Lotus Elan

Loudspeaker damage when the boot is closed

PostPost by: JonB » Sat Mar 31, 2018 1:32 pm

Not sure this is the correct forum to post this, but there goes.

When the boot on my Plus 2 is closed, it creates a pressure wave that makes the parcel shelf lift. Since the rear speakers are mounted in the shelf, the cones also move, but by what looks like an alarming amount. This morning I discovered that the cone surrounds have failed and the speakers are toast. A new pair is on order but I am worried the same may happen to them - although I have to admit the old speakers are at least 25 years old and the foam surrounds are crumbling anyway. So, how best to proceed? I would be thinking in terms of isolating the speakers from the boot space to protect the cones. I do not think I have the space beneath the shelf to build enclosures. I may be able to relieve the pressure by fitting a dummy grille that equalises the pressure between the boot and cabin, but that runs the risk of increasing noise.
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PostPost by: elanfan1 » Sat Mar 31, 2018 4:56 pm

Just close the boot gently?
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PostPost by: JonB » Sat Mar 31, 2018 5:03 pm

I got into the habit of dropping it. But even if I do close it gently, I may still drop it occasionally.
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PostPost by: RichC » Sat Mar 31, 2018 10:13 pm

i think I've slipped into a parallel universe :shock:
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PostPost by: The Veg » Sun Apr 01, 2018 3:18 am

The false-grille idea is intriguing. Maybe to reduce the noise from that, line the boot with closed-cell foam?
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PostPost by: StressCraxx » Sun Apr 01, 2018 3:51 am

The foam around the speakers breaks down over time. Most of the better new ones use a plastic cone with a foam surround. The higher the wattage capacity the better.
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PostPost by: JonB » Sun Apr 01, 2018 9:37 am

@Veg, the Plus 2 boot is already lined with the horsehair matting material. Mine isn't - another thing to fix, although I do have carpets.

@StressCraxx, I know.. can see it crumbling. Maybe this is due to me actually using the speakers. They weren't connected when I got the car and there was no head unit either. I wonder how long they had been unused for? Anyway, they sounded really good with my Bluetooth head unit for a while, but I think the bass has ripped the foam apart. I've ordered a set of JBL coaxial speakers with polypropylene cones and foam surrounds. Maybe they will be able to withstand the pressure fluctuation of closing the boot.

Incidentally, you can repair rotted out foam surrounds. I've done it on a pair of B&O bookshelf speakers. You pull all the old foam off, clean up the adhesive and glue new foam rings on. They are available, and I may repair the old speakers for use in the front of the car.

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PostPost by: pauljones » Sun Apr 01, 2018 10:13 am

Big fan of JBLs great choice. Reminds me of my youff.
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PostPost by: Spyder fan » Sun Apr 01, 2018 4:06 pm

Junk the radio and listen to the music under the bonnet? :mrgreen:
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PostPost by: Spyder fan » Sun Apr 01, 2018 4:21 pm

Seriously, I have radio/mp3/cd in both my cars, they may as well be disconnected. I never use them as I?m always concentrating on driving, even when doing a long haul to Castle Combe or Up North or overseas. One of the true joys of a classic even a heavily modified classic like my +2 or S4 is the sheer unadulterated noise/vibration/seat of the pants experience of being fully in control/responsible for the machine that conveys you.

If you must listen to the radio/cd/mp3 then fit speakers in the door cards and into the C pillars, remove the parcel shelf speakers or isolate them with a false platform beneath the parcel shelf.

I have door card/ under dash and C pillar speakers in my +2, they work quite well. Nowhere near as good as my VW Golf GTD speakers, but that?s a car that needs some redeeming features. It?s boring to drive and could probably drive itself with a software upgrade.
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PostPost by: JonB » Sun Apr 01, 2018 6:17 pm

Spyder fan wrote:Junk the radio and listen to the music under the bonnet? :mrgreen:


Oh, no. Not that old chestnut again. :roll:
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PostPost by: pauljones » Sun Apr 01, 2018 7:32 pm

Jon,

Alan wouldnt hear a radio over his induction roar, if he got bored with that then he'll have his exhaust to amuse himself.
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PostPost by: denicholls2 » Mon Apr 02, 2018 1:52 pm

It's not too likely that the low-frequency (in your case, 1hz) compression damaged your speakers. A better bet is higher-frequency (~32 hz bass) in combination with disintegration from 25 years of ozone. Aside from being more careful in closing the boot, I would not fret much about the compression, which is basically the volume of the boot lid for the last 1/8"-ish of closure on the gasket where the air stops having another place to go quickly.

The amplifier puts the cones through a whole lot more stress than that when you turn up your favorite tunes.

Isolating the cones would minimize to eliminate this effect, but likely at the expense of low-end response. However, if the system uses a single driver for all frequencies (not too likely), the two should be isolated from each other to avoid sounding like mud. Low frequencies sound like mud anyway so less of a concern. :wink:
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PostPost by: JonB » Sat Apr 14, 2018 11:18 am

The new JBLs are in and they do not sound as good as the old speakers. I did look at them prior to fitting and thought the movement of the cones was a bit stiff - over damped perhaps - and this looks to be inhibiting the bass response a little. I've decided to go ahead with the plan to refurbish the old speakers with new foam surrounds and spent this morning cleaning the cones and chassis. I'm hoping to fit them in the front floor wells (not the door cards, as they will only get bashed by feet sliding in and out of the car).
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PostPost by: john.p.clegg » Sat Apr 14, 2018 12:52 pm

PVA brushed on the cones makes them damp proof...

John :wink:
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