Altec 604 D Enclosures

Hi everybody,
I received from GPA my pair of 604 D.They remag. them and changed the LF cones.I also bought from them their N1600-16 crossover.After a pretty long breaking in period,i tried them at a friend's place.He has got a pair of 604 E with original cones ,a pair of "interesting" enclosures.So we could compare the two pairs of speakers in the same room and the same enclosures using the GPA crossover.The first conclusion is that the 604 D reconed by GPA sounded much better than the 604E with their original cones.Our best guess is his speakers probably need a remag.and may be a change of surround to perform optimally.The second obvious conclusion is that GPA did a very good job and that people should not hesitate sending their Altec to GPA for reconing.
Now come my questions regarding the enclosures.My friend has a pair of BR enclosures with the following external dimensions in feet :Height 3.05;Width 2.13;Depth 1.48.
Internal volume is about 11,3 cubic ft (from which one has probably to deduct the volume of the driver).The cabinets are bottom vented and the vents are actually two rectangles(1.0x1.5 feet) cut in the bottom of the enclosures and facing the floor.The 4 feet are 2 inches high.The walls are made of pretty thin(O.6 inch) and light plywood(Density about 0.5 when Baltic plywood is 0.7).No braces.The only internal damping consist of thin felt covering the internal walls. Those speakers are driven by high quality SE 300 B amplifiers.I was expecting from those speakers a lot of disturbing vibrations but actually they sounded pretty good and the only limit i could find was that i would have preferred the bass to go lower.So should i simply copy those light,inexpensive ,easy to built enclosures for my 604 D or should i try to improve them and in this case how?Charly 1944

For real?! That puts the tuning up around 72 Hz whereas a typical Altec tuning would be around 40-42 Hz.

GM

I had an E and a C, the C was way better sounding than the E, It dawned on me that the E crossover is supposed to be 1500 and I was running it with the same GPA N-1600 crossover your using. Not sure if that's why it didn't sound as good, but it could have been. The cabinet you described reminds me of my ex brother in laws Klipsch Cornwalls. When I saw the insides of them all I remember saying is they look like wooden bird cages. they were very light in weight. I was about 14 at the time so....yeah.
I'm glad to hear you got them back and that they sound great. I can't wait to see what cabinet design you go with but there are some real beauties out there.
These are my favorite for looks.
http://www.jacmusic.com/Yamamoto/Spe...604/YS-604.htm
These seem pretty cool too.
http://www.audiocircle.com/index.php?topic=54147.0

Quote:

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Originally Posted by GM

For real?! That puts the tuning up around 72 Hz whereas a typical Altec tuning would be around 40-42 Hz.

GM

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GM, how does floor loading, especially in this case being only 2"/50mm off the floor, have an effect on port calcs/sizing?

Quote:

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Originally Posted by GM

For real?! That puts the tuning up around 72 Hz whereas a typical Altec tuning would be around 40-42 Hz.

GM

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Thanks GM,
Pretty high tuning indeed.No wonder that i found it could have gone lower in the bass.What options would you recommend to go for.I dont mind wether it is an OB (provided it is not too big) or a BR solution.Thanks.
Charles.

If your dims are correct ? 11.3 cubic ft. Is a very large cabinet for the 604.You would typically see like a 9 cubic ft cab for the 604 (620 A or B) being considered a large cabinet.Also sounds like those cabinets could use some stiffening/bracing.If you like those cabs you could add some length to the vents to lower the tuning.

It doesn't surprise me though that the new recones/remag's sound better.I had a similar experience with my 416-8B's.The surrounds and or spiders are the issue.They either stiffened up or they loosened up/sagged.When that happens the sound quality suffers.

One other thing if you build something similar I would go with round ports as they are easier to add length to then square/rectangle IMHO.

"Sound is Round"

I think GM has posted a MLTL box design for 604s on this site or perhaps AA High Efficiency, but it should be easy to find. I don't know if anyone has built it.

