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View Full Version : A7 Model 19 help....please



handsome
11-10-2014, 10:52 AM
Hi all,
I am very new to the Altec world and despite a lot of online research remain confused......I have the following 'bits' : 902-8A, 811B, 416-8C & A7 enclosures, I do not have a crossover. I think what i have is Model 19 drivers and an A7 enclosure, is this correct?

Money is unfortunately tight for me so I will not be buying any other driver/enclosure bits. Also due to financial constraints i am (obviously) rather nervous of blowing a driver. i intend building a crossover myself and would prefer a passive crossover (safer) but active will be quicker to whip up initially, so my questions are:

1. What crossover frequency?
2. What slopes?
3. Which Altech passive crossovers (if any) can i use?
4. If anyone has some schematics for suitable passive networks could you please pass on or point me at them?
5. I have seen many crossover schematics but they look rather complicated obviously some additional EQing is going on what corrections are these relevant to my 'bits' of course?

If i am posting on the wrong forum i do apologise. Any assistance will be greatly appreciated.

speakerdave
11-10-2014, 11:09 AM
How could it be that an active crossover would be "quicker to whip up initially"?

To use an active crossover would require a total of four channels of amplification. Is there some confusion about terminology?

To build any crossover you will need to buy parts. Do you have any sense what that would cost?

Using those 811 horns your crossover frequency should be no lower than 800Hz.

I think you should hunt down a pair of Altec 801-8A crossovers for now.

handsome
11-10-2014, 11:20 AM
How could it be that an active crossover would be "quicker to whip up initially"?

To use an active crossover would require a total of four channels of amplification. Is there some confusion about terminology?

To build any crossover you will need to buy parts. Do you have any sense what that would cost?

Using those 811 horns your crossover frequency should be no lower than 800Hz.

I think you should hunt down a pair of Altec 801-8A crossovers for now.

I guess I meant active would be quicker than passive....i have a bucket-load of op amps, polyprop caps and resistors etc hunting down the right value inductors bothers me more (our postal system is a bit buggered right now so rather dubious of delivery times from overseas).

I see on another post 1200Hz is recommended for the 811B and 902A.....

speakerdave
11-10-2014, 11:27 AM
You can design and build all the necessary power supply and circuitry?

You have the necessary amplifiers?

handsome
11-10-2014, 11:43 AM
Yeah i build tube amps for a hobby, never done speakers though. I am just confused re: the crossover as i asked in my questions. The drivers are all Great Plains Audio and almost brand new but the damn tings have been gathering dust for over 2 years and am tired of walking past them.....just want to be sure that i am getting the right components. I see the N1201-8A is correct for the Model 19 but will that sound/work well in the A7 enclosure?

speakerdave
11-10-2014, 11:56 AM
Is your question about the behavior of the A7 horn up to that frequency? I don't know the answer to that. Have you tried asking the denizens of the Altec user group board?

speakerdave
11-10-2014, 12:04 PM
I hope my questions have not been insulting--I just can't tell from your posts what your background in these areas consists of. IN CASE you decide it might be a good idea to do some review about speaker systems and crossovers and all, the Rane Company has a library on their website which is a reliable source of information: http://www.rane.com/library.html

If you decide to use an active-high level-electronic-crossover you can protect your compression driver diaphragms with a protection capacitor. There is a page in one of the JBL electronic crossover guides which can be used to decide what value to use. JBL 5235 Manual Section 3-3 Table 2. You can find that with Google.

handsome
11-10-2014, 12:11 PM
Thank you I appreciate your assistance. I have seen some altec crossover designs but no-one says what kind of crossovers they are e,g 2nd order, 3rd order, Butterworth, Linkwitz-Riley etc. Also as mentioned there seems to be some extra EQing going in in the designs i have seen. I simulated the Model 19 crossover and it appears to use a 3rd high pass but a 2nd order low pass plus i have Model 19 drivers in an A7 enclosure.....hence my confusion. Was just hoping one of the gurus would advise me.....no doubt i shall eventually get to the bottom of it - one always does and learn something along the way!

speakerdave
11-10-2014, 12:14 PM
I think the gurus are all at lunch. :p

Alien_Shore
12-30-2014, 11:41 AM
Hi all,
I am very new to the Altec world and despite a lot of online research remain confused......I have the following 'bits' : 902-8A, 811B, 416-8C & A7 enclosures, I do not have a crossover. I think what i have is Model 19 drivers and an A7 enclosure, is this correct?

