Your thoughts please... OB full range and bass

[mltube]

This is my first open baffle and had a question or two for those of you that have more experience. I do not know where to begin, and I have checked the online calculators but I am still too green in this area.

My full range speakers are two 12"Heppners with wizzer cone, and I have two 18" Heppners for bass response. Limiting the full range to low mid-bass is what I was thinking of, but what do I know, "Greenhorn here".

What I was hoping to achieve could go two ways, one amp and passive crossover, or two amps with preamp control unit controlling both. The amps are Vac. Tube. I have used the 12's with (sub one watt and the sound plenty loud in a 16' x 22' room) they can handle 50w ea. (vaccum tube watts).

I can handle the twin amp configuration, but if I were to use a single amp where would you recommend crossover points? The single amp configuration will have 40w/ch so it will drive them just fine.

Suggestions and constructive critizism welcome, and by the way I do not have the specs or freq. range of the speakers as I bought them second hand.

Just looking for ideas and or a crossover points that you may recommend.

[Rudolf]

Originally Posted by mltube

I can handle the twin amp configuration, ...

... meaning you already have built it? Or having a plan how to go about it?

... but if I were to use a single amp where would you recommend crossover points? The single amp configuration will have 40w/ch so it will drive them just fine.

Any idea, how high the 18" will go without resonances or distortion? 200Hz? 400 Hz?

Rudolf

[mltube]

Hello Rudolf, and thank you for replying.

... meaning you already have built it? Or having a plan how to go about it?

I have several amps that I have built that could work here, but will have to build a control unit.

Any idea, how high the 18" will go without resonances or distortion? 200Hz? 400 Hz?

I only know that the speakers were from a Hammond pr-40 tone cabinet as organ accessory originally.
I have had great success with the full-range 12" Heppners made for Hammond, and thought the 18's would work great IMHO.

All of these were used as open baffle in the tone cabinets and sounded great. The 18's go very deep, as to cause hair to tingle 20 feet away with only 16 watts.

I am working with specs that are unknown to me, as to why I am asking, hoping that someone may have some idea of a safe freq range to begin with. I am a little frustrated, as the information on the net shows very little, and I do not want to damage them with careless "hot" testing.

Thank you again for your reply,

Michael (mltube)

I will spend this day doing research for the specifications.

[Godzilla]

Endorphine from Kingston Kitchen

perhaps something like this might work for you?

[Rudolf]

Originally Posted by mltube

I am working with specs that are unknown to me, as to why I am asking, hoping that someone may have some idea of a safe freq range to begin with. I am a little frustrated, as the information on the net shows very little, and I do not want to damage them with careless "hot" testing.

You can't destroy a 18" driver without a crossover except by over-excursion. You can put higher frequencies at it without any problem I could think about.

If you put the 18" on a 20" wide baffle and cross over at 200 Hz that would be fine IMHO. You need to EQ the dipole roll off. You should at least be able to measure the voice coil resistance. From that one could start to think about a inductance coil value.

[mltube]

Thank you all for the information, now I will go to work without worry.

Have a great day,

Michael

[mashaffer]

Here's my two pfennig. Without having specifications (you could measure if you want) you might be better off to biamp and use a line level crossover (it doesn't have to be active necessarily). That way you can experiment with crossover points and set levels to suit.

The 12" FR will be fine with no crossover in this case, at least for initial testing. The idea is that the 18 will be used to supplement the lows where the 12 is running out of steam.

So put the 12s on the baffle that you want to use and run some test tones. Using either your ears or a measuring device (cassette tape deck with $30 condenser microphone gives a useful enough measurement) determine where the approximate -3dB point is.

Now put the 18s in a nice H-frame and build a 2nd order passive line level low pass filter with turn over frequency at this frequency and put it either at the input to your bass amp or in its tape loop if it has one. Now adjust the gain of the bass amp to give the desired result.

Play with different crossovers to your hearts content (parts for the LP filter are about $4) and once you have you crossover point chosen you can get fancy about your filter design.

[mltube]

Now put the 18s in a nice H-frame and build a 2nd order passive line level low pass filter with turn over frequency at this frequency and put it either at the input to your bass amp or in its tape loop if it has one. Now adjust the gain of the bass amp to give the desired result.

Hello Mike,

Thank you,

You must have been reading my mind with the H-frame box, it is exactly what is being assembled on the shop bench.

I am going to use an active tube crossover for the bass amp, and dial it in with my audio tone generator. (I am kinda curious how low these will go)

This is all starting to make a lot of sense now.

Been building tube gear for years and have only used ready-made speakers or full-range thus far.

I can not wait to hear the fullrange set with the bass filling the bottom end.

Thank you for the information and have a great day,

Michael (mltube)

[Godzilla]

Are you going open baffle or sealing the main driver up?

[mltube]

Godzilla,

Are you going open baffle or sealing the main driver up?

All open baffle, because it sounds soooo good. I experimented a little with the 12" fullrange with no baffle at all when I first recieved them, and to my suprise everything was crystal clear and good bass. After that experiment I mounted them into 3/4" scrap pine board 24" X 36" and the bass improved ten-fold, and then the 18" on the same size board. The 18" Bass was very deep and powerful enough to disturb the neighbor nextdoor, and it was only driven by my 6973 se amp @ 5 or so watts.

I guess you could call me a convert now, because all box speakers went to storage.

The openess of music passages draw me in like never before and is absolutely tireless.

Have a great day,

Michael (mltube)
<temp here 98 deg F and rising so aircond is maxed and on with the music... )>