Hi Klaus,

Spec sheet on the bass driver you plan to use here:
http://www.greatplainsaudio.com/downloads/515_G.pdf 

Just to be clear, mid bass to me means from 60Hz - 240Hz.

Throat diameter : 9.9 inches ?
I'm just a beginner, and will refrain from writing about things I haven't proven for myself (I have only "proven it" in the case of the upper bass horns), but if you haven't already done so, read the following thread (scroll down to the paragraph near the image of the black JBL enclosure):
http://www.goodsoundclub.com/Forums/ShowPost.aspx?postID=806#806 

Regarding the alnico option: If it were me, I would probably buy one of each driver (ferrite and alnico) and compare them.

Crossing the bass horn at 500Hz to an S2 : If using a 6dB/octave slope, I might start to get a bit nervous about running an S2 that low.

I use one pair of S2s to cover a theoretical 800Hz to 3200Hz into a 180Hz Tractrix, and have heard no signs of distress at all (still need to measure the output and see where it is really rolling off when taking into account the combined effects of the horn+room).

The diaphragms you describe seem to be one of the later versions, which are referred to as the "plastic-suspended" variety.

Best of luck,

jd*

Klaus,

The 515-8GPH were in same scale as the 515G with slightly above 35Hz resonance frequency and 103 sensitivity -  a very good candidate for 60Hz horn. The 10” throat? No bolls to go for 9”, how about 8”?  I’m just kidding. The throat is that I always has issues with use 15” driver for horns – they kind of make people to go for larger throats but I would like to see 60Hz horn with smaller diver, let say 10” driver in 7”-8” throat. How, where to found a 10” driver that would have sound and characteristics of 515 drivers… Do not ask me… :-(

The S2’s diaphragm with clear plastic outer suspension is an original Vitavox cone that they did as a substitute for metal suspension in order to add a slightly more power handling for the S2 driver.

The Alnico vs. Ferrite on 515 driver? If you cross it at 500Hz and most likely with second order then I would say that there is no differences. Alnico is important to provide transients at mid and higher frequencies it would be less affective, if any at bass. Not to mention that it would make the bass channel more vulnerable to DC component demagnetizing. Alnico is better reacts to low level signal but it might be negligible in your case. If you do have a luxury to choose type of magnet in your 515 then I would go with a magnet that would depend from your amp. The basic rule is that I formulate for myself is following: SS PP amps must not driver Alnico and SETs must not driver ceramic frequency above 500Hz-1000Hz. If you use SS PP amp then a ceramic magnet is a must as Alnico would too much highlight imperfections of PP topology. With 500Hz crossover it become not so critical.

Romy the Cat wrote:

Hi Romy! The 515-8GPH were in same scale as the 515G with slightly above 35Hz resonance frequency and 103 sensitivity -  a very good candidate for 60Hz horn. The 10” throat? No bolls to go for 9”, how about 8”?  Got the balls, but not the room;-) with the lenght of about 51", backchamber included, the mouth will be quite close to the place where my living voice airpartner -clone (pic on peter empsons site) sounds best.. this folded horn(open bachchamber...somewhat boomy bass) works in same frequency range, so i thougt it will be a good place to start with the straight fronthorn.and a listening distance of 11ft is not really much... The S2’s diaphragm with clear plastic outer suspension is an original Vitavox cone that they did as a substitute for metal suspension in order to add a slightly more power handling for the S2 driver. i searched your site and the web, but could not find a pic with the same diaphragma. it seems to be completely alu, but with a clear plastic-ring glued over the border of the hemisphere and the flat part with the grooves.its not the same like the white suspension, its just a 0,2 inches wide ring of clear something, the suspension itself seems to be alu. bought it new in 1994 as far i remember.(hard for me to find the right words, i apologize for my bad english..). red part in the pic alu, black clear plastic. The Alnico vs. Ferrite on 515 driver? If you cross it at 500Hz and most likely with second order then I would say that there is no differences. Alnico is important to provide transients at mid and higher frequencies it would be less affective, if any at bass. Not to mention that it would make the bass channel more vulnerable to DC component demagnetizing. Alnico is better reacts to low level signal but it might be negligible in your case. If you do have a luxury to choose type of magnet in your 515 then I would go with a magnet that would depend from your amp. The basic rule is that I formulate for myself is following: SS PP amps must not driver Alnico and SETs must not driver ceramic frequency above 500Hz-1000Hz. If you use SS PP amp then a ceramic magnet is a must as Alnico would too much highlight imperfections of PP topology. With 500Hz crossover it become not so critical. have a we91-style 300b, ouput amouphous core frome tribute, very detailed and sweet at the same time. hard to deside, my budget is limited, but i dont want to make to much compromisses... thx, klaus Rgs, Romy the Cat

jessie.dazzle wrote:

Hi Klaus, Spec sheet on the bass driver you plan to use here: http://www.greatplainsaudio.com/downloads/515_G.pdf

got it, thx. used this data to simulate in hornresponse,looks very promising. but i know...its just a simulation........

jessie.dazzle wrote:

Throat diameter : 9.9 inches ? I'm just a beginner, and will refrain from writing about things I haven't proven for myself (I have only "proven it" in the case of the upper bass horns), but if you haven't already done so, read the following thread (scroll down to the paragraph near the image of the black JBL enclosure): http://www.goodsoundclub.com/Forums/ShowPost.aspx?postID=806#806

whats wrong with 9,9"? its rougly 55% of sd? you think, 43" is too short for a 62hz horn?
btw, i follow your project with interest! i searched this forum since weeeks before asking stupid questions;-). sometimes its hard to understand...the language...

jessie.dazzle wrote:

Crossing the bass horn at 500Hz to an S2 : If using a 6dB/octave slope, I might start to get a bit nervous about running an S2 that low. I use one pair of S2s to cover a theoretical 800Hz to 3200Hz into a 180Hz Tractrix, and have heard no signs of distress at all (still need to measure the output and see where it is really rolling off when taking into account the combined effects of the horn+room). The diaphragms you describe seem to be one of the later versions, which are referred to as the "plastic-suspended" variety.

will try 2nd order at 500, but also 700 1st order. we will see. the diaphragma, please look at my reply to romy!
i would like to try different diaphragmas( especially the real metals, my instinct tells me they would sound very good with my poweramps), but as you know, they are difficult to find and expensiv, my budget is limited. same for the alnicos, the price is 50% higher, no easy decision for me.

thx, klaus

chaos wrote:

i searched your site and the web, but could not find a pic with the same diaphragma. it seems to be completely alu, but with a clear plastic-ring glued over the border of the hemisphere and the flat part with the grooves.its not the same like the white suspension, its just a 0,2 inches wide ring of clear something, the suspension itself seems to be alu. bought it new in 1994 as far i remember.(hard for me to find the right words, i apologize for my bad english..). red part in the pic alu, black clear plastic.

Anything like this?

chaos wrote:

…i dont want to make to much compromisses...

It is not about compromises. With two ways design everything is pretty straight forward. When you will be doing your 60Hz horn include into your design a perspective lover midrange channel from approximately 300-to 1000Hz. I know, you not doing it but if your consider it architecturally while you do your midbass horn then it will be much ease for your what you decide to try it.

chaos wrote:

..but as you know, they are difficult to find and expensiv, my budget is limited. same for the alnicos, the price is 50% higher, no easy decision for me.

Klaus,

Yes, I assumed that you had found the spec sheet; I only included the link for the convenience of others following the thread.

Klaus wrote :

"...whats wrong with 9,9"? its rougly 55% of sd? you think, 43" is too short for a 62hz horn?..."

About a year ago, in discussing the design of a 45Hz mid bass horn using a 15 inch driver, Guy Sergeant asked how I arrived at the ratio of throat to diaphragm area... At 16", the driver you are using is slightly larger, but here is what I answered ("ø" = Diameter) :

"...The ratio I used for the 45Hz horn is about 65% of the ø of the diaphragm when measured WITHOUT THE SUSPENSION. 

         ø of diaphragm WITHOUT suspension (AK151) : 11.25 inches 
         ø throat (45Hz horn in the illustrations) : 7 inches 
         Ratio : About 65%

I arrived at this ratio via the following logic : 
This is a bass horn, and, based on all information I have been able to gather, it needs to be long to be effective... I will be using it down to about 60Hz ; a 60Hz wave measures about 18 ft in length... I targeted a half wavelength dimension at 55Hz (though I'm not sure this is anything to go by). I also looked at other horns which don't simply use the diameter of the driver as a throat diameter, taking info from horns in a local audio shop and also from various postings on the web.

If you take Romy's Upper-Bass horn for example : 

         ø of diaphragm less suspension (Fane 8M) : 6 inches 
         ø throat : 4 inches 
         Ratio : About 65%

Space considerations aside (just move), if you are going to all the trouble of building a large horn, in the end you will expect performance; I feel that you will be doing nearly the same work as would be the case with a smaller throat, while getting only some of the performance.

Klaus wrote :

"...will try 2nd order at 500, but also 700 1st order..."

As far as the driver is concerned, you should be OK with either.

"...i would like to try different diaphragmas (especially the real metals, my instinct tells me they would sound very good with my poweramps)..."

Going by your latest info on diaphragms, I'm not sure what you currently have :Try to post a good image.

Romy wrote :

"...When you will be doing your 60Hz horn include into your design a perspective lower midrange channel from approximately 300-to 1000Hz. I know, you not doing it but if your consider it architecturally while you do your midbass horn then it will be much ease for you when you decide to try it..."

And later...

"...I would like do not screw you up implanting in your head the idea of a dedicated channel between your midbass horn and MF. At this point it does not matter to you but sine you told that you are planning to go for 250hz Lecleach later then you would need to think about it. The biggest question you would need to answer is what Lecleach horn to get for your S2: 180Hz, 250Hz, 330Hz, or 400Hz. That would all depend from where and how you will be intending to cross your S2 driver and that would be all depend from how good your upper know of your midbass and how deep are you willing to load your S2 into the depth of your MF horn (lower horn rate = longer horn = more HF attenuation + more beaming + less transients + less LF lower knee equalization). Soon or later you need to take all of it for considerations..."

In my original reply, I also started to suggest leaving room for additional horns, but stopped myself. If you can conceive your project such that you are able to start to use the system, and progress in such a way as to allow growth without waste (wasted effort, wasted cash), you will be doing the right thing; for that, Romy's comments above are extremely good advice. To that I would only add the following : Start saving up now for a second pair of S2s.

jd*

jessie.dazzle wrote:

To that I would only add the following: Start saving up now for a second pair of S2s.

Yes and no. I used the second S2 for lower MF range but it is not only way to go. I would propose that any driver with large aluminum cone would be a good candidate. The ceramic S2 is good choice. The Altec 288 and up would work. There are tones of other drivers. When we think about lower knee of a compression driver we always think it in context of it’s upper knee. However in our case the S2 cares upper region. So, listing just one lover range driver (in my case it is from 600 to 1000 fist order) I have to admit that in such a narrow band path many other drivers would do. I would like to have that driver to sit in 150-180Hz exponential horn and then play with drivers, trying to load it as low and the driver/horn can handle. The good part about the lower MF channel is that it is not so critical for directivity and it might be positioned relatively offside

Klaus, I like your view on the applied horn math. There are a lot of people who use a lot of not-useful math for horns – I never understood it and never considered it necessary. Your circulation of Throat’s space vs. mouth space does make sense. In fact what you are trying to do is what I processed a few years ago. I did not go for doing it but somebody who has opportunities and desire to leave a mark on the subject need to come up something like this. Let me explain what it is.

We have a good algorithm that perfectly correct predicts the tratrix horn rate from the mouth and throat sizes.

http://www.goodsoundclub.com/Docs/TractrixCal.xls

What however we do not have is an objective tool that depict the amount of pure horn equalization vs. direct sound from a driver though the norm. It would be very easy to do in the same Excel - if to have or to know how to obtain the data. I would like to input the diameter of mouth rate, horn profile and driver resonance and I would like to see wee 3 curves. First parabola will be the rate of change of horn gains (emulation) with the change of throat’s size. The second I would like to see the rate of distortion change with the change of the throat’s size. Third (A & B) I would like to see rate of distortion change with change the frequency with which the horn get high-passed and low-passed.

Unfortunately we do not have this data properly accumulated and interpreted.

.…as everything was discussed here before.

chaos wrote:

…when i tried your recommendation with s2 and 3uF cap my "basshorn" refused to roll of;-)

This is normal, I have written about it many times. Those large bass drivers have a lot of inductance in Voice Coil, the inductance that warys with excursion BTW and while the driver operates the generated inductance in the driver “talks” with the low-pass inductance in filters, canceling it out. At the time I used passive low-pass filter on my upperbass horn I was utilizing inductor of 2 or 3 times more than it was necessary. Actually a passive low-pass crossover for bass driver might not be circulated but should be made by measuring the actual driver response behind the crossover. That is nomal.

chaos wrote:

you said, you heard 515´s in basshorns, nothing was working, what was the reason in your eyes(ears)? dont want to repeat someone else mistakes...

I think it is too large driver. I would like to see a driver with the same specks but 8-10”.

chaos wrote:

you implanted the idea of a 300-1000 horn in my head(was not that difficult, want to get out the max within my options), so maybe you can answer some questions: should it sit right over the midbass? midrange inside on earlevel? 2405?mr between midbass and lower mr? s2..of course jezzie is right, but i simply cant affort to buy it at the prices they have now.was expensive for me 15years ago, but still a bargain.

It is hard to say over the distance – you need to architect your own horn positioning. I personally very much advocate what Macondo does layout-wise. Look across the site. There is a lot of information about it.

chaos wrote:

what driver would be ok for lower mr? any new production ones?  of course i would like to go all out, but its simpy not possible in this case;-((((

It depends what architect you would chose for yourself. We know that the lower MF driver much be time-align and conspiring the length of the horn you would agree to use you will instantly have the through diameter that you need. Then you might look for drivers.

chaos wrote:

s2dia...does it make sense to look for the white ones? where?

I do not know. I have just one clear cone and because of it I never look to use them and never experimented with them. Then might be fine cone and you would not need anything else for your S2. Somewhere with the Vitavox thread I told where the “Vitavox Mike” lives nowadays – he might help with cones if you need them.  The however became ridiculously expensive nowadays. An economic and making sense alternative for you would be to get S3 drivers. They are not good HF ceramic version of S2 but they might be OK for lover MF. Also they have the same diaphragms as S2 has, so buying the S3 you would essentially buy a set of other diaphragms for your S2.

Romy the Cat wrote:

(This is normal, I have written about it many times. Those large bass drivers have a lot of inductance in Voice Coil, the inductance that warys with excursion BTW and while the driver operates the generated inductance in the driver “talks” with the low-pass inductance in filters, canceling it out. At the time I used passive low-pass filter on my upperbass horn I was utilizing inductor of 2 or 3 times more than it was necessary. Actually a passive low-pass crossover for bass driver might not be circulated but should be made by measuring the actual driver response behind the crossover. That is nomal.

chaos wrote:

macondo: searched it, but its far out;-) you and jezzie work on another base.

Klaus, it does not need to be searched - Macondo has own page:

http://www.goodsoundclub.com/MacondoAcousticSystem.aspx

I would like to note that Macondo, or what Jessie does is not a “work on another base”. In context of conversation regarding a proper positioning of 3-4 way horns (it was what you was asking) I feel that the Macondo/Jessie/Cessaro configurations is exemplary. In fact I personally feel that there are no other configurations that might compete. I is not my attitudes to support my ego but rather the outcome of long thinking and many experiments and visualization of many well defined objectives with fewer compromises. Once again – the conversation was about a positioning of upperbass and upper horn channels.

chaos wrote:

anything wrong with a square mouth on the midbass (or should it it be in a special width/height ratio)? would give me the right height of upper mr when i go 4way....

Klaus, no one would give you a definitive answer to it. A rectangular mouth creates harms in imaging department but with frequency lowering the amplitude of rectangular mouth’s problems is lowering as well. It would be difficult to say belong which frequency the rectangular mouth stops to be a problem as the rectangular imaging problems with dropping of frequencies got offset with benefits of rectangular coupling. The rectangular bass horns better coupling to room boundaries and might get more result in horn imbedding. Read the following thread:

http://www.goodsoundclub.com/Forums/ShowPost.aspx?postID=4421

How, pretend that you have 60Hz spherical and rectangular horns but the rectangular, being load with long side to walls, gives you +3dB-4dB. If that 60Hz horn does not shoot up to 2000Hz (and it must not) then would a higher imbedded sensitivity of the rectangular horn overweight the hypothetic imaging problem? It would certainly do for me, not to mention that no one has a luxury to make those experiments and we are talking about pure assumed judgment. I know that if I go for my 50Hz horn then it will be rectangular… BUT … I have to admit that the spherical 50Hz is so maximalistcly-beautiful idea! Still, I admit that rectangular bass horn has many reasons to sound better.