Options for fast bass

[oon_the_kid]

Hi,

I am looking at how to design for a fast sub, fast as in good transient response. Before I begin, maybe a bit of background. I am planning to mate it with a Markaudio alpair 6 satelite. Now the thing with maiting it with a 6 cm driver is, the sub actually has to do quite a bit of normal bass too. I find the bass from most sub a bit too wooly, does not fell like a punchy bass from a well built floor stander. Good for HT rumble, but not good for a double bass.

So, basically a tight and accurate bass is important, very low end is secondary. Maybe something in the design philosophy of this one:

http://www.philjonespuresound.com/PJWeb13_PSW1.aspx

So I would like some advice on how to build such a sub. Since I am not a real woodwork guy, I would probably a) buy a speaker cabinet and put in a suitable driver b) buy an old second hand sub and replace the driver and modify it.

There seems to be quite a bit of fallacy and facts running around the internet so it would be good if some of you guys help clear it up for me especially if it is a misconception.


a) I should be using a sealed cabinet for better tightness and clarity. Cabinet size would be about Vas.

b) I should be using smaller speakers, or speaker with a high force factor / moving mass ratio.

c) the high inductance and hence the emf from the subwoofer at near fs is the problem, causing poor bass response.

However looking at these constraints, i noticed that for b) the speaker would have to be a 7" or 8" subwoofer drivers. 10" drivers have significantly higher Mms. Alternatively I could use normal 10" woofers which have smaller Mms rather than subwoofers but their Vas tends to be quite huge.

I might be interested in this:
http://www.wavecor.com/html/sw178wa01.html
Has anybody used this driver before and can comment on it.

Or is there another 10" driver that you might want to recommend?

To cater for the poorer low end response, I would like to add in a 5 band graphic equaliser (for the bass band only), which also helps for tuning of the room and to compenste for the bass roll off.

So overall, it would be a 7" or 8" sub in a sealed enclosure with a 5 band graphic equaliser on the inputs.

Any comment is greatly welcomed.

Oon

[Matsumoto]

Hi,

I'm a recent new member of this forum.
I hope this kind of information could be useful for you;

Recently I have studied a subwoofer integration to my desktop audio system.
The target was to create earphones-like very tight and clear super bass (down to 30 Hz flat).

Although the circumstances maybe much different from your listening style, I believe the basic theories could be applicable also to you.

I�fve found bellows are very important besides the unit design;
1) Standing wave effect (sound reflections from walls) in the room should be reduced.
For that:
- Find the best position of the subwoofer anywhere in the room
- or install it very near from you (delay control necessary)
(see attached figure)

2) Equalize the output and phase delay accurately based on measurements at the actual listening position.

3) Digital signal processing is quite useful for the adjustments

4) Relatively small sealed enclosures for the main speakers (maybe 2 �c 3 L for Alpair 6)

5) A sealed enclosure could be better also for the subwoofer (or duct stuffing)

For details, please see my own Blog
http://lean-audio.blogspot.com/

[tinitus]

If you want "fast" bass look at good BIG PRO woofers

Smaller woofers going low tend to get "slow" and blurred

[tritosine]

http://www.resolutionmag.com/pdfs/SWEETS~1/LOWFRE~1.PDF

[planet10]

Fast is just a bad term to use. Simply, a fast woofer has good hi-frequency response. Put a low pass filter on it, and it is no longer fast.

What i think you are looking for is a bass driver that accurately reacts to the input signal without. This probably comes down to a good motor design, low inductance, good downward dynamic range, and low group delay when it gets into the box.

dave

[tinitus]

Well, you can actually have a bass that is too fast, which means its out of phase resulting in poor timing
Bass is best when slow and relaxed
Besides, bassplayers are slow guys with slow instruments
You cant play fast on tuba either

What I desire is the clear pitching from the strings on a contrabass

But to quit the bogus, I think that theoretically you need a woofer thats good and clean all the way up to its natural rolloff
It will give you the chance to try crossing a bit higher as I reckon your fullrange needs some support in lower mid/midbass

Im thinking whether the new underhung midwoofers from Tangband would work nice

[PeteMcK]

I don't think you need a sub, I think you need a pair of woofers that respond low - The Wavecor drivers look suitable, but will probably need a notch for that HF peak.
BR will give you a much more solid bass, and you won't need the eq - less strain on your amp
Using a 1st order xover, you can also use the woofers to compensate for BSC

[Thawach]

If you want "fast" bass look at good BIG PRO woofers

tinitus i don't understand why big woofers will be fast. and if 30" driver(fostex) do u think it will be fast?

Fast is just a bad term to use. Simply, a fast woofer has good hi-frequency response. Put a low pass filter on it, and it is no longer fast.

planet10! i ever heard Scan Speak 18W8535(7")driver for sub. i think, fast is good. fs of it around 25 hz. 54 litre vent box. -3db about 35 hz
when put low pass filter about 100 hz. it still be fast. sorry! planet10 i understand the meaning for your reply a little.


regards

TW

[planet10]

Originally posted by Thawach
planet10! i ever heard Scan Speak 18W8535(7")driver for sub. i think, fast is good. fs of it around 25 hz. 54 litre vent box. -3db about 35 hz
when put low pass filter about 100 hz. it still be fast. sorry! planet10 i understand the meaning for your reply a little.

As soon as you put a LP on it, it can't be fast, because there is no signal to be fast. You are using the wrong word. a 100 Hz signal just isn't fast. A 20k one is.

dave

[tinitus]

Originally posted by Thawach


tinitus i don't understand why big woofers will be fast. and if 30" driver(fostex) do u think it will be fast?

TW

What Dave says is true
But we also know perfectly clear what you mean by "fast" bass
Unless if it means that you have listened to people saying that small woofers are "faster"
They are, as Dave explained, only at higher frequencies

Bigger woofers are considered "faster" because they move less, due to their bigger size
Lets refrase and say, more responsive, at low frequencies

When you refer to "fast", it actually means "tight", precise bass
Its mostly related to driver Qts, and the following box design
Small woofers designed to be "tight", easily results in thin almost absent bass
You could call it "mouse" bass
Small genuine sub drivers going really low is a different matter

Big woofers have more volume, and are better suited fore a design with "tight" bass
Such a driver will have a big powerful "motor", and therefore subjectively sound more responsive
Even with a "tight" design you will still hear the bass as BIG
But one should still take great care not to get boomy sound
The catch is that one cant expect to "feel" the subbass, but its more like something you "hear", which is actually really nice in the long run
Some prefer dipole bass fore the same reason
I believe many are using your driver in a dipole setup
To get the right balance it would need to be active

Theres actually a lot more to it than that, and its too complicated to explain like this
And there still remains the room issues
It will never just be "plug and play"