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Passive crossover design

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URL: https://forum.speakerplans.com/forum_posts.asp?TID=95547
Printed Date: 17 November 2017 at 7:19pm
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Topic: Passive crossover design
Posted By: Modeller
Subject: Passive crossover design
Date Posted: 19 April 2016 at 12:37am
Hello, I'd like to design a passive crossover for a modelling project I have underway at the moment.

I have two drivers, both with a limited acoustic range, but because of space constraints these are the only ones I can use. The bass/mid driver tails off dramatically at about 10kHz down to 13kHz and the tweeter starts at approx 2kHz to 20kHz. I'd like to have my crossover engage the tweeter at around 8-9Khz.

Is there a simple PCB design using standard components that I could build to these specs?

Any help you could give would be much appreciated.
Steve



Replies:
Posted By: Conanski
Date Posted: 19 April 2016 at 2:05am
There are all kinds of textbook crossover design tools on the web that will show you what component values are needed to generate your crossover. Designing a passive crossover that sounds good goes way beyond a basic crossover though, and that is because the acoustic result is the product of the output from the crossover and the speakers they are attached to which usually have a response that is far from textbook. And you may also want to consider the polar response(horizontal coverage) you want to achieve when selecting a crossover frequency, the response of low frequency drivers narrows to a beam in front of the driver at pretty low frequencies, a 15" beams above 1khz for example, a 12" at 1.2khz and that is why most PA speakers systems have relatively low crossover frequencies. If you don't care at all about off axis coverage then use whatever crossover frequency you want.. higher is better for high frequency drivers, I'm trying to make you aware of of the tradeoff you are making.


Posted By: haymere
Date Posted: 19 April 2016 at 6:38am
I want to do the same thing but a much more common scenario at say 1.6khz

Can you post some links

Also where is best to get quality components in the uk


Posted By: Earplug
Date Posted: 19 April 2016 at 9:55am
Take your pick:

https://www.google.es/search?q=crossover+design&ie=utf-8&oe=utf-8&gws_rd=cr&ei=vPEVV6jJOoGoa7iwk_AO#q=crossover+design+calculator

Smile





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Earplugs Are For Wimps!


Posted By: Modeller
Date Posted: 19 April 2016 at 1:10pm
Thanks Conanski and especially Earplug for the link.

Using the first link in the search it came up with a very simple crossover, attached below. This crossover links two 8 Ohm drivers at 8kHz.

My application is a very low fidelity project – we're not talking audiophile quality. The sounds I'll be reproducing are engine, mechanical and environmental sounds, rather than expansive musical tone, so this simple layout seems to suit my application.

One more question – where do I buy the parts?




Posted By: Earplug
Date Posted: 19 April 2016 at 5:44pm
Blue Aran:

http://www.bluearan.co.uk/index.php?id=CNVMPC25082_4PK&browsemode=manufacturer" rel="nofollow - http://www.bluearan.co.uk/index.php?id=CNVMPC25082_4PK&browsemode=manufacturer

(Use 3 in parallel)

http://www.bluearan.co.uk/index.php?id=CNVFCS016&browsemode=manufacturer" rel="nofollow - http://www.bluearan.co.uk/index.php?id=CNVFCS016&browsemode=manufacturer

Monacor:

http://www.monacor.co.uk/categories/film-capacitors/vnr/112300/" rel="nofollow - http://www.monacor.co.uk/categories/film-capacitors/vnr/112300/

http://www.monacor.co.uk/categories/air-core-coils/vnr/124760/" rel="nofollow - http://www.monacor.co.uk/categories/air-core-coils/vnr/124760/




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Earplugs Are For Wimps!


Posted By: Andy Kos
Date Posted: 20 April 2016 at 9:24pm
This is very close to being ready to launch for public use:

http://www.bluearan.co.uk/speakerwizard_design/Crossover_Designer.php" rel="nofollow - http://www.bluearan.co.uk/speakerwizard_design/Crossover_Designer.php

just chuck in what you want on the left, and it will tell you what need from standard parts.

