Can someone help me build Altec 620 cabinet for 604-8H III

Greets!

Hmm, since BB ply is normally 5x5 ft, why not make them 60", so they can sit hard on the floor for max bass coupling, which by happy happenstance the 39.5" driver height puts it almost exactly at the 0.349 mathematical acoustic ideal for the 1/3 position?

This of course allows either an ideally shorter depth or greater net Vb, i.e. greater bass acoustic efficiency [my preference of course! :)].

Note that with speakers near/at a wall you ideally want your ears at a room odd harmonic also, so at a glance it looks like 3/5ths back is your best option overall.

Note too that ideally a large acoustic absorber needs to fill the speaker corner cavities.

Vent tuning depends on a number of variables with the room's acoustics being the dominant one, though Altec typically tuned its home speakers in the ~35-42 Hz range. Typically I recommend tuning to ~Fs, especially if coupled to a high output impedance.

GM
 
Good Day GM,

Thank you for responding. i purchased BB ply in 4x8 ft sheets at Whittelsey wood products here in Fl. This project started as a Stonehenge type cabinet so I had them cut the sheets into 4ft lengths leaving me with 4x4 sheets to transport and not 4x8. For some reason 4x8 sheets seem to be getting heavier. So I’m locked in at ~ 48” high. But I do get your point with the 60” cabinet.

I am doing some research at MJK’s site and getting a better understanding of using the worksheets. So far my SPL response charts look quite favorable for an MLTL with Inside dimensions 45.5” x 17.5” x 28.5” ~ 13 cubic ft. with a Cross-section of 498.75 sq. in. Port radius = 4”. Driver at 16” from top. Port at 38” from top, Fs = 28.10 Hz.

You made mention of near wall placement and the ear having to be at a room odd harmonic. Is this being considered because of the narrow baffle deep design cabinet where BSC becomes an issue? I have been loosing sleep over building a narrow cabinet vs a 30” W x 19D deep cabinet the narrow cab looks great but the bass efficiency might be better with a 30” baffle.
I have been looking at the MLTL design you did for the 416 and it seems to be a very successful project. No questions of bass efficiency there. I have also looked at the use of passive baffle step correction circuits and I’m leaning towards the 30” baffle design. Plus the Model 19 sounds great it is exactly 30” wide.

How do I get the driver to 39.5” high? I initially went with the stands because of all the designs on line utilizing the bottom port and stand I assumed there was some advantage to the bottom port in an MLTL design. I prefer the port to the lower front and the use of a platform to elevate the cabinet. A solid dead platform ~ 6" high. Any suggestions will be appreciated.

Anthony
 
The Altec 604-8H horn will support some flexibility in desirable ear height listening level ... 39" is just a good approximation for a seated adult in a chair.

There are a few early-tech MLTL cabinets for the Altec 604-8H which put the port on the bottom of the cabinet and use (adjustable height) legs for final in-room bass tuning, and also to raise the tweeter horn closer to optimum ear level. One design goal is to avoid a direct path from the port to the listener's ears, especially for the wide bandwidth generated by the Altec 604-8H cone. Naturally, heavy carpet will change the bass tone compared to a tile floor, and legs with height tuning might be necessary. The legs must be high enough (1.5x - 2x port diameter) to avoid port air compression.

If I had a 48" max-height cabinet, I would put the port on the bottom and add adjustable legs ... a proven short-box design. The Jay Fisher build with adjustable bottom legs gets positive reviews.
OR...MAYBE
Want to do more unique engineering? Post #17 shows Jean Hiraga displaying his Altec 604 MLTL speaker. Port air exits out of bottom side-slots. You could build a similar bottom platform to disperse the bottom port output on 3-sides. YOU STILL WANT some adjustable spacing(height) between the cabinet port and platform slots ... a few flat boards(shims) will give you in-room bass tuning.
 

