Altec 604s "built" into a Bookshelf?

[GM]

My ears are ~ 45 inches from the floor at listening position.

Thanks again for everyone?s assistance.

You?re welcome!

OK???..


Again, it depends on the system?s output impedance [total series resistance the driver[s] ?feel?], the amount of room/boundary gain and desired LF response. GPA is a manufacturer that must CYA itself against product liability, so it?s in their best interest to suggest an alignment that pretty much protects the driver against over excursion damage at rated power. They may also believe this is an optimum alignment for all I know, but from long experience it sure isn?t my idea of one except when the other considerations dictate it.

Again, my attitude when there?s not enough measured data to make a well informed choice is to recommend the largest acceptable cab since it has the most tuning flexibility, i.e. it?s a lot easier to ?shrink? a cab than it is to ?stretch? it if the bass line sounds unacceptably ?lean?.

Based on published specs, your acoustically relatively large room and high [unknown] output impedance amp, a reasonable worst case would be a ~23.3 ft^3 net cab tuned to Fs if a matching impedance and due to true half space [2pi] loading, it can be reduced to its Vas rating or ~11.65 ft^3 net without any obvious loss of LF acoustic efficiency down to ~25 Hz in a sim.

If you built them full size, they would probably sound too ?boomy? and have problems with TT ?rumble? if spinning vinyl, so they would need to be empirically damped to deal with this. For my personal use, this is the way I would go since it?s the best size overall for a sealed alignment if desired, but I tend to prefer a much ?tighter? [damped] compression horn-like presentation than most folks, so quit recommending it once I found out folks were mis-tuning and/or reducing cab net Vb to get the [vintage] ?tone? that sounded best to them.

In short then: ~9.0-23.3 ft^3 net/tuned to measured Fs, your call.

Make it the max height and post new internal [i.d.] dims once a net Vb is chosen for more design details.

GM

[Encyclopediabsh]

LP/ear height of 45" (1150mm) seems a little high? I'd expect around 37" (950mm) to be about norm

With a 41" long cabinet, and driver at .349 down that puts the driver at around ~36" by my calcs, so just about perfect. Out of curiosity what is the tweeter height of your ANs in their current setup?

I've also got 604s in ~11cu.ft cabinets, and the same amp, great combo. I believe 250k is the input impedance, not sure on exact output impedance as it's a SEP design and would depend on Shindo's implementation (feedback, opt, etc), could be worth sending an email to check. I have been meaning to for a while just not got 'round to it

Omodo - my listening room also doubles as our family room, so not ideal circumstances and seating. For critical listening, I use a dining room chair in LP1, which puts my ear at ~45 inches from the floor. LP2 is in a dining room chair as well.

The AN tweeter sits at ~41 in from the floor. The base of the bookshelf cabinet I am constructing is 9 in above the floor, and I have the AN speakers on a pull-out shelf 3 inches tall - in effect a 9+3=12 in stand for the speakers.

I am thrilled to hear the 604s are a good match for the Cortese - what model 604 are you using? 8 or 16 ohm? Any tips for success?

[Encyclopediabsh]

GM/Others - after remeasuring to correct inside dimension, let's go with

Width = 27.5 in
Depth = 22.5 in
Height = 45.0 in

Internal volume calcs at 12.2 cu ft, which should allow for some bracing to take overal volume down to ~11.7 cu ft. I will using 3/4" piece of birch ply for the baffle unless anyone suggests 1" signfiicantly better.

Need to know optimal vertical location for the 604 driver and location and size of the front-mounted tuning vent(s) when possible -

Thanks again

[GM]

You?re welcome!

Material stiffness increases at the cube of thickness, making ?? to 1? a ~2.37x increase in rigidity, so in theory well worth it, but all things considered, a vertically braced ?? thick panel is just as good, if not better, for a lot less $$$/effort and if you break the baffle up into sections with the driver and vent areas removable, then effective stiffness increases to the point of rendering the subject moot.

The trade-off of course is a lot more mounting hardware and potential for air leaks of which even a tiny amount will ruin a reflex?s tuning. If the driver is front mounted, then brace a one piece baffle the same and preferably all the panels due to their size.

OK, there?s at least four different ?optimal? driver locations depending on who you ask and/or what works best overall for the needs of the app:

At the extreme closed end [opposite where the vent is]. Typically for subs or when coupled to a horn or other driver on top.

Down 0.21. Some folks believe this is optimal based on simple ? WL closed pipe theory.

Down 0.349. MJK?s conclusion based on wave theory, so very popular.

Mine, which is based on mechanical resonance theory, varying based on length and cross sectional area [CSA] or down 0.4588 in your case.

The further down the pipe within the lower limit, the less damping material required to smooth out its harmonics, but the less pipe action [acoustic efficiency] as the trade-off, so in the scheme of things performance wise; lower is better for wide BW use, though never having compared my way to MJK?s, don?t know if there?s an audible difference or if it?s enough to matter. I?m guessing probably not in most cases unless it changes the fundamental ?tone? of a male voice.

In short, driver cutout centerline anywhere between ~15.71? ? 20.65? i.d. down from the top would be ?optimal? with as little as ~9.45? down if you think a higher stuffing density is OK.

Conventional wisdom dictates the vent system be near/at the bottom, though at least one designer uses MJK?s software to shift it up the pipe a bit whereas again, I calculate it a bit differently to get a specific type of alignment for when the speakers are well away from any wall boundaries. In your case it would be near/at the bottom front.

