Design that has 24 db/octive roll-off at 100 Hz

[Jimmy154]

I have 2 amps that were designed for Acoustic Research speakers. I would like to use them and some 15's in speakers I hope to build. The amps are carver sunfire rated at 500 watts (think they're really 500 rms? The subs I have can handle like 750 rms, but I can get smaller subs if the amps are over-rated). They have a fixed x-over at 100 Hz. I think the slope might be 36 db/octive, but more likely I think they're 24 db/octive.

So I'm looking for a design that will roll-off at the bottom end at 100 Hz at 24 db/octive. I think it will have to be ported. Sealed will not work I think because I would have to use large inductors at 100 Hz or bi-amp to achieve 24 db/octive. I've seen focal do this kind of ported midrange, so I figure it might sound good if done right. Are these assumptions correct?

Any body know of a ported design like this? Maybe tang bang, maybe MTM I think it might have to be a fairly loud design to match my subs.

[Bose(o)]

Sorry, having trouble decyphering your question....is that a subwoofer you want to build or a full-ranger that reproduces signals from 100Hz and above.

[Jimmy154]

My fault, I have some amps and 15's. The amps are 24 db/octive LP at 100 Hz for those subs. Subs and amps are not built yet, but I already have them.

I'm looking for a design that's 24 db/octive HP at 100 Hz. I seen some one build a MTM tang band out of W3's and some tweeter, but I can't find them now. I don't know how great ports will sound or even if or how much out-of-phase they are with the midrange driver. It's hard to find designs that are ported (roll-off 24 db/octive I assume) and have an f3 of 100 Hz and are loud enough for my 500 watt subs.

I got another idea maybe I can HP a 2-way sealed that rolls-off at 100 Hz with a cap giving me a total 18 db/octive roll-off which should match the 24 db/octive pretty well, no?

[Timn8ter]

YGM

[sreten]

I think the slope might be 36 db/octive, but more likely I think they're 24 db/octive.

I really don't like conjecture. You are asking for an answer to a
question based on an assumption, even if the answer is correct
its the probably the wrong answer.

You need be definite about this and the type of slopes used.
(Butterworth / Bessel / Linkwitz-Riley)

The only specs I can find say 36dB/octave at 100Hz and 3.2KHz.
This is a highly dubious specification in my opinion, even if its
referring to eventual acoustic slopes.

AR's homepage doesn't seem to be available.

http://www.hometheaterhifi.com/volum...rs-1-2000.html

Indicates the speaker has a line level LFE direct input.
This makes the crossover specification extremely dubious in my opinion.

Apparently there is a full review of the AR1 in June 99 Stereophile
magazine, does any have this ? does it contain measurements ?

sreten.

[kelticwizard]

Originally posted by Jimmy154


So I'm looking for a design that will roll-off at the bottom end at 100 Hz at 24 db/octive. I think it will have to be ported. Sealed will not work I think because I would have to use large inductors at 100 Hz or bi-amp to achieve 24 db/octive. I've seen focal do this kind of ported midrange, so I figure it might sound good if done right. Are these assumptions correct?

Any body know of a ported design like this? Maybe tang bang, maybe MTM

I do believe a ported design such as this is doable. I would recommend a midbass/midrange with a Qts of 0.25 or so. This will give better transient response, allow you to move the F3 or F6 up to the point you wish. It also moves the tuning frequency somewhat below the passband, which would be desirable. The slope should be anywhere between 3rd order and 4th order.

I can vouch for the slope being good, but I cannot vouch for the advisability of the approach, since I do not know if the ported speaker will gently remove itself from the circuit below the crossover frequency, or if it will draw power at those frequencies and cause undesirable effects. I would have to get advice on that from someone else. I have never done it this way.

But slopewise-yes, I think it can be done. Gotta run, will do some simulations later tonight if I have the time.

[kelticwizard]

You might try asking your amp question at this Classic AR site.
http://www.arsenal.net/speakers/ar/ar.htm

I agree with Sreten, it is important for you to know the slope of the active crossover in the amp, if it has one.

It can be tested with the use of a freeware tone generator and a simple voltmeter. Voltmeters, if you don't have one, are highly borrowable-most people do have them-or very inexpensive, (like 15 bucks). Run a series of test tones from your computer via a $3 cable from Radio Shack or similar store, and measure the voltage.

Will give details tonight.

[Jimmy154]

It's never as simple as I think it's going to be.

Kelticwizard I have the tone generator (audiotester) and the $20 worth of wires from radioshack and home depot. And the friend with the voltimeter also .

I'm getting ahead of myself (since I don't know the slope of those sub amps), but Timn8ter seems to have a pretty good design to match my subs http://www.alegriaaudio.com/aural_imaging_isa.htm. Only thing is those Tang Band W3's have a stamped steel magnet, which I like to avoid like the plague . What does YGM mean?

The midbass/midrange with a Qts of 0.25 sounds like a better idea (damn W3's with their stamped steel frames), but I have no designs yet. I don't want to design my own x-over I think . What does "It also moves the tuning frequency somewhat below the passband" mean?

[sreten]

you really need some hard information on the amplifier
or be able to analyze what happens to the speaker
connections signal on the amplifier board.

A 24bB/octave reflex @ 100Hz with a straight connection
will overload hideously on low bass.
The original AR1 speakers appear to use a sealed alignment.

Like I said the basic information about the AR1 speaker is
extremely dubious.

I extremely recommend getting hold of the Stereophile review.

sreten.

[Jimmy154]

The only difference I remember between the AR1 specs and the 315HO specs (I used to own a pair of 308HO, that's why I remember looking at the 315HO specs years ago) at AR website is that the 315HO has 24 db/octive slopes all through the speaker and AR1 has 36 db/octive slopes. All the 310HO-315HO had sealed woofers. My 308HO was vented, that little beast . Numerous noise violations and an aventual arrest thanks to my friends . . . ah precious drunken non-memories .

I'm not sure how to find that magizine. Maybe in that dreaded place the libriary. I don't know how a review will give me specs on the sub amp, seems doubtful. But I will try testing it with a signal generator and a voltimeter, as soon as I find out how.