I'm with Phillip. My loudest vacuum is definitely my 10 amp Royal Upright. My quietest is my Electrolux Model G without the PN. With the PN, it gets pretty loud too.
Believe it or not, one of the quietest vintage vacuums I have ever come across was a Sanyo bagless canister vac made in the early 1970's. My father was the advertising manager for Sanyo Canada in the 1970's and one day he brought one of these home. In those days, Sanyo was selling a lot of audio cassette players and recorders, so they used the term for their bagless canister vac as well. The vac was really,really quiet. It was first sold in blue and grey, then there was a red version with a transparent dust container. Sears sold a brown and beige Kenmore version called the "Let's Clean"!!!!!
Hated emptying the dirt out of that blue vac! The cassette had a fine mesh filter that needed to be wiped with a paper towel to get off all the hairs, and there was another cloth bag "downwind" that had to be shaken out producing a mini duststorm in our garage!
I guess our 1970 version was a forerunner to the one you see in the link below
one has to be the pink Hoover (587??) that was my Grandmother's and the loudest without a doubt, was the Hoover Dimension 1000.
However, with all respect to both machine's as they've gone to the trash (talk to my ex...) or wherever witches suffering mid-life crisis' send old vacuum's to, the Dimension was noisy mainly due to the PN. That Quadrafelx could wake the dead! Yikes...
Now that I think about it, I don't think my Royal 10 amp is the loudest vacuum I own. I'm pretty sure it's my circa 1968 Dial-a-Matic. When I refurbished it, I tore it completely apart and removed all the rotting foam rubber. That included that foam tucked inside the motor housing. When I did that, it turned an already loud vacuum into a SCREAMER!
My quietest vacuums would be my Filter Queen 350, Lux XXX and G, Royalaire 260, and Electro-Hygiene 966. Loudest would be my Royal 1028Z and Sanitaire S663.
Jeff
My loudest vac is my Fairfax. Loudest monster I have ever had. It is mostly used at 8am on the morning after the brats upstairs were jumping off furniture or stomping or what ever it is they do that makes my light fixtures and pictures on the wall rattle until midnight. I'm sorry, but I truly detest those two.
My quietest vacs are my 3 amp Royals. Nice to run, not that great at deep cleaning my carpets. I use the Kirby G6 or the Fairfax for deep cleaning.
How did you modify your 608's nozzle to include the deodorizing chamber, anyway? I know none of the Royal commercial vacuums ever did originally... unless you were to use the one mounted in the belt opening similar to the Electro-Hygiene model 285.
My loudest would probably be a toss-up between the Shop Vac, Hoover Elite, and Eureka Boss Lite . The quietest would be my Eureka Mighty Mite, then the Kenmore/Sanyo Let's Clean and Penncrest Constellation. Kenmore Progressive and Whispertones would be in between with the Eureka 1934B.