Ot15tb drivers

[Camillo]

Hi, i've built the OT15 TallBoy. The goal was to make a cabinet to give away to a music store as a secret christmas gift. Last weekend we had a band playing and they needed a basscab so during soundcheck i ran to get the half-ready build and finished the last screws on the back plate, no top section, just a 15".

After the gig, the bassplayer who at first seemed worried to play at a ply-finished, not ready cab came and asked about it since "it might be the best cabinet i've ever played".

So.. Now i want to build another.

But for the existing one i want to put a top section that is possible to turn off and I want a mid driver that is easier to get a hold off here and my questions, since i'm not putting the cbmra in this one (due to time, budget and availability) are:

What are the most important thiele in closed back alternative drivers?

Fs?
Qts?
Vas?
Power handling?

How bad is it to close an open one, maybe calculating the box and what to think of then. (plans says must use a closed back, i know)

Are there other elements, maybe from eminence aswell, since its out of stock here.

Thanks! The build is super Even when not done yet!

Tag: alpha 6cbmra closed back sealed back midrange

[Bill Fitzmaurice]

Fs is the only spec to be concerned with in a closed back. I can't recommend anything not knowing where 'here' is, you should add it to your profile. I assume it's not the US, as the CBMRA is plentiful here.

[Camillo]

Fs is the only spec to be concerned with in a closed back. I can't recommend anything not knowing where 'here' is, you should add it to your profile. I assume it's not the US, as the CBMRA is plentiful here.

Thank you Bill.
Is there a frequency range you could name to stay within? The cbmra will be my guture option when It's available for my own box. It can be found here (sweden) but at a way too high price whre its not out of order and it'll probably be a larger order from the US when i'll build more cabs. It's also discontinued in the larger shops.

Would it be better to close the back of one and have it tuned to a close fs of the cbrma than buying a closed back with an fs far from the spec?
Lower is preferable to higher than the cbrma?

[Bill Fitzmaurice]

It's not possible to duplicate a closed back with an open back, you can't make the chamber small enough. There are other driver options. Here's two:
https://prvaudio.com/products/prv-6-5-i ... 00seal-v2/
https://celestion.com/product/tf0615mr/

[Camillo]

I see. I tried since i had one at home before i read this. Got it down to under 0.1 litres in an angled frame, filled the remaining millimeters with foam-tape. It sounds okay but low in the response. It was a 6 ohm so I modified the x-over to the middle of the parameters between 4 and 8 ohms.

I found a closed back but 4 ohms, is the response going to be higher then?

Modifying the x-over in the same ways as the dual 8 in the bass section? Should i keep searching for an 8 ohm instead? Will double check if i find the ones u sent on the sites here,

[Bill Fitzmaurice]

4 ohms would require a complete redo of the bandpass filter, and it will have 3dB higher voltage sensitivity.

[Camillo]

4 ohms would require a complete redo of the bandpass filter, and it will have 3dB higher voltage sensitivity.

I see, double the CAP value and halfing the inductors is not a way then?

As an electric bass-cab, run it like a three-way aswell? The Speakon plate have an on-off option so i will be able to chosse, just havnt seen a 3-way basscab

[Bill Fitzmaurice]

Correct on the filters. I wouldn't use a tweeter on a bass cab that has a midrange.

[Camillo]

Correct on the filters. I wouldn't use a tweeter on a bass cab that has a midrange.

Can i connect the tweeter crossover after the high pass section in the bandpass crossover? Ergo, taking the signal before the 0.45 mh/5.6 CAP to the tweeter? Would they interfere with each other?
In that case i could put a double switch there that either gives signal to the tweeter section and The low pass on the mid, or it omits the tweeter and The low pass of the mid sending full high passed signal to the midrange..

Or, if the bass has a rolloff, would it be possible to run it full and keep the tweeter on for the highs as other basscabs, excluding the mid and have a tweeter with it for the top top section (with a pot if the high frequencies are much louder than the rolloff) ?

Most bass players here run tube amps and old cabs so imitating that sound would okay as an alternative with switches if that is how old drivers sound but i guess that would be without a tweeter at all maybe...

I guess this is like the celestion?

Edit: i saw now that celestion and Monacor is the same.

[Camillo]

Correct on the filters. I wouldn't use a tweeter on a bass cab that has a midrange.

Maybe and odd question, but this is how i mean, puttning a double switch but i guess It might be faulty. I cant take + and - to the tweeter from after the high pass section of the mid, it would interfere with the tweeter high pass? As in the picture.

Otherwise,
Is it enough to break the - side of the filter to turn off the driver or/and The + side?

Thank you, or anyone that knows:)

[Bill Fitzmaurice]

Don't do that. If you see the need to attenuate the tweeter use an LPad.

[Camillo]

Don't do that. If you see the need to attenuate the tweeter use an LPad.

Ah, i see. I wanted to be able to switch between 2-way and 3-way, thats why:) i used a premade circuit board for the mid so i can turn off the highs, i'll simpky put a switch on the tweeter aswell then to turn that off when running 2-way. Then i have a cab that can be used fullrange with the 15" only for el. Bass, 3-way for pa and 2-way for el. Bass with extended mid/high where the mid plays all the way up. Fun! Thank you!

I also wonder, off topic, are you making more designs? And are there any new inventions on sight in the speaker front that is... Pioneering?

[Bill Fitzmaurice]

I don't have anything to add at this point, but if I had enough requests for something I'd look into it. As for having the mid playing all the way up the issue there is that dispersion narrows as you go higher in frequency. That, not HF extension, is the primary reason for using progressively smaller drivers. A midrange that reaches 10kHz on-axis isn't much good if it's -10dB or more at 30 degrees off-axis.

[Camillo]

I don't have anything to add at this point, but if I had enough requests for something I'd look into it. As for having the mid playing all the way up the issue there is that dispersion narrows as you go higher in frequency. That, not HF extension, is the primary reason for using progressively smaller drivers. A midrange that reaches 10kHz on-axis isn't much good if it's -10dB or more at 30 degrees off-axis.

I see, so on a small stage there probably is no issue if the cab is placed correctly, with just the mid?
I will have a tweeter on it anyways so it'll be up to the player with the settings i guess, it already got 5/5 from its first time being used with only bass.

My concern was that it might be too.. Detailed? (picking up too much "top sound" ?) in the mid/top section compared to a bass-cab without mid/tweeter, based on what bassplayers normally play on, but that was simply a thought and a guess Thats why i wanted all the settings with/out tweeter, Mid with extended frequency range and 15" bass only.

Perhaps easier to mic it with bass only-option when not using direct out from old tube amps..

I'd never build those small horns people use to put their telephone or small aux-speakers in, but i would build Bill Fitzmaurices version if It's possible to calculate anything useful out of it Also a fun way for people to interract with horn speaker builds for the first time no answer required for that thought