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View Full Version : Would large home amps drive small (3678) cinema speakers?



kenratboy
01-11-2010, 07:37 PM
From reading this (and other) forums about using pro speakers for home use, I have come under the impression that while sensitive, these speakers need a LOT of power and a LOT of current to sound good, even at low volume levels.

For the small guys (like the 3678 screen channels), instead of using the DSi amps (I would use one on the subwoofer without question, partly for massive amounts of power, partly for the needed EQ features) for the speakers, what about big home amps?

For example, Emotiva rates this at 200x3 at 8 ohms.

http://emotiva.com/xpa3.shtm

Or Outlaw's version:

http://www.outlawaudio.com/products/7500.html

Would an amp like this be able to drive these speakers well for even a larger HT space (5,000+ cu. ft.) - or would there be real benefits of the DSi amps?

Thanks!

jcrobso
01-12-2010, 08:40 AM
1st. The size and the acoustics of the room.
2nd. The sensitivity of the speakers.
3rd. What are you listing to.
4th. How loud do you want it to be?
There are other things also, but these are the first ones that came to mind.
Bass requires the most power and the biggest speakers. Also due to the response cure of human hearing. (http://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves) the bass needs to be 10~20db louder to be heard at the same level as a 4kHz tone. Also every time you double the distance from the speaker the level drops by 6db.
Pro speakers are designed to fill very large rooms and will require a big amp to do so.
Now in you living room they will just be loafing to give you 100db with just a couple of watts. You still need a big amp for the bass.

kenratboy
01-12-2010, 08:58 AM
I guess what I am getting at is in response to what a few people here have said.

Simply because the 2226 woofer is such a beast, even at very low levels, it needs a lot of current to sound good (to literally get the woofer moving at all). I am not sure this is true, hence my question.

In theory, if I hooked up a $500 Denon or Yamaha to the 3678's, would it even sound good at low levels due to the relatively low current compared to a beefy home amp, or a DSi series pro amp?

Robh3606
01-12-2010, 09:20 AM
In theory, if I hooked up a $500 Denon or Yamaha to the 3678's, would it even sound good at low levels due to the relatively low current compared to a beefy home amp, or a DSi series pro amp?

Why wouldn't it?? A small home amp could drive them in your livingroom. Even if you are using a seperate 1000 watt amp you would only be drawing a couple of watts so no real current draw. In general stand alone amps sound better but there is no reason to think it can't sound decent using an HT reciever to power them. Just try it out in stereo with whatever you have available. The whole idea is the be on the right side of the power curve. After the first 100 watts it's all just a couple of Db of headroom. Using that first 100 watts the best way you can is where it really counts.

Rob:)

Tom Brennan
01-12-2010, 09:24 AM
Yes. I've had good results with 2226s with small tube amps even. They are sensitive and easy to drive, a few watts will drive you out of the house.

Those 3678s are interesting speakers, kind of a JBL version of an Altec 19 in a utility format. Price is nice too. Were I single I'd be tempted to replace my Martin Logans with a pair. ;)

jcrobso
01-12-2010, 09:52 AM
It is a beast because of how loud it can play with a BIG amp. I have used them in a large Church, I could shake the pews with them.

kenratboy
01-12-2010, 10:03 AM
Yes. I've had good results with 2226s with small tube amps even. They are sensitive and easy to drive, a few watts will drive you out of the house.

Those 3678s are interesting speakers, kind of a JBL version of an Altec 19 in a utility format. Price is nice too. Were I single I'd be tempted to replace my Martin Logans with a pair. ;)

Thanks. I guess I got bad info.

I am guessing the 3678's would not need a lot of power in a smallish room to play LOUD. However, I have had issues driving large towers with smaller amps. Flat, undefined bass. Put a bigger amp into the equation (my Primare, which I could probably use as a welder), and the bass was significantly better (along with the rest of the sound). Isn't some of this due to a higher-current amp that is able to grab and control the woofers, even at lower levels? Does damping factor and other parameters play into this?

One concern I had on the 3678 was the 90x90 horn. Is that too wide for home use (or does that mean you will need carpeting, and an acoustically-treated ceiling)?

