loudspeaker impendance

[VJ]

Hello,

A simple question: I have a home cinema amplifier (Marantz SR-6001). The technical specification of the amplifier section list:

AUDIO SECTION
Power Output (20 Hz – 20 kHz/THD=0.08%)
Front L&R ..........................................8 ohms 100 W / Ch
Center .............................................8 ohms 100 W / Ch
Surround L&R .......................................8 ohms 100 W / Ch
Surround Back L&R ..................................8 ohms 100 W / Ch
Front L&R ..........................................6 ohms 120 W / Ch
Center .............................................6 ohms 120 W / Ch
Surround L&R .......................................6 ohms 120 W / Ch
Surround Back L&R ..................................6 ohms 120 W / Ch
Input Sensitivity/Impedance ........................168 mV/ 47 Kohms
Signal to Noise Ratio(Analog Input / Pure Direct) . 105 dB
Frequency Response
(Analog Input / Pure Direct)
................................................... 8 Hz – 100 kHz (± 3 dB)
(Digital Input / 96 kHz PCM)
................................................... 8 Hz – 45 kHz (± 3 dB)

Can I connect speakers with this specification:

Frequency ............ Minus 3db at 55hz and 22khz.
Sensitivity  ......... 90db spl (1w @ 1m) 4 ohm.
Sound  ............... Compatible with amplifiers from 10w - 100w output.

Or are there reasons to look for other speakers? (I have not bought the speakers yet)
Thanks!


Jörg

[MultimediaMan]

6/8 Ohm resistance is fairly standard for Home Theater.

4 Ohm parts are generally for Car Audio

You are overdriving the Amp by running lower impedances: there really isn't a good "electrical" way around this. It could run hotter than a toaster oven in some configurations.

There are ways to mitigate some of the risks: if you are running the drivers in well-dampened sealed enclosures, it will raise the dynamic impedance of the speaker and make it less likely to overdrive the amp. But IMHO, it isn't worth the risk.

http://en.wikipedia.org/wiki/Electrical_characteristics_of_dynamic_loudspeakers

[VJ]

The speakers I was looking at are these:

http://www.scandyna-speakers.com/Products/Minipod.aspx

(so not car audio... )

I have a pair of these ( http://www.scandyna-speakers.com/Pro...cropod_SE.aspx ), connected to an amplifier of the same manufacturer as the speakers (which is a Class D BTW), and the sound is just amazing for their size. So given their good quality, I was hoping to use their larger model in a 5.1 system, also because I love the design. I got the amplifier from my parents, who upgraded theirs (but kept their speakers).

Quite surprisingly, their center speaker lists 8 Ohm: http://www.scandyna-speakers.com/Products/Cinepod.aspx

[Umfriend]

4 Ohm speakers are actually quite common in Europe. 8 Ohm was more prevalent, uhm, around 30 years ago.

I think the issue is that at 4 ohm it may deliver more power but that (a) the PS may not be able to deliver (causing clipping) and that (b) the power transistor may be delivering more current than it is rated for.

I think you should be fine though. I have never actually heard of an amp blowing out. Most simply do not turn volume to 0 ohm and from a brand like Marantz I would expect some decent circuitry protection.

[Evildead666]

I have done a bit of playing with audio hardware in the car and home, and have come to the conclusion that 4 Ohm is for car use only.
6/8 Ohm is what is used in household settings.

I wouldn't try 4 Ohm on my home Amp, since it would be outside the specs.
You can find good 6-8 ohm speakers

[VJ]

Umfriend: Well, I also don't expect much problems (the spec sheet of the speakers mention they are compatible with 100W amps, presumably because they never get turned up to the point where it can cause problems), but just want to make sure. This particular Marantz model does have a history over going into protection mode for overheating though (which is a problem, as it has to be serviced then). But it would be positioned in the open, so with plenty of ventilation around it. I sent an email to Scandyna, and they said it should be no problem with this amplifier.

Evildead: well, these speakers are clearly not for car use... Perhaps they are specified differently (e.g. that they specify the lowest impedance across the frequency range, whereas others specify an average value or so)?

[gt40]

That amp has provisions for 2 sets of front speakers (A,B), that as far as I can tell, would be hooked in parallel when both are switched on. As long as you only hook up one set to the front, I don't see there being a problem.

[Umfriend]

VJ, blew up your amp yet?

[VJ]

Hehe... no... but I don't have it configured yet... The amp is still in Belgium, and I still need to get the speakers... The whole thing was just to make sure I have my options open. I'd probably get the amp here in September.

[Greebe]

Speaker impedance ratings are at best ambiguous. There is the Transient impedance and there is steady state, nominal impedance curves. The later is normally used. Lower impedances relates to power output of the amplifier final (output stage). Many of these 4 ohm speaker designs cannot be used, heck some speakers with an 8 ohm rating can cause serious issue with most amps rated for the load. When there is a bass kick typically the impedance can drop to below 1 ohm. Unless you only listen at low levels, amps will current clip, producing massive amounts of much higher freq distortion, pOOf your tweeters just blew out.

Some amps do fine with these loads dispite being out of "spec" I would suggest before you buy, goto the various high end / DIY audio forums and research what your particular amp can do/handle. Do the same for the speakers.

Marantz doesn't make amps that typically can do these loads (high current/low impedance), the specs speak for themself. They do make a very clean amp, low distortion, high S/N ratios, just not really capable of any extreme impedence changes.

Amps, as imperfect as they are, if looked at from what an amp is, should be, if truely capable would have power ratings like this...

