Acoustic Boom

[Wooster]

I am cursed (?) with sensitive hearing and tinnitus.  I have applied lots of sound deadening products to my car with success. Bought it from:  https://www.silentcoat.co.uk/ 

Tyre roar is (now) almost non existent.

However, I'm now very aware of a 'booming' noise whenever the car goes over a bump in the road. Road seams etc.  (I'm guessing the 'booming' noise was previously masked by the tyre roar.)
All UK cars were all fitted with 195/55/R16 tyres and wheels. I've seen many USA cars specified with 185/65/R15.  Smaller wheels and taller side walls - which I've been told will reduce the 'booming' noises in the car as there is a larger side wall to flex and absorb the shocks from the road.  Put the numbers into here and it shows they are compatible. Tire Size Comparison

Does anyone have any experience of a 04-15 Prius with 65 section tyres?  

Or, does anyone have experience of removing any resonant boom from a Prius?

 

[kithmo]

But then you'l have to buy a new set of wheels too and some wheels are more prone to noise transfer than others.

[Ancient Nerd]

I had an early (weasel warranty) Gen 3 T-Spirit with 17 inch wheels. I bought a set of 15 inch Enzo W alloy wheels, fitted with 65 profile Goodyear winter tyres. These were noticeably quieter than the 17 inch 45 profile summer tyres. I regretted it every spring when I had to go back to the 17 inch wheels.

I am still using these winter wheels and tyres on my present Gen 4, where there is not the same advantage,  as I made sure to get the less pretty, but otherwise much better 15 inch wheels. In my opinion,  the Enzo W wheels are better quality than the original Toyota wheels - probably not surprising as they are intended specifically to survive winter use. 

My son took over my previous 2007 Gen 2, and bought an identical set of 15 inch wheels, but fitted with Fulda (German subsidiary of Goodyear) Winter tyres, because they had a lower db noise rating. These also were excellent, and quieter than the original 16 inch wheels/tyres (always Michelin Energy). The 15inch wheels fitted perfectly in place of the original 16 inch ones. 

I have a slight vested interest here as he has asked me to eBay these, as he has now replaced the Gen 2, at 185,000 miles, with an Auris HSD.

[Gerg]

I'm not sure if this helps:-

I had a Mazda 6 (2007) hatchback which was factory-fitted with 205/55 x 16 wheels/tyres,  The car suffered the booming you mention, I think.  I fitted some second hand Mazda wheels with 195/65 x 15 tyres which were a fitment in some countries but not the UK.  I can't remember the tyre brand, but not Chinese made.  I did this as a attempt to improve overall refinement.

The change did improve the booming a bit, but certainly didn't remove it, a passenger would have struggled to tell the difference.

When I test drove a (then new, next model) 2010 Mazda 6 on 18 inch wheels, I was really surprised how bad the 'boom' you mention was, every major road imperfection was like a small explosion going off in the car, although it was reasonably quiet apart from that. I don't know how anyone would tolerate that.

I have also tried the 'Mazda' experiment on a Skoda Superb (2009), i.e. 16" to 15" tyres/wheels exactly as above.  Again, a small improvement in noise, but not much. The Skoda was less prone to booming than the Mazda, and again the improvement was quite small.

Although the 15" tyres are taller than the 16" they replace, their recommended pressures are usually higher, which mitigates the potential benefits a little. 

If you wanted to see what improvement in 'booming' the taller tyres might offer, why not drive for a short while with deliberately underinflated tyres?  Say, by 4 - 5 psi?  Obviously only briefly, and not at any speed!  When I changed wheel sizes on the two cars above, the steering became less sharp, and understeer was more apparent if 'pressing-on' a bit - so like if you had under-inflated tyres!  As an aside, the steering became a little lighter and the fuel consumption improved slightly with the smaller wheels, exactly as you would expect.

I would be interested to know what sound deadening made the most difference to your Prius, and/or what panels have been worked on so far, was this fitted by yourself or at their premises?.

HTH

[Wooster]

Hello Gerg - and thanks for your thoughtful comments.  I'll try the 'lower the tyre pressure' idea. 

I notice you've a 2013 Auris.  Does this car have less 'boom' resonance than the other cars you've driven.  You said about the 2013 Mazda 6 that 'I don't know how anyone would tolerate that' - about the acoustic boom.  So, should I assume your Auris is appreciably better?  What model Auris do you have?