If you're more interested in the technical side of things, try this:

http://www.bluearan.co.uk/speakerwizard_design/Crossover_Calc_v2a.php" rel="nofollow -


Posted By: studio45
Date Posted: 21 April 2016 at 1:10pm
The various wizards (that's a very good one by the way Andy, thanks!) make calculating your basic filters very easy, you shouldn't have any problems there. I charged right into the field that way before I even understood what an inductor does. However, all my first attempts sounded pretty terrible, even though I used the right filter components. It was this point that I realised there were several important things I had to understand, as well as the basic filters:

-L-Pads
-Asymmetrical filters (Highpass and lowpass at different frequencies) 
-Notch filters 
-Zobel networks
-Shelf filters (aka "baffle step correction")
-Series resonant filters to equalise HF response
-importance of proper winding technique (if making your own coils). 
-the differences between cheap and expensive capacitors, in terms of sound and longevity.
-Speaker dispersion and how it should influence choice of crossover point.

If you want to really understand, be prepared to read up on all or most of that ^^. 


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Studio45 - Box Builder Commotion Soundsystem -Mobile PA


Posted By: DJ-Versatile
Date Posted: 28 April 2016 at 3:28pm
Sorry to hi-jack this thread a little, but I have a question or two. For instance if i'm making a Sub and a full range box and wanted to HPF the sub at 35hz and LPF at 120 hz, then HPF the full range box at 120 hz. 

I would need to build 2 crossovers rated at 8 ohms with the above values to put in the dedicated box. Would the Amp then see 4 or 16 ohms? The aim is to get it to a 4 ohm load....

help me... my eyes have gone square from staring at the screen!


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If you are the smartest person in the room, you're in the wrong room....


Posted By: odc04r
Date Posted: 28 April 2016 at 3:47pm
When a passive crossover is working in its passband, it contributes effectively a zero resistance in series with the driver assuming no other eq etc is built in.

I advise getting LTspice and learning how to use it to sim crossovers with AC and transient analysis. Little bit of a learning curve but all the parts you need are as basic as it gets so drawing out the schematic is easy enough.


Posted By: Andy Kos
Date Posted: 28 April 2016 at 3:57pm



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just a guy with a warehouse and a few speakers... www.bluearan.co.uk


Posted By: DJ-Versatile
Date Posted: 28 April 2016 at 4:04pm
Thanks, i'll look into it now!

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If you are the smartest person in the room, you're in the wrong room....


Posted By: snowflake
Date Posted: 28 April 2016 at 5:24pm
Originally posted by DJ-Versatile DJ-Versatile wrote:

Sorry to hi-jack this thread a little, but I have a question or two. For instance if i'm making a Sub and a full range box and wanted to HPF the sub at 35hz and LPF at 120 hz, then HPF the full range box at 120 hz. 

I would need to build 2 crossovers rated at 8 ohms with the above values to put in the dedicated box. Would the Amp then see 4 or 16 ohms? The aim is to get it to a 4 ohm load....

help me... my eyes have gone square from staring at the screen!

use an active crossover with separate subs and tops


Posted By: DJ-Versatile
Date Posted: 28 April 2016 at 5:40pm
I always do usually, but i was wondering if there was a way to do it passively as the system i'm designing is meant to be as portable as possible without going active.  

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If you are the smartest person in the room, you're in the wrong room....


Posted By: markie
Date Posted: 28 April 2016 at 5:50pm
Passive crossovers on sub are rather inefficient, need huge inductors which add weight to the box and cause a worldwide copper shortage. Go active from sub to mid/top.


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If it's got wheels or tits it's gonna cost a fortune


Posted By: snowflake
Date Posted: 28 April 2016 at 5:57pm
use a LPF first and then split it to high and low. fit the crossover in the top box so they can be used alone.

you will need huge components to do even the 120Hz crossover passively. the 35Hz HPF is better done by an amp or crossover with an active filter.