Here's another one: 6moons audio reviews: Steph?n's Altec 604 Dream Speaker

That's an older review I think GM has done some updates since then.Dunno ? Hopefully he can confirm this or not.

Here is some info on yet another 604 MLTL: Serious Stereo Ultimate Transmission Line Speaker. The ultimate High Efficiency Speakers found anywhere

Restricting the vent via boundary loading creates a form of band-pass loading [think R-J style reflex loading] and while I'm sure that the wave equations can optimize the gap for 'x' amount of gain, I've never seen it published and even if I did, don?t have a clue how to manipulate it, so I have to find the amount I want empirically. Basically, it lowers tuning due to air mass loading, so can either shorten a vent or increase its area [Av] for a given Fb same as a vented TL [MLTL] does.

I worked up a simple way to find a minimum gap before it begins to audibly affect speaker response that?s based on speaker base area from empirical data and should have ?run the numbers? before posting as I get a pretty high minimum, so in theory there is some loading going on, lowering tuning [Fb], but would have to be measured or at least listen to test tones to find out how much.

Then again, this much vent area Vs cab base area makes it almost a simple TL, which by itself would be tuned to ~78.5 Hz, so ignoring floor gain, around 70 Hz may not be that far off. In retrospect, considering its age, I wonder if it?s not tuned same as an early A7, which puts it around 65 Hz, not a high tuning for the early ?50s/604D. This would imply a fairly significant amount of floor gain.

GM

Quote:

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Originally Posted by charly1944

Thanks GM,

What options would you recommend to go for.

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You?re welcome!

While OB, IB are theoretical ideals, there?s nothing intrinsically wrong with the existing cabs that maybe some additional damping, adding bracing and reducing vent area to lower tuning can?t solve and large enough to allow for an adequate amount of EQ/tuning options, though ideally we need their new GPA specs, especially since I seriously doubt they?re even remotely close to OEM.

Otherwise, at least as large an internal volume [Vb], though taller to make them an offset driver MLTL tuned around/at Fs and use some form of EQ to ?fill up? the cabs as required to tonally balance them in-room. This assumes of course the re-cones aren?t as ?weak? [high Qts] as some other recent GPA re-cones I?m aware of.

GM

The 6 Moons and SS MLTLs are based on a private design I did for Jay Fisher, who shared my PMs with them without bothering to tell me, though he did ask me some technical Qs for a 'friend'. I had to learn about them both from others some time after the article was published. For sure, I never would have approved of any of my PMs being published verbatim, especially partly out of context as was done in the 6 Moons article nor willingly helped a 'for profit' venture who later claimed he changed it enough to make it 'his' design.

Don't recall any updates, the design started out as one of my default floor loaded MLTL alignments and JF shortened it and relocated the offset driver a bit differently than I recommended due to WAF? considerations. I used MJK's software to alter the vent length, made some bracing, damping, driver support, floor spacing recommendations and AFAIK, that's what was built. If there were other changes, I'm not aware of them nor care to be.

GM

Thanks David,
It looks interesting but probably difficult to implement for me.Is the MLTL solution considered as the state of the art solution for a 604? I look forward to getting some guidance from GM.

Sorry GM,
My message to David where i said i was looking for your guidance went through just before i could read yours. Let me make sure that i understand your comments(Dont forget that i am French and although my English is decent i tend to miss some subtleties of your language and certainly miss a lot when it comes to technical terms).I understand that there is nothing fondamentally wrong with my friend's enclosures and that improvements can be achieved.Do you mean that optimally i should get those reconed drivers measured in terms of impedance and TS parameters in order to adjust the dimensions of the enclosures and the vent.If yes this is a bad news because i will need a lot of help to measure those drivers.But i am ready to go for it. Few questions:
If we are making the assumption that indeed those reconed 604 D dont have the 604 E characteristics,i guess we have to use the trial and error approach rather than any approach based on modelling.What elements could we easily and reversably change to lower the tuning ;Ex:If i have to reduce the vent,should i make drastic changes and is there a formula to help me in doing that.Same thing with the feet :to day,2 inches.Should i change that and by how much .The dimensions of the enclosure without changing the volume:Higher,deeper? Sorry if my questions dont make sense but i badly need specific(and if necessary ,iterative) recommendations to make progress.
Thanks in advance.
Charles.

