Bottom ports for the first time

[taz13]

I think lots that are on this forum have a few sets of speakers and recievers pre amps and pre pros and power amps. I know I have a few piles and I am in lust with Jons Mt8a and need to learn a few new construction techniques.
One is I like pine and fir so I started looking at them. Next step was to pick up fir panels laminated from 3/4 stock and laminate 1/4 hdf to the pine and cut all long edges to 45' miters. Now I have mitered panels to work with and I substituit them for ply or mdf and glue into boxs. Then use the method of layer that Thomas describes on a thread to put bracing in from the bottom to top. Glue top and bottom plugs in and fire up router cut all openings. Install 4" bottom firing port, stuff and install the xovers and drivers, hook up system, listen adjust and enjoy and then say ok whats next.
Okay, I decided lto do a listening test. Digital panny sa xr25 with a digital satillite input driving in 2 channel Vifa 2 way TM vs Sony MD into a Velleman hybrid preamp driving a Behringer europower 1500 with Vifa 2.5 way TMMW rear ported speakers. Really apples and oranges but fun.
Results, panny and 2 ways are a clear winner in price and have a more noticable bottom end. The 2.5 ways and big power are great sounding and can be enjoyed for hours and hours. No sub needed on either system. More experimenting with systems are always ongoing. :T

[JonMarsh]

Looks like you're having fun there! Which Vifa woofers are you working with?

Interestingly, I've been messing around with laminated pine panels with 1/4" HDF on them, too; I'm doing an experiment for an "Arvo Part", trying that in comparison; and if it works well, may use it for the "Saint-Saen" line array.

The other likely material for the line array is just layered BB ply, with HDF on front, maybe back, too. I'm working on ideas for making them look nice; came up with some possiblities while at ThomasW's this month. Just have to visit my local Rockler store and see what I can come up with later this month.

~Jon

[Hank]

Here's something I've been thinking about for quite a while:
Inside layer 1/2" or 3/4" Solid Core Plywood
Constrained layer of the Parts Express Vinyl Damping sheet
Outside layer of 3/4" MDF

What do you think, Poohbah's?

[taz13]

The 2 ways are using P21W-10-08 mid woof with D25AG3506 tweeters and are currently my favorite combination for just always having on. Now with the bottom port they are very room friendly and easy to set up.
The 2.5 ways use the P21W-20-08 mid woofs with a rear firing D75MX41 dome mid and the D25AG0506 tweeter, I love the sound of this set up but, these speakers are a pain to get set up. With a rear port and reflecting mid on the back, placement can be a pain to get right. If you like a symetrical set up, you won't like these speakers because they don't work like that. It is also half the fun, tweak the location and start listening, make notes and do it again until you are happy. And then do the whole set ups and combinations over just because its fun.
When the above doesn't work then go make sawdust and try something new.
Can we say M8ta with a round back and top and bottom plates. Covered in 1/4" x 7/8" thick solid wood bead and cove purpleheart and walnut. Just waiting to see final xover and driver combos, but boxes are already in the design and layout stage.

[JonMarsh]

Here's something I've been thinking about for quite a while:
Inside layer 1/2" or 3/4" Solid Core Plywood
Constrained layer of the Parts Express Vinyl Damping sheet
Outside layer of 3/4" MDF

What do you think, Poohbah's?

I've done some constrained layer stuff in the past, haven't found it to be worth the hassle, but maybe I just wasn't doing it right. There was an article in AudioXpress or SB about this, came to similar results.

Are you thinking outer layer of 3/4" MDF for the finishing properties? And by solid core ply, do you mean appleply (really maple), or BB ply?

My own experience increaseingly says go for maximum stiffness... which has
me leaning towards BB play with 1/4" HDF.

But you know, like Chairman Mao said, let a thousand schools of thought bloom in the spring.... or something like that.

Sounds like you've got a good candidate for an R&D project, Hank- just how to go about it best, and get some "hard" data? Build an "ultra" stiff encolsure, with one removable wall, and try different constructions on that wall, with an accelerometer driven by pinknoise at high power, to measure flex and Q? Probably a water fall plot would be good, but even just a spectrum analysis with continuous pinknoise would be helpful.

Or do like I do; give it the knuckle rapp test, try flexing a long piece, scratch your head, and make a decision.

~Jon

[taz13]

Or do like I do; give it the knuckle rapp test, try flexing a long piece, scratch your head, and make a decision.

You just have to love engineering from the school of TLAR or in this case TSAR. :lol: pretty much describes most of my translations from paper to product.

Hank
I don't know if you are familar with strip boat building as they practiced in the 20s, but that is the principal that I am experimenting with right now for making a formed laminated hardwood speaker box. And then I will worry about damping from the inside. See expoxyworks winter 2004. I have built cedar strip canoes and have the tools so I just have to try this on the M8ta with faceted front.

[JonMarsh]

I bet that could work pretty well- keep us informed, and if you can, pictures of course!


Keith Kider did a construction technique which he called "translam"; it sounds like yours could be similar - his page is here....


Keith Kider Translam


Unfortunately, for me to do this, I'd have to be "crazy", not just mentally disturbed, as I don't have access to a local CNC setup, and would have to do it with a router and pattern bit in BB ply or appleply.

Now, if I wasn't doing so many dipole projects, I'd probably have to try this...

[taz13]

Trans lam is not really the same but works great for making complex shapes and forms, think bowl and vase shaped speaker boxes with either pearl or stone finish.tedious to cut sand and finish but results can be spectacular
Strip building is a boat building method that i know and understand and that I think could easily be adapted for box making. Bonus is when you make the cabinets, unlike when I make canoes you don't have to take out the station moulds because they are the cabinet bracing. And no veneering as you are using real wood on the outside layer, with epoxy to glue and seal. Inner layers are 1/8 " ply or veneer cut in strips and glued and stapled on the bias Staples are removed and sealed before next layer goes on etc.
With a high gloss polished finish on say walnut with maple top and bottom plates. :T

[Hank]

But you know, like Chairman Mao said, let a thousand schools of thought bloom in the spring.... or something like that.

Jon obviously was smoking something other than Marlboro's in the 70's.

Or do like I do; give it the knuckle rapp test, try flexing a long piece, scratch your head, and make a decision.

NOW we're on the same wavelength.

I don't know if you are familar with strip boat building as they practiced in the 20s,

Hey, I'm not THAT old!

Methinks we're going off the deep end here. If Jon and I had SO's, we'd not be on this forum on Sunday afternoon/evening. Take pity on us.

Well, my son Taylor played in Texas Stadium Friday in the latest in his series of football playoff games. Good game, and we won 31 - 28. Bad news is that on the way back to Austin, a deer bolted across the highway 'bout midnight and took out the left headlight, damaged the hood, left fender, driver's door and passenger's door. I had declined the rental car insurance, so it's my responsibility, and my insurance deductable is large, so I'm screwed. My planned trip to CES in January is now cancelled. Oh well, no one was hurt, and it was the rental car instead of my beloved Lucille. :T

[JonMarsh]

Hey Hank,

Never got near any of those nasty Marlboro's...

Actually, I was just taking a break Sunday afternoon from splitting my system up into an HT system (relocated) and two channel audio only. Finished it up and was watching a movie Sunday evening... gotta make room for all these new speakers to test and evaluate, and the Saint Saen and Arvo don't really fit well into an HT form factor.



Sorry to hear about your deer incident, and the cancelled CES trip! Better a rental, though, than your own car!