Amplifier for bass duties

[bumpy]

I have gone active on my 3 way open baffles and looking to optimise the 15" woofers which have a 150 Hz low pass filter and 20Hz high pass filter.

Assume therefore that worthwhile output is required up to say 300Hz - the male voice is barely audible when that low.

I currently use a Rotel 820 AX that has been modified and improved. It is 2x30watts and gives adequate volume. The driver itself is vintage and has a maximum limit of 35 Watts, so my challenge is to find an amp that has the best possible SQ at low frequencies - it seems daft paying a fortune to amplify all those 'wasted' frequencies over 300 Hz.

So any suggestions

[Ali Tait]

Yes. I use Behringer Inuke. 3000w and very high damping factor. Ideal for this application and not expensive either.

[bumpy]

Yes. I use Behringer Inuke. 3000w and very high damping factor. Ideal for this application and not expensive either.

Thanks Ali.
Some little while ago I fed, by mistake, 1000W of power to a pair of vintage Saba midrange drivers. The result was a big bang and shower of sparks as the voice coil incinerated and the paper cone exploded. I am now very wary of feeding large amounts of power to my vintage bass drivers that I would have difficulty replacing at £1000.

That's the only reason I am looking for a low power amp to do this job. Unless someone can demonstrate to me that low power and high SQ bass are mutually exclusive!

[Ali Tait]

Yes can understand that, but I guess doing the same with a 30w amp wouldn’t do a vintage driver any favours either. The Inukes have volume controls for each channel, so safe to use imo.

[bumpy]

I appreciate what you are saying, that there is masses of reserve power to control the bass unit, stop/start damping factor etc but my questioning mind would ask.

"Does this massive power reserve equate to better sound quality overall? In fact do convention criteria such as imaging, separation between instruments, correct tonality, musicality etc even apply over these lower frequencies?

[Macca]

I appreciate what you are saying, that there is masses of reserve power to control the bass unit, stop/start damping factor etc but my questioning mind would ask.

"Does this massive power reserve equate to better sound quality overall? In fact do convention criteria such as imaging, separation between instruments, correct tonality, musicality etc even apply over these lower frequencies?

Yes they do - consider middle C on a piano, you wouldn't consider that to be in the bass spectrum but it's 261 Hz

I guess 35 watts is the continuous power handling for the bass driver? If so you could safely go for a more powerful amp. If it is peak power then I would think about replacing the drivers with something more modern. I appreciate the romance of using vintage but they aren't automatically better. Especially in the context of an active system.

Otherwise I'd stick with the Rotel as I don't see anything to be gained with a different amp given the system is active.

[bumpy]

Yes they do - consider middle C on a piano, you wouldn't consider that to be in the bass spectrum but it's 261 Hz

I guess 35 watts is the continuous power handling for the bass driver? If so you could safely go for a more powerful amp. If it is peak power then I would think about replacing the drivers with something more modern. I appreciate the romance of using vintage but they aren't automatically better. Especially in the context of an active system.

Otherwise I'd stick with the Rotel as I don't see anything to be gained with a different amp given the system is active.

Thanks Macca

I was really just asking for reassurance of something I really knew - that all the criteria I expect of a driver should be present :)

Out of interest I did buy and install a pair of 15" Eminence Alpha drivers which are highly regarded by OB designers but they were easily outperformed for SQ by the vintage Altecs. Thinking aloud, this was before I went active on the bass and removed mid bass duties from the driver by reducing the low pass filter from 450Hz to 150Hz. I must give it another try.


I don't play a musical instrument, but interested in what note is equivalent to 150Hz?

[Macca]

closest is the D below middle C 155hz (I had to look that up obvs)

[Ali Tait]

I used the Inuke for my previous OB’s which were active and used a pair of 15” Alphas, and also on my Bastanis, which use an 18” Goldwood driver.

[bumpy]

Have tried the Eminence Alphas against the Altec 416Bs over the selected range of 20Hz to 150Hz. The Altecs have altogether much better sound quality, but I guess that's why they have such a good reputation and despite being 60 years old, still command top money. By ear they have pretty close sensitivity, with the Eminence being a shade louder.

So the next experiment is to drive the Altecs (just over this range) with different amplifiers. The three I have available could not be more different.

Rotel 820 AX (Class A/b?)
ICE 1000Wpc power amp Class D
Decware Taboo single ended pentode valve amp

[sailor]

The 416 is probably the best I've heard. This driver in a big box about the size of a refrigerator, Onken, Altec A5 or even a large Karlson is amazing but for OB should high-pass an octave higher. Install a simple cap/resistor at the input to the pre or power amp. Just need to know the input impedance which you can get from the manufacturer. The 416 can play up to 1200Hz and was used with the 511 or 811 horns.

Use subs blended at about 50Hz for fullness. It's the price you pay for trying to squeeze bass out of a low Qts driver with no box. Also, removing the bottom octave will tax the Altecs less and allow higher SPLs.

The Eminence Alphas are popular because their puny little magnets resulting in high Q do not control the cone from flapping around giving the impression of bass but it's ill defined as you heard. I know the Alphas well, listening to some now.

It's safe to drive the 416's with big power, just be sensible, lovely drivers.

[Metlor]

A Rotel RB850 (power amp mind) would probably do the trick, and run a fair bit cooler than the 820.

Faital Pro make some good bass drivers, not too pricey either.

[bumpy]

A Rotel RB850 (power amp mind) would probably do the trick, and run a fair bit cooler than the 820.

Faital Pro make some good bass drivers, not too pricey either.

Good shout on the amp. :thumbsup:

[philv]

Usher r1.5 reference.