Correct, the Shuttle can only do down to 4ohm. Most of the new, lightweight, high power amps will only go down to 4ohms.
Enjoy the benefits of a premium membership!
Upgrade Account
-
TalkBass has been independent since 1998. Add your voice.
Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
Join free Log in
Want zero display ads or expanded classifieds tools? Compare plans.
Switchable 4 ohm, 8 ohm Cabinet
- Thread starter Blah114
- Start date
Correct, the Shuttle can only do down to 4ohm. Most of the new, lightweight, high power amps will only go down to 4ohms.
billfitzmaurice
Commercial User
- Sep 15, 2004
- 16,860
- 278
- 76
- Disclosures
- Owner, Bill Fitzmaurice Loudspeaker Design
The catch here is "assuming your amplifier delivers double the wattage into the 4-ohm load". At low power levels that's usually the case. But not at full tilt, where power supply sag limits the actual power increase with a halving of the load impedance. A 200 watt amp at 8 ohms might deliver 300 watts into 4 ohms at full power. So the net increase with two cabs is more like 5dB at full tilt.
More pertinent in this case, a 4 ohm cab versus 8 ohm cab will only give about 2dB higher output if the amp's at full power, which really isn't worth the bother. If your amp won't drive one 8 ohm cab as loud as you need to be you really need to add another cab or get a bigger amp, or both.
If you do 2/3 the power will go into the 4 ohm cab and only 1/3 into the 8 ohm.
- Nov 24, 2008
- 4,343
- 7,163
- Disclosures
- Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
Bill, you're correct - most amplifiers will current-limit and therefore fail to behave as a constant-voltage source at their upper limits. Thanks for adding this information, as the way I left it was incomplete and therefore misleading.
Actually, Bill's post is the kind of overgeneralization I kind of wince at. Per your bolded part of his post, yes, if you have a little 112 8ohm, adding another 8ohm 112 would of course make much more sense than feeding more power into a similar small 112 at 4ohms. You would get the increased power, and the additional cone area, and of course, not push one little driver past its limits (thermal, xmax, everything).
However, going from 300 to 400 or 500 watts into, for example, a 410 cab can be the difference between a compressed low end and clamping of the transients, and an open, full, noncompressed, even tone. And... the 2db to 3db more volume... if you do your planning right that is FREE and noticeable volume (i.e., if you know you are only going to use a single, large, multidriver cab with a moderate powered SS head, it's literally silly to not get the 4ohm version). Said another way, having 'just enough clean power' for your needs can be a night and day difference between having just slightly less than is needed. And again, it's not just about pure volume!
It really isn't that black and white, and the general statements like above IMO do not tell the whole story and can be misleading.
I don't get how doubling the cone area results in lots more SPL. To my understanding (well, my current understanding, at least) it will result in (VERY rough numbers) twice the cone area having half the excursion, so zero net change in pressurizing. (Please read through my very rough rounding of numbers & stating of concepts.)
Trying a restatement, one 4 ohm 12 gets 100 watts, which moves it back & forth 1/2". A pair of 8 ohm 12s each get 50 watts, which moves them each back & forth 1/4". No net difference.
Stretching my point to an absurd level, I read the 'increased speaker area' theory to mean you can fill a stadium with bass by using a 10 watt amp & a huuuge number of 12s.
Where am I misunderstanding things here?
- Nov 24, 2008
- 4,343
- 7,163
- Disclosures
- Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
JustDavid, the example you gave is correct. So is the one I gave. We're describing different situations.
My example starts with one 8-ohm cab, and adds a second 8-ohm cab (in parallel). Each driver would receive equal wattage, until the amplifier runs out of juice.
Your example starts with one 4-ohm driver, and compares it to two otherwise identical 8-ohm drivers (in parallel). You have correctly described how the wattage would be allocated.
