New DIY MTM Towers designed by Dennis Murphy and Paul Kittinger


Sailor Mike

Some info about bass alignment with a SET amp.
The higher output impedance of a valve amp, particularly a SET, will raise the Qes which then raises the Qts. This affects the bass alignment, typically it causes a hump in the response at very roughly 100Hz.
Fortunately this can be fixed, by calculating Qes and then modelling in Winisd, adjusting the port tuning to improve things.
I have posted how to do this in Diyaudio, multi way speakers, a thread 'SET Friendly MTM, Seas ER18RNX and 27TDFC'.
Using Winisd, different box frequencies can be tried and results for frequency response and group delay can be seen, and tuning changed to reduce the hump while keeping group delay below 10mS, as suggested by an expert. In my case, 30Hz looked good and the result sounds good.
Winisd will also find the port length for you.
This process is highly recommended if you want to use these great speakers with a SET amp. I can't say if it's worth doing for a PP valve amp which should be fine as is, but if anyone has an issue with bass quality it might be worth doing the maths and modelling it.

I do hope people (Dennis in particular) do not take this as in any way criticising this excellent speaker! It is not meant that way; it's just a tip about matching them, as matching amp and speakers is important.

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