Anyone heard of series crossovers?

[Lawrence001]

I've just bought these speakers and the seller said they have a "series crossover based on the Acoustic Reality model". I said I would like a bit more treble and he suggested I can change the Caddock resistor, but I can't see one. What's the thing that looks like a transistor (but with 2 legs) on a heatsink? Actually I can't see a capacitor either... https://uploads.tapatalk-cdn.com/20181217/6b7890ebeeedec96248c0a94688c6fbd.jpghttps://uploads.tapatalk-cdn.com/20181217/e74ed54f4ff39651838853792cbd1bda.jpg

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[YNWaN]

There is a resistor, an inductor and a capacitor (doh, no there isn’t), all good quality. The top left is the capacitor (nope, it is an inductor - obviously!), the lower middle is the inductor and the thing attached to the heat sink is the resistor.

[Lawrence001]

And I thought there were two inductors, shows what I know! I didn't know they made resistors like that either, it's smaller than usual, are they made out of silicon rather than whatever the bigger ones are?

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[struth]

film power resistor i think

[Lawrence001]

If anyone can guess the circuit from looking at the 3 components, is there a simple way of increasing the output from the tweeter (or padding down the mid bass)? Alternatively, could it reverse the phase of the tweeter, so I could try switching the tweeter wires around?

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[YNWaN]

Apologies, of course there are two inductors and no capacitors at all. That’s the problem with assumption - I presumed there was a capacitor is series with the tweeter as this is usual.

http://i1151.photobucket.com/albums/o624/6thplanet/arserialxover_zps2fb8a07d.jpg

[YNWaN]

Looking closer the red inductor has 2.00 mH printed on it so I guess that is in series with the woofer. Yes, it looks like the foil one is across the tweeter.

[Macca]

How does it work without a capacitor? Why does the tweeter not blow?

[Firebottle]

Because the inductor is a low impedance at low frequencies, as opposed to a capacitor being a low impedance at high frequencies, and the inductor being in parallel with the tweeter.
If a capacitor is used it is in series with the tweeter.

[Macca]

Because the inductor is a low impedance at low frequencies, as opposed to a capacitor being a low impedance at high frequencies, and the inductor being in parallel with the tweeter.
If a capacitor is used it is in series with the tweeter.

An inductor won't protect the tweeter from receiving LF though which is why you need the capacitor. So what stops LF going to the tweeter?

[walpurgis]

How does it work without a capacitor? Why does the tweeter not blow?

L1 will be draining some LF away from the tweeter.

[Macca]

L1 will be draining some LF away from the tweeter.

But L1 is an inductor. Clearly I'm missing something but I don't know what.

[Firebottle]

The impedance drops as the frequency drops, so L1 shunts the lf away from the tweeter.

[Firebottle]

In other words the LF takes the path of least resistance, in this case through L1.

[Lawrence001]

Presumably the inductance of L1 is much lower than the tweeter at the dangerous frequencies and almost all the current flows through it.

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[Macca]

Thanks I get it now.

[Lawrence001]

Am I right in thinking if I put another resistor in parallel with the one in there now, it will reduce the output of the mid/bass driver? I'll see what value's in there now and buy a few cheap high power ones to play with, any suggestions, I think quite a bit of power might be dissipated there? I guess I can't increase the output of the tweeter easily.

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[walpurgis]

Am I right in thinking if I put another resistor in parallel with the one in there now, it will reduce the output of the mid/bass driver?

Yes, that is correct, but you may find yourself with a low system impedance.

[YNWaN]

To be honest, as you are clearly unhappy with the current results, I would just bin the crossover and use a traditional first order. To start with I would connect the bass driver directly, with no crossover components and use a single capacitor (2.2 to 4uF to experiment) in series with the + of the tweeter.

[Lawrence001]

I think the design is tuneable (if that's a word) so I'd rather pursue that avenue at first, especially as the components seem very nice. But if the issue (for my ears) lies in the inductors rather than the resistor then it does seem a big job.

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[fatmarley]

The design is tuneable to a certain extent but it relies heavily on drivers that will work with this crossover. I just simulated the AR crossover using the last design I built and I couldn't for the life of me achieve anywhere near a flat response. The best I could get drove the impedance down to around 3ohm, but even then the response was as wonky as hell, and off-axis would have been all over the place.

[Macca]

, but even then the response was as wonky as hell, and off-axis would have been all over the place.

Although that doesn't seem to bother the designers of some speakers even if it should.

