My A7-500s. A journey

[dominique-tanguy]

... I also need to pull out a lot of energy around 220Hz with EQ. It's a notch of -9dB and a Q of 2.2. Without that EQ there is no way I can get the box flat. But pull it out and tune the port right and the box plays right on down to where a big box should play.

If I measure the box 1 meter from the front, it does not play so low. But back where I sit it does, and is nice and flat. Must be room gain making up for it.
I don't know if this 220Hz peak in common in this box, but both mine suffer from it. If you have some method of EQ, I suggest you try this.

Dear all,

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

[Altec Best]

Dear all,

This is my first participation to this forum and I need to introduce myself. I am 54, French but living in Cologne, Germany. 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 ! Have you tried a 416 ?

I'm looking forward to you pictures/attachments !

[dominique-tanguy]

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

[Panomaniac]

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.

[GM]

I gave up and just use digital EQ for the ~220Hz bump.

Adding big enough 'wings' to double its effective mouth area should flatten it out, shifting the peak higher up to fill in the dip that should be above it, i.e. smooth out its horn gain BW somewhat. I assume it will require re-doing the XO though.

WRT efficiency, IIRC a fully flattened A7 in stock tune is ~96 dB/m/2 pi, so you appear to have significant room gain to get more than this down to < 30 Hz. I'm [Altec] 'green' with envy.

GM

[dominique-tanguy]

Dear GM,

I agree. Yesterday, I did some measurement removing the back panel, to verify if this peak had something to do with resonances. It is still there, slightly attenuated, showing that it is created by the front load of the horn. I already use small wings but I will do more measurements this week-end with larger wings.

Thank to all for your inputs!

I will publish the schematic of my crossover as soon as I can publish links.

Dominique Tanguy

[Panomaniac]

Yes, thanks GM. Do need to try the wings. My first pair (Jean Hiraga's) had them. Must have been why they sounded more balanced. Doubling the mouth area means some big old wings, tho!
As for the lower F3, I think that comes from my higher Qt drivers and their weak magnets. I'm not unhappy with the trade off. Doubt they are doing 96dB/W

[Altec Best]

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.

Adding big enough 'wings' to double its effective mouth area should flatten it out, shifting the peak higher up to fill in the dip that should be above it, i.e. smooth out its horn gain BW somewhat. I assume it will require re-doing the XO though.

WRT efficiency, IIRC a fully flattened A7 in stock tune is ~96 dB/m/2 pi, so you appear to have significant room gain to get more than this down to < 30 Hz. I'm [Altec] 'green' with envy.

GM

Don't you just Love when a plan comes together !

I guess you will be off to the lumber yard ? But what about the WAF ? Will those wings be able to Fly by the wife ?

[Panomaniac]

My wife has to ask permission to enter the music room. I don't decorate her living room, she does not bother my music room. That way I can have any damn speaker I want.