The sound deadening applied to my Prius was installed by me.  I've done just about everywhere!  Doors, floor, roof, tailgate, the floor of the rear hatch.  I fitted their Damping Mat and put their Noise Isolator on top. (Pics on their website.)  Most of it didn't do a great deal - but it's difficult to be accurate.  I didn't do it all at once, so any change was gradual.  However, by far the most effective area was to put the mat and isolator over the rear wheel arches.  (Having taken out the boot area lining stuff.)  It just made the tyre roar seem as it is was a lot further away.  The car is now a great motorway cruiser.  Rough surfaces are so much quieter.  But around town....  Road seams, drains, manhole covers, cats eyes - all drive me to distraction.

Regards

[PeteB]

I did notice when being driven in Prius minicabs, that if the driver had not extended the boot cover there was noticeably more road noise, even more noticeable if I was sitting in the back.

My last Prius (Gen 3 on 15" wheels) was much quieter after I switched to Dunlop Sport BlueResponse tyres, which I chose because as well as having fairly good ECO and Wet ratings they had a lower noise rating than other brands I was looking at.

While sound insulation can make a difference, much road noise is transmitted though the frame of the car and would only be helped by changes to the suspension mountings and other key parts, or indeed wheels/tyres.

Sound is quite subjective, I think the ear/brain has a sort of automatic level control so I use Digital Sound Level Meter from Maplin (£40 in 2014) to compare cars, tyres etc.  I go to a particular stretch of road on a dry day (be in trouble if they resurface it!) when I test drive different vehicles or change tyres (my Nokian winter tyres are 2 db louder, for example).  It does confirm that  my hearing doesn't tell me the whole story.

When I first had a Gen 1 Prius from 2002, I was pleased with the quietness, but after many thousands of miles I started to think it wasn't as quiet as all that, until I went in other cars and was reminded how good it actually was.  I think as my ears got used to the volume, they noticed it more.

[Gerg]

The Auris is a 2013 Icon Hybrid.  So, it's running on 195/65 x 15 tyres as standard. 

I chose this trim level to get this size tyre, basically.  The car doesn't exhibit much 'boom' noise over road irregularities - the fact that I found it generally quieter than a Prius Gen 3 (17") tested some years back was a part of the decision to buy it 16 months ago.

There isn't much evidence of effort to quieten the car (e.g. the doors are very tinny), except in the boot sides/ rear wheel arch.  Toyota have put some mass onto the wheel arch and some soft backing to the trim (picture).

It would be very useful if there was some way of determining a car's weak points from a body resonance or lack-of-sound-proofing point of view, so you could judge if quietening it down was practical or relatively inexpensive task; I don't know of anyone or anywhere.  If looking over a car in a showroom I'll usually tap panels to check for 'tinniness' and lift trim where I can to see what is underneath, to see how it should be done.  Boots of large-ish Audis are well made in this respect, for example. And large Lexus don't have very 'dead' panels when tapped, which is a surprise.

With work, I used to visit Jaguar Land Rover's R&D premises, on occasion, but was never able to find a way of chatting to the people who know about all this.  At JLR there is a whole department simply called 'Squeaks and Rattles'.  I never had an excuse to go in there!

I have been considering fitting some extra sound proofing onto the rear wheel arches for a while ; I would be interested as to how you fitted the materials together to make such a complicated shape.  Does a hot-melt glue gun come into it?

But, back to your Prius, just out of interest:-

Does the boom happen to you if you are sat in the back, being driven?

Does the fuel tank level make any difference, i.e. quieter when full?

What about if a window is slightly lowered, better when ajar?

Does having the boot full make any change to it?

 

 

[PeteB]

3 minutes ago, Gerg said:

But, back to your Prius, just out of interest:-

Does the boom happen to you if you are sat in the back, being driven?

Does the fuel tank level make any difference, i.e. quieter when full?

What about if a window is slightly lowered, better when ajar?

Does having the boot full make any change to it?

My Gen 3 Prius was a T3 (hence 15" wheels), which was the only model I would have for that reason (the only equipment it didn't have that I really wanted  was  cruise control, but my dealer fitted the switch and hey presto, instant cruise control).

I didn't ever notice a boom in that and found it very quiet in front or back, especially after the Dunlops went on.  Those on 17" wheels always seemed harsher and louder, but I can't say I was aware of a 'boom'.  I didn't notice any difference with fuel level or boot load, except when the rear seats were down, when there was a little more road noise.  Opening a window above 30 mph mainly generated more wind noise.

My current Gen 4 Prius is much quieter still (except on very rough road surfaces), and in the pre-launch blurb I saw I diagram (which I've never been able to find again since) which showed a massive (8 fold IIRC) increase in sound deadening material over the Gen 3, plus the front windows are laminated with a middle layer which was claimed to be sound reducing.  Certainly when a diesel or someone playing loud music is alongside in a traffic queue, opening a window demonstrates how effective this is.  I've never sat in the back of this one or had a full  boot.

