the ultimate A7 components

[jack6428]

I am considering upgrading my A7's.

They currently have:
416A 16ohm woofer
511B horn with 802D alnico driver
N500G crossover

a) If I upgrade to a 515 woofer, what version would be the best?
What is a 3156 woofer (I can get a pair right now)?
What impact would using an 8 ohm woofer instead of a 16 ohm have?

b) Can I send in my drivers to turn them into 909A or 902A? Which one is preferred? Also, I have a pair of 806-8A drivers, which are a little newer than the 802D's, but I've been told they are not as good as the 802D and are not alnico magnets - is this true?

C) Is the 500 Hz crossover a better choice than an 800 Hz? Is there a better choice than the N500G I have?

D) What is biamping? Does it replace the crossover?

Jack

[taudo]

Jack,

Here is my two cents on this topic. FWIW, I'm currently upgrading my A7's, too. I'm also building in a subwoofer and there is a great thread here about doing this (building subwoofers into 825/828 cabinets)

> D) What is biamping? Does it replace the crossover?

1) In biamping you _do_ eliminate the passive crossover - and the insertion loss and distortion it creates. It also allows much more headroom and less liklihood of clipping. You use an electronic (active) crossover between the preamp and the amps. One amp is used to power each driver, so in a classic A-7 one would amplifiy all the frequencies above 500 Hz or so and another all the frequencies below. Most active crossovers have adjustable crossover points - and often delay circuits to allow you to electronically time-align drivers that are not physically aligned. I've chosen a Rane AC23B active crossover (a stereo 3-way unit) but haven't had time to play with it much. Several others on this board have commented favorably on it, and that is why I chose it. Plus, I love Rane's documentation! ( A little sense of humor never hurt!) Rane's AC 22B is a two way unit of the same design. (The "B" units have balanced XLR inputs instead of balanced TRS [i.e. phone plug] inputs.) It is also a good idea to go to Rane's website and read their tech notes on interfacing unbalanced gear with balanced stuff.

> a) If I upgrade to a 515 woofer, what version would be the best?

2) Generally, I think people feel that 515-G's are the best - but being a 416 guy myself, I'll defer to others with more experience than I have.

3) In a biamped situation I'm not sure that the impedance of the driver would make that much difference as most amps can drive a wide impedance range - but the audio engineers here will set me straight on that if I'm wrong.

HTH, Good luck! Keep us posted on your progress

taudo

[taudo]

Jack,

One more thing - I sure recommend having Bill at Great Plains Audio remag and, if needed, recone/rediaphragm your drivers [only the alnico need remag]. I had him do one of my sets and was truly impressed! My 416's and drivers look and sound brand new. He can also change the impedance of the voice coils for you to all match up.

taudo

[jack6428]

Hi Taudo,

I'll start looking into those bi-amp (tri-amps) you advised.

I didn't mention it earlier, but I'm getting a pair of empty A7 enclosures (curtosy of fellow user board member "acre"). Also, I have A7 components I put into my own cabinets in the 70's. They have (each):
1 - 416-8A
1 - 421-8H series II (guitar speaker)
1 - 811B horn with 806-8A driver
1 - N801-8A
I will be probably be raiding these cabinets of their parts.

I am thinking of using the new A7 empties to supplement the bass on the A7's I just got.

What would you think of using a tri-amp and sending the highs to the horn, the mid to one bass enclosure, and the lows to the other bass enclosure? If this makes any sense, what speakers should I use for the mid vs bass?

Jack

[taudo]

Jack,

Again, here's my non-expert, non-engineer take on this:

The 825/828 cabinets consist of a short midbass horn and a big bass reflex enclosure. The only "magic" is the horn, which rolls off at something like 125 Hz (from what others have said). Given that, the horn is of no use for low bass.

The bass reflex portion of the cabinet is just that - no better than any other. And it is quite big. Modern hi-excursion (sub) woofers are capable of making huge bass in small enclosures - so why fill up your room with an extra set of 10 cu ft enclosures if you don't have to? See BobR's comments in the thread "Small boxes for sub woofers".

It took me a while to get used to the idea of thinking of 15" drivers like my 416's as, basically, midrange speakers but that seems the best way to me. Therefore, I decided to add a sub to the existing 828 cabinet. Several others here have done so and the reports have indicated good results. I haven't got mine completed yet, but initial testing with small 12" standalone subs made a surprising improvement and convinced me to continue the project.

The advantage of the build-in is that no other boxes are needed.

Of course, if you decide to triamp the system you will need to give careful consideration to the choice of the _six_ channels of amplification then needed. Again, my take is that you need a fairly large solid state amp for the subs, and your choice for the MR and HF.

There is one other thing: I'm pretty convinced that subs contribute something important to the sound field and probably _should_ be as physically close to the MR and HF as possible. When I experimented with my standalone subs, I found that using only one (in summed mode) really made the stereo image flat in a way that I wouldn't have guessed. Using stereo subs close to my 828's gave a glorious soundfield! I was surprised, too, to find exactly this described in the Avantgarde literature I received only last night. Maybe it's a well-known phenomenon that I simply missed, but it's real. So, I'm thinking that where the subs are located is more important than often mentioned.

