Precision devices

[Geenius]

.........How long have you been playing?

Just over 25 years of which the first 10 only on bass-guitar

 

[paulspencer]

Is that a double bass I see there?

There's nothing like acoustic double bass, I just recently bought a Dianna Krall live in paris DVD just to hear the double bass! Although, sadly, it revealed that the bass from my mains is far better than my subs

I'm keen on trying dipole bass properly as I'm convinced its the only kind that will really satisfy me as getting the most accurate bass I can get, especially for double bass!

One thing I'm curious about is how large PA drivers compare to some of the better subs with shorting rings and/or XBL2 or competing technologies, when it comes to accuracy.

How big are those PD drivers? The magnet looks huge!

 

[Geenius]

Is that a double bass I see there?

There's nothing like acoustic double bass, I just recently bought a Dianna Krall live in paris DVD just to hear the double bass! Although, sadly, it revealed that the bass from my mains is far better than my subs

I'm keen on trying dipole bass properly as I'm convinced its the only kind that will really satisfy me as getting the most accurate bass I can get, especially for double bass!

One thing I'm curious about is how large PA drivers compare to some of the better subs with shorting rings and/or XBL2 or competing technologies, when it comes to accuracy.

How big are those PD drivers? The magnet looks huge!

Yep that's a double bass, 3/4 size German model from the late 1960's.

The PD's are 21" woofers. Fs is 22Hz and Sd 1630cm2 each. Xmax is 12mm and the displacement limit is stated to be 38mm. BL is a huge 34,28T/m.

I owned a Velodyne DD15 before this but always had the impression it sounded like a large heavy cone in a small box. It went flat down to 15Hz, great for popular music and home theatre but being a fan of classical music and jazz I was never completely happy with it.

 

[paulspencer]

Tony, there's nothing quite like double bass. I once heard a local band which had a double bass, seeing them live the bass player used a bow (which I hadn't ever seen before) and I was impressed!

The PD's are 21" woofers. Fs is 22Hz and Sd 1630cm2 each. Xmax is 12mm and the displacement limit is stated to be 38mm. BL is a huge 34,28T/m.

WOW!

12mm one way xmax?

I owned a Velodyne DD15 before this but always had the impression it sounded like a large heavy cone in a small box. It went flat down to 15Hz, great for popular music and home theatre but being a fan of classical music and jazz I was never completely happy with it.

I'm surprised to hear that. I've never heard a velodyne. It's a servo sub? I would have thought that it would work well for jazz as well. So you like the PD much better?

 

[Geenius]

12mm one way xmax?

The voice-coil winding depth is 30mm and the magnet gap height 15mm's. That would be 15mm peak-peak displacement, PD state 12mm Xmax but I'm not sure if that is one way or peak-peak. But with all that cone area the air displacement should be enough even if it is only 6mm one way.

I'm surprised to hear that. I've never heard a velodyne. It's a servo sub? I would have thought that it would work well for jazz as well. So you like the PD much better?

Don't get me wrong, the Velodyne is very very good, it's me, I want the best when it comes to bass quality. The Velodyne is a servo controlled sub with digital room correction. I will probably order their SMS-1 which is the digital control unit from the DD-series and build my own sub(s). I haven't tested the PD's enough yet to tell which I like best but the PD's certainly have the potential.

 

[jdunham]

Kevin,

I noted you said you could only house a 12" driver.

This is what I did with 2 x 15" drivers. They don't use any more frontal area that a 12" would take up on the front:

Not really a sub-woofer as such (flat down to 30hz), but great up to 200hz where the font-horn takes over. My room is 12' x 18'.

I've been really pleased with these.

I am using Lambda TD15's but I was going to buy the PD's if not - they are good units.

Regards,

Jonathan

 

[derf]

One thing I'm curious about is how large PA drivers compare to some of the better subs with shorting rings and/or XBL2 or competing technologies, when it comes to accuracy.

To be honest, shorting rings/other fancy technology just can't compete with sheer surface area, when it comes to bass reproduction. If it was a choice between a 12" with shorting ring etc and an 18", I'd pick the bigger driver any day(all else being equal).

I think a lot of the 10"/12" subs around today are a product of people wanting deep bass and small size, which is fine, but with it comes limitations. Limited SPL, higher distortion, only good up to 100-150hz(a product of being long throw?).

I'd seriously consider the 15"/18" offerings from Eminence, in particular the Delta15LF and the Sigma Pro.

The Delta driver is cheap as chips over here(around £50 a piece), has good Xmax, around about the right Qts. 2 a side in a W/H/Flat baffle would be a great proof of concept and wouldn't cost the world to implement.

 

[paulspencer]

Jonathan, I'm curious why you have angled those dipoles as you have!

