possible

Do you want a sealed box or a ported (usually lower f3 but bigger box) ?
Either is fine.

Are you making your own box ?
Yes, am planning to, however am also looking at buying a sub in the used market. Any recommendations ? This is for music listening only, not movies etc. Looking for accurate distortion free sound.
 
#5
GM,

Thanks for the rules of thumb etc. I was wondering, given that information, how to scour the internet to find the driver in question. I found a site that somewhat caters to querying i.e. loudspeakerdatabase.com

Are there other databases that are exhaustive, or this information is not generally collated ?

I found a few drivers that potentially would work, on the site mentioned prior.

Thanks once again for the help.
 
#7
Without qts, vas, and fs, there is no way to know what it will do without testing it.

On that 8", hard to know how much eq boost then subsonic protection that is done by its subwoofer amp.

Here are some quick tips i go by.

Ported.
I usually look for qts near .4, then that driver makes for a box as big as Vas, and you tune to its fs, that is now its f3 (3db down).

You can get around this quick rule using a low qts driver with a very low fs, but that is usually a big 15, think qts .25 - .3, fs 20hz. Off the top of my head, i think f3 tuning around 30hz in a much smaller box than qts .4

Sealeds.
If you want f3 close to 30hz.......
Usually bigger drivers with qts above .4 and again low fs.
Box can get big.

In general, porteds are smller and have higher f3.
But it can be hard to tune low (30hz) in a smaller box.
And passive radiators add to the cost.

If you toss us qts, fs, and vas, we can toss back box size, f3, tuning, etc.
I have an excel file at work where i enter driver specs and it crunches the numbers.
 
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#9
Accurate ?

People get hostile over that one.
To me the phase angle wrap at the subwoofer point is where you hear problems.
I stuffed my 15s' port (tuned 27hz).
It wasn't any faster than the ported, just an octave less bass.
I think tuning 30hz and below is fine.
Even on the books, the transient response is the same as a sealed an octave above tuning.

I'd swear there was a 12" dayton that would have ported around 2.5ft3 and 25hz tuning.
 
#12
Thanks Norman.


I've been using an online calculator too. I'll take the tips provided and find something as the loudspeaker database allows to do queries. That would be my best bet.



Thanks for the Dayton recommendation, however, on the parts express site this is the box info:


Optimum Cabinet Size (determined using BassBox 6 Pro High Fidelity suggestion)

  • Sealed Volume 0.3 ft.³
  • Sealed F3-78 Hz
  • Vented Volume0.75 ft.³
  • Vented F3-47 Hz

Does that mean that 30Hz cannot be achieved ?
 
#14
#16
I used typical 4th order ported equations, and .707 qtc for sealed.

You can make a ported box whatever size you want and tune wherever.
The equation i used is an old one, but gives max flat to a low f3.
You can make it bigger and tune lower, makes for higher f3 but lower f9.
Ebs, or extended bass shelf.

My buddy would use ported sbb4, best transient response (due to tuning to fs becoming system f9).
Then he adds boost, subsonic filter at tuning (+6db).
That makes for a small box, deep extension, and huge headroom, especially for a woof/sub that naturally has no low bass (qts under .35).

In a sub, i like 30hz tuning better than 40hz, more boom, less thunk.
But this stuff can be very subjective.
 
#17
Is this for a house or a car ?

The rs265ho (wow, many great reviews on parts express).
but, you said keep it under $100.
The Dayton is $153

Speaker Stats
fs 27.6 hz
vas 1.23 ft3
qts 0.45

I get...………….

Standard ported
vb 1.76 ft3
f3 23.55 hz
tune 24.68 hz

Sealed
VB = 0.84 Ft3
fsb = 43.36 hz
F3 = 43.37 hz

I like that driver sealed for a car, would work nicely.
I try to aim for qtc .707 with F3 near 45hz for a vehicle.

But, a ported has less excursion near tuning = less travel = less harmonic distortion, but can bottom out from frequencies below tuning.

The $150 tymphany, I get...…….

Speaker Stats
fs 22.4 hz
vas 4 ft3
qts 0.399

Standard ported
vb 3.86 ft3
f3 22.76 hz
tune 22.65 hz

and sealed qtc .707
VB = 1.87 Ft3
fsb = 39.69 hz
F3 = 39.70 hz

Notice, peerless goes a little lower (sealed), but has a bigger box.
And qts = .4, so Vb ported = Vas

Dayton has a slightly bigger coil, so less heat melting, but usually bottoming it out will kill it faster. Peerless is a single coil also.
 
#18
The problem with the RS265HO is it's a dual 4 ohm voice coil sub. The Dayton amp he provided in his original post only handles 4 and 8 ohm loads, thus he can't run a 2 ohm load on that amp by wiring it in parallel, and if he runs it in series he'll lose half the power to the sub.
 
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