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So far my SPL response charts look quite favorable for an MLTL with Inside dimensions 45.5” x 17.5” x 28.5” ~ 13 cubic ft. with a Cross-section of 498.75 sq. in. Port radius = 4”. Driver at 16” from top. Port at 38” from top, Fs = 28.10 Hz.
I have been loosing sleep over building a narrow cabinet vs a 30” W x 19D deep cabinet the narrow cab looks great but the bass efficiency might be better with a 30” baffle. Anthony

Attached Shindo example of a wide(maybe 32") bottom ported cabinet on legs for the Altec 604-8H. MIGHTY FINE wood work. I would flush mount the Altec.
Attached Jay Fisher example of a narrow(maybe 18.75") bottom ported cabinet on height adjustable legs. Popular design thanks to web articles.

Neither of these boxes look like "ideal" dimensions for optimized MLTL performance designs. Both of these speakers look like they were size-designed for specific room requirements. Suspect both sound pretty good. Hope these pics help you decide upon wide vs. narrow front baffle. If you post your final design dimensions and MJK spreadsheet printout, I suspect you will get a few experts willing to double check and recommend bracing + stuffing before you route holes.

The free "Baffle Edge Diffraction Simulator By Jeff Bagby Version 1.20" can help you model both wide/narrow baffle effects, plus a crude model for room placement.

Does your speaker have these T/S parameters from the Altec website?
Altec 604-8H
Xmax 0.15 (inch)
Re (ohms) 6.50
Vd 19.20 (cu. in.)
Fs 28.10
Vas 19.73
Qts 0.27
Qms 7.10
Qes 0.28
 

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Good Day Line source.
Thank you very much for responding. You have given me lots of options to review. I have read the review of the 6moons MLTL designed by Jay Fisher, GM very successful project i'm not sure why you think they are not "ideal" dimensions for optimized MLTL performance designs. What do you consider ideal MLTL dimensions for this driver?

I am using the Altec T/S parameters you posted. I did not save the simulation I did previously and I made an attempt today to do another. I'm not sure what i'm doing incorrectly but my results do not look good. i posted over at the yahoo groups to get some clarification and have a better understanding of the work sheets. I will post my results when I resolve this issue.

Does placeing the narrow baffle cabinets closer to the wall eliminate the use of baffle step compensation or is it still necessary to install a passive network between the amplifier and driver?
I do appreciate your input.

Anthony
 
Greets!

You're welcome!

Hmm, the ones I saw posted there looked horrible since you calc'd BL wrong; it should be around 15.12 N/A with those specs according to Hornresp
.

WRT its inductance [Lvc], all it does is change the response slope from flat to rising up through the mid-bass and short of measuring yours, 1.3 mH is what I use to sim all of Altec's/GPA's 416, 515 drivers and their 604, 605, etc., variants, which is the highest I can recall seeing measured, so in the scheme of things low enough to be insignificant for simming except XO design.

WRT cab internal dims, these are large enough to benefit from using either a golden or [room] acoustic ratio for width x depth to minimize the amount of wall damping required to quell its eigenmodes. I see yours is probably close enough to the golden ratio, but never did any experimenting, so not sure.

Short answer, the wall is the 1st odd harmonic of an enclosed square, round or rectangular space, so the ear should be at an odd one also.

Driver, vent location is near enough to my default odd harmonic, so should perform well with minimal damping.

Maybe this + all its associated links will help to understand the basic acoustics of room, sealed, reflex, TL, horn cab design: Resonances of open air columns

Narrow, deep cabs, especially those near/at a wall causes excessive [by 'old school' standards] loss of efficiency/fidelity due to the large electrical components required in a passive BSC filter plus there's the higher amplitude of the lower frequency eigenmodes generated between the large baffle/wall distance and why modern day narrow speakers need to be pulled well away from the wall [towards a null] to smooth them out somewhat.

Bass efficiency per se isn't the issue here since the WLs are so long in a typical HIFI/HT app; it's the tonal balance between the lows and highs that BSC robs us of mids/HF efficiency, so the wider the baffle, the less BSC required.

WRT risers, obviously they can't be too rigid/massive with sandboxes once being popular along with my preformed concrete slabs being an excellent 'el cheapo' choice.

If I were in your situation though, I'd get more wood and extend the cab to the full 60" i.d. height, i.e. flanged/spliced open bottom cab bolted, gasketed or bonded internal plates/whatever to an open top riser, which BTW can be out of MDF since It's just a stub; plus you could either double up its thickness or add marble/whatever slabs to it if you wanted a more 'massive' looking, yet functional, base.

