8mm Forum: Seeking extension speaker advice

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Posted by Adrian Winchester (Member # 248) on December 22, 2014, 09:40 PM:

Some time ago, I urgently needed a more powerful extension speaker for a shop I presented on 16mm and Super 8 in a hall. I don't use additional amplification but I needed a speaker that could cope with a 25 watt Eiki amp turned up fairly high. I opted to but this 100 watt PA speaker, which was amazing value at £29 including delivery:
http://www.astounded.com/pulse-pvs8-8-100w-passive-pa-speaker.html?cPath=262_7_49
Despite the price, I was generally impressed by the full-bodied sound this provided, which certainly beat the previous speaker I'd used. However, certain higher frequency sounds cause some distortion even though the speaker shouldn't be under strain. I'm not sure, therefore, if this means the speaker has a fault, or if it could possibly be something to do with using film projectors? It's said that projectors are not great in terms of higher frequency sounds, so I'm not sure if they could mean a problem in using a speaker?

Any thoughts - or perhaps speaker recommendations, if anyone has bought one for film use in medium-sized halls and been happy with it - would be appreciated.

Posted by Steve Klare (Member # 12) on December 22, 2014, 10:59 PM:

The problem you run into is often external amps and/or speakers are actually too good for cinema sound purposes.

A long time ago when theatrical sound was first being refined, they found that a lot of nastiness went on in the higher end of the audio spectrum, and they rolled off the gain well below the 20 kHz that a really decent (young, usually) set of human ears can pick up, but it sounded better that way and remained the standard.

The GS-1200 as an example doesn't venture north of 12.5 kHz, and that's about as good as we have.

Now we go hanging really good external modern hi-fidelity equipment on that signal. Why should we worry? There's nothing up there in the teens , right? Well, no, there actually is. There is tape hiss and distortion and all sorts of stuff that doesn't sound very nice without benefit of "signal" to cover it up.

I run a pretty recent (and decent) external stereo amp and nice speakers with the audio outputs of my projectors and it sounds good, but one of the first things I had to do to civilize this setup is dial back the high frequency signal going into the amp.

I had to fool those speakers into thinking they weren't as good as they really are.

After the film, when I'm playing music through them they can go all out!

Probably the best thing you can do with what you are using is dial back your tone control if you have one.

Posted by Graham Ritchie (Member # 559) on December 22, 2014, 11:10 PM:

Reading the specs I cant find what the speaker impedance is, hopefully the resistance of the speaker is not less than what is recommended for the projector amp.

Another thing distortion can be down to the poor "old amp" not being up to it and matched to operate with that kind of speaker.

What I would do, is to plug the "aux out" on the projector to a external amp and let a more powerful external amp do the work.

My guess that would work fine with your new speaker [Smile]

Posted by Adrian Winchester (Member # 248) on December 22, 2014, 11:30 PM:

Thanks Steve & Graham for your thoughts. At a screening (of 'The Rocky Horror Picture Show') at the weekend, I did have to turn the treble control most of the way down during the songs, but the sound seemed better during dialogue without it cut so much. If the speaker isn't at fault, I wondered if disconnecting the high frequency horn (if feasible) could be an answer?

In fact the Eiki ENT I'm using doesn't have an aux out, just a standard jack socket for a speaker. But I don't think the distortion is down to the amp struggling - the weekend show was in someone's house with the volume not needing to be turned up a lot. The sound seemed very good other than certain frequencies seemingly causing a 'rasping' effect on the cone.

Posted by Paul Mason (Member # 4015) on December 23, 2014, 04:56 AM:

Hi Adrian,
You shouldn't really get serious distortion unless something is wrong and you need to go through a process of elimination.

If the speaker is faulty it may sound OK except when certain frequencies cause voice coil rubbing on the magnet. Try a good pair of headphones or another speaker.

The projector amp may be the cause especially if it's overloaded by the speaker as many projector amps don't like speakers of less than 6 ohms or it may be a fault not previously apparent.

Finally the distortion may be on the film soundtrack itself so try it on another projector. I wouldn't disconnect the piezo horn as the bass speaker will sound very muffled but they are designed to provide high frequencies at high power so they will mercilessly show up any distortion in the signal when working correctly.

