My A7-500s. A journey

[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.

[Altec Best]

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.

Now were talking ! I have it the same way !

[dominique-tanguy]

Good morning!

Just a quick report on some testing done yesterday. It is a pity that I cannot post pictures because they would help to understand the issue... I did comparative measurements with the microphone placed close de to 515-8G, in order to avoid room reflexions. The first one is clearly showing a very accidented bumb of nearly 10 db between 160 and 300Hz with a peak value at 230 Hz. Adding some padding behind the driver smoothen the FR curve at 160 Hz, giving a better transition (a - 3d dip at the transition disappear).

I have the added a wing at the top of the cabinet (horizontally). Very spectaculaire effect.The peak at 230 Hz is reduced by 4 db.

Then I have tried an Hiraga receipt. I have put a "curtain" inside the cabinet hanging below the driver. For the moment, it is taking only 1/3 of the height. The effect is also spectacular. It is changing the FR curve at the transition (160 Hz). The effect is between 120 and 160 Hz. The level increase by 3 to 4 db, smoothening the transition. I will continue durng the week-end.

I will try to post pictures on Sunday (3 days...).

Edit 29 July: I succeeded posting the pictures!! The blue curve is measured 10 cm from the port, the green right in front of the 515-8G, same plane.

My goal is to improve as much as I can by tuning the cabinet, and ultimately gor for a "passive.active EQ". I would like to get some information about how to calculate an R/C filter that I could insert between my pre-amp and amp to eliminate this bump...

Dominique Tanguy

[Panomaniac]

Good work Dominique! I look forward to seeing your photos. I have a thick pad of fiberglass behind my drivers. So thick that it compresses when the rear panel is installed. It's a brace and a pad in one.
What did you use for the curtain? Felt? Something else?

[dominique-tanguy]

Good morning Panomaniac,

I started with felt, 5 mm thickness, but I had only one small piece left and it was too short. I replaced it today with a piece of thick fabric. Very good result. I am posting the measurements so that you can compare the shape of the bump with the one posted above.

The improvement is coming from the curtain, the padding and the top wing. Unlike you, I am sharing the leaving room with my wife and I believe that with the top wing solution, I have reached the WAF limit...

[Altec Best]

Wow Dominique ! Very Nice ! Love the flying 1505 horn. The frequency plots are they smoothed to 1/6th octave ?


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