Help please.

[jackfish]

I am in the process of building new cabinets for a double Large Advent speaker system with the acoustic centers of the speakers aligned. However, to begin my design sketches I would like to know the horizontal distance between the centers of the drivers on the original Large Advents with the masonite ring around the woofer and the masonite square under the tweeter. If someone could get their tape measure out for me I would appreciate it. Thank You.

[Doug G.]

I'm assuming you mean with the speaker laying on its side. I get 12" measuring the distance between the planes and about 12 5/16" measuring directly from the center of one driver to the other.

Doug

[Doug G.]

Oops, forgot. Sounds like a great project. You are going to put all the drivers into one cabinet? Probably with a divider in the middle?

Doug

[jackfish]

Doug, yes I will put four drivers in a single cabinet with the tweeters moved back from the woofer baffle to align the "acoustic" centers. Do you know if just doubling the volume of the enclosure for the two woofers will work or is there another formula applied when doubling the woofers in an enclosure. I saw where someone calculated Q and Vas for the Large Advent woofer (masonite ring) here:

Measured voice coil DCR (Re) with a Fluke meter at 4.83 ohms.

Piston diameter measured (estimated) at 20 cm = 7.87"

Used Liberty Audio Suite (LAUD) added mass method, delta mass = 52 grams for -33% delta f.

Midband (80 Hz) test voltage was about .5 Vrms.

Woofer had been used (broken in if you believe in such things) with music before testing:

Fs = 18.23 Hz

Vas = 250 liters or 8.82 cu ft

Re = 4.83

Qe = .364

Qm = 2.93

Qts = .324

Mms = 42.28g

Cms = 1.80 mm/N

Bl = 8.02 Tm

no = .400 %

SPLref = 88 dB

Does anyone have the same information for the New Large Advent woofer?

[dynaco_dan]

Hi Jay;

Just a thought for now, Jay.

I believe you need to keep the enclosures separate inside.

Each woofer needs it's own original enclosure volume rather than twice the volume.

I do believe that the bass will sound different otherwise.

I would definitely allow extra measurements for added solid wood bracing, which the originals don't have, not plywood or MDF, on all surfaces.

AR-3A's have substantial bracing in their enclosures, just to name one.

Another thought, 45 degree cut strips of solid wood glued into the joints will make the cabinets stronger.

Other suggestions that may be of interest to you, something Frank of avahifi.com suggested, plasti-clay or Plastercene, what we played with in elementary school, coat the entire inside of the cabinet about 1/4" or more and non working structure of the drivers.

Something I read about years ago, was coating the entire inside of the enclosure, except working structure of the drivers with car body undercoat.

Only read that one once, and no further comments about it.

Both these ideas are to reduce the cabinet resonances.

Frank claims that the putty method alone truly sonically improves the sound.

He guessed at about 5 - 10 pounds per enclosure.

Heating the putty for one minute in a microwave oven makes it softer to work with, so he says.

Good luck.

[jackfish]

Thanks for the input. I understand now I will have to make separate acoustic suspension enclosures for each woofer. I don't have my book on building speakers in front of me right now, but if I reduce the height of the enclosure and increase the depth is there some ratio of dimensions that cannot be violated? 52" tall woofer enclosures with the tweeters on top of that is going to be too tall. I'd like to bring the woofer segment down to about 36"-40" tall or two 18"-20" tall enclosures for each woofer. Maybe I could incorporate the tweeters into the top woofer enclosure maintaining the correct volume but also accommodating the vertical alignment to center the tweeter and woofer drivers.

[Carlspeak]

The Loudspeaker Cookbook which has become a bible for speaker builders says the following about two woofer formats:

Fs will be the same as for a single driver

Qts will be the same as for a single driver

Vas (and associated box volume, Vb) will be twice that of a single driver.

Combined impedance will be half that of a single driver in a parallel connection and twice the value of a single unit when connect in series.

Voltage sensitivity will increase +3dB for a parallel connection and

-3 dB for a series connection compared to a single driver. Since any two drivers operating in phase will increase the power sensitivity by 3 dB over a single driver, the parallel connection for a given volume setting on an amplifier, will give a total of 6 dB greater SPL. A series connected pair, for the same volume setting, yields a identical SPL of a single driver.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[Pete B]

>Thanks for the input. I understand now I will have to make

>separate acoustic suspension enclosures for each woofer. I

>don't have my book on building speakers in front of me right

>now, but if I reduce the height of the enclosure and increase

>the depth is there some ratio of dimensions that cannot be

>violated? 52" tall woofer enclosures with the tweeters

>on top of that is going to be too tall. I'd like to bring the

>woofer segment down to about 36"-40" tall or two

>18"-20" tall enclosures for each woofer. Maybe I

>could incorporate the tweeters into the top woofer enclosure

>maintaining the correct volume but also accommodating the

>vertical alignment to center the tweeter and woofer drivers.