Posted By: Modeller
Date Posted: 28 April 2016 at 6:56pm
Originally posted by Earplug Earplug wrote:

Blue Aran:

http://www.bluearan.co.uk/index.php?id=CNVMPC25082_4PK&browsemode=manufacturer" rel="nofollow - http://www.bluearan.co.uk/index.php?id=CNVMPC25082_4PK&browsemode=manufacturer

(Use 3 in parallel)

http://www.bluearan.co.uk/index.php?id=CNVFCS016&browsemode=manufacturer" rel="nofollow - http://www.bluearan.co.uk/index.php?id=CNVFCS016&browsemode=manufacturer

Monacor:

http://www.monacor.co.uk/categories/film-capacitors/vnr/112300/" rel="nofollow - http://www.monacor.co.uk/categories/film-capacitors/vnr/112300/

http://www.monacor.co.uk/categories/air-core-coils/vnr/124760/" rel="nofollow - http://www.monacor.co.uk/categories/air-core-coils/vnr/124760/


Much appreciated Earplug. Are these available any smaller? I have just a few millimetres to cram all this in. Is there are simple variable crossover on a chip available?


Posted By: Andy Kos
Date Posted: 28 April 2016 at 7:13pm
Originally posted by Modeller Modeller wrote:

I have just a few millimetres to cram all this in. Is there are simple variable crossover on a chip available?

Not in passive format, only active.

Thing is with passive components they need to be a certain size in order to handle the power levels.

An active crossover does this at line level (before the amplifier) where the power levels are minimal.


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just a guy with a warehouse and a few speakers... www.bluearan.co.uk


Posted By: DJ-Versatile
Date Posted: 28 April 2016 at 8:23pm
Thanks for your help guys! 

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If you are the smartest person in the room, you're in the wrong room....


Posted By: snowflake
Date Posted: 29 April 2016 at 10:47am
if u r worried about portability it is worth considering that the weight of two or three huge inductors is possibly more than a 1U active crossover


Posted By: DJ-Versatile
Date Posted: 29 April 2016 at 11:09am
Originally posted by snowflake snowflake wrote:

if u r worried about portability it is worth considering that the weight of two or three huge inductors is possibly more than a 1U active crossover

Crikey! OK, I've had a little redesign and know where I am headed with it now.

Thanks for everyones help as always!Thumbs Up


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If you are the smartest person in the room, you're in the wrong room....


Posted By: Modeller
Date Posted: 29 April 2016 at 1:46pm
Originally posted by Andy Kos Andy Kos wrote:

Originally posted by Modeller Modeller wrote:

I have just a few millimetres to cram all this in. Is there are simple variable crossover on a chip available?

Not in passive format, only active.

Thing is with passive components they need to be a certain size in order to handle the power levels.

An active crossover does this at line level (before the amplifier) where the power levels are minimal.
Thanks Andy, but I only have 3-5 Watts in my system. Is there an alternative, less precise way I could adapt to use as a low power crossover?


Posted By: Earplug
Date Posted: 29 April 2016 at 5:35pm
You could try lower power/voltage components, eg:

http://www.digikey.com/product-detail/en/wurth-electronics-inc/74458303/732-3931-2-ND/3316515" rel="nofollow - http://www.digikey.com/product-detail/en/wurth-electronics-inc/74458303/732-3931-2-ND/3316515

2 of those in parallel.





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Earplugs Are For Wimps!


Posted By: Modeller
Date Posted: 21 April 2017 at 1:15am
It's been a while from when I originally posted this (the model world moves very slowly...) but I've got some details on the amp I'm tied to using.

As I said in a previous post, this is for model sounds, so high fidelity is not a key requirement, but separating the frequencies is quite important.

The amp is 3W at 4-8Ohm. I'm going to be using 3 drivers (1x sub, 2x mono mid/high). I need to build a passive crossover to suit and select the drivers most suitable within these limits. Any help with the crossover would secure my gratitude for life!