On some cars I have experience a booming when a window is open at speed, but can't say I've noticed it in the Prius.  These days I like to reply on the pollution filter in a ventilation system.

[Wooster]

PeterB and Gerg - thanks for your thoughts.  I've tried to all of your points:

I've never noticed that the rear boot cover made any difference - but I do always have it closed.  I have Michelin Cross Climate tyres fitted.  Much better grip than the original Bridgestones and much quieter too.  Lots of reviews have commented on how quiet they are, and this was a major factor in choosing them. 

Suspension Mountings!  Oh yes, a major factor, but not something we can do anything about.  In the course of my 'searching' this subject, I came across this website.  It makes interesting reading.  UK vs USA spec cars, higher profile tyres and the importance of sub-frames.  Have a look:  http://elevatingsound.com/a-crucial-element-needed-for-a-truly-quiet-car-subframes/

Yes, road noise is subjective.  It probably varies (or, my perception of it) with my mood and how tired I am.  I've a sound meter on my smart phone - but I don't know how accurate it is, even from one day to the next.  I'm still working on this.

I've never been driven anywhere in my Prius - so can't compare.  Opening a window just increases the wind noise - so can't tell if it effects the boom.  However, just my chance, I left my tailgate open, and had to get something from the cabin.  Got in the cabin and shut the drivers door out of habit.  The volume of acoustic boom was truly staggering!  Did it several times to confirm.  Shut the tailgate and repeated closing the drivers door- it had returned to normal.  Not having any real knowledge of acoustics has left me baffled by this.  But, shutting the drivers door with the tailgate open is 10 times noisier than with the tailgate closed.

Having 'stuff' in the boot makes no difference.  But I have a DIY toolkit that probably weighs 25Kg.  If I put it in the boot, I think it reduces the boom.  But again it's very subjective. 

Oh, Gerg, we sound very much alike.  I, too, tap the door panels of cars to see how 'tinny' they are.  Your Auris pic looks very similar to my Prius.  All the sound deadening material I bought had peel off backing.  For awkward areas I used brown paper to make a template.  Put the paper template on the material, marked it out and then cut it.  Tried the cut material in position, just to check.  Inevitably I'd have to make adjustments, and make a few cuts or trim a bit.  When I was happy, I removed the peel off backing and put it in place.  Only word of warning, it is incredibly sticky, where ever it touches, it sticks.  Permanently.  You can't move it around at all. 

The Auris Hybrid - you have an Icon, but I thought the 'Active' model had the taller tyres as standard.  Am I mistaken or have they changed the spec over the years?  https://www.toyota.co.uk/new-cars/auris/index/specifications

Interesting the Gen 4 Prius has much more sound deadening material.  Toyota wouldn't do this if there wasn't a need - so we can't be alone.  I have a copy (attached) of the "2010 Prius Media Preview".  Page 26 says it has "Reduced Noise, Vibration and harshness over the previous model".  So, reducing the cabin noise is an endless quest!  It's a very technical subject, and I can imagine Acoustic Engineers sitting at huge PC screens, altering details on their 3D model of a new car - using the computer to see what happens when some subtle change is made.  All very scientific.  What I've done - buying some material and putting it on panels - is incredibly crude.  Very hit-and-miss.  If anyone is going to fit sound deadening material, I'd be very cautious.  What I've done - I'm sure - is made my Prius so quiet in one area (tyre noise) that the other noise (boom) is now staggeringly obvious.  Maybe Toyota get a balance in the noises you can hear. 

Think I've addressed all your points.  If anything need clarification, or I've missed something - just tell me!

 

 

2010 Prius Technical.pdf

[Gerg]

Ah, yes!  I have used the stick on sound deadener; I put some in the Auris front doors a few days ago.  I was thinking that you may have decided to go for a further layer of foam (for decoupling) and an airtight layer of mass (mass-loaded vinyl?) to finish it off.  I've only ever tried to use all three layers in a few locations, and they were always horizontal, and the results didn't seem to justify the extra work.  If your road noise is greatly subdued, then that is likely pointless to go to those lengths.  I struggled to find somewhere to buy the top layer (MLV), and then when I did, I had changed the car.  (I went to Siderise near Ipswich in the end for the MLV - but it does have lingering plastic odour).