Posted by Paul Browning (Member # 2715) on December 23, 2014, 07:26 AM:

Hi Adrian, With no aux out, your kind of limited to what you can do to improve the overall sound. I can tell you that you will not get much of smoother sound out of a piezo horn, they sound harsh all the time, a bullet tweeter would have been better. With an aux out you could have put in a little graphic to tune up the sound, and used a powered speaker.

Posted by Adrian Winchester (Member # 248) on December 23, 2014, 09:04 AM:

Thanks for the further replies - I'll try some more tests, including trying to put another sound source through the speaker. This is 8 ohms so I'm sure I'm not overloading it. Ironically, despite the problem I've mentioned, part of the reason why I haven't been inclined to go to the expense and added work of incorporating a separate amp into my shows is that the combination of the projector (which always sounded fine via my previous speaker, which has no tweeter) and the new speaker has meant the best 16mm sound I've ever had! However that's no consolation when certain frequencies, particularly in relation to music, cause the distortion which might be the rubbing that Paul refers to. It may well be the speaker that's at fault, but I was hesitant to think that having bought it new.

Posted by Paul Browning (Member # 2715) on December 23, 2014, 09:30 AM:

The voice coil rubbing in the magnet would cause the bass end to distort rather than the "top end" Adrian, the action of the peizo horn tweeter, acts without any moving parts like a speaker cone does. You could check this however, but you would need to take off the front grill to do this, and with out any power to the speaker hold your hands horizontal about centre of the speakers outer edge, flat hands to the cone, push up and down gently, you should not feel the voice coil rubbing on the fixed magnet, if you do, then this is not good news, and a fault of manufacturing if this is a new speaker. It should go back immediately for replacement, it can happen and does. If you have used this and has improved your sound from your 16mm projector, then it sounds fine, but the tweeter for me is where you should focus your attention, they always sound "screechy and harsh" no matter what you do with them.

Posted by Brian Fretwell (Member # 4302) on December 23, 2014, 10:39 AM:

Apart from over running the amplifier enough to cause clipping of the output which might generate harmonics that could upset the tweeter I can't think any explanation of this. What does it sound like at low levels?

Posted by Paul Adsett (Member # 25) on December 23, 2014, 02:20 PM:

I always run the AUX out of my S8 projectors into a Yamaha 10 band stereo graphic equalizer, and then into my Sony stereo Amp. With the graphic equalizer you can dial out the high frequency hiss and the low frequency hum, and if you are inclined you can do custom GE settings for individual films to get the best sound possible.

Posted by Adrian Winchester (Member # 248) on December 23, 2014, 06:50 PM:

Thanks again for the replies. I think seasonal activities are going to dominate the next few days and temporarily halt further tests, but I'll report back in due course!

Posted by Maurice Leakey (Member # 916) on December 29, 2014, 02:44 AM:

Adrian
Your existing projector speaker should be able to supply adequate sound for a large hall, I've never had any problems with speakers as supplied with projectors.
A good arrangement is to use two 12" old Bell & Howell speakers in parallel. The two 16 ohms so wired will present 8 ohms to your projector.
As mentioned by fellow members, your new modern speaker is just too good to mate with older amplifiers and the low quality of film sound.

Posted by Joe McAllister (Member # 825) on January 18, 2015, 08:40 AM:

Hi Adrian
as many of the previous replies suggest putting a high quality speaker on the end of your projectors amp may just be giving you a HiFi demonstration of the limitations of cine sound, both tracks and amp quality.
Also amplifiers generally have a "sweet spot" on the volume control beyond which you are exceeding their limitations and just adding distortion. Using your new speaker you may be turning your amp up to drive the heavy speaker and therefore not getting optimal quality. Maurices' solution of using speakers designed for the job is worth exploring otherwise using an external amp could be a solution. Without an aux out you might find a boffin who could wire you up a pad which is basically a resistance that allows you to use your loudspeaker output and run it into an aux input on another amp.
The best sound I have managed from an unaided projector at home has come from using a very old hi fi speaker designed for use with low wattage amps like the leak TL 12. Too big for carting about as it has a folded horn design but excellent at home.
If you were doing frequent shows away from base you might consider column speakers which are cabinets with several small speakers mounted in a line one above the other which would throw the sound more directionally than conventional speakers are designed to do. Chris Taylor in the old cine magazines had a lot to say on their design construction and use, if you cant find ready mades.
One drawback of cine sound is that the tracks are somewhat compressed. There was available sometime ago some hi fi accessories called companders which decompressed audio during playback, i believe the Logo was DBX. Never had the chance to experiment with them but thought they might provide an improvement. Another gadget I'd love to try was the active Loudspeakers made by Phillips which would amplify signals from a another amp connected via the speaker socket and modify the playback tone to maximise the bass and treble quality by listening to the acoustic of the room it was situated in. I believe they were called Motional Feedback speakers.

