resistance is futile? ohm[y] gosh!!

[Justin Carnecky]

Hi all

I need to understand exactly how speaker sensitivity / resistance works. I have the basic idea i think. A speaker of higher sensitivity requires less power to reach the same db as a speaker of lower resistance. Or in plainer english, 1 watt of power will cause more db from a speaker of higher sensitivity. Am I right here?

Now, how does this come together with the resistance of a speaker? how much better (or worse) does a 4ohm speaker perform than an 8ohm speaker, if they both have the same sensitivity?

What are the key technical factors to look for when choosing speakers? Is it a higher sensitivity with lower resistance?

Also, I see that power amplifiers also rate much higher when driving speakers of lower resistance. Is this automatic? I.e. if i unplugged 8ohm speakers and jacked in 4ohm speakers into the same amp, would it start punching out more power based on some rule of physics? Or does the amp need to be 'told' that it is driving lower resistance speakers.

My understanding is that if i buy 4ohm speakers that have the same sensitivity as [my old] 8ohm speakers. I will get double the db out of them / will only need to turn my amp half way as high as i did before to get the same db as the 8ohm speakers.

confusion.......

Regards
Justin

[Sealed]

Hi all

I need to understand exactly how speaker sensitivity / resistance works. I have the basic idea i think. A speaker of higher sensitivity requires less power to reach the same db as a speaker of lower resistance. Or in plainer english, 1 watt of power will cause more db from a speaker of higher sensitivity. Am I right here?
- Yes. 89db/1w/1 meter needs more power to reach 96 db than something rated at 94db/1w/1m

Now, how does this come together with the resistance of a speaker? how much better (or worse) does a 4ohm speaker perform than an 8ohm speaker, if they both have the same sensitivity?
- One has nothing to do with the other. You can have an 8 ohm speaker with 101db/1w/1m sensitivity or a 4 ohm speaker with 80db/1w/1 meter. The ohm rating is essentially the overall load, crossover + drivers, and the woofer is the hardest load, where the tweeter is the easiest.

What are the key technical factors to look for when choosing speakers? Is it a higher sensitivity with lower resistance?
- None. The key factor is how good they sound to you.

Also, I see that power amplifiers also rate much higher when driving speakers of lower resistance. Is this automatic? I.e. if i unplugged 8ohm speakers and jacked in 4ohm speakers into the same amp, would it start punching out more power based on some rule of physics? Or does the amp need to be 'told' that it is driving lower resistance speakers.
- A "good" amplifier will be stable at 4 ohms. Many cheap amps/recievers are not. A lot of cheap amps can only drive simple 8-ohm speakers. Where a GOOD amp will have the power and design that it will double power into 4 ohms. Even a simple Adcom or Rotel amp will produce 100 watts into 8, about 200 watts into 4.

My understanding is that if i buy 4ohm speakers that have the same sensitivity as [my old] 8ohm speakers. I will get double the db out of them / will only need to turn my amp half way as high as i did before to get the same db as the 8ohm speakers.

-- Ohms have nothing to do with loudness (not directly). If the new speakers are 4 ohms, and your amp can drive them, they will achieve the same loudness. If the old speakers are 92db 1w/1m and the new speakers are 96db/1w/1m (8 or 4 ohm) they will get louder with less power.

confusion.......

Regards
Justin

[Justin Carnecky]

Hi all

I need to understand exactly how speaker sensitivity / resistance works. I have the basic idea i think. A speaker of higher sensitivity requires less power to reach the same db as a speaker of lower resistance. Or in plainer english, 1 watt of power will cause more db from a speaker of higher sensitivity. Am I right here?
- Yes. 89db/1w/1 meter needs more power to reach 96 db than something rated at 94db/1w/1m

Now, how does this come together with the resistance of a speaker? how much better (or worse) does a 4ohm speaker perform than an 8ohm speaker, if they both have the same sensitivity?
- One has nothing to do with the other. You can have an 8 ohm speaker with 101db/1w/1m sensitivity or a 4 ohm speaker with 80db/1w/1 meter. The ohm rating is essentially the overall load, crossover + drivers, and the woofer is the hardest load, where the tweeter is the easiest.

