$1000 to spend on 12" or 15" Subwoofer - Page 2 - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 20th August 2008, 06:37 PM   #11
diyAudio Member
 
Join Date: Feb 2004
Location: Texas
Default inductance is relative to motor strength

The absolute value of inducatance is not a good indicator, just as the absolute BL value is no meaning without comparing it to Rdc of voice coil (so-called BL^2/Re value). All these values are scalable with respect to Rdc. Actually, the importance of inductance is determined by a lot more factors.

In subwoofer application, the transition point from a back-EMF dominating frequency band to a inductance-dominating band indicates where the motor structure begin to lose firm control of cone motion. Maybe a better word is equilibrium point and for most woofers it occurs between 60hz to 120hz. At frequencies below this equilibrium point, back-EMF dominates the impedance value, and above this point, back EMF is so low, that is becomes more like current drive. Coincidentally, that minimal impedance frequency point is way higher with smaller woofers, or woofers with smaller xmax. All these come into play when some people would prefer to use multiple small woofer to get the SPL up vs one large woofer. There is no doubt that a woofer with a higher equilibrium point would sound better controlled.

So now let us see what can move the equilibrium frequency point up.

First, bigger magnet. Bigger magnet increase BL value with everything else unchanged. Higher BL values increase the back-EMF and push it's equilibrium point to inductance to a higher value.

Second, lower moving mass. Lower moving mass would also increase back EMF at higher frequency point.

Three, Faraday ring. Only faraday rings are thick enough to contribute at frequencies below 100hz. Copper sleeves is not thick enough to reduce inductance below 100hz.

So the opposite of all above can cause the equilibrium frequency point to move down. But what else can cause it to move down? The widening of magnetic gap. Certain high excursion drivers try to stuff as much wire in the gap in order to increase the "L" value in BL. But increase in L value also increases inductance, so it appears the equilibrium point should remain unchanged. But in reality, widening gap reduces B value, so it is more like use a smaller magnet now. As a result, it causes the point to move down. In addition, the more wires, the heavier cone, .....

One may ask why cone control (or having an EMF dominating impedance in subwoofer) is so important. Because the engergy inside the enclosure wants to escape. If a woofer does not have firm control of the cone, that cone can move in response to that energy and give the energy a passway to outside. It defeats the purpose of having a tank-like enclosure. A woofer with firm cone control creates a different dimension of clean sound. Here I emphasize "dimension" because another dimension of clean sound is from low distortion and these two are completely orthogonal. It is always good to have both, instead of only one of them.

BTW, those who are more familiar with T/S equivalent circuit of a woofer may already understand this. The cone mass is represented as "capacitor" in that equivanet circuit, which has a 180 degrees phase difference with voice coil indutance. In addition, lower cone mass yields a smaller cap value and therefore higher impedance. And unfortunately, the voice coil inductance will counteract with that and cause the impedance to look smaller and make it appear as if the woofer has a heavier cone. That is another way to look at the impact of inducantace.

__________________
Servo Subwoofer kits > Rythmik Audio | Articulate bass for the discerning audiophile .:: Brian Ding
  Reply With Quote
Old 20th August 2008, 10:22 PM   #12
diyAudio Member
 
Join Date: Feb 2004
Location: Texas
Default Re: inductance is relative to motor strength

Quote:
Originally posted by rythmikaudio

In subwoofer application, the transition point from a back-EMF dominating frequency band to a inductance-dominating band indicates where the motor structure begin to lose firm control of cone motion. Maybe a better word is equilibrium point and for most woofers it occurs between 60hz to 120hz.

To put things in perspective, Peerless 12" XLS and XXLS have that equilibrium point at 160hz or so vs a 15" TC 2k at 60hz. That is a huge difference. Effective inductance is four times when the equilibrium point is cut in half.
__________________
Servo Subwoofer kits > Rythmik Audio | Articulate bass for the discerning audiophile .:: Brian Ding
  Reply With Quote
Old 20th August 2008, 11:16 PM   #13
pjpoes is offline pjpoes  United States
diyAudio Member
 
Join Date: Jan 2005
Location: New York
Send a message via AIM to pjpoes
I also think another read of Krutke's article is worthwhile if all you took away from it was the issue of high inductance and higher distortion. He also mentioned the rise in response contributing to the third harmonic distortion, and being audible still. That whole part is still true of the Tumult as far as I know (based on its response measurements I have seen), and most other top end subwoofers I have seen or measured.

As I mentioned, I have talked with some of the designers of these drivers, and my discussion with them has always indicated that the trade-offs made by high excursion drivers, even those with lower distortion motors, was detrimental to sound quality. The impression I got was that designing a driver to have long excursion, produce deep bass in a small box, and have more linear travel at higher excursion area's required that you give up better sound at more reasonable levels as a result of increased distortion and noise.

I really think that the biggest improvement in these drivers has been more in reducing mechanical noise than in the area of distortions.
  Reply With Quote
Old 5th November 2008, 11:43 AM   #14
diyAudio Member
 
Join Date: Jun 2008
What, would you say, is a low enough excursion driver? I.e. how little excursion must I have to be really safe? If I am building a sub woofer to play 20Hz and 30Hz tones, should I go for 10" Seas drivers with +/-6mm (12mm p-p) linear excursion?

Would you say that 12" Peerless XLS (25mm p-p) is better or worse than a 12" Shiva-X (54mm p-p) or Acoustic Elegance AV12-X (46mm p-p), for playing at low to moderate levels?

Is it any different if my aim is to reproduce perfectly from 20Hz to 100Hz, instead of 50Hz to 500Hz?
  Reply With Quote
Old 6th November 2008, 10:36 AM   #15
simon5 is offline simon5  Canada
diyAudio Member
 
Join Date: Nov 2004
Location: Québec, Québec
soundengine355 have a high budget...

