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Author Topic: Higher dampening factor for folded horn subs?  (Read 10535 times)

Kyle Gerhart

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Higher dampening factor for folded horn subs?
« on: January 11, 2016, 07:40:24 am »

Hello,
It's that magical time of the year, time to clean out and test all of the gear before any upcoming gigs. In passing I spoke to an engineer who made a comment to me that the subs in the system that I am using could achieve a tighter sound from using amplifiers with a higher damping factor. I've heard of this, but I haven't played with it. Mostly due to lack of time and honestly not caring about this particular system that much. But because I will be cleaning everything out and putting everything into new road cases, I figured it might be time to ask the experts....so this is what I'm working with


Subs: 4 cerwin vega ab-36c (single 18" folded horn ) 8ohm 1600w program/ 3200 peak

Amps to chose from

Cv-2800 ( 2800w@ 4ohm bridge mono/ 1800w @8ohms bridge mono) Dampening factor: 350
Cv-1800 (1200w @8ohm bridge mono) Dampening factor: 280

Current configuration is two subs in parallel at a 4ohm load by a cerwin vega CV-2800 bridged (2800w @4ohm) the amp rack sits behind the speakers and is connected by a 8' long 12 gauge cable. From the math I've done the total effective power damping is 108.77
With each sub running at 1382w. This has been the setup mainly to save weight and power draw. I am willing to sacrifice both if the subs end up performing better.

I have plenty of cv1800 and 2800's in stock to play with.

Which of these setups would give the tightest sound out of my 1 note wonder subs ?

(1) cv1800@8ohm per 1 sub = 1192w, 148df

(1) cv2800@8ohm per 1 sub= 1788w, 165df

(1) cv2800@4ohm per 2 subs= 1382w, 108 df


Thanks for your help







« Last Edit: January 11, 2016, 07:45:07 am by Kyle Gerhart »
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Ivan Beaver

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Re: Higher dampening factor for folded horn subs?
« Reply #1 on: January 11, 2016, 07:56:41 am »

Once you figure in the WHOLE signal path resistances/impedance (wire-connectors etc), you will quickly realize that the "damping factor" of the amp is no big deal.

However there are 2 things that will make it as high as possible.

1: Use LARGE wire.

2: Use a high impedance for each speaker run.  So if you want to parallel cabinets-do it at the AMP-not the speaker.

Also make sure you use high quality speaker connections-not 1/4" etc.
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John Roberts {JR}

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Re: Higher dampening factor for folded horn subs?
« Reply #2 on: January 11, 2016, 09:56:05 am »

What kind of engineer?

As Ivan offered modern amps are not the weak link.

JR
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Kyle Gerhart

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Re: Higher dampening factor for folded horn subs?
« Reply #3 on: January 11, 2016, 10:05:33 am »

Once you figure in the WHOLE signal path resistances/impedance (wire-connectors etc), you will quickly realize that the "damping factor" of the amp is no big deal.

However there are 2 things that will make it as high as possible.

1: Use LARGE wire.

2: Use a high impedance for each speaker run.  So if you want to parallel cabinets-do it at the AMP-not the speaker.

Also make sure you use high quality speaker connections-not 1/4" etc.

Ok. Great to know.

With the info that I have given, which of the setups would you recommend I use..
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John Roberts {JR}

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Re: Higher dampening factor for folded horn subs?
« Reply #4 on: January 11, 2016, 10:13:13 am »

Ignore amplifier DF, select amps based on power output and what the speakers can handle.

JR
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Ivan Beaver

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Re: Higher dampening factor for folded horn subs?
« Reply #5 on: January 11, 2016, 11:46:45 am »

Ok. Great to know.

With the info that I have given, which of the setups would you recommend I use..
Consider also that when you bridge an amp-the damping factor (at the terminals) is HALF that of a single channel

This is because one channel is in series with the other.

If you want the highest number, then don't bridge the amp.

Use a large amp.
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Kyle Gerhart

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Re: Higher dampening factor for folded horn subs?
« Reply #6 on: January 11, 2016, 01:27:04 pm »

Consider also that when you bridge an amp-the damping factor (at the terminals) is HALF that of a single channel

This is because one channel is in series with the other.

If you want the highest number, then don't bridge the amp.

Use a large amp.

Noted, but not in the bosses non existent budget .. I did not know this about when bridging an amp. Is this true if I am using the NL4 output on the amplifier or just when you use the terminals?
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David Sturzenbecher

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Re: Higher dampening factor for folded horn subs?
« Reply #7 on: January 11, 2016, 01:40:04 pm »

Noted, but not in the bosses non existent budget .. I did not know this about when bridging an amp. Is this true if I am using the NL4 output on the amplifier or just when you use the terminals?