Money is unfortunately tight for me so I will not be buying any other driver/enclosure bits. Also due to financial constraints i am (obviously) rather nervous of blowing a driver. i intend building a crossover myself and would prefer a passive crossover (safer) but active will be quicker to whip up initially, so my questions are:

1. What crossover frequency?
2. What slopes?
3. Which Altech passive crossovers (if any) can i use?
4. If anyone has some schematics for suitable passive networks could you please pass on or point me at them?
5. I have seen many crossover schematics but they look rather complicated obviously some additional EQing is going on what corrections are these relevant to my 'bits' of course?

If i am posting on the wrong forum i do apologise. Any assistance will be greatly appreciated.

There have been many production configurations of the "A7" over the years, but you have the components of an A7 system.
The components you have are suitable for a crossover of 800 to 1200+ Hz. The GPA 416 is a great driver - I have a pair and they measure beyond their (conservative) published specifications. For example:
63948
Slope is going to be a matter of preference and how the components mesh together in your system. If this system is to be used for music playback (like home audio), you'll probably want a higher crossover point (1200 or more) with that smaller HF horn. There are some standard Altec passive crossovers you can use, and since you're on a tight budget, you'll probably want something like the N12XX series that have shelving controls. Ideally you should get a friend with some measurement gear to come over and help you sim your system and build the passive XO that suits your ears. Either that, or borrow someone's active crossover and use that to zero in on the XO point, type, and slope that is best. Then you can sim and build that.

If you go the "generic" route, the Altec N1209 (http://www.hostboard.com/forums/f700/179374-altec-n1209-8a-network.html) is a decent choice. I used that on my garage setup for a while, before I simmed and built a custom passive XO:
https://farm8.staticflickr.com/7017/13445540304_7e941e3b2b.jpg

Fort Knox
12-30-2014, 02:23 PM
Thank you I appreciate your assistance. I have seen some altec crossover designs but no-one says what kind of crossovers they are e,g 2nd order, 3rd order, Butterworth, Linkwitz-Riley etc. Also as mentioned there seems to be some extra EQing going in in the designs i have seen. I simulated the Model 19 crossover and it appears to use a 3rd high pass but a 2nd order low pass plus i have Model 19 drivers in an A7 enclosure.....hence my confusion. Was just hoping one of the gurus would advise me.....no doubt i shall eventually get to the bottom of it - one always does and learn something along the way!

I know what your speaking of w/the complex model 19 x/o ...
Its for tuning a flat baffle sp. to a horn sp.
The A7 does not have that issue...

Horn Fanatic
12-30-2014, 08:24 PM
Hi all,
I am very new to the Altec world and despite a lot of online research remain confused......I have the following 'bits' : 902-8A, 811B, 416-8C & A7 enclosures, I do not have a crossover. I think what i have is Model 19 drivers and an A7 enclosure, is this correct?

Money is unfortunately tight for me so I will not be buying any other driver/enclosure bits. Also due to financial constraints i am (obviously) rather nervous of blowing a driver. i intend building a crossover myself and would prefer a passive crossover (safer) but active will be quicker to whip up initially, so my questions are:

1. What crossover frequency?
2. What slopes?
3. Which Altech passive crossovers (if any) can i use?
4. If anyone has some schematics for suitable passive networks could you please pass on or point me at them?
5. I have seen many crossover schematics but they look rather complicated obviously some additional EQing is going on what corrections are these relevant to my 'bits' of course?

If i am posting on the wrong forum i do apologise. Any assistance will be greatly appreciated.

Should you wish to use a passive network, GPA has a crossover network for the Model 19 components. I am unsure if it comes with a variable L-Pad, but if a network is designed properly a variable L-Pad is not necessary. A 12dB per octave slope (2nd order), is usually the norm, and are quite easy to build. You may even want to Google Jeff Marquardt, as he may have a network designed for the Model 19 components. If he does I would recommend using his.

One thing about how high frequency horns are designed. The cutoff frequencies of the flare rate are typically one octave below what the crossover frequency is. For example, the 811 is roughly a 400Hz horn, and the 511 is roughly a 250Hz horn. You can safely cross your 811 over at 700Hz without any ill effects. It would also make the horn less beamy and allow a more seamless acoustical match to the woofer. It's when the crossover frequency reaches or is equal to the cutoff frequency based on the flare rate of the horn that phase cancellation problems occur.

H.F.