Rescued 215BH's

[sturoc]

Just rescued 2 - 215Bh cabs, I paid $150.
They have blown drivers although I have not got into them in depth to see if all 4 are indeed shot.

One cab is in great shape tolex has it's dings and scratches. The other cab will need a tolex redo and some filler round a couple of corners in the wood. Fortunately I have access to a full wood shop here, so working on them is no prob.
I may sell one of them when finished as they are BIG cabinets and I am not into being that loud !
i can see how they would make fine PA upper bass cabs as well.

Now the big Q: what drivers would be a good replacement for these ?
Do you think it was a fair price for the 2 ? they were originally asking $ 175 .

[claytoy]

why not rebuild the drivers that are in there now? cool find they make a great stack

[sturoc]

I have actually over the many years I have been playing never had to do this.
These look like the stock drivers. One set, when moving the cone by hand you can feel the voicecoil (?) rubbing.
Is that symptom repairable  ?
Are these ancient spkrs worth the repair to begin with considering what's out there these days?

[sturoc]

Drivers are Sunn Magna 158's so I consider these originals.
Found a guy in C Springs: http://www.peakspeaker.com/
$60 a driver for a complete overhaul and recone.
Older Dude with a panache for the vintage good stuff too.

Will start a restoration thread when things get rollin complete with photos.

[Isaac]

When you get them back in shape, remember to turn the bottom one over so that the two horn flares face each other. That will lower the cutoff frequency by about an octave, IIRC, and give you a bit more "oomph" on the bottom end.

[sturoc]

I would love to keep them both and for sure would 'couple' them in that way Issac.
Finances being what they are, when done may have to sell one cab.
If I do side by side coupling ( vertically )  would the result be the same ?

[EdBass]

It doesn't matter if it's horizontal or vertical alignment*, speakers will "couple" when they are within a certain proximity causing a 3 dB gain (or lack of loss) over a non coupled speaker from a specific frequency and below. The roll off point of the individual drivers/cabinets actually remains the same; but there is a 3 dB enhancement of the individual driver's/cabinet's response curve from a specific frequency and under.
The actual frequency that this effect begins at varies mostly dependent on the distance between voice coils, but is also effected by ambient air temp, humidity, etc..

For example, if the voice coils of two 15's are 18" apart in a cabinet, they will "couple"; showing a 3 dB increase from about 185-190Hz and below at room temperature (70ish Fahrenheit).
It doesn't matter if they are in the same cabinet, or if the cabinets are ported or not.

This is one of the basic principles of the current cutting edge line array configurations, but it's certainly nothing new; it's also the reason that PA cabinets were generally columns of series parallel wired small drivers in the 60's and early 70's, before the electronically crossed over, combination driver, point source cabs gained such widespread popularity.





*While vertical alignment may have dispersion advantages over horizontal alignment, coupling advantages aren't one of them.

[sturoc]

Nice info Ed,
Is there a certain distance where the coupling starts at or intersects,
i.e. the wave emanating out from each driver meeting at a certain point in time/distance ?
Or is it more 'global ' for lack of a better word.

[EdBass]

As I posted, it varies; "The actual frequency that this effect begins at varies mostly dependent on the distance between voice coils, but is also effected by ambient air temp, humidity, etc.."

There are different schools of thought, I personally use .25% of the length of a frequency's waveform for my calculations, and center to center for my measurements.

Also, all of the drivers need to be on the same plane and the gain increases exponentially as the frequency drops, the waveform lengthens, and more drivers couple.
Think "Bose", or "Phil Jones Bass". 



An extremely simplified explanation; there is a whole lot more to “Mutual Coupling”, but we are straying WAY off topic, plus this isn't really the forum for this conversation. 

[sturoc]

Gotcha on those points,  Interesting science will read up further.

[EdBass]

Gotcha on those points,  Interesting science will read up further.

Quite interesting indeed. The concept is ancient; I've been aware of it for 40 years, and there is still disagreement among serious acoustic engineers in published papers (as opposed to "internet gurus" posting on forums  ) about the actual parameters.
In your research you will find things like < .5 of the waveform, loss of effect @ >385 Hz, etc..


So, figure it out and let me know, OK?   

[sturoc]

Will do, with a pm so to not clog up the threads !

[Isaac]

Ed, I wasn't talking about coupling the drivers. I was talking about coupling the horns. Multiple horns do couple, and it does lower the cutoff frequency, as it doubles the horn mouth area.

Coupling the horns vertically instead of horizontally won't make a much difference in the way it affects the horn cutoff frequency. It might work even better, as there is a "mirror" effect caused by sources close to boundaries such as floors and walls. It might also affect the polar response a bit. The sound tends to spread out parallel to the horn flare, so, if the cabinets are vertical, the horn flare is horizontal and the frequencies affected by the horns will tend to spread more horizontally than vertically.