Derf, is that based on actual comparisons or your theoretical gut feeling?

For the larger driver to be more linear means that its excursion would need to be more linear. This is easier to achieve with less excursion, however, it doesn't necessarily follow that less xmax and more SD means lower distortion.

 

[derf]

Jonathan, I'm curious why you have angled those dipoles as you have!

As am I, do tell!.

For the larger driver to be more linear means that its excursion would need to be more linear. This is easier to achieve with less excursion, however, it doesn't necessarily follow that less xmax and more SD means lower distortion

To the best of my knowledge, in it's most basic terms excursion=distortion. Excursion is a product of a driver working hard to reproduce whatever signal it's being fed.

These long excursion drivers are truly a marvel of engineering and allow people to achieve deeper bass in smaller living circumstances. However, given the inclination/larger space/need for more spl etc, I believe any comparable 18" with normal excursion(say 5-6mm), would be able to provide lower distortion for the same input and spl level.

Given that the typical 18" has twice the surface area of the typical 12", it just seems very logical to me that this'd be the case.

Unfortunately, at this point it's just my theoretical ramblings, although I'm hoping someone who has actually done some tests/has some proof of this will chime in.

Of course, if I've got this wrong, I'm willing to take a slap on the wrists too. Aslong as my knowledge of things progresses, I don't mind being told I'm wrong once in a while.

 

[maiky76]

Hi!

Maybe this could be interesting for you!

the device is:
http://www.behringer.com/DSP1124P/index.cfm?lang=ENG
And it shoulb have a very close over all performance compare to Velo's one, much cheaper at least.

Some "how tos" to turn it in a very user friendly device.
http://www.snapbug.ws/bfd.htm
http://homepage.ntlworld.com/john.mulcahy/roomeq/index.html

You can even use a DCX2496 from behringer wich is a unmatch Q/P audio digital eq, I had one for a while. I loved it. In addition the DCX could be use for many aims that should interest you!

@+
Maiky

 

[jdunham]

defr and paulspencer,

The reason for the angled baffles can be read about here:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=57187&highlight=

In short the reasoning is that they can be used in corners, and in so doing decrease the amount of dipole roll-off by using the walls.

Mine are pretty flat without any EQ from 200hz and downwards.

BTW, derf is correct on his assertions - there are quite a few reasons why a larger cone driver is better than a small/higher excursion one. Ironically, cost is often another one of them!

Regards,

Jonathan

 

[jdunham]

Sorry, correct link below:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=57187&highlight=cdw

 

[paulspencer]

To the best of my knowledge, in it's most basic terms excursion=distortion. Excursion is a product of a driver working hard to reproduce whatever signal it's being fed.

For a given driver, distortion will increase with excursion, but if you are comparing two (very) different drivers, it will not always be true that the one with less excursion will have lower distortion! That would be an apples to oranges comparison. Also drivers can now be designed to have a ruler flat BL curve and suspension curve so that there is a much smaller increase in distortion for excursion.

It is much easier to use drivers with a larger SD and then only have to keep it linear over a smaller xmax. Then again, this requires a larger driver with a bigger basket, and this involves cost. Apparently there isn't really any increase in materials involved in XBL2, it's really just a clever design involving two VC gaps, so in fact it may be cheaper to produce such drivers, as they may in fact require less materials. What they actually sell for, and which is better value, is influenced by a range of factors.

As I recall, there were distortion measurements of the Tumult vs the Maelstrom. IIRC, the Tumult had lower distortion.

 

[derf]

For a given driver, distortion will increase with excursion, but if you are comparing two (very) different drivers, it will not always be true that the one with less excursion will have lower distortion! That would be an apples to oranges comparison.

I'm not sure if you've correctly interpreted what I meant to say or even if I've read what you've said above as you intended it to read.

I'm not trying to say that the driver with less *potential excursion*(in this case X model pro 18") has less distortion because it has less potential excursion, but because it achieves the same spl level for the same input as the (longer excursion) 12" by having a much higher surface diameter and therefore having to move less.

Ok, it's kind of apples and oranges in the way we're pitching 12" drivers in general against 18's, but the intended use is the same(dipole bass).

It is much easier to use drivers with a larger SD and then only have to keep it linear over a smaller xmax. Then again, this requires a larger driver with a bigger basket, and this involves cost. Apparently there isn't really any increase in materials involved in XBL2, it's really just a clever design involving two VC gaps, so in fact it may be cheaper to produce such drivers, as they may in fact require less materials. What they actually sell for, and which is better value, is influenced by a range of factors.

From what I can remember the 12" drivers Linkwitz uses cost around about the same price as entry level Eminence 18" woofers, what'd be really nice to see is a tests comparing the smaller Linkwitz drivers and the larger Eminence ones.

That, for me would be very interesting.

