Need advice on OB with Tone Tubby

[anilva]

Hi,

I am in the process of making a OB with one 12" Alnico Tone Tubby (8 ohms) crossing over to a 8 ohms Fostex FE126E.

I intend to use a 1st order passive crossover. My plan is to crossover around 500Hz from TT to Fostex. Any suggestions/comments/advice on the crossover point?

My design is based on:

Tiny Alnico Open Baffle

but with a fostex instead of a Lowther.

Thanks in advance.

Cheers.

[Josephjcole]

How loud do you like to listen? A 4.5" cone with less than .5mm xmax isn't going to be able to play very loudly with out distortion in the situation you describe. Maybe a 12 db/octave crossover?
Joe

[anilva]

Originally Posted by Josephjcole

How loud do you like to listen? A 4.5" cone with less than .5mm xmax isn't going to be able to play very loudly with out distortion in the situation you describe. Maybe a 12 db/octave crossover?
Joe

Loudness is not a criteria for me. I am looking at transparency and soundstage from a OB. Fostexs are pretty efficient as well.

Cheers.

[Josephjcole]

Originally Posted by anilva

Loudness is not a criteria for me. I am looking at transparency and soundstage from a OB. Fostexs are pretty efficient as well.

Cheers.

Sure thing. I just did a quick estimation and it looks like the fostex exceeds xmax at 5watts. I'm not trying to discourage you, just want you to be aware of the limitations. I imagine it could be quite nice within those limitations. I'm afraid I don't have any experience with open baffle so I can't really help you there. Have you read MJK's write up with fostex/eminence open baffle? I imagine you can find most of the info you need there.
Best of luck
Joe

[holdent]

I just did a quick estimation and it looks like the fostex exceeds xmax at 5watts

I get a little more than 7 watts will exceed the xmax of the FE126E between 70 to 100 Hz with a 1st order xover at 500 Hz. The simplest way around a possible xmax limitation is switch the xover to a 2nd order at 500 Hz. Then the only real limitation is the ultimate power handling of the FE126E. Note that at 15 watts (the Fostex-rated input power of the FE126E) the driver should be producing about 103 dB at 1 m simulated. I used the FE126E measurements from Fostex FE126E + rather than the Fostex published data to run the sim.

I tried simulating the Tone Tubby in an OB using the data from http://www.hempcone.com/pro/pdf/TT%20Spec_'s%200609.pdf but for MJK's MathCad files I also need the Bl, Sd, and Le which aren't provided. The 16ohm version may be better because its Qts is a more OB-friendly 0.9 (rather than the 8 ohm version with a Qts = 0.56). However, if I'm reading the data sheet correctly, both versions have a high Fs (100 Hz and 120 Hz for the 8 and 16 ohm versions respectively). You won't get deep bass from these speakers without some bass boost.

I hope this helps.

[anilva]

Originally Posted by holdent

I get a little more than 7 watts will exceed the xmax of the FE126E between 70 to 100 Hz with a 1st order xover at 500 Hz. The simplest way around a possible xmax limitation is switch the xover to a 2nd order at 500 Hz. Then the only real limitation is the ultimate power handling of the FE126E. Note that at 15 watts (the Fostex-rated input power of the FE126E) the driver should be producing about 103 dB at 1 m simulated. I used the FE126E measurements from Fostex FE126E + rather than the Fostex published data to run the sim.

I tried simulating the Tone Tubby in an OB using the data from http://www.hempcone.com/pro/pdf/TT%20Spec_'s%200609.pdf but for MJK's MathCad files I also need the Bl, Sd, and Le which aren't provided. The 16ohm version may be better because its Qts is a more OB-friendly 0.9 (rather than the 8 ohm version with a Qts = 0.56). However, if I'm reading the data sheet correctly, both versions have a high Fs (100 Hz and 120 Hz for the 8 and 16 ohm versions respectively). You won't get deep bass from these speakers without some bass boost.

I hope this helps.

Thanks. This helps a lot. I have known earlier that 16 ohms version has higher Qts but chose not to go with that due to my amp limitations. I need to make do with 8 ohms. I did plan for a sub woofer reinforcement considering the high Fs of TT.

My question primarily is around the crossover point I need to pick from where TTs pick up and Fostexs leave. TTs are known to go upto 1K I guess without beaming issues, therefore does it make sense for the crossover point to be little higher than 500Hz and may be 800Hz? Thanks, I can look at 12 dB crossover to avoid xmax of Fostex.

Regards

[holdent]

I think that you're better off keeping the xover to the FE126E at around 500 Hz and consider looking for a different woofer than the Tone Tubby.

Frequently to get a smooth transition from the bass driver to full range driver the xover points have to be quite different. In MJK's OB study at http://www.quarter-wave.com/OBs/OB_Design.pdf, the crossover points were set at 200 Hz and 500 Hz. Josephjcole earlier referenced his work - it will likely help you alot to look it over. Martin has an excellent discussion about woofer selection. [Note that some have disagreed with Martin's use of high Qts drivers and prefer to use lower Qts drivers with bass boost].

[anilva]

So I am going ahead with a design which has a crossover of 200Hz for the woofer and the Fostex FE-126E being crossed over at 500Hz. Both crossovers will be 12 dB/Octave. The Fostex going to be mounted little off-centre and mirro images are going to be made for Left and Right.

Cheers.