design question

[Rick Craig]

I already know the answer but I thought this might be of help to a few of the readers here. Recently I came across a 2-way speaker array where the woofer section sensitivity was several db higher in level than the tweeter array. To compensate for the difference the designer used large inductor values to reduce the level of the woofers - somewhat like a huge amount of baffle step compensation.

Here's the riddle for everyone - what do you think the consequences would be?

[Hdale85]

Well I recently built the LineUp Maxx's and I used a large aircore inductor in my woofer section (5.5mh). Later Jed told me that it results in a more mild bass but a better midrange. In a 2 way I'm not sure though as these are 3 ways. But the bass is still pretty good and my midrange is amazing so I'm not worried about it Others used an iron core inductor instead.

[cjd]

Great question. Not the kind of thing I've ever really given thought to either, as the woofer sensitivity is almost always holding me back overall.

High impedance in an inductor in a woofer circuit will, I believe, soften bass and make midrange stand out a bit more (this in response to Dougie's comment). This is the same reason padding down bass response is problematic in general.

The slope with this large value inductor would be well below the actual crossover frequency and would get into the highpass created by box tuning, which will throw that off. I believe that tends to cause a sharp rise at the tail end (perhaps akin to undersizing box). Should really go model this out - I'm curious to see if the tools actually deal with this type of thing well.

[Jed]

Well I recently built the LineUp Maxx's and I used a large aircore inductor in my woofer section (5.5mh). Later Jed told me that it results in a more mild bass but a better midrange. In a 2 way I'm not sure though as these are 3 ways. But the bass is still pretty good and my midrange is amazing so I'm not worried about it Others used an iron core inductor instead.

Dougie- I was referring to the DCR of the aircore, though. The 14 gauge aircore you used has slightly higher DCR, than say for example a large iron core inductor of the same value. The result is less resistance on the low range of the bass frequencies, which elevates the response slightly. My comment about the midrange refers to the aircore's sonic characteristics versus the iron core, where the former might have less saturation or less distortion than the ironcore.


Rick, can you give us more info, like was the response flat, even though they used the large inductor? What does the impedance look like, are there any dips? What size inductor are we talking here? Over 15mh or 6 mh?

Kinda hard to know what type of answer you are looking for with the original question.

[Hdale85]

Well in general larger inductors usually have higher DCR don't they? Or maybe larger just means higher mh and the guage determines the DCR. This is probably the case as I don't really know a ton about speaker design :B

[cjd]

Dougie- I was referring to the DCR of the aircore, though.

Hah! I was right.

I believe Rick is talking about essentially low-passing the woofer at, say, 20Hz (or at least, using an inductor that would usually be used to cross the system that low) so that it's down a bunch of dB by the time it's in its usable range.

This would also do funky things at Fs I think.

C

[augerpro]

Were they large DCR values also or just mH? Large DCR would have a large effect on Qts. I believe cjd's comment is the biggest concern, causing large peaking in the bass region. I'm guessing ringing or huge group delay in teh bass would be the result?

[Brian Bunge]

Wouldn't a lot of power also be dumped into the inductor(s)? If so I would think that would reduce the overall sensitivity of the woofer array.

[JoshK]

How about increasing reactance and producing more back EMF?

[Rick Craig]

Great question. Not the kind of thing I've ever really given thought to either, as the woofer sensitivity is almost always holding me back overall.

High impedance in an inductor in a woofer circuit will, I believe, soften bass and make midrange stand out a bit more (this in response to Dougie's comment). This is the same reason padding down bass response is problematic in general.

The slope with this large value inductor would be well below the actual crossover frequency and would get into the highpass created by box tuning, which will throw that off. I believe that tends to cause a sharp rise at the tail end (perhaps akin to undersizing box). Should really go model this out - I'm curious to see if the tools actually deal with this type of thing well.

You're on the right track. Go do some modeling and post your results.

[Rick Craig]

Dougie- I was referring to the DCR of the aircore, though. The 14 gauge aircore you used has slightly higher DCR, than say for example a large iron core inductor of the same value. The result is less resistance on the low range of the bass frequencies, which elevates the response slightly. My comment about the midrange refers to the aircore's sonic characteristics versus the iron core, where the former might have less saturation or less distortion than the ironcore.


Rick, can you give us more info, like was the response flat, even though they used the large inductor? What does the impedance look like, are there any dips? What size inductor are we talking here? Over 15mh or 6 mh?

Kinda hard to know what type of answer you are looking for with the original question.

No measurements or crossover info has been provided yet by the manufacturer. If you get a chance take one of your designs and model the effects while trying to emulate the same thing. Post the results here if you can do it.

[Rick Craig]

Hah! I was right.

I believe Rick is talking about essentially low-passing the woofer at, say, 20Hz (or at least, using an inductor that would usually be used to cross the system that low) so that it's down a bunch of dB by the time it's in its usable range.

