Background drone?

[biggles330d]

Random question, but does anyone else have a dull background droning noise, fairly low pitched and not loud when driving. It's unrelated to engine revs, sort of increases with speed. When stopped it's not there. I don't think its tyres as it doesn't really change with different road surfaces. My A110 has the standard exhaust.

I think it's always been there since new. I hadn't been out in the car for a while but did 60-70 miles on friday, mix of motorway, a road, b road, not going fast, just normal. Mix of standard and sport mode. Car drives totally fine but once I 'tuned' into the background drone it was there constantly.

It's hard to describe but not a resonance as such, doesn't come and go with speed / revs. I don't think it's wind noise, I don't think it's driveline. The car has 8500 miles on it so it's nothing worn out. I can only think it's a consequence of the aluminium shell and given I hadn't driven the car for a little while it suddenly became obvious. I'm sure it's nothing, but curious to know if anyone else notices something similar?

[marrow]

Hi - I test drove a A110GT for a long weekend last year and noticed a drone coming from the bulkhead when driving. It sounds like what you describe. I found it slightly annoying to be honest. Might it be the sound actuator?

[Julian Thompson]

The door is acoustically a bit of a disaster so the “upgraded” speakers playing into the standard mounting and panel is a topic that could be debated on another day. (I own an audio manufacturing business and have done some in-depth work on the A110.)

So to answer your question - The inner door has a piece of white foam that resonates pretty dreadfully at about 140hz which will very likely be what you are hearing.

As part of the work I was doing I did lots of sound tests and removed those pieces, replacing them with some solid fairly thick carbon fibre panels fastened in with rivnuts which solves that particular 140hz issue. I think undamped the C/F pieces cost 350g per side. (Damped they were more, but performed better obviously.)

There are tonnes of other issues in there that we had to fix in the quest for sound but that particular one is likely the answer to your question.

This is the piece:



And this is the fix for that:



Hope that helps.

PS - edited to add I just noticed the image is of a prototype version with few rivnuts. We ended up with evenly spaced fastenings about every 3” for optimum result.

PPS (and O/T) for those hoping this fix cleans up the horrific midbass mess in the car the answer is “to an extent” - it helps a lot (we were trying to fix the sound by adding hardly any weight) - but by stiffening this inner panel the net result is to make the outer skin move a fair bit more which then needs another fix. I can go into that if anyone is interested and we did end up with an amazing sounding car but it’s veering well off topic. Sorry!

Edited by Julian Thompson on Sunday 21st April 22:28

[biggles330d]

Thanks, that's interesting to see. So, speakers aside (I have the Focal upgrade without sub), did your addition of this different panel in the door noticeably remove the drone? I hadn't considered it might be the doors as it sounded a bit behind my ears but I assume the whole cabin is in effect a sound chamber.

[Julian Thompson]

Unfortunately I can’t answer that because everything we have done has been sound focussed. It’s only an idea for you to consider, because I was amazed how badly that foam “talks” at the sort of frequency that you’re probably looking at.

(From an audio point of view it acts like a giant passive radiator in the door - you’re listening to the whole panel not the speaker, which is one of the reasons why it sounds so awful.)

You could easily test the idea though by popping off the door cards and go for a drive with a helper to press on that foam thing as you drive, see if it stops it. If it does we did test some thick neoprene rubber versions which worked well too, and brought an element of damping to the situation without adding more. This kind of thing (we only had red rubber kicking around!):



The other thing you can do is install an app on your iPhone that plays tones. I use one called sonic, which is free. You can then play any frequency through your speakers, adjusting it with your finger on the screen - you can use it to help you detect cabin resonances. Obviously in this case in the door the speaker will directly impact the resonance so it’s a little less helpful but it can be a good technique to help you use the stereo to locate cabin rattles and vibrations caused by transmitted noise in the chassis.

[neil-g8km6]

Hi Julian, really interesting read on your method to eliminate the sound problem. Did you attach the neoprene with double sided tape? Carbon fiber, could that be replaced with easily available plywood sheet glueing a thin sheet of high density foam to the back?
Thanks for your input.

[Julian Thompson]

When we removed the oem white panels we used a knife blade carefully which leaves enough very powerful adhesive to bond the neoprene without any non oem glue:



When we fitted the carbon fibre we used petrol to remove that glue as it was very tough stuff.

You could definitely use plywood, with some damping mat on the back, though you do have a thickness limitation before you would touch the inner panel of probably about 6mm or so.

[Julian Thompson]

Thing is, if you do that, what happens is that the outer panel resonates worse than it did, so you’re still left having to fix that if you’re trying to improve the audio. (For just sound level in the car fair enough.)

We used a single layer of damping on the outer panel but then we bonded some aluminium to the crash beam and the sound damping. (See pic).

We wouldn’t recommend bonding the aluminium directly to the outer skin of the door without the sound deadening as the alloy will expand and contract - you probably do need the butyl layer between the alloy and the panel, and we recommend flexible adhesive to ensure that the panel isn’t restricted.

