Back EMF

bhobba · « **Reply #60 on:** 13 Nov 2007, 05:37 am »

Quote from: gerado on 13 Nov 2007, 04:45 am

I started off with only knowledge how to turn on a soldering iron
have both a GK and LF from kits.
The LF was more like an assembly task rather than building.
Real easy

I am sure

. Seriously though, with all the great people on-line to help, if I take my time, I suspect I will be able to get there. I plan to set up my system in stages. First getting the DEQX and speakers and using an old Rotel 5 ch amp I have sitting about (if it still works - its been 5 years since I fired it up). Next stage - Hugh's amps. After that - maybe some Empirical Audio mods to the DEQX to run directly from the USB of a computer.

Thanks
Bill

gerado · « **Reply #61 on:** 13 Nov 2007, 06:27 am »

Bill
keep in touch
my DEQX arrives in a day or so and have no idea how/what to modify , though Kyrill has made good recommendations, (Kyrill you ready

)
we might start another thread soon....
I will definitely need help

AKSA · « **Reply #62 on:** 13 Nov 2007, 07:40 am »

Bill,

The Soraya CB105 is sold only as a plug 'n play retail product so that I can fully control quality. All other products are kits, however.

Formulae?

The only ones I use are Ohms law and the reactance equations, with these engineering limits are established, and then the tweaking between these values begins........

Cheers,

Hugh

bhobba · « **Reply #63 on:** 13 Nov 2007, 11:17 pm »

Quote from: gerado on 13 Nov 2007, 06:27 am

My DEQX arrives in a day or so and have no idea how/what to modify , though Kyrill has made good recommendations, (Kyrill you ready )
we might start another thread soon....
I will definitely need help

Since I have not got mine yet (I am waiting for their new model to be released and my money issues to fully abate) I don't know how much help I will be. But off the top of my head my recommendations would be to bed it down in your system, then think about possible mods. With a product like that I think the biggest bang for your buck will be in getting those distortion producing grossover components removed from your speaker. As Andy and Hugh have kindly pointed out, removing all the crossover components may not be optimum - impedance correction may still be of value so some experimentation in that area may be worthwhile. Or perhaps, getting new speakers using some of the modern wonder drivers like the Seas magnesium cones. Cone breakup and other problems that make it difficult to design speakers using them all disappear with a DEQX.

A possibility I am looking at is:
http://www.bamberglab.com.

I recently wrote to Equinox audio who claim they do custom speaker designs but they have not replied - which to me is not a good sign. Phil Bamberg, by reputation, is a very good crossover designer and has used a DEQX on his product. I am sure he can advise on the optimum impedance correction, if any, to get the best out of the DEQX, for his speakers - which look quite modestly priced for what you get.

Beyond that I have heard good things about computer audio - ie using a battery powered laptop as your drive. Getting the DEQX modified to accept that input direct would seem to hold promise:
http://www.audiocircle.com/index.php?topic=32168.0;wap2

I must admit to being a little confused about what was written. I can not see how mains grunge can get in from a battery powered lap-top - which leaves me scratching my head why his problems did not totally disappear when he used a lap-top. Maybe Hugh or Andy can comment.

Thanks
Bill

gerado · « **Reply #64 on:** 13 Nov 2007, 11:24 pm »

Thanks Bill

you mention that there is a new model coming? What do you know, because I asked specifically about this before I ordered mine and they denied there was a new one coming out.

bhobba · « **Reply #65 on:** 14 Nov 2007, 02:32 am »

Quote from: gerado on 13 Nov 2007, 11:24 pm

you mention that there is a new model coming? What do you know, because I asked specifically about this before I ordered mine and they denied there was a new one coming out.

It is going to be released in January. Initial impressions was that it is audibly superior to the current model. The difference mentioned was the use of linear supplies. It will be more expensive though. Unless you want it immediately I would contact them and get the new model. The guy I was speaking to really knew his stuff. I find they give really good customer service so if you contact them I think you will get the current information.

