DIY tweeter/crossover options

[Beer of the Bass]

After reading through the other recent thread about adding tweeters to existing cabs, I have been weighing up the possibility of adding a tweeter to one of my cabs. (I thought I would start a new thread rather than continuing that one, as it would be a bit of a derailment from Kevin's original question about modifying his own cab)
I'm using a pair of home-built ported 1x12" cabs using the Eminence Beta 12. Because they're DIY cabs, I have no concerns about re-sale value and no worries about cutting a hole in the baffle of one. For electric bass, I don't want or need a tweeter for the sound I like, but when I use one of the cabs with double bass I feel like I could do with a touch more air in the highs. So I would need something which didn't affect the sound of the 12" when the tweeter is switched off. I guess that would suggest that simply high-passing the tweeter rather than using a full 2-way crossover might be the way to go.
I know there's a lot of talk about how complex crossover design can be, but if I was to do a bit of reading, pick out a tweeter that extended down to around 2KHz (like some of the P-Audio offerings), calculate the inductor and capacitor values using an online calculator and wire it up with some form of switchable or variable attenuation, how badly could I go wrong? I would probably try it externally before cutting a hole in my baffle. Worth looking into, or a fool's errand?

[Bill Fitzmaurice]

[quote name='Beer of the Bass' timestamp='1473329249' post='3129094']if I was to do a bit of reading, pick out a tweeter that extended down to around 2KHz (like some of the P-Audio offerings), calculate the inductor and capacitor values using an online calculator and wire it up with some form of switchable or variable attenuation, how badly could I go wrong?
[/quote]The problem is that those calculators assume a resistive load at the exact value of the driver nominal impedance. That's not what crossovers actually have to deal with. It will work, but not necessarily well. As for running the woofer full range, if you do there can be destructive interference between the woofer and tweeter outputs.
One award winning commercial cab I designed went through a full year of Beta testing with many component combinations before the manufacturer settled on the final crossover design. It can make that much difference.

[stevie]

While Bill is perfectly correct about the need to custom design crossovers, have you had a look at what bass speaker manufacturers are actually fitting? The last commercial speaker I measured was an Eden and it looked like the crossover had been designed by the tea boy.

There will eventually be a two-way 12" design with a proper crossover in the Cabinet Diary thread, as I'm starting on one at the weekend. Don't hold your breath though.

I'd give it a go, BoB. Try a 3.3uF film capacitor and a .35mH inductor in a second order circuit and stick an L-pad on the end. Switch the polarity of the HF unit to taste. It's not going to be optimal, but it will probably work. The P.Audio HF units are unbeatable for the money.

[Beer of the Bass]

[quote name='stevie' timestamp='1473349278' post='3129408']
While Bill is perfectly correct about the need to custom design crossovers, have you had a look at what bass speaker manufacturers are actually fitting? The last commercial speaker I measured was an Eden and it looked like the crossover had been designed by the tea boy.

There will eventually be a two-way 12" design with a proper crossover in the Cabinet Diary thread, as I'm starting on one at the weekend. Don't hold your breath though.

I'd give it a go, BoB. Try a 3.3uF film capacitor and a .35mH inductor in a second order circuit and stick an L-pad on the end. Switch the polarity of the HF unit to taste. It's not going to be optimal, but it will probably work. The P.Audio HF units are unbeatable for the money.
[/quote]

That does sound fairly acheivable, if I do get around to it. I realise it's unlikely to be particularly flat around the crossover region, but I'm not out by much if I don't like it.

[stevie]

That's true. So when you're ready to have a bash, let me know and I'll send you the capacitor and inductor.

[Phil Starr]

There's a lot to think about but in the end you don't get many flat response bass speakers, they are musical instrument speakers and a non flat response might be pleasing without being 'right'.

There's a few considerations:

the beta has a huge peak above about 700Hz peaking between 1000 and 3000Hz. That complicates the crossover design, if you already have too much output at 2000Hz then adding in a tweeter at that frequency is going to create quite a peak! Conventionally you'd probably use the crossover roll off to reduce that peak and then roll in the horn so that the response was flat at the crossover point. Electrically the two drivers would be crossing over at different points but the aim would be to get a more or less flat response. You'd also need to take into consideration the phase response of both speakers.

The horn is going to be much more efficient than the Beta meaning you'll need to use some resistors to pad down the power to the horn whilst keeping the impedance seen by the crossover at your target value (8ohms probably)

You need to decide if you are just going to use a high pass filter to the horn or a full 2 way crossover so the two speakers won't both be producing the same frequencies to avoid some of the problems above.

Stevie has some software to design a crossover and may be willing to help you design what you need. Alternatively you could buy a ready made crossover which will work but not exactly match the drivers you will be using. It'll split the power for you and you will probably be OK with the sound even if it isn't exactly hi fi. You can use plenty of calculators on the internet to pad down the horn by whatever no of decibels you choose so that won't be a big problem. I notice that blue Aran do a 3.8kHz crossover that seems to have some padding built in for the horn http://www.bluearan.co.uk/index.php?id=BMAFD2CXFE&browsemode=category.

The other consideration is that you need to match the horn to the needs of electric bass, there's almost no output apart from fret noise above 4000 Hz so you may not find too much of an improvement. A mid range driver may be more effective than a horn designed for a PA speaker.

[Kevin Dean]

I'm going for a horn in a separate box . a mate of mine who use to work for JBL is going to wire it all up for me , Ive come up with a couple of designs so it can be attached & removed from a cab & change the angle . I'll post some pics once done .

[Beer of the Bass]

[quote name='stevie' timestamp='1473365071' post='3129563']
That's true. So when you're ready to have a bash, let me know and I'll send you the capacitor and inductor.
[/quote]

Cheers for the offer, Stevie. I think what I'll do first is to take a cab to a rehearsal this week and mess around a little more with EQ and raising and/or tilting it. If I still can't get enough of what I want to hear that way, I'll have a go at the tweeter idea. So far I've only used these cabs for double bass a couple of times, so I'm still getting used to them.

Edited September 11, 2016 by Beer of the Bass

[Beer of the Bass]

After having a good play around with one of the cabs with double bass last night, I think I'll shelve the tweeter idea for the moment. I found that if I tilt the cab back by propping something under the front edge and take down the high mid control on my amp (a GK MB200) while boosting the highs a little, things get much clearer and more pleasant sounding. IIRC the high mid control is centred at about 1KHz, so I guess the Beta's high sensitivity around there is unflattering with the double bass without some EQ. I do really enjoy the sound of these cabs with electric bass though, so there's always going to be some tweaking when using one rig for both.