Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

Opinions: Tweeter Crossover - High vs Low?
Opinions: Tweeter Crossover - High vs Low?
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 19th July 2017, 10:53 PM   #1
ReDress is offline ReDress  Canada
diyAudio Member
 
Join Date: Jul 2014
Default Opinions: Tweeter Crossover - High vs Low?

Hey everyone - I'm looking for some opinions on this matter, in regards as to whether or not you guys prefer to cross a tweeter higher or lower (with regards to its operational range)

Do you prefer to cross higher, so as to have the tweeter play with potentially less distortion and such (due to it having to handle a lesser frequency range), yet you might have to deal with a 3-way, as well as taking into account the ctc of the drivers...

Or

Do you prefer to have the tweeter play more into the midrange, and worry less about ctc (and potentially be able to stick to a 2-way design), yet you'll have to worry about greater distortion and the possibility of burning out the tweeter...

But I'll digress, I don't think there is really a correct answer to this question...more so interested in a discussion upon this idea (obviously what is best will vary case to case)

Much love/many thanks in advance everyone for your thoughts
  Reply With Quote
Old 19th July 2017, 11:23 PM   #2
CharlieLaub is offline CharlieLaub  United States
diyAudio Member
 
Join Date: Mar 2007
Location: California
Opinions: Tweeter Crossover - High vs Low?
OK, this thread should have lots of opinions. Here's mine.

Short answer: the lower you can cross to a "tweeter" the better. 1.5kHz or less! But you need a driver capable of that.

Long answer:
1. A lower tweeter crossover point helps to prevent lobing and improves integration with the next lower band. The tweeter and mid have certain physical dimensions. This means they can only be put so close together, and usually this distance is a couple of inches. Keeping the crossover point low helps to prevent lobing that will occur because the acoustic centers are not coincident.

The problem is that your typical "dome" tweeter is on the order of 1" or so in diameter. It only has so much radiating area and Xmax capability, even if the unfiltered passband extends down into the 500Hz-1kHz range. The driver just cannot create enough SPL without reaching Xmax, or the distortion level starts rising to unacceptable levels. Usually a tweeter crossed to low sound "shouty" and this is apparent at higher playback levels. Even if you horn load the tweeter you still cannot really cross below 1kHz.

Using a larger format tweeter introduces a new set of problems. A larger "tweeter" e.g. a 35mm dome often has problems at its high end - narrowing off axis response the most common one. Some people like to try and use large ribbon or AMT type drivers. These also have the problem that, off axis and at high frequencies, the response droops badly. You are just trading off one problem for one or more different problems.

There is some evidence that crossing over in the range 700Hz-1kHz is "best". It's just not possible to do that with pretty much any tweeter available. But there is a type of driver that CAN be crossed over in that range (or even lower): the full-ranger.

Full rangers have improved quite a bit in the last 5-10 years. You can now find small full rangers that how sufficient sensitivity and HF extension to integrate with a woofer and serve as a tweeter. When they are small, e.g. 3" diameter or less, the off axis response in the highest frequencies is sometimes quite tweeter like, but this depends on several factors like motor design, cone, etc. I built several different systems using the Tang Band W2-800SL as a tweeter, which is a fine example of a full-ranger that can be used as a tweeter. For example, I used it in an MTM crossed at 750Hz. Very nice. More recently I found a BMR type driver with some promise, until I discovered some serious aging issues. The Peerless/Vifa TC9 and TG9 are good examples of full rangers that can function as tweeters, although they don't quite reach 20kHz. Not every full ranger driver is a good choice but if you look around there are a few candidates.

Finally, by using a full-ranger crossed low you can avoid a big hole or discontinuity in the power response around the M-T crossover point that is often found with M-T systems using a dome tweeter. Food for thought. But that's a whole new topic in and of itself, so I will stop there.
__________________
Visit my Audio Web Page <<--CLICK TO LEARN MORE-->> Get my LADSPA plugins

Last edited by CharlieLaub; 19th July 2017 at 11:28 PM.
  Reply With Quote
Old 19th July 2017, 11:40 PM   #3
planet10 is offline planet10  Canada
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Opinions: Tweeter Crossover - High vs Low?
Quote:
Originally Posted by ReDress View Post
Hey everyone - I'm looking for some opinions on this matter, in regards as to whether or not you guys prefer to cross a tweeter higher or lower (with regards to its operational range)
I prefer to cross lower, such that the centre-to-centre distance from midbass to (mid)tweeter is at or less than the wavelegth of the frequency of the crossover. Usually 250-450 Hz.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 19th July 2017, 11:45 PM   #4
planet10 is offline planet10  Canada
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Opinions: Tweeter Crossover - High vs Low?
Quote:
Originally Posted by CharlieLaub View Post
You can now find small full rangers that how sufficient sensitivity and HF extension to integrate with a woofer and serve as a tweeter.
My favorites are the Fostex FF85wk and the Mark Audio Alpair 5.2. Althou a 4 my absolute favorite is the Alpair 7.3.