GM
 
I have read the review of the 6moons MLTL designed by Jay Fisher, GM very successful project

Greets!

FWIW, I didn't have anything to do with the 6 Moons cab/article and only found out about it many 'moons' after it was published. Ditto the Dennis Fraker version Jay contributed to. I wasn't a 'happy camper' to see bits of some of my PMs to him published without my knowledge or even edited to bare technical essentials.

I did help Jay with a number of builds including some Altecs of which one pair was built and they look nothing like these other two. It's wide, flat [driver depth IIRC] and short enough to just barely be called a MLTL and with a visibly lower driver location. Its custom legs are delicate looking works of art, but don't recall if he made them or farmed them out.

By all accounts its performance up against a wall is 'smooth, full as a baby's bottom' with no BSC or other filters other than a stock XO and coupled to a high output impedance tube amp. The 6 Moon's motor brace is from the stillborn 604 ML-horn design IIRC. Unfortunately all my info, pictures are locked up in a pair of damaged HDs.

GM
 
GM--The photo came from the 6Moons website article. Internal cabinet dimensions discussed: 23.125"W x 18.4775"D x 42.5"H

--I ran a crude baffle+room sim of a 32" wide vs. 20" wide front baffle. As expected, this CRUDE simulation shows that some(more?) baffle step compensation is desirable for a 20" wide baffle than for a 32" wide baffle. As expected, the narrower 20" baffle sims are slightly smoother over the midrange frequencies.

Anthony--What cabinet shape would best fit your room, furniture style, and also pass "family review"?

Anthony--"why you think they are not "ideal" dimensions for optimized MLTL performance designs. What do you consider ideal MLTL dimensions for this driver?"

If you did not already have 48" cut plywood, a taller cabinet with ~58" internal line height sims best for low bass + modest resonances. A longer line allows me to glue/nail only Owens 705 fiber board on the walls around the speaker, and still have room for enough fiber-fill in the bottom T-line. To my ears, this construction sounds best with wide bandwidth full range and coaxial drivers.
 

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Good Day GM, Linesource,

GM.... "Hmm, the ones I saw posted there looked horrible since you calc'd BL wrong; it should be around 15.12 N/A with those specs according to Hornresp
.
WRT its inductance [Lvc], all it does is change the response slope from flat to rising up through the mid-bass and short of measuring yours, 1.3 mH is what I use to sim all of Altec's/GPA's 416, 515 drivers and their 604, 605, etc"

.....Thank you both for your very informative response it will become reference material as I go through this process. Today I did a couple simulations using the Parameter values GM suggested. The problems were corrected. I attempted to post the results here but quickly learned there is more to it than cutting and pasting.

GM.."If I were in your situation though, I'd get more wood and extend the cab to the full 60" i.d. height,"

....I can do this and I have enough material on hand to do so. Short Story, I had the 604's in JBL 4507 cabs 5 cu ft cabinets dimensions 30" H x 21.5 W x 17.5D these had helper woofers, same cabinet with JBL 2235H they were bi amped and stacked. The stack measured 60"H x 21.5W x17.5D and sounded great. I decided to change this system, I wanted to experience the 604 at its full potential. I want to experience the imaging of a true point-source driver..
However, I had no idea a 60" tall cabinet would be part of the equation. But in my communication with you and Linesource you're suggesting this is the best option..

Linesource asked "What cabinet shape would best fit your room, furniture style, and also pass "family review"?
We all like the look of the narrower cabs but our experience with the Mod 19 tells us that the wider cabinets produces good bass and the horns could always be attenuated to suit the room. However recent discussion with my wife she is asking the question " How wide do you have to build them and not have to use BSC" GM gave me some info on how the narrow cabinets perform close and away from the wall. linesource posted some simulations he did.on placement. I have to study them.
Tomorrow I will post room dimensions and give an idea of the layout of the room..
Thanks Much
Anthony
 
GM--The photo came from the 6Moons website article.

--I ran a crude baffle+room sim of a 32" wide vs. 20" wide front baffle. As expected, this CRUDE simulation shows that some(more?) baffle step compensation is desirable for a 20" wide baffle than for a 32" wide baffle.