Cheers, Steve


Posted By: Earplug
Date Posted: 21 April 2017 at 11:34am
For what you´re trying to do, just use a 2-way passive and then add a piezo tweeter. No need to complicate this any more.

Or better, just use this:

http://www.ebay.com/itm/DC-5V-20W-2-1-Dual-2-Channel-3D-Surround-Digital-Stereo-Class-D-Amplifier-Board-/172625385634?hash=item28314658a2:g:LVIAAOSwU8hY8Nz~" rel="nofollow - http://www.ebay.com/itm/DC-5V-20W-2-1-Dual-2-Channel-3D-Surround-Digital-Stereo-Class-D-Amplifier-Board-/172625385634?hash=item28314658a2:g:LVIAAOSwU8hY8Nz~




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Earplugs Are For Wimps!


Posted By: markie
Date Posted: 21 April 2017 at 1:07pm
I've often looked at these 2.1 amps but they never seem to mention any filter frequency for the sub output. Do they have a filter? Or are you supposed to be clever enough to work one into the circuit somehow.


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If it's got wheels or tits it's gonna cost a fortune


Posted By: Modeller
Date Posted: 21 April 2017 at 1:33pm
Thanks Earplug, but this is way too big for our application. I was hoping somebody could specify components specific for our needs.


Posted By: snowflake
Date Posted: 21 April 2017 at 2:01pm
Originally posted by Modeller Modeller wrote:

Thanks Earplug, but this is way too big for our application. I was hoping somebody could specify components specific for our needs.


if you aren't worried about high fidelity just run the mid driver full range - it will roll off by itself at some point and putting high frequencies through it won't do any damage. put a capacitor in series with the tweeter and change the value till the tweeter rolls off at approx the same place as the mids. even a decent polypropylene cap of the correct uF value will be pence rather than pounds.


Posted By: Modeller
Date Posted: 21 April 2017 at 2:46pm
Thanks Snowflake, but I'm afraid that means not a lot to me at the moment. If you could start from the basis I know nothing at all. I have designed my own cabinets in the past, but I've used off-the-shelf crossovers or salvaged units and bought drivers to suit. This is a ground up design and I'm free to choose components suitable.

I need an unpowered unit that is very small – to fit in a model – that can separate the bass frequencies from the mid/highs at the point where the mid/high drivers are effective. How do I work out which components I need depending on the switch to the next driver? If, for example, I need the switch at approx 8kHz, what do I need to achieve that and what would the wiring diagram look like? I can then get it produced at my factory.

Thanks in advance and apologies for my total lack of knowledge.
Steve


Posted By: odc04r
Date Posted: 21 April 2017 at 3:19pm
There is no getting away from a little bit of measurement and maths required for best results vs least effort. Although just taking values directly from spec sheets would do it.

Read this page thoroughly first of all, it might answer quite a lot of your questions: http://sound.whsites.net/lr-passive.htm" rel="nofollow - http://sound.whsites.net/lr-passive.htm


Posted By: markie
Date Posted: 21 April 2017 at 3:21pm
If you don't need high fidelity why not use a simple full range driver, which will eliminate the crossover entirely.

If you include a sub driver the necessary crossover components will inevitably be big.

If you want some extra high end then use a mid driver plus a piezzo tweeter. Piezzos don't need a crossover, just a  resistor in series.


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If it's got wheels or tits it's gonna cost a fortune


Posted By: Earplug
Date Posted: 21 April 2017 at 3:29pm
Originally posted by markie markie wrote:

I've often looked at these 2.1 amps but they never seem to mention any filter frequency for the sub output. Do they have a filter? Or are you supposed to be clever enough to work one into the circuit somehow.


I´ve never actually used any of those, but I presume that they do come with the filters built in. The blurb seems to indicate that it does, but who knows. Maybe send the seller a question.