Here the system i am listening to now with FF85wKeN & 2 sidefiring Silver Flute W14eN.

Click the image to open in full size.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 20th July 2017, 02:02 AM   #5
Pallas is offline Pallas  Pakistan
diyAudio Member
 
Join Date: Aug 2004
Quote:
Originally Posted by ReDress View Post
But I'll digress, I don't think there is really a correct answer to this question...more so interested in a discussion upon this idea (obviously what is best will vary case to case)
There is a correct answer: whichever approach that leads to flat and smooth axial response, and smooth off axis response. There's no reason to settle for less today.

As a general rule, that either means a 3-way with a small-flange tweeter and a small mid, some degree of waveguide loading on the tweeter, or both.
__________________
Serious Audio Blog
  Reply With Quote
Old 20th July 2017, 04:54 AM   #6
Fernando R is offline Fernando R  United States
diyAudio Member
 
Join Date: May 2017
Location: Charlotte NC
The most satisfying speakers I have ever made have crossed over at 3Khz or above. I may be overly sensitive in the lower ranges but that is how I hear it. I find it interesting that despite all the directivity arguments, some of the most highly regarded British speakers ever from companies like Spendor (BC1, D7), Harbeth and B&W, are based on 7 and 8 inch drivers crossing over at or above 3 KHz. The BBC LS3/5A which was famous for its incredible midrange was based on a 5.25" driver crossing over at 3 KHz. SB acoustics in their new 2.5 way kits, cross both the Satori MW16P and 17MFC driver at 3 KHz.
  Reply With Quote
Old 20th July 2017, 11:46 AM   #7
suzyj is offline suzyj  Australia
diyAudio Member
 
suzyj's Avatar
 
Join Date: Jan 2006
Location: Western Australia
My Ariels are crossed over at 3.8KHz and that works well because the P13WH midbass drivers are smooth and have low distortion to that point. I've been playing with some SB12NRX drivers and while they're nice and smooth to 10KHz, they have a significant cone breakup spike that's seen as an increase in third harmonic distortion at 3KHz.

My plan with these speakers is to cross over below this point - probably at 2KHz if I can get away with it. See the attached plot showing the distortion peak at 3KHz.

I guess that means it depends. There's nothing arbitrary. Choose the point that gives the best performance for the specific set of drivers and their relative positions on the baffle.
Attached Images
File Type: jpg SB12NRX no EQ distortion plot.jpg (120.3 KB, 358 views)
__________________
http://www.suzyj.net
  Reply With Quote
Old 20th July 2017, 01:24 PM   #8
Zvu is offline Zvu  Serbia
diyAudio Member
 
Zvu's Avatar
 
Join Date: Jan 2009
Location: Belgrade
General rule (of mine) would be that if you want to cross it at 2KHz or less (depending on steepness of the filter), waveguide is perfect solution. It isn't a must have by any means, but it would be just silly not to use it. It controls the directivity (no blooming between 3-5KHz), it enables you to use electrical filter higher in frequency to achieve lower crossover point, it keeps the distortion low, it pushes the acoustic center of tweeter closer to the acoustic center of the mid-woofer etc.

The only thing that waveguide doesn't help with is center to center distance - but in my experience, in practice this has never been an issue. I have never heard any negative effects induced by ctc distance because of using a waveguide, and i listen from about 2,2m-2,5m distance. Further from speakers you go, the less of a "problem" it is.
__________________
Not for fainthearted

Last edited by Zvu; 20th July 2017 at 01:39 PM.
  Reply With Quote
Old 20th July 2017, 03:23 PM   #9
CharlieLaub is offline CharlieLaub  United States
diyAudio Member
 
Join Date: Mar 2007
Location: California
Opinions: Tweeter Crossover - High vs Low?
Quote:
Originally Posted by suzyj View Post
My Ariels are crossed over at 3.8KHz and that works well because the P13WH midbass drivers are smooth and have low distortion to that point. I've been playing with some SB12NRX drivers and while they're nice and smooth to 10KHz, they have a significant cone breakup spike that's seen as an increase in third harmonic distortion at 3KHz.

My plan with these speakers is to cross over below this point - probably at 2KHz if I can get away with it. See the attached plot showing the distortion peak at 3KHz.

I guess that means it depends. There's nothing arbitrary. Choose the point that gives the best performance for the specific set of drivers and their relative positions on the baffle.
Yet another person who only looks at the on-axis response! Ignorance is bliss I guess.
__________________
Visit my Audio Web Page <<--CLICK TO LEARN MORE-->> Get my LADSPA plugins
  Reply With Quote
Old 20th July 2017, 03:43 PM   #10
system7 is offline system7  United Kingdom
diyAudio Member
 
system7's Avatar
 
Join Date: Aug 2008
Location: Portsmouth UK
Bit harsh there, Mr. CharlieLaub. And what are you saying anyway? Something about dispersion?

