Query on N1201-8A Network

[ngccglp]

Hi,

Recently I acquired a VOTT A7-X and the components are 828C/416-8B/511B/802-8G/N1201-8A.

The N1201-8A is used by the Model 19 which has the 811B, and the 416-8B is not horn loaded.

On the N1201-8A there are 'OPTIMUM' markings for both the MID and HF LPADS. May I know if these OPTIMUM markings apply to the A7-X as well since the horn and the enclosure are different. More specifically, I would assume the 416-8B in the 828C would have higher sensitivity rating than when its used in the Model 19.

OR are the N1201-8As used in the A7-X modified to compensate for the different enclosures?

Thanks.

[bowtie427ss]

More specifically, I would assume the 416-8B in the 828C would have higher sensitivity rating than when its used in the Model 19.

All else being equal(which it seldom is) your assumption is correct. But, we're only talking a few db, and only in the region where where the midbass horn loads the 416 which is from a little above 100hz to a little below 1khz.

Compared to the Nineteen's LF section, the 828 is going to have a broad hump in the midbass, and roll off more quickly at the extremes of it's range, particularly on the LF end.

[ngccglp]

All else being equal(which it seldom is) your assumption is correct. But, we're only talking a few db, and only in the region where where the midbass horn loads the 416 which is from a little above 100hz to a little below 1khz.

Compared to the Nineteen's LF section, the 828 is going to have a broad hump in the midbass, and roll off more quickly at the extremes of it's range, particularly on the LF end.

Hi Bowtie,

Thanks. So the perceived mismatch in the low and high levels is really caused by the hump in the 828 enclosure. I played some pink noise and noticed the hump around 200 to 400 hz region. At the crossover point of 1200 hz, the levels were quite even when the Lpads are at the optimum positions. No wonder even when I turned the mid lpad to maximum position it is still not able to match the hump caused by the horn loading. I am not able to get a more tight and clear mid bass because of the hump.

[GM]

Yep, the FR of the 416-8B is optimized for the M19 or similar rather than for the A7 series as earlier models were, which had a much elevated ~500 Hz - up break-up modes BW to blend to the mid-bass horn, extending its high eff. response out to around 1600 Hz for an 800 Hz XO point; so ideally an older 416 or even later 421 or 515 is a better choice for the A7 series.

GM

[ngccglp]

Yep, the FR of the 416-8B is optimized for the M19 or similar rather than for the A7 series as earlier models were, which had a much elevated ~500 Hz - up break-up modes BW to blend to the mid-bass horn, extending its high eff. response out to around 1600 Hz for an 800 Hz XO point; so ideally an older 416 or even later 421 or 515 is a better choice for the A7 series.

GM

Thanks GM.

Will it help if i biamp, and cross at 500 hz, to level the response around 500 hz between the 511 and 828, and maybe add a simple RC circuit to flatten the response of the 511?

[GM]

You're welcome!

Yes, this is what I wound up doing when the dbx digital EQ, etc., came along and determined that compression horns seem to have a certain synergy with passive contour shaping that I had up to that point taken for granted, so got my 'cake and eat it too' with high power, low output impedance for 'heart attack' fast transients, yet with no obvious digital 'grunge' typical of early SS amps presumably due to the extra series resistance pre-loading the amp up to its working 'sweet spot' that apparently all SS amps have to a greater or lesser extent; though admittedly McIntosh's SS amps with output trannys [2100-2200? series] did the horns best overall, just not enough for me to justify the 'insane' prices after having to sell my prized Porsche to fund the many thousands [in 1980 $$$] required just for the dbx electronics and a then just arrived Mc2500 amp.

Don't know about equivalent performing amp prices today, but the now crude/low tech dbx electronics are easily bested by mostly freeware these days and with many more features to boot!

GM

[ngccglp]

You're welcome!

Yes, this is what I wound up doing when the dbx digital EQ, etc., came along and determined that compression horns seem to have a certain synergy with passive contour shaping that I had up to that point taken for granted, so got my 'cake and eat it too' with high power, low output impedance for 'heart attack' fast transients, yet with no obvious digital 'grunge' typical of early SS amps presumably due to the extra series resistance pre-loading the amp up to its working 'sweet spot' that apparently all SS amps have to a greater or lesser extent; though admittedly McIntosh's SS amps with output trannys [2100-2200? series] did the horns best overall, just not enough for me to justify the 'insane' prices after having to sell my prized Porsche to fund the many thousands [in 1980 $$$] required just for the dbx electronics and a then just arrived Mc2500 amp.

Don't know about equivalent performing amp prices today, but the now crude/low tech dbx electronics are easily bested by mostly freeware these days and with many more features to boot!

GM

Thanks GM.

I also noticed there are many variations in which the 511B horns are mounted on top of the 828 enclosure, some with the horn flange flush with the front of the 828, some with the mounting bracket flush with the front edge, some few inches inwards. Is there a correct or optimum setting?

Thanks.

[GM]

Yes, it varies with the XO's point/slope order and don't know what it is for the N1201, though it can be found empirically, but currently don't have access to my 'library', so need someone else to post either the proper offset or tech bulletin to find it.

GM

[ngccglp]

Yes, it varies with the XO's point/slope order and don't know what it is for the N1201, though it can be found empirically, but currently don't have access to my 'library', so need someone else to post either the proper offset or tech bulletin to find it.

GM

I think the N1201 is crossed at 1200 hz second order

[GM]

Right in that it's nominally 1200 Hz, but due to its design it's not fixed like a textbook one is. Anyway, I meant I don't know the horn mounting bracket location Altec used as this design change to the A7 was after I quit paying attention to what they were doing nor would have ever considered using such a high XO point with the 511 except 1st order.

That said, I found this that implies the bracket is at the front edge, but no way it's going to be correct for a 500, 800 or 1200 Hz XO point regardless of slope order, though probably 'in the ballpark' for 1200 Hz, so again, you really need to set it empirically if you want to get it right: ALTEC LANSING A7-8G VOTT SPEAKER SYSTEM Manual (Page 2 of 3)

Ah! Found the tech bulletin on-line: http://audioroundtable.com/misc/Altec_AN-9.pdf

Donald Patton has kindly offered his test disc to us to do this if you don't have the necessary test gear and/or computer software: Model 19 digital delay

GM

edit: BTW, at this high XO point, don't be surprised if in actual testing the horn bracket ideally needs to be somewhat forward of the front of the cab due to the 511's much longer physical/acoustical path-length than the 800's, 811's the cab was designed for.

GM