GoodSoundClub - Romy the Cat's Audio Site - This new midbass horn dilemma

Horn-Loaded Speakers
Topic: This new midbass horn dilemma

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Posted by noviygera on 01-25-2014

I got this new midbass horn to replace the Edgar 80Hz straight horn. It is made by Funktion-One and they claim it plays down to 90hz. I could not get it to play below 120Hz and I am trying to figure out why.
Pictures are:mouth measurements with no filter

Impedance response

midbass horn photo

15" driver. The mouth is 39"x17". It is 34" deep from mouth to driver. Looking at the impedance sweep, there is a resonance at 80hz.
So the thing is that it sounds much better than the Edgar midbass but I cannot get it to play to 90Hz or even 100Hz, but I would like to. Because the sound is promising.
What is it that's preventing to play down to the claimed 90Hz? Too small back chamber? If that is the case I am willing to spend time and effort to enlarge the back chamber... Recommendations?
Thank you!Gera

Posted by Romy the Cat on 01-25-2014

noviygera wrote:
I got this new midbass horn to replace the Edgar 80Hz straight horn. It is made by Funktion-One and they claim it plays down to 90hz. I could not get it to play below 120Hz and I am trying to figure out why.

15" driver. The mouth is 39"x17". It is 34" deep from mouth to driver. Looking at the impedance sweep, there is a resonance at 80hz.
So the thing is that it sounds much better than the Edgar midbass but I cannot get it to play to 90Hz or even 100Hz, but I would like to. Because the sound is promising.
What is it that's preventing to play down to the claimed 90Hz? Too small back chamber? If that is the case I am willing to spend time and effort to enlarge the back chamber...

Gera, I do not know the horn and the driver they use. The miss presenting the measurements by companies is a common thing and it might be the case.

The horn is kind of strange for 90 Hz. With mouth 39"x17". You have 660 sq inch that is neat half of what you need to get a full 90Hz. I do not do exact circulation but my 36” spherical horn has 1017 sq inch and it rated for 115Hz. In addition my horn has much smaller mouth which accuses higher horn EQ. The Funktion horn has a bit driver, unnecessary phase plug… strange horn. From a different perspective they rate it i109dB sensitive, if it is true then it is very good but I do not think it is true. Even if they make 103dB driver (which would be VERY good) I doubt that this horn will yield 6dB gain. It might do it at 180Hz but not at 100Hz. So it was mis-advertising, very frequently happens BTW…

Anyhow, if you do like the sound of the horn then there are a few things you might try. First, the resonance at 80hz is obviously too low. You can try to raise it by changing the size of back chamber will work but it is re-building the horn and I do not know if you want to do it.

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PageIndex=1&postID=6011#6011

If I were use I would target 110Hz of resonance and will see what happens.

Also, my 115Hz upperbass in my former listening room did 90Hz as it was installed in active spots:

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PageIndex=1&postID=4421#4421

In my current listening room I have 130Hz and this is normal. Move your upperbass to the active location of your room and you might get much better response.

Many people feel that it is super important to get max LF response from the upperbass and I do not feel it is right direction. It is more important to make the upperbass do not strained. It is very hard explained over internet what does it mean. A few days ago I had a visitor who after a few hours of listening of my playback was asked what was the most characteristic behavior of my playback. He said that it the playback has a surprising enthusiasm to push sound out itself. He was very intelligent guy in my estimation and he did pick “it”. The reason I am saying it to illustrate that the enthusiasm of pushing sound out does not come from stressing of the channel but from making each channels to operate in the zone of own topological comfort. If you upperbass does not go too low in your room them do the best to the topology of the upperbass and then let the midbass channel to handle the rest. Horn people love to stretch the channels to the margins and it is not good in my view.

Rgs, Romy the Cat.

Posted by noviygera on 02-06-2014

Romy,

Thank you for your response. I am trying to figure out this horns and I did additional measurements. The phase plug is an interesting part of forming of the the horn throat expansion and because it is quite big and so looks like it is also a "throat area adjustment" for the rectangular horn flare. Maybe it also reduces the parallel surfaces interaction in the throat area.

After some additional measurements the actual throat opening area is 52.5 inches sq. I took the area of rectangular throat at its smallest cross-section(13x5) and subtracted the phase plug area at that point (4 diameter). This gives the 52.5 sq. inch area of throat. Cone area is 122 sq. inch

This calculates (if I am correct) to compression of 1:2.3

I will continue to experiment with this midbass and one thing that came to mind is that it was designed to be used in multiples, lets say, TWO pairs. this will provide the doubling of mouth area as you mentioned, that was needed for a 90Hz horn. I will put them together (stack the pair) and see what happens.

One question to your response. You mentioned the resonance of 80Hz is too low for this horn and to raise it to 110. What benefits does this usually bring, this equalization of resonance to horn cutoff?

Regards, Gera

Posted by Romy the Cat on 02-06-2014

noviygera wrote:
One question to your response. You mentioned the resonance of 80Hz is too low for this horn and to raise it to 110. What benefits does this usually bring, this equalization of resonance to horn cutoff?

It is hard to explain in words. Generally if you match the resonance with your horn rate or bring it to a very close proximity then you have slightly different texture of bass. Sound becomes less hallow, softer, more meaningful and stickier to the room. You will get very minor gain from horn but it is not the objective. The main point is that bass become like it is not out of absolute phase, if you know what I mean. There is a catch however. If you set the precise matching of resonance and horn rate then you might want to review it with time as the driver will get softer with time as it will break in.
I think it is very educational to set the driver in the proper resonance and to spend some time to hear it. Then open up some back chamber and to hear how sound will be changing as the resonance frequency will be dropping. As you get your personal sonic reference of what happen with bass you will be able to make your own judgment.

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