And yes, it seems to be an interesting speaker. Big enough to make a project like this worth its while (come on, it can put out 'THX levels' in a commercial cinema!), yet I could see placing three of these on the floor below a screen without having to go through too much work (they are the same height as a tower speaker, and not much taller than a big center channel on a stand)

Eaulive
01-12-2010, 10:41 AM
I guess what I am getting at is in response to what a few people here have said.

Simply because the 2226 woofer is such a beast, even at very low levels, it needs a lot of current to sound good (to literally get the woofer moving at all). I am not sure this is true, hence my question.

No offense intended but this statement obviously comes from somebody that lacks even the most basic knowledge of electronics.

The current draw is directly proportional to the voltage applied and the resistance of the load. There's no way to have more current flow in a given load without increasing the voltage, hence the loudness of the sound.

Any 8 ohms speaker will draw 1A when driven by a voltage of 8Vrms, no matter the amplifier.

Ruediger
01-12-2010, 11:26 AM
Hi kenratboy,

what You heared may be based on facts. I am writing this with care because some “audiophile people” invent all kinds of junk theories and we must keep these apart from proper engineering sciences.

Below You find the abstract of an AES paper which describes the phenomenon You heared about (or a similar one). Well known designers of real world professional amplifiers such as Douglas Self take these things seriously. See "Self on Audio", year 2000, page 332, "Loudspeaker undercurrents".

The conclusion is not that the 2226 is so hard to drive and thus needs a super amplifier. The conclusion is rather that if You want to hear the full potential of good speakers You need a very good amp as well. If You had Bose speakers You would not need to think about this :)

Ruediger (proud owner of two Yamaha MX-1)

Peak Current Requirement of Commercial Loudspeaker Systems

Measured terminal impedances of several commercial loudspeaker systems are developed into their equivalent electrical circuits by using the Brune network synthesis method. The synthesized circuits accurately describe the properties of the load as seen by the amplifier feeding the loudspeaker system. A group of non-sinusoidal audio signal sequences, which cause the loudspeaker system to draw momentary currents considerably in excess of what could be expected from the rated terminal impedance is identified using computerized network analysis methods. The maximum value of peak current of peak current reported for a commercial loudspeaker system is 6.6 times larger than that of an eight ohm resistor. The current peaks typically last a few hundred microseconds. The current peaks are caused by simultaneous parallel excitation of several of the drivers of a multiway system, by summation of cancellation currents originating from the energy stored in the mechanical and electrical reactances of the circuit, and by impedance transformation effects in the crossover network. The results imply that for short periods of time, an amplifier should be able to drive, with full output voltage swing and without appreciable distortion, loads equal to a resistor of one ohm.

Authors: Otala, Matti; Huttunen, Pertti
Affiliations: Otamation Inc., Helsinki, Finland ; Polarpro Inc., Kuusamo, Finland(See document for exact affiliation information.)
AES Convention:79 (October 1985) Paper Number:2293

Eaulive
01-12-2010, 11:40 AM
Hi kenratboy,

what You heared may be based on facts. I am writing this with care because some “audiophile people” invent all kinds of junk theories and we must keep these apart from proper engineering sciences.

Below You find the abstract of an AES paper which describes the phenomenon You heared about (or a similar one). Well known designers of real world professional amplifiers such as Douglas Self take these things seriously. See "Self on Audio", year 2000, page 332, "Loudspeaker undercurrents".

The conclusion is not that the 2226 is so hard to drive and thus needs a super amplifier. The conclusion is rather that if You want to hear the full potential of good speakers You need a very good amp as well. If You had Bose speakers You would not need to think about this :)

Ruediger (proud owner of two Yamaha MX-1)

Peak Current Requirement of Commercial Loudspeaker Systems

Measured terminal impedances of several commercial loudspeaker systems are developed into their equivalent electrical circuits by using the Brune network synthesis method. The synthesized circuits accurately describe the properties of the load as seen by the amplifier feeding the loudspeaker system. A group of non-sinusoidal audio signal sequences, which cause the loudspeaker system to draw momentary currents considerably in excess of what could be expected from the rated terminal impedance is identified using computerized network analysis methods. The maximum value of peak current of peak current reported for a commercial loudspeaker system is 6.6 times larger than that of an eight ohm resistor. The current peaks typically last a few hundred microseconds. The current peaks are caused by simultaneous parallel excitation of several of the drivers of a multiway system, by summation of cancellation currents originating from the energy stored in the mechanical and electrical reactances of the circuit, and by impedance transformation effects in the crossover network. The results imply that for short periods of time, an amplifier should be able to drive, with full output voltage swing and without appreciable distortion, loads equal to a resistor of one ohm.

