[kinku]

After long discussions here and in different forums I finally built my first full range speakers. I used Fostex FF125WK. Used the bass reflex enclosure from their data sheet with 3/4 inch MDF panels. Filled the speaker with polyfill.Polyfill is heavily stuffed towards the back wall and lightly towards front with a tunnel to port for air movement.
I did not have the equipment to countersink the driver ,but instead used the felt pad from maddy sound,which almost blend with the edges,sinking the speaker edges in the baffle.
The box reinforced inside with battens on one side and all back and front walls and also two between front and back and top and bottom through the middle cavity part of box.
Listening test show better than expected results ,but has to say there is listening fatigue unless I use tone controls.
I measured both speakers separate at 1meter with REW and the results can be found in the attachment.They need baffle step compensation as I can guess.
Plots are1/1 octave smoothed for SPL and 1/3 smoothed for phase
I am waiting to hear from you all for improvements/suggestions.

[JCS]

Hi Kinku,

The FF125wk is a nice driver!  I expect you will need BSC, but first, you need break-in.  You may have heard this already, but for those who are not SFRD fanatics: my experience with several different Fostex drivers is that they don't sound too good for the first 100 hrs.  Then things start to improve; expect improvement through 400-500 hrs.  Some of my Fostex drivers sound better to me at 2000 hrs than they did at 500 hrs.  Single full range drivers are a different sort of beast from the drivers found in most multi-way speakers.

And if you want something different from the BR box, my favorite design is the Metronome.  Not sure about protocol around here, so I don't want to post a link; but if you put "Metronome speaker design" into a popular search engine, you can find another forum with lots of info.

Cheers,  Jim

[kinku]

Thanks Jim. I like their sound already. The mid range is just amazing. I know they may benefit from a BSC. I am looking around to see which should set at as the frequency to use for calculations.Baffle width is 7.1 INCH. with DCR 7.1OHM .From plots its look like center frequency is at 800Hz where baffle steping starting at 1.2k.Correct me please if wrong.
Also wondering that small peak at 7k is causing some fatigue on prolonged listening with female voices. It is more eveident in 1/3 octave smmothed plots.I have read a thread in Diy audio but could not reach any conclusions.

[kinku]

Surprised to see no one is interested in this thread

[ejfud]

Nice build!

Now that you've lived with them for a bit, can you share the strengths and weaknesses of your build?

[kinku]

It is only been few hours of listening,due to my work schedules and house hunting etc. I would say less than 50 Hours all together.
I can say for sure these speakers are amazing for their midrange reproduction . Sound is just sweet and has the right timbre with male voices. I am not sure the female voices have shrillness or coloration,but not as right as male voices.
Excellent with violin ,gave me goose bumps on certain solo concerts. It is near perfect as you hear the original violin performance without a mic and speaker.
It needs baffle step correction for sure.I am waiting for second measurements after about 200 hours as some suggested in other forums.Also need some help as unable to decide to go with calculations using width of baffle or use the plots from speakers, to get the center frequency.
I have stuffed inside of the box with polyfill from walmart ,about 6 oz in each box. I have not played with adjusting the density of packing. But pretty sure this is the maximum I can fit in a volume of 0.32 cubic feet.I have to experiment with taking it out. I left a track of around 1.6 inch between port and speaker for air movement. with port size being 1.5 inch inside. The part immediately behind speakers is loosly packed ,leaving a hollow cavity behind and near the back wall it is dense packing.There is this hollow cavity that tapers down to port opening with no filling at all.
My ears are not as sensitive as one of my friends and we both experienced the fatigue after listening to them for 30 minutes.He also mentioned shrillness from one of them which needs further evaluation. Both have peaks at around 7KHz.
 I have battens going behind speakers between top and bottom and and front and back for bracing. I covered them with felt pads yesterday and also the top part of back wall with felt, in case reflections causing the peakiness and fatigue. Just started listening back few hours ago,things have improved since then.
Imaging is perfect and sound stage is great,no need for a tweeter with these speakers.
I would do measurements again in few hours with felt pads inside and see how things look.Now they are just playing random tracks for breaking in.

[JohnR]

Well done! It's nice to get a project done.

Hm, low-end response doesn't really look like a BR... It may help to measure just the port to see what the tuning frequency is. Less smoothing would also help to see what's going on.

[kinku]

Thanks John. Can you please explain how to measure the ports?Also if possible please elaborate on normal low end response.
I calculated it to be 54 HZ.with port air movement well below 18 with 1.5 ID 4 inch flanged tube.
What are the possibilities for the low bass response?
Please see my 1/3 octave smoothed plots

[jparkhur]

Are you measuring with a good mic?  Not sure on this part.  If you are using a mic from a computer, they are rolled off.  That may or may not be an issue.  I have done 5 or 6 similar boxes with different vents and the 125  will go to 60's easy and the top end does not show the rise either?

Jon

[Guy 13]

Hi kinku and all Audio Circle members.
Reading your post and some other posts on extended range drivers in bass reflex and transmission line enclosures make me want to experiment with some smaller than 8" extended range drivers.
They are not expensive, plus the enclosures are also fairly small.
Everybody seems to say the same thing, mids are very natural.
Fostex, Audio Nirvana, Tang Band and more...

Guy 13

[JohnR]

Can you please explain how to measure the ports?

Hi, just put the microphone right at the port output. You won't be measuring only the port output but that will dominate, so you should be able to see the peak response at the tuning frequency. Unibox will show you what to expect to see (others might too).

[kinku]

jparkhur I am using the microphone,Dayton EMM-6.
I am going to measure ports in few minutes and update it John.
My design with bassbox 6 shows a 3 db roll off at 72Hz(F3, 70), and 6dB at 60Hz.
The plots shows 6dB roll off at 67 Hz and 3db at 108Hz.
What are the possibilities here? I guess the heaving damping inside is the reason.
Port tuned  at 48Hz .Please see the plots from port at 1inch distance, 1/3 octaves moothed

[JohnR]

Hi kinku, your port measurement looks pretty good, the tuning seems OK. I'll try to do some sims in the next day or so to see what i can figure, perhaps 48 Hz is too low for that driver? Will update.

[kinku]

Thanks John.I too think 40Hz would be too low.I went ahead and reduced the port length by half inch. Now tuning frequency at 56.Hz.Also removed packed polyfill stuffing and made it loose.Lined the walls with half thickness(more or less half of owens corning R-6.7 from home depot).
Awaiting the glue to dry up around ports.
I will update the new measurements. I used the dimensions from FF125WK driver data sheet for constructing the box. Internal volume 0.32cubic feet.
I think it needs a Baffle step compensation circuit. Do not know which direction to go.

[MJK]

The FF125WK driver has an fs of about 70 Hz so I think you are still tuned way too low. I would raise the BR tuning to be between 70 and 75 Hz and also apply a BSC filter. Without those two changes I do not think you will get a decent SPL response.

[kinku]

Thanks Martin. I was wondering where you are?
As a learning point what should I expect when I get the port tuned to 70 Hz vs 55Hz in sound quality?
I was scratching my head,from JohnR's comment.
Martin what should be the center frequency for BSC circuit?

[MJK]

I don't post much on forums anymore, it got to be too much of a hassle.

To size a BSC circuit I have a short write-up to explain the process

http://www.quarter-wave.com/General/BSC_Sizing.pdf

and an Excel speakersheet that automates the calculations

http://www.quarter-wave.com/General/BSC_Calculator.xls

that should help.

If you tune the box too low then the SPL response will start rolling off slowly well above 100 Hz and then at 24 dB/octave below 50 Hz, the entire bass output will sound thin and weak. If you raise the tuning frequency to about 70 Hz then the SPL response will be flatter down to 70 Hz and then roll off at 24 dB/octave. The bass will not go deeper with the higher tuning but it should sound better, a sub can fill in the rest. Any of the freeware programs will calculate the SPL response for a BR box like yours and should show you the trade-offs.

[JohnR]

I was scratching my head,from JohnR's comment.

Sorry  I modeled it and Martin is right, 70 Hz would work better with that driver.

[kinku]

Thank you.You guys are awesome.. ..I am going to work on it today to bring tuning up to 70Hz. I am keeping the mic at less than an inch distance from port's mouth.Is that the correct way ? I am getting values as much differ in 4-5 Hz with slight chnage in mic position.
Please see the SPL response with port tuned? to 71.2Hz,blue with old port and pink with port tuned to 71.2.any suggestions?

[MJK]

I am not exactly sure what I am looking at in your plot. You describe measuring the port at a 1" distance but I think the plot is the system SPL response. There looks to be a 6 dB rise from 400 to 1500 Hz, appears to be a baffle step response. Also, the bass starts to role off at 100 Hz which seems a little early.

Does your measurement set-up monitor the input signal and adjust the output response or are you just monitoring the response?

Have you measured the T/S parameters of the drivers?

How much smoothing are you applying?