Thermal compression/HE
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 24th August 2008, 02:32 PM #1 Anglo   diyAudio Member   Join Date: Mar 2008 Thermal compression/HE Boys! I have a question where I would need the answer to be backed by some good mathematics - so this forum would be the one to post this! So, most boys here- myself included - would prefer (for lack of a better word) high eff. drivers i.e 98db and up over say 89db speakers. It is claimes (my belief) that HE drivers are more dynamic than LE speakers. However, the numbers below show me that they have peaks in areas where sonically we would say they are dynamic because they have 16db peaks in areas we are sensitive. If the LE drivers were amped properly, would they be as dynamic as HE or would they crush with thermal compression? SO let's take some popular HE speakers vs popular LE speakers: ---- HE ---- FOSTEX 168ES 80hz = 83db 1700hz = 96db 7000hz = 99db 16db difference VISATON B200 80hz = 84db 1600hz = 97db 3000hz = 102db Differnce of 18db LE speakers AudioTechnology 18cm 80hz = 87db 1900hz = 93db 3000hz = 95db Differnce of 8db Vifa P17W50008 80hz = 85db 1800hz = 89db Difference of 4db Thanks in advance,
 25th August 2008, 12:48 AM #2 Brett diyAudio Member     Join Date: Jan 2002 You have some overlapping issues here that are not necessarily the same thing. Power compression is the reduction in efficiency as the voice coil heats. It's easy to get the heat in, but harder to remove it and the timescales are different. Second, there is no reason why a high efficiency driver need to have any worse break up than a similar sized less efficient one. That comes down to design choices. Most of the truly efficient drivers are either from the Pro field, where thermal management is far more important than domestic use (run higher powers, lower crest factors and for longer) of wideband drivers like Fostex and some Visatons. Considering that many of the latter have a markedly rising response, and the half power point of most types of music is < 500Hz, I don't find them to be all that efficient, but there are some exceptions. In the Pro field, most drivers only attempt to cover part of the spectrum, are typically crossed actively and with steep slopes so out of band misbehaviours are fsr less important than for a full ranger. One of the 15's I use has a bit of a peak at 2k, but I don't care as I cross it at 250Hz with a LR24. Run wideband it sounds OK but not great.
 25th August 2008, 12:58 AM #3 Anglo   diyAudio Member   Join Date: Mar 2008 Thanks for the response. So, from what you've said, what are the REAL adavantages of using HE drivers vs LE?
Brett
diyAudio Member

Join Date: Jan 2002
Quote:
 Originally posted by Anglo Thanks for the response. So, from what you've said, what are the REAL adavantages of using HE drivers vs LE?
Reduced thermal compression and in many cases, greater cone area as efficiency is also proportional to Sd.

SPL is determined by volume displacement of air. The less the cone has to excurse for a given SPL (high or low) because of greater Sd, the less weaknesses in it's motor and suspension design will be apparent. That is in all designs, the further away from the rest point of the driver it has to move for a given SPL, the lower the distortion due to non-linearities in the suspension, inductance and BL.
The problem with larger drivers is the enclosure is larger for the same efficiency and F3 point. I will happily give up physical size for the ease of presentation and large dynamic reserves such systems can have.

Plus higher efficiency gives you a far greater choice of amplification.

Like all engineering problems it's about balance of compromise and the intended goal of the product/system.

 26th August 2008, 06:23 AM #5 noah katz   diyAudio Member   Join Date: Jul 2004 Location: Mountain View, CA "Second, there is no reason why a high efficiency driver need to have any worse break up than a similar sized less efficient one. That comes down to design choices." There is very often a direct connection, seen often in full range drivers w/high efficiency and ragged freq response related at least in part to thin, low mass cones. Cone bending stiffness decreases with the cube of thickness decrease and consequent lower breakup freq. __________________ ----------------------------------------- Noah
Brett
diyAudio Member

Join Date: Jan 2002
Quote:
 Originally posted by noah katz "Second, there is no reason why a high efficiency driver need to have any worse break up than a similar sized less efficient one. That comes down to design choices." There is very often a direct connection, seen often in full range drivers w/high efficiency and ragged freq response related at least in part to thin, low mass cones. Cone bending stiffness decreases with the cube of thickness decrease and consequent lower breakup freq.
I don't use fullrange drivers as I feel they are too flawed, so I don't factor them in. Used defined bandwidth with similar freq ranges, my comment stands.

 26th August 2008, 04:37 PM #7 Anglo   diyAudio Member   Join Date: Mar 2008 ...and your comment stands on a subjective level or there is a measurement that can allow me to see the differences. By the way, I am in HE camp. So, I am not arguing with you, but moreover I would love to have some real math or measurements to back up this subjective response.
 26th August 2008, 07:15 PM #8 gedlee   diyAudio Member     Join Date: Dec 2004 Location: Novi, Michigan I agree with Brett here. There is no reason that HE should be any worse in FR than LE, but there is a very strong reason why they would have less thermal compression. And at any rate the systems all need to be EQ'd (aka the crossover) to be flat so the higher breakup modes are irrelavent anyways. There really is no way arround the fact that HE means less thermal compression; its theoretically correct, I've measured it, you can hear it. Pretty much closes the loop I would say. __________________ Earl Geddes Gedlee Website
Brett
diyAudio Member

Join Date: Jan 2002
Quote:
 Originally posted by Anglo ...and your comment stands on a subjective level or there is a measurement that can allow me to see the differences. By the way, I am in HE camp. So, I am not arguing with you, but moreover I would love to have some real math or measurements to back up this subjective response.
Read the datasheets. All of the info is there and I have explained why previously. I seldom discuss 'subjective' qualities of anything audio any more.

 26th August 2008, 07:50 PM #10 Anglo   diyAudio Member   Join Date: Mar 2008 Can you provide me with a link on some datasheets containing info on this? Thanks again for all your help guys.

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