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Earplugs Are For Wimps!


Posted By: Earplug
Date Posted: 21 April 2017 at 3:42pm
Originally posted by Modeller Modeller wrote:

Thanks Snowflake, but I'm afraid that means not a lot to me at the moment. If you could start from the basis I know nothing at all. I have designed my own cabinets in the past, but I've used off-the-shelf crossovers or salvaged units and bought drivers to suit. This is a ground up design and I'm free to choose components suitable.

I need an unpowered unit that is very small – to fit in a model – that can separate the bass frequencies from the mid/highs at the point where the mid/high drivers are effective. How do I work out which components I need depending on the switch to the next driver? If, for example, I need the switch at approx 8kHz, what do I need to achieve that and what would the wiring diagram look like? I can then get it produced at my factory.

Thanks in advance and apologies for my total lack of knowledge.
Steve


If this is going to be some sort of commercial product, maybe you really need to find/hire someone to design the unit for you and get it done properly, rather than flapping around when you don´t seem to understand the very basics needed to get going.

You´ve already been given plenty of good advice on how to get this done. Maybe do some reading:

http://forum.speakerplans.com/newbie-essential-reading_topic14681.html" rel="nofollow - http://forum.speakerplans.com/newbie-essential-reading_topic14681.html




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Earplugs Are For Wimps!


Posted By: Modeller
Date Posted: 21 April 2017 at 5:15pm
No problem Earplug, if that's what it takes.

A previous question on this website helped us produce a debut model that won a lot of incredible reviews, so with that success in the bag I wanted the relationship to continue.

As we produce models that give very generous donations to industrial heritage charities (£12,500 so far), we need to keep costs down as low as possible, so asking the right enthusiastic people for as little financial outlay as possible is our aim.

We all have our specialities, but crossover design is not one of mine or my electrical engineer's, who is more geared toward drive and supply systems. In assisting (in more than just general terms) you will help donate over £10,000 to another charity preserving Britain's proud and pioneering industrial heritage, but I'm not forcing you to do that.


Posted By: markie
Date Posted: 21 April 2017 at 8:13pm
You'll find people on here are very helpful, but you really need to give us more information.

1). How much room have you got to fit the amp and speakers.

2). How are you going to power it, mains or batteries.

3) What sort of sounds are you trying to reproduce.


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If it's got wheels or tits it's gonna cost a fortune


Posted By: odc04r
Date Posted: 25 April 2017 at 10:45am
Originally posted by Modeller Modeller wrote:

No problem Earplug, if that's what it takes.

A previous question on this website helped us produce a debut model that won a lot of incredible reviews, so with that success in the bag I wanted the relationship to continue.

As we produce models that give very generous donations to industrial heritage charities (£12,500 so far), we need to keep costs down as low as possible, so asking the right enthusiastic people for as little financial outlay as possible is our aim.

We all have our specialities, but crossover design is not one of mine or my electrical engineer's, who is more geared toward drive and supply systems. In assisting (in more than just general terms) you will help donate over £10,000 to another charity preserving Britain's proud and pioneering industrial heritage, but I'm not forcing you to do that.


That's all fine but part of a relationship is being honest. So you should have said it was a semi commercial design with charity affiliations in your first post, people wouldn't have minded but engineers are a cranky bunch at the best of times.

Anyways if your engineer knows what a Laplace transform is he can figure out a crossover. The design of plant control systems have a lot in common with crossovers in terms of a transfer function and its associated gain/phase.

You will have to provide quite a bit more data on your drivers etc if you want serious answers.

Edit: Because I can't spell sometimes


Posted By: studio45
Date Posted: 25 April 2017 at 2:06pm
I think I'm getting a clue here....This isn't for a soundsystem, it's a scale model of some machine or other, and you're putting a very small set of speakers into it because you want it to make the same noises as the full-sized version?

