[Moonfly]

Simple question, not so simple answer.

So, how do you go about deciding what your targets are when looking at drivers. There must be some defining values you look for if your after a certain sound.

Anyone experienced enough to educate me here?

Cheers

[Badger0-0]

Try reading this;

Thiele/Small - Wikipedia, the free encyclopedia

And especially this;

SoundStage! Max dB - Fast Bass, Slow Bass - Myth vs. Fact (06/1999)

[stevefish69]

Originally Posted by Badger0-0

Try reading this;

Thiele/Small - Wikipedia, the free encyclopedia

And especially this;

SoundStage! Max dB - Fast Bass, Slow Bass - Myth vs. Fact (06/1999)

Thanks Badger - Interesting read there

[Badger0-0]

Originally Posted by stevefish69

Thanks Badger - Interesting read there

No worries steve

I think I know what Moonfly is getting at , hence the second link in particular

[Moonfly]

Your right about musicality Badger, but probably not in the same context as myself, probably.

I already read the Wiki article, and this one, but what I particularly mean, is if your after a certain type of sound or performance, how do you go about targeting the correct parameters when looking at driver statistics and how do you know what values these should have.

Ive been doing a fair bit of reading about sub woofery in general and I'm really trying to understand how they work better. I suppose I think that the better I understand something the better I can get out of it etc etc. I think I'm at the point where the real nitty gritty is my only real unexplored area.

[Moonfly]

OH AND MODS, IF YOU COULD CORRECT THE SPELLING IN THE TITLE THAT WOULD BE GREAT, CHEERS

[Badger0-0]

Originally Posted by Moonfly

Your right about musicality Badger, but probably not in the same context as myself, probably.

I already read the Wiki article, and this one, but what I particularly mean, is if your after a certain type of sound or performance, how do you go about targeting the correct parameters when looking at driver statistics and how do you know what values these should have.

Ive been doing a fair bit of reading about sub woofery in general and I'm really trying to understand how they work better. I suppose I think that the better I understand something the better I can get out of it etc etc. I think I'm at the point where the real nitty gritty is my only real unexplored area.

I think your problem is not sub bass, but more bass.
I'd be looking for speakers with 8" drivers myself

But even then, you'll still have a problem, because nothing sounds like the real thing.

[Moonfly]

I think your exactly right.

As it happens thats one exact avenue ive been looking into, only not 8".

XTZ 99.38

Maybe a little too much, but im considering no sub for music.

[Badger0-0]

Originally Posted by Moonfly

I think your exactly right.

As it happens thats one exact avenue ive been looking into, only not 8".

XTZ 99.38

Maybe a little too much, but im considering no sub for music.

You still won't be happy

Good luck in your search.

But it seems you're looking for lower-mid bass, not sub bass.

Fwiw, that's what I crave.

And that's the hardest to find, imo.
It's also the most expensive

[m4rky_m4rk]

Originally Posted by Badger0-0

I think your problem is not sub bass, but more bass.
I'd be looking for speakers with 8" drivers myself

But even then, you'll still have a problem, because nothing sounds like the real thing.

Yes, I agree with that.

Maybe you should be looking at new, bigger speakers before throwing the PB baby out?

[KhalJimbo]

If ihave been reading correctly you're after speakers that give bass good enough without having to use a sub?

That's an expensive choice but as said before you need 8" drivers in the speakers and alot of money lol

Is that what your qeustion is?

[stevefish69]

Moonfly - Have you thought about the second hand market. You can pick up some top notch main speakers with multiple 8 or 10" drivers for a fraction of their original RRP.

[recruit]

I'll have a pair of ProAc Future .5's going up for sale soon...

http://www.proac-loudspeakers.com/pt5.php

[Moonfly]

Originally Posted by Badger0-0

You still won't be happy

Good luck in your search.

But it seems you're looking for lower-mid bass, not sub bass.

Fwiw, that's what I crave.

And that's the hardest to find, imo.
It's also the most expensive

Bang on the money there mate. As it happens I found it in the MK MX series subs, but as ever that SVS low end grunt was undefeatable and I'm looking at other methods of adding that bass 'sound' to my system. Basically decided the only way of keeping that bottom end prowess was with the SVS, but I could replace the MK sound some other way, probably.

I may yet share one other idea Ive been having, but not sure yet as I'm to proud

Originally Posted by m4rky_m4rk

Yes, I agree with that.

Maybe you should be looking at new, bigger speakers before throwing the PB baby out?