WRT vent size, for the kind of specs Altec or similar have; due to the pipe?s ? WL action impacting vent damping, it depends on the driver location, with it decreasing in area to keep vent length short with increasing driver distance from the closed end of the pipe.

Or, you could use the largest size as the pioneers of audio chose to maximize vent efficiency, but if you tune to actual Fs as you normally should when using a high output impedance amp, this just means that you?ll probably need to damp it more in your app to keep it from sounding ?boomy?. Only one way to know for sure though.

Anyway, vent area decreases from ~132.73?^2 - ~95?^2 as the driver ?slides? down the pipe with vent length shifting from 0.75? [baffle thickness] to 3? respectively. This assumes a ~22? wide slot vent down 39? i.d. with of course its height being variable.

I?ll post 2 pi [1/2 space] loading sims including aperiodically sealed [highly damped vent] as time permits, so with your near 1 pi [1/4 space] loading combined with no way to accurately sim a current [tube] amp?s impact on driver performance and with no room eigenmodes consideration that will cause peaks/nulls in the lower octaves, they will be strictly for driver/vent comparison purposes.

GM

[Encyclopediabsh]

In short, driver cutout centerline anywhere between ~15.71? ? 20.65? i.d. down from the top would be ?optimal? with as little as ~9.45? down if you think a higher stuffing density is OK.

Completely understand this part as to options for mounting driver

Anyway, vent area decreases from ~132.73?^2 - ~95?^2 as the driver ?slides? down the pipe with vent length shifting from 0.75? [baffle thickness] to 2? respectively.

Concerning the vent location, sounds like the bottom front is best. However, concerning the vent size, since planning on using 3/4" birch ply, are you saying the vent should be~132 sq inch? Just wanted to make sure, that seems fairly large. For 132 in sq equates to 18 in x 7.5 in. Hope I'm not asking a dumb question here...

[GM]

No, not a dumb question, ~accurately calculating vent area/length is fairly complex, especially in high aspect ratio cabs long enough to have 1/4 WL pipe [TL] loading affecting it. Even the math intensive simming software I use has an inaudibly small error when the vent is any shape but round.

For the sims then, driver down:
~9.45? = 13? i.d. diameter vent
~15.71? = 12?
~20.65? = 11?

Again though, all this assumes a 33 Hz Fs, so best to build it so that the vent area/length can be adjusted for max power transfer efficiency when a high output impedance amp is used, though it may be a moot point because I?m pretty sure you?ll find them too ?boomy? in-room, forcing a high enough vent stuffing density to flatten their response, shifting Fb lower in the process if not re-tuned.

In my haste, I see I made a typo and left off some vent details, so have edited my prior response per below:

GM

+++++++++++++

Or, you could use the largest size as the pioneers of audio chose to maximize vent efficiency, but if you tune to actual Fs as you normally should when using a high output impedance amp, this just means that you?ll probably need to damp it more in your app to keep it from sounding ?boomy?. Only one way to know for sure though.

Anyway, assuming a 33 Hz Fs, vent area decreases from ~132.73?^2 - ~95?^2 as the driver ?slides? down the pipe with vent length shifting from 0.75? [baffle thickness] to 3? respectively. This assumes a ~22? wide slot vent down 39? i.d. with of course its height being variable.

[Encyclopediabsh]

Thanks so much for the details GM.

I'm inclinded to try the baffle construction method suggested (removable sections for the driver cut out and vent area). If anyone has tried this method, could you please post some pictures so I can have a better idea of how to build it?

[omodo]

Thanks so much for the details GM.

I'm inclinded to try the baffle construction method suggested (removable sections for the driver cut out and vent area). If anyone has tried this method, could you please post some pictures so I can have a better idea of how to build it?

The Shindo Latour is a perfect example of removable baffle construction

I've done a couple of mockups in Sketchup based on the dimensions mentioned in this thread. As drawn the baffle can be flipped to alternate between the 15.71" and 20.65" driver offset. The model on the left has a 22" x 5.14" slot which is equivalent to a 12" diameter port (~15.71” = 12” diameter port), the model on the right has a 22" x 4.32" slot which is equivalent to an 11" dia port, top of the slot is 39" down, length of port not drawn. As you can see a 22" wide port at 39" offset on your baffle doesn't leave you a lot of room for a removable port board

The horizontal guide running at approx. chest height on 'the dude' is your 45" ear height, baffles are drawn 9" off the floor, the other guidelines show the ID of your enclosure (27.5 W x 22.5 D x 45 H). The driver board is 500mm W x 655mm H, baffle cutout for the board is 420mm W x 575mm H, driver cutout is 359mm dia, sorry about the units.





Is this what you had in mind GM?

[mah]

My effort. Butt joints with glued corner blocks and glued 'plate' across the rear of the joints. I used 2 crossmembers with a divider panel glued on to form a beam for rigidity.

[Encyclopediabsh]

Thanks everyone for the replies so far. MANY apologies, but just notice a typo on the dimensions earlier in the thread - my attached drawing was correct, but the width was a typo. Correct inside dims are:

Width = 20 in
Depth = 22.5 in
Height = 45.0 in

Is there a rough formula for calculating the vent area needed based on dimensions alone?

I am embarrassed and apologize again for the misinformation...