A7 Port advice

[Elitopus1]

I would like to stiffen the flares on my 828 clone cabs. The problem is the motor board doesn't extend all the way to each side wall. Maybe I should either replace the motor board with the wider version or find some other way to seal off the flare area. I have heard about filling it with sand but worry about blowing out the flare

Also in response to GM's post about cab resonate frequency, have you worked with MDF 828 cabs? I have heard that their resonate frequency is much lower than plywood since they are less rigid. That is one of my reasons for extra bracing

[GM]

Add closure boards like I did. For sure you have to stiffen the flares at least as well as the original 825's before filling them. FWIW I used kitty litter by drilling holes in the top and sealed them up with a bonded on full size 3/4" thick marine grade [or BB, appleply] plywood horn 'sled', which does double duty as horn panel stiffener.


No, but other MDF cabs and yes, compared to plywood they are less rigid, though the 828 with its bonded on front panel and 'skids' are theoretically more rigid than a stock 825. Their sheer mass though results in a lower Fs, so makes pushing it high enough is problematic.


I'm no degreed structural engineer, nor know all the necessary math, but experience designing big, heavy, electrical equipment for all manner of shipboard apps, seismic rated for nuclear power plants, etc., 'tells' me that traditional bracing would likely require mass quantities of channel iron to push it to >500 Hz, so better overall to brace by adding more mass, like a second MDF or 1" BB ply skin to at least push it down to, and preferably below, the horn's ~150 Hz lower limit. At this combined weight, I seriously doubt there will be any need for paver or any other kind of blocks, especially once the HF horn system is dealt with. Castors and push bars will be the order of the day.


GM

[Elitopus1]

Ah very good info. The previous owner of my cabs already added a extra layer of plywood on the bottom. I think I will go ahead and add a layer on top of them also. Good BB ply should be relatively void free.

They are on casters so weight is no big deal. I do move them around a bit to vacuum the dog hair that accumulates behind them.

So you would suggest adding extra pieces on the sides of the motorboard rather than replace the board itself? I had thought about adding a piece of plywood across the whole thing. That would give me more woofer excursion clearance also.

Kitty litter, I knew there was something else I had heard of for filling the horns. Its heavy but not as heavy as sand.

[Tax]

Hello,

I run 825s, 515Bs, and 802Ds like you. Got my 825s for free, last December. The drivers I got for free, two years ago, from audiophiles in Kansas City I had audio and triode amp- mentored in previous years.

Find a port suggestion, many here will give you good input, use it, and proceed in this order :

The first thing I suggest is to stabilize the stock 5/8ths thick 825 box,

I suggest you do as I did, and put NO BRACING inside. The cheapest, easiest way to stabilize the 825 box, AND KEEP IT STOCK, is to add mass loading.

We have a large hardware chain in the USA named Lowes, and in their Garden Center, they have " concrete patio tiles ", which are about 11 1/2 inch square and roughly 1 3/4s inch thick. Each weighs about 17 pounds, cost about $1.48 a tile. I added about 300 pounds of these tiles to each enclosure, on top, mostly at the rear, and the AMOUNT of weight was selected by MY ear, till I was satisfied. Total cost, maybe $75, and it is REVERSIBLE. Do this first. Tiles come red and gray, I chose reddish ones.

The second thing I would do is optimally wire the amp to crossover, the crossover itself, and the crossover to the drivers with FAR better ( heavier in most cases ) wiring, to improve your system's transfer efficiency. See details of what I did, wiring wise, in my post in this thread :

URL :

See my post #8, regarding decent wiring, in this URL : ..Proposed Parts List for Model 19 Crossover

The 800HZ 12 dB crossover is what I prefer ( A7-800 ) over the 500 HZ frequency. But the third thing "I" would like to suggest is you re-do the crossover with FAR better caps, better wiring, and maybe better inductors. One cap that NEEDED to be in " my " crossover for the VOTTs to display magic pleasing to me, was a DynamiCap 4.0 uF E series, in all four positions, as part of a "bypass" to an other special high-current, uber low ESR cap I used to get the 8.62 uF Butterworth / 16 Ohm crossover cap value. I will be happy to share the cap specifics privately.

After you do all three suggestions FIRST, you can play with port size. NO rush. The correct size YOU and YOU ALONE select by ear. Its a function of many factors, but YOU alone can decide that by listening.

If you have any questions, or need help, email me as I check that often [email protected]

What sotra nice amp you going to use on them.??

