New soundproofing project

For all technical questions. VIEWABLE without login, you need to register (free) to be able to post a question.
Post Reply
Sunfly
UKPOC Full Member
Posts: 483
Joined: Tue Sep 29, 2009 9:19 pm
Drives: 24V Probe 1997 GTS
Location: Gloucester and Minchinhampton
Contact:

New soundproofing project

Post by Sunfly » Mon Aug 06, 2018 9:30 pm

Just started the long awaited soundproofing project on my 24v.

Took the rear interior, (back to the front of the rear seats) out, but not before I took it for a spin down a local stretch of motorway with a decibel meter. Average 71db with 75db max. I also checked a Jag XE on the same stretch at average 67db with 75max to give me a benchmark, both at 80mph (It was sweltering in the Probe with the windows closed and the fan off!)

I was a bit surprized at how close the two readings were but the Jag is quiet and the Probe is not, so I guess perception is more important than the db reading. Anyway, I have a figure to improve on and another to aim at.

I'll take some pics and let you know how I get on. I've got 2mm sound deadening to kill the drumming, 10mm acoustic for the floor and 6mm acoustic for the vertical surfaces. Most of the noise is coming from the tyres as the pitch changes dramatically with different road surfaces.

Bob

david_toft
UKPOC Full Member
Posts: 32
Joined: Sat Nov 12, 2016 2:47 pm
Drives: 1995 24v

Re: New soundproofing project

Post by david_toft » Mon Aug 06, 2018 10:36 pm

The noise readings are on a logarithmic scale so 4db is a large difference. 2 noise sources at 67db will give a noise level of 70db, so the Probe is more than twice as loud as the Jag

Sunfly
UKPOC Full Member
Posts: 483
Joined: Tue Sep 29, 2009 9:19 pm
Drives: 24V Probe 1997 GTS
Location: Gloucester and Minchinhampton
Contact:

Re: New soundproofing project

Post by Sunfly » Mon Aug 06, 2018 11:42 pm

As they say... you learn something new every day and I didn't know that! I assumed it was linear. Thank you very much for that information David and can I assume from that that the noise doubles every three db?

Just out of interest, when finished with the run I turned the radio volume up until I got to 75db. It was very loud indeed, bordering on uncomfortable. Just shows what you tolerate as "normal".

Armed with that info, I'm very much looking forward to seeing how much I can reduce the noise level by. Tapping my way about the empty boot space I reckon the floor pan would hold its own in a Jamaican steel band. Ford could have done a better job of soundproofing given the buying price!

david_toft
UKPOC Full Member
Posts: 32
Joined: Sat Nov 12, 2016 2:47 pm
Drives: 1995 24v

Re: New soundproofing project

Post by david_toft » Tue Aug 07, 2018 11:50 am

Yes it doubles for every 3dB.
Was your meter reading dB or dB(A) as this can further confuse things. The human ear doesn't hear lower frequencies as loud as higher ones so the (A) rating biases the readings to take this into account
You can make big improvements to a noise source but if was not the major one in the first place you won't notice any difference
This article is interesting relating to tyre noise
http://elevatingsound.com/your-guide-to ... oad-noise/
particularly the comment at the bottom

Sunfly
UKPOC Full Member
Posts: 483
Joined: Tue Sep 29, 2009 9:19 pm
Drives: 24V Probe 1997 GTS
Location: Gloucester and Minchinhampton
Contact:

Re: New soundproofing project

Post by Sunfly » Wed Aug 08, 2018 12:08 am

Bugg...d if I know David, and I was only using a phone app anyway, but it was a bit of fun to do. I guess the point is, though the app might be wildly inaccurate, that doesn't really matter as it is only a benchmark to compare the Jag and any improvement against. The guy that sold me the insulation told me not to pay too much attention to a db meter and to trust your ear instead. You remember I said the Probe sounded much noisier for very few extra db's then you explained why! I guess that's what he meant. I'll be happy now if I get a good result by ear. From your article, it didn't sound as though you have much choice except for weight and speed, but I'm pleased to have that info for next time!

User avatar
Scooby
UKPOC Full Member
Posts: 8204
Joined: Sun Aug 07, 2005 12:28 pm
Drives: 2x24v ('95/'97)
Location: Kingdom of Saudi Arabia (for now)

Re: New soundproofing project

Post by Scooby » Thu Aug 09, 2018 9:50 am

I soundproofed Japha during the initial rebuild after the first respray.
No idea if it made any difference because I changed the exhaust at the same time and the new one is chuffing loud!
Being happy doesn't mean everything's perfect.
It means that you have decided to look beyond the imperfections.