Posted by Brian Fretwell (Member # 4302) on January 19, 2015, 03:35 AM:

DBX was mainly used to compress on recording and expand on playback. I don't know what it would have done when expanding non-DBX tracks as they would not have had the same compression profile, though I suspect it would have increased noise but made the sound more "lively" as it was a rival to Dolby in the noise reduction area and preventing recording loud sounds distorting.
I saw a film on motorbike racing on 16mm using the system at a Widex (the Watford one) and it was very good at coping with the range of sounds.

Posted by Steven J Kirk (Member # 1135) on January 26, 2015, 06:21 PM:

I use NT 1 machines. I have a step-down adapter from Boss, a unit exactly designed to take a speaker output and create two line level signals. From that into a stereo amp and speakers. 16mm optical can sound perfectly fine like this.

Here is a similar device on eBay:

http://www.ebay.co.uk/itm/SPEAKER-TO-RCA-CONVERTER-HIGH-TO-LOW-LINE-LEVEL-ADJUSTABLE-CABLE-ADAPTER-NEW-/360549598576?pt=UK_In_Car_Technology&hash=item53f26e4570

Couldn't find the Boss device right now but look amongst car audio. They also do a hum bucker.

Posted by Adrian Winchester (Member # 248) on August 22, 2015, 08:50 PM:

Further to the discussion above, I've discovered that although it's not made obvious, the later Ekis such as SSLs and SNTs do have an aux out of sorts: it's the same standard jack output as for a speaker, but using a suitably wired stereo jack plug, you get the right output for an amp.

Secondly, in view of the 8/16mm soundtrack limitations with regard to higher frequencies, I was suprised to see this speaker that the seller says if for a Bauer P8:
http://www.ebay.com/itm/Lautsprecher-fur-16mm-Filmprojektor-Bauer-P8-alle-Modelle-mit-Garantie/111595852982?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%

I wonder if this really is a Bauer 16mm speaker?

Posted by Steve Carter (Member # 4821) on August 23, 2015, 04:09 AM:

I never used speakers with tweeters or horns when I used to do film shows,tried them and had all sorts of extra noise.So like Maurice I got two old 16 ohm speakers and wired them in parrallel giving 8 ohms, the sound was always so much more pleasing to myself and the audience...

Posted by Maurice Leakey (Member # 916) on August 23, 2015, 04:17 AM:

I doubt if the speaker shown is a Bauer product. I have a P8 and see from attached specs that Bauer offered three extension speakers for this model.

A 20/30w speaker incorporated in the side cover (which my projector came with.)

A 50/70w hi-fi speaker in a case measuring 385mm wide, 400mm high, 210mm deep.

A 20/30w high frequency range speaker with identical dimensions as above 50/70w.

The speakers also have BAUER emblazoned on them!

Posted by Martin Jones (Member # 1163) on August 23, 2015, 04:56 AM:

The original post directs one to the speaker "specification".... which appears NOT to tell you the "power handling capability" of the speaker. It simply says "Power 100W"
The question is "what Power?"
Many speaker specs are for "peak music power" which makes the speaker seem to be a bargain..... but such a speaker will only handle about 12.5W of "RMS power" (the industry standard measurement) which is the measurement used for the output of decent quality amplifiers.
So a 25 watt (RMS power) amplifier working at near full output into a 100 watt (peak music power) speaker will overload the speaker.... and distortion will be the result.

Not necessarily the problem here, but never ignore this "specification" trick often applied to make equipmemt appear to be better than it is.

Posted by Steve Carter (Member # 4821) on August 23, 2015, 05:31 AM:

Keep the cabinet, and put a decent speaker in it...

Posted by Brian Fretwell (Member # 4302) on August 23, 2015, 06:21 AM:

The other trouble is that with a high rating (seems 4 times that of the amp here) it is easy to turn the level up and cause "clipping" of the signal causing distortion. This produces extra high frequency signals, due to harmonics, that can damage the tweeter if there is one as this is usually of a much lower power rating than the woofer.

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