One option would be an active crossover, do it all digitally, just dial in the slopes until you're happy. In theory at least you'd gain in sound quality that way. But you'd need two power amps.

[fatmarley]

Yes, active would give a much better chance of success.

I like the challenge of passive crossover design but it's very time consuming, and in my case, surprisingly expensive - It's not just the calibrated measurement microphone, DATS and software, but the boxes of capacitors, inductors and resistors that that I need to make quick changes to the crossover. With active it's so incredibly quick and easy to adjust the crossover - Most people who try it never go back to passive.

[Macca]

Yes, active would give a much better chance of success.

I like the challenge of passive crossover design but it's very time consuming, and in my case, surprisingly expensive - It's not just the calibrated measurement microphone, DATS and software, but the boxes of capacitors, inductors and resistors that that I need to make quick changes to the crossover. With active it's so incredibly quick and easy to adjust the crossover - Most people who try it never go back to passive.

I've spent whole days tweaking passive crossovers, you improve one area of the sound, and another gets worse. Possibly the most frustrating thing I've ever done and that's saying something.

[Lawrence001]

Now there's an idea, I bought a behringer crossover unit the other week...

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[Lawrence001]

The design is tuneable to a certain extent but it relies heavily on drivers that will work with this crossover. I just simulated the AR crossover using the last design I built and I couldn't for the life of me achieve anywhere near a flat response. The best I could get drove the impedance down to around 3ohm, but even then the response was as wonky as hell, and off-axis would have been all over the place.The drivers are Scanspeak 18W/8535-00 mid-bass units & Vifa XT25TG30-04 tweeters. If I can find their parameters, will they show if they are suitable? The cabinets are 20L sealed towers with some concrete, I presume on the baffles. They weigh a ton!

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[Lawrence001]

The values of the components are 0.11mH, 2.0mH and 7.5 ohms. Is there a relatively simple program that would simulate the frequency response in a 20L sealed enclosure with the driver parameters I can get online? I'm hearing the treble down around 5-6db at a guess. Or potentially there's some cancellation where the drivers cross over if they're out of phase but I suspect that's not the case from what I'm hearing.

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[fatmarley]

The values of the components are 0.11mH, 2.0mH and 7.5 ohms. Is there a relatively simple program that would simulate the frequency response in a 20L sealed enclosure with the driver parameters I can get online? I'm hearing the treble down around 5-6db at a guess. Or potentially there's some cancellation where the drivers cross over if they're out of phase but I suspect that's not the case from what I'm hearing.

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The drivers are Scanspeak 18W/8535-00 mid-bass units & Vifa XT25TG30-04 tweeters. If I can find their parameters, will they show if they are suitable? The cabinets are 20L sealed towers with some concrete, I presume on the baffles. They weigh a ton!

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Unfortunately not. The only way to know for sure is to take measurements and use software to find a crossover that works. Loudspeaker design done properly is not simple. A hell of a lot of people seem to think you can just guess or use your ears to design a crossover. Once you actually take real measurements and start moddelling crossovers, you realise that it's virtually impossible to design a crossover by ear.

People who design crossovers by ear have lots of badly recorded cds that they don't play. The better your crossover design skills get, the more of those "badly recorded cds" you can play.

[Lawrence001]

Unfortunately not. The only way to know for sure is to take measurements and use software to find a crossover that works. Loudspeaker design done properly is not simple. A hell of a lot of people seem to think you can just guess or use your ears to design a crossover. Once you actually take real measurements and start moddelling crossovers, you realise that it's virtually impossible to design a crossover by ear.

People who design crossovers by ear have lots of badly recorded cds that they don't play. The better your crossover design skills get, the more of those "badly recorded cds" you can play.That's what I'm asking, is there a program I can use to model the speakers, I'm not suggesting I tune them by ear (yet).

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[fatmarley]

That's what I'm asking, is there a program I can use to model the speakers, I'm not suggesting I tune them by ear (yet).

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Xsim is free and popular.

[dave2010]

Xsim is free and popular.I guess you're way ahead of me - and know about the easiest to use current tools. I was going to mention SPICE - but it may be too old now - not sure if there are any useful derivatives. Chances are there are digital simulators which can do the job - including matching the responses of all the units - but maybe there aren't many free to use ones.

[Lawrence001]

Thanks, I'll try Xsim when I get the chance.

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[Lawrence001]

In the meanwhile I've bought some cheap caps and resistors to have a play. Can't imagine they'll get here quickly at this time of year though..