PB going no where just yet. I'm currently thinking the XTZ's are the way forward, and perhaps with their own amp.

Originally Posted by Earthworm Jim

If ihave been reading correctly you're after speakers that give bass good enough without having to use a sub?

That's an expensive choice but as said before you need 8" drivers in the speakers and alot of money lol

Is that what your qeustion is?

In that respect I'm on about music not movies, I always run the SVS for movies. The speakers I'm looking at have a ribbon tweeter, a 6.5" mid driver, and a 10" ported/sealed bass driver.

Originally Posted by stevefish69

Moonfly - Have you thought about the second hand market. You can pick up some top notch main speakers with multiple 8 or 10" drivers for a fraction of their original RRP.

I always consider second hand products, but speakers arent my field of expertise really so when they are out of my B&W/MA/KEF knowledge comfort zone I'm at a bit of a loss.

Originally Posted by recruit

I'll have a pair of ProAc Future .5's going up for sale soon...

http://www.proac-loudspeakers.com/pt5.php

I'll take a look, but be warned SWMBO makes up for a fair bit of the decision.

Cheers.

[Moonfly]

Originally Posted by recruit

I'll have a pair of ProAc Future .5's going up for sale soon...

http://www.proac-loudspeakers.com/pt5.php

Unfortunatley, neither of us are a fan of veneered finishes

[Nimby]

Fast bass is not a myth. The author has simply never heard an IB.

The only T-S parameter you really need is Sd.

Throw away the box and keep adding more Sd until the cones stop moving at any frequency and any SPL.

That's fast bass.

No waiting for cone movement to start and stop because it never has to.

That's fast bass.

When the bass you previously thought was impressive becomes unpleasantly violent.

That's fast bass.

That's an IB.

Not for the faint-hearted.

[witwald]

Originally Posted by Moonfly

So, how do you go about deciding what your targets are when looking at drivers. There must be some defining values you look for if your after a certain sound.

The first thing to consider when looking at driver Thiele-Small parameters is Fs, the driver's free-air resonance frequency. For a subwoofer, you'd generally want a –3 dB frequency of lower than 30 Hz. This calls for a driver Fs below 30 Hz for most vented-box and closed-box enclosures. If you would like to use a closed-box design, then an Fs of 20 Hz or lower will usually produce a –3 dB point in the 30 Hz range, once the added stiffness of air in the enclosure raises the resonance frequency of the system.

One also needs to consider the Vas value, which represents the equivalent volume of air that has the same compliance as the driver's suspension system. If the Vas is very large, say 200 litres, then the enclosure volume will also generally be quite large, possibly in the 80–100 litre range.

The driver Qts value also gives some clues as to what type of enclosure it might be best suited to. For example, a driver with a Qts value of around 0.40 requires an enclosure volume that is almost equal to the driver Vas value to get a correctly tuned vented enclosure. If the driver's Vas is large, say 200 litres, you'll need a large vented enclosure. For this design, the theoretical box tuning frequency, Fb, will also be close to the driver Fs.

However, in a closed box, the situation is somewhat different. A driver Qts = 0.40 can produce a maximally-flat closed-box tuning of Qtc = 0.71 if the enclosure volume is made about 1/3 that of the Vas value (with allowance for box filling material). Hence, a driver Vas = 200 litres requires a closed-box enclosure of only 70 litres or so. This is considerably more compact than the vented enclosure for the same driver.

In general, low-Qts drivers, with Qts in the range 0.20–0.30, are better suited to vented enclosures. That's because the sealed enclosure for such drivers needs to be quite a bit smaller than the Vas of the driver to get a flat frequency response. The small enclosure size of the closed box raises the system resonance frequency quite a bit, which means that the bass response is not as extended as that of the same driver in a correctly tuned vented enclosure.

Using a Linkwitz Transform Circuit with a closed-box enclosure does change the design parameters a little bit. Extra bass extension can be easily added to a closed-box subwoofer with a relatively compact enclosure. This is achieved with the use of a boost in low-frequencies provided by the equalised response of the power amplifier. This makes a closed-box subwoofer design able to achieve similar, if not better, low-frequency output than a vented-box system using the same driver, without any of the problems associated with port noise.

In the end, if high output levels are required in the low-frequency range of subwoofers, then large diameter drivers with a high linear excursion capability are required, as are low driver Fs resonance frequencies. Drivers such as these generally have large Vas values that require commensurately larger enclosures for correct system tuning.

[witwald]

Originally Posted by Nimby

Fast bass is not a myth.

