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Replacement speaker for an old Acoustic 136 cabinet?

#21
Bob Lee (QSC) said:
I have an Acoustic 136 also. It does have a large vent at the bottom. I don't know if there was any significant deliberation or calculation in the enclosure design.
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That's what I remembered. In this case, off the top of my head the Delta A platform would be limited to <200 watts "RMS" below about 65Hz-70Hz, so relying on a "600 watt" manufacturer provided rating would be really misleading IMO and ultimately lead to player disappointment when driven harder.
 
#23
Was also wondering about 600 watt power handling with 2.5" VC. May be it's nothing but a typo/error.
Sometimes those things happen (unfortinatelly) even at manufacturers with high reputation.


May be getting "old school" like EVM-series drivers is a better approach to an "old school" built cab for driver choice?
Just a thought.
 
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#25
BassmanPaul said:
I couldn't let this pass. In those days 100W SS was about the maximum that you could attain. Power was calculated the same way as it is nowadays by honest engineering. There's no way that this amp could put out 500W it didn't have the supply rails to do that.
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As I said, I am a neophyte here, I got that info from this forum, read the second post down...I'm sure I interpreted it incorrectly.

Acoustic 140
 
#26
Recoil Rob said:
As I said, I am a neophyte here, I got that info from this forum, read the second post down...I'm sure I interpreted it incorrectly.

Acoustic 140
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Some of what he says is accurate. Marketing has played fast and loose with power ratings in the past. peak versus continuous. Even back in those days the "good" companies published honest ratings. Others not so much.

The overdrive characteristics of tubes allow them to compress the signal in a pleasing way. IIRC even harmonics against the odd for SS. Something like that anyway - I curse my lousy memory.

The fact remains that we, as players, are more concerned with continuous power and peak has little relevance.
 
#27
BassmanPaul said:
The overdrive characteristics of tubes allow them to compress the signal in a pleasing way. IIRC even harmonics against the odd for SS.
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Even plus odd harmonics (it's fairly difficult to produce artifacts that are only even harmonics). A perfectly symmetrical overdrive characteristic would produce only odd harmonics.
 
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#28
At some content (gradient overload characteristic) even the odd order Harmoncs may be perceived as "musical" Harmonics.
Lots of folks believe tubes would strongly "prefere" the even order Harmonics which is a myth anyway.
With tube preamps there may be some emphasize either to the 2nd or the 3rd order Harmonic but it's designers goals how to "balance" the distribution within meaningful range.
While with tube power amps (class AB) there is an strong emphasize to odd order Harmonics rather than even order (although it's an all over tube design)

Based on schematic drawing the 140 amplifier should provide around 85 watt 1% THD at 4 Ohm load.
Acoustic liked it in the old days to rate power for 10% THD.

Don't know if the 140 can savely be run at nominal loads smaller 4 Ohm. At a 2 Ohm load the power might (theoretically) reach around 140 watt 10% THD.
Ddn't read the manual!
 
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#29
Even harmonics are always consonant with the fundamental and its octaves. Odd harmonics at some point move away from consonance, esepcially in chords (that's why a heavily fuzzed guitar often sounds better playing 5th chords with no 3rd). A reasonably balanced combination of both tends to yield a nice, rich tone, but that's not always what's desired. The world would be dull if all musical notes had the same timbre.
 
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#30
Guitar amp designers struggle very hard to figure best balance of distortion content respectively balancing of even and odd order amaount of THD.
Well designed preamps can work out minor and major chords in a reasonable better tonal "timbre" than
most of "budget" pedals that often need mixing of dry to the wet to sound acceptable at best.
It's kinda science on it's own with lots of different tonal goals possible.

Yes, there is this distinct unalterable reason why power chords became so popular.


Btw it's very impressing that spectrum of a single note becomes at mids and treble increasingly dissonant to the fundamental. Responsible are the odd order Harmonics which are "naturally" part of every musical instrument.
 
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#31
OK, the last 5 posts have me in deeper than I want to be right now but thanks to all.

Will probably go with the Eminence Delta 15a as suggested.

Unless, (can of worms) since 8 ohms is now in the game, are there any other manufacturers I should consider?
 
#34
Recoil Rob said:
OK, the last 5 posts have me in deeper than I want to be right now but thanks to all.

Will probably go with the Eminence Delta 15a as suggested.

Unless, (can of worms) since 8 ohms is now in the game, are there any other manufacturers I should consider?
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For 70 liters net volume and Fb 55Hz then response will look like this:
upload_2016-9-10_16-46-27.png

Higher cab tuning would even increase the noticeable "hump"


May be it's a good idea to block the port completely for the Dela 15a to get a response more like
upload_2016-9-10_16-47-52.png
 
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#35
ThisBass said:
May be getting "old school" like EVM-series drivers is a better approach to an "old school" built cab for driver choice?
Just a thought.
Click to expand...

Meant as supplement:
EVM 15L response at cab tuning Fb 50Hz
upload_2016-9-10_17-11-21.png


EVM 15L response at cab tuning Fb 65Hz
upload_2016-9-10_17-13-21.png



As the acoustic cab is of rather "oldish" construction I suppose the tuning > 55Hz (gues assertion)

The EVM-15L is a pretty efficient driver which is a big plus with rather weak power amp like the 140
 
#37
OK, the interior of the speaker compartment measures 25L x 21.5H x 8 D = 4300 cubic inches = 70.46 liters (nice estimate ThisBass!)

It has two ports at the bottom, each measures 5 x 1.75 = 8.75 x 2 = 17 sq. inches.

The cabinet still has the original fiberglass insulation in there.

Enough info to model?


thanks,

Rob
 
#40
What you have is a very different cabinet than the one in the picture you posted initially. That's what drove many of the comments.
 

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