Here's the lowdown on my build.
http://www.hostboard.com/forums/f700...-building.html
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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.
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.Quote:
Originally Posted by Panomaniac
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
Greets!Quote:
Originally Posted by charly1944
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
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.Quote:
Originally Posted by charly1944
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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