Thanks
Bill

kyrill · « **Reply #66 on:** 14 Nov 2007, 12:09 pm »

hmm

DEQX will (probably) not update the core of their software or core topology as it is already so good. Easy to update are the "default" everywhere else happening shortcuts and component choices to keep cost as low as possible. coupling caps, power supplies and so on and probably the casing.

DEQX does not support at all any modification. I got zero advice, zilch support in trying to get info to implement an USB port.
a certain "Allan" even stop answering at all even after polite repeated emails for slight advices or help

you would probably loose any guarantee ( like by other manufacturers) when modding in the guarantee period.

Helas they dont inform customers ( after sale) of the growing development in their hardware and of any possible hardware (evolutionary) update...
for instance my board revision has a max output of 1.5V. 2 revs furhter they included jumpers to choose up even to 4 Volts

only by probing into this matter, this info was released

So i would not characterise their client support as good. sufficient would be a better word. They are a universe apart from the support of how Aspen was in history up until now.

gerado · « **Reply #67 on:** 14 Nov 2007, 12:25 pm »

Going off topic a bit but...

I enquired about the new model 3 , feeling rather annoyed because I specifically asked about a new model before ordering. In writing I have confirmation that the new model is the same mother board. The power supply is bigger and some balanced outputs included in a bigger case. It is not a replacement model the 2.6 continues, just for a different market. For me because I did ask specifically before ordering they offered that after the release in ?Jan 2008 they will upgrade to new box etc if I require for the price differential of the 2 models. Sonically there may not be any difference unless the power supply is really superior but I have no information on this. Might be no point if the mods everyone suggests includes power supply mod but the bigger case may be an advantage unless keeping USB mods outside the box is better.

bhobba · « **Reply #68 on:** 14 Nov 2007, 05:37 pm »

Quote from: kyrill on 14 Nov 2007, 12:09 pm

So i would not characterise their client support as good. sufficient would be a better word. They are a universe apart from the support of how Aspen was in history up until now.

Since I haven't actually purchased the product yet, I suspect, like just about every company out there, they will answer questions etc, and generally oblige you, until you actually give them your dosh. Once you do that, I suspect their level of service will go down. Hugh, of course, does not fall into that category. If I got a mod done, I fully expect it to void support and warranty. I would not get it done until I had fully bedded it down.

Thanks
Bill

gerado · « **Reply #69 on:** 20 Nov 2007, 11:14 pm »

Since back EMF is a bad thing , does it not make sense to have a high pass filter on the base driver as well. Say 30Hz cut off , rather than rely on the drivers natural roll off. Will it not clean up the sound a fair bit if the driver is not receiving signals it cannot reproduce well and limit wide excursions causing lots of EMF. The same could be argued for the tweeter for a low pass filter perhaps.
Or is my logic all wrong?

kyrill · « **Reply #70 on:** 20 Nov 2007, 11:42 pm »

i read somewhere on this forum Hugh's amps did not sound better with Zobel on that particular speaker, it didn't need it
so somehow it all depends..

andyr · « **Reply #71 on:** 21 Nov 2007, 02:33 am »

Quote from: gerado on 20 Nov 2007, 11:14 pm

Since back EMF is a bad thing , does it not make sense to have a high pass filter on the base driver as well. Say 30Hz cut off , rather than rely on the drivers natural roll off. Will it not clean up the sound a fair bit if the driver is not receiving signals it cannot reproduce well and limit wide excursions causing lots of EMF. The same could be argued for the tweeter for a low pass filter perhaps.

Or is my logic all wrong?

I don't think you have any logic, Theo!!??

Regards,

Andy

AKSA · « **Reply #72 on:** 21 Nov 2007, 03:14 am »

Andy,

Be nice!!

I think Theo has plenty of logic!!

Theo,

The back EMF issue is these days well handled by very low Zout amps, which short out the back EMF appearing after the event at the driver terminals, and by a shorting ring within the driver which cancels out a large portion of it before it even gets to the driver terminals.

