Optimized cabinet for 416B ???

[GM]

>WinIsd will give a warning if vent air velocity gets to high but I have not tested the threshold for accuracy. If you like more area, 2 ea. 4?pvc vents should be 7.09? long, the two vent alignment will yield a maximum air speed of 42.9 ft/s at 16Hz with 60 watt input.
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Greets!

R. Small did numerous listening tests and concluded that a vent mach less than 5% SoS (~17 m/sec or ~56.5 ft/sec) wouldn't generate any excessive noise at the driver's peak displacement, so is input power dependent. The commonly used Margolis/Small approximate formula for the minimum vent diameter required at whatever the driver's chosen displacement is:

Dv (min) = (20*Vd^0.5)/Fb^0.25

where:

Dv = vent diameter (mm)
Fb = cab tuning frequency
Vd = driver displacement (cm^3), normally (Sd*Xmax)

So with a 16 Hz Fb and the 416's 19.2"^3 (314.63 cm^3) Vd, it needs greater than ~177.38 mm (~6.984") diameter, or its equivalent area if multiple vents are used.

GM

[GM]

>GM,
I liked your idea of triangular speakers, so Saturday I started nailing up some dummy cabinets, scale 1:1........
=====
Greets!

Reviewing some sims I did awhile back based on some proven designs I've built, there was only two vented corner loaded ones that I figure will work and the smaller of the two is still 8.344 ft^3 net tuned to Fs with a 35.53" i.d. height, 40.28" i.d. wide baffle. The one I prefer is 15.3 ft^3, but it's not viable at what I consider the optimal listening distance. :^(

Never done any sealed other than for horn loading, so doing a bit of simming...... We can use anything from ~1.0 ft^3 on up, but any reasonable size one will require a sub. That, or trade a considerable amount of efficiency for BW using a Linkwitz Transform electronic ckt.. At a glance, it looks like it would be down around 92-93 dB/W/m.

GM

[Adhoc]

Trial ...

[Adhoc]

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[Adhoc]

Hi all,
Those 2 weeks got quite long, more like 7 weeks. Anyhow, I tried out 4 dummy cabs, built scale 1:1, how they felt in the room. Came to the conclusion that GMs proposal of triangular speakers should be the one to go for. Baffel width ^~32" x H ~51" should give a net internal volume of about 5.6 ft^3. accounting for woofer volume and bracing.

Time changes though... Good thing: Got my hand on 3 pcs 604-8K, new in box, 2 weeks ago. Bad thing: Noticed the mitered joints for the triangular speaker were not good. Turns out a cast iron part in my 1970 table saw has a crack in it. Cast iron is hard to repair and probabaly no spare parts avaiable anymore either. So, a bit annoyed I stroke the triangular speakers and built some shoe boxes instead.

This is what came out: An extremely sturdy nice looking cab. Outer dim. H 30.5" xW 20.3x D 24.6". Inner dim. H 28.5" x W 18.2" x D 22.5". Internal volume 6.5 ft^3, net after deducting bracing and woofer volume 5.9 ft^3. Weight empty 121 lbs.

The 416-8B is front mounted in a recess, the rim 5.5" below top surface. 2 recessed front mounted tubes with flared ends for venting, inner dia 97 mm / 3,8", centre is 8" above the bottom. The horn is on top on a T-shaped sled, installed 3 threaded inserts in the sled so it can be tilted back-forth, left-right. With 4 wheels under the cab centre of the horn is at height 3.5" at its lowest position.

Questions I hope you more experienced guys can help me with:
1 Suitable amount of damping material?
2 How much does damping material affect the virtual volume felt by the speaker? I have seen figures ranging from +10% to +30 without any good explanations/specifications for the number, which one is to trust?
3 Suitable tuning frequenc and tube length.

To take in consideration:
1 These will mainly be used as surround/back speakers for DVD-A, SACD and home theatre. -I will have the 3pcs 604-8K as front speakers, together with 2 subs for the low end, ~< 80Hz.
2 I will use 5/8" thick glass fibre "boards" for cabinet damping, 1 or several layers. Its density is 6 lbs/ft^3. This type is lot more effective than the type used for house insulation or dacron/pillow filling. I tested how much I could install without blocking passage to vent tubes, maximum = 2,16 lbs/ft^3. According to BobR and GM in a prevoius thread, 1-2 lbs/ft^3 is necessary to be audible around Fb, while 0,5-1 lbs/ft^3 "muffles" midbass/lower mids.
3 Lowest possible "rumble" bass is not the aim, a good and "snappy" one is.
4 I'll get active filters for all 5 speakers with separate SS amps for low, mid and HF. I have a Rane AC23 now and will get some more AC22.
5 The screen in the home theatre is 75" wide. Front wall is 12.24' wide, side wall 18.96'. Visual sweet spot at 10.6' or further back, Audio sweet spot probably at around 11.7' or so. This would place the surround speakers at about 6.5' distance, if corner placed.

I hope someone has an answer to these tricky questions.

Cheers for now.

[Adhoc]

Correction: heigth for the horn is at 35.5" = ear level when seated.