Hi sorry i did get back to earlier and thanks for the pictures.I like the OB very much but i am wondering how big they are and how do they perform,specially when it comes to low freq.Regarding the difference of performance of your 604 E vs C,they are indeed different drivers with different surround and i doubt that the the GPA crossover is equally adapted to both of them.There is also a distinct possibility that your E and your C are not in the same"shape".Did you check the surrounds,the spiders and the level of magnetisation of both pairs?
Charles;

Hi, GM

I didn't have any idea that Fisher had shared your design and PMs without permission, otherwise I never would have referred the OP to the sites. That really wasn't kosher for those boys to do that, and I hope it hasn't discouraged you from sharing your ideas with us DIY folk.

Best wishes,
David

Greets!

No biggie, it's old news and no, for the most part it hasn't, though I now limit most help to on-line Qs.

GM

Charles, interesting to hear you are from France, are the enclosures based on Jean Marie-Piels speakers? I only have the following small picture from Revue Du Son No. 225 Dec. '98, but from what you describe they could be very similar. Unfortunately I do not have the article but would love to see a scan if you can locate a copy.

Quote:

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Originally Posted by charly1944

Sorry GM,

(Dont forget that i am French


Do you mean that optimally i should get those reconed drivers measured in terms of impedance and TS parameters in order to adjust the dimensions of the enclosures and the vent.If yes this is a bad news because i will need a lot of help to measure those drivers.But i am ready to go for it. Few questions:



What elements could we easily and reversably change to lower the tuning ;Ex:If i have to reduce the vent,should i make drastic changes and is there a formula to help me in doing that.Same thing with the feet :to day,2 inches.Should i change that and by how much .


The dimensions of the enclosure without changing the volume:Higher,deeper?

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No apologies needed, it happens sooner or later to all of us. ;)

No, I didn’t know you were French [or I forgot, a real problem for me now] as like so many Europeans, your English is as good or better than way too many public school educated locals, at least around me.

Correct, I’m really disappointed GPA doesn’t include as standard, or at least offer, the T/S specs for a reasonable price upon request. Actually, since they know the various specs of the sub assemblies [Mms, Cms, Re, etc.], they could easily calculate them in an Excel or similar spreadsheet ‘close enough’ for cab design.

The only real variable would be how well they drained, re-magnetized the magnets, but in a cab large enough to allow some tuning flexibility, this hopefully won’t be an issue, though again, there’s been some re-cones where the re-charge didn’t go well, which results in an unacceptably high Qts. Since yours sound good, odds are that they are fine.

Anyway, try to get them from GPA and if you can’t, then experimenting with vent tuning is easier than learning, doing T/S measurements if you have no one local to do it for you.

WRT tuning, the math is fairly intensive for other than a simple reflex, but I can sim different vent lengths close enough using MJK’s software and if you choose to use a bottom loading vent, calculate a minimum stand height.

Again, the cab would be taller with height typically based on seated ear height for an offset driver layout that requires the least amount of internal damping, so for ~38” it would be around 62” i.d. [inside dimension] for 11.3 ft^3 using 19 mm thick construction and assuming setting on the floor with the vent on one of the sides near/at the bottom. Width x depth would normally be an acoustic or golden ratio to minimize internal damping. Using the golden ratio, this would be ~22.58” x 13.95” i.d..


Anyway, just an example...........