With this modification the sound is absolutely transformed. Weight penalty is around 10kg though, so it’s a trade off I’m afraid. We just couldn’t avoid the butyl, even after many hours of research.



We also had to cast a new speaker mount but again I’m heading off topic a bit

Edited to add: We will recover the 10kg with the AST coilovers, so my OCD doesn’t get too troubled, but they are out of stock at the moment.

Edited by Julian Thompson on Monday 22 April 15:56

Edited by Julian Thompson on Monday 22 April 16:24

[biggles330d]

Julian, are you selling aftermarket audio kits for the A110 then or is this a professional research project on your own car? I'm quite impressed with the focal audio but presumably there is demand out there for what you are doing? I doubt the original A110 engineering brief dwelled heavily on audio performance as a priority.
Just curious!

[Julian Thompson]

Good question. Part of the ethos of the brand is trying to debunk the nonsense in car audio, as there is just so much of it at every level. The idea of doing the Alpine was to prove what could be achieved on almost no equipment, just with extensive research on the installation environment.

So at present we don’t offer any installation kits as a brand, but it’s definitely something that I’ve become interested in more. I think this A110 will probably end up being used as a demo at the shows this year as we think it is seriously impressive!

The car literally only has two 4 inch speakers, run off the head unit (!) amplifier. I have just returned yesterday from the Emma European sound quality finals in Austria and having auditioned some of the cars there for reference I can honestly hand on heart say the Alpine sounds stupidly good for what it is! It wouldn’t win, but I guarantee if you get chance to hear it I will be surprised if you are not impressed!

We did spend many hours working on angles etc, with mocked up speaker pods, then moulded some resin speaker panels from a plug. These have a great mass, being resin, and provide a phenomenal base for bass. I also squirted some white dye into them to match the car, if we do choose to change the oem grilles and show them off a bit.

The drivers themselves are designed specifically for SQ and have multi piece neo magnets and carbon cones. They are bloody light too, so the standard alpine deck moves them fine. We are using no tweeters in this install and the top end is completely fine. The imaging and staging is really strong. It’s obviously not “loud” or bass heavy, but crikey it’s clean!

We did test the six inch versions of the drivers:



- but they just move too much air for the construction of the doors and you’d need to add an absolute tonne of sound deadening to them to actually calm them down and truly hear the speaker, meanwhile without having to use any eq by using a small driver the vocals and transients are hugely sweeter. Additionally we noted that we ran out of puff easier on the little amp. This is the basic problem with the standard car - they should possibly have put the speakers in the kick panels, and then they could have had stiffness more without us having to add weight into the doors and the path lengths would be a bit better as well as being able to cope with the larger driver. Aaanyway, we didn’t want to modify the car to get a result so doors and factory locations was where we were. It’s set up as per sound quality rules for competition so drivers side = sweet spot but it’s still very good both sides which is something you don’t get nowadays very often as they all use DSP and time alignment which makes the passenger side sound dreadful.

Some pics for inspiration:







So then we could make these:











Sorry the last one is blurry, I realised I didn’t have a good finished picture - I videoed the installation series in case I felt brave enough to put it on you tube!

Anyway hope that’s interesting. You could definitely take some of the ideas and fix up the standard car or focal car pretty well with a similar plan.

I’m in Cheshire so if anyone fancies having a listen to it and a brew you’re very welcome

Edited by Julian Thompson on Monday 22 April 17:14

Edited by Julian Thompson on Monday 22 April 17:25

Edited by Julian Thompson on Monday 22 April 17:27

[7en]

All of this is great Julian, thanks for sharing.

I love my audio and planned on adding some deadening to the doors, and possibly floor too for road noise. I've never modified car acoustics before, only added the usual aftermarket HU, speakers, sub etc. This gives a good idea of how to go about it. I do plan on keeping the Focal system but would like to upgrade to a Focal premium spec by adding the petite Focal amp to drive the speakers and a sub, building a wooden enclosure behind the passenger seat for an OEM fitment.

We defintiely need an Audio thread.

[Julian Thompson]

7en said:

All of this is great Julian, thanks for sharing.

I love my audio and planned on adding some deadening to the doors, and possibly floor too for road noise. I've never modified car acoustics before, only added the usual aftermarket HU, speakers, sub etc. This gives a good idea of how to go about it. I do plan on keeping the Focal system but would like to upgrade to a Focal premium spec by adding the petite Focal amp to drive the speakers and a sub, building a wooden enclosure behind the passenger seat for an OEM fitment.

We defintiely need an Audio thread.

Before you add the amp, stop wasting the energy into moving panels and stuff as per above. Sound travels through metal and plastic much faster than through the air, so as alluded to you basically are listening at the moment to the door panels, as a complete vibrating blob, and the sound off the speaker cones is coming to you later.

Also I forgot to mention for those without the focal, the factory non focal tweeters can be improved by de-throttling them. I think they did this to make them sound bad and make it essential to “upgrade” because the actual domes are silk and sound fine.

Cut off the plastic cover and let the dome actually play:



Also, the capacitor is really the wrong value as they have them starting to play by 12khz so basically they’re almost switched off. I did some experiments running them from even as low as 3.5k and they’re hugely better. (That’s a 50p capacitor to just solder in.

