Speaker Impedance

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I would love to try a few of your small full range drivers but all of my hand built tube amps need 8 ohm impedance. My single ended transformers only have an 8ohm secondary. your drivers are all 4ohm as far as i can see. seems my only options are to either change output transformers or order 2 pairs and build a bi-polar speaker system. Neither of which are cost effective for me. Do any of your drivers come in 8ohm impedance?
Thanks,
Paul

my amps,
DIYTube ST-35, SE 6EM7, SE EL-84, SE KT-88

Speakers,
Zigmahornets with drivers scavenged from a Yamaha center channel speaker
or the FE-127 Fonken with FE-103 drivers.
 
I would love to try a few of your small full range drivers but all of my hand built tube amps need 8 ohm impedance. My single ended transformers only have an 8ohm secondary. your drivers are all 4ohm as far as i can see. seems my only options are to either change output transformers or order 2 pairs and build a bi-polar speaker system. Neither of which are cost effective for me. Do any of your drivers come in 8ohm impedance?
Thanks,
Paul

my amps,
DIYTube ST-35, SE 6EM7, SE EL-84, SE KT-88

Speakers,
Zigmahornets with drivers scavenged from a Yamaha center channel speaker
or the FE-127 Fonken with FE-103 drivers.

+1
 
IIRC, the Alpair 10.2 is 'rated' at 6 Ohms, though the impedance plot appears to put it generally (well) above this. That is, if the chart for the 10 on the Mark Audio site is for the 10.2...

Edit: It looks like the details for the Alpair 10 on the Mark Audio site are for the previous version. If so, I would like to see the impedance plot for the new version.

Cheers.
 
Last edited:
frugal-phile™
Joined 2001
Paid Member
CHR70.3 is likely going to be 8 ohm at user request. A12 is nominal 8 ohms. 6 ohms is close enuff to 8 to break into a sweat. Twins of the 4 ohm drivers is not a hardship (twin EL70s in a good cab stun people with their bass capabilities)

But one needs to remember that impedances are nominal. They do not look like a straight line at all.

I just measured 10 Alpair10.2, I'll run downstairs and generate a postible curve.

dave
 
frugal-phile™
Joined 2001
Paid Member
A typical curve from a set of 10 drivers. This would be called an 8 ohm driver. Note that over most of the range it is >8 ohms.

dave
 

Attachments

  • A10g2-imp.gif
    A10g2-imp.gif
    24.1 KB · Views: 247
A typical curve from a set of 10 drivers. This would be called an 8 ohm driver. Note that over most of the range it is >8 ohms.

dave

Not sure this is the right thread for this but... All of cone impedence graphs I have seen look similar to this. Big spike at free air resonance, followed by a long shallow depression through its midband , and a rise from there to its upper frequency range. Even though the audio output is relatively flat. Does this mean some of the output in a cones upper operating range (highe impedence) is actually from resonance (distortion) ? Just wondering.
 
Why is cone resonance 'distortion?'

Welcome to the myth of 'pistonic' drive units. It doesn't work that way. All wideband drive units produce the majority of their BW through controlled resonance of the cone / cones / parts thereof. Note the word 'controlled.' That is of course the critical point, i.e. how well controlled it is. That's down to the design of the cone, suspension & the motor structure. Many midbass units grab a useful extra octave or so through the same. The top end of the audible BW of many tweeters is also achieved through this. No big deal.
 
Thanks . This forum is the first place I've received a reasonable sounding answer. However, controlled or otherwise, a resonance is not part of the original signal, and I would consider it to be a distortion . In view of the tiny distortion numbers in the most decent components upstream from the speakers in the signal chain, maybe this is why we can always easily hear the difference between live and recorded so easily.
 
A piece of paper / plastic / ceramic / metal / whatever suspended by rubber / foam / whatever moving backward and forward isn't part of the original signal either.

Ultimately, what you're trying to do is create a pressure-wave, or to put it another way, excite the air in the listening room at a desired frequency. As frequency rises, you require less movement of a cone for obvious reasons, and indeed, as cone sizes increase, so the practical maximum upper BW limit drops. So, you design the cone to flex (aka 'resonate'), the tiny movement creating the HF output. This in itself is no more or less of a distortion than the driver moving back & forth is. It only becomes a distortion under either condition if the signal is amplified incorrectly etc. How well it achieves this is down to the driver design. As noted, purely pistonic action is a bit of a myth and to achieve something approaching it with dynamic drive units is neither simple, easy, nor cheap, owing to the limited BW a drive unit can achieve supposedly pistonic behaviour across. Think 3 way, minimum.
 
Last edited:
Hi Guys

I think misuse of the term ‘resonance’ is part of the problem here. From a physicist’s perspective there are two characteristics of resonance that are undesirable in a driver, namely, (i) increased amplitude at some frequencies which would lead to a non-flat frequency response, and (ii) energy storage, which would lead to smearing of the impulse response.

I think it’s better to model the driver as a lossy transmission line – think of driver movement as a mechanical impulse, due to the voice coil/electromagnetic motor, applied at the centre of the cone. The mechanical impulse starts at the middle of the cone and propagates outwards towards the surround. At low frequencies there is little loss and the mechanical movement propagates all the way to the surround without attenuation so that the movement is pistonic. At mid frequencies, the losses in the flexure of the cone cause the mechanical movement to be attenuated as it propagates towards the surround so that the movement ceases to be pistonic and a smaller area of the cone radiates. At very high frequencies, the mechanical losses in the cone may be so great that only the dustcap contributes to the acoustic radiation.

regards,
Rod
 
Hi Gazzagazza

Hadn't heard of one of those, but from Wikipedia's description, it seems you're right.

I notice that the curvature on Mark's cones, and others, could well alter the stiffness versus radius in the manner required. Getting the correct balance of stiffness and loss versus radius would be no mean feat though.

regards
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.