Options for fast bass

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#62
"I knew it was low. As far as i know, it's above 100hz that the difference in the quality of bass between monopole/sealed box and dipole becomes apparent."

One must take into account the time constant. Sealed subs, because the box is not vented, can have the tendency for the voice coil to heat up over time as music is played. This leads to compression (there is a lot of data on this, so this effect is real) as the voice coil heats.

The open back quality of dipole speakers allow that heat to easily dissipate resulting in lower electrical compression.

Also, the compressed air in a sealed box will cause increased distortion of the woofer cone, while dipole subs do not suffer from this effect.

Dipole/open baffle and infinite baffle subs have distinct advantages over sealed box subs.

Retsel
 
#63
Telstar said:


I knew it was low. As far as i know, it's above 100hz that the difference in the quality of bass between monopole/sealed box and dipole becomes apparent.

It is also a good idea to actually go with a closed sub for <100hz, 80hz being a very good choice.
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Remember we're talking about bass here - subwoofers! In that context, 80 Hz is not low, it's high. Don't forget, many cross their subs at 40 Hz or let their mains run full range and fill in the bottom octave with the sub. I used to do this in the past as my subs weren't accurate in the 40 - 80 Hz range.

My thoughts are that open baffle yields the most benefit from 200 Hz up to the tweeter xo point. But now we are talking about midrange, not bass.

I'd be happy to have monopole below the dipole roll off point (around 300 Hz) but that would increase the complexity of my system for no real reason.

Open baffle is most evident in the midrange, where it gives a different sense of ambience related to the reduced side wall reflections and increased rear radiation.

Retsel said:
One must take into account the time constant. Sealed subs, because the box is not vented, can have the tendency for the voice coil to heat up over time as music is played. This leads to compression (there is a lot of data on this, so this effect is real) as the voice coil heats.

The open back quality of dipole speakers allow that heat to easily dissipate resulting in lower electrical compression.

Also, the compressed air in a sealed box will cause increased distortion of the woofer cone, while dipole subs do not suffer from this effect.

Dipole/open baffle and infinite baffle subs have distinct advantages over sealed box subs.

Retsel
Click to expand...

One could also argue that a vented box could in fact lead to more power compression due to reducing excursion. It's now possible to give it more power without running out of excursion. In real use the VC may see more power as a result.

Sealed vs OB regarding power compression is an interesting issue. I find it hard to believe that the VC heat is much related to being confined to a box, unless it's very small. I doubt typical subwoofer box sizes would result in much impact.

You would also have to consider how much power is actually required to achieve a certain output level. It's an academic comparison, however, as a dipole vs monopole are doing a different job. You need probably 4x the drivers to do the same job, and this is going to be the significant factor. Each will probably see less power, added to the fact that they aren't working against the air.

Does the air in a sealed box increase distortion compared to OB?

According to Danley, it's preferable to use the air spring to make a driver more linear, at least in horns. I recall comments that the air is more linear than the driver, and a smaller rear chamber leads to lower distortion.

OB makes greater demands on the motor to be linear, especially relative to excursion.

I tend to think that if you want the best possible bass, and cost is no object, then the best possible solution is likely to be IB. With no limits at all, I'd probably go for the Rythmik kits that use GR drivers, get a large number and mount them in a series of manifolds in many different locations (floor, walls, ceiling) to get a nice smooth response.
 
#65
I would agree, even potentially to up higher still, but I believe the greatest benefit is achieved in the midrange. My system is dipole from 80 - 3500k. I've used the same drivers in a box, eq'd to the same response. The conversion lost nothing (not even output) but gained a much more stable and large sound stage and less coloured midrange.

I expect to move towards a Geddes waveguide based system in the near future. Then it becomes difficult to retain dipole top end.

This is off topic!
 
#68
A steady-state bass signal may not be 'fast', but decay time after removing the stimulus can vary with vented designs, which are higher-order mechanical systems than sealed boxes are, and will require more time to come to rest after removing the stimulus. I don't believe rise time is what is at issue when people discuss 'fast' bass -- instead, decay time and extended upper bandwidth are desired.

If more impact or 'slam' is desired, then the best approach is actually a sealed enclosure with a rolled-off bottom end, combined with a mid-high Qtc between 0.6 and 0.8.

I would suggest that the OP pursue a critically-damped sealed system with a Qtc less than or equal to 0.5. Look for a driver with a very low Qts (0.2 - 0.3) and high volume displacement and power handling. Then design a sealed box large enough to keep the Qts between 0.4 and 0.5, and be prepared to dump plenty of power into it and keep an close eye on diaphragm excursion.

This driver might be suitable:
Tang Band W69-1042J
 
#69
Oops, exceeded the 'edit' timeout.


This driver might be suitable:
Tang Band W69-1042J

Try two of these in 2.6 cubic feet, sealed. A critically damped sealed design (Qtc = 0.50) has a F3 of only 77 Hz, but the variation over the range from 35 Hz to 80 Hz is only +/-3dB, with an average sensitivity of 87dB 1w/1m for the two drivers (the overdamped sealed design sucks away 6dB of sensitivity). Power with no more than 200 watts, with both drivers in parallel (and ideally, mounted on opposite sides of the enclosure).

For a small set of speakers to use at the PC, this should be just what the doctor ordered.
 
#73
Have any of you tried PPSL (push-pull slot loaded)?

It may be implemented as sealed, vented, di-pole, etc.

An externally hosted image should be here but it was not working when we last tested it.


Posted by Les Hudson ( M ) ) on January 4, 2009 at 19:04:39
In Reply to: nice job !!!!!!!!! posted by Norman Bates on January 4, 2009 at 17:47:51:

I was expecting it to take some time to get aquainted with the way that it sounds but I knew within seconds that it was what I wanted. It's cleaner , faster and the kind of bass that usually comes from servo systems. I'm even able to drive the woofers much harder before cone break up.

My actual tuning came out to 33hz. and they sound very linear up to 400hz. Thanks

Some other projects from Les, just to see where he has been (front-load horns, rear-load horns, vented horns, di-pole, various direct radiator, etc):

http://gallery.audioasylum.com/cgi/view.mpl?UserImages=33876&session=
 
#74
djk,
very cool way to use push pull!

I like at that and immediately get an idea. This would look great. High gloss paint finish where the internal of the slot port and the inside of the "manifold" is white, and the rest of the box is black. Blue LEDs inside the white parts (or even make them blue) - very novel look in the dark! .... sorry, getting distracted here!
 
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