Introduction to designing crossovers without measurement - Page 12 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

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 16th April 2013, 11:17 AM   #111
AllenB is offline AllenB  Australia
diyAudio Member
 
Join Date: Oct 2008
Quote:
Originally Posted by CRESCENDO View Post
I wish there were a way to measure the signal-out of my dbx Driverack 260 and translate that into accurate x-over components.
The way I'd normally do this is to loop it in with a sound card for the response, then overlay this with a crossover simulator then play with some values. Of course this would imply having a proper impedance plot already done.

You could sweep it with a generator and measure with a voltmeter and plot the response by hand if you preferred.

Quote:
completing the following formula...
Sounds reasonable. One way I used to do this was to use a larger resistor (more than 100 ohms and preferrably 1k). Connect a 10 ohm resistor in place of the speaker and adjust the voltage across the 10 ohm resistor until it is 10mV (or some convenient multiple thereof). Replace the speaker and the voltage you measure in millivolts across the speaker will equal the impedance. You could sweep the frequency and gauge the trend in the curve.
  Reply With Quote
Old 18th April 2013, 12:22 PM   #112
diyAudio Member
 
Join Date: Dec 2009
Location: California
As long as this is just as accurate, this sounds much easier/quicker. Will I still place the 1k resistor inline with the negative side of the speaker and keep it in the "loop" when replace the speaker with the 10 ohm resistor?

Many thanks for the suggestion and direction.
  Reply With Quote
Old 19th April 2013, 12:40 AM   #113
AllenB is offline AllenB  Australia
diyAudio Member
 
Join Date: Oct 2008
You place the 1k between the amp and one speaker terminal, and the other speaker terminal goes to ground. The 10 ohm resistor replaces the speaker while you calibrate.
  Reply With Quote
Old 19th April 2013, 01:27 AM   #114
diyAudio Member
 
Join Date: Sep 2012
Location: Maine, Bangor-area
AllenB,

Thanks very much for your tutorial! Your post #67 is amazing.

An idea that I have to refine designing crossovers without measurement is this. A better approximation of the actual impedance of a driver at the cross-over frequency than the stated, rated or nominal impedance of the driver is equal to 1,2 times Re.

Take for example the Morel MDT-12 tweeter. This tweeter is described as 8 Ohm. However, at frequencies above resonance, the actual impedance of the tweeter is less than 8 Ohm from resonance at about 1 kHz, to 10 kHz. Multiplying DCR or Re of the tweeter equal to 5,1 Ohm times 1,2 equals 6,1 Ohm. From 2 kHz to 5 kHz impedance of the tweeter equals about 6,0 Ohm.

Would you agree with this, or do you think that calculating in this manner would result in only a marginal improvement?

Regards,
Pete
  Reply With Quote
Old 22nd April 2013, 03:08 AM   #115
mart.s is offline mart.s  United Kingdom
diyAudio Member
 
Join Date: Dec 2008
Hi Excellent tutorial, Ive only just come across it after Months of experimentation.

What is the main reason for very poor off axis treble response? and roughly how much attenuation would I get with a 4 ohm resistor in series before the tweeter? (no L pad)

I am am crossing over at quite a high fq as the woofer goes to 4K (and pretty smooth) and I prefer a smoother less fatiguing sound at the top end. I think the woofer is an old monitor audio modified version of the Seas P17RCY and the Tweeter is an Audax TWO25 series. I'm using a 3rd order X-over due to the high tweeter fs of 1090 but I seem to be getting really bad off axis response and poor punch in the mids.
  Reply With Quote
Old 23rd April 2013, 02:39 AM   #116
AllenB is offline AllenB  Australia
diyAudio Member
 
Join Date: Oct 2008
Quote:
Originally Posted by cT equals piD View Post
Would you agree with this, or do you think that calculating in this manner would result in only a marginal improvement?
This seems reasonable but it comes down to what accuracy means and how important it is.

Variations in the impedance can result in variations in the response. When you measure the impedance as a curve, including phase, and do the same with the response taking into account the acoustic nature of the driver and its mounting by measuring it at various angles, then you should get few surprises in the result. Flattening the impedance is simply a way of reducing one of the more significant variables in this case.

If you have less information that this then obsessing over a component value can sometimes be hit and miss. It's not like one value will necessarily be perfect. Often you'll find that one sounds good in some ways and another in other ways, but neither may fix everything.
  Reply With Quote
Old 23rd April 2013, 03:10 AM   #117
AllenB is offline AllenB  Australia
diyAudio Member
 
Join Date: Oct 2008
Component accuracy often recieves more attention than it deserves. In many cases with electronics in general, there is less point in matching components to greater than 10% than there is in ensuring a competent design. With regards to speakers this means that it is more important to control the propagation of sound, ie. that it gets out into the room smoothly and in a way that suits the room, the driver and the application. Only then will finer control of the response through the crossover give more of the expected result. (Not saying you can't make a difference with small component changes, just that it will be more experimental and less certain of the result.)