What are the key technical factors to look for when choosing speakers? Is it a higher sensitivity with lower resistance?
- None. The key factor is how good they sound to you.

Also, I see that power amplifiers also rate much higher when driving speakers of lower resistance. Is this automatic? I.e. if i unplugged 8ohm speakers and jacked in 4ohm speakers into the same amp, would it start punching out more power based on some rule of physics? Or does the amp need to be 'told' that it is driving lower resistance speakers.
- A "good" amplifier will be stable at 4 ohms. Many cheap amps/recievers are not. A lot of cheap amps can only drive simple 8-ohm speakers. Where a GOOD amp will have the power and design that it will double power into 4 ohms. Even a simple Adcom or Rotel amp will produce 100 watts into 8, about 200 watts into 4.

My understanding is that if i buy 4ohm speakers that have the same sensitivity as [my old] 8ohm speakers. I will get double the db out of them / will only need to turn my amp half way as high as i did before to get the same db as the 8ohm speakers.

-- Ohms have nothing to do with loudness (not directly). If the new speakers are 4 ohms, and your amp can drive them, they will achieve the same loudness. If the old speakers are 92db 1w/1m and the new speakers are 96db/1w/1m (8 or 4 ohm) they will get louder with less power.




THanks, this makes it a lot clearer, but still not crystal clear. Lets say i have a fairly good amp (Rotel 2x200W into 8ohm) and a pair of 8ohm 86db/1w/1m speakers. THen I go and buy a set of 4ohm 86db/1w/1m speakers. Now all of a sudden my amp is pushing out 2x400W AND my speakers are a lot easier to drive (lower resistance). So logically, turning the amp up to halfway should now produce a hell of a lot more sound then it did with the 8ohm speakers right (more then double the sound - because i am pushing twice the power into a speaker that is more easily driven) ?

Regards
Justin

[markw]

Generally amps are much happier with a higher impedance load. They respond by running cooler, producing less distortion and lasting longer.

As far as that "turning it up" thing goes, that has to do with an amp's gain, not it's power output. You may well have to turn it up just as high.

Given the choice, opt for the 8 ohm speakers. Likewise, don't shop impedance, shop sound first and, if you choose 4 ohms be sure your amp is happy with that.

[bturk667]

When you write your amp would be pushung out 2x400 into a 4 ohm speaker, well, that is not necessarily true. An amp can only do this if it is capable of doing it. Not all amps double their power from 8 ohms into 4 ohms. 4 ohm speakers are harder for a amp to drive. Reduced resistence means the amp has to provide more current which is harder.

Think of it this way. Say a 4 ohm load is like pedaling a bike in second gear. It easy, less resistance, but know try to provide a constent rate of speed, especially a high rate of speed, (high wattage, higher current). You would have to pedal like a mad man to do this; you would exert a lot of energy. Then take into account that impedance is generally not very flat in most speakers through the frequency range, it's more like a rollercoaster. Know you are exerting a lot of energy to keep up with the changing impedance, while keeping a constent speed.

Know flip the bike into fifth gear, (8 ohms). Sure, there is more resistance, but it is a lot easier to pedal at, and maintain higher rates of speed (wattage/current). Hell, it's easier to maintain any speed. This is why amps have an easier time with higher impedances, especially tube amps, which provide more current into higher impedances.

Remember, 4 ohm speakers demand more current than 8 ohm speakers. This is what seperates the men from the boys, if you will, when it comes to amps. Most recievers and cheap quality amps have a hard time with a 4 ohm load; especially at higher volume levels. This is why so many people and salesman tell you to buy the biggest amp you can. Proportionately, it is eaiser for a big amp to provide current into 4 ohms, than a smaller, less powerful one.

I know it is confusing, but I hope this helps to better understand impedance and its relation to speakers.