If that's right, then this might be much simpler. You probably don't need high-fidelity speakers to reproduce machinery clanking or engine noise. Run that bass-mid driver full-range, and connect up the tweeter with a 1uF cap in series. Add a 4 or 8 ohm resistor before the cap if that makes it too bright. That will start bringing the tweeter in at about 15kHz assuming it's 8 ohms, which might seem high - but the response shape of most tweeters is far from flat and the effective acoustic crossover point will be much lower.


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Studio45 - Box Builder Commotion Soundsystem -Mobile PA


Posted By: Modeller
Date Posted: 25 April 2017 at 4:36pm
That is correct Studio45, the sounds are industrial (engine and other noises) but what I have found on the previous model is that the bass driver has too much to do and colours the top end especially. What I plan to do is single out bass notes up to about 8kHz and have the mid/highs handle everything else.

The amp I am using is 3W at 4-8Ohm. The driver selection will depend on the final enclosure design which I will run by you here later, but I only have about 40mm width and no more than 60mm length. I'm looking at the height now, but will probably be in the order of 30mm or so.

The sound unit will incorporate 3 small speakers (sub, 2x mono mid/high) from which I hope to design a good below 200Hz bass response, lower if possible at approx 70-80Db, which I think is achievable. I managed below 250Hz with a pair of 34mm round full-range speakers in a reflex enclosure, so with a 40x60mm sub in a similar enclosure I hope to achieve better results.

At the moment I'm looking at a compact transmission line design, but I've not finally decided yet. I really want to crack the crossover and driver selection before I start on the enclosure.

Thanks again


Posted By: odc04r
Date Posted: 26 April 2017 at 8:22am
You sound like you have a pretty good idea of what you want. Conventionally the xover is the last part of the system to be built and installed but as you are at a premium with space I see why you are thinking about it now.

The best bet is probably keeping it simple. The bass driver already has a modest roll off due to its natural inductance. If you measure its impedance and do some simple maths you could double the roll off slope with an appropriately sized series capacitor.

Your problem is going to be that steeper filters for good sub/high separation require more passive components and complex design. Is it possible to apply active filtering before an amplifier? That might solve a lot of your problems and with surface mount parts an active xover could be made very small.




Posted By: Modeller
Date Posted: 26 April 2017 at 1:33pm
In an ideal world an active crossover would be great, but I have run out of power sources already because of moving parts, lights, etc. In fact, I need more! I'm afraid it has to be passive.

I'll work on a selection of drivers over the next few days and post them here.

Thanks


Posted By: odc04r
Date Posted: 26 April 2017 at 2:45pm
Really? An active processing board would only take mA of power for a few op amps. I find it hard to believe that cannot be spared unless you are on a super tight power budget? If low power was a concern you could probably get that down to microamps with the right op amps. Stereo amplifier for your sub/top split and off you go.


Posted By: studio45
Date Posted: 26 April 2017 at 3:41pm
Originally posted by odc04r<br><br>The best bet is probably keeping it simple. The bass driver already has a modest roll off due to its natural inductance. If you measure its impedance and do some simple maths you could double the roll off slope with an appropriately sized series capacitor<br><br>[/QUOTE odc04r

The best bet is probably keeping it simple. The bass driver already has a modest roll off due to its natural inductance. If you measure its impedance and do some simple maths you could double the roll off slope with an appropriately sized series capacitor

[/QUOTE wrote:



You would want a series inductor, not a cap. If you wanted to make a second-order filter, the cap would go to ground *after* the inductor. If you just use a cap to ground, the impedance will drop to near zero at high frequencies, which will make your amp unhappy

You would want a series inductor, not a cap. If you wanted to make a second-order filter, the cap would go to ground *after* the inductor. If you just use a cap to ground, the impedance will drop to near zero at high frequencies, which will make your amp unhappy and suck all the drive signal away from the tweeter.