You also need to consider the facts regarding perception and common sense. Would you rather have a few peaks in the response in the bass range or in the sensitive upper midrange region? If there was a peak in one of your speakers would you rather the other side be perfect on its own, or match the other one?

Component tolerances were once in the order of plus and minus 50%. This was not only due to manufacturing errors but also due to changes as they age and changes with the weather, as well as drifting as they warmed up. This wasn't enough to prevent good products from being made. Having built numerous of these valve amplifiers using antique parts, I normally don't worry about better than 10% in resistances/voltages except in specific parts of a circuit, where I wouldn't bother with any better than 1%.

Last edited by AllenB; 23rd April 2013 at 03:18 AM.
  Reply With Quote
Old 23rd April 2013, 05:10 AM   #118
AllenB is offline AllenB  Australia
diyAudio Member
 
Join Date: Oct 2008
Quote:
Originally Posted by mart.s View Post
I am am crossing over at quite a high fq as the woofer goes to 4K (and pretty smooth) and I prefer a smoother less fatiguing sound at the top end. I think the woofer is an old monitor audio modified version of the Seas P17RCY and the Tweeter is an Audax TWO25 series.
There are a couple of common reasons that the top end might sound rough or fatiguing. Since you seem to prefer the woofer to play higher in frequency, I'd assume it's due to the off axis sound up high. This can come down to personal preference but I prefer less.

As a woofer goes higher in frequency, it produces less off axis sound. Just to illustrate, imagine taking a small stone and dropping it into a pond. Note the width of the ripples. Now take some sand and drop it over that wider area. The ripples will have trouble forming as the parts do not add properly and they partially cancel one another. Woofers will lose most of this energy off to the sides, more with increasing frequency.

Having been in this situation I understand the temptation to try and run the better driver as wide in frequency as possible to get the best out of it. What you end up with in this case will be reflections that are more loud above the crossover frequency than below due to the tweeter and its wider radiation.

When you listen to speakers in a room, you can expect the lower frequencies to be coming from all around, and you can make a choice to taper this off so that the higher frequencies are mostly coming to you directly. What you want to avoid is reducing the off-axis sound at some frequency and allowing it to be present again at higher frequencies, which is what you have when you cross a woofer quite high to a dome tweeter.

It could be worth exploring some different types of speaker, and there are two common alternatives that can achieve this end. One of them is to use a larger driver for the treble. An example would be using a small full range driver. The advantages of this are that the treble will be more direct (meaning less reflected sound) and therefore more relaxed even when designed for the same level on your listening axis as a dome. You'll also be able to cross lower in the midrange (good), and you'll be able to use a larger woofer. This format has come to be known here as a F.A.S.T.

The other is to use a horn to control the dispersion in the treble. A waveguide is a kind of horn that has been designed primarily for controlling the directivity. It is usually conical or similar. If you know the woofer and the waveguide angle you want to use, you find the frequency where the woofer radiation narrows to that amount and make sure the waveguide and tweeter can be crossed that low.

Last edited by AllenB; 23rd April 2013 at 05:16 AM.
  Reply With Quote
Old 23rd April 2013, 05:39 AM   #119
Jay is offline Jay  Indonesia
diyAudio Member
 
Join Date: Feb 2003
Location: Jakarta
Quote:
Originally Posted by AllenB View Post
Component accuracy often recieves more attention than it deserves.
But may be it receives less attention than it deserves in a complex crossover. For high order filter (3rd order electrical with correction and above), measurement and simulation cannot tell everything what the drivers do. So attention must be paid more here (voicing), resulting in non-standard component values.
  Reply With Quote
Old 23rd April 2013, 06:25 AM   #120
AllenB is offline AllenB  Australia
diyAudio Member
 
Join Date: Oct 2008
I agree that tweaking will always be there for most of us, and it may get specific, which I mentioned...
Quote:
Originally Posted by AllenB
Not saying you can't make a difference with small component changes,
The message I was trying to give is that sometimes the crossover is seen as a source of problems (such as some acoustic issues) that a crossover isn't able to fix.
  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
WinSpeakerz vs others for measurement & crossovers rick57 Multi-Way 8 12th December 2010 10:20 PM
Designing crossovers using Vidsonix Virtual Crossover triode4 Multi-Way 0 28th October 2007 01:22 AM
A brief introduction WayneM Introductions 7 30th April 2005 01:23 AM
Designing passive tri-mode crossovers? Datoyminaytah Multi-Way 9 4th September 2004 12:33 PM
Designing for guys who like designing Sch3mat1c Tubes / Valves 14 31st August 2003 11:46 AM


New To Site? Need Help?

All times are GMT. The time now is 08:48 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