GM

Hi GM,
I dont know where you are located in the US but it seems to me that you are on the site either very early in the morning or very late at night!
Actually GPA told me that they are not used to measure the speakers as a standard service .Since i insisted to get my 604 measured after the reconing(i was advised by Jeff Markwart that it would be useful for cabinet and crossover design)they accepted to do it but then had no time to actually perform the measurements.I guess they had other priorities and actually i was not ready to wait for weeks.
For now and without measured elements to guide me ,i guess i have multiple options
1.To copy my friend's enclosure and to change(reduce) the dimensions of the vent and assess the results by listening.
2.To keep the same design (bottom vent boxes)but change the dimensions of the boxes and of the vent while keeping the total volume.In this option i noticed that for the width vs depth they are a lot of acoustic ratios published and none of them correspond to the golden ratio.So i am a little bit at loss when it comes to select one of those.Any recommendation?Regarding the height, my ear are at about 3 feet from the floor.So what could be the ideal dimensions of the boxes(without the stands).And what distance should i keep between the upper part of the speakers(rear mounted)and the upper part of the front baffle?Last but not least ,what should be in this set up, the dimensions of the bottom vent to get to an around 40 hz tuning?By the way,Altec Best suggested to go for circular vent rather than rectangular one.
3. to change the design and go for an MLTL( or a OB if the dimensions are reasonable in this relatively small room -12x16 feet).
What would you advise me to do .
GM,if i take too much of your time,let me know,i will understand.
Thanks,
Charles

Charles,

Are you able to take advantage of the room corners? In other words, might you be able to "build-in" large floor to ceiling corner IB boxes canted approx. 30 degrees towards the listening position? If so, this would be my first choice and you could add eq or series resistance to balance the system. This layout also gives you maximum boundary reinforcement while minimizing diffraction and creating a pseudo early-reflection-free zone, not to mention using the minimum floor space. Also, if your corner walls are sufficiently rigid, you may be able to get by with building just a well reinforced front baffle screwed and sealed to wall, floor and ceiling furring strips -- it doesn't get much easier than this. A 4' wide (standard for plywood in the USA) baffle set at 30 degrees will yield about 25 cubic feet.

Building a large enough closed box will also mean that you can stop agonizing over your speakers' TS measurements -- they are what they are, and as long as the pair are more or less the same, you will be in business.

Best wishes,
David

As for Open Baffle, here is a pair of 605As that I showed at the Lone Star show. The helper woofer is an 18" pro model with its own amp and active crossover.
Lone Star Audio Fest 2010, Dallas Texas | Hifi Zine

Quote:

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Originally Posted by Panomaniac

As for Open Baffle, here is a pair of 605As that I showed at the Lone Star show. The helper woofer is an 18" pro model with its own amp and active crossover.
Lone Star Audio Fest 2010, Dallas Texas | Hifi Zine

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OMG!!! That's you??? I was totally checking the links out that you posted on Audio Circle Last night. I wondered if that was you and wanted to ask you about your comment that you made about OB crossovers being totally different than the bass reflex crossovers. I was wondering what the differences would be? But maybe we can start a new thread instead of hijacking this one. Nice OB design BTW. ;)

Yeah, that's me. And yes, we should start another thread about Open Baffle design.

Thans Panomaniac,
Very interesting indeed and not too bulky.The only problem i have with this system is that it uses a helper woofer + an extra amp + an extra active crossover.I really want to keep my system very simple for two reasons:
1.Space in the room:I already have two preamp(one per channel)and two monoblocks amplifiers(300B),on top of a tuner,a turntable which takes space,a CD player.I dont see myself adding an amp and an active crossover to all that.
2.Apart from the space i have a tendency to try to go for simple systems with no subwoofer.I dont mind sacrificing part of the low end(and by the way the upper end of the spectrum that i hear less and less) and i am more and more striving for systems which are musical ,lively and natural.
Thanks again for the suggestion;
Charly.

Il n'ya pas de quoi!

The helper woofer is silent on some tracks, you won't hear it on "girl with guitar" tracks, but it really helps when you need it. The bass amp need not be complicated. A simple plate amp will do, you can even run the subs mono from the plate amp without too much penalty. Use your 300B amps for the 604s.

