New 604 cabs

[GM]

You're welcome!

It's a matter of comparing 'apple to apples', so without knowing its damping properties, no way to compare how much thickness one = the thickness required for the other.

GM

[GM]

Agreed, though the 'big box' stores around me that sell whole house insulation also sell the preferred 1" acoustic fiberglass. I've also been able to get free s-c-r-a-p-s from heating/AC contractors. Indeed, I lucked up last year and scored a bundle of pre-cut sheets that took two king size bed sheets to haul it away just for the asking.

Note that any non-parallel sides can't generate any eigenmodes (standing waves) of note, so normally don't need any damping as long as the cab is sufficiently rigid/massive.

WRT 'perpendicular to the vent', just to clarify, this is to its internal opening as opposed to its length since lining the wall opposite a port (parallel) is used as a tuning tweak and as a next to last resort damping perpendicular walls, with damping the vent's exit the final one.

Note that this assumes a minimum distance of the vent's internal opening being greater than its radius x 0.732 (0.8488 if a flanged tube is used) away from any parallel or perpendicular surfaces otherwise the vent's output will be modified by boundary loading and any insulation will tend to severely restrict its output, defeating the purpose of reflex loading unless it's to damp a too high Qts driver (AKA an aperiodic alignment).

Some believe a spherical cab (ball) is the perfect solution, but what it does is create a ~infinite number of eigenmodes all centered around a single frequency (deep null/peak) equal to its diameter/2 which is worse than the dreaded cube WRT the amount of damping required. Of course if the ball/cube's size sets the first mode above the speaker's BW, such as a small BW limited 'sub', then there's nothing to excite it, ergo no damping required if the cab is rigid/massive enough to not 'squeak'/whatever.

The ideal reflex cab then has enough non parallel sides to ensure a rapid decay of all reflections to minimize any damping required/maximize system acoustic efficiency.

Bottom line is that damping is a powerful tuning tool, so ideally should be dialed in and once you hear no audible difference to the good to ALL the folks who are going to be living with them, then you're done whether it seems too little or too much by accepted standards, what Altec/whoever did or recommended.

GM

[dr.joe]

My latest dumb question about my Iconic 704-8A with Iconic DN704-8S2 networks in 8.8 cu. ft. BR cabinets

What changes/improvements can I expect from lining the interior of the speaker cabinets with damping material (whether lining three non-parallel sides as Todd advises or all panels except the front baffle as others recommend)?

As the drivers and crossovers break in, the sound, subjectively at least, keeps improving. The cabinets are not at all resonant: even at high volumes, it's difficult to tell that music is playing by placing my hand anywhere on the outside of the cabinet. That is, my ears know (of course!), and I can feel deep/loud bass notes from the floor, but the cabinet panels seem pretty much inert.

MF and HF are vivid and clear and getting more so...instruments are clearly separated. Bass is not at all boomy.

Hence my question. Can I expect, for example, the mids and highs to become clearer? The bass to become tighter or softer? Or...?

I just don't want to mess up a good thing!

TIA,

Joel.

[bfish]

Lookin' good Willie!

Yeah, once you scrape off the extra sauce, that sandwich actually tastes like meat.

[drummerwill]

So I decided to add a little more stiffness to my Baltic Birch cabinets




Then I added a little Poly foam to 3 sides as reccommended by GM I think!




Listening test so far show tighter bass as expected. Thats kinda what the goal of the venture was when I started. I wanted to make sure the box wasn't adding any flabbiness to the bass.
But I think I got a little more Crispness to the highs. This was more of a surprise than I had anticipated. The 604-8K's I had felt with MDF cabs were a bit too shrill and the Baltic's were more smoother with the hi mids.
I think tighting the cabinets added more sweetnees to the mids.......JMHO !

Have Fun!

[drummerwill]

Thanks again GM

I wasn't exactly clear on that 3-sided thing, but I think I've got it now.

I'll listen for a while, then I'll try taking the insulation off the floor and try it on the back.

I can say this setup is sounding pretty good as is.

Have fun!

[GM]

Personally, as me n' Todd recommended, no damping on the floor (at least initially), i.e. the three non-parallel walls are the top, one side and back. Also, due to the way it's braced, these need to be wrapped with damping also.

GM

[GM]

<font color="#FFFFFF" size="1">[ November 29, 2008 12:27 AM: Message edited by: GM ]</font>

[GM]

You're welcome!

As a general rule, even if you prefer a minimalist damping routine such as shown in original Jensen Ultraflex/Onken designs there should always be damping on any parallel reflecting surface directly behind the driver such as your bracing and a typical cab's rear panel as they will modulate the driver with out-of-band noise as bad or worse than any that can emanate from a too large/long vent system beginning in frequency at ~2x whatever the distance is between the baffle and flat panel, peaking based primarily on its narrowest dimension, so a dowel will peak high enough that its acoustic energy is too low to matter and the rear panel peaking low enough that it typically takes either a fairly thick/dense material attached to it or a hanging curtain between the two surfaces or equivalent loose amount of stuffing to quell them.

In a BR, stuffing is normally to be avoided since it tends to reduce vent output too much, though again, it's a powerful/flexible tuning option if it tends to either have too much vent noise or sound too 'boomy' ('one note') in room.

WRT high aspect ratio cabs such as yours, there should always be damping at the end furthest from the vent due to its 1/4 WL pipe resonances that can be strong enough to reduce the required vent length for a given Fb, so if it's a baffle thickness vent as many Altec designs spec, this means it has should be larger, though normally the lower tuning won't be audible except in very long (tall) cabs, so normally nothing to be overly concerned about. Of course this only refers to custom designs where you 'stretched' an alignment into a tower design as any Altec or other brand original tower speaker will have the correct vent size for a given Fb.

GM

[dr.joe]

Here's my Iconic 704-8A in imitation Stonehenge V cabs: 51.5" H x 23.5" W x 19.5" D. 8.9 cu. ft. minus volume taken up by driver and braces. All panels 1.75" (0.5" birch ply + 0.75" MDF + 0.5" birch ply). 3 x 3.5 in. diameter round ports.

Still have to apply Tung oil, settle on the Iconic SuperCrossover Type 2 or the GPA N604-8A crossover (have both), and install the damping sheets.

Many thanks to Todd, GM and others for much valuable information.

(Apologies for lousy image quality: never used a camera before.)