This would also do funky things at Fs I think.

C

Not quite that low :lol:

Try taking the woofer section from one of your designs and crossing it at 850hz. You'll need to reduce the midband by at least 3-6db.

[Rick Craig]

Were they large DCR values also or just mH? Large DCR would have a large effect on Qts. I believe cjd's comment is the biggest concern, causing large peaking in the bass region. I'm guessing ringing or huge group delay in teh bass would be the result?

I don't know the exact values but the peaking is going to be a problem whether a low or high DCR coil is used. The interaction of the woofer's parameters, box tuning, coil DCR, and the transfer function of the crossover will determine what happens.

As far as the group delay and ringing I don't know how audible that would be but thanks for bringing that up.

[Rick Craig]

Wouldn't a lot of power also be dumped into the inductor(s)? If so I would think that would reduce the overall sensitivity of the woofer array.

Good to hear from you again. The issue here is reducing the sensitivity of the woofer line to match the tweeter line so higher DCR may be involved. You may know more about this than you realize :W

[Rick Craig]

How about increasing reactance and producing more back EMF?

I didn't consider that but you have a good point. I wonder if anyone has ever tried to quantify the results (audible or measureable) from a large amount of EMF on a amp?

[Brian Bunge]

Good to hear from you again. The issue here is reducing the sensitivity of the woofer line to match the tweeter line so higher DCR may be involved. You may know more about this than you realize :W

Rick, that's kind of what I was thinking. I was assuming higher DCR, which would increase series resistance, which would in turn lower sensitivity. I remember using large coils for car audio subs in the absence of an electronic crossover and how much power it would rob from the actual driver.

[cjd]

I wanted to ponder this before modeling to see if I could use it as a judge of how far off what I think I know is from reality.

Ultimately I think the trick is, what is meant by "very large value inductors" - transfer function tells the tale most specifically, and response does mirror it. But 850Hz in a 2-way didn't cause any undue strain (mild symptoms in the transfer function). Pushing that a little closer to insanity starts to highlight the inherent problems in shaping response - I was not actually able to get something like this to work well in attempting a 2-way with response always being too low through the midrange. Of course, this may well be one of the inherent problems with this approach. It would work with, say, that B&C midrange PE had on sale the other day that has a sharply rising response up to 2kHz.

Anyhow, I am attaching an example with the RS225-4 (single driver) pushed to a bit of an extreme to highlight what I'm seeing (and indeed, pretty much what I was expecting). This is a single 10mH inductor on the woofer. Tweeter is 2 components.

Impedance in this example peaks at somewhere beyond the range of the graph, but I'd guesstimate 100ohm at 450Hz. Your amplifier should love that. Adding a cap to the woofer simply adds a knee at a higher frequency - in this way I can start to get things to an almost work able state, aside from the peaking issues in the bass, but crossing quite low still.

No matter what I do I am unable to avoid a huge hole in response due to the rising impedance of the high inductor value without pushing the crossover excessively low - in this case, running the tweeter without a filter (27TDFC). A nice smooth dip from 200hz to 1000Hz of ~5dB. Dropping the inductor to 5mH flattens response with a bubble from 50-400Hz of 5dB - the transfer function starts to clean up. So it starts to look almost reasonable. Impedance, too, works out OK though in this case with no filter on the tweeter it dips pretty low at 100Hz.

C

[Hank]

Yes, soaks up power per Brian, but not necessarily from higher DCR (you could use 12-ga wire in the inductor after all) - it's the impedance increase. And, if you ignore the CR in an LCR net, then things change for the worse.

[Brian Bunge]

Yeah, Hank. I was sort of lumping all that together. I'm a bit fuzzy on all the inductive and capacitive reactance stuff. I do remember that impedance changes with frequency though!

[Rick Craig]

I wanted to ponder this before modeling to see if I could use it as a judge of how far off what I think I know is from reality.

Ultimately I think the trick is, what is meant by "very large value inductors" - transfer function tells the tale most specifically, and response does mirror it. But 850Hz in a 2-way didn't cause any undue strain (mild symptoms in the transfer function). Pushing that a little closer to insanity starts to highlight the inherent problems in shaping response - I was not actually able to get something like this to work well in attempting a 2-way with response always being too low through the midrange. Of course, this may well be one of the inherent problems with this approach. It would work with, say, that B&C midrange PE had on sale the other day that has a sharply rising response up to 2kHz.

Anyhow, I am attaching an example with the RS225-4 (single driver) pushed to a bit of an extreme to highlight what I'm seeing (and indeed, pretty much what I was expecting). This is a single 10mH inductor on the woofer. Tweeter is 2 components.

Impedance in this example peaks at somewhere beyond the range of the graph, but I'd guesstimate 100ohm at 450Hz. Your amplifier should love that. Adding a cap to the woofer simply adds a knee at a higher frequency - in this way I can start to get things to an almost work able state, aside from the peaking issues in the bass, but crossing quite low still.