100w into 8ohms (nominal)
200w into 4ohms
400w into 2ohms
800w into 1ohm
1600w into 0.5 ohm
3200w into 0.25ohm
etc etc etc
This is linear current amplification at it's simplest form

The reasons for the wantent need for more power outweighs the limits many amps are capable of and is nothing more than a marketing trick to squeeze out every last dB of sound level possible. Remember to increase the output level by 3 dB the output power must double. This is the same caca the car audio industry pimps to the BOOM BOOM BOOMERS. More watts = more SPL's, while completely ignoring the speakers efficiency, many which are not more than 82dB/W/m eg horribly ineffecient. On the flipside, Car amp designers have shrugged off the typical irrevalent psycho babble the Audiophile/high end audio industry designers neglicted to address, current capacity. Their amps can typically goto 1ohm or less, they aren't perfect power curves like mentioned above, but are a damn sight closer than 99.9% high end audiophile amps can do. Most high end amp designers look at is keeping the distortion/s/n ratios in check, while neglicting the current portion, which requires massive power transformers, huge caps, monster sized heatsinks and completely redesigned final... which add a huge amount of weight and additional cost of manufacture.

Typical audio amp are of Transimpedence designs, also known as a voltage amplifer
Newer solid state designs which handle high current/low impedence are Tranconductance designs. There are hybreds of these two and a few others not mentioned. FYI old school transconductance amps were tube amps. Transimpedance amps you do not go below min rating, but can go up in impedence without harm. Transconductance amps reguire you to have a maximium impedance of no more than rated for or LESS. A bad thing to do with most any transconductance amp is turn it on without a load, they fry.

[Greebe]

The speakers I was looking at are these:

http://www.scandyna-speakers.com/Products/Minipod.aspx

(so not car audio... )

They might as well be, kevlar is not a good material for speaker cones. Only good for enviromental extremes.

I have a pair of these ( http://www.scandyna-speakers.com/Pro...cropod_SE.aspx ), connected to an amplifier of the same manufacturer as the speakers (which is a Class D BTW), and the sound is just amazing for their size. So given their good quality, I was hoping to use their larger model in a 5.1 system, also because I love the design. I got the amplifier from my parents, who upgraded theirs (but kept their speakers).

Cute

Quite surprisingly, their center speaker lists 8 Ohm: http://www.scandyna-speakers.com/Products/Cinepod.aspx

They are 8 ohm because they wired the 2/ 5" drivers in series. 4
+4=8

[VJ]

Thanks for the nice explanation!

They might as well be, kevlar is not a good material for speaker cones. Only good for enviromental extremes.

B&W also uses Kevlar cones...
(the designers of Scandyna came from B&W)

They are 8 ohm because they wired the 2/ 5" drivers in series. 4+4=8

Makes a lot of sense...

The main thing is: I know these speakers sound amazing, particularly for their size (and I'm quite critical when it comes to audio). Furthermore, the design really would fit my interior (mainly modernist interior). Not so many amps however indicate a 4 Ohm rating. I posed the question to Scandyna, and they said it would be no problem to combine their speakers with this amp.
What I seem to understand from all it is that it would be a problem at high power, but that it would be at a point that would make it far too loud anyway... (so that point of high power where problems occur would realistically never be reached, even though it is technically reachable with the setup). Is this it?

You also mention "when there is a bass kick"... but would setting the crossover frequency in the amp prevent very low bass tones to be sent to the speakers in the first place? Or does the kick not have to be that low?

[Greebe]

Depends on if you cross the speakers over like used in Sub Sat installs. True subs are always crossed over at or below 100Hz where this impedance drop occurs (also same region where it spikes). If the speakers are run full range then they could induce this issue, but rather doubtful as they are only 5" drivers, ain't gonna get that bass from them anywho ... albiet anything sent to the speaker below the port frequency will unload the driver (out of phase) and has very nasty effect on not just sound, but the impedance curve becomes wacked

B&W, LOL ok everyone is allowed to make SOME mistakes, besides that kevlar makes them look perdy and bullet proof (bwahahahaha)

Peerless makes a phenominal 6.5" driver utilizing a nomex cone with an inverted dust cap that'll blow most any other speaker out of the water for it's size, price, and astonishingly clean undistorted response and it's on sale...

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-1092

These are the same drivers as used in the Elsinore

http://www.customanalogue.com/elsinore/elsinore_index.htm

which is the only speaker that I am currently aware of which can reproduce a square wave... delightful speakers if you can afford them assembled, as a kit or DIY.

Another smaller design based on the same driver, the Veeper

http://www.lonesaguaro.com/speakers/VP/Veeper.html

Boxes can be of any shape within limits of course, those cute curves do nothing to minimize defraction and greatly hinder it.

Tho I doubt I'd use the tweeter the Veeper uses, probably use a dual concentric ring radiator tweeter, perhaps a Vifa

[Greebe]

I've been looking at replacing the speakers my son has in his BR just because. And I'm hyper fickle when it comes to reproduction. Don't spend the most on speakers to get the quality sound you are looking for, be smart about it and save a Bbbbbundle.

A smallish high end 2 way monitor I can build for under $300/pr, sold! Anything similar from any known manufacture will cost 2-3x this for the same quality.

[Umfriend]

I don't see why Kevlar would be worse than Nomex (unless you play with fire)? Kevlar is stronger and AFAIK, ideally, a driver has absolute stiffness and no weight.

Also, the quoted impedance of a speaker system, which is a rather simplification of the resistance properties of such system, should be about 1.15 x the minimum impedance so that even a 4 Ohm system should not ever reach 3, let alone 1 Ohm. Of course, the phase characteristics are important as well.