Model 19 and 17

[GM]

Thanks Cris and GM, I have not set down the money yet, no. The cost of new GPA 604 with crossovers, once here on my side of the Atlantic, will be more than the 416/802/511/ + crossover of choice combo. However as you point out with regard to WAF there is still the possibility of a graceful retreat to 604?s with which I don't doubt I could live happily for many years.

GM, regrettably my ceiling is not high enough for mounting anything above the doors and I do not have ready access to a supply of 414?s at a good price.
I like the idea of a "colour matched double expanded knit grill" I could engage my wife in the endeavour and get max buy-in from her to boot as she is quite nimble with the knitting needles (or do you call the pins in english)

Tom I heard M. Logan?s similar to yours years ago and was quite impressed, they however do not fare well on a low wattage diet from simple tube amps.
Regards
Kjartan

Greets!

You're welcome!

Bummer.

Needles.

Yeah, I never had any real problems with SAF with any of my long term relationships or builds done for others, though one did complain about me rebuilding a motorcycle in the house over one particularly frigid Winter, using the kitchen sink as a parts washer since it is stainless steel, but never any audio related complaints. Except for my mom, I wouldn't do finished systems. It was up to the owners, so where there were Significant Others (SO) to consider, I'd get them involved right from the beginning if they should any kind of interest (positive or negative), though I did help them in some cases.

I wish I still had the picture of a set of full height column speakers one lady friend marbled with paint. Once done, folks were hard pressed to not believe they had been carved from Georgia marble. Wallpapering and covering the speaker completely with cloth with a finished wood/marble/slate top and bottom were popular, but those times were the heyday of butcher block, so I'll let your imagination run wild with that one.

My fave was the real Bamboo wood papers. Expensive, but fabulous looking with the right decor. Many though were just wall or furniture matched with the rest being left unfinished since they typically were living relatively transient lifestyles, moving them from college dorm to apt. to trailer and finally to vans during that craze.

Anyway, there's many ways to make a tophat covered with expanded double knit to cover horns and woofer to get a nice finished look. There's a dude on the net that covers his wall horns with artistic silkscreen covers, so they look like paintings, but can't find the link ATM.

GM

[mah]

Kjartan,

I am about to put build 16 cu.ft. enclosures(think A8, double the depth) with 511Bs on top and maybe a JBL tweeter, too. I don't have WAF concerns but have been considering appearance options of this combination. One option is concealment behind a furniture screen which uses grillcloth or suitable fabric in its frame.

The following link is for Oriental screens but will give you the general idea:

http://www.orientalfurniture.com/oriental-furniture/Room-Divider-Folding-Screens.html

Happy building, Marshall.

[GM]

Possible configuration: naked (but painted) 511/802's on top of cabinets that are 60-65cm wide, approx. 45cm deep (under 50cm at least) and height should be appropriate for persons sitting approx 3.5meters in front of the speakers.

Would it be possible to get reasonable performance from the 416-8A's in 8.5 cubic feet (~240L = .6m W x .4m D x 1m H) MLTL or BR enclosures.

Greets!

Regardless, WRT cab/horn height, the DIY standard is to put the tweeter (horn) centerline at ~seated ear height, but some of us prefer to get it up a bit higher and angle it down as required and many folks are quite happy with the A7's height, splitting the difference between the average seated ear height and the average standing height some of us prefer.

WRT depth, a 416A is normally rear baffle mounted and with the lip of the 511 flush with the front of the baffle it's right at 17.25" to the rear of an 802D, so add 0.125" for the 802-8G's longer length and the minimum depth is 17.3875" assuming a stock N501-8A (500 Hz/2nd order) XO is used. For a higher XO point and/or slope the horn would move forward some, but best to assume a 'worst case' scenario.

So, assuming 42" H x 24" W x 17.3875" deep overall dimensions (o.d.) and 0.75" thick material = ~14,477"^3 - ~1000"^3 for the 416, vent and bracing = ~14,144"^3/~8.378 ft^3 net.

This yields a ~65 Hz F3/half space when tuned to a ~25 Hz Fs, so up against a solid (outside) wall will lower it a Hz or two. IOW, net efficiency over its pass-band will be up to +3 dB depending on how rigid/massive the wall/floor construction is, reducing the amount the horn will need shelving, but net F3 won't audibly change.

But this assumes a very low output impedance source, so with your amp's high output impedance, the speaker's rising response will flatten out somewhat and F3 should be in the 35-40 Hz BW with a typical ~2.5 ohms. If it's more, then damping the vent and/or increasing its length or even sealing it off may be required if it sounds under-damped ('loose'/'flabby') or causes any room 'boom'. If this isn't 'reasonable', then I guess you'll either have to make the cabs larger or add a sub system.

Regardless of what box dims you use, place the driver at the extreme top and at least a 5" i.d. pipe vent near/at the bottom. It's length will need to be tuned to Fs to maximize LF BW efficiency. Based on a 25 Hz Fs, ~8.378 ft^3 net and a 5" i.d. pipe, a 5" vent length is a good starting point with longer tuning it lower and vice versa.