I discovered your link a few years ago, and his point about sub-frames is very relevant.  My old Mazda 6 had a front sub-frame, but then they mounted it solidly to the body!  A missed opportunity, but that arrangement probably improved steering feel fractionally, and saved them some money.  In the Mazda, in stages, I put dampener on the doors, floor, boot, wheel arches, bonnet and roof.  And fitted some rubber under the fuel tank securing straps.  All of these made a difference, and Mazda had made the car so that all of these jobs were quick to do with minimal bleeding required.  I didn't think the car was *that* quiet afterwards, but, exactly as you say, other noises start to become apparent when the 'sound floor' goes down.  In the Auris, I'm always aware of the grinding noise the brakes make, but as PeteB says above, with time you start to hear 'quiet' as 'just normal'.  The Auris is quite good for noise and at steady speeds is not  much different to a Nissan Leaf, which has the benefit of all that Battery mass hanging off it, so just hearing the brakes is probably an achievement.

You seem to notice the 'boom' quite badly (obviously), those questions were, using my old, misty, school-physics-taught-principles to consider what might be at the root of this.

In a clear case of 'over-thinking', I was pondering:-  constructive interference (seating position), the booming (amplification) from the empty fuel tank, giving air pressure shocks a additional release path (window ajar), and just simply filling the boot cavity to stop resonance, and if extra mass on the boot floor reduced the amount it might flex.

I wonder if so many of these problems could be cheaply removed at the design stage, if manufacturers thought that it would sell more cars.  I sometimes marvel at what gets through to production, when if only they'd asked me first, I could have pointed out some of their mistakes!

 

[PeteB]

Cars have certainly got massively quieter since the cars I rode in during the 1960s and 70s.  Taller gearing, quieter engines, better aerodynamics, better sound insulation and tyres have all helped.

A 957 cc Mk1 Fiesta I bought in 1980 (my first brand new car) was doing about 4,500 rpm in 4th (top) gear at indicated 70 mph (a true 63 mph*) and while it was fairly quiet (for the day) up to around 45 mph, it made one hell of a din at higher speeds.

However, my previous car, a 903 cc 1977 Fiat 127, was pulling nearly 6,000 rpm at the same speed (even bigger speedo error - about 12%!).  I often drove it between Sheffield and my home in Surrey (200 miles each way), and on the motorway I would start off cruising at 55 mph which was as much as my ears could stand.  But as the journey progressed a blend of wanting to arrive the same week and my ears adjusting to the noise level my speed gradually crept up to 70.  When I got out of the car at the end I felt a bit deaf like I'd just come out of a disco!

In 1984 I traded to a 1200 cc Vauxhall Nova, which Drive Magazine (the AA's magazine they sent to members in those days) described as being "uncannily quiet", was a revelation compared to just about anything else I travelled in at the time (even some 2 or 3 litre cars seems much louder).  I had ordered a 5 speed gearbox as an option which IIRC was and extra £150 or so (on a car costing £5,000 before discount - it was a GL).  It pulled just 2,500 rpm at 70 mph in 5th, and even doing that speed in 3rd used less rpm than the Fiat did in top.

 

[* before anyone asks, the local traffic police had a couple of posts ¼ mile apart on an M25 link road which they used to check their own speedos, so I typed up a ready reckoner and with a stop watch I was able to check.]

[PeteB]

36 minutes ago, Gerg said:

...I wonder if so many of these problems could be cheaply removed at the design stage, if manufacturers thought that it would sell more cars.  I sometimes marvel at what gets through to production, when if only they'd asked me first, I could have pointed out some of their mistakes!

I think I'm right in saying that some manufactures have a system that sends 'cancelling' sound via the car's Speakers that reduces the effect of some noises in the car.

On the other hand, a couple of Lexis Hybrids in F-Sport trim actually make artificial engine noises though the hi-fi to make it sound as if the car is changing gear when accelerating hard!  

[Wooster]

Don't know if anyone is still following this post, but....

I've given up with the noise in my current Prius and bought a 2010 model.  A TSpirit with a 'moon-roof' so it has 65 section tyres.

It was good to 'chat' to you all.   Andrew

[kithmo]

Moon-roof on a UK spec Prius ?

Do you mean solar roof ?

Moon-roof is a US term for what we call a sunroof, not available over here on the UK Prius.

[Wooster]

You're right.  Solar Roof is the UK term.  (But it's the same as the US moon roof isn't it?)

Point I was making is that although it's a TSpirit, it has 65 section tyres. 

Something to do with keeping the weight of the car down , once the solar roof was installed.

Regards to all

[FROSTYBALLS]

Moon roof is the US name for a glass panelled roof, which may or may not include a panel that can be raised for additional ventilation.

The nearest UK equivalent is now the panoramic or glass roof - again which may or may not include a panel that can be raised for additional ventilation.

A solar roof is a glass panelled roof that includes built in solar panels to provide an element of Battery charging.

The term sunroof has largely fallen out of use.