Again, HTH! Ain't this a load of fun!!

taudo

[jack6428]

OK Taudo,

I'll forget about the tri-amp.

On the subwoofer. Are you saying put another woofer in the existing bass enclosure. Would it be in parrallel with the existing and / or does it have a separate amp? What kind of woofer would it be?

As I sit here typing this with my new A7's blasting in the backround I must ask (maybe should be another thread) what is the best way to keep the sound from going thru my window to the neighborhood?!

Jack

[taudo]

Jack,

> I'll forget about the tri-amp.

====
I hope I didn't give you _that_ impression! Bi or tri-amping is one of the biggest improvements you can make - although it does require some thinking and planning. Lots of guys here will help if you've got the urge!
====

> On the subwoofer. Are you saying put another woofer in the existing bass enclosure?

====
Yes. You make a board to close off the large port and mount the new subwoofer there. In addition, you have to close off that section of the enclosure from the horn section, and strengthen the area behind the new subwoofer. Again, see the thread about "Subwoofers in 825/828 enclosures" for instructions.
====

>Would it be in parrallel with the existing and / or does it have a separate amp?

====
You _could_ do it either way, but using a separate amp for each of the drivers (i.e., triamping)is clearly the best way. The other way is to make the A7 system a 3-way system with a new 3-way passive crossover.
====

>What kind of woofer would it be?

====
That depends alot on just how humungous a bass response you want and the budget you have for speakers. Many here have used the 18" JBL 2245, and some have recommended the 18" 2242. The Bag-End Infra 18" driver is another possibility. I chose to try the experiment with a JBL 2235 (15").

Subs are designed to have very large cone excursion and to move alot of air. Those design criteria limit their upper end somewhat, though. The point is that 416's and 515 are designed to have limited excursion and don't make really strong bass. Their MR is much better though, at least in general.
====

> what is the best way to keep the sound from going thru my window to the neighborhood?!

====
My guess would be very expensive double glazed windows! Fortunately, I live on 30 acres and can't bother anyone but the foxes who live nearby!
====

taudo

[jack6428]

Hello again Taudo,

I'll read more on the sub in the same bass enclosure as you recommed. I'm assumming it will tell me whether I have to make another angled horn wood or if it's just mounted flush with the front plane.

I am think you are saying that a bi or tri amp is better than a passive crossover.

If I go with the new sub in my existing bass enclosure, will the tri-amp separate the frequency distribution? If so what ranges does it send to each (horn, existing 416, new subwoofer)?

Would the 421 guitar woofers that I have from my home-made speakers I mentioned earlier be candidates for the subwoofers?

New question - why does my new A7 enclosure have the bass section with the wood flared on the two sides and botton but the top is at a 90 degree angle to the woofer?

Jack

[taudo]

Jack,

> I'm assumming it will tell me whether I have to make another angled horn wood or if it's just mounted flush with the front plane.

====
Flush with the front plane.
====

>I am think you are saying that a bi or tri amp is better than a passive crossover.

====
Yup, by a bunch!
====

> If I go with the new sub in my existing bass enclosure, will the tri-amp separate the frequency distribution?

====
What splits up the frequencies is the active crossover. The amplifiers are just power amps.
====

> If so what ranges does it send to each (horn, existing 416, new subwoofer)?

====
All the active crossovers I've seen have a knob that lets you vary the crossover frequency for each driver/amp. Therefore, you can set the frequency that sounds best to you.
====

>Would the 421 guitar woofers that I have from my home-made speakers I mentioned earlier be candidates for the subwoofers?

====
I don't have the ability to look up the specs on the 421 right now (believe it or not I'm at work!) but usually guitar speakers are not good candidates for subs.
====

>New question - why does my new A7 enclosure have the bass section with the wood flared on the two sides and botton but the top is at a 90 degree angle to the woofer?

====
That is the MR horn. Ideally, it would be much longer, and all four sides would diverge according to the appropriate math function. However, the A7 horn is a compromise between horn efficiency and reasonable size/shape. Not perfect, but not bad, either (IMHO).

On the inside of the cabinet, can you see the _inside_ of the curved horn flares or are they sealed off?

taudo

[jack6428]

Hi taudo,

I hope I'm not getting you in trouble at work. My last office space had the computer screen in full view of people walking by (my back to the hall) - I actually got a motion activated squirel to alert me.

Anyway, thanks for all the great input!

Most of my recommendations so far, other than direct feedback from board members (I've only been revived by this placed for about a month), have been from a web link on one of my former posts called "should I keep my VOT's or upgrade", it was a link to some Altec Tech named Jim Dickinsen called "Soundpractices". He said the 909A is the preferred upgrade to the drivers. What do you (or anyone else) think?

Also, he said the 802G was the last last alnico drive. Do you know if (from my homemade stuff) the 806 driver I have is not alnico. If so, can I turn it into a 909A or do I need to send them the 802D's off my new A7,s?

Jack