I'm not exactly following what your planning to do here. Are you talking about a woofer-tweeter-tweeter-woofer (WTTW) layout?

In any case, it is best to have all the drivers as close as possible, to improve the off axis smoothness of the response. The fairly large driver spacing was a mistake in the original Large Advent, in my opinion.

Pete B.

[Pete B]

>Doug, yes I will put four drivers in a single cabinet with

>the tweeters moved back from the woofer baffle to align the

>"acoustic" centers. Do you know if just doubling

>the volume of the enclosure for the two woofers will work or

>is there another formula applied when doubling the woofers in

>an enclosure. I saw where someone calculated Q and Vas for

>the Large Advent woofer (masonite ring) here:

>

>

Measured voice coil DCR (Re) with a Fluke meter at 4.83

>ohms.

>Piston diameter measured (estimated) at 20 cm = 7.87"

>Used Liberty Audio Suite (LAUD) added mass method, delta mass

>= 52 grams for -33% delta f.

>Midband (80 Hz) test voltage was about .5 Vrms.

>Woofer had been used (broken in if you believe in such things)

>with music before testing:

>

>Fs = 18.23 Hz

>Vas = 250 liters or 8.82 cu ft

>Re = 4.83

>Qe = .364

>Qm = 2.93

>Qts = .324

>Mms = 42.28g

>Cms = 1.80 mm/N

>Bl = 8.02 Tm

>no = .400 %

>SPLref = 88 dB

>

>Does anyone have the same information for the New Large Advent

>woofer?

These are my measurements and let me just warn you that although many suggest such a high delta mass as I used here, I prefer less as I believe that such a high value introduces measurement error with many drivers. I was just following the common guidelines here, and it took some thinking to refresh my memory about this measurement method. Fortunately, the delta mass is only involved in a few parameters, Vas, Mms, n0, and SPLref. It would be best if everyone measuring drivers would report their results since a statistical average would be better.

What was good about the measurement was the low Fs, indicating a good loose surround used in the rebuild.

Pete B.

[jackfish]

I was thinking of WWTT. If, indeed the woofers can be in the same enclosure, then all of the drivers can be in close proximity. The tweeters would be in a plane behind the woofer baffle to align the acoustic centers of the drivers, similar to the old Technics Linear Phase speakers in an attempt at better time coherence amongst all of the drivers.

[Pete B]

The WWTT has a problem where the distance from the farthest woofer to the tweeters is long, and therefore the off axis response will suffer with asymmetrical lobing.

Putting the woofers in one large box can be a problem. The box resonant modes will be lower in frequency with a larger box, and might fall into the woofer pass band. The longest dimension is usually the problem, but making them all the same aligns all the primary modes. Most damping materials are more effective at higher frequencies and it is therefore better to have the modes higher up.

It's complicated, safest is to use a divided box.

Pete B.

[Guest SpruceMoose]

here's a quick look at what i did for a set of doubles:

http://www.classicspeakerpages.net/dc/dcbo...mesg_id=2&page=

the speakers are 4 feet tall, 18 inches wide, and about a foot deep at the base. the woofer chamber is divided with a sloped piece of mdf, with one chamber slightly bigger than the other to help avoid overlapping resonances.

more details here:

http://www.classicspeakerpages.net/dc/dcbo...g_id=110&page=6

[jackfish]

SpruceMoose, that looks like the route I will have to go. Do you have any dimensioned diagrams of your design? Also, what modifications did you do to your Dual 1245? I have one in very good shape and would like to make it better.

[Guest SpruceMoose]

here are the outside dimensions:

48" tall

18.5" wide

14" deep at the base.

starting at 12" up from the bottom the cabinet tapers to 10" deep at the top.

made with 3/4" mdf.

a seperator baffle starts at the front of the enclosure between the woofers and goes to the back, sloping downwards (i think).

all access is from the woofer holes.

the tweeters are both mounted in the upper half's air space. since they are sealed back tweeters they do not need seperate chambers.

i used some original foam and some foam i had lying around. 5 pieces, 2" thick x 12" square in each chamber. the tweeters are mounted next to each other, above the top woofer. this puts them at ear level when seated on the couch.

the "outboard" tweeters are angled in towards the center of the listening room to widen the "sweet spot", much like toeing in a set of speakers.

the original crossovers were used, and the 2 "systems" in each enclosure are wired in parallel, giving about a 3 ohm load to the amp. no problems driving the setup with my kenwood vr6070. it is driving the 2 double l/r speakers, a double advent center channel, a pair of minimus-7s on the right wall, a pair of minimus-7s on the left wall, and a pair of minimus-7s on the rear wall.

can be made WAY too loud with very little effort. great for movies (nobody believes my speakers are about 30 years old), and wonderful, as always, for music in 2-channel mode. or fake surround if you like.

as for the Dual, i just made an mdf base with leftover scraps and painted it with a gray version of the black granite paint i used on the advents. no big deal.