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High Pass a hard-to-drive speaker - Now Easy????

Good Morning,

My understanding is that the low frequency register is by far the hardest portion of the audio spectrum to drive in terms of power requirements.

If we change things around a little bit and high-pass the speakers crossed over at 80hz or so with a powered sub, how much easier do the speakers become to drive? Just a little bit? Or a lot?

In my case, I'm running Dynaudio S1.4s which need a lot of power (current especially) to sound open as opposed to congested. I'm using a Plinius SA102 which does the job quite well. If I high pass these speakers at 80hz, do the speakers become orders-of-magnitude easier to drive? Do you think I could get by with a 40WPC push-pull tube amp in this case? What about something like a Lamm 18WPC SET? An 8WPC 300B amp?

Is there an easy way to measure this? Ie - Run the speakers full range, and measure how much power the speakers are demanding, and then run them high-passed and measure how much power they need.

Reason for my inquiry - In theory, by definition, speakers that are hard drive require use of high-powered amplifiers, which by definition are always a major comprimise and less transparent than low-powered amplifiers. I'm wondering if a tough-to-drive speaker can overcome this limitation by not requesting the hardest-to-drive frequencies from the amplifier.

Thanks, and I appreciate your thoughts on this interesting subject

Todd
goatwuss
goatwuss OP
877 posts
 
Gregm - Thanks for the reply

"Good hi-powered amps are invariably expensive. But NOT, by definition, compromised as you seem to believe."

I respect your opinion on this, but it is contrary to my understanding and experience. This is a discussion for another thread, though.

"OTOH, if yr Plinius is doing the job and you already have it, why change it???"

The reason is that I've found high-quality tube amps to sound much more musical than any SS amp that I've heard (a lot, including brands like Halco, Spectral, Boulder, etc). The Plinius is great for what it is, but what I'm interested in doing is driving a hard-to-drive speaker with a lower-powered tube amp. I'm interested in finding out if this is plausible by bypassing the hard-to-drive frequencies via a high-pass filter.
gregm
3,405 posts
 
Should be able to, using a line level filter & bypassing the internal hi & low passes on the b/pass section.
OTOH, you'll have to pray that tonality & voicing b/ween the different amps are compatible -- because you'll hear the bass amp, 60Hz upwards, easily...

Whatever you do, look for the Dynaudio xover schematic! Cheers
audiokinesis
2,747 posts
 
Typically it's the woofer that sets the system efficiency. Taking a low-efficiency system and high-passing it at 80 Hz won't change the efficiency. Depending on what the impedance curve looks like, once highpassed the speaker may or may not present a significantly easier load.

I would guess that you would gain two or three dB of headroom by not asking your amplifier to reproduce the bottom two octaves.

Once you've made the decision to go with a subwoofer, if your intention is to significantly increase your system's headroom, then it would make sense to go with main speakers that trade off (unused) bass extension for higher efficiency. All else being equal, trading off one octave of bass extension will buy you about 9 dB greater efficiency, and that would make things a lot easier on your amp.
gregm
3,405 posts
 
Duke: one octave for 9db?? I was banking on the standard +6db energy/octave. Can you give a quick pointer on how you obtain this (I'm sincerely interested -- not contesting :)). Cheers
braro
87 posts
 
I tried to run my Vandy 3A Sigs (a difficult to drive speaker) with 125 tube watts (EL34s). I have (2) 2WQ subs and model 5 x over thinking the same. For me, in my room it just did not work. I had to go to large solid state to get the sound I was after. I think I could have gotten there with big tubes also but I wanted to try solid state.
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