Suzy's Ariels were designed by Mr. Lynn Olson, who is a great authority on tweeter distortion:
Quote:
Originally Posted by Lynn Olson
A common but unsuspected cause of sibilance is crossing the tweeter too low, or using a shallow-slope crossover. Many designers - unfortunately, a lot of them in the high-end biz - forget that direct-radiator drivers increase excursion at a rate of 12 dB/octave. Thus, it takes a 12 dB/octave highpass filter to merely keep excursion constant in the frequency range between nominal crossover and the Fs of the tweeter.

For example, if the tweeter has a typical Fs of 700 Hz, and the intended crossover is 2.8 kHz (again, typical), it takes a 12 dB/oct electroacoustical filter to merely keep excursion constant in the very critical 700 Hz ~ 2.8 kHz range. Part of the reason that this range is so critical is that audibility of distortion is at a maximum in the 1~5 kHz region. (Perception of distortion similar to, but not quite the same as, the Fletcher-Munson curve.)

Staying with the same example, if the electroacoustical filter is 1st-order (6 dB/octave), then excursion actually increases from 2.8 kHz on down, until 700 Hz is reached. Below 700 Hz, the excursion finally starts to decrease, but not very fast, only 6 dB/octave. This is troublesome because the maximum spectral energy of many recordings is around 300~500 Hz, so energy from this range can crossmodulate with the tweeter output.

This is why auditioning with little-girl-with-a-guitar program material and a full choral piece sound different. The LGWAG is spectrally sparse, and there isn't as much chance the tweeter will be struggling with IM distortion. Throw a dense, high-powered spectrum at the loudspeaker, though, and the tweeter will start to scream - and it is very audible on massed chorus as complete breakup.

At any rate, regardless of distortion of a particular tweeter (none of them are free of IM distortion), crossovers matter. Many designers want to take the tweeter as low as possible because the polar pattern is prettier and certainly measures nicer, but the inevitable price to be paid is more IM distortion resulting from increased excursion (the linear region is most tweeters is less than 1mm). Choosing a crossover is a difficult tradeoff between narrowing of the vertical polar pattern, IM distortion from out-of-band excursion, and how close the designer wants to approach the region of midbass driver breakup. The tradeoff is made more difficult when a rigid-cone (Kevlar, metal, ceramic, etc.) midbass driver is chosen, because the onset of breakup commonly falls in the 3~5 kHz region, right where the ear is most sensitive to distortion.

As you can see, the worst possible solution is a 1st-order crossover combined with a midbass driver that has a severe breakup region (Kevlar drivers, I'm looking at you). The 1st-order crossover fails to control out-of-band excursion, so program material in the 700 Hz-2.8 kHz region results in IM distortion in the tweeter's working range, while plenty of midbass breakup in the 3~5 kHz range gets through as well. And midbass breakup sounds the same as a bad tweeter, since the distortion and resonances fall in the same frequency range.

As a side note, most transistor amplifiers (including very expensive high-end products) go from Class A operation to Class AB around 1 watt. Feedback helps, but cannot fully overcome the two-to-one shift in transconductace as the AB region is traversed. In addition, thermal tracking is typically several seconds to a minute late (depending on the thermal mass of the heatsink and location of bias sensor), so the correct AB bias point is actually several seconds behind the program material. There are various sliding bias-tricks available (which avoid complete turnoff and associated switching transition), but they are all several seconds late. The more output transistors, the more AB transitions there are, since it is impossible to have transistors exactly match the switching transition - in production, they are matched for beta (current gain), but not usually for other parameters. Change the die temperature a bit, and the careful hand-matching goes away.

To recap, if you want lots of sibilance, use a midbass driver with severe breakup in the 3~5 kHz region (this is usually obvious from unsmoothed FR curves), pick a tweeter with limited excursion capability (not always spec'ed), select a 1st-order crossover at a low crossover frequency, and use an amplifier with a very large heatsink, many transistors, and somewhat unstable Class AB biasing (thermal overshoot). That should do the trick. Plenty of distortion from many different sources, even though the overall FR curves may look harmless.
Can you have sparkling treble but without sibilance
__________________
Best Regards from Steve in Portsmouth, UK.
  Reply With Quote

Reply


Opinions: Tweeter Crossover - High vs Low?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Low power High quality amp for driving a tweeter:ideas? marcelooms Solid State 6 8th December 2016 01:10 PM
Open baffle Low crossover freq tweeter modification oon_the_kid Multi-Way 18 21st September 2015 09:01 PM
Low tweeter crossover point? mike_6289 Multi-Way 15 8th October 2014 05:15 AM
ribbon planar tweeter with low crossover frequency LineArray Planars & Exotics 2 19th June 2008 09:13 PM
Low- vs. High- Order Active Crossover askbojesen Multi-Way 9 8th October 2003 03:50 PM


New To Site? Need Help?

All times are GMT. The time now is 01:42 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki