Combination speaker/earphone baseplate?
En avant
I ride with a Schuberth C3 which is a nicely quiet helmet. When I commute (a simple half-hour ride to work) I'd like to use in-helmet speakers as it's less hassle and they work OK in such a quiet lid. However, when I head out on longer weekend rides and tours I much prefer to use my custom earphones.
Has Sena thought about making a baseplate similar to the SMH-A0304 but with both attached helmet speakers *and* an earphone jack? Just like on a cel phone, when someone plugs the earphones in to the jack the speakers would shut off, making it quick and easy to choose what type of audio output to use that day. I think a lot of commute+tour combo riders like myself would appreciate that kind of option.
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Thanks a lot for your feedbacks so far and please understand that the reason why we do the survey is to better support your riding. Any inconveniences so far from earbud clamp, we really would like to improve the performance and reliability from the newer ones. We got back to you since we have some progress in the development and would like to finalize the design. Any feedbacks are all right if it helps to provide better ones for you guys.
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I want to add that I don't think it's necessary to turn off the attached speakers when earbuds are plugged in.
The only reason I can even see for bothering to do that is if you think it will reduce the drain on the battery.
Leaving the speakers on when the earbuds are in, as I have my g/f's helmet clamp setup, is not a problem. With earbuds in, you can't hear the speakers over the earbuds. And even if you could, they would be playing the same thing as the earbuds, so what's the problem.
On the other hand, if you leave the attached speakers on 100% of the time, this would afford the option to let the rider listen to the speakers and let a passenger plug into the rider's helmet clamp earbud jack so that the passenger can listen to the same music as the rider.
In any event, the most complete solution would be to have the firmware offer a setting to control whether the speakers turn off when something is plugged into the earbud jack.
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I understand Stuartv's point about leaving the speakers connected, what's the harm, except as he points out, it may impact battery life. Since with them connected in parallel to the speakers means the amp is driving a much lower imprudence, that must take more power and hence reduce the time before re-charge is required. My main usage will be on long trips away and it HAS to keep fully functional for 10-12 hours without needing a re-charge. Currently that's possible, but once you start driving a significantly lower impedance will that still be the case?
But that wouldn't even be a concern if the speakers are disconnected when the earbuds are plugged in and since having both on at the same time doesn't really offer any benefit (unless you want rider and pillion's helmets tied together with a cable) I maintain that having the speakers disabled when the earbuds are plugged in is the best way to go. Trying to offer this as an option in firmware might be nice, but I suspect it would really complicate the hardware design.
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Actually, I've just thought that if you really need the speakers to stay on, that would be a simple hardware mod to add a small switch that allowed you to keep them on simultaneously. I suspect most users won't require that, but if you did it would be easy to achieve.
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I use earbuds exclusively and don't have the speakers installed. I hope that you develop the new clamp with true stereo sound through the earbuds.
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@Ken: If they did implement it where it was a lower impedance with both plugged in, the result should still be that the rider turns the volume down, so the net difference in power, between using earbuds alone versus earbuds + speakers, should be the power required to drive the speakers - and at a much lower volume than they would be driven if they were being used by themselves.
My expectation is that the difference in battery life would be pretty darn small.
That said, it wouldn't really affect any of my use cases if the speakers turned off when earbuds are plugged in. But, I am a firm believer in keeping things simple - especially in the design of motorcycle-related components. Adding a switch that turns off the speakers is an extra and unnecessary component. That component could fail and leave the rider with the speakers turned off permanently. Thus, why I personally would prefer them to just be left on, no matter what. But, as a secondary choice, which I think would be more reliable against mechanical failures, is my suggestion for a firmware-based option and electronic switching of the speakers. A mechanical switch that always turns off the speakers seems to be the most prone to failure and would be my last choice.
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Dave Yeager, the input socket isn't switched. I looked at putting a switched socket there, but judged it too invasive WRT the PCB.
My mod has a 3.5mm socket hanging off a lead out of the clamp, with no hacks to the hardware. The mod could easily be cleanly reversed.
Stuartv has added a 3.5mm socket to the bottom of the clamp, which required cutting away some plastic.I haven't tried having the speakers operational at the same time as the earbuds, but Stuart thinks it is OK. So... the 'cleanest' mod might be cutting PCB tracks to the input socket, and wiring its pins to the speaker outputs. The downside of this is lack of waterproofing once you use that socket, and the fragile nature of it, just supported by the PCB and nothing else. Such arrangements always end up failing after a lot of use.
I like Steve's idea of mounting a switched socket at the bottom of the clamp.WRT ease of plugging in earbuds, I find it hard with my socket mounted on the helmet collar. It is difficult to locate the socket even with bare hands. So I tend to plug in before putting on the helmet -not ideal. I think a socket on the bottom of the clamp would be easier to locate and plug in to with the helmet on.
The earbud socket needs to be 3.5mm, not 2.5mm or some other connector.
1. All (normal) earbuds come with a 3.5mm stereo (or stereo + mic) plug.
2. A 3.5mm socket & plug is sturdier than a 2.5mm set.Maybe this isn't the place to mention it, but...
I have a BikerCom system sitting in a drawer unused. Maybe they are better now, but it is very limited despite being expensive, and the concept potentially very flexible (base Bluetooth unit).
I got upgraded by the dealer. The first version had a clamp system like the SMH10. The later version has only the comms part, with a mini-USB style connector for charging and going to the helmet speakers & microphone.
So imagine a wired version of the SMH10 with no clamp. Connection to the helmet via a plug-in (waterproof) plug & cable.
The BikerCom fastens to the helmet with a simple spring clip. It can easily be beefed up with velcro (supplied). No deadly metal screws that could penetrate the skull in event of an impact on that side.
No clamp, making it cheaper and more reliable.
The BikerCom connector is a 10pin plug. Room for separate speaker/earbud circuits under firmware control, Steve.
I prefer that type of physical setup. The single downside is that if you want to do some home wiring, those 10pin plugs are a bitch to wire, being so small. (I did buy some on the net.)
That downside would be removed if the cable had transition 2/3pin connectors to the speakers & mic inside the helmet, so one could buy the connectors or easily hack the supplied ones.Hopefully that is some food for thought, SENA.
Since there are two Kens on this forum, maybe I should be referred to as KenW, the other one KenG. :)
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It wasn't me that added a socket to the bottom of the clamp. I just modded the internals on my g/f's helmet clamp so the Aux In is now an Aux Out. She plugs her earbuds into the jack that was supposed to be for MP3 in. The wired speakers on hers are still attached and functional, but she can't hear them or even tell that they're working when she has the earbuds in and plugged into the helmet clamp.
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No sorry, it was Steve Z who added a socket to the bottom of the clamp. He sent me a photograph of it. I thought he'd put it on this forum too.
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Regarding plug size, the 3.5mm plug is large, particularly if you have to use a re-wirable one on the earbuds. I assume no-one else has tried this, but one of those 3.5mm plugs WILL NOT FIT THE SMH10. That's not just me, it's a physical impossibility as there is insufficient clearance around the (input) socket in the clamp. So, if we're talking some form of re-design, this needs to be addressed and to save space I suggested using a 2.5mm socket. These are commonly used on smartphones and I'm not aware of them causing a problem with any lack of robustness. If there is a problem with all these sockets it's that they simply come loose from the PCB. It's not the strength of the component itself, but rather how it is attached to the PCB so no reason for a 2.5 to be more prone to failure than a 3.5.
With some talk here of having 2, or even 3 sockets in the clamp, the size of the sockets will have to be considered since I don't think there's room for 3 x 3.5mm sockets and with space to use a re-wirable type plug. However, I appreciate that earbuds normally seem to be supplied with 3.5mm plugs, so maybe we do need to stick with that size socket. But Sena must ensure sufficient clearance so accept ANY 3.5mm plug and I think there should be ONLY ONE socket - for the earbud output. Any disconnection of the mic and/or speakers should be handled by small in-line connectors. Otherwise I'm concerned at the amount of 'stuff' that would be hanging off the outside of the helmet, making it all more prone to water ingress and snagging etc.
I have previously used an intercom system that had all the wiring plug directly into the unit itself, i.e. no electrics whatsoever in the clamping device. That is a VERY BAD design and was one of my main reasons for switching to the SMH10. In order to handle all connections, the plug needs to be multi pin and almost certainly small and somewhat fragile. In any case, it needs to be plugged in and unplugged for every ride which is impossible to do with gloves on, likely to be physically tricky to do being small and with so many pins and also constantly having to flex and stress the wiring when trying to get it plugged in and/or unplugged. In my experience of this type of system, it was a total PIA to connect every time and in a very short space of time the wiring failed. I had several sets of speakers and the wiring failed on all of them within a matter of days of each other.
The way the SMH10 connects to its clamp is a joy to use and every time I'm thankful that it's not stressing any wiring which as we know, once installed doesn't require messing with. Really, we don't need to be looking at any redesign of that. Fortunately, I doubt that's on the table anyway. My guess is Sena are simply looking at a modified design of clamp which I think is all we need.
I would like to say again though that Sena need to look at the stereo problem and fix that. Not many have commented on this, but I think we need to make Sena aware there is a problem with their current earbud clamp that needs to be corrected in the design of this new clamp.
I'd also be keen to get some more feedback from Sena on this. What IS the timescale. What thoughts do THEY have on potential design features?
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Excellent to see the thread I started so long ago getting answered, thank you! :) Here's my survey response:
1) Yes, I swap.
2) Speakers permanently installed. Too difficult to take out all the time and the custom in-ear-monitors (IEMs) I use are flush so don't interfere with the extra padding speakers create.
3) Here's how I envision it working, in the 'keep it simple' way: Just like the normal clamp with permanently attached speakers/mic, but with a separate headphone jack. One plugs in headphones and the speakers turn off. Unplug headphones and the speakers turn back on.
I would not want a jack or bulky connector for the speakers; either permanently wired or some kind of small or internal connector. The only jack should be for the when-desired earbuds/IEM's. This way when I do a quick ride or commute I simply put on the helmet, but when I climb on the bike to do a Nice Long Ride I can take the time to put the IEM's in and then plug them into the Sena once the helmet's on. Just be sure to make that jack easy to find and use with the helmet already on the head! :)
As for microphone, please keep the option of either a boom mic unit or a wired-mic unit at the time of purchase. I buy boom mic ones for my flip-front helmet, and wired ones for standard full-faced ones; having the option is important, but no need to make them swappable (I think buying one clamp unit to keep with each helmet is acceptable; install it once and leave it there for the life of the helmet IMHO).
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Oh -- and yes, please use a *NORMAL* heaphone jack size. Stereo is a must. Most IEMs come with the normal sized plug to be used in any music player. Putting a special or smaller plug would not be good.
Don't bother with four-ring jacks (stereo+mic); three-ring (stereo) is fine. Permitting stereo+mic would just up the complexity/cost, maybe cause problems with using normal earphones, and there'd be too much wind while riding to get any real use out of an inline-cord microphone on earphones anyways.
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1) Yes, I swap. Helmet speakers for riding 50 miles or under (usually local). Earbuds for trips. I have Westone UMC3X; bought them when my Etymotics gave up the ghost.
2) Speakers permanently installed. No reason to ever take them out.
3) Keep it simple. An earphone jack is all I need. Don't care if it turns the helmet speakers off or not. I just need a place to easily plug my earbuds.
I am looking seriously at the SMH-10R. Need an earbud socket for them, though. It's my only concern.
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Thank you for all your sincere feedbacks. Sena will get back to you with new clamp kits for both speakers and earbud. It is supposed to come out within a couple of month. We will get back to you when ready.
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Since Sena's combined clamp may still be some way off, I've modified an AO302 clamp as described in several threads here (and elsewhere). I cut just the 3 traces on the board and added the links to ensure correct stereo output. But, I've had some problems in use and I thought I'd see what others here have experienced.
First of all, I have previously been using an AO302 which was modified to include a 3.5mm jack socket on the speaker output wires from the clamp and the equivalent plug on the wires to the speakers. In this way I could plug in either the speakers or earbuds which are specially moulded ones I had made for me by Ultimate Ear here in the UK.
I immediately discovered that the volume from these earbuds was MUCH louder than when the speakers were connected. This was of course not only due to them being stuck in my ear, but also as we know, the impedance of earbuds is lower than that of the (albeit small) speakers. While connected and switched on, I can hear a distinct background hiss. It is NOT affected by the volume control and not really intrusive while riding since with other noise I don't seem to hear/notice the hiss.
Recently I obtained some Etymotics MC5 earbuds and these play at a much lower volume so their impedance is undoubtedly higher than the Ultimate Earbuds, although still lower than that of the speakers. The hiss with the MC5s is still there and unaffected by the volume control, but it is at a lower level and so for a given volume of any audio to which I am listening, it is even less intrusive than with the Ultimate Earbuds.
So far, so good. Then I modified a std. AO302 clamp.
I first tried a couple of 4 hour rides using the Etymotics which was entirely successful. They are indeed very comfortable under the helmet (after the hassle of getting the helmet on without dislodging them - but that's another story:-) and the audio quality was good. On top of the hiss, there is also a small amount of buzzing, presumably this is the interference that ensues from connecting the SMH10s stereo channels -ves to ground (as discussed here and elsewhere). But still only very low level and hardly noticeable above the aforementioned hiss and not at all while riding.
I subsequently tested the Ultimate Earbuds and found that they also exhibit the same buzzing, at about the same level relative to their background hiss. So both louder than the MC5s, but still acceptable when riding.
So nothing really unexpected in all that.
Then I went for a ride yesterday with the modified clamp and the Ultimate Earbuds. All was good as I set off and listening to some music as I rode to meet up with others for our ride. Shortly after we all set off and I was in Intercom mode with a friend (about 1.5 hours from when I originally started) I remarked that I could hear a fairly continuous crackling, over and above any other background noises. This crackling steadily became worse until after another hour or so, I was being subjected to such a high volume of white noise that I couldn't make out anything being said over the Intercom. An hour or so later, somewhat perturbed (and getting a headache from the white noise in my ears) I disconnected the earbuds and reverted to just speakers which were functioning perfectly. I tried the earbuds again several times but no better. In fact by the time I returned home, as soon as I connected the Ultimate Earbuds there was an extremely loud screeching obliterating anything else. Disconnect them and the speakers are again perfect. So I tried the Etymotics MC5s instead and was surprised to find they were absolutely fine, no increased level of any unwanted noise. Hmmm.
On a hunch, I left the SMH10 charging overnight and tried again this morning and found that the Ultimate Earbuds are now working perfectly again. So, what's going on here?
Well, my thoughts are as follows:-
Connecting earbuds in parallel with the speakers DOES reduce the impedance as seen by the amp as I have opined before and while this may not materially affect battery life (still ok for 4-5 hours, but may suffer over longer periods) it DOES mean that the amp is having to work harder. This doesn't present any apparent problem when the battery is in a full state of charge, or when the higher impedance Etymotics are used with the speakers, or with just the speakers or with just the Ultimate Earbuds. But, when the latter are connected in parallel with the speakers, the impedance is so low that when the battery charge drops slightly, the voltage must drop sufficiently to cause the amp to misbehave. The low input voltage and trying to drive such a low impedance creates instability in the amp output and generates horrific noise levels. This does rather support the idea that any new clamp Sena produce should switch the speakers OFF when the earbuds are connected.
I can think of a number of solutions to this:-
1. Wire some resistors into the Ultimate Earbuds connection so their impedance is increased to at least the same level as that of the MC5s.
2. Instal a switch into the clamp to allow the speakers to be manually turned off.
3. Instal a switching jack socket for the output so speakers are disconnected when earbuds are inserted.
4. Replace the current jack socket with a switching one.
The problem with 4. is that finding one suitable to replace the original on the PCB will be hard, if not impossible.
Although others have effected 3. with the new socket on the underside of the clamp, I am concerned any plug inserted into such a socket will interfere with any jacket being worn and that contains shoulder protection and will hence be much higher and closer to the helmet and the SMH10 and clamp.
So the jury is still out on the cure, but I'd appreciate any comments others may have on this and whether they have experienced similar problems and/or if they have any other suggestions as to the cause.
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I'm glad these mod ideas and how-to's are here and I may even get up the courage to try them. Thank you to the forum members! Clearly this feature should have been on the original model.
Sena: Why have you made your customers wait for over 18 months for such an obvious --and wanted-- feature? And we're still waiting with no stated delivery date.
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Released.... Shipping available in the mid July. Also, the A0303/0304 clamp kits are improved as well reflecting the higher volume request. Thanks for your sincere feedbacks. Enjoy riding with Sena!
http://www.senabluetooth.com/products/acc_SMH-A0305.php
http://www.senabluetooth.com/products/acc_SMH-A0306.php0 -
Ooooohhhhh, nnooooooo!!!!
How could you have missed the mark by so thoroughly?! We have asked for a helmet clamp where we can plug in earbuds and stil have the attached speakers - either working in parallel or switched off.
Requiring use of a big fat coiled cord with a propietary connector on the end, in order to use my earbuds is completely a non-starter! I already have too much extra cord to manage, just from the earbuds themselves. Adding that thick, heavy coiled cord just won't work! And, I have to wonder, what will keep the weight of that cord and the wind from pulling the connector apart at the end of the coiled cord? If the connector locks together, what will keep the weight and the wind from damaging the cord that comes out of the helmet clamp over time?
if you had just altered the A0304 kit to include your stock helmet speakers with a mini-headphone plug on the end of their cord, that would have been a much better solution than this, and functionally identical. (But still not precisely what we were asking for.)
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Love it!
It'll do almost exactly what I want it to do and is close to what I've already done to my Original base. I assume we'll get a set of helmet speakers with the new connector wit the base?
As far as excess wire/cable just coil it up and secure it with a small cable tie or a Velcro strip. That's what I do for mine now, It's never pulled out of the connector after 20k+ miles using it that way.
Can't wait to buy mine.
Thanks, Sena.
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Tom, is yours using the same kind of connector that Sena is using on this new helmet clamp?
is your connector oriented so that pulling straight down on the cable is how you disconnect it? This new Sena clamp appears to have a wire coming out of the back of the clamp and the coiled cord would be hanging from it, so gravity would actually be pulling in the direction of disconnecting it. As opposed, for example, to modifying the Aux In jack to be a Headphone Out jack, where, to disconnect, you pull the plug out to the rear, instead of down. Disconnection by pulling to the rear means gravity (and a heavy cord) are not constantly working to make it disconnect on its own.
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As I said before, if you take an A0304 clamp and get some helmet speakers that have a headphone plug already on the end, you would have exactly the same functionality as this new A0306 clamp - with none of the problems - like proprietary connectors, just as one example.
I cannot fathom why Sena would go to production with these 0305 and 0306 kits instead of just making a version of the helmet speakers they already have but with a headphone plug on the end, and packing those in with the existing 0303 and 0304 kits. And, of course, assuming the new designs for 0303 and 0304 fixes the issues with the existing earbuds plugs.
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Stuartv,
I use my SMH-A0303 base with the original helmet speakers. This required disconnecting the speakers from the original base and adapting the 3.5mm coiled extension cable that came with one of my Sena assemblies. The adaption amounted to removing the socket (female) end and soldering the connectors to the speaker wires. This leaves the coiled extension wire hanging behind me when not in use. When I'm riding in town I connect the helmet speakers to the 3.5mm socket on the SMH-A0303 and when I'm heading on a trip of more than 20-30 minutes I plug in my earbuds which I've coiled so that only about 6" is available.
The main difference that I can see from my setup is I'll now have virtually no cable when the helmet speakers are attached and pretty much the same cable hanging around when I used the earbuds.
I suspect this was the least expensive way to get a suitable product to us quicky. The new speakers and the earbud extension cable use a lot of parts from the SMH5
It'll work for me.
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Can you (Sena Development) tell us how this new clamp will satisfy the "higher volume requests"? Is it a more efficient speaker, or, lower electrical impedance? Or, was something done in the clamp. And since 1 clamp must service both speakers or earbuds, where did the 74 ohm resistors end up? In the connector?? Just curious.
I too am not crazy about the extra cable, but it does provide a strain relief. I have used the one that came with the original unit, and just coiled up the earbud cable into a small bundle.
Also, what about price for the new clamps?
Thanks! Anxious to test it out.
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I'm inclined to agree with Stuartv on this. How can they have got it so comprehensively wrong. Didn't I say "let us know your plans before you do anything so we can comment and help prevent you doing something stupid that we don't want". Ha, so much for that.
Also, like Dave Yeager I'd like to know what's been done in the amp etc. How have they got around the problem of the differential signal to the speakers, yet a common ground for the earbuds and the massively different impedance?
There were 3 problems to solve.
1. Impedance matching
2. Differential amp output to earbuds with a common ground
3. Physically connecting earbuds and/or speakers
Seems to me we have NO IDEA about 1. and 2. and they've comprehensively f****d up 3.
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Actually Ken, in the original configuration the speakers were nominal 32 ohm transducers, 38mm, rated at 200mW I believe. My aging Etymotic ER-6i earbuds are nominal 16 ohms. Kinda backwards, right! Not knowing the amp details it is hard to guess how they improved SPL of the speakers, but it should have been relatively easy to drop in lower impedance devices - 16, or even 8 ohms will draw more current (if the amp can supply), and provide more headroom (less clipping).
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My new Etymotics MC5s are also 16 ohm, but the Ultimate Earbuds are only 4 ohm, which perhaps explains the problem I had with them in parallel with the speakers when battery charge got a bit low,
I'm going to add some resistors to try and counter that. I've also been looking for a small switch to enable the speakers to be switched on and off at will. Not found anything suitable yet though.
I was thinking about the problem with the common earth of the earbuds. What if the additional resistors were inserted between the earbud ground and each channel ground. So there was twice the resistance value between the channel grounds which ought to maintain decent separation between the channels while providing a common ground for the earbuds and also some additional resistance to better match the impedance of the speakers. Wouldn't that eliminate, or at least reduce the problems when adapting the 302 clamp?
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I agree, the new clamp is a massive fail. Short cable earphones are few and far between. Instead of designing a cable management solution, allowing to securely wrap the excess cable around the baseplate, Sena introduces more dangling cables and connectors. Not what we need at 60MPH. Also no mention of fixing the common ground problem. Why introduce new hardware if it can't even play stereo audio properly?
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I have gone through a few of these with the earbud plug. The wires pull out to easily causing it to work. The only thing I have found to slow this down is by multilayer shrink wrap over the wires. Sena, PLEASE make this stronger!!!! You are on the right page, just toughen this up!!!