Otherwise, I'd try to get the T/S parameters and work with GM to design a nice MLTL box. You can start with what he's given you and work on the ports.

David,
The only corners i could use are covered from floor to ceiling by bass traps(minichunks) made of rockwool and covered by 5 thin panels of wood of 2'x2' for each corner not to deaden the room.I would have to remove 3 of them in each corner to allow enough space for the two 604 and enough air around the drivers.I will then have in each corner one covered bass trap of 2'x2' at floor level and another one at ceiling level ,leaving enough space in between for a baffle about 3.5' wide 6.0' high ;I dont know wether this is enough to do the trick. If i get rid of the 2 bass trap together,i dont know what kind of impact it will have on the acoustic of the room which i spent months to treat acoustically with decent results for a relatively small room. By the way,when you refer to" Eq or series resistance to balance the system" ,how do you achieve that?
Any way we have got a potential option that i could work on with some additional guidance.
Regarding closed boxes not to have to worry about measures of the speakers,how big is "large enough"?I have to tell you that the 11.3 cb feet of my friend 's speakers are the maximum size i can accomodate .Actually i would prefer taller but not as wide boxes.
Thanks again for your input David.
Charly.

I don't have any bass problems with mine and I'm running them in open backed 12 foot cabs against the wall and driving them with a 16 wpc Marantz receiver. I shot a couple of videoa of them tonight in case you want to hear them.
http://www.youtube.com/watch?v=QOXRV...ature=youtu.be

http://www.youtube.com/watch?v=fgTzB...ature=youtu.be

Thanks Cradeldorf,
On my computer,it very difficult to give justice to your speakers.If i understand well, you have simply build boxes with no back panels,the walls of your room being the back panels!Interesting and pretty simple.What dimensions?

Shame on me!
When giving you the volume of the enclosures that i listened to at my friend place i gave the right external dimensions but the internal volume is 8.26 cubic feet( that is in good French 230 liters and not 320 liters!).So forget about the11.3 cb ft that i mentionned at the beginning of the post and which made the enclosures so big for a pair of 604.
I dont know wether this is going to encourage you to help me or to prevent you to do so.We shall see.
Dyslexic Charly.

Here's the lowdown on my build.
http://www.hostboard.com/forums/f700...-building.html

Nice looking cabs. I see you went with the compact bookshelf model. :p

Hi Cradeldorf,
At least when you go for big,you DO IT!Beautiful beasts !If i put those in my room i dont think i can open it anymore.Anyway,well done and thanks for the pictures.
Charly 1944

Il y a de quoi,Panomaniac,
Let me know wether we should go on in French!Actually,your suggestion to go for an MLTL solution guided by GM after measuring my speakers is probably the more reasonable one.But it implies that i equip myself with measuring devices (an adapted mike and a sound card i guess), that i learn how to properly use them, and that when the measures are done, GM agrees to help me and has enough time to guide me in the design and the buiding process.He will tell me wether this is the case but i understand he his pretty busy with his house .So all that may take time.
Meanwhile i am tempted to try to improve my friend's enclosures by two combined approaches:
1. Reduce the size of the present rectangular opening empirically, the way Altec Best recommended ,and test the impact on the performance,simply by listening.This will be done on monday on my friend's speakers.
2.If that works,Change then the dimensions of the enclosures while keeping the same internal volume in order to get the height of the speaker more in line with my ear level .So increase the height of the boxes and reduce the width and the depth accordingly.My challenge here is to select a good a ratio to reduce resonances and minimize damping.They are many golden/desirable ratios published and i have no clue wether some have proven better than others.Help is welcome.
This will cost me around 400 USD and allow me to listen to music while preparing the MLTL solution if i am not totally happy with what i have.
Any thoughts,monsieur ?

