Hello from the netherlands! (again)

[Carneoleon]

Hey everyone,

I'm Jory, from the Netherlands, and plan on building an OmniTop12, and some time later another.
I'm 22, and almost graduated electrical & electronics engineering.

My goal is to go loud with (relatively) little power. The sound system i'm planning on building will be low-budget, power will be supplied with a battery and solar panel. So that's where the bfm designs come in!

For the low-end i'll be building 2 tapped horn with cheap second hand car subwoofers.

[Ryan A]

Hello and welcome (again)

Sound like you know what you want to do. Keep us updated with a build log and pictures.

As for this:

For the low-end i'll be building 2 tapped horn with cheap second hand car subwoofers.

It sounds like it could be a bit underwhelming. Why not just build a BFM folded horn to go along with the tops?

[Carneoleon]

Thank you! And will do!

I don't build a bfm sub because i can build 2 tapped horns for the price of a suitable driver for one bfm sub. And if the hornresp sims are accurate, they shouldn't be underwhelming. Coupled they should have a sensitivity of 100-103 db/m/w. Useable frequency range would be 35-120Hz. The pair will also get about 4 times as much power as the omnitop.

Edit:

Actually, i've compared the sims with the 20inch t39 (which is about the same size), and at about 40-50Hz it is more sensitive. Above 70 the titan is more sensitive. Now all i wish is that the sim is accurate

[Ryan A]

Very well. If you have the means to design and build your cabs around the drivers you have, that's great. Good luck with your venture...

[Bill Fitzmaurice]

Actually, i've compared the sims with the 20inch t39 (which is about the same size), and at about 40-50Hz it is more sensitive. Above 70 the titan is more sensitive. Now all i wish is that the sim is accurate

You also need to compare the sims for maximum output based on driver excursion (xmax) as well as voice coil rating (Pe). Sensitivity alone does not make for a valid comparison.

[Carneoleon]

It will reach it's Pe and xmax at about the same level, 34V (400W).
On it's own it will do 122-125dB.

Not that it's important, because i'll be running them at half power. Can't supply that much power with battery's and cheap amps.
Now i don't know what the max-spl of a t39 is. But IIRC it should be limited to 50V? with a 6 Ohm lab12 that is about the same amount of power? Just guessing here.

Anyway, not relevant for my situation, as both subs can easily handle the available power.

[bitSmasher]

Hey, another person interested in battery power!
What capacity battery, and what amps are planned?
I'm working towards a reasonably sized system with the end goal being OT12 on top. Reckon a pair of them running on a Tripath chip amp would be impressively loud, and the bass will need some power behind it to keep up.
Definitely post more as you build, and I can recommend a good forum for battery-specific systems if you need to discuss that further

[Grant Bunter]

It will reach it's Pe and xmax at about the same level, 34V (400W).
On it's own it will do 122-125dB.

Not that it's important, because i'll be running them at half power. Can't supply that much power with battery's and cheap amps.
Now i don't know what the max-spl of a t39 is. But IIRC it should be limited to 50V? with a 6 Ohm lab12 that is about the same amount of power? Just guessing here.

Anyway, not relevant for my situation, as both subs can easily handle the available power.

I take it your amp is car audio, as 34V/400W is below 3 ohms in load.

Yes the limit for a lab 12 is 50V in the T39. There's 2 ohms of acoustic impedance in that cab as well, so, for one cab, the displacement limit is 312.5W for an maximum output 26dB above it's 1W/1M response.

Forum member Sine143 has a great description on different sub types:
http://badmansound.biz/subwoofer-design ... tions.html

Have a look, there are some points in that page that should perhaps be included in your decision...

[Carneoleon]

We are still figuring out howmuch battery capacity we can get, but we'd like to have 100-200Ah @12V. Coupled with about 100Wp of solar power.

I'll be using a single TDA7498 for the OT's. They should get about 80W each.
I'll use a single TDA7498E for each sub. 220W @ 3 ohms.

Actually the nominal impedance is 4 ohms, but de Re is 3 ohms, and the impedance drops that low too. (35V for the 400W figure)
So using nominal impedance the limit is 289W.

Quote from that website:

Distortion is not filtered out as seen with Front loaded horns, as the rear wave is produced directly in the mouth and does not travel through any folded horn path. Given that max excursion is seen within the passband, that means distortion can be very high when the cab is pushed to its limits.

This is only the partial truth AFAIK. I'd say that the distortion is about the same as with a closed or ported box driven to the same limits. But because the output is about 6-9dB higher the relative distortion (the percentage) is a lot lower then a closed or ported box. I'm not an expert, but this quote is implying (in my eyes) that it will sound heavily distorted.

Tapped horns do not gain a lower corner frequency from being used in multiples. While they do display a generally flat frequency response as a single unit, this is as good as it gets. Doubling cabs produces a 6 db increase in output, just as we see with vented designs.

Well that is something i know isn't true. I can clearly see the roll-off lowering if i sim with mulitple cabs.
16 cabs vs 1

[Patrick Mos]

Nice to see you here Jory!

[Grant Bunter]

Something seems to be amiss with your 16:1 cab sim.

A 5dB overall increase in output with 16 cabs compared to 1 cab is miniscule, when it is widely accepted that just doubling cabs adds 6dB.
From another thread:

I don't understand how doubling the power can yield a 6dB increase in level.

If one speaker is reproducing 100db spl with one watt input, how does a second speaker producing 100db spl at one watt placed beside the first one achieve 106db spl combined?

Because you're doubling both power and radiating area. Each gives an additional 3dB.

The nature of FLH's means they don't output the same harmonics as vented boxes.
It is often commented on here, with the term "clean". I think the comment about tapped horns means they will still produce 2nd and 3 order harmonics, as distinct from THD...

[Carneoleon]

Hey, patrick!

That reminds me, i still owe you an email!

You're missing the point there, the chart was to show the lowered roll-off.

That 6dB is because it also adds double power, i've put te cabs 4S 4P, so the same power is used.

But let's compare it same way bill does with the(same sized) 20" t39.



The t39 you can add 20db for max output.
The tapped horn you can add 24dB for max output.

The 24" t39:


Add 26dB for max output

Won't a FLH still produce (and perhaps even amplify) the 2nd harmonic? if I observe the spl chart the t39 is most sensitive from 100-200Hz, so any 2nd harmonic from the 50-100Hz band will be reinforced, right? Or am I missing something here?

[Bill Fitzmaurice]

Something seems to be amiss with your 16:1 cab sim.
A 5dB overall increase in output with 16 cabs compared to 1 cab is miniscule, when it is widely accepted that just doubling cabs adds 6dB.

Only when parallel wired. His are wired series/parallel.

The nature of FLH's means they don't output the same harmonics as vented boxes. It is often commented on here, with the term "clean". I think the comment about tapped horns means they will still produce 2nd and 3 order harmonics, as distinct from THD...

2nd and 3rd harmonics are THD. Tapped horns have higher THD than FLHs because the driver is exposed to the air. For the same reason they have higher excursion. Those factors, and wonky response in the 100Hz-150Hz region, are what you trade off for the smaller size factor that results from having no rear chamber.

if I observe the spl chart the t39 is most sensitive from 100-200Hz, so any 2nd harmonic from the 50-100Hz band will be reinforced, right? Or am I missing something here?

FLHs have high THD when the source signal is lower than the horn cut off frequency, so a T39 will only have high THD if one doesn't high pass. In that case THD would only be significant for a short time, as you'll blow the driver from over-excursion.