Image
Mem No.137. per ardua ad astra

Sunfly
UKPOC Full Member
Posts: 483
Joined: Tue Sep 29, 2009 9:19 pm
Drives: 24V Probe 1997 GTS
Location: Gloucester and Minchinhampton
Contact:

Re: New soundproofing project

Post by Sunfly » Fri Aug 10, 2018 12:31 am

Been working hard on the soundproofing and a couple of interesting issues have turned up. Firstly there is quite a bit of factory fitted sound deadening mat, however its very hard now to the point of being brittle. So I'm wondering if its effect has been diminished by age and hardening. As I've got sufficient material, I'm going over every surface including the original areas to try and reduce the drumming.

Secondly there are void spaces below the B pillar area, i.e. just behind the front seats and behind the seat belt anchors. the space is closed by a rubber molding but I think this space may be a bit of an echo chamber and its unprotected by Ford soundproofing, so I want to get some mat in there. Near side is empty, but the drivers side has a module in there with a lot of wires going to it, so a serious bit of the electronics. Can anyone tell me what it is please.

Finally, I'm going to have trouble acoustic insulating in the area either side of the rear seat as its not a single surface and there are a lot of wires etc. I was thinking of covering everything in a poly membrane, similar to the door arrangement and sticking the acoustic insulation to that but I'm wondering is by so doing I might lock some of the electronics the wrong side of a vapour barrier. What do you think?

I believe the vapour barrier in a door is there to keep leakage past the window from damaging the door card, carpets etc, but I wouldn't have the same risk of water or moisture in the areas I'm considering, Plus it will be impossible to completely seal the double skin areas as you have the air spill vent on the right hand boot near the rear washer bottle. (I think I may have just answered my own question but I'd be interested to hear any comments!

jrh
UKPOC Full Member
Posts: 451
Joined: Wed May 13, 2009 9:37 pm
Drives: 94probe

Re: New soundproofing project

Post by jrh » Fri Aug 10, 2018 7:23 am

I know it has the boot carpet plonked on top of it but that nice piece of hardboard over the spare wheel must pick up a lot of vibration too. It is not insulated on the underside so is a virtual drum skin.

Sunfly
UKPOC Full Member
Posts: 483
Joined: Tue Sep 29, 2009 9:19 pm
Drives: 24V Probe 1997 GTS
Location: Gloucester and Minchinhampton
Contact:

Re: New soundproofing project

Post by Sunfly » Fri Aug 10, 2018 7:59 am

jrh wrote:
Fri Aug 10, 2018 7:23 am
I know it has the boot carpet plonked on top of it but that nice piece of hardboard over the spare wheel must pick up a lot of vibration too. It is not insulated on the underside so is a virtual drum skin.
Quite so John, so I have covered that with heavy 10mm acoustic foam designed for floor use so that ought to fix that. I also wonder if firm tightening of the spare wheel may help to dampen vibrations in the wheel well. For a belt and braces job I'm going to put foam on the back of all the liners too.

Its a bit of a black art is sound waves and vibration, so I'm never sure if I'm doing wrong or right. I remember some years ago from my marine years we had a lot of trouble with a generator vibrating on load and doing damage to couplings and mounts. We got a vibration consultant in who took a load of measurements of the plinth it was sat on. Two days and a lot of calculations later, he said weld this design of brace in this position on the plinth which the shipyard did and the problem went away. The engine and the plinth were so in tune with one another that they set up their own harmonic frequency and it was bad. As soon as the frequency of the plinth was altered, one cancelled the other and all was nice and smooth running. Same sort of principle with sound I believe.

jrh
UKPOC Full Member
Posts: 451
Joined: Wed May 13, 2009 9:37 pm
Drives: 94probe

Re: New soundproofing project

Post by jrh » Fri Aug 10, 2018 9:06 am

Yes, there wasn't much that was 'not moving' on a ship, at some speed or other. Best not to look at the stretch on the cylinder head studs as they
fired on every revolution and open switchboards shaking like a leaf in the breeze !
Just amazing it all hung together for so long. Those were the days
Looking forward to meeting up at Ryhope.

Post Reply

Who is online

Users browsing this forum: No registered users and 10 guests