Note that doubling the input wattage does not double the cone excursion. Each doubling or halving of input wattage affects the excursion by a factor equal to the square root of two, so it takes two doublings (or two halvings) of wattage to double (or halve) the excursion, resulting in a 6 dB change in sound pressure level.
It looks like in the absurd case the theory I embrace leads to efficiencies greater than 100%, but that's because we haven't looked at the acoustic interaction between the drivers yet. The net pattern narrows and comb filters increasingly with each additional driver, and the upper limit of efficiency is probably closer to 25% to 50%. This is where a large horn excels, as it is more coherent (less cancelling due to comb filtering) than a wall of woofers - but that's another topic.
My example starts with one 8-ohm cab, and adds a second 8-ohm cab (in parallel). Each driver would receive equal wattage, until the amplifier runs out of juice.
Your example starts with one 4-ohm driver, and compares it to two otherwise identical 8-ohm drivers (in parallel). You have correctly described how the wattage would be allocated.
Note that doubling the input wattage does not double the cone excursion. Each doubling or halving of input wattage affects the excursion by a factor equal to the square root of two, so it takes two doublings (or two halvings) of wattage to double (or halve) the excursion, resulting in a 6 dB change in sound pressure level.
It looks like in the absurd case the theory I embrace leads to efficiencies greater than 100%, but that's because we haven't looked at the acoustic interaction between the drivers yet. The net pattern narrows and comb filters increasingly with each additional driver, and the upper limit of efficiency is probably closer to 25% to 50%. This is where a large horn excels, as it is more coherent (less cancelling due to comb filtering) than a wall of woofers - but that's another topic.
- Feb 12, 2006
- 60,951
- 5
- 220,594
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
You are correct. There is a 3dB increase from doubling the power and there is SOME increase from mutual coupling al low frequencies but rarely 3dB as claimed by many. This coupling falls off as the number of drivers increase though, as the spacing becomes too large to gain the benefit.
Now the 3dB gain for doubling power is also good until you get closer to the RMS power handling of the driver... at that point non-linearities begin to become important. The general term for this is power compression and has several primary mechanisms, including electrical, thermal, mechanical and magnetic.
billfitzmaurice
Commercial User
- Sep 15, 2004
- 16,860
- 278
- 76
- Disclosures
- Owner, Bill Fitzmaurice Loudspeaker Design
The doubling of cone area and drive motor doubles the radiating efficiency of the system, with a finite limit of 25% efficiency from direct radiators. The concept is called mutual coupling, and has been known in the audio engineering community since at least 1940, most comprehensively described by D.B Keele, AES preprint 3193 (1991).
i hear ya, but i think the idea was more on a power/volume train of thought rather than tone effects of wattage.
If you read enough of my posts you know that i am big on lots of power and on modularity. That's not for everyone. However, I get to play a lot of gigs with one 15" where in the past i would have had to use two cabs because i use more power now.
On a related topic to your quoted post, lots of times i bring two cabs and don't hit them so hard to take advantage of the tone difference experienced when you're not beating the crap out of a cab.
but, in terms of plain old volume, given two identical cabs save impedance, if the 8 ohm version isn't loud enough for your needs with your amp, the chances that the 4 ohm version will be are virtually nil. IMHO.........
billfitzmaurice
Commercial User
- Sep 15, 2004
- 16,860
- 278
- 76
- Disclosures
- Owner, Bill Fitzmaurice Loudspeaker Design
+100. Ask anyone who wants to go 4 ohms why and 99.9% of the time the answer will be "So I can get all the watts out of my amp." Two assumptions are behind that statement. One is that watts and perceived loudness are directly proportional. The other is that a speaker requires its full rated power input to reach its full output capability. Both those assumptions are unfounded.but, in terms of plain old volume, given two identical cabs save impedance, if the 8 ohm version isn't loud enough for your needs with your amp, the chances that the 4 ohm version will be are virtually nil. IMHO.........
the speaker only store I frequent.. has something like this.. they suggested that I simply connect the speakers physically different if ever needed.
T.
T.