Reston en Anglais, pour nos chers Anglosaxophones. ;)

Good idea to get something going for right now, your approach seems reasonable. Measuring the T/S parameters can be done fairly cheaply with a volt meter and some resistors, but it's tedious. I use the little WT3 from Parts Express, but the original Woofer Tester II (WT2) is supposed to be even better. They make measuring the drivers a snap. Once you get accurate T/S parameters for your drivers, then GM can proceed, if he has the time. You'll want to define your maximum dimensions before he starts, tho. That way he won't go to the trouble of designing an optimum box, only for you to find it too big. Figure out how big you can go first, then see if he can do something with that. Right, GM?

I think you'll be very happy with a reasonably sized MLTL for the 604s. I had a pair here in giant boxes, and they were among the most dynamic drivers I've ever heard. They were GPA recones and new diaphragms, BTW. Next step is crossover. Have a good look at Jeff Markwart's designs.

FWIW, even tho I had been listening to big Altecs since birth, I didn't know anything about them until I moved to Paris and got tangled up with the Revue de l'Audiophile crew - many years ago. Sure opened my eyes and ears! Now I'm an Altec junkie and find myself in good company here.

Quote:

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Originally Posted by Panomaniac

They make measuring the drivers a snap. Once you get accurate T/S parameters for your drivers, then GM can proceed, if he has the time. You'll want to define your maximum dimensions before he starts, tho. That way he won't go to the trouble of designing an optimum box, only for you to find it too big. Figure out how big you can go first, then see if he can do something with that. Right, GM?

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It would certainly be best, but in the scheme of things, accurately finding each driver's Fs since he's driving them with 300Bs is all that really needs measuring assuming his friend's speaker's 'footprint' is still acceptable and even these can be found 'close enough' empirically via vent tuning and white noise to find where the woofer stalls out same as most DIYers once did.

Really, T/S specs are all about seeing how small a cab one can get away with and still have acceptable [mid] bass response. When size isn't a major issue, tuning flexibility normally increases with increasing size up to I.B. requirements.

Anyway, I already 'ran the numbers' earlier this week that should be vent tunable from ~27-42 Hz depending on driver Fs, just can't do an accurate sim without T/S, so just a matter of writing up a response while I'm in 'rain delay' mode.

GM

Quote:

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Originally Posted by charly1944

Hi GM,
I dont know where you are located in the US but it seems to me that you are on the site either very early in the morning or very late at night!

Actually GPA told me that they are not used to measure the speakers as a standard service .Since i insisted to get my 604 measured after the reconing(i was advised by Jeff Markwart that it would be useful for cabinet and crossover design)they accepted to do it but then had no time to actually perform the measurements.I guess they had other priorities and actually i was not ready to wait for weeks.

For now and without measured elements to guide me ,i guess i have multiple options

1.To copy my friend's enclosure and to change(reduce) the dimensions of the vent and assess the results by listening.

2.To keep the same design (bottom vent boxes)but change the dimensions of the boxes and of the vent while keeping the total volume.In this option i noticed that for the width vs depth they are a lot of acoustic ratios published and none of them correspond to the golden ratio.So i am a little bit at loss when it comes to select one of those.Any recommendation?

Regarding the height, my ear are at about 3 feet from the floor.So what could be the ideal dimensions of the boxes(without the stands).And what distance should i keep between the upper part of the speakers(rear mounted)and the upper part of the front baffle?

Last but not least ,what should be in this set up, the dimensions of the bottom vent to get to an around 40 hz tuning?By the way,Altec Best suggested to go for circular vent rather than rectangular one.

3. to change the design and go for an MLTL( or a OB if the dimensions are reasonable in this relatively small room -12x16 feet).

What would you advise me to do .

GM,if i take too much of your time,let me know,i will understand.

Thanks,
Charles

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Greets!

I live in a suburb of Atlanta, Ga. [EST] and being a life long insomniac, am up all hours, typically just ?cat napping? when I can since retirement.