[RGA]

The terms get confusing. Sensitivity and the speaker's ohm(impedence) are not related. Class A amps don't double into 4 ohms either. The Sugden A21a is 25 watts at 8 ohm and at 4ohms...it is not necessary for amplifiers to double into 4ohms - just that it can actually drive 4ohms.

Also speaker ratings are often misleading. A speaker may be nominally(averaged) rated as 8 ohm s but may have impedence dips at certain frequencies to below 3ohms requiring the amp at those dips to increase power to meet the demand.

A speaker is kind of like a bucket asking to be filled with water(power). It's going along playing some music and suddenly someone hits a pedal organ passage and asked the amplifier for dopuble or triple the power...if the amp can't muster it FAST enough it sounds smudged. Most so called high current amps can muster momentary spikes but not long and really I'm suspicious of the claims of high current by outfits like Denon/Marantz/HK etc.

Think of impedence as efficiency and the db rating as sensitivity. A speaker with high sensitivity but low efficiency will still be tough to drive for many amps.

My speakers are 90db sensitive and never dip below 5 ohms(Usually around 10-13ohms) making it a very easy to drive speaker.

None of these things have to do with the actual quality of sound of the speaker - but it can certainly save money on amplifiers and allow for more choice. My speakers for example would be happy with a 8watt Single ended tube amplifier - and play very loud - or will be happy with 250 watt Bryston Mono-blocks. Some speakers would have to have the Brystons and could not be run from the 8 watt SET amp.

Since there are so many speaker choices I would choose the high sensitive high efficiency design. The ~115db sensitive Klipshhorn would play louder with a 1 watt amp than an 82 db sensitive speaker with 300 watts

db=watts(82 db sens speaker to get to 115db)
82=1
85=2
88=4
91=8
94=16
97=32
100=64
103=128
106=256(Max db with 300 watt amp)
109=512
112=1028
115=2056watts!!! (required to equal same volume with that 1 watt amp and super high efficiency speakers)

---- now you know why some people love horns. If you give the 115 db speaker 2 watts you get 118db). to get the same with the 82db speaker you need 4112 watts.

But you also have to look at the maximum the speaker can handle - very few speakers can take more than 300 watts so inmy example the maz would be 106db.

By the way 90db is considred LOUD - 100db can harm your hearing and physically hurt.


Bturk667 provides a good analogy and why tube amplifiers and especially SET amps get a lot of complaints from people. Most SETs are very low power and do not double into lower impedences. Thus if a speaker has a minimum impedence of 2 ohms the SET wil not be able to meet that demand and will putter out causeing flabby bass response or a soft mushy treble or BOTH. This is not a fault of the amp it is a fault with the buyer who ddn't do his/her homework.

People buying SET's will go with a high sensitive efficiency horn or an Audio Note speaker where the impedence is very easy and the sensitivity is relatively high. This ensures the amp doesn't weaze and will provide ample bass depth and treble extension that the best solid state amps provide as well as providing perfect linearity which no solid state amp has at any price.

Since speaker distorion dwarfs any distorion level in a tube amp that is not a concern anyway...people complain about the 1.2% distortion but forget about the 10% sdistortion put out by speakers(when was the last time you ever saw a speaker provide a distortion figure). So the high efficiency speaker built for the SET will take the SET's higher sitrtion but the speaker has less so it's a wash. - and then there is the type of distortion.


Blah blah blah...what to look for --- is what sounds the best...build your system around the speakers - I personally like to keep my options open...so I prefer higher efficiency and higher sensitivity...but if you love something like Magnepan or electrostats buy those and make sure you get a BIG ASS Rotel or Bryston power and you're fine.

[92135011]

if you want an idea of what loud is...
this is from a physics text book

all figures in dB

airplane 150
jackhammer or machine gun 130
siren 120
busy traffic 80
vacuum cleaner 70
normal talking 50
rustling leaves 10

Anythinig above 90 dB recommends using ear plugs if it is during a prolonged period. Remember to preserve your ears so you can enjoy your music.

