Need help - Altec 418B

Greets!

You're welcome! Now you see why I asked about any size limitations. ;)

No, being a much larger/taller cab it only needs a 6" diameter (~28.274"^2/182.412 cm^2) x 1.5" long vent to tune it to around 32 Hz, but in the interests of some extra tuning flexibility, an 8" should be used, which with 2.5 ohms series R and baffle thickness cutout should be ~half space max flat (~41 Hz) with the lowest practical tuning (~32 Hz) requiring a 4.5" long vent (shown with vent centered at 35.5" i.d. down from the top).

Backed up to a wall or near a corner with this low a tuning it should be nominally flat all the way down (except for room modes of course and assuming the amp has what it takes) and able to do all but 64 ft organ pipe fundamentals and some movie, etc., extreme LFE special effects.

GM
 

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GM,

Thanks

As of my understanding, you prefer the vent 8" for tuning flexibility, and series a 2.5R to the speaker ( is this 2.5R works as XO to cut off from 1,200hz down )
So the vent dimension is 8"W x 1.5"H x 4.5"D and 35.5" I.D. down from the top. Do I mount the driver in between the top panel and top of the vent?

Albert
 
Greets!

You're welcome!

Correct.

Huh?! None of this has anything to do with an XO point.

Please re-read my #19 post. It's an assumption on my part to hopefully not make the cab unacceptably too small. If the bass winds up being too weak sounding, then use a cheap pot to dial in some more series R and replace it with a non-inductive wire wound power resistor assembly of whatever the pot's measured resistance setting is with the understanding that efficiency falls with increasing R.

?? An 8" diameter (~50.266"^2/324.293 cm^2) hole doesn't convert into a 8" W x 1.5" H slot, but a ~50.266/8 = 6.283" H one.

The 1.5 - 4.5" dims is the range of vent depths I recommend.

Ideally you would use 8" internal diameter (i.d.) pipe lengths to experiment with, but if you prefer to make/use different depth wooden slot vents, then I recommend a 13.625" W x3.6875" H (13-5/8" x 3-11/16") by the different depths centered at 35.5" i.d. down from the top.

Yes, driver at the extreme top front of the cab with the vent down near the bottom to create a MLTL.

GM
 
GM,

'The 1.5 - 4.5" dims is the range of vent depths I recommend.'

is it deeper the vent -4.5"- better the bass?

' then I recommend a 13.625" W x3.6875" H (13-5/8" x 3-11/16") by the different depths centered at 35.5" i.d. down from the top.'

I'll make to exact size.

'driver at the extreme top front of the cab with the vent down near the bottom to create a MLTL.'

So the driver is 15" and I'd put the driver at 9" I/D down from the top.
Is it OK?

Albert

BTW I'm going to make the box 42"H x 27.75"W x 17.75D
 
Greets!

If by 'better' you mean it plays to a lower frequency before the box unloads and can't control the woofer any longer, then yes. If you mean the most chest slamming/'thumping' bass, then the higher tuning (short vent) is theoretically what you want, but the room dominates down low, so will boost the LF BW in non easily predictable ways and why you typically need to experiment with at least a high/medium/low tuning, i.e. 1.5"/2.6"/4.5" long vents.

Well, 'extreme top' with a 15" diameter frame = 7.5" down from the top, but I doubt there's an audible difference at 9" down from a strictly driver/vent distance POV. Depending on the XO point/slope you wind up using for whatever mids/HF source you perch on top of the cab though, it might make a difference due to the extra distance between their acoustic centers, so considering this I recommend installing the driver as close to the top as practical, i.e. same as an 825/828 (A7) cab.

Note that all dims are inside (i.d.) and approximate in case you're converting to metric.

Note too that the suggested design is based on the listed dims as being outside dims (o.d.) with a 0.75" material thickness, making the internal dims 40.5"H x 26.25"W x 16.25"D.

GM
 
Greets!

You're welcome!

Depends on personal preference and XO point/slope, but the 802D/808-8A except loaded with an 8 ohm HIFI diaphragm would be the period correct choice and probably the best performer overall considering you'll be driving them with a high output impedance. If you want a bit more 'sparkling' highs, then the 802-8G used in the original M-19.

GM
 

Gwho

Member
2008-10-14 10:51 am
I know this is a very old thread but there is little in here about the Altec 418B driver. I am hoping that GM finds this thread again. I know these are musical instrument speakers but found a pair in nice condition and would like to use them. I have a pair of Altec Santana cabinets that are about 3 cubic feet in volume where I will use the 418B. I was hoping to use the 418B for a lower range of 80-150hz and and upper range of 500-800hz for a stereo speaker (possibly with a horn on top). Would the 418B work well in a sealed cabinet? Would a port help lower the bottom end even with the low enclosure volume? If so, what should the port size be for such a small enclosure (or would it cause more problems). I put the speakers in the Santana's and they sound good. They actually have a lot of pop. I would add subwoofers for the low end.

I just wanted to get your opinion since you seem to be knowledgeable on vintage Altec speakers.

Best Regards,
Gary
 
I didn't think a day would come when GM no longer had opinions to share! But I guess I don't hang out here very often.

I, too, recently picked up a MINTY set of 418Bs in a strange "NSC" cabinets that have 511Bs on top. I thought they'd be great garage speakers, but am now wondering if they deserve a higher use. And whether that higher use should be leaving them as-is or re-coning them as 416Bs.

The current cabs only give them about 3 cu ft sealed. If I have the chance to hook them up this weekend, I'll let you know how that seems to work.

Paul
 
Greets!

Long time no hear!

They're guitar drivers and while it's my understanding they can be reconed they won't perform like a 416B, so I'd just damp the alum. dustcap for other apps unless you like sizzling breakup modes above ~1435 Hz and being AlNiCo, vent it with a tiny hole scaled off the 803 15" frame is close enough: Altec 803

My MI speaker designs began with the 421-8H, so any prior to it were normally used in whatever box[es] Altec recommended.

No clue what a 'NSC' cab is.

Again though, ask the more driver tech experienced over at the AUB as I've never been interested in modding/reconing, etc., drivers in general and especially prosound since I had Altec's full service S.E. distributor and always at least one large prosound retail shop for it and other brands a 'stone's throw' from my home/work and skip over any threads on the subject.
 

Gwho

Member
2008-10-14 10:51 am
pjanda1,

Thank you for letting me know about your find. I read a thread in hostboard about the 418b that had knowledge about the 418 said that they were very good for 3 cubic foot sealed but would roll off at about 70hz with an upper end of up to 8khz.

Regards,
Gary