No matter what I do I am unable to avoid a huge hole in response due to the rising impedance of the high inductor value without pushing the crossover excessively low - in this case, running the tweeter without a filter (27TDFC). A nice smooth dip from 200hz to 1000Hz of ~5dB. Dropping the inductor to 5mH flattens response with a bubble from 50-400Hz of 5dB - the transfer function starts to clean up. So it starts to look almost reasonable. Impedance, too, works out OK though in this case with no filter on the tweeter it dips pretty low at 100Hz.

C

I wouldn't expect the 27TDFC to sum very well since 850hz is way below where it typically would cross. Is your RS225 sealed or ported? It would be interesting to see how the filter gain would vary with the two different box impedances. The commercial speaker uses a fairly high Fs woofer with a high Qts and is ported.

[Rick Craig]

Rick, that's kind of what I was thinking. I was assuming higher DCR, which would increase series resistance, which would in turn lower sensitivity. I remember using large coils for car audio subs in the absence of an electronic crossover and how much power it would rob from the actual driver.

With car subs and the typical 2-4 ohm impedances the DCR of the inductor is a greater percentage of the total resistance than with a 6-8 ohm driver; as a result, it has a greater impact on the electrical damping.

[augerpro]

Chris's graph kind of confirms what I was expecting. Considerable peaking in the bass. Rick is this some sort of PA woofer where the designer is attempting to use the peaking in the bass to get more usable lowend from this high Fs driver? Perhaps in an OB configuration?

Also brings up a question which I've never gotten a very satisfying answer-if there is large peaking in the transfer function, but the actual response is flat, is their really any ringing?

[cjd]

Rick: I was just messing with raw data pulled off PE's site, so that would be infinite baffle numbers, I believe sealed. I was on the train and curious.

Also brings up a question which I've never gotten a very satisfying answer-if there is large peaking in the transfer function, but the actual response is flat, is their really any ringing?

Back before I understood what I was doing wrong, I did something like this on a tweeter transfer function. It was quite audible.

[Dennis H]

Rick is this some sort of PA woofer

He mentioned it's an array (line array?).

[Andy_G]

deleted

[Rick Craig]

He mentioned it's an array (line array?).

Yes.

[Rick Craig]

Chris's graph kind of confirms what I was expecting. Considerable peaking in the bass. Rick is this some sort of PA woofer where the designer is attempting to use the peaking in the bass to get more usable lowend from this high Fs driver? Perhaps in an OB configuration?

Also brings up a question which I've never gotten a very satisfying answer-if there is large peaking in the transfer function, but the actual response is flat, is their really any ringing?

Part of it is an attempt to lower the -3db point for a home audio array with several woofers. One of the problems from creating a large peak in the transfer function with a passive crossover is that the impedance can dip really low. That in combination with a large phase angle in the lower octaves is not good for your amp :x .

[cjd]

Yeah, I ran into the 1ohm range when I was actually running the tweeter full range to *attempt* to bridge the gap.

C

[ch83575]

There was a speaker from a weird brand that the local hi-fi store was carrying for a while that I suspected used a technique like this. I forget the brand, but it was a medium sized stand mounted monitor... but the bass was pretty intense. I think the used a strange tuning + a super large inductor to get bass that you have never heard from a stand mounted speaker before. BUT you could only turn the preamp up about half way. The employees knew where you had to stop, but if somebody asked for louder the amp would go into protection mode. Not crap amps either... i think they were running Linn Klouts at that point, those amps had some balls. One of the employees would say they took a small neutron star to power them. They never opened one up to inspect, but this scenario is what everybody expected was going on.

-Chad

[Mark Seaton]

I already know the answer but I thought this might be of help to a few of the readers here. Recently I came across a 2-way speaker array where the woofer section sensitivity was several db higher in level than the tweeter array. To compensate for the difference the designer used large inductor values to reduce the level of the woofers - somewhat like a huge amount of baffle step compensation.

Here's the riddle for everyone - what do you think the consequences would be?

Hi Rick,

It's not entirely clear here what you're fishing for here, but so long as the impedance remains reasonable for the intended application and the network doesn't result in counter-productive peaking around the low frequency impedance peaks/dips, do we care? Obviously the net response of the woofer and the HF drivers need to integrate properly, and depending on the system and components used you could have some excess phase rotation, but in the end this is why we have measurement gear and modeling tools. A few frequency response and impedance measurements of the various components tells all.

If anything, I'd say too many get way too caught up in target responses for crossovers. There are benefits to many of the topologies, but most don't look at the bigger picture and combined response of the driver, crossover and of course the drivers being mated. For some (many?) applications, a driver with a perfectly flat response without a crossover isn't terribly useful. :roll: