JF Vented Horn

Hi Jake, good to see someone likes to have a close look at things other than 'what does it sound like'. I would not be too worried about your impedance plot. Sometimes you will experience a phenomenon called chart wrapping, where if a recorded value disappears off the scale of the plot, it will actually be plotted at the recorded value minus the total value of the chart. Your charthas a maximum value of 60 ohms, and you were expecting a total value of over 70, and it's been plotted at 12ohms. Which would make it about 72 ohms?.
Many other factorscan contribute to an anomalous plot, and the preditive functions of hornresp cannot foresee every occurence. It may just be a stray combination of port and horn resonances, oran inherent property of the driver itself.
However the dip has been caused, it does not seem to bea detrimentalflaw, unless you are experiencing someacousticproblems at that frequency?.
I'm looking forward to seeing what you get from this hybrid.
Keep up the good work.We need a few more designsbeing shown on this forum.

Thanks for that. The chart actually adjusts to what ever value comes up, i could put in 150r and it would just expand the range and shrink the scale down (if you get me) but the other things you mention could well be correct.

Im not experiancing any accoustic problems at that frequency, its sounds great until you get to 100Hz then there seems to be a bigpeak in SPLuntil 102Hz then it levels out again. Although i have not properly braced the cab yet or glued the top on, but i can EQ that out later!

I have decided to only show the plots and stuffon this forum, and link to them from speakerplans incase anyone over there is interested (hi guys!). I seem to have a mental problem where i composively readALL new posts ALL the time on SPandfind there are too many posts for me to keep up with nowadays, I dont get anytime to work! so I try and stay only on this forum during the day because i can keep on top of it!

its that speakerplans bug, ive got it bad, as has deadbeat it seems , its a clever design, effectivley your now getting avariation on a6th order bandpass if im not mstaken (with horn as second flared port) albeit without secondary hornloading you gain the smaller size but it just intersts me that you can get a linear response from a design like this with a standard port being so much less efficent than a horn... any clues peeps?

Jake, this is excellent work. I waited before coming in as many people seem to abandon their projects before getting to the all-important tuning stage that you have now reached. Perhaps I can help here a little:

Jake_Fielder wrote: Im not experiancing any accoustic problems at that frequency,

You need to understand this artifact. Even if there are two peaks, neither seems high enough compared to the prediction. Try smaller frequency increments in that area.

Jake_Fielder wrote: its sounds great until you get to 100Hz then there seems to be a bigpeak in SPLuntil 102Hz then it levels out again.

Could be a room or boundaryeffect. this is why impedance measurement is easier to get right than SPL measurement. Try it outside.

Jake_Fielder wrote: Although i have not properly braced the cab yet or glued the top on,

You must do somehting to keep the cabinet rigid when testing. Try going to the local nightclub and getting some fat girls to come and sit on the sub. Or borrow some gold bars from the bank. Gold is quite heavy. Plus audiophiles can be made to believe all sorts of sound quality voodoo when you bring the old Au intothe equation. Alternatively, get oddjob from Goldfinger to hold the cabinet together tightly. He takes his hat off to a lady, you know.

Jake_Fielder wrote: but i can EQ that out later!

I'll pretend I didn't see that!

Jake_Fielder wrote: I have decided to only show the plots and stuffon this forum, and link to them from speakerplans incase anyone over there is interested (hi guys!). I seem to have a mental problem where i composively readALL new posts ALL the time on SPandfind there are too many posts for me to keep up with nowadays, I dont get anytime to work! so I try and stay only on this forum during the day because i can keep on top of it!

I'm really your boss. Ha ha not realy. But had you going there.

sKs01 wrote: its that speakerplans bug, ive got it bad, as has deadbeat it seems

, its a clever design, effectivley your now getting avariation on a6th order bandpass if im not mstaken (with horn as second flared port) albeit without secondary hornloading you gain the smaller size but it just intersts me that you can get a linear response from a design like this with a standard port being so much less efficent than a horn... any clues peeps?

Yes it is like a 6th order bandpass except that the horn is not a low-pass filter, so the useful response goes higher, as I described in the FSP_MAJIKBOKS thread.

A port is not less sensitive than a horn in every case. If a horn has a very high compression ratio or its mouth area is not enough to couple to the airload, then it might have quite a low efficiency. A port can have a high efficiency if it has a low inertience, which requires a large chamber. So it is possible to have ports that are more efficient than horns.

However you produce them, lower frequencies require more cabinet volume to get the same efficiency.In Chris H's design, he chose not to provide alarge chamber for the ported section, enabling him give more space to the horn part and get better performance higher up. It's a tradeoffbut you get to make the choice up front when you use simulation software.

much obliged jsg, more bedtime reading is required. though i roughly understand all the principals stated i still need to get to grips with the finer points of a design like this.

Edited by: sKs01

jsg, the bandpass guru, speaks again. Good work Jake. This is perhaps the best speaker to have ever come out of Norfolk! (Until i build some monsterhorns, something in the pipeline[img]smileys/smiley2.gif[/img] )

jsg wrote: In Chris H's design, he chose not to provide alarge chamber for the
ported section, enabling him give more space to the horn part and get
better performance higher up. It's a tradeoffbut you get to make the
choice up front when you use simulation software.

I wouldn't have said my rear chamber was that small, in fact I believe it's over 100L which is what I'd use for a pure reflex design. In fact the rear chamber and port are a almost identical in size to a 15" reflex design I did years ago!

The big difference between my design and Jakes is that mine is a more of a pure horn (no defined front chamber) and his is a BPH (large front chamber) , assuming he has stuck to something similar to the early drawings. When I was doing the design, a pure horn seemed to work better with the port assistance for a best of both worlds design.

chaudio wrote:

jsg wrote: In Chris H's design, he chose not to provide a large chamber for the ported section, enabling him give more space to the horn part and get better performance higher up. It's a tradeoff but you get to make the choice up front when you use simulation software.

I wouldn't have said my rear chamber was that small, in fact I believe it's over 100L which is what I'd use for a pure reflex design.  In fact the rear chamber and port are a almost identical in size to a 15" reflex design I did years ago!

The big difference between my design and Jakes is that mine is a more of a pure horn (no defined front chamber) and his is a BPH (large front chamber) , assuming he has stuck to something similar to the early drawings.  When I was doing the design, a pure horn seemed to work better with the port assistance for a best of both worlds design.

OK but you do accept that lower frequencies require more space to get the same efficiency right?

And that if you'd have made the rear chamber bigger, and the port inertience lower, you could have got more output down there at the expense of a bigger cabinet?

And that you made the decision to go with your current design based on simulations?

These are the points I'm trying to make.


Edited by: jsg

Yes!

I went with a reasonably large rear chamber in order to get half-decent efficiency from the port and try and keep up with the horn output. However, too large a chamber (or too high a tuning) and the port resonance has too high a 'Q' and you just get a lump at the tuning frequency rather than a nice extension to the response.

And yes, it was designed using Hornresp (and knowledge gained from previous failed attempts at 15" horns)

Hi JSG and others, cheers for all the comments. im kind of on holiday at the mo, but im finishing off the bracing and stuff of the first cab tonight then i'll take another imp. plot in the middle(ish) of my garden. Then i'll catch up with everything thats been said.

Cheers guys

Jake