Happy to answer any questions if anyone needs a hand, no probs.

[Julian Thompson]

7en said:

All of this is great Julian, thanks for sharing.

I love my audio and planned on adding some deadening to the doors, and possibly floor too for road noise. I've never modified car acoustics before, only added the usual aftermarket HU, speakers, sub etc. This gives a good idea of how to go about it. I do plan on keeping the Focal system but would like to upgrade to a Focal premium spec by adding the petite Focal amp to drive the speakers and a sub, building a wooden enclosure behind the passenger seat for an OEM fitment.

We defintiely need an Audio thread.

Also forgot to say, definitely add a little soft damping for reflections behind the driver as that makes a massive difference too (yellow arrow)

Also, add some aluminium channel bonded again to the bottom of the door bar to butyl against the skin behind the speaker (red arrow)

And finally drill out the 3 rivets holding the second plastic ring to the door, and epoxy the plastic ring to the door, securing with nylocs and some decent bolts. That’s an important step as that back ring leaks bass like a sieve. (Blue arrow)

[7en]

Thanks again Julian, I'm going to remove the door cards soon to deal with rattles and planned on adding some sound deadening at the same time.

I think I'll probably go with just sound deadening at first and have a look at the inner door to compare with your photos before going further.

I do have questions regarding the deadening, whether you think it's worth adding deadening to the body coloured/inner door panels as well as the inside panel, and would deadening be suitable to cover the hole left by removing the foam cover?

[Scott-R]

Unrelated question to the audio bits and bobs, but for taking the door card off, I see one plastic cap covering a bolt near the door handle, and after that, is it just clips that need unpopped? I’ve got a rattle that I want to try track down in my drivers door

[Julian Thompson]

7en said:

Thanks again Julian, I'm going to remove the door cards soon to deal with rattles and planned on adding some sound deadening at the same time.

I think I'll probably go with just sound deadening at first and have a look at the inner door to compare with your photos before going further.

I do have questions regarding the deadening, whether you think it's worth adding deadening to the body coloured/inner door panels as well as the inside panel, and would deadening be suitable to cover the hole left by removing the foam cover?

Yes, all of it, but you’re trading weight off. The flat areas of the plastic card only make a huge difference. We used some thicker mat near the speaker and thinner mat further out. The more you dare use in every circumstance will bring better results at the expense of weight. This is as far as we have dared to go:



The use of the carbon panel with a layer of damping, used as a stressed member really really helps the inner metal door, so although you could definitely get results damping that the majority of the work is done by the carbon panel. I’m sure you could just deaden over it as that would work like the neoprene but it’s a bit of a bodge perhaps and it won’t have the same structural benefit to unifying that as a baffle.

But yes, more = better sonically until you’re unhappy with the weight.

[7en]

Scott-R said:

Unrelated question to the audio bits and bobs, but for taking the door card off, I see one plastic cap covering a bolt near the door handle, and after that, is it just clips that need unpopped? I’ve got a rattle that I want to try track down in my drivers door

I think there's another screw on the edge of the door card near the hinges, and possibly another at the other end.

The vibration/rattle I usually have disappears by simply touching the body coloured panel, the most common place being around the tricolor or the opening handle. I also think the cable for the handle can tap inside making some noise.

I plan on stripping and felt taping pretty much every contact surface.

[7en]

Julian Thompson said:

7en said:

Thanks again Julian, I'm going to remove the door cards soon to deal with rattles and planned on adding some sound deadening at the same time.

I think I'll probably go with just sound deadening at first and have a look at the inner door to compare with your photos before going further.

I do have questions regarding the deadening, whether you think it's worth adding deadening to the body coloured/inner door panels as well as the inside panel, and would deadening be suitable to cover the hole left by removing the foam cover?

Yes, all of it, but you’re trading weight off. The flat areas of the plastic card only make a huge difference. We used some thicker mat near the speaker and thinner mat further out. The more you dare use in every circumstance will bring better results at the expense of weight. This is as far as we have dared to go:



The use of the carbon panel with a layer of damping, used as a stressed member really really helps the inner metal door, so although you could definitely get results damping that the majority of the work is done by the carbon panel. I’m sure you could just deaden over it as that would work like the neoprene but it’s a bit of a bodge perhaps and it won’t have the same structural benefit to unifying that as a baffle.

But yes, more = better sonically until you’re unhappy with the weight.

Good to know Julian. It looks like you've used a combination of Roadkill Expert, Stealth and Ultimate deadening.

In the end I'm willing to sacrifice some weight as I enjoy music as much, if not more than driving and love being able to appreciate both at the same.

I wonder did you add the foam on the top left of the door card as pictured? I know this is a source of door card rattle, perhaps Alpine are now adding foam in the factory.

[Julian Thompson]

Yeah we just happen to have an account for those deadening types but they’re all the same. Just choose best value.

You’re quite right - that foam was factory.

[Cheekyweekesy]

Thanks Julian this is great stuff, what thickness of neoprene rubber did you use the replace the white foam panel?