Since you have such a high budget, I'd contact John from Acoustic Elegance. I'd use one AV15-H which has one of the lowest Le available and a respectable 46mm of xmax p-p.

You ask him to custom built it, to add the Appollo upgrade on it, which will add two massive aluminium faraday rings to further reduce Le and increase power handling.

Then I'd purchase two PR18-2500 from him, ask him to add as much mass as the PR can handle.

You maximum enclosure size give about 100 liters internal volume net. So that would be great with dual PR18 with a custom AV15-H.

That finishes my realistic suggestion. Then to go overboard...

To go further, you'd need to ask John to add a sensing coil to that massive custom AV15-H and contact rythmikaudio to custom build a servo amplifier for that custom AV15-H... but I'm dreaming a bit there !
__________________
DIYaudio for President !
  Reply With Quote
Old 6th November 2008, 01:31 PM   #16
MaVo is offline MaVo  Germany
diyAudio Member
 
Join Date: Jan 2006
This zaph article is pure rhethorics and basically says that a good designed low xmax driver sounds better than a badly designed large xmax driver, which is no wonder at all and no indicator about soundqualities relation to xmax or individual cases, where distortion measurements render such arguments useless but entertaining.
  Reply With Quote
Old 6th November 2008, 03:29 PM   #17
diyAudio Member
 
Join Date: Feb 2004
Location: Texas
Quote:
Originally posted by MaVo
This zaph article is pure rhethorics and basically says that a good designed low xmax driver sounds better than a badly designed large xmax driver, which is no wonder at all and no indicator about soundqualities relation to xmax or individual cases, where distortion measurements render such arguments useless but entertaining.
Most people will not look into this type of details. Let me just share a few points:
1) We all build solid enclosure to "contain" internal standing wave retransmit through enclosure walls. A typical knocking test is suffice. Now try that on your cone and you can see how solid our cone is. Cone is part of transducer and part of enclosure. It needs to follow the input signal and yet at the same time effectively resist the standing wave acting on it just like any other part of the enclosure (otherwise, it defeat the purpose of having a solid enclosure). The ability for the cone to resist standing wave push is related to the back EMF to inductance ratio. I don't need to say more. Larger excursion drivers simply have weaker back EMF to inductance ratio (for the most broad frequecies). Traditional test procedure cannot test this because it completely replies on steady state signal. It is like determine a car's performance using straight road. We should try a couple of turns. Most people will not do that because it is very subjective impression for these experience. So what do engieers do? drop it from the test.

2) In the T/S parameters, the equivalent circuit represents the cone mass is the driver's impedance is a capacitor, which has an opposite phase of inductor. As a result, they substract from each other and that is not good at all. Let us say the indutactance have 1ohm reactance and distortion is 10%, that is 0.1ohms of distortion. Let us say the mass reactance is 0.9ohm and is pretty linear. Because they substract from each other, the net reactance is now only 0.1ohm. No other thing can cancel that 0.1ohm distortion, so what is the distortion percentage now? It is 100%. When you look at the inductance by itself, most people say it is no big deal. Sure. Now add the motional impedance of speaker.
__________________
Servo Subwoofer kits > Rythmik Audio | Articulate bass for the discerning audiophile .:: Brian Ding
  Reply With Quote
Old 6th November 2008, 06:01 PM   #18
simon5 is offline simon5  Canada
diyAudio Member
 
Join Date: Nov 2004
Location: Québec, Québec
Thank you for sharing your knowledge. That was a very interesting post !

What do you think about my idea ? Your current sensing coil on a AE AV15-H ?

I purchased an amplifier from your company in the past. After 4 years it's still going strong. I think your Servo line of subwoofers are the best value available for Servo controlled subwoofers, if not the best Servo controlled subwoofers at any price.
__________________
DIYaudio for President !
  Reply With Quote
Old 7th November 2008, 02:28 AM   #19
diyAudio Member
 
Join Date: Feb 2004
Location: Texas
Quote:
Originally posted by simon5
Thank you for sharing your knowledge. That was a very interesting post !

What do you think about my idea ? Your current sensing coil on a AE AV15-H ?

I purchased an amplifier from your company in the past. After 4 years it's still going strong. I think your Servo line of subwoofers are the best value available for Servo controlled subwoofers, if not the best Servo controlled subwoofers at any price.
Glad to hear that. The idea of AE AV15-H is pretty good. But I need to get the right power amp for that project.
__________________
Servo Subwoofer kits > Rythmik Audio | Articulate bass for the discerning audiophile .:: Brian Ding
  Reply With Quote
Old 7th November 2008, 07:27 AM   #20
simon5 is offline simon5  Canada
diyAudio Member
 
Join Date: Nov 2004
Location: Québec, Québec
Quote:
Originally posted by rythmikaudio
Glad to hear that. The idea of AE AV15-H is pretty good. But I need to get the right power amp for that project.
Yeah, sorry, I always dream about the perfect subwoofer driver...

Also, if you put an Apollo upgrade on it, might need an even bigger amplifier since thermal power handling will increase again and we will get less distortion...

You like strong aluminium cones, those new AE aluminium cones can hold a person standing on it. Last generation was alot weaker. I don't know if they are stronger than yours OTOH.
__________________
DIYaudio for President !
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
TB3/1000 is alive ! ("European 833A") ReinoutdV Tubes / Valves 68 6th November 2010 07:19 AM
if you had $1000 to spend on two towers, what would you get? clipper10 Multi-Way 0 4th April 2003 05:01 AM


New To Site? Need Help?

All times are GMT. The time now is 12:07 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2