Not surprised with GPA?s ?attitude? towards your request.

Yes, there are a lot of acceptable ratios and since the wider the baffle, the better overall, it really boils down to how wide [or deep] you can tolerate. I have a nomograph that makes it easy to see if ?w? x ?d? preferred is an acceptable ratio and how close I can match it, so not a problem.

For a ~36? floor/ear height it would be around 54.25? i.d. [inside dimension] for ~11.3 ft^3 using 19 mm thick construction and assuming setting on the floor with the vent on one of the sides near/at the bottom. Width x depth would normally be an acoustic or golden ratio to minimize internal damping.

Using ~24? x 15? i.d., makes it ~the same o.d. width as your friend?s cabs and an acceptable acoustic ratio. Driver offset from the top would be ~18.93? i.d..

Since you?re driving them with 300Bs, tuning them to Fs will need to be found empirically if you want the most efficient power transfer, so a removable vent baffle is a good plan. In this case, square or rectangular is easier to adjust tuning as you start with a probably too large a hole and progressively block it off until Fs tuning is found, then make a permanent vent baffle with the correct area as opposed to trying many different diameter ones.

The 604D had a 40+ Hz Fs, though it seems reasonable that the re-cone Fs will be closer to 30 Hz like later models, so allowing for up to a ~42 Hz tuning [Fb] just in case, a baffle thickness ~12? diameter [~113.1?^2 area] reflex vent is probably the largest and ~4? [~12.57?^2] the smallest needed if Fs should be really low like some E series. If the vent turns out needing to be < ~6? [~28.27?^2] though, then it needs to be tuned with a ~6? diameter pipe of the correct length.

Note that even tiny air leaks will raise Fb.

Internal damping would be Altec?s recommended top, one side and back with 1? acoustic fiberglass insulation or similar, though being a MLTL it?s typically not necessary to damp below ~ the cab?s midpoint. Some folks find even this amount too much due to the cab?s naturally high vent damping, so you may find that just a pad at the top, one side and back opposite the driver is sufficient. One person even wound up with no internal damping for a similar alignment S.S. driven 515B MLTL, only ?critically? damping the vent.

WRT bracing high aspect ratio cabs, what matters most is to run panel type stiffeners down the long panels, adding at least one set of interlocking stiffeners to tie all six sides together, positioned to also support the driver. Some folks use ?window? bracing, but these may negate some of the ? WL TL action, so don?t recommend them. Since the highest pressure is at the closed end, you can?t hardly make the top too rigid/massive, so making it double thickness or at least well braced is a good plan. If the bottom is setting on the floor, it normally doesn?t need any bracing other than any required to make the cab stable. Spaced up on legs, it ideally should be as rigid/massive as the top.

WRT OBs, it should be extremely rigid/massive to compensate for the lack of tie bracing, with sand filled double plywood panels proven to be an acceptable tradeoff between performance, weight for < ~0.7 Qtb systems. As Qtb increases, the panels need to become increasingly absorptive to damp system ?ringing? to the point where some folks have made excellent performing OBs and even TLs from braced Styrofoam or insulation board for very high Qts drivers.

WRT panel size/shape, this is so room, placement and system Qtb dependent that most folks just make it as large as they can accept in the desired location and then EQ it to get the best overall tonal balance. Again, using golden or acoustic ratios for the panel and even driver location is desirable.

As for what type of cab loading is best overall in your room, OB, IB or ideal compression horn is the theoretical ideal, but to go low with any authority with the first two requires a considerable amount of acoustic efficiency and the MLTL adds ~6 dB, so to match it with an OB would take at least one closely coupled 'helper' 15" woofer and 2x times the power, a significant price adder.

GM

Quote:

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Originally Posted by charly1944

Actually GPA told me that they are not used to measure the speakers as a standard service .Since i insisted to get my 604 measured after the reconing

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Hi Charly ! I had a similar experience with my re-cones. I needed them measured as well.So I asked Bill and he said it was really something they didn't want to do.But I paid him for the service and they came back with the T/S parameters.What was more important to me was that the recones were matched since my project is a dual woofer (416B) Corner box.