If you did not already have 48" cut plywood, a taller cabinet with ~58" internal line height sims best for low bass + modest resonances.

Greets!

Ah! Thanks! That's what I get for not doing more than confirming this was the one with the special motor brace and for some reason remembering the speaker being front vented.

Nice to know a reflection sim reflects reality. ;) Which program? Basta?

Yeah, to the first approximation, speaker height is a function of design ear height, so for most [seated] folks and optimum driver location along the line it's 56-64" i.d. IME before I could sim one. ['optimum' varies with whom you ask and/or what simming program is used and how one interprets it]

Of course if max TL pipe action is desired, the driver and vent should be at the extreme ends.

GM
 
Probably OT ..... but Altec 604 + JBL 2235H ...seems hard not to love....
Did you tweek around this 2-box system?

The Altec 604-8H in a ported 5cuft volume has limited air-dampening, and can generate unnecessary large Xmax cone movement. Noisy port.

The Altec 604-8H in a sealed 5cuft volume (with absorption fiberglass lining the walls) models to -3db at 100Hz with a Qtc ~0.5 (over damped, some find the sound "dry"). A sealed 3cuft volume moves the Qtc ~0.58 which often sounds more dynamic(just right), but not as loose (for a 15" cone covering up to 1500Hz) as Qtc of 0.7 or above. Tweeks? Better bracing? Better absorption lining? From my big box room sims, baffle step droop peaks ~100Hz, so a clever crossover ~100Hz should allow a "simple and clean" drive signal for the Altec 604 cone - which has 1500Hz responsibility.

The JBL 2235H has a low'ish Qts of 0.25, and in a 5cuft ported cabinet tuned to 33Hz produces excellent bass at 93db/watt. So, to avoid throttling down the Altec 604-8H dynamics, bi-amping is necessary. When placed around walls, a complex bass equalization is required for a flat response, so a bass amp with an INPUT equalizer(active is better than passive) is required so the amp directly drives the 2235H. Adding an active crossover Linkwitz Transform would allow the same Qtc~0.6 sealed cabinet alignment for the JBL 2235H, with optional deep bass extension.

Probably OT
 
.....Thank you both for your very informative response

However recent discussion with my wife she is asking the question " How wide do you have to build them and not have to use BSC"

Greets!

You're welcome!

This is a function of the room's response and if it doesn't have enough of the right gain BW, then you could mount the drivers in the back wall and the 'baffles' still wouldn't be big enough.

All these low Qt drivers were designed to be driven with a high output impedance, then use variable damping [bass, treble tone controls] to tonally balance the system. This way, efficiency is preserved, though bass typically sounds a bit 'flabby'/'loose' [under-damped]; whereas with modern amps one has to shelve some portion of the mids-HF BW to balance out down to around 150 Hz or so, then either use bass boost and/or room gain to balance it out down to 40-20 Hz [typically Fs], which when done right yields 'heart attack' 'fast' bass, though all this really means is that the bass is critically damped instead of under-damped and is properly tonally balanced to its upper harmonics where the 'fast' part ['snap'] of the bass line resides.

Anyway, unless you have a relatively large, open room like mine, 30" is typically the point of diminishing returns and otherwise up to 25% of the room width/channel IME and why I have my 30"ers diagonally in the corners of a 16 ft wide room as I don't have the space for 48" wide baffles positioned out in the room.

GM
 
The Altec 604-8H in a sealed 5cuft volume (with absorption fiberglass lining the walls) models to -3db at 100Hz with a Qtc ~0.5

ABOVE IS INCORRECT for sealed 5cuft volume with absorption material on walls.

CORRECT:
The Altec 604-8H in a sealed 5cuft volume (with absorption fiberglass lining the walls) models to -3db at 80Hz with a Qtc ~0.6.

This would allow you to just seal up any ports on the 5cuft JBL 4507 cabinets ... if you have not already run this experiment. Fiberglass batts without Formaldehyde have less itch ... sealed box = no strands into home.
 
Probably OT ..... but Altec 604 + JBL 2235H ...seems hard not to love....
Did you tweek around this 2-box system?