The term is certainly outmoded, and would be better described by 'reactive kickback', and since pretty much all drivers are designed to operate with voltage sources this is what we are stuck with. To me, it's a bit like wheels on cars, they are made with rubber and synthetic polymers. No one ever considers making them from bamboo, or hemp, or glass fibre, for example.

I hope this is not too simplistic, but I for one am happy with the diversity of drivers out there, there are some very good ones. And the non-ideal behaviour can be tamed with careful crossover design, something not so amenable with an active system.

Cheers,

Hugh

gerado · « **Reply #73 on:** 21 Nov 2007, 03:23 am »

Andy,

ohh y a pepble so unkaind

brj · « **Reply #74 on:** 21 Nov 2007, 03:33 am »

Ignoring whether you actually need a Zobel with a given amp, can it actually hurt anything? Or perhaps the more general question... how much does the parts quality of caps, inductors and resistors in parallel with a circuit, rather than in serial, affect the sound?

Thanks!

gerado · « **Reply #75 on:** 21 Nov 2007, 03:44 am »

Thanks Hugh
part of my question was referring to any benefits if one narrowed down the frequency band a driver is exposed to. For example a base driver has no protection on the low frequencies an amp throws at it , irrespective if it can reproduce them or not. If a base driver starts to roll off below say 40Hz is it a good thing to filter out frequencies bellow this, so that the driver can operate cleanly in its optimal frequency band?

Tliner · « **Reply #76 on:** 21 Nov 2007, 04:52 am »

Hi All,

From many years of rooting around with speaker designs I have found that a Zobel is frequently used to manage a driver roll off knee at crossover. Often some drivers display a harshness/loudness at the XO point and the transition from one driver to the other is not seamless due to a higher SPL of one driver.

To design a seamless transition (when it is seamless you can't hear one driver overpowering the other) a fair bit of playing with the resistor and to a lesser extent the capacitor of the Zobel to raise or flatten the knee at the roll off point. Software will indicate the steepness or angle (depends which way the graphs are interpreted) at the knee when one changes the resistor values to raise or reduce the dB at the xover region of the driver concerned. Now these changes may not suit a particular amp (older designs?) and on other amps there appears to be no affect at all. I assume that the back EMF will affect some amps more than others. However , usually an audible change will be heard when the Zobel is included or altered. A Zobel is used to even out the performance of the drivers. A speaker designer is not too fussed about the back EMF as long as the speakers sound good. That's right Hugh?

Now to bring something else into the debate is to Bi-Wire the speakers or not. There is a difference in "sound" in some systems when Bi-Wiring is incorporated with some speaker amp combinations more than others. I am lead to understand that Bi-Wiring is supposed to reduce EMF bouncing around between the speakers and the amp at least so that there is nothing audible. I recon the jury is still out on Bi-Wiring but there is a relation to back EMF.

Continue on boys,

Laurie.

andyr · « **Reply #77 on:** 21 Nov 2007, 08:25 am »

Quote from: Tliner on 21 Nov 2007, 04:52 am

Hi All,

I am led to understand that Bi-Wiring is supposed to reduce EMF bouncing around between the speakers and the amp at least so that there is nothing audible.

Laurie.

Hi Laurie,

A commercial speaker designer/mfr of my acquaintance reckoned the main gain as a result of bi-wiring was to effectively increase the guage of the "earth/return" leg (and hence reduce the overall 'R')!

In other words if you single-wired but added a second earth/return wire, you'd get the same benefit. I have never experimented with this concept.

Regards,

Andy

kyrill · « **Reply #78 on:** 21 Nov 2007, 11:34 am »

why only the return leg? the hot leg in bi-wiring is also doubled
so the total wire resistance relative to amp output impedance is halved?

Or is my logic all wrong?

AKSA · « **Reply #79 on:** 21 Nov 2007, 11:37 am »

Your logic is entirely correct, Kyrill!!

Biwiring really does mean four wires.....

BUT I think there is much in what Andy says - thicker wires do it for me....

Cheers,

Hugh