GM

[KBergsson]

Thanks a lot GM, for your effort. I think a cabinet like this would be an acceptable compromise for both parties
Regarding the vent/port what are the constraints, e.g. if implement it as a slit at the bottom of the cabinet (and not a tube) what dimensions are the critical ones, i.e. the length (or "tube" length) is a tuning parameter but what about the minimum height of the vent/slit is that critical as long as the vent area (as seen from front), and thus the air volume in the vent is the same?

Marshall thanks for the idea, but oriental screens are not a solution in my case because of the form of my livingroom.

Regards
Kjartan

[GM]

Greets!

You're welcome!

The vent's cross sectional area (CSA) sets its vent mach for a given length and power output while CSA combined with its length (vent volume (Vv) sets its tuning frequency for a given cab volume (Vb).

From this we see that within reason the slot's shape isn't too critical, though at aspect ratios > ~9:1 like was used in the original A8, the vent starts becoming increasingly resistive, so for a given tuning (Fb) it will have a higher F3 than predicted. It's a good way to damp any peaking at Fb and provide a bit of protection below it, so I assume that's why Altec used it since small cinemas probably wouldn't have any more electronics than absolutely required to get high intelligibility sound at relatively high SPL.

I don't have any software sophisticated enough to accurately calculate slot vents plus ideally all vents should be tuned individually in-room for a HIFI/HT app for best performance, so becomes a tedious affair for all but simple tube vents that can easily be swapped out using rope caulk or similar to temporarily seal it to the baffle.

So, to convert it to a high aspect ratio slit it requires a CSA that results in too high a tuning if round, though with the same vent length, and use damping material to resistively load it if required. It requires easy access to the rear of the slot, so ideally needs to be on a removable panel, same as the driver.

The trade-off though is a higher F3 (up to 10 Hz), but the room typically has a big affect on it when placed near/at a boundary, so may be a good thing. You can also vary the output impedance to flatten it if over-damped, though again, not many 'free lunches' in audio, so the trade-off is some efficiency loss.

Anyway, using the A8's proven 1:16 ratio and increasing its CSA to that of a 5.5" dia. pipe (~23.758"^2) and using the same 5" length is probably as good a size as any to start with = ~1.22" H x 19.5" W slot. If it has any 'boom' in the mid-bass/bass, then begin damping the vent and if it sounds too 'thin', then either shelving the HF more and/or increasing the output impedance and/or making a larger slot vent are your options.

If nothing you do winds up being acceptable, then I assume the room plus speaker positions relative to the listening position are to blame and this is where having an acoustically large cab is beneficial since it allows much more tuning flexibility, but at ~25-30 ft^3 being required for the older 416s, not an option for many folks.

GM

[KBergsson]

Thanks GM for your trouble.
I have now got pictures of the 802-8G's, they have the tangerine phase-plug and look almost like brand new. They are restored by a true enthusiast. He has measured them to 6.38 and 6.28 ohm respectively. They are a production pair as their serial numbers are in sequence. I will get info on the restored 416-8A?s later.
Regards
Kjartan

[KBergsson]

Hi, I now got info on the 416-8As, these are actually Heathkit 401-149. Measurements are 6.87 Ohm and Fres=22.6 Hz the other 6.75 Ohm and 22.9 Hz after cleanup. Both look brand new and have original numbered cones.

Is there a sonic difference between the Altec 416-8A and the Heathkit 401-149 or are these the same speakers?

Regards
Kjartan

[GM]

The ones I've seen were 416-8Z, i.e. no magnet pot (rear cover), so has a bit weaker motor (higher Qes, Qts, lower B*L).

GM

[BugC]

Hi GM,

I would like to seek your advice on a somewhat similar project I'm doing. (Kjartan, sorry for hitching on your thread) ... I just acquired a pair of unfinished enclosures with internal dimensions of 42" (H) x 26" (W) x 16" (D). 3/4" marine plywood was used for the enclosures. I was thinking of the Simple Model 19's but decided against it because it would take longer to finish. ( I can do my project only during Sundays)

I would like to use these enclosures with a new pair of GPA 416-8C's along with pairs of Altec N1201-8A's x-overs, 811b horns with GPA 902-8A drivers. The horns will be mounted on top of the enclosures. What would be the optimum size for vents of these enclosures? ... BTW, I'll be driving these speakers with a pair of SET300B monoblock amps in a room 12' (W) x 20' (L) x 9' (H).

Thanks in advance for your advice!
BugC

[GM]

Greets!

Based on published specs this box is theoretically way too small for a usable gain BW down to Fs, especially once the SET's high output impedance is factored in, but if backed up against a wall it may still be a viable tuning if there's enough room gain, so the range would be from a typical vintage Altec tuning up around 35-36 Hz = (2) 4" diameter x 0.75 - 1" long vents down to Fs tuning at up to 5 - 6" long. These assume the driver is at the extreme top and the vents are side by side near/at the bottom. The usual bracing/damping requirements of MLTLs apply of course and that during tuning the cabs should be in the final resting place and with the horns disconnected. Don't be surprised if each cab sounds best with different tunings since room eigenmodes dominate down this low.

If none work, then with Fs tuning (long vents), try adding series resistance with an adjustable pot and if that doesn't work, then based on your input I'll look at other tuning ranges, though of course for best results I'll need measured driver specs and total output impedance (amp + speaker wiring + XO components resistance).

Regardless, once dialed in, please let us know the details of the final set-up for future reference.

GM