 

[PeteB]

4 hours ago, Wooster said:

Point I was making is that although it's a TSpirit, it has 65 section tyres.

For some reason around 2012 Toyota started selling the Solar roof model with 17" wheels and a gunge kit, despite the web site and all the blurb saying they still has 15" wheels.

One person on the Yahoo Prius-UK group bought one and ordered the roof specifically to get the 15" wheels, and despite getting soem compensation out of Toyota was never happy, and is currently selling the car after just 3 years (kept his Gen 2 for 10 years).

Another member of this group was taken by surprise but grew to like the 17" wheels.

Personally, I can't help wondering whether they are in breach of the type approval for the model, since that was the reason given by Toyota officials at the pre-launch events that they had to ditch the spare and fit lighter wheels.

[Heidfirst]

7 hours ago, PeteB said:

For some reason around 2012 Toyota started selling the Solar roof model with 17" wheels and a gunge kit, despite the web site and all the blurb saying they still has 15" wheels.

It's common practice for Toyota Gb to supply a gunge kit rather than a spare when a panoramic roof is fitted - the glass roof is heavier than the normal steel so the gunge kit rather than spare is to counterbalance the weight (& hence also keep the emissions down).

[PeteB]

3 hours ago, Heidfirst said:

It's common practice for Toyota Gb to supply a gunge kit ...

...also keep the emissions down).

and no doubt the cost!

It was mainly the switch to the heavier 17" wheels that surprised me (and the guy from the Yahoo group).  The extra drag has a negative impact on CO2 and mpg too, as well as a host of other downsides that some will overlook because they prefer to look of the 17" wheels.

[Heidfirst]

6 hours ago, PeteB said:

and no doubt the cost! 

If they can keep it down 1 group for tax it's worth it to them.

It was mainly the switch to the heavier 17" wheels that surprised me (and the guy from the Yahoo group).  The extra drag has a negative impact on CO2 and mpg too, as well as a host of other downsides that some will overlook because they prefer to look of the 17" wheels. 

That's the marketing dept. for you - the UK has a perverse liking for large alloys even if they are more prone to damage, give a harder ride & worse economy ... 

 

[Gerg]

Obviously, you must report back on the Gen. 3's quietness etc.! 

It would be interesting to see if, since you'd modified it, the Gen. 2 ended up as a quieter car than your new one,  'boom' apart, of course.

Back to an earlier point, I sat in a CT200 a few days ago, the doors sounded very cheap when tapped, but sounded expensive when closed.  I wonder how they do that?

 

[Wooster]

Are you still following this topic?

The Gen 3 with 65 section tyres is quieter than my Gen 2 Prius.  However, I had the (3 brands of ) tyres replaced with Michelin Cross Climate's which have a good reputation for a quiet ride.  The whole car is more refined, even if I have a few dash board rattles that I'll need to track down and cure!  A huge change for me (also) is going from a basic T3 to a TSpirit.  Have to get used to keyless entry,  the car parking itself, rain sensitive windscreen wipers etc, etc. 

I'll probably add some sound deadening material in the Spring - when it gets warmer. You can always make a vehicle quieter....   !

Seasons Greetings to anyone reading this.

[Gerg]

You may have already seen these descriptions of the changes made from the Gen. 2 to Gen. 3 etc. (And Gen. 4).

This link is to an article on the same topic written by a member of the French HybridLife website.

http://www.microsofttranslator.com/bv.aspx?from=&to=en&a=http%3A%2F%2Fhybridlife.org%2Flibrary-articles%2Fles-secrets-de-technologie-du-systeme-hybride-de-toyota-prius-3-une-lecon-damelioration-continue.13%2F

If you rummage around that site, you'll find topics where members go to extreme lengths to quieten their cars.  Top marks for effort!

You may have to register (it's free) after your 'guest' reading-rights have been used up.

 

 

Prius Changes over time.doc

136221_2016_Prius_Press_Release.pdf

[Wooster]

Hi again.  I've never heard of this site, so I looked forward to 'rummaging around. 

Regretfully, when clicking on your link is says:

"Cannot translate provided url."

Thanks for the attachments.

 

[Gerg]

Hi,

I can't get the link to work either.

I've just copied another link from the site:-

http://hybridlife.org/threads/schemas-de-fonctionnement-du-systeme-hybride-de-toyota-lexus-dans-les-differentes-phases.1284/

Or try this:_

http://hybridlife.org/threads/toyota-prius-3-joints-de-seuil-de-portes.2559/

Sadly, I can't find the original article, but articles by 'parkerbol' and 'Hortevin' look interesting, especially under the sub-heading 'acoustique' of course.

HTH.