Low-frequency bass is "slow" by definition; after all, it's bass response.

Throw away the box and keep adding more Sd until the cones stop moving at any frequency and any SPL.

For a given required SPL, you need a certain Sd (cone area) and Xd (cone excursion) combination to produce the required output levels. The more Sd you have, the smaller the Xd required. However, the Sd still has to move. For example, to reproduce a 20 Hz sine-wave, it has to move at 20 Hz. For lower frequencies it will move more slowly, for higher ones more quickly.

That's fast bass.

I think that bass response without (much) overshoot would probably be classed as "fast bass". Infinite baffle (IB) systems generally have drivers that have a Qts of less than 0.50, so they have a very heavily damped bass response.

No waiting for cone movement to start and stop because it never has to.

The cone, be it a small cone with large excursion, or a large cone with smaller excursion, always has to start and stop –there's no escaping that need.

[Nimby]

Originally Posted by witwald

The cone, be it a small cone with large excursion, or a large cone with smaller excursion, always has to start and stop –there's no escaping that need.

With respect; you are missing the point.

A single cone moving far enough to reproduce a low frequency fundamental has infinitely greater problems accelerating and returning to its rest point than many large cones. (each with their own motor) Each cone moving over a fraction of a millimetre to reproduce the same tone at the same overall level as the single driver.

Moreover, pure sinewaves are as rare as hen's teeth in the real world. Sinewaves are not even found in most pipe organs. So a single cone is further handicapped in that it has to reproduce multiple frequencies superimposed on its already extended cone travel in trying to reproduce the fundamental cleanly.

Few real sounds start slowly, build to peak and then die away equally slowly.(except for those elusive sinewaves) Most sounds start with a broadband, sharply rising, (transient) leading edge covering a great many different frequencies (harmonics and subharmonics) simultaneously and then die away relatively rapidly.

The multiple large driver cones of an IB can easily superimpose harmonics onto the fundamental since the cones are almost at rest under normal listening levels at all frequencies. This is why IBs are so superior for reproducing pipe organ music where subtleties in the interplay of the great pipes are clearly displayed without delay, distortion or colouration.

True IB subwoofers aim (roughly) for a system Q of .7 to maximise their freely extended ULF. Even if one starts with lower Q drivers the system Q will probably approach .7 (or higher) by the time it has been EQ'd with a BFD.

[Welwynnick]

Originally Posted by Nimby

Few real sounds start slowly, build to peak and then die away equally slowly.(except for those elusive sinewaves) Most sounds start with a broadband, sharply rising, (transient) leading edge covering a great many different frequencies (harmonics and subharmonics) simultaneously and then die away relatively rapidly.

The multiple large driver cones of an IB can easily superimpose harmonics onto the fundamental since the cones are almost at rest under normal listening levels at all frequencies. This is why IBs are so superior for reproducing pipe organ music where subtleties in the interplay of the great pipes are clearly displayed without delay, distortion or colouration.

I have some ideas about IBs that I'll describe in a bit, but thinking sideways for a moment, do people ever use different drive units in an IB array, or are they always the same?

And are there any good reasons why it should or shouldn't be done that way, or is it because everyone has always done it that way?

Nick

[Moonfly]

Wouldn't using different drivers with different parameters just lead to distortion, and an inability to effectively EQ the whole system?

[Welwynnick]

Why would that be, if each driver is working in its linear region, and those outputs are superimposed on eachother?

Nick

[Moonfly]

Well, are you talking about drivers intended to take care of a particular frequency range or different drivers taking care of the same range, i.e the sub bass region?

I would have thought drivers with different TS parameters, all doing your 80hz and under range, would be a mess. All taking different loads from their amps, all naturally resonating at varying frequencies, and some better at a particular range than others. IMO it just wouldnt work, well not as well as a regular IB setup anyway.

If your talking about using one driver from 0-10hz, then another from 10-20 and so on. I guess it could work, but I cant see the pay off being worth it against a well setup IB using a good driver throughout. For a start working like that, you would need a fair amount of processing, with a seperate one for each driver at the given range etc, then you would have the mess of getting each driver to work well with the next to come together in one harmonious bass system. I dont know of any system working like that now and to me I cant see such a system being cohesive. It sounds to me like using 5 engines in a car instead of a better engine with 5 gears. An IB is more like using an engine with more cylinders to get more power out of it, to have each one different just isnt plausible. I also dont know of any driver thats good for say only a 10hz range.

I'm no expert on IB's though, so I could be wrong.