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[fatmarley]

In the meanwhile I've bought some cheap caps and resistors to have a play. Can't imagine they'll get here quickly at this time of year though..

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It wont do any harm to try but as Martin experienced in post #24, you'll most likely find that as you improve one aspect, another will get worse. The best way to explain would probably be for me to do a video to actually show on my pc monitor what happens when you adjust the components of a crossover, but I'm not sure i can be bothered with all the hassle, so i'll try to explain in writing.

A bigger cap on the tweeter will let more low frequencies through to the tweeter BUT instead of filling a dip at the crossover, you could actually make the dip worse! With good crossover design software you have target curves (1st order, 2nd order, 3rd order etc) that you can place on the screen at your chosen crossover frequency. You adjust the slopes (play with component values) to try and match the target curves as best you can. Done properly (easier said than done) your crossover should be in good phase alignment either side of the crossover and will produce a flat frequency response. With an even order filter, you should get a wide deep null at you listening height (and distance) when you reverse the polarity of one of the drivers.

This is just a basic description but there's just so much to learn that the best way is to buy a good book. The loudspeaker design cookbook is probably the most popular but even that doesn't cover everything you need to know.

[Lawrence001]

I understand everything you say and appreciate your help but I'd like to give it a chance before I give up on the current crossover.

The cap is actually an optional one in parallel with the woofer. The resistor would change the value shown (I can halve or double going series or parallel without removing the one in place) which will show me which direction sounds better (ie makes treble relatively louder) then I can fine tune. My only concern with this is that the large inductor value is cutting off the mid range too low and none of this will help that. But it's surely worth a go for £4 expense and an hour of my time.

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[fatmarley]

I understand everything you say and appreciate your help but I'd like to give it a chance before I give up on the current crossover.

The cap is actually an optional one in parallel with the woofer. The resistor would change the value shown (I can halve or double going series or parallel without removing the one in place) which will show me which direction sounds better (ie makes treble relatively louder) then I can fine tune. My only concern with this is that the large inductor value is cutting off the mid range too low and none of this will help that. But it's surely worth a go for £4 expense and an hour of my time.

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Yes it's worth a try. You never know, you may get lucky.

[Lawrence001]

Plus my Parasound pre amp has tone controls, hadn't thought of that having used only the direct inputs before [emoji3]

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[Lawrence001]

Realised they're stuffed pretty tightly with wadding which might be the cause of the strangled sound, unfortunately while removing it one tweeter got damaged so I won't know for a while if it's sorted the problem. The picture shows what I could reach but there's more at the bottom. The cabinets are lined with foam sheets so I don't mind removing as much as possible to free up the sound.https://uploads.tapatalk-cdn.com/20181224/d5a4355d168b9f3ee55c3914b17acf9a.jpg

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[fatmarley]

I don't know how accurate the T/S parameters are for the Scan woofer but without stuffing you should get a box Q of about 0.9. I'd be happy with that, but you'll have to trust your ears because Scanspeak published T/S parameters don't often match the measured results.

[Lawrence001]

Well I got the tweeter repaired that was quite an effort. However, it turns out the issue was not any lack of treble at all but that strangled mid range, there's more going on there than I give credit for, I often think of treble when really I should mean upper mid range. They're sounding pretty good now, no immediate desire to play with the crossover, just give them a few weeks to bed in and get used to the presentation which is not the same as my IMFs I had got used to.

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[Lawrence001]

Holy cow these are good, maybe there's something to be said about these crossovers. The bass reminds me more of the IMFs than I initially thought. I.e. deep and tight but not in your face. Not bad for a pair of closed box moderate sized floorstanders

I might have been lucky in the stuffing issue inasmuch as I couldn't reach the bottom so only removed the top half. I have a theory that has released the mid range in an open box at the top but the tightly packed stuffing at the bottom has lengthened the apparent length of the cabinet seen by the sound wave (by slowing it down) and effectively formed a long closed pipe for the bass. Probably utter balls but they sound good and it makes me feel happy to think that :)

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[Macca]

Stuffing a speaker like that always kills the sound IME, not surprised they are sounding better now.

[fatmarley]

There's nothing special about the AR crossover, apart from being a series one. Some people say that series crossovers sound better (Tony Gee is a big fan (http://www.humblehomemadehifi.com/index.html)), but it's far, far more important to have a flat frequency response and good phase alignment throughout the crossover at the listening position. There's a chance that a better crossover could give another "Holly cow" moment, but without good measurements, it's impossible to say.