Altec vintage woofer question

[Rigbot]

I have a pair of Altec 515 8ohm woofers that I had rebuilt by GPA. I want to use them in a custom home speaker project with a pair of Altec 604/605 co-axials. The plan is to use the 515s in an Isobaric configuration so that the box doesn’t have to be 8+ cubic feet. Which co-axials use the same woofer as a 515 8ohm?
Thanks,
Rigby

 

[Tom Brennan]

That's an interesting idea.

The woofer of the 604 is generally considered to be a 515, (and that of the 605 a 416) thus one of the later 8 ohm 604s such as the 604-8G could be suitable. I'd look up the TS parameters of the various 604s and see how they match those of your 515s.

 

[bowtie427ss]

604 LF section was based on the 515, 605 LF section was based on 416.

 

[Rigbot]

That's an interesting idea.

The woofer of the 604 is generally considered to be a 515, (and that of the 605 a 416) thus one of the later 8 ohm 604s such as the 604-8G could be suitable. I'd look up the TS parameters of the various 604s and see how they match those of your 515s.

Thank you, that’s exactly what I was looking for. Unfortunately, I have two pair of 605s and and no 604s. How different are the 505 and 416?

 

[Tom Brennan]

Thank you, that’s exactly what I was looking for. Unfortunately, I have two pair of 605s and and no 604s. How different are the 505 and 416?

The 416 has a smaller magnet and lower sensitivity. But it also goes lower in the bass for a given cabinet size. I've owned both 605s and 604s and found both very satisfactory. The 416 should go nicely with your 605s; they're not uncommon and a pair of 416s are cheaper than a pair of 604s.

Do you find the 605s satisfactory? Since you have 2 pair how about using a pair in a box as dipoles; one in the front of the box and one in the back wired out of polarity? They could be cool. Big box though.

 

[GordonW]

The only issue I see with an isobaric arrangement, would be that the rear frame of a 604 is so deep, that the tunnel between it and a 515 would be VERY long.

That not only makes for a lot of used-up cabinet volume for the isobaric chamber- but, you also get into a regime where the enclosure volume between the woofers- and its inherent "air spring" effect of the air within- can make it NOT act like a true isobaric.

In addition- most isobaric woofers are NOT used into the midrange. The reflections of the midrange (which has wavelengths short enough to be for a half-wave to be "contained" inside the dimensions of the isobaric chamber, potentially) off of both woofers would be bouncing around inside the isobaric chamber- which would do who-know-what to the frequency response of the woofer (due to cancellations/coupling at random locations at random frequencies).

Regards,
Gordon.