Kyle,
Why would there be a difference?  They are the exact same connection.
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John Roberts {JR}

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Re: Higher dampening factor for folded horn subs?
« Reply #8 on: January 11, 2016, 02:03:44 pm »

Kyle,
Why would there be a difference?  They are the exact same connection.
Because when you drive the loudspeaker bridged you have two amplifier output impedance's in series, instead of one so DF is roughly halved all else equal.

This falls under the category of true but irrelevant... Wire losses will still dominate DF in use with modern solid state amplifiers.
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A larger lesson here is that internet threads generally end up full of numerous true facts but not all are significant. Learn to separate the wheat from the chaff.

JR
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Luke Geis

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Re: Higher dampening factor for folded horn subs?
« Reply #9 on: January 11, 2016, 02:53:27 pm »

The theory behind it is simple really, but the reality is that DF goes completely out the window in a hurry under typical deployments. The deployment of the amp and speaker is where the real cream is. The rule is very simple though. Get as large of ga. cable as you can and run as short a cable as you can. The DF of the amp is of no big deal.

As Ivan has mentioned the DF is a combination of the resistance of the speaker and cable. The output impedance of the amp is what determines its DF. To best maintain DF you have to run large wires at very short distances. Pretty much any cable gauge that is over 50' is going to reduce DF to below the acceptable DF of 20. That is right, a DF of 20 is what is considered acceptable and any lower will have obvious signs of low DF. So what happend to the other 280 - 480 DF that the amps said I have? The cable and speakers is what.

What is DF in an amp? It is the ability of the amp to control the movement of the speaker despite physics ( inertia in this case ). That is, if the speaker is pushed out by the amp and the amp stops telling the speaker to move outwards, the speaker will continue ( within the confines of physics ) to move outward. This movement presents a current in the speakers coil that is then sent back to the amp. I believe the technical term is flyback? This flyback is out of phase with the voltage that the amp is trying to send and will therefore interfere with the signal the amp is sending. At really low ( sub 20 DF ) DF ratio's, the effect is an obvious looseness or smoothness in the bass notes ( lack of definition is a good term ) and the highs are often subdued and softened up as well. It can sound good in fact, but is can also sound bad. A good DF is said to be anything above 50. So an acceptable DF is 20 and good / greater is anything that is higher than 50. In reality we are happy to get anything between 20 and 50. DF is also really of concern for the low frequencies only.

If your amp says it has a high DF it is most likely because it has a really low output impedance. There is nothing wrong with that, but is a way that manufacturers get a really good number to use as a selling point. In reality though, an amp with a DF of 100 will work just fine. Ready for the bad news......???? An amp with a DF of 500 pushing a speaker of 4 ohms, with a cable that is 50' long and of 14ga., will have a DF of 15.4.......... If that amp was pushing 100 watts to that speaker, the wattage loss from the long thin ga. speaker cable would be 12 watts. So not only are you loosing DF your also loosing wattage! In this case 12%.  An amp with a DF of 300 would not change the wattage loss but the DF would only drop to 15.09, or less than 1!!! So you can now see why a higher / lower DF amp is not a big deal.

To keep wattage loss down and the DF up you want larger ga. cable and as short a cable run as possible. Ideally you don't want to run the amp in bridge mode, but you will see that it really doesn't matter. If you take an amp with a DF of 500 and use 10ga. wire that is only 5' long, pushing a 4 ohm speaker, you will have a DF of 222.22! This number assumes a stereo amp deployment, so halving or even doubling the output impedance again would not greatly effect the outcome. For an extreme example, an amp with a DF of 1000 would end up with a total DF of 285.71. Halving the DF to 250 would drop the total down to 153.85. The DF of 285.71 is better, but not going to be noticeably better than 153.85 really. So what about wattage loss? In this case you would only loose about half a watt!

Keeping the speaker impedance up also helps. In our worst case scenario above with a 50' 14ga. wire pushing a 4 ohm load we got a DF of 15.4. If we were to use an 8ohm speaker we would increase the DF to 29.88! Oh wait, all of a sudden we have nearly double! What about a 16 ohm load? Almost another doubling with a new total of 56.4. This is why running subs in parallel down to a 2 ohm load is not a good idea. At 2 ohms the DF would drop to 7.82....... Now I mention that subs are of the only major concern for DF. Subs are typically either 4 or 8 ohms loads. The easy answer is don't go below 4 ohms and follow the simple rules. Large gauge wire that is as short as is practical for the job.

Here are a couple links and one has a calc:

http://www.bcae1.com/dampfact.htm

http://eaw.com/amplifier-damping-factor-more-is-better-or-is-it/
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Re: Higher dampening factor for folded horn subs?
« Reply #9 on: January 11, 2016, 02:53:27 pm »


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