the best 515's for midrange

[jack6428]

My first VOTTs were handmade by me in jr-hi (early 70,s). They had VOTT components but were in straight front cabinets. These are now being used for my home theater (different room).

These A7's were bought this summer from the original owner who bought them in the late 60's for his home stereo and has not used them much in the last couple of decades. I don?t think they were ever overpowered They are mint. The 416 (these are 416A or -8A) cones look and sound great, except sometimes if I crank up the bass, they max out and hit the front wood (one reason I want separate subwoofer).

I am seriously considering keeping the 416?s (not changing to 515?s). Reconing locally is over $150 (with Altec parts) and not sure of remag cost. I know it's hard to say, but what would the benefits be to recone and remag these 35yrs speakers that have had little wear? Can I get them reconed to a higher power (like the HP option they offer on the 515)?

Regarding putting the future sub in the bottom of the A7, I have not read all the links on this site yet, but am concerned about:

- having to add massive reinforcement to these mint cabinets
- will the subs bass reflex alter / interfere with the intended design of 416?s only
- what port size to use (although I have read that the current huge rectangular opening is not really even the best size, even though it is Altec?s design ? read it?s should theoretically be something like 7 or 17 sq-in?s)

Currently the A7?s are in the corners at 45 to each wall in a 30 ft wide room. If I don?t put the subs in the bottom of the A7?s, I have two choices:

- Put on side walls (flat against wall), the sub cabs would be about 14 inches deep so the sub front vertical corners would touch (at a 45 degree angle) the front vertical corners of the A7?s --- will this cause some type of interference with the A7?s?.
- Build a cabinet to put under the A7?s (except this would raise the horn higher, which would no longer make it the same height as my ears when sitting in my chair --- not sure if this is a big deal?
- If I build a cabinet to put under the A7, should I build one with the sub front rim flush with a flat baffle or should I acquire or build some 816?s (flared horn cab very similar if not exactly like the flared wood on the A7)?

Jack

[amh]

Jack,

Hey, the only dumb question is the one you don't ask. Now we're pushing the envelope on my knowledge base too. For us hobbyists some of these concepts are pretty tough to grasp. To alot of the guys here they're second nature. That's why I lurk around here, it's a learning thing.

So you experts chime in and help out where I mess up.

I think you need to separate the two concepts of horn loading and ported reflex enclosures. A horn's frequency response is a function of the horn's size and shape, and the driver's parameters. A horn is really like a transformer that couples the driver to the air. No ports needed. Generaly, the larger the horn, the lower the frequency. As far as the rear enclosure for a front loaded horn, I don't have a formula for that. Another board member here thinks the volume of the top of your A7 with horn flares filled as well, is about right. Since you are sub-woofing you would XO your 416 at say 150Hz-200Hz and use it as strictly horn loaded from there up to the next XO point. Because your A7s horn rolls off at about 120Hz on the low end you should be OK. It's tough to think of a 15" driver as a midrange isn't it.

Senior members....What is the relationship between the box that closes of the back of a driver and a horns performance(in front loaded horns)?

Now your sub would be a true bass reflex enclosure. No horns involved. Here's some formulas for that. They should be valid for drivers with a Qts of .8 or less, and should yield an optimized enclosure. Minus port tweaking.

Where Fo=free air resonance of driver
Qts= Q of driver
Vas= compliance of driver

For Vb
Vb=Qts^2.87 x 15 x Vas

For bass cut off, or F3
F3=Qts^-1.4 x 0.26 x Fo

Next figure the frequency of resonance for the enclosure, or Fb.
Fb=Qts^-0.9 x 0.42 x Fo

Finaly, you can figure the port duct length for a given port area(choose a port area that fits your baffle and won't whistle, then use this formula to get the duct length).

Duct(port) length, or Ld.

Ld=(2691 x Sd)/(Vb x Fb^2) - 0.88 x Square root of Sd

Where Ld=duct length in inches
Sd= Duct area in sq inches
Vb= enclosure volume in cu ft
Fb= enclosure resonant frequency in Hz

Miserable to write out without the right keys so see if this helps.

First multiply your desired duct area(sd) by 2691. Next divide this intermediate result by the volume, Vb, and then divide this second result by the square of Fb. From this number subtract 0.88 times the square root of the duct area, Sd, to obtain the final result.

Now for your Rane RA30. That won't help you with time delay or phasing. It will help you set up your EQ though. It is just basicaly a spectrum analyser. Your AC22 will allow you to set some delay.