Hi GM,
You replies are as dense as they are interesting!
Could you please clarify few points for me:
1.What WRT stands for?
2.When you refer to" offset driver from the top",are you measuring this distance from the center of the driver(as opposed to from the top of it) to the top of the front baffle minus the thickness of the wood used?
3.Baffle thickness reflex vent of 4'' (min) to 12'' (max):Are you refering to a vent which depth is just the thickness of the wood(3/4 inch)?

Enough for the clarifications.Let me now report what we have done with my friend's enclosures yesterday ( i don't know wether you read that i made a mistake when communicating the volume of his enclosures.They are actually,8.3 cub.ft and not 11.3 .Quite a subtantial difference):
I made two small panels of wood,5 mm thick fitting in the inside of the box, in which i cut two different vents (respectively A: 11.8'x7.8 ' for the first one and B:8.9'x5.9' for the second one) of much smaller size than the present bottom vent.Using the (B) panel just laid on the on bottom, and therefore reducing the substantially the present vent resulted in a dull and flatsound.The music was gone!We then try the A solution:The results were close to the one obtained with the original vent with may be a slightly better bass,but no substantial improvement.This mean that for a given height of the feet(2'') the results are not very sensitive to the size of this type of vent unless you change it drastically.We also tried the smallest vent(B) with higher stands but it was not better.Further increasing the feet height(from 2 to 4'') while keeping the original vent gave a brighter and more open sound but at the expense of a lack of precision in the mid and high freq.The only thing we did not try was to shorten the feet (to 1.5 inch for instance) in order to get a deeper bass while keeping or improving the overall balance and quality of sound .So the original set up and the set up with vent reduction A were about the best one in terms of outcome with small differences not justifiyng a change.I dont know wether the conditions of experiment were good enough to draw these conclusions but it is indeed disappointing and tells me that we could not improve what the gourou, who inspired this design more than 20 years, did at this time.
So i am stuck with a present enclosure giving a pretty decent result (although not enough bass),that i could assemble in a day,with speakers the centers of which are probably to low for my ear level (25.2')
As as said i dont see myself going for an OB solution if it requires additional amplifiers,speakers and and crossover.I am not sure i understand the principle of an MLTL and what i read in French was pretty obscure about it although i understand it is a pretty efficient approach interms of bass extension.I never listened to MLTL loudspeakers,at least to my knowledge, but if you think a well designed MLTL will give additional bass extension while preserving the musicality of those vintage design i am ready to go for it and to get equipped so that i can measure the Fs of the drivers(as well as the other TS parameters).Panomaniac indicated to me an easy way to do so with Dayton WT3 (or 2) ,apparently pretty simple to use,but after a check these tools would not allow me to measure the freq.response and i believe if i go for this project i should have the necessary measuring equipment and capabitities to assess what i do by measuring as well as by listening.Could you give me a link where i can see plans of the type of MLTL you are considering so that i have a good feel about the construction of it.
I like the idea of a removable vent baffle so that one can easily adjust the vent until one reaches the desired results.I guess that would be the back panel since i tend to favour rear mounting speaker and removable back panel is the only solution to easily access the speakers(By the way, I have no clue about the pros and cons of vent on the back versus the front vs the bottom).Should i understand that then,, you move to a permanent panel with a circular vent of the same surface as the square or rectangular one previously selected?
In terms of external dimensions, 25.6 ' width is clearly a maximum that i can accomodate.Sligthly less is better.When it comes to depth ,around 18 ' is a max as it would put the back the enclosure about 20 ' away from the bass trap in the corner.i am pretty free with the height which could go as far as 51.2 inch including feet.
I guess it is getting late here and it is about time for me to get some sleep and to let you go for a nap!Thanks a lot for sharing your precious knowledge.
Charles.

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