The 'Art' of speaker emulation

[ROOG]

I’ve seen it touched upon a few times on this forum that adding an attenuator and taping off a feed for head phones from tube amps results in a poor sound through the head phones. I can understand this, as the speaker and the power stage of the amp must have quite an effect on the overall sound.

A recent posting mentioned a “black box”, described as the 'speaker emulator' on a Traynor amp circuit diagram.

So given that valve amplifier manufacturers don’t like to spend any more than they have to on anything, would our resident experts be so kind as to hint at what the likes of Traynor and H&K do to produce a speaker emulated line signal from their tube amps?

Cheers

[ICBM]

I’ve seen it touched upon a few times on this forum that adding an attenuator and taping off a feed for head phones from tube amps results in a poor sound through the head phones. I can understand this, as the speaker and the power stage of the amp must have quite an effect on the overall sound.

A recent posting mentioned a “black box”, described as the 'speaker emulator' on a Traynor amp circuit diagram.

So given that valve amplifier manufacturers don’t like to spend any more than they have to on anything, would our resident experts be so kind as to hint at what the likes of Traynor and H&K do to produce a speaker emulated line signal from their tube amps?

Usually something fairly simple involving an EQ shape roughly like that of a guitar speaker frequency response, done with various caps and resistors, rather than an attempt to accurately 'model' the full reactive response - but it's close enough for most purposes. At its most basic, a cap in series (to cut deep lows) and one in parallel (to cut highs) gives very roughly something that will work, although most of the circuits are a bit more complex than this.

I'm pretty sure the H&K Red Box is a bit more sophisticated than this, though.

If you want to see a typical speaker response, here's the Celestion Greenback -



All guitar speakers are roughly similar, despite the apparently fairly big differences in perceived tone.

[MRLEON83]

for me , the art of speaker emulation is - taking the send from the effects return and putting it through a speaker convolution - give it a go - it is awesome!

[ROOG]

Cheers ICBM, that would certainly be a nice simple way to do it. So that might be stretching the term emulation a bit

MRLEON83, this "speaker convolution", is this some kind of computer based solution?

[uncle_psychosis]

MRLEON83, this "speaker convolution", is this some kind of computer based solution?

Convolution is a mathematical way of combining two sounds (well, combining any kind of things that have frequency content). The basic idea is that by convolving a dry input signal with the response of an amplifier, the result is what the signal would sound like if you put it through the amp.

I think there are quite a few commercial applications that will let you do this, and if you know what you're doing you could probably write one yourself in Matlab or similar.

[koneguitarist]

Just buy a Peavey EDI box, did a test in studio with one, when recording last CD, engineer wanted to use his mic set up, I wanted to use the SM57 and a ambient mic arrangement. We put my EDI box in and A/B them all the SM57 AND ambient mic was best but the EDI box won against SM57 on its own, and a stereo set up of Sennheisers that the Studio wanted to use came last
Cheap as chips, but I allways keep one in back of amp for gigs where I might need it. This was a recent gig with EDI box.

http://youtu.be/lmiiz2ROm5Q

[ICBM]

Just buy a Peavey EDI box, did a test in studio with one, when recording last CD, engineer wanted to use his mic set up, I wanted to use the SM57 and a ambient mic arrangement. We put my EDI box in and A/B them all the SM57 AND ambient mic was best but the EDI box won against SM57 on its own, and a stereo set up of Sennheisers that the Studio wanted to use came last
Cheap as chips, but I allways keep one in back of amp for gigs where I might need it. This was a recent gig with EDI box.

http://youtu.be/lmiiz2ROm5Q

+1, but especially that the 57 + ambient mic arrangement (I like the Rode NT-1A) does kill everything else.

I don't have an EDI, although I remember trying one once and thinking it was good. I have a Red Box, which seems pretty good too.

[koneguitarist]

I liked the Red box, but it was a bit expensive at the time, and comparing the two I didn`t think the extra outlay was justified at the time(back in late 80`s early 90`s) plus the red box came with a battery, the Peavey was passive.
Funnily enough of all the amps I have had, it works best with JCM800`s, I can`t tell when speaker stops and EDI takes over, copies the old Celestion tone spot on.
I think it was the SM57 and AKG 414 or something like that that I used. Funnily enough, i just posted the finished track in the listening lounge, that was the two mics used, see if you can recoginse guitar and amp tones !

[erictheweary]

just having a quick look at the EDI. So, plug amp into it then back out to the speaker and take an XLR from the EDI out to the desk? And I could get one from £65.And tape it to the back of something and leave it there?No batteries required. Hmmm.

[ICBM]

Yes.

Like the Red Box, it's even simpler if the amp has two speaker jacks - just connect the box to the second speaker jack, which does not even need a speaker cable if the power to the cab isn't going through it. This is better because it avoids the potential unreliability of passing the speaker current through an extra cable and two jack connections - I'm not sure why they don't mention this in the Red Box manual, maybe they do with the Peavey.

The Red Box doesn't require batteries either if the desk it's connected to has phantom power.