So you only have to deal with a few watts. Perhaps the passive is not such a terrible idea then. Possibly simpler than designing an active one, *if* your drivers are well-behaved. 
For a start, a second-order Linkwitz-Riley at 8 kHz for 8 ohm drivers requires 320uH and 1.24uF. http://uk.rs-online.com/web/p/wire-wound-surface-mount-inductors/6934665/" rel="nofollow - Here  is a very small surface-mount inductor rated for 500mA and you could use tiny 10v electrolytics for the caps. For 4 ohms, use 160uH and 2.5uF. To go down an octave, double all values.

Do you have an impedance measuring rig? It will tell you how well-behaved your drivers are. If the impedance graph has big features on it that are not to do with the fundamental resonant frequency of the drivers when mounted in your box, or the impedance has risen more than 25% above nominal at your chosen crossover frequency, a passive network will probably not be a good solution. 
Getting a flat transfer function out of a simple passive filter requires a pretty flat impedance and frequency response from the terminating driver. To deal with impedance variations you need to start adding different types of filter to the passive, which will quickly double or triple its physical size. 
Whereas an active filter can be made vanishingly small using surface-mount tech, and wouldn't need the extra networks to provide a flat transfer function - the amplifier's voltage-drive characteristic takes care of that.


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Studio45 - Box Builder Commotion Soundsystem -Mobile PA


Posted By: odc04r
Date Posted: 26 April 2017 at 9:56pm
Ah yes, sorry was being dumb there. Don't think about crossovers and do other work at the same time. That would have ended up being an resonant LC series notch filter with regard to voice coil current.

I'd still go active. Basically if you have an amplifier in the mix already, you have what you need for active filtering in terms of power rails. Current draw is no concern. Even if it has to be single voltage rail with coupling capacitors involved.


Posted By: Modeller
Date Posted: 13 May 2017 at 12:21am
Thanks again for all the help. I'm narrowing down driver selection, but I'm stuck on basic principles.

Let's say I choose 3 drivers all rated at 8 Ohm. After the crossover (depending on its design) one feed will go straight to the sub, so this feed is still rated at 8 Ohm, and another feed will be split between two drivers, so these will be rated at 4 Ohm. Is this correct? How will a basic resistor-based crossover change this perception?

Also, I think I have found a really good driver for the sub, but this is rated at 16 Watts, and I only have a 3 Watt amp. What will happen to either the amp or the speaker if I attempt to drive it?


Posted By: odc04r
Date Posted: 13 May 2017 at 11:06am
You can't implement a can't implement a crossover with just resistors, they are not a frequency dependent component in terms of their resistance. What you can do with them is implement a level matching network such that the SPL of different drivers fed from the same amplifier is compensated such that they work well together. E.g. a mid driver that is more efficient than a sub but you only have one amplifier channel to run them both from and you want to match the levels - so the mid is going to need a resistive network in front of it to pad the output down.

Your speaker and amplifier combo will be fine.

Edit: Sorry I just realised you said resistor network after the crossover itself. With the addition of a Pi network to any driver you can make the amplifier 'see' any load you wish. But power will be dissipated in the resistors.

When a crossover is operating in its passband, the load the amplifier sees is just the driver as the crossover is in series with it and contributing minimal resistance.

At the 3dB crossover point between drivers you will see a little bit of extra resistance from the network added to each driver, and then those in parallel. So for a 4 and 8 ohm driver ignoring the extra crossover resistance in series the amp will see a load of 8//4 ohms (approximately).

Read this web page thoroughly and all  the answers you need are in it - http://sound.whsites.net/lr-passive.htm" rel="nofollow - http://sound.whsites.net/lr-passive.htm Section 6 deals with attenuation of signal post-crossover whilst maintaining a desired impedance.

If you are unsure of your designs, simulate them using LTSpice, TINA, or any other electronics simulation package before you build.


Posted By: Modeller
Date Posted: 16 June 2017 at 3:07pm
It's been a while as I've been hunting down appropriate drivers. I think I've found something perfect for the application – the Peerless TC55FD00-08. It has a good frequency response, and if I use them in pairs and tune the response of each I can use one for lower frequencies and one for higher. That is a very loose plan anyway.