Since April, I have been working on a SET DC coupled Type 45 amp, 1.5 Watts or so, and whatever I did in the amp-build, was heard, LOUD AND CLEAR - on the speakers. Suggest a two stage 2A3 amp, DC coupled, as a good design. I can help you, if you DIY, with that.

Consider these three suggestions, then YOU need to choose the port size for your system, by your ear !!!

Have fun, I am.

Jeff Medwin Low Ohms

Thank you Low Ohms!

I will email for advice. I am travelling for the next 3 weeks.

My cabinets could actually be 828's. They were built around 1970. They are 3/4 MDF with a veneer on the outside.

I am starting off with a 28" x 5" port and will experiment from there.

Will look into mass loading.

Kind regards
Tax

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Mine is 10"x7.5". I read somewhere that 75" is a good number for the port. My cabs also had the horns stuffed in the bottom when I got them. I had to cut a piece of plywood for the port area because that piece was missing.
The current port sounds much better than A7's I have heard with factory ports. Mine are tuned much lower. I would try other sizes and experiment but I like this setup too much

Thank you!

Could you share your experience with the Emilar EH-800 horns? Mine came with Emilar hirns but I changed them to 511B's to keep them traditional.

Kind regards
Tax

[Elitopus1]

Could you share your experience with the Emilar EH-800 horns? Mine came with Emilar hirns but I changed them to 511B's to keep them traditional.

I prefer the bowtie horns over the 511b. You should experiment with both and I bet the Emilar will win. I prefer the EH500 even more but I am waiting to get a second one. They are hardish to find with the Emilar 2"-1" adaptor.

Good luck with your Altec project!

[Tax]

I prefer the bowtie horns over the 511b. You should experiment with both and I bet the Emilar will win. I prefer the EH500 even more but I am waiting to get a second one. They are hardish to find with the Emilar 2"-1" adaptor.

Good luck with your Altec project!

Thanks!

That is good to know. I will experiment with the Emilar.

[LowOhms]

Thank you Low Ohms!

I will email for advice. I am travelling for the next 3 weeks.

My cabinets could actually be 828's. They were built around 1970. They are 3/4 MDF with a veneer on the outside.

I am starting off with a 28" x 5" port and will experiment from there.

Will look into mass loading.

Kind regards
Tax

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Thank you!

Could you share your experience with the Emilar EH-800 horns? Mine came with Emilar hirns but I changed them to 511B's to keep them traditional.

Kind regards
Tax

I traded off 511's, knowing I was going to an A7-800 in my smallish room. The Emilar EH-500, or my clone, a SHOWCO 9000, needs a one to two inch adapter to be usable on an 802. I use an 802 to get HIGHS !! Eight ohm stock ALTEC diaphragm, sounds best, fastest transient response vs 16 Ohms.

I am an ALTEC newbie, other than in the 1950s when my Dad ran 604Bs. Many people LOVE the EH-500. Currently, in 2015-2016, the Emilar EH-500 ( not 800 ) is a Joe Roberts ( Sound Practices ) highly favored small format horn. Needs the adaptor to work

Altec speakers are not much of a problem, or a weak link, the AMPS are, as always, IMHO !!

Jeff Medwin Low Ohms

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I prefer the bowtie horns over the 511b. You should experiment with both and I bet the Emilar will win. I prefer the EH500 even more but I am waiting to get a second one. They are hardish to find with the Emilar 2"-1" adaptor.

Good luck with your Altec project!

How about any JBL one to two inch adapter Don ???


Jeff

[Elitopus1]

How about any JBL one to two inch adapter Don ???


Jeff

They are the wrong bolt pattern, I would have to drill them.

The Emilar EE1-2 adaptor has a VERY smooth transition to the horn. Emilar had tight tolerances on their parts. There are some for sale on Jammin Jersey that are overpriced. If I find another EH500 horn without the adaptor I will probably buy one from them

[Altec Best]

Panomaniac did some extensive port tuning to the 825/828 cabinet in his A7-500 setup... I would skim through his thread to learn about what he had found on port dimensions for those cabinets...

My A7-500s. A journey

[Tax]

Panomaniac did some extensive port tuning to the 825/828 cabinet in his A5 setup... I would skim through his thread to learn about what he had found on port dimensions for those cabinets...

My A7-500s. A journey

Thanks Altec Best!

I have read that thread and am in touch with Panomaniac.