311-60 Horn Equalization

[gwho]

I am going to build a two way speaker (maybe a 3 way with a ribbon for hf). I recently found and purchased a pair of 311-60 horns that I will mate with 288-8k drivers. I have a general question about equalization. When you eq a horn is there a significant tradeoff that occurs? In boosting frequencies am I reducing the dynamic range of the horn? I apologize if this question has been answered but I can't seem to find much about this other than most horns need equalization.

Regards,
gwho

[Earl K]

You should first determine the need for HF boost ( by measurement, with a calibrated test mic (http://www.minidsp.com/products/acoustic-measurement/umik-1) & some free test software, such as REW (http://www.roomeqwizard.com/) .
- Typically, the 288 ( with a healthy diaphragm ) when mounted onto a 60 degree radial , doesn't need much HF boost ( if any ) to sound quite HiFi ( and tonally balanced ).

Your diaphragms might need replacing ( since you feel the need to EQ ) .

FYI, 288 diaphragms are very prone to "work hardening" with moderate SR usage, due to their suspension design & the choice of aluminum alloy type ( it's quite soft ) . I've seen measurements of "Work-Hardened" diaphragms where the HF content takes a nose-dive after @ 3-5K .

GPA replacement diaphragms for the 288 (http://www.ebay.com/itm/Altec-Lansing-GPA-288-291-299-Replacement-HF-Diaphragms-/331520203420?pt=LH_DefaultDomain_0&hash=item4d3024da9c) are a huge ( huge ) bargain at $100.00 ( & it's best to buy some now, before Bill ponders retirement ) .

:)

Yes, boosting EQ reduces headroom within the amplifier .

Typically, I find it sounds best to suppress the mid-range below a certain frequency with resistors & to then restore the HF above the same frequency ( with a small capacitor ).

[gwho]

Earl K,

Thank you for the response. The 288-8Ks originally had MR94A horns on it. With the Manta Ray horns there was no issue with the treble response. It sounded quite good. The problem is the MR94A's are quite large and the wife voted a big no about bringing them into the house. Thus, I searched for a smaller horn. The 311-60 are the right size but sound much more rolled off than the MR94A's. I have replaced the diaphragms with the great plains units so I know the diaphragms are good. I was not sure of the eq tradeoff if the high frequencies were boosted how that would affect the dynamics.

Regards
gwho

[Earl K]

Boosting any part of the spectrum ( reproduced by an amplifier ) will reduce the available headroom of that amplifier ( before it distorts ) / hence dynamic range is impacted directly .

Since you seem resistant to following proper EQ protocol ( ie; measure first , then design a filter ) , here's a ( shot-in-the-dark ) HF ( restoration ) filter to try out ( just wire-up the HF portion ) .

http://www.audioheritage.org/photopost/data//500/Altec_30904_30923_filter.jpg

:)

PS : nice to hear you are working with new diaphragms :applaud:

[gwho]

Earl K,

Thanks for the filter design. I will take measurements per your suggestion to determine where the roll off occurs. I will buy a good microphone and try out REW. I may be able to get my hands on a DEQx unit that includes speaker measurement and electronic crossovers. Once again thanks for answering my question much appreciated. If the speaker eq is significant and reduces the dynamic range I may add a high frequency tweeter.

Regards,
gwho