This got me thinking about enclosure designs, and I've attached my current favourite. I'm a little worried by phase alignment from the port, but I'm hoping your combined wisdom can help out in that regard, plus any design enhancements you suggest.

The design is totally open, except that I would like to keep within these rough limits (51mm wide FIXED, 63mm long, 62mm tall). Internal baffling is also open – I will be injection-moulding these especially for the model from a high density polymer.

The floor is yours.




Posted By: Modeller
Date Posted: 21 June 2017 at 10:40am
I'd really appreciate some feedback on the enclosure design please.

I've tried a very simplified transmission line arrangement, although I'm not sure about the parallel escape channel.


Posted By: odc04r
Date Posted: 21 June 2017 at 4:30pm
You would simulate that enclosure as a straightforward reflex. Where a reflex stops and a TL begins is another subject of discussion, but if the port is not long enough to support a 1/4 length bass cut off standing wave then it is a port assisted design, or reflex.

The driver you have chosen has a quoted bandwidth of 200-20KHz, is this the only driver in the system? It will not produce any bass or low mid but will be alright to reproduce vocals and most instruments. Think of any portable radio and you are not far off.

I cannot find any TS specs for the driver but because they are such tiny little things there is no design here to be had really. Stick them in anything and they will sound the same. Make a compact sealed box for them and keep it as simple as possible to aid the overall design. There is no point at all in porting them at all. You will need to filter sub 200hz content (if it exists in your sources) before you apply it to them else they will die very quickly at any kind of power.

If you are playing only known prerecorded audio, then you can filter the tracks using a PC before applying them to the system to save you having to do it with physical components.



Posted By: Modeller
Date Posted: 23 June 2017 at 3:02pm
Thanks.

The speaker was tested from 200Hz, but looking at the signal response it actually rolls in at about 150 ( http://www.tymphany.com/peerless/driver-search-results/driver-detail/?id=1079" rel="nofollow - http://www.tymphany.com/peerless/driver-search-results/driver-detail/?id=1079 ). I was hoping to reinforce and extend that with enclosure design. With a sealed enclosure I would just replicate the tested results. My problem, which I'm all too aware of, is a very limited volume.

The audio source is full range, recorded with professional equipment, so the only limitations are the output devices.

My thoughts, crazy as they are, would be to use this unit to reproduce frequencies up to somewhere between 500-1000Hz and then roll in a similar but separate driver for up to 20kHz. Don't worry, I know this is insane overkill for what is a scale model, but I'm already pushing boundaries with design so why not audio and electrical performance too?

Cheers


Posted By: odc04r
Date Posted: 23 June 2017 at 3:16pm
It'll produce sound under 200Hz sure, no driver has a brickwall response. But depending on where its resonance is the excursion under that point for a given power level compared to above it will be large, = dead driver with much less power than its quoted rating. So that all depends on how you plan to drive it. Measure a units impedance over the audio bandwidth to figure out where resonance is. Very easy to do with an external soundcard and one resistor + REW.

As it is rated to perform to 20KHz why do you want to put another tweeter above it? Simple is your friend when designing. Surely if it is just reproducing machine noises anyway the bandwidth required is going to be quite limited. Nothing higher than a few KHz I would imagine? If you must have another driver I am sure there are plenty of small dome HiFi tweeters that would fit the bill. Again you can often go lower than their suggested bandwith, if you are easy with the drive signal.


Posted By: Modeller
Date Posted: 23 June 2017 at 3:54pm
Thanks, that's very sound advice.

I'll do some testing when the samples arrive next week. Before I commit to an injection-moulded enclosure I'll be playing with some high density 3D printed prototypes. I've got a couple different designs planned, but I am very open to having one suggested. I'll even send you the prototype unit once it's been tested. A genuine offer for someone with a flair for small design challenges.



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