[E-Stat]

...but if you love something like Magnepan or electrostats buy those and make sure you get a BIG ASS Rotel or Bryston power and you're fine.
:)

Yes, I find a "BA" pair of VTL tube monoblocks works quite nicely with my 'stats.

rw

[Laps]

I recently noticed that my speakers (Phase Tech rated at 4 ohm) sounded distorted when wired to the McIntosh amp through the 8 ohm connection. I switched the cables over to the 4 ohm and the distortion resolved and the amplifier now runs cooler, rather than hotter. Any ideas as to why it sounds better at the 4 ohm and runs cooler, I had thought that the lower ohm resistance meant higher temps. Also, I've had an "imbalance" between right and left sound quality (regardless of the ohm selection or speaker placement, I've even swapped out interconnects and cable and switched the two speakers without any effect).

[Norm Strong]

"sensitivity" of a speaker is defined as the Sound Pressure Level (SPL) on-axis, 1 meter away, when 2.83 volts rms is applied to the speaker terminals. If the impedance of the speaker happens to be 8 ohms, then 2.83 volts will work out to 1 watt. If the speaker happens to be 4 ohms, it will take 2 watts to achieve the advertised SPL.

The reason sensitivity is specified in this fashion is because it's easier to measure in practice. The impedance of every speaker varies all over the map depending on frequency.

[Geoffcin]

I recently noticed that my speakers (Phase Tech rated at 4 ohm) sounded distorted when wired to the McIntosh amp through the 8 ohm connection. I switched the cables over to the 4 ohm and the distortion resolved and the amplifier now runs cooler, rather than hotter. Any ideas as to why it sounds better at the 4 ohm and runs cooler, I had thought that the lower ohm resistance meant higher temps. Also, I've had an "imbalance" between right and left sound quality (regardless of the ohm selection or speaker placement, I've even swapped out interconnects and cable and switched the two speakers without any effect).

Hi, your Mac uses an output transformer, so you should use the taps that match the impedance that your speakers present to get the best match. If there's an inbalance in sound between the channels then you should take the amp to a tech. It may be as simple as adjusting the bias.

[Laps]

Thanks G., I actually just received the amp back from McIntosh Labs to have it serviced and they did set the bias, but get this: Last night I was making adjustments to the treble and balance and the gain on the Velodyne (this is an older unit, an ULD-15 I believe, so that connections are from preamp to Velodyne out to the amp) and as I turned the bass control down on the McIntosh the imaging became perfectly balanced between the two speakers! Wierd stuff. And yes I have the speaker connects on the McIntosh on the 4 ohm posts. I still can't believe how much cooler the amp runs now on the 4 ohm as opposed to the 8 ohm connections. It's probably one reason why the front panel lights had burned out previously (due to the excessive heat when connected to the 8 ohm posts). Hard to believe I had been listening to it that way for YEARS, but that's another story.

[Geoffcin]

Thanks G., I actually just received the amp back from McIntosh Labs to have it serviced and they did set the bias, but get this: Last night I was making adjustments to the treble and balance and the gain on the Velodyne (this is an older unit, an ULD-15 I believe, so that connections are from preamp to Velodyne out to the amp) and as I turned the bass control down on the McIntosh the imaging became perfectly balanced between the two speakers! Wierd stuff. And yes I have the speaker connects on the McIntosh on the 4 ohm posts. I still can't believe how much cooler the amp runs now on the 4 ohm as opposed to the 8 ohm connections. It's probably one reason why the front panel lights had burned out previously (due to the excessive heat when connected to the 8 ohm posts). Hard to believe I had been listening to it that way for YEARS, but that's another story.

I guess I'm lucky in that my preamp has two outputs, with one going directly into my amp, and the other to the subs. I use splitters at the ends of the RCA jacks to send input into both channels of the Sub's inputs, as I use TWO subs.

I would definitely go from the preamp DIRECTLY into the amp if at all possible. I don't trust the line outputs from subs, there's just too much high current going at the plate amp, bound to be some kind of crosstalk or worse.