Sena SMH-A0303 Helmet Clamp Kit for Earbuds
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I have just returned from a 4 day trip exclusively using my earbuds from Ultimate Ear with my SMH10 and clamp modified to connect the earbuds in parallel with the speakers, but with my 'adjustments'. Here's what I did and how it turned out:-
I cut all 4 traces on the back of the clamp's PCB. Wired both +ves directly to the socket, but with a 75ohm resistor between the socket ground and each -ve. In this way, I added 75ohm to the resistance of each earbud, but also 150ohms between the 2 -ves.
The good news is that the additional resistance prevented the amp from becoming unstable and this setup ran ALL day without bother. It was either providing sat nav instructions or intercom so working all day long. No problems with battery life or screeching instability at any time.
Audio quality from the earbuds seemed fine. No different from any previous test with different connections etc.
All audio output could be set to an acceptable volume. With no addn. resistors the iPhone's sat nav app's beeps, warnings etc were way too loud. Now, no problem.
Even with the earbuds connected, stereo separation sounded 100% from the speakers. I realise it may not have been absolutely 100%, but it sounded that way to my ears (I use a test file that lets me test the audio channels), so that's good enough.
The not so good news is that stereo separation with the earbuds is not at all good. L audio is almost as loud (but not quite) from the R earbud and vice versa.
As I'm not an electronics engineer I don't entirely understand the results. The 150ohms between the L & R channel -ves is obviously sufficient to prevent any noticeable cross bleed at the speakers, even when the earbuds were actually connected. But there was nearly 100% bleed when listening to the earbuds. Can anyone explain this?
The volume from the earbuds is still very much louder than from the speakers, but this can be adjusted down with larger resistors used. Also, I cannot help but think that higher resistances in the -ves would help to reduce the cross bleed. So I was thinking of trying some 270 or even 500ohm resistors instead of the 75s I'm currently using. IOW, try to balance the perceived volume between speakers and earbuds by adjusting the value of those resistors and hopefully the higher resistance will help to reduce or even eliminate the stereo bleed at the earbuds.
Does this make sense or is the stereo cross bleed not related to the value of these resistors? Any electronics engineers here?
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Ken Gillett, you have two issues: just enough knowledge to be dangerous, and looking for problems where there are none.
1. The 'cross bleed' is totally caused by your resistors. Draw the circuit up on paper, then work out where the signals go. If the left channel goes positive, it will drag your common ground positive because it is 37 ohms from ground. The earbuds are likely less than that impedance. If the right active output is fixed at that moment (no right channel sound), there will be a voltage across the right speaker by virtue of the ground moving relative to the right channel output. (I hope that makes sense.)
2. You seem obsessed with your idea of 'impedance matching'. (Judging by this and previous posts.) Why do you think resistors in series with earbuds are a good idea? The theory for power amplifier choice with big speakers used to be, and presumably is still, get as low an output impedance as possible, to give maximum damping on bass speaker cones. I can't think why the same principle doesn't apply to earbuds. The only good reason for series resistors, and probably why Sena use them in the socket headset, is to prevent a short to the output amp in event of earphone short, or while plugging & unplugging. I've modified three headset, used all them for many thousands of kms (two Ulysses AGMs, Adelaide to Mildura via Tasmnania, and Adelaide to Maryborough QLD and back). They have been fine, and still are. No resistors.
3. Doesn't the iPhone have a volume control? Just wiind it back a bit if the navigation beeps are too loud.
4. The headset has a volume control. Why does that have to be at the same level for both speakers and earbuds? If you swap over frequently, that might be a good idea. If not it doesn't matter.
If you want to get the same volume into earbuds and speakers by using resistors into the earbuds, then the resistors have to be in the active line. Otherwise you will get the crosstalk you are noticing. Resistors like that are impossible to do with the simple switching socket I use. But for your setup with speakers and earbuds both active, it is very doable.
My two bob's worth.
Ken.
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