Thanks GM. I've read some of that before, from you, but I don't think I've seen it all written up in one spot before. I wish I had a pair of cabinets to work on now :D ....... I sold my 828's awhile back.
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Thanks GM. I've read some of that before, from you, but I don't think I've seen it all written up in one spot before. I wish I had a pair of cabinets to work on now :D ....... I sold my 828's awhile back.
Well I will definitely be bracing. There are a number of large areas the vibrate. In fact, when I first had them outside a plane flow over (not low) and I could feel the cabinet walls vibrate. Not good!
The side walls under the horn flare vibrate a lot as do the lower front panels where the ports are. Those could certainly use bracing. The lower back panel also vibrates a bit.
In other words, any large unbraced area vibrates.
I have some 2x2 lumber that has been drying in the attic for about 20 years. I'll use that for horizontal bracing. Will try to use the 3/5th rule when placing the braces. I'll look for hot spots after that as GM suggests. Might add mass to those.
I'll let you know how it goes!
So raising the reosnant frequency of the cab is one strategy. (correct?)
What then happens if we add post-tensioning? (cables or chain with turnbuckle)
This would tune it higher with a minimum investment in additional weight.
- or is making a drum a bad idea?
- or, does it just end up ripping the nice bracing job you've just done, off the interior walls?
You're welcome! Yeah, I've regurgitated/debated my thoughts on this, and many other, audio related subjects in bits n' pieces so many times on various forums and in private that I'm completely burned out on them. I hope folks will copy/save it as I edit it instead of continuing to ask the same basic questions over n' over. Hopefully in the not too distant future I'll collect some links with pictures and maybe make (or have drafted) some annotated sketches for clarification and get it all published in one place somewhere.Quote:
Originally Posted by Audio_by_Goodwill
GM
Correct. See my edit: http://www.hostboard.com/forums/show...=1#post1809271Quote:
Originally Posted by gearfreak
GM
Dear all,Quote:
Originally Posted by Panomaniac
This is my first participation to this forum and I need to introduce myself. I am 54, French but living in Cologne, Germany. I am passionate by Aviation, music and photography.
When I discovered this thread, I suddenly realized that I was not alone anymore! I went through the same journey with the same loudspeaker and despite the thread has been quiet for a while, I could not resist to post my contribution.
Like Panomaniac, I did the bracing and dumping of the horn and I found by testing that reducing, but also tuning the port was improving a lot the bass response.
I am using a different loudspeaker (GPA 515-8G) and a passive crossover (Wonderful serie crossover, I will create a post on this crossover). Despite that, the attached impedance curve is very similar to the one posted by Panomaniac (Sorry, attachement not possible before 3 days).
I am also facing the problem of the 10 db bump at 220 Hz, which seems to be common to all VOT. I would like to avoid the EQ as I am using an integrated amplifier (Accuphase E-530) and still listen a lot of vinyls.
- Is there a possibility to reduce this bump with some internal modification (dumping…)?
- Has somebody established what could be the best modern loudspeaker for this cabinet (Vas, Qms, Qts…)?
I wanted to post images but I will not be authorized before 3 days. Sorry...
Thank you in advance for your participation!
Dominique Tanguy
Hey Dominique ! Welcome to the board ! :smile2: Have you tried a 416 ?Quote:
Originally Posted by dominique-tanguy
I'm looking forward to you pictures/attachments !
Dear Altec Best,
So far, the 416-8A is first on my list. I got an offer from Per Hasling, in Danemark, for a pair of restored 416-8A. On paper, they look better adapted to the 825 cabinet that the 515-8G. But according to the result obtained with the 515-8G, I am not so sure...
I will publish measurements as soon as possible...
Have a nice day!
Dominique Tanguy
Bonjour Dominique!
I gave up and just use digital EQ for the ~220Hz bump. It works. I have a passive crossover in the works and it may include passive correction for that bump, I don't know.
Oddly, because of my strange reconed 416s a closed box has been best for me. They just seem to work best in a big closed box. So the lower front panels were removed and replaced with a single piece, no more port.
After a lot of work, I've ended up with a 3rd order low pass (electrical) at 460Hz and 3rd order high pass at 610Hz. That actually puts the acoustic crossover point at 675Hz. I'm using the 1005 horn and ceramic magnet 288s on top + Fane ring tweeters. It's sounding very nice now.
Should be since it's where the horn 'gets up on the pipe', to use a race motor tuning phrase to describe the beginning of its max performance RPM [BW] range. You can see it in the impedance plot.Quote:
Originally Posted by Panomaniac
GM