The Altec 604-8H in a ported 5cuft volume has limited air-dampening, and can generate unnecessary large Xmax cone movement. Noisy port.

The Altec 604-8H in a sealed 5cuft volume (with absorption fiberglass lining the walls) models to -3db at 100Hz with a Qtc ~0.5 (over damped, some find the sound "dry"). A sealed 3cuft volume moves the Qtc ~0.58 which often sounds more dynamic(just right), but not as loose (for a 15" cone covering up to 1500Hz) as Qtc of 0.7 or above. Tweeks? Better bracing? Better absorption lining? From my big box room sims, baffle step droop peaks ~100Hz, so a clever crossover ~100Hz should allow a "simple and clean" drive signal for the Altec 604 cone - which has 1500Hz responsibility.

The JBL 2235H has a low'ish Qts of 0.25, and in a 5cuft ported cabinet tuned to 33Hz produces excellent bass at 93db/watt. So, to avoid throttling down the Altec 604-8H dynamics, bi-amping is necessary. When placed around walls, a complex bass equalization is required for a flat response, so a bass amp with an INPUT equalizer(active is better than passive) is required so the amp directly drives the 2235H. Adding an active crossover Linkwitz Transform would allow the same Qtc~0.6 sealed cabinet alignment for the JBL 2235H, with optional deep bass extension.

Probably OT

I sincerely hope the mention of my dual cabinet system did not cause confusion. I no longer have this system. I sold the JBL 2235 and the 4507 cabinets. However I did tweek around with the system. The 4507 has four ports you can close ports and tune to cabinet to different Hz. I used them approximately 4' off the back wall to my ear they sounded best there. I think no matter what speakers I put in the room they sound best 4-5' away from the wall.

I did a rough draft of the room layout hopefully this helps with selecting practical cabinet dimensions for the size room. The foot print of the 4507 worked well at 21.5" wide due to the width of the room, they sounded good, nice quick defined bass lines. However, at low level late night listening the depth was not as efficient, I always thought it was due to room acoustics. I installed an Eq.as an experiment and remember the base was prefect in the room.

The Model 19's at 30" wide consumed the front of the room and somehow didn't leave enough room for the sound stage. The bass was deep but not as defined in some cases not as quick. Again at low level late night listening a little more depth will be nice. The type of depth I get when I use an Eq. Maybe the room needs Eq just on the lower end. Just maybe.

The model 19's are in a bigger room and they sound better there. Please excuse me my observations are based only on what I hear.

Anthony
 

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620 speaker cabinets

Don't know if these are still for sale just thought i would pass it on to you. These are heavy and out the country may end up being to expensive but you never know till you ask. Plus they are MDF witch is IMO the best speaker cabinet material and it's veneered on both side and looks to be super high quality. He says in add he will sell separately.

ALTEC 604-8G & 620 ENCLOSURES
 
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Don't know if these are still for sale just thought i would pass it on to you. These are heavy and out the country may end up being to expensive but you never know till you ask. Plus they are MDF witch is IMO the best speaker cabinet material and it's veneered on both side and looks to be super high quality. He says in add he will sell separately.

ALTEC 604-8G & 620 ENCLOSURES

Thank you for the link but I already own a pair of 604's. This ad has been around for a very long time it must be sold.

Anthony
 
Good Day,

After carefully considering the information and recommendations given to me by GM and LineSource. I have gained a better understanding of the MLTL speaker cabinet design. This communication has also motivated me to look into MJK's website, study his worksheets and simulate ideas myself. The learning curve has begun and is still in progress. These men are an asset to the DIY audio community and I appreciate them.

I now have dimensions for a MLTL cabinet I will like to build. 60"x26"x19" O.D. (HxWxD} CSA = 428.75 sq.in. Internal Vol. = 14.5 cu. ft. I have attached a partial worksheet. As always you input is appreciated.

Anthony
 

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Greets!

Looks typical for 416/515 based drivers before any series resistance is added, though I made the vent depth just baffle thickness and raised it up a bit to smooth out the phase flips in the mids/lower HF, but vent damping will do it too and sometimes preferred due to room/boundary effects down low near/at tuning.

GM