[Laps]

Unfortunately my preamp, also a McIntosh, doesn' t have a 'sub out' and since the Velodyne is an active amp itself with its own servo there isn't any other connections I can make that will allow the Velodyne to actively remain in the loop. If I use any other preamp out connection, such as 'tape' or 'aux', then the Velodyne will remain at a constant volume and not vary with the volume setting on the pre-amp. I've excluded the Velodyne completely from any input just to see how the main speakers sound and surprisingly there is very little difference. One day I'll have to upgrade the pre-amp to allow for a 'sub out' connection, don't want to get rid of the Velodyne as of yet. I assume the new preamps from McIntosh would solve the problem but I haven't been to the local dealer in quite some time.

[markw]

Some "Y" connectors on the preamp's output will send the signal to both your amp and the sub simultaneously. Essentially, that's what a second sub out is anyway.

[kfalls]

I recently noticed that my speakers (Phase Tech rated at 4 ohm) sounded distorted when wired to the McIntosh amp through the 8 ohm connection. I switched the cables over to the 4 ohm and the distortion resolved and the amplifier now runs cooler, rather than hotter. Any ideas as to why it sounds better at the 4 ohm and runs cooler, I had thought that the lower ohm resistance meant higher temps. Also, I've had an "imbalance" between right and left sound quality (regardless of the ohm selection or speaker placement, I've even swapped out interconnects and cable and switched the two speakers without any effect).

McIntosh's are a bit of a different animal in that they use an autotransformer output which has taps for certain impedances (16, 8, 4,...). This is why McIntosh say they can provide rated output at any load. Ideally the most power is transferred from amp to speaker when impedances match. A good analogy would be similar to connecting two different size hoses together. Water input from the smaller (4 ohm) will never be able to fill the larger hose (8 ohm) to the same pressure. Inversely, water input from the larger hose (8 ohm) will never be able push all of its capacity through the smaller hose (4 ohm). But when you have hoses of the same size you will get the maximum amout of flow (power transfer) at a constant pressure.

To me amplifiers are all about how much current it will handle. Is the wire in the power transformer large enough to handle the current? Can the drivers and output transistors handle the currents of their particular circuits? Can the power supply provide enough power (current and voltage) without clipping?

[Laps]

Some "Y" connectors on the preamp's output will send the signal to both your amp and the sub simultaneously. Essentially, that's what a second sub out is anyway.


You're right, how simple! Where can I get RCA type Y-connectors? I would need single male into split female connections.

[markw]

... Radio Shack, www.partsexpress.com or practicaly any audio hardware purveyor. No need to spend big bux here.

[thepogue]

reading this thred make me proud I hang out here ...lots and lots of good info!!! I'm putting you all in for a raise this year!!! :D

[Laps]

Thanks for everyones suggestions. I did an Internet search last night and found that Monster Cable makes a small male-to-female (split) y-adapter that will fit directly to the posts on the Main output. I'll run cables from there (main out) on the preamp to the amp and to the Velodyne subwoofer. I found a vendor that carries the Monster Cable y-adapters, WildWest Electronics, so should have them in a few days and I'll post an update and opinion as to any sonic benefits by going this route.

[aimen]

Ohms Law is a mathematical equation that shows the relationship between Voltage, Current and Resistance in an electrical circuit. It is stated as:

current = volts / resistance

1 volt having 1 ohm resistance will produce 1 ampere (1 watt = 0.35375 amp)

so if u wont to produce 100watts; so higher the resistance the less volts are needed
thus easier to drive

for more detail goto http://www.ohmslaw.com/ohmslaw.htm

[Laps]

Here's the update I promised. I put Y-adapters (from Monster Cable) on the MAIN output from the McIntosh pre-amp. They split the signal TO the subwoofer amp (Velodyne) and TO the McIntosh amp (for the main speakers). The sound improvement was incredible. The clarity and brightness of the mids and highs is like having a new system. Obviously, the Velodyne was putting a dampener on things. I still have the servo capability of the Velodyne unit in conjunction with the pre-amp so I'm all set!