[Nimby]

Good questions. I broke all the rules in using two sets of different drivers. One type of driver had a 13Hz Fs and the other 32Hz. Not only this but the drivers of each set had a different impedance so had to be wired differently. I ended up with one set all in parallel for 2 Ohms and the other series parallel for 4 Ohms. This had to be compensated for on the EP2500 channel control "volume" settings.

Each set of drivers had its own particular bandwidth and would play quite independently of the other set despite both being fed with exactly the same signal. In the end I had to EQ each set quite separately using REW to match the individual set's responses to a nominal flat line as best I could. This took some time because I kept feeling the cone surrounds of each set while trying to match their excursions.

Trying to use them in unequal but opposing sets produced serious vibrations due to a lack of cancellation of reaction forces over the entire IB bandwidth. They were paying their own tunes with no overlap. So I had to remove all the drivers and fit them back in one opposed set at the top and the other set opposed at the bottom of the manifold (box). Driver reaction forces are now safely cancelled.

It sounds superb with brutal power and amazing transparency but has lost some of the tactile floor movement. I am still not completely satisfied I have achieved perfection and may make further changes when in the mood.

As a guiding rule I would strongly suggest the use of only one type of IB driver throughout the installation. Not only did the raw excursions of my drivers mismatch wildly with frequency but when doing so they acted as nearfield dampers on the other set.

I look forward to your ideas on IBs. We IB owners are always open to potential improvements over the standard (opposed driver manifold) model.

[Moonfly]

Thats interesting Nimby, was that intentional or just because those are the drivers you had.

It does sound as though it brought some headaches though. Is there any benefit of that over same type drivers, I find it hard to think why it would, but thats probably not saying a lot

[Nimby]

I happened to have both sets of driver and wanted to experiment with an 8 x 15" IB.

The old set was just sitting in boxes after replacement with the new.

The cheapest kit, you will ever own, is always what you have now.

Change always means extra expense.

[Welwynnick]

Originally Posted by Nimby

As a guiding rule I would strongly suggest the use of only one type of IB driver throughout the installation. Not only did the raw excursions of my drivers mismatch wildly with frequency but when doing so they acted as nearfield dampers on the other set.

I look forward to your ideas on IBs. We IB owners are always open to potential improvements over the standard (opposed driver manifold) model.

Great to have some real experience rather than just speculation. A lot of stereo speakers seem to be two and a half way these days, with different bass tuning. They have separate, rather than shared chambers, though.

My thoughts about IB relate to the effect of the loading on the phase characteristics. With an active sealed sub, the driver resonance is high because the box volume is low - so the air spring is stiff. The sub is forced by EQ to work in the LF roll-off region below this resonance, with the EQ compensating for the falling acoustic output.

So far so good. But in this condition, the impedance to the motion of the driver is predominantly in proportion to, and in phase with, the displacement of the driver. The motor is effectively pushing against a spring, and this impedance dominates the mass of the driver and the impedance of the suspension. The sub has become a static driver - it is no longer dynamic at all.

In the IB case, the acoustic suspension acts as a soft spring - softer than the suspension. This means the dynamics are dominated by the mass of the driver and the stiffness of the suspension. Above the very low free-space resonance, the driver's behaviour is dynamic - the same as a conventional, passive moving coil speaker working within its passband. In this case, the mass of the driver dominates the impedance, and the motor uses its energy accelerating the driver backwards and forwards.

The consequence of this is that the force applied to the driver by the motor is no longer in phase with the displacement of the driver - its in phase with the acceleration of the driver. And acceleration is the first time differential of velocity, which is the differential of diplacement. Each differential adds a 90 degree phase difference, so velocity is 90 deg ahead of displacement, and acceleration is 90 deg ahead of velocity.

This means to me that an active sub working at low frequencies below its resonance, will tend towards being 180 deg out of phase with the pass-band audio. Thats the consequence of it behaving as a static, rather than dynamic driver.

An IB driver though, will continue working in its dynamic range, so the displacement will continue to be 180 deg out of phase with the electrical signal but in phase with the rest of the music. And thats got to be better?!

Nick

[Russell.Williams]

Hang on! I need to get a coffee whilst Nimby picks the bones out of that one.

Russell

[Nimby]

Originally Posted by Russell.Williams

Hang on! I need to get a coffee whilst Nimby picks the bones out of that one.

Russell

Coward! Come back!

[Nimby]

Nick

I understand all the words but not in the order you used them.

I am still worrying over the final question mark.

Are you telling us? Or asking for our agreement?