 

[paulspencer]

derf, I think we actually agree in principle, that, all other things being equal, a driver which gets its displacement more from large SD rather than high xmax is likely to be more linear. Although of course there will be examples where the higher xmax driver has a motor system that is more linear over its larger xmax, and will have lower distortion.

Normally those large SD drivers achieve more output but less extension. However, subs with good distortion performance may get the same performance given the same extension, perhaps even better performance. The PD driver with 12mm p-p xmax has only about 2L of displacement, less than some 12" drivers. A pair of XLS 12" drivers have more displacement. I think those PA drivers have the advantage of more top end, however, dipoles often have a limited top end due to resonance issues.

Ok, it's kind of apples and oranges in the way we're pitching 12" drivers in general against 18's, but the intended use is the same(dipole bass).

It's an apples - oranges comparison if you say the 18 will have lower distortion due to lower xmax. However, if you measure them both for the same task, it's a fair comparison. It's one I'd be interested to see.

From what I can remember the 12" drivers Linkwitz uses cost around about the same price as entry level Eminence 18" woofers, what'd be really nice to see is a tests comparing the smaller Linkwitz drivers and the larger Eminence ones.

I'd like to see that as well ... I'll be even more interested down the track when I have the space and budget to build a very large OB bass array with impressive SPL as well as SQ!

 

[agrobler]

my two cents

I've wondered about this a while ago, but with little practical experience, I am left with rudimentary physics... Apologies in advance if I'm not very clear...

When using a large lower excursion cone vs a smaller large excursion cone, for a given (same) frequency and spl, all that changes is the distance the driver has to move within the period of one cycle... This means that the one driver (smaller one) has to accellerate faster to reach greater distance, even if both drivers are linear at said spl and Hz, the small one is trying to setup the same pressure variations much faster than the large one, actually this is wrong, overall the same pressure variation is set up, but it has to set up a larger pressure variation in a smaller cross section area ( imagine smaller diam tube with longer length). Air is lossy and not an ideal liquid it is compressible, has mass and will move in all direc.s if hit from one side... if you try to move it very fast it will tend not to follow... so maybe we can say the pressure variations are more ordered with lower excursion

OK so first thing, most instruments going low is large with small excursions the bass drum flexes maybe 2 mm... so the type of acceleration we get of the air is similar to the larger cone for most bass instruments... except perhaps pipe organ. the reason is you are creating a similar "looking" pressure wave to the instrument.

Second thing, with large cone, you have a greater surface area to circumference ratio... so you have less "fall-off" of air at the edge because pressure to the side is lower than pressure to the front...
Same effect with hornloading, I think - you are moving the air more effectively, in effect creating large driver / more orderly air movements...

Mmm... this sounds so much more impressive and logical with

 

[paulspencer]

When using a large lower excursion cone vs a smaller large excursion cone, for a given (same) frequency and spl, all that changes is the distance the driver has to move within the period of one cycle

Actually I think there is a bit more to it than that.

There is the suspension linearity as it relates to excursion, and the BL curve. An ideal driver would have a perfectly flat suspension and BL curve in its operating range. In practice the BL curve won't be perfectly flat, and an ideal driver would have stiffer suspension at extremes of excursion to compensate for a non flat BL curve.

Pro drivers are designed for higher power handling, hence they will have often have higher inductance. Some argue that this is significant for bass. Adire claim low inductance gives "fast bass," although the validity of this depends on your definition of "fast bass" but in this case they mean in a more literal sense - the speed at which a driver responds to transients.

Compression is also going to be different. There is compression due to the power applied, and how effective heatsinking is. Also there is compression related to the movement of air.

I think in general the bigger driver is favoured in accuracy, however, a better engineered smaller driver may turn out to be more economical, smaller and have better performance.

To give a definitive answer on which is more accurate, however, is something which requires measurements IMO.

 

[agrobler]

Sorry for giving the impression that cone acceleration and SA to circumference ratio is the only factor that is important, that's certainly not the case.

I just tried give my view that when all the engineering and specifications of the drivers are taken into account - or corrected for - there are still some basic things which are not the same and can probably not be compensated for...

I also should have stated clearly that I don't know if this is, in practice, a very large preactical effect/drawback.

 

[Geenius]

Time for a little update. The Precision Devices PD2150's have been playing for a couple of weeks now in various configurations varying from closed box seperates to stacked di-pole (see photo). The best so far is the stacked di-pole, this has the best bass I have ever heard and I am still only running them on a simple passive 2nd order low-pass network connected parallel to my main speakers. Bass is just there, no colouration, no limited dynamics, no boxy-ness, just clear clean deep bass. Can't image how good it will be when driven active and with digital room correction.

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

 

[paulspencer]

Tony, is that a U frame?