Authors: Otala, Matti; Huttunen, Pertti
Affiliations: Otamation Inc., Helsinki, Finland ; Polarpro Inc., Kuusamo, Finland(See document for exact affiliation information.)
AES Convention:79 (October 1985) Paper Number:2293

You're gonna kill the poor guy, he doesn't even know what Ohm's law is and you're jumping right away into reactance and AC circuits :D

Tom Brennan
01-12-2010, 12:52 PM
I am guessing the 3678's would not need a lot of power in a smallish room to play LOUD. However, I have had issues driving large towers with smaller amps. Flat, undefined bass. Put a bigger amp into the equation (my Primare, which I could probably use as a welder), and the bass was significantly better (along with the rest of the sound).

One concern I had on the 3678 was the 90x90 horn. Is that too wide for home use (or does that mean you will need carpeting, and an acoustically-treated ceiling)?




Well it's hard to tell how a given speaker is going to sound with a given amp. When I bought my Martin Logans I'd planned on using a 75 wpc Denon receiver that with my Altec 19s sounded great. But with the MLs the Denon sounded dead, flat and lifeless and my little EL 84 Jolida with about 15 watts a channel sounded much better. So I ended up buying a more powerful EL 34 Jolida with a claimed 50 watts a channel. And a remote, gotta have a remote. ;)

IME&O 90 degree horns sound just right in most home situations; I've used horns as narrow as 60 degrees and as wide as 120. The 60s were too beamy and the 120s too diffuse though the 120s did sound kind'a neat bouncing sound off the side walls--BIG image. But too big and not as well "anchored" as 90s.

Note that these are my opinions and experiences in my rooms and with my associated gear; don't take any of this as gospel.

kenratboy
01-12-2010, 12:54 PM
I know what ohms law is (I am vaguely familiar with TS parameters, mostly from using WinISD, reading some speaker design books, etc.), but I am certainly not at a point where I have a good grasp and the ability to interpret these numbers.

To take a step back, the issue was framed that the moving mass of the driver was so heavy, a wussy amplifier would have an issue controling the woofer. The amp would tell the woofer to move, but not have the ability to stop and reverse that movement. I personally do not have the knowledge to know if that is true or not, but *intuitively* it makes sense.

And no, I am not offended, I am grateful you are taking the time to teach me about the hobby I love.

If we were to boil it down to a more qualitative level - would the amps I have in the first post (~200 watt consumer home amplifiers) be able to drive these speakers easily to THX (105 db.?) levels in a ~5,000 cu. ft. room? Is there anything the DSi offer which would make them a compelling choice for these speakers in a home environment (I understand the DSi is the amp to get for a 4645C subwoofer).

Tom Brennan
01-12-2010, 01:27 PM
To take a step back, the issue was framed that the moving mass of the driver was so heavy, a wussy amplifier would have an issue controling the woofer. The amp would tell the woofer to move, but not have the ability to stop and reverse that movement. I personally do not have the knowledge to know if that is true or not, but *intuitively* it makes sense.



They also have a powerful and sensitive motor to move the cone. How well the cone stops (transient response) is determined mostly by the cabinet design; cones heavier than that of the 2226 and with less powerful motors can be designed in proper cabinets to have excellent transient response.

I think you have plenty of power, 200 watts from a competently designed amp is alot no matter how you dice it. The speakers have a sensitivity of 98db so to hit 105db should take about 8 watts; I don't think dynamic compression is an issue yet at that low a volume.

But if you're really worried about it buy a couple QSC RMX 850s from Guitar Center for 325 bucks each. Those drove the 2226s in some bi-amped CS-3115s I had to house shaking levels with no sweat. I was probably using 10 watts. ;)

kenratboy
01-12-2010, 01:38 PM
How is the sound quality on those cheaper pro amps? I know compared to home gear, they are sold at MUCH lower margins, so $500 in the pro world might cost you $1000 in the consumer world. However, I have to imagine they are willing to cut a few corners in the sonics department for the sake of lower cost and higher power. I would rather spend a few more bucks to gets something that would really let the speakers shine.

rlsound
01-12-2010, 01:48 PM
QSC DCA or CX amps are good pro amps for home use. Inrush protection so you won't pop breakers on power up, both lines are similar, although the gains is different.

JBL 4645
01-12-2010, 02:02 PM
JBL Danger low power
http://www.jblpro.com/pub/technote/lowpower.pdf (http://www.jblpro.com/pub/technote/lowpower.pdf)

kenratboy
01-12-2010, 02:02 PM
QSC DCA or CX amps are good pro amps for home use. Inrush protection so you won't pop breakers on power up, both lines are similar, although the gains is different.

Would these be considered to be some of the higher-quality and better-sound pro amps out there?

kenratboy
01-12-2010, 02:07 PM
JBL Danger low power
http://www.jblpro.com/pub/technote/lowpower.pdf (http://www.jblpro.com/pub/technote/lowpower.pdf)

Very relevant, and I deal with this on a daily basis at work (I sell home audio gear ;) ).

However, my question might be ludicrous vs. insane amounts of power (which around here, seems to be par for the course, which is great!)

Despite wanting gear like this, I don't like to listen super loud. What I *DO* like is having a momentary peak which is clean, uncompressed, and will sound great.

Tom Brennan
01-12-2010, 02:07 PM
Ken---I used the QSC mostly to just drive Altec and JBL woofers in bi-amped hi-fis and it did that in stellar fashion. I did use the QSC fullrange for a short time driving some small KRK monitors and it sounded fine.




http://i254.photobucket.com/albums/hh92/Irishtom29/hi%20fi/1941.jpg

JBL 4645
01-12-2010, 02:14 PM
^^^^A mix of different amps kinder like my set-up vintage Marantz 1050 to run the HF LCR control 5 Alesis RA300 to drive the LF LCR and single centre back Marantz 1030 to drive the surrounds arrays no sweat. The Alesis RA300 in bridge runs the JBL 4645 2240 sub no sweat at all.

JBL 4645
01-12-2010, 02:22 PM
Would these be considered to be some of the higher-quality and better-sound pro amps out there?

If you asking what amps? I heard JBL Urei 6290 at the Empire pushing 13.000KW THX that was hard at some 20 meters away with the original JBL system. The newer in my signature uses Crown amps pushing an insane 56.000KW JBL THX wicked!

Crown amplifiers CTS 2000 for the five-screen array
http://sales.concert-systems.com/sales/CRO-CTS2000.html (http://sales.concert-systems.com/sales/CRO-CTS2000.html)

Crown CTS 3000 for the five-screen array and sub bass array
http://sales.concert-systems.com/sales/CRO-CTS3000.html (http://sales.concert-systems.com/sales/CRO-CTS3000.html)

Crown CTS 8200 for the surround array
http://sales.concert-systems.com/sales/CRO-CTS8200.html (http://sales.concert-systems.com/sales/CRO-CTS8200.html)


I’d hunt down some vintage JBL Urei 6290 I guess they must be cheap as chips today. Those new Crown amps cost an arm and leg brand new.

I seen QSC used at the Warner Village and I think there the same model from 1994 when I was shown one of two THX booths.

I later saw them last year now under the name VUE West End.

Not sure of the model number of the QSC guess you’d have to look under the THX certified listing of 1994, they could be newer QSC amps?

They sound brilliant in the THX screens loud crisp plenty of cinematic loudness that hit me in the chest on X-Men Origins Wolverine.

Edit:
A rare view of the rack used in the VUE the layout looks the same as it was last year October 2nd 2009. The picture isn’t good because I used the camera and so you can’t see the detail unless I had a scanner. Picture was published in home cinema magazine Home Cinema Chose October 1995.

Eaulive
01-12-2010, 02:28 PM
If you asking what amps? I heard JBL Urei 6290 at the Empire pushing 13.000KW THX that was hard at some 20 meters away with the original JBL system. The newer in my signature uses Crown amps pushing an insane 56.000KW JBL THX wicked!

I know you mean 56000W of 56kW, but some around here may understand that this theater has 56MW of sound amplification :D

Just a note. ;)

kenratboy
01-12-2010, 02:37 PM
What does the CTs series offer over the DSi series?

And 56,000 watts is lame. The $79.99 surround around system I got at the Wal*Mart puts out 2,000 watts! :D

JBL 4645
01-12-2010, 02:42 PM
I know you mean 56000W of 56kW, but some around here may understand that this theater has 56MW of sound amplification :D

Just a note. ;)
Okay, okay enough of your piss taking! If you like to convert the number from watts to volts, then knock yourself out.

JBL 4645
01-12-2010, 02:50 PM
What does the CTs series offer over the DSi series?

And 56,000 watts is lame. The $79.99 surround around system I got at the Wal*Mart puts out 2,000 watts! :D
You sure they didn’t buy a bulk from some dodgy guy selling them off the back end of lorry? :D
Well if you happen to score on the lottery you’ll need £250.000 grand or what ever in dollars?

jcrobso
01-12-2010, 02:52 PM
You are better off having more power than any expected peaks would need. Back to one of my questions, how loud do you want to go?
One thing to remember is that for every 3db increase in sound level the power to the speaker is doubled.
Lets say you are 2 metes away from the 2226, one watt will give you about 94db sound level, 2 watts = 97db, 4 watts =100db, 8 watts = 103db,,,, 128 watts = 115db. This is for one speaker add 3 db for using two speakers.
If you want to be able to handle peaks of 115db with out clipping you need an amp with at least 150W/channel.
Keep in mind that 120 db IS VERY LOUD, I doubt that you would every play that loud.:blink:
My AV receiver has 110w/channel and in my 14x17x9 LR and I can reach about 114db peaks. at normal levels I have plenty of head room.
Yes QSC makes very good amps!!!:D

JBL 4645
01-12-2010, 02:59 PM
^^^^
Crown Amplifier Power Required
http://www.crownaudio.com/apps_htm/designtools/elect-pwr-req.htm (http://www.crownaudio.com/apps_htm/designtools/elect-pwr-req.htm)

kenratboy
01-12-2010, 03:11 PM
^^^^
Crown Amplifier Power Required
http://www.crownaudio.com/apps_htm/designtools/elect-pwr-req.htm (http://www.crownaudio.com/apps_htm/designtools/elect-pwr-req.htm)

For the 3678's, 3m away, 105 db. (is that THX?), 98 db., says I need 45 watts (excluding headroom). 200 watts would give me ~112 db.

JBL 4645
01-12-2010, 03:43 PM
For the 3678's, 3m away, 105 db. (is that THX?), 98 db., says I need 45 watts (excluding headroom). 200 watts would give me ~112 db.

So they say. 85db peak in the middle thou a few do grumble it’s too loud in the cinema.

What size is 5000cufeet converted to room width length height? I know the number larger then my small living room.

Each has to have the same frequency response after its been EQ so no dramatic peaks of any of the LCR produces uneven tonal timber issues, same thing with the surrounds.

Subs should be with tiny fraction db but noticeable when playing back a scene while muting the sub on/off.

I aim for possible flat tonal sound with the limited parametric EQ bands I have on the DCX2496 Behringer which has 9 per 6 channels for LF/HF.

Voices pan nice a smoothly or sharp panning when it just sounds on left or right then into the centre or surrounds.

When playing wideband pink noise and add each channel one at time the level yes does double by around 3db. I read in THX interview in reprint Audio magazine September 1989.

Typical specs
Screen channels left, centre and right should test within ±2db of ISO2969 curve, 40Hz to 16KHz when measured with pink noise and temporal and spatial averaging throughout the listening area at seated ear height. Bass extension should go to 25Hz by means of subwoofers. The calibrated sound pressure level, for absolute levels during the mix correctly, should be maintained within ±2db over the seating area. The system must be capable of playing any film format without clipping distortion.

Eaulive
01-12-2010, 06:04 PM
Okay, okay enough of your piss taking! If you like to convert the number from watts to volts, then knock yourself out.

Ok, no need to get excited, I didn't put enough smileys?

rlsound
01-13-2010, 09:34 AM
Screen channels left, centre and right should test within ±2db of ISO2969 curve, 40Hz to 16KHz when measured with pink noise and temporal and spatial averaging throughout the listening area at seated ear height.

I was under the impression that the THX Crossover